Hydrodynamic instabilities in inertial fusion
International Nuclear Information System (INIS)
Hoffman, N.M.
1994-01-01
This report discusses topics on hydrodynamics instabilities in inertial confinement: linear analysis of Rayleigh-Taylor instability; ablation-surface instability; bubble rise in late-stage Rayleigh-Taylor instability; and saturation and multimode interactions in intermediate-stage Rayleigh-Taylor instability
Modeling hydrodynamic instabilities of double ablation fronts in inertial confinement fusion
International Nuclear Information System (INIS)
Yanez, C.; Sanz, J.; Olazabal-Loume, M.; Ibanez, L. F.
2013-01-01
A linear Rayleigh-Taylor instability theory of double ablation (DA) fronts is developed for direct-drive inertial confinement fusion. Two approaches are discussed: an analytical discontinuity model for the radiation dominated regime of very steep DA front structure, and a numerical self-consistent model that covers more general hydrodynamic profiles behaviours. Dispersion relation results are compared to 2D simulations. (authors)
Energy Technology Data Exchange (ETDEWEB)
Casner, A., E-mail: alexis.casner@cea.fr; Masse, L.; Huser, G.; Galmiche, D.; Liberatore, S.; Riazuelo, G. [CEA, DAM, DIF, F-91297 Arpajon (France); Delorme, B. [CEA, DAM, DIF, F-91297 Arpajon (France); CELIA, University of Bordeaux-CNRS-CEA, F-33400 Talence (France); Martinez, D.; Remington, B.; Smalyuk, V. A. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Igumenshchev, I.; Michel, D. T.; Froula, D.; Seka, W.; Goncharov, V. N. [Laboratory of Laser Energetics, Rochester, New York 14623-1299 (United States); Olazabal-Loumé, M.; Nicolaï, Ph.; Breil, J.; Tikhonchuk, V. T. [CELIA, University of Bordeaux-CNRS-CEA, F-33400 Talence (France); Fujioka, S. [Institute of Laser Engineering, Osaka University, Suita, Osaka 565 (Japan); and others
2014-12-15
Understanding and mitigating hydrodynamic instabilities and the fuel mix are the key elements for achieving ignition in Inertial Confinement Fusion. Cryogenic indirect-drive implosions on the National Ignition Facility have evidenced that the ablative Rayleigh-Taylor Instability (RTI) is a driver of the hot spot mix. This motivates the switch to a more flexible higher adiabat implosion design [O. A. Hurricane et al., Phys. Plasmas 21, 056313 (2014)]. The shell instability is also the main candidate for performance degradation in low-adiabat direct drive cryogenic implosions [Goncharov et al., Phys. Plasmas 21, 056315 (2014)]. This paper reviews recent results acquired in planar experiments performed on the OMEGA laser facility and devoted to the modeling and mitigation of hydrodynamic instabilities at the ablation front. In application to the indirect-drive scheme, we describe results obtained with a specific ablator composition such as the laminated ablator or a graded-dopant emulator. In application to the direct drive scheme, we discuss experiments devoted to the study of laser imprinted perturbations with special phase plates. The simulations of the Richtmyer-Meshkov phase reversal during the shock transit phase are challenging, and of crucial interest because this phase sets the seed of the RTI growth. Recent works were dedicated to increasing the accuracy of measurements of the phase inversion. We conclude by presenting a novel imprint mitigation mechanism based on the use of underdense foams. The foams induce laser smoothing by parametric instabilities thus reducing the laser imprint on the CH foil.
Hydrodynamic instabilities in an ablation front
International Nuclear Information System (INIS)
Piriz, A R; Portugues, R F
2004-01-01
The hydrodynamic stability of an ablation front is studied for situations in which the wavelength of the perturbations is larger than the distance to the critical surface where the driving radiation is absorbed. An analytical model is presented, and it shows that under conditions in which the thermal flux is limited within the supercritical region of the ablative corona, the front may behave like a flame or like an ablation front, depending on the perturbation wavelength. For relatively long wavelengths the critical and ablation surfaces practically lump together into a unique surface and the front behaves like a flame, whereas for the shortest wavelengths the ablation front substructure is resolved
Hydrodynamic instabilities in an ablation front
Energy Technology Data Exchange (ETDEWEB)
Piriz, A R; Portugues, R F [E.T.S.I. Industriales, Universidad de Castilla-La Mancha, 13071 Ciudad Real (Spain)
2004-06-01
The hydrodynamic stability of an ablation front is studied for situations in which the wavelength of the perturbations is larger than the distance to the critical surface where the driving radiation is absorbed. An analytical model is presented, and it shows that under conditions in which the thermal flux is limited within the supercritical region of the ablative corona, the front may behave like a flame or like an ablation front, depending on the perturbation wavelength. For relatively long wavelengths the critical and ablation surfaces practically lump together into a unique surface and the front behaves like a flame, whereas for the shortest wavelengths the ablation front substructure is resolved.
Mix and hydrodynamic instabilities on NIF
Smalyuk, V. A.; Robey, H. F.; Casey, D. T.; Clark, D. S.; Döppner, T.; Haan, S. W.; Hammel, B. A.; MacPhee, A. G.; Martinez, D.; Milovich, J. L.; Peterson, J. L.; Pickworth, L.; Pino, J. E.; Raman, K.; Tipton, R.; Weber, C. R.; Baker, K. L.; Bachmann, B.; Berzak Hopkins, L. F.; Bond, E.; Caggiano, J. A.; Callahan, D. A.; Celliers, P. M.; Cerjan, C.; Dixit, S. N.; Edwards, M. J.; Felker, S.; Field, J. E.; Fittinghoff, D. N.; Gharibyan, N.; Grim, G. P.; Hamza, A. V.; Hatarik, R.; Hohenberger, M.; Hsing, W. W.; Hurricane, O. A.; Jancaitis, K. S.; Jones, O. S.; Khan, S.; Kroll, J. J.; Lafortune, K. N.; Landen, O. L.; Ma, T.; MacGowan, B. J.; Masse, L.; Moore, A. S.; Nagel, S. R.; Nikroo, A.; Pak, A.; Patel, P. K.; Remington, B. A.; Sayre, D. B.; Spears, B. K.; Stadermann, M.; Tommasini, R.; Widmayer, C. C.; Yeamans, C. B.; Crippen, J.; Farrell, M.; Giraldez, E.; Rice, N.; Wilde, C. H.; Volegov, P. L.; Gatu Johnson, M.
2017-06-01
Several new platforms have been developed to experimentally measure hydrodynamic instabilities in all phases of indirect-drive, inertial confinement fusion implosions on National Ignition Facility. At the ablation front, instability growth of pre-imposed modulations was measured with a face-on, x-ray radiography platform in the linear regime using the Hydrodynamic Growth Radiography (HGR) platform. Modulation growth of "native roughness" modulations and engineering features (fill tubes and capsule support membranes) were measured in conditions relevant to layered DT implosions. A new experimental platform was developed to measure instability growth at the ablator-ice interface. In the deceleration phase of implosions, several experimental platforms were developed to measure both low-mode asymmetries and high-mode perturbations near peak compression with x-ray and nuclear techniques. In one innovative technique, the self-emission from the hot spot was enhanced with argon dopant to "self-backlight" the shell in-flight. To stabilize instability growth, new "adiabat-shaping" techniques were developed using the HGR platform and applied in layered DT implosions.
Wang, LiFeng; Ye, WenHua; He, XianTu; Wu, JunFeng; Fan, ZhengFeng; Xue, Chuang; Guo, HongYu; Miao, WenYong; Yuan, YongTeng; Dong, JiaQin; Jia, Guo; Zhang, Jing; Li, YingJun; Liu, Jie; Wang, Min; Ding, YongKun; Zhang, WeiYan
2017-05-01
Inertial fusion energy (IFE) has been considered a promising, nearly inexhaustible source of sustainable carbon-free power for the world's energy future. It has long been recognized that the control of hydrodynamic instabilities is of critical importance for ignition and high-gain in the inertial-confinement fusion (ICF) hot-spot ignition scheme. In this mini-review, we summarize the progress of theoretical and simulation research of hydrodynamic instabilities in the ICF central hot-spot implosion in our group over the past decade. In order to obtain sufficient understanding of the growth of hydrodynamic instabilities in ICF, we first decompose the problem into different stages according to the implosion physics processes. The decomposed essential physics pro- cesses that are associated with ICF implosions, such as Rayleigh-Taylor instability (RTI), Richtmyer-Meshkov instability (RMI), Kelvin-Helmholtz instability (KHI), convergent geometry effects, as well as perturbation feed-through are reviewed. Analyti- cal models in planar, cylindrical, and spherical geometries have been established to study different physical aspects, including density-gradient, interface-coupling, geometry, and convergent effects. The influence of ablation in the presence of preheating on the RTI has been extensively studied by numerical simulations. The KHI considering the ablation effect has been discussed in detail for the first time. A series of single-mode ablative RTI experiments has been performed on the Shenguang-II laser facility. The theoretical and simulation research provides us the physical insights of linear and weakly nonlinear growths, and nonlinear evolutions of the hydrodynamic instabilities in ICF implosions, which has directly supported the research of ICF ignition target design. The ICF hot-spot ignition implosion design that uses several controlling features, based on our current understanding of hydrodynamic instabilities, to address shell implosion stability, has
Laser driven hydrodynamic instability experiments
International Nuclear Information System (INIS)
Remington, B.A.; Weber, S.V.; Haan, S.W.; Kilkenny, J.D.; Glendinning, S.G.; Wallace, R.J.; Goldstein, W.H.; Wilson, B.G.; Nash, J.K.
1993-01-01
An extensive series of experiments has been conducted on the Nova laser to measure hydrodynamic instabilities in planar foils accelerated by x-ray ablation. Single mode experiments allow a measurement of the fundamental growth rates from the linear well into the nonlinear regime. Two-mode foils allow a first direct observation of mode coupling. Surface-finish experiments allow a measurement of the evolution of a broad spectrum of random initial modes
Hydrodynamic instability experiments on the Nova laser
International Nuclear Information System (INIS)
Remington, B.A.; Glendinning, S.G.; Kalantar, D.H.
1996-08-01
Hydrodynamic instabilities in compressible plasmas play a critical role in the fields of inertial confinement fusion (ICF), astrophysics, and high energy-density physics. We are, investigating hydrodynamic instabilities such as the Rayleigh-Taylor (RT) instability, at high compression at the Nova laser in a series of experiments, both in planar and in spherical geometry. In the indirect drive approach, a thermal x-ray drive is generated by focusing the Nova laser beams into a Au cylindrical radiation cavity (hohlraum). Issues in the instability evolution that we are examining are shock propagation and foil compression, RT growth of 2D versus 3D single-mode perturbations, drive pulse shape, perturbation location at the ablation front versus at an embedded interface, and multimode perturbation growth and nonlinear saturation. The effects of convergence on RT growth are being investigated both with hemispherical implosions of packages mounted on the hohlraum wall and with spherical implosions of capsules at the center of the hohlraum. Single-mode perturbations are pre-imposed at the ablation front of these capsules as a seed for the RT growth. In our direct drive experiments, we are investigating the effect of laser imprinting and subsequent RT growth on planar foils, both at λ Laser = 1/3 μm and 1/2 μm. An overview is given describing recent progress in each of these areas
Hydrodynamic instabilities in astrophysics and ICF
International Nuclear Information System (INIS)
Paul Drake, R.
2005-01-01
Inertial fusion systems and astrophysical systems both involve hydrodynamic effects, including sources of pressure, shock waves, rarefactions, and plasma flows. In the evolution of such systems, hydrodynamic instabilities naturally evolve. As a result, a fundamental understanding of hydrodynamic instabilities is necessary to understand their behavior. In addition, high-energy-density facilities designed for ICF purposes can be used to provide and experimental basis for understanding astrophysical processes. In this talk. I will discuss the instabilities that appear in astrophysics and ICF from the common perspective of the basic mechanisms at work. Examples will be taken from experiments aimed at ICF, from astrophysical systems, and from experiments using ICF systems to address issues in astrophysics. The high-energy-density research facilities of today can accelerate small but macroscopic amounts of material to velocities above 100 km/s, can heat such material to temperature above 100 eV, can produce pressures far above a million atmospheres (10''12 dybes/cm''2 or 0.1 TPascal), and can do experiments under these conditions that address basic physics issues. This enables on to devise experiments aimed directly at important process such as the Rayleigh Taylor instability at an ablating surface or at an embedded interface that is accelerating, the Richtmeyer Meshkov evolution of shocked interfaces, and the Kelvin-Helmholtz instability of shear flows. The talk will include examples of such phenomena from the laboratory and from astrophysics, and will discuss experiments to study them. (Author)
Laser driven hydrodynamic instability experiments
International Nuclear Information System (INIS)
Remington, B.A.; Weber, S.V.; Haan, S.W.; Kilkenny, J.D.; Glendinning, S.G.; Wallace, R.J.; Goldstein, W.H.; Wilson, B.G.; Nash, J.K.
1992-01-01
We have conducted an extensive series of experiments on the Nova laser to measure hydrodynamic instabilities in planar foils accelerated by x-ray ablation. Single mode experiments allow a measurement of the fundamental growth rates from the linear well into the nonlinear regime; multimode foils allow an assessment of the degree of mode coupling; and surface-finish experiments allow a measurement of the evolution of a broad spectrum of random initial modes. Experimental results and comparisons with theory and simulations are presented
Numerical analysis of anisotropic diffusion effect on ICF hydrodynamic instabilities
Directory of Open Access Journals (Sweden)
Olazabal-Loumé M.
2013-11-01
Full Text Available The effect of anisotropic diffusion on hydrodynamic instabilities in the context of Inertial Confinement Fusion (ICF flows is numerically assessed. This anisotropy occurs in indirect-drive when laminated ablators are used to modify the lateral transport [1,2]. In direct-drive, non-local transport mechanisms and magnetic fields may modify the lateral conduction [3]. In this work, numerical simulations obtained with the code PERLE [4], dedicated to linear stability analysis, are compared with previous theoretical results [5]. In these approaches, the diffusion anisotropy can be controlled by a characteristic coefficient which enables a comprehensive study. This work provides new results on the ablative Rayleigh-Taylor (RT, ablative Richtmyer-Meshkov (RM and Darrieus-Landau (DL instabilities.
Hydrodynamic instabilities in beryllium targets for the National Ignition Facility
Energy Technology Data Exchange (ETDEWEB)
Yi, S. A., E-mail: austinyi@lanl.gov; Simakov, A. N.; Wilson, D. C.; Olson, R. E.; Kline, J. L.; Batha, S. H. [Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, New Mexico 87545 (United States); Clark, D. S.; Hammel, B. A.; Milovich, J. L.; Salmonson, J. D.; Kozioziemski, B. J. [Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551 (United States)
2014-09-15
Beryllium ablators offer higher ablation velocity, rate, and pressure than their carbon-based counterparts, with the potential to increase the probability of achieving ignition at the National Ignition Facility (NIF) [E. I. Moses et al., Phys. Plasmas 16, 041006 (2009)]. We present here a detailed hydrodynamic stability analysis of low (NIF Revision 6.1) and high adiabat NIF beryllium target designs. Our targets are optimized to fully utilize the advantages of beryllium in order to suppress the growth of hydrodynamic instabilities. This results in an implosion that resists breakup of the capsule, and simultaneously minimizes the amount of ablator material mixed into the fuel. We quantify the improvement in stability of beryllium targets relative to plastic ones, and show that a low adiabat beryllium capsule can be at least as stable at the ablation front as a high adiabat plastic target.
Hydrodynamic instability growth and mix experiments at the National Ignition Facility
Energy Technology Data Exchange (ETDEWEB)
Smalyuk, V. A.; Barrios, M.; Caggiano, J. A.; Casey, D. T.; Cerjan, C. J.; Clark, D. S.; Edwards, M. J.; Haan, S. W.; Hammel, B. A.; Hamza, A.; Hsing, W. W.; Hurricane, O.; Kroll, J.; Landen, O. L.; Lindl, J. D.; Ma, T.; McNaney, J. M.; Mintz, M.; Parham, T.; Peterson, J. L. [Lawrence Livermore National Laboratory, NIF Directorate, Livermore, California 94550 (United States); and others
2014-05-15
Hydrodynamic instability growth and its effects on implosion performance were studied at the National Ignition Facility [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 443, 2841 (2004)]. Implosion performance and mix have been measured at peak compression using plastic shells filled with tritium gas and containing embedded localized carbon-deuterium diagnostic layers in various locations in the ablator. Neutron yield and ion temperature of the deuterium-tritium fusion reactions were used as a measure of shell-gas mix, while neutron yield of the tritium-tritium fusion reaction was used as a measure of implosion performance. The results have indicated that the low-mode hydrodynamic instabilities due to surface roughness were the primary culprits for yield degradation, with atomic ablator-gas mix playing a secondary role. In addition, spherical shells with pre-imposed 2D modulations were used to measure instability growth in the acceleration phase of the implosions. The capsules were imploded using ignition-relevant laser pulses, and ablation-front modulation growth was measured using x-ray radiography for a shell convergence ratio of ∼2. The measured growth was in good agreement with that predicted, thus validating simulations for the fastest growing modulations with mode numbers up to 90 in the acceleration phase. Future experiments will be focused on measurements at higher convergence, higher-mode number modulations, and growth occurring during the deceleration phase.
A comparison of hydro-instabilities in CH, HDC, and beryllium ablators on NIF
Smalyuk, V. A.; Robey, H. F.; Ali, S.; Berzak Hopkins, L. F.; Casey, D. T.; Celliers, P. M.; Clark, D. S.; Felker, S. J.; Field, J. E.; Haan, S. W.; Hammel, B. A.; Hsing, W. W.; Kroll, J. J.; Landen, O. L.; Lepape, S.; Macphee, A. G.; Martinez, D.; Milovich, J.; Nikroo, A.; Pickworth, L.; Stadermann, M.; Weber, C. R.; Kline, J.; Loomis, E.; Yi, A.
2017-10-01
A comparison of the hydrodynamic growth in plastic, high-density carbon, and beryllium ablators will be presented in indirect-drive implosions on National Ignition Facility. This comparison is based on experimentally measured instabilities in all phases of implosions for the three ablators. The 2-D and 3-D perturbations were measured at the ablation-surface with the Hydrodynamic Growth Radiography platform. In the deceleration phase of implosions, innovative self-emission and ``self-backlight'' techniques were used. Results of the 3-D perturbation growth including engineering features will also be presented for convergence up to 20 and compared for the three ablators. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Study of the Rayleigh-Taylor instability at the ablation front
International Nuclear Information System (INIS)
Salvatore, Patricia
2000-01-01
Inertial confinement fusion in indirect drive consists in irradiating with ultra powerful laser beams the internal wall of a heating cavity which contains a capsule enclosing the thermonuclear fuel. During laser-matter interaction, laser light is converted into x-rays onto the hohlraum walls. The x-rays capsule heating produces a matter expansion, this one induces a pressure accelerating the capsule wall which implodes and compresses the fuel. The limit between the expanded plasma and the accelerated one is named ablation front. A light fluid (the ablated plasma) accelerating a heavy one (the shell) seeds Rayleigh-Taylor instability. To perform experiments, we used the Phebus facility at Limeil-Valenton CEA (the most powerful laser in Europe). After frequency conversion, each laser beam can deliver onto a target an energy up to 3 kJ at 0.35μm wavelength. In the United States of America and in France, more powerful laser facilities are planned to deliver an energy about 1 MJ: the National Ignition Facility (Lawrence Livermore National Laboratory, California) and the Laser MegaJoule (CEA, Bordeaux). Hydrodynamic instabilities take an important part in the definition of these facilities. Two main experiments were carried out on the Phebus laser. We studied the Rayleigh-Taylor instability at the ablation front with a modulated CHBr plane target stuck on the gold hohlraum wall. During the september-october 1996 experiment, a x-ray device was used. We observed the temporal evolution of the target modulations by x-ray imaging cinematography which recorded face-on radiographs. The second experiment was performed with collaboration of the Imperial College of London. Two high spatial resolution devices (less than 5 μm) were used in order to study short wavelengths modulations. The first diagnostic recorded side-on observations of target acceleration, the second one was used to measure the instability growth with face-on radiography. We studied this growth in a modulation
International Nuclear Information System (INIS)
Kilkenny, J.D.
1994-01-01
As shown elsewhere an ablatively imploded shell is hydrodynamically unstable, the dominant instability being the well known Rayleigh-Taylor instability with growth rate γ = √Akg where k = 2π/λ is the wave number, g is the acceleration and A the Attwood number (ρ hi - ρ lo )/(ρ hi + ρ lo ) where ρ hi is the density of the heavier fluid and ρ lo is the density of the lighter fluid. A theoretical understanding of ablative stabilization has gradually evolved, confirmed over the last five years by experiments. The linear growth is very well understood with excellent agreement between experiment and simulation for planar geometry with wavelengths in the region of 30--100μm. There is an accurate, albeit phenomenological dispersion relation. The non-linear growth has been measured and agrees with calculations. In this lecture, the authors go into the fundamentals of the Rayleigh-Taylor instability and the experimental measurements that show it is stabilized sufficiently by ablation in regimes relevant to ICF
International Nuclear Information System (INIS)
Bud'ko, A.B.; Liberman, M.A.
1992-01-01
In the framework of WKB approximation the problem is studied of stabilizing the Rayleigh - Taylor instability with unhomogeneous convective flow, developing in the ablation zone during the ablative acceleration of the laser target plasma. The eigenvalue (instability growth rates) problem is reduced to solving an algebraic equation with the coefficients depending on the unperturbed profile structure of hydrodynamic variables. For the important case of the incompressible plasma subsonic flow, the instability growth rates is shown to vanish at k=k 0 =max(2(g|∇ ln p|) 1/2 /ν). The consistency condition of the model consists in the smallness of the local Froude number in the region of instability development. However, as seen from the comparison with the numerical calculations, the model is well appicable also for the case of the sufficiently abrupt density gradient provided the Froude number is of order of unity
Self-consistent model of the Rayleigh--Taylor instability in ablatively accelerated laser plasma
International Nuclear Information System (INIS)
Bychkov, V.V.; Golberg, S.M.; Liberman, M.A.
1994-01-01
A self-consistent approach to the problem of the growth rate of the Rayleigh--Taylor instability in laser accelerated targets is developed. The analytical solution of the problem is obtained by solving the complete system of the hydrodynamical equations which include both thermal conductivity and energy release due to absorption of the laser light. The developed theory provides a rigorous justification for the supplementary boundary condition in the limiting case of the discontinuity model. An analysis of the suppression of the Rayleigh--Taylor instability by the ablation flow is done and it is found that there is a good agreement between the obtained solution and the approximate formula σ = 0.9√gk - 3u 1 k, where g is the acceleration, u 1 is the ablation velocity. This paper discusses different regimes of the ablative stabilization and compares them with previous analytical and numerical works
Energy Technology Data Exchange (ETDEWEB)
Peterson, J. L.; Clark, D. S.; Suter, L. J. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Masse, L. P. [CEA, DAM, DIF, 91297 Arpajon (France)
2014-09-15
Defects on inertial confinement fusion capsule surfaces can seed hydrodynamic instability growth and adversely affect capsule performance. The dynamics of shocks launched during the early period of x-ray driven National Ignition Facility (NIF) implosions determine whether perturbations will grow inward or outward at peak implosion velocity and final compression. In particular, the strength of the first shock, launched at the beginning of the laser pulse, plays an important role in determining Richtmyer-Meshkov (RM) oscillations on the ablation front. These surface oscillations can couple to the capsule interior through subsequent shocks before experiencing Rayleigh-Taylor (RT) growth. We compare radiation hydrodynamic simulations of NIF implosions to analytic theories of the ablative RM and RT instabilities to illustrate how early time laser strength can alter peak velocity growth. We develop a model that couples the RM and RT implosion phases and captures key features of full simulations. We also show how three key parameters can control the modal demarcation between outward and inward growth.
International Nuclear Information System (INIS)
Bul'ko, A.B.; Liberman, M.A.
1992-01-01
The authors use the WKB-approximation to treat the problem of the stabilization by an inhomogeneous convective current of the Rayleigh-Taylor instability developing in the ablation zone when the plasma of laser targets is accelerated by ablation. The problem of the eigenvalues - the instability growth rates - is reduced to the solution of an algebraic equation with coefficients which depend on the structure of the unperturbed profiles of the hydrodynamic variables. They show for the practically important case of subsonic flow of an incompressible plasma that the instability growth rate vanishes for k = k o = max[2(g|∇lnρ|) 1/2 /v]. The condition for the self-consistency of the model is that the local Froude number be small in the region where the instability develops; however, comparison with numerical calculations shows that the model is also applicable in the case of rather steep density gradients when the Froude number is of order unity. 32 refs., 2 figs
International Nuclear Information System (INIS)
Haan, S.W.; Herrmann, M.C.; Dittrich, T.R.; Fetterman, A.J.; Marinak, M.M.; Munro, D.H.; Pollaine, S.M.; Salmonson, J.D.; Strobel, G.L.; Suter, L.J.
2005-01-01
Targets meant to achieve ignition on the National Ignition Facility (NIF) [J. A. Paisner, J. D. Boyes, S. A. Kumpan, W. H. Lowdermilk, and M. S. Sorem, Laser Focus World 30, 75 (1994)] have been redesigned and their performance simulated. Simulations indicate dramatically reduced growth of short wavelength hydrodynamic instabilities, resulting from two changes in the designs. First, better optimization results from systematic mapping of the ignition target performance over the parameter space of ablator and fuel thickness combinations, using techniques developed by one of us (Herrmann). After the space is mapped with one-dimensional simulations, exploration of it with two-dimensional simulations quantifies the dependence of instability growth on target dimensions. Low modes and high modes grow differently for different designs, allowing a trade-off of the two regimes of growth. Significant improvement in high-mode stability can be achieved, relative to previous designs, with only insignificant increase in low-mode growth. This procedure produces capsule designs that, in simulations, tolerate several times the surface roughness that could be tolerated by capsules optimized by older more heuristic techniques. Another significant reduction in instability growth, by another factor of several, is achieved with ablators with radially varying dopant. In this type of capsule the mid-Z dopant, which is needed in the ablator to minimize x-ray preheat at the ablator-ice interface, is optimally positioned within the ablator. A fabrication scenario for graded dopants already exists, using sputter coating to fabricate the ablator shell. We describe the systematics of these advances in capsule design, discuss the basis behind their improved performance, and summarize how this is affecting our plans for NIF ignition
Huntington, C. M.; Shimony, A.; Trantham, M.; Kuranz, C. C.; Shvarts, D.; Di Stefano, C. A.; Doss, F. W.; Drake, R. P.; Flippo, K. A.; Kalantar, D. H.; Klein, S. R.; Kline, J. L.; MacLaren, S. A.; Malamud, G.; Miles, A. R.; Prisbrey, S. T.; Raman, K. S.; Remington, B. A.; Robey, H. F.; Wan, W. C.; Park, H.-S.
2018-05-01
The Rayleigh-Taylor (RT) instability is a common occurrence in nature, notably in astrophysical systems like supernovae, where it serves to mix the dense layers of the interior of an exploding star with the low-density stellar wind surrounding it, and in inertial confinement fusion experiments, where it mixes cooler materials with the central hot spot in an imploding capsule and stifles the desired nuclear reactions. In both of these examples, the radiative flux generated by strong shocks in the system may play a role in partially stabilizing RT instabilities. Here, we present experiments performed on the National Ignition Facility, designed to isolate and study the role of radiation and heat conduction from a shock front in the stabilization of hydrodynamic instabilities. By varying the laser power delivered to a shock-tube target with an embedded, unstable interface, the radiative fluxes generated at the shock front could be controlled. We observe decreased RT growth when the shock significantly heats the medium around it, in contrast to a system where the shock did not produce significant heating. Both systems are modeled with a modified set of buoyancy-drag equations accounting for ablative stabilization, and the experimental results are consistent with ablative stabilization when the shock is radiative. This result has important implications for our understanding of astrophysical radiative shocks and supernova radiative hydrodynamics [Kuranz et al., Nature Communications 9(1), 1564 (2018)].
International Nuclear Information System (INIS)
Srinivasan, Bhuvana; Tang, Xian-Zhu
2014-01-01
In an inertial confinement fusion target, energy loss due to thermal conduction from the hot-spot will inevitably ablate fuel ice into the hot-spot, resulting in a more massive but cooler hot-spot, which negatively impacts fusion yield. Hydrodynamic mix due to Rayleigh-Taylor instability at the gas-ice interface can aggravate the problem via an increased gas-ice interfacial area across which energy transfer from the hot-spot and ice can be enhanced. Here, this mix-enhanced transport effect on hot-spot fusion-performance degradation is quantified using contrasting 1D and 2D hydrodynamic simulations, and its dependence on effective acceleration, Atwood number, and ablation speed is identified
Shigemori, Keisuke; Sakaiya, Tatsuhiko; Otani, Kazuto; Fujioka, Shinsuke; Nakai, Mitsuo; Azechi, Hiroshi; Shiraga, Hiroyuki; Tamari, Yohei; Okuno, Kazuki; Sunahara, Atsushi; Nagatomo, Hideo; Murakami, Masakatsu; Nishihara, Katsunobu; Izawa, Yasukazu
2004-09-01
Hydrodynamic instabilities are key issues of the physics of inertial confinement fusion (ICF) targets. Among the instabilities, Rayleigh-Taylor (RT) instability is the most important because it gives the largest growth factor in the ICF targets. Perturbations on the laser irradiated surface grow exponentially, but the growth rate is reduced by ablation flow. The growth rate γ is written as Takabe-Betti formula: γ = [kg/(1+kL)]1/2-βkm/pa, where k is wave number of the perturbation, g is acceleration, L is density scale-length, β is a coefficient, m is mass ablation rate per unit surface, and ρa is density at the ablation front. We experimentally measured all the parameters in the formula for polystyrene (CH) targets. Experiments were done on the HIPER laser facility at Institute of Laser Engineering, Osaka University. We found that the β value in the formula is ~ 1.7, which is in good agreements with the theoretical prediction, whereas the β for certain perturbation wavelengths are larger than the prediction. This disagreement between the experiment and the theory is mainly due to the deformation of the cutoff surface, which is created by non-uniform ablation flow from the ablation surface. We also found that high-Z doped plastic targets have multiablation structure, which can reduce the RT growth rate. When a low-Z target with high-Z dopant is irradiated by laser, radiation due to the high-Z dopant creates secondary ablation front deep inside the target. Since, the secondary ablation front is ablated by x-rays, the mass ablation rate is larger than the laser-irradiated ablation surface, that is, further reduction of the RT growth is expected. We measured the RT growth rate of Br-doped polystyrene targets. The experimental results indicate that of the CHBr targets show significantly small growth rate, which is very good news for the design of the ICF targets.
New mitigation schemes of the ablative Rayleigh-Taylor instability
International Nuclear Information System (INIS)
Azechi, H.; Shiraga, H.; Nakai, M.; Shigemori, K.; Fujioka, S.; Sakaiya, T.; Tamari, Y.; Ohtani, K.; Watari, T.; Murakami, M.; Sunahara, A.; Nagatomo, H.; Nishihara, K.; Miyanaga, N.; Izawa, Y.; Ohnishi, N.
2005-01-01
The Rayleigh-Taylor (RT) instability with material ablation through the unstable interface is the key physics that determines success or failure of inertial fusion energy (IFE) generation, as the RT instability potentially quenches ignition and burn by disintegrating the IFE target. We present two suppression schemes of the RT growth without significant degradation of the target density. The first scheme is to generate double ablation structure in high-Z doped plastic targets. In addition to the electron ablation surface, a new ablation surface is created by x-ray radiation from the high-Z ions. Contrary to the previous thought, the electron ablation surface is almost completely stabilized by extremely high flow velocity. On the other hand, the RT instability on the radiative ablation surface is significantly moderated. The second is to enhance the nonlocal nature of the electron heat transport by illuminating the target with long wavelength laser light, whereas the high ablation pressure is generated by irradiating short wavelength laser light. The significant suppression of the RT instability may increase the possibility of impact ignition which uses a high velocity fuel colliding with a preformed main fuel. (author)
Bender, Jason; Raman, Kumar; Huntington, Channing; Nagel, Sabrina; Morgan, Brandon; Prisbrey, Shon; MacLaren, Stephan
2017-10-01
Experiments at the National Ignition Facility (NIF) are studying Richtmyer-Meshkov and Rayleigh-Taylor hydrodynamic instabilities in multiply-shocked plasmas. Targets feature two different-density fluids with a multimode initial perturbation at the interface, which is struck by two X-ray-driven shock waves. Here we discuss computational hydrodynamics simulations investigating the effect of second-shock (``reshock'') strength on instability growth, and how these simulations are informing target design for the ongoing experimental campaign. A Reynolds-Averaged Navier Stokes (RANS) model was used to predict motion of the spike and bubble fronts and the mixing-layer width. In addition to reshock strength, the reshock ablator thickness and the total length of the target were varied; all three parameters were found to be important for target design, particularly for ameliorating undesirable reflected shocks. The RANS data are compared to theoretical models that predict multimode instability growth proportional to the shock-induced change in interface velocity, and to currently-available data from the NIF experiments. Work performed under the auspices of the U.S. D.O.E. by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344. LLNL-ABS-734611.
Energy Technology Data Exchange (ETDEWEB)
Egly, H
2007-10-15
This thesis deals with the dynamics of accelerated ablative front spreading in Inertial Confinement Fusion experiments. ICF is designed for the implosion of a deuterium-tritium spherical target. The outer shell, the ablator, is irradiated providing a high level pressure inside the target. During this first stage, the ablation front propagating inwards is perturbed by hydrodynamics instabilities, which can prevent the fusion reaction in the decelerated stage. We propose here a study on Rayleigh-Taylor instabilities during ablation process, in the two dimensional case. In order to obtain a numerical solution, we perform an asymptotic analysis in the limit of a high temperature ratio, between the remaining cold ablator and the hot ablated plasma. This study is divided in two steps. First, the thermo-diffusive part of the set of equations is approximated by a Hele-Shaw model, which is then perturbed by the hydrodynamics part. Using a vortex method, we have to solve the advection of a vortical sheet moving with the ablation front. We compute the numerical solution on an Eulerian mesh coupled with a marker method. The thermal part is computed by implementing the Fat Boundary Method, recently developed. The hydrodynamic part is obtained from a Finite Volume scheme. (author)
Energy Technology Data Exchange (ETDEWEB)
Casner, A., E-mail: alexis.casner@cea.fr; Masse, L.; Liberatore, S.; Loiseau, P.; Masson-Laborde, P. E.; Jacquet, L. [CEA, DAM, DIF, F-91297 Arpajon (France); Martinez, D.; Moore, A. S.; Seugling, R.; Felker, S.; Haan, S. W.; Remington, B. A.; Smalyuk, V. A. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Farrell, M.; Giraldez, E.; Nikroo, A. [General Atomics, San Diego, California 92121 (United States)
2015-05-15
Academic tests in physical regimes not encountered in Inertial Confinement Fusion will help to build a better understanding of hydrodynamic instabilities and constitute the scientifically grounded validation complementary to fully integrated experiments. Under the National Ignition Facility (NIF) Discovery Science program, recent indirect drive experiments have been carried out to study the ablative Rayleigh-Taylor Instability (RTI) in transition from weakly nonlinear to highly nonlinear regime [A. Casner et al., Phys. Plasmas 19, 082708 (2012)]. In these experiments, a modulated package is accelerated by a 175 eV radiative temperature plateau created by a room temperature gas-filled platform irradiated by 60 NIF laser beams. The unique capabilities of the NIF are harnessed to accelerate this planar sample over much larger distances (≃1.4 mm) and longer time periods (≃12 ns) than previously achieved. This extended acceleration could eventually allow entering into a turbulent-like regime not precluded by the theory for the RTI at the ablation front. Simultaneous measurements of the foil trajectory and the subsequent RTI growth are performed and compared with radiative hydrodynamics simulations. We present RTI growth measurements for two-dimensional single-mode and broadband multimode modulations. The dependence of RTI growth on initial conditions and ablative stabilization is emphasized, and we demonstrate for the first time in indirect-drive a bubble-competition, bubble-merger regime for the RTI at ablation front.
International Nuclear Information System (INIS)
Fujioka, Shinsuke; Shiraga, Hiroyuki; Nishikino, Masaharu; Shigemori, Keisuke; Sunahara, Atsushi; Nakai, Mitsuo; Azechi, Hiroshi; Nishihara, Katsunobu; Yamanaka, Tatsuhiko
2003-01-01
The temporal evolution of the density profile of a directly laser-driven polystyrene target was observed for the first time using an x-ray penumbral imaging technique coupled with side-on x-ray backlighting at the GEKKO XII [C. Yamanaka et al., IEEE J. Quantum Electron. QE-17, 1639 (1981)]-High Intensity Plasma Experimental Research laser facility (I L =0.7x10 14 W/cm 2 , λ L =0.35 μm). This density measurement makes it possible to experimentally confirm all physical parameters [γ(k),k,g,m,ρ a ,L m ] appearing in the modified Takabe formula for the growth rate of the ablative Rayleigh-Taylor instability. The measured density profiles were well reproduced by a one-dimensional hydrodynamic simulation code. The density measurement contributes toward fully understanding the ablative Rayleigh-Taylor instability
International Nuclear Information System (INIS)
Delorme, Barthelemy
2015-01-01
Numerous designs and experiments in the domain of Inertial Confinement Fusion (ICF) show that, in both direct and indirect drive approaches, one of the main limitations to reach the ignition is the Rayleigh-Taylor instability (RTI). It may lead to shell disruption and performance degradation of spherically imploding targets. Thus, the understanding and the control of the initial conditions of the RTI is of crucial importance for the ICF program. In this thesis, we present an experimental and theoretical study of the initial conditions of the ablative RTI in direct drive, by means of two experimental campaigns performed on the OMEGA laser facility (LLE, Rochester). The first campaign consisted in studying the laser-imprinted ablative Richtmyer-Meshkov instability (RMI) which starts at the beginning of the interaction and seeds the ablative RTI. We set up an experimental configuration that allowed to measure for the first time the temporal evolution of the laser-imprinted ablative RMI. The experimental results have been interpreted by a theoretical model and numerical simulations performed with the hydrodynamic code CHIC. We show that the best way to control the ablative RMI is to reduce the laser intensity inhomogeneities. This can be achieved with targets covered by a layer of a low density foam. Thus, in the second campaign, we studied for the first time the effect of underdense foams on the growth of the ablative RTI. A layer of low density foam was placed in front of a plastic foil, and the perturbation was imprinted by an intensity modulated laser beam. Experimental data are presented: backscattered laser energy, target dynamic obtained by side-on self emission measurement, and face-on radiographs showing the effect of the foams on the target areal density modulations. These data were interpreted using the CHIC code and the laser-plasma interaction code PARAX. We show that the foams noticeably reduce the amplitude of the laser intensity inhomogeneities and the
Direct-drive–ignition designs with mid-Z ablators
Energy Technology Data Exchange (ETDEWEB)
Lafon, M.; Betti, R. [Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Laboratory for Laser Energetics and Fusion Science Center, University of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Anderson, K. S.; Collins, T. J. B.; Epstein, R.; McKenty, P. W.; Myatt, J. F.; Shvydky, A.; Skupsky, S. [Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623 (United States)
2015-03-15
Achieving thermonuclear ignition using direct laser illumination relies on the capability to accelerate spherical shells to high implosion velocities while maintaining shell integrity. Ablator materials of moderate atomic number Z reduce the detrimental effects of laser–plasma instabilities in direct-drive implosions. To validate the physics of moderate-Z ablator materials for ignition target designs on the National Ignition Facility (NIF), hydro-equivalent targets are designed using pure plastic (CH), high-density carbon, and glass (SiO{sub 2}) ablators. The hydrodynamic stability of these targets is investigated through two-dimensional (2D) single-mode and multimode simulations. The overall stability of these targets to laser-imprint perturbations and low-mode asymmetries makes it possible to design high-gain targets. Designs using polar-drive illumination are developed within the NIF laser system specifications. Mid-Z ablator targets are an attractive candidate for direct-drive ignition since they present better overall performance than plastic ablator targets through reduced laser–plasma instabilities and a similar hydrodynamic stability.
International Nuclear Information System (INIS)
Shigemori, K.; Azechi, H.; Fujioka, S.
2003-01-01
We present recent results on the hydrodynamic instability experiments on the HIPER (High Intensity Plasma Experimental Research) laser facility at ILE, Osaka University. We measured the Rayleigh-Taylor growth rate on the HIPER laser. Also measured were all parameters that determine the RT growth rate. We focused on the measurements of the ablation density of laser-irradiated targets, which had not been experimentally measured. The experimental results were compared with calculations with one dimensional simulation coupled with Fokker-Planck equation for electron transport. (author)
CHF Enhancement by Surface Patterning based on Hydrodynamic Instability Model
Energy Technology Data Exchange (ETDEWEB)
Seo, Han; Bang, In Cheol [UNIST, Ulsan (Korea, Republic of)
2015-05-15
If the power density of a device exceeds the CHF point, bubbles and vapor films will be covered on the whole heater surface. Because vapor films have much lower heat transfer capabilities compared to the liquid layer, the temperature of the heater surface will increase rapidly, and the device could be damaged due to the heater burnout. Therefore, the prediction and the enhancement of the CHF are essential to maximizing the efficient heat removal region. Numerous studies have been conducted to describe the CHF phenomenon, such as hydrodynamic instability theory, macrolayer dryout theory, hot/dry spot theory, and bubble interaction theory. The hydrodynamic instability model, proposed by Zuber, is the predominant CHF model that Helmholtz instability attributed to the CHF. Zuber assumed that the Rayleigh-Taylor (RT) instability wavelength is related to the Helmholtz wavelength. Lienhard and Dhir proposed a CHF model that Helmholtz instability wavelength is equal to the most dangerous RT wavelength. In addition, they showed the heater size effect using various heater surfaces. Lu et al. proposed a modified hydrodynamic theory that the Helmholtz instability was assumed to be the heater size and the area of the vapor column was used as a fitting factor. The modified hydrodynamic theories were based on the change of Helmholtz wavelength related to the RT instability wavelength. In the present study, the change of the RT instability wavelength, based on the heater surface modification, was conducted to show the CHF enhancement based on the heater surface patterning in a plate pool boiling. Sapphire glass was used as a base heater substrate, and the Pt film was used as a heating source. The patterning surface was based on the change of RT instability wavelength. In the present work the study of the CHF was conducted using bare Pt and patterned heating surfaces.
Hydrodynamic instability of compressible fluid in porous medium
International Nuclear Information System (INIS)
Argal, Shraddha; Tiwari, Anita; Sharma, P K; Prajapati, R P
2014-01-01
The hydrodynamic Rayleigh -Taylor instability of two superposed compressible fluids in porous medium has been studied. The dispersion relation is derived for such a medium by using normal mode analysis. The RT instability is discussed for various simplified configuration. The effect of porosity and dynamic viscosity has been analyzed and it is observed that porosity and dynamic viscosity have stabilizing effect on the Rayleigh- Taylor instability of compressible fluids.
Ji, H.; Burin, M.; Schartman, E.; Goodman, J.; Liu, W.
2006-01-01
Two plausible mechanisms have been proposed to explain rapid angular momentum transport during accretion processes in astrophysical disks: nonlinear hydrodynamic instabilities and magnetorotational instability (MRI). A laboratory experiment in a short Taylor-Couette flow geometry has been constructed in Princeton to study both mechanisms, with novel features for better controls of the boundary-driven secondary flows (Ekman circulation). Initial results on hydrodynamic stability have shown negligible angular momentum transport in Keplerian-like flows with Reynolds numbers approaching one million, casting strong doubt on the viability of nonlinear hydrodynamic instability as a source for accretion disk turbulence.
Hydrodynamic instabilities in inertial confinement fusion
International Nuclear Information System (INIS)
Hoffman, N.M.
1995-01-01
The focus of these (two) lectures is on buoyancy-driven instabilities of the Rayleigh-Taylor type, which are commonly regarded as the most important kind of hydrodynamic instability in inertial-confinement-fusion implosions. The paper is intended to be pedagogical rather than research-oriented, and so is by no means a comprehensive review of work in this field. Rather, it is hoped that the student will find here a foundation on which to build an understanding of current research, and the experienced researcher will find a compilation of useful results. (author)
Statistical approach of weakly nonlinear ablative Rayleigh-Taylor instability
International Nuclear Information System (INIS)
Garnier, J.; Masse, L.
2005-01-01
A weakly nonlinear model is proposed for the Rayleigh-Taylor instability in presence of ablation and thermal transport. The nonlinear effects for a single-mode disturbance are computed, included the nonlinear correction to the exponential growth of the fundamental modulation. Mode coupling in the spectrum of a multimode disturbance is thoroughly analyzed by a statistical approach. The exponential growth of the linear regime is shown to be reduced by the nonlinear mode coupling. The saturation amplitude is around 0.1λ for long wavelengths, but higher for short instable wavelengths in the ablative regime
Hydrodynamic stability theory of double ablation front structures in inertial confinement fusion
International Nuclear Information System (INIS)
Yanez Vico, C.
2012-11-01
For moderate-Z materials, the hydrodynamic structure of the ablation region formed by the irradiation of high intensity laser beams differs from that of low-Z materials (hydrogenic ablators). In particular, the role played by the radiative energy flux becomes non-negligible for increasing atomic number material and ended up forming a second ablation front. This structure of two separated ablation fronts, called double ablation (DA) front, was confirmed in the simulations carried out by Fujioka et al. In this work a linear stability theory of DA fronts is developed for direct-drive inertial confinement fusion targets. Two models are proposed. First, a sharp boundary model where the thin front approximation is assumed for both ablation fronts. The information about the corona region that permits to close the sharp boundary model is obtained from a prior self-consistent analysis of the electronic-radiative ablation (ERA) front. Numerical results are presented as well as an analytical approach for the radiation dominated regime of very steep double ablation front structure. Second, a self-consistent numerical method where the finite length of the ablation fronts is considered. Accurate hydrodynamic profiles are taken into account in the theoretical model by means of a fitting parameters method using one-dimensional simulation results. Numerical dispersion relation is compared to the analytical sharp boundary model showing an excellent agreement for the radiation dominated regime, and the stabilization due to smooth profiles. 2D simulations are presented to validate the linear stability theory
Numerical simulation of anisotropic preheating ablative Rayleigh-Taylor instability
International Nuclear Information System (INIS)
Wang Lifeng; Ye Wenhua; Li Yingjun
2010-01-01
The linear growth rate of the anisotropic preheating ablative Rayleigh-Taylor instability (ARTI) is studied by numerical simulations. The preheating model κ(T)=κ SH [1+f(T)] is applied, where f(T) is the preheating function interpreting the preheating tongue effect in the cold plasma ahead of the ablative front. An arbitrary coefficient D is introduced in the energy equation to study the influence of transverse thermal conductivity on the growth of the ARTI. We find that enhancing diffusion in a plane transverse to the mean longitudinal flow can strongly reduce the growth of the instability. Numerical simulations exhibit a significant stabilization of the ablation front by improving the transverse thermal conduction. Our results are in general agreement with the theory analysis and numerical simulations by Masse. (authors)
Spontaneous generation of spiral waves by a hydrodynamic instability
Habibi, M.; Møller, P.C.F.; Ribe, N.M.; Bonn, D.
2008-01-01
The coiling of a thin filament of viscous fluid falling onto a surface is a common and easily reproducible hydrodynamic instability. Here we report for the first time that this instability can generate regular spiral patterns, in which air bubbles are trapped in the coil and then advected
Landau-Darrieus instability in an ablation front
International Nuclear Information System (INIS)
Piriz, A.R.; Portugues, R.F.
2003-01-01
An analytical model that shows the conditions for the existence of the Landau-Darrieus instability of an ablation front is presented. The model seems to agree with recently claimed simulation results [L. Masse et al., Proceedings of the 1st International Conference on Inertial Fusion Sciences and Applications (Elsevier, Paris, 2000), p. 220]. The model shows that the ablation front can be unstable in absence of gravity when the thermal flux is inhibited within the supercritical region of the corona
International Nuclear Information System (INIS)
Aglitskiy, Y; Metzler, N; Karasik, M; Velikovich, A L; Zalesak, S T; Schmitt, A J; Serlin, V; Weaver, J; Obenschain, S P; Gardner, J H
2008-01-01
In inertial confinement fusion (ICF) and high-energy density physics (HEDP), the most important manifestations of the hydrodynamic instabilities and other mixing processes involve lateral motion of the accelerated plasmas. In order to understand the experimental observations and to advance the numerical simulation codes to the point of predictive capability, it is critically important to accurately diagnose the motion of the dense plasma mass. The most advanced diagnostic technique recently developed for this purpose is the monochromatic x-ray imaging that combines large field of view with high contrast, high spatial resolution and large throughput, ensuring high temporal resolution at large magnification. Its application made it possible for the experimentalists to observe for the first time important hydrodynamic effects that trigger compressible turbulent mixing in laser targets, such as ablative Richtmyer-Meshkov (RM) instability, feedout, interaction of an RM-unstable interface with shock and rarefaction waves. It also helped to substantially improve the accuracy of diagnosing many other important plasma flows, ranging from laser-produced jets to electromagnetically driven wires in a Z-pinch, and to test various methods suggested for mitigation of the Rayleigh-Taylor instability. We will review the results obtained with the aid of this technique in ICF-HEDP studies at the Naval Research Laboratory and the prospects of its future applications.
Numerical Simulation of Anisotropic Preheating Ablative Rayleigh–Taylor Instability
International Nuclear Information System (INIS)
Li-Feng, Wang; Wen-Hua, Ye; Ying-Jun, Li
2010-01-01
The linear growth rate of the anisotropic preheating ablative Rayleigh–Taylor instability (ARTI) is studied by numerical simulations. The preheating model κ(T) = κ SH [1 + f(T)] is applied, where f(T) is the preheating function interpreting the preheating tongue effect in the cold plasma ahead of the ablative front. An arbitrary coefficient D is introduced in the energy equation to study the influence of transverse thermal conductivity on the growth of the ARTI. We find that enhancing diffusion in a plane transverse to the mean longitudinal flow can strongly reduce the growth of the instability. Numerical simulations exhibit a significant stabilization of the ablation front by improving the transverse thermal conduction. Our results are in general agreement with the theory analysis and numerical simulations by Masse [Phys. Rev. Lett. 98 (2007) 245001]. (physics of gases, plasmas, and electric discharges)
Nucleosynthesis and hydrodynamic instabilities in core collapse supernovae
International Nuclear Information System (INIS)
Kifonidis, K.
2001-01-01
Hydrodynamic instabilities are of crucial importance for the explosion of massive stars as core collapse supernovae, for the synthesis of the heavy elements, and for their injection into the interstellar medium. The processes hereby involved are studied by means of two-dimensional hydrodynamic simulations which follow all phases from shock revival to shock breakout through the photosphere of a massive star. The computed distributions of radioactive elements are compared to observational data of SN 1987 A and other supernovae. While we find good agreement of our models with observations of Type Ib supernovae, the high velocities of iron group elements observed in SN 1987 A cannot be reproduced. Possible reasons for this discrepancy are discussed. Hydrodynamic instabilities are of crucial importance for the explosion of massive stars as core collapse supernovae, for the synthesis of the heavy elements, and for their injection into the interstellar medium. The processes hereby involved are studied by means of two-dimensional hydrodynamic simulations which follow all phases from shock revival to shock breakout through the photosphere of a massive star. The computed distributions of radioactive elements are compared to observational data of SN 1987 A and other supernovae. While we find good agreement of our models with observations of Type Ib supernovae, the high velocities of iron group elements observed in SN 1987 A cannot be reproduced. Possible reasons for this discrepancy are discussed
Hydrodynamic model for ultra-short pulse ablation of hard dental tissue
Energy Technology Data Exchange (ETDEWEB)
London, R.A.; Bailey, D.S.; Young, D.A.; Alley, W.E.; Feit, M.D.; Rubenchik, A.M. [Lawrence Livermore National Lab., CA (United States); Neev, J. [Beckman Laser Inst., Irvine, CA (United States)
1996-02-29
A computational model for the ablation of tooth enamel by ultra-short laser pulses is presented. The role of simulations using this model in designing and understanding laser drilling systems is discussed. Pulses of duration 300 fsec and intensity greater than 10{sup 12} W/cm{sup 2} are considered. Laser absorption proceeds via multi-photon initiated plasma mechanism. The hydrodynamic response is calculated with a finite difference method, using an equation of state constructed from thermodynamic functions including electronic, ion motion, and chemical binding terms. Results for the ablation efficiency are presented. An analytic model describing the ablation threshold and ablation depth is presented. Thermal coupling to the remaining tissue and long-time thermal conduction are calculated. Simulation results are compared to experimental measurements of the ablation efficiency. Desired improvements in the model are presented.
Hydrodynamic instabilities in inertial confinement fusion
International Nuclear Information System (INIS)
Freeman, J.R.
1977-01-01
Inertial confinement fusion targets generally consist of hollow high-density spheres filled with low density thermonuclear fuel. Targets driven ablatively by electrons, ions, or lasers are potentially unstable during the initial acceleration phase. Later in time, the relatively low density fuel decelerates the dense inner portion of the sphere (termed the pusher), permitting unstable growth at the fuel-pusher interface. The instabilities are of the Rayleigh-Taylor variety, modified by thermal and viscous diffusion and convection. These problems have been analyzed by many in recent years using both linearized perturbation methods and direct numerical simulation. Examples of two-dimensional simulations of the fuel-pusher instability in electron beam fusion targets will be presented, along with a review of possible stabilization mechanisms
Coherent structures in ablatively compressed ICF targets and Rayleigh-Taylor instability
International Nuclear Information System (INIS)
Pant, H.C.; Desai, T.
1996-01-01
One of the major issues in laser induced inertial confinement fusion (ICF) is a stable ablative compression of spherical fusion pellets. The main impediment in achievement of this objective is Rayleigh-Taylor instability at the pellet's ablation front. Under sufficiently high acceleration this instability can grow out of noise. However, it can also arise either due to non-uniform laser intensity distribution over the pellet surface or due to pellet wall areal mass irregularity. Coherent structures in the dense target behind the ablation front can be effectively utilised for stabilisation of the Rayleigh-Taylor phenomenon. Such coherent structures in the form of a super lattice can be created by doping the pellet pusher with high atomic number (Z) micro particles. A compressed-cool pusher under laser irradiation behaves like a strongly correlated non ideal plasma when compressed to sufficiently high density such that the non ideality parameter exceeds unity. Moreover, the nonideality parameter for high Z microinclusions may exceed a critical value of 180 and as a consequence they remain in the form of intact clusters, maintaining the superlattice intact during ablative acceleration. Micro-hetrogeneity and its superlattice plays an important role in stabilization of Rayleigh-Taylor instability, through a variety of mechanisms. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Medvid’, A., E-mail: mychko@latnet.lv [Riga Technical University, 3 Paula Valdena Str., LV-1048 Riga (Latvia); Mychko, A.; Dauksta, E. [Riga Technical University, 3 Paula Valdena Str., LV-1048 Riga (Latvia); Kosyak, V. [Sumy State University, 2, Rymskogo-Korsakova St., 40007 Sumy (Ukraine); Grase, L. [Riga Technical University, 3 Paula Valdena Str., LV-1048 Riga (Latvia)
2016-06-30
Highlights: • We found two laser induced threshold intensity for CdZnTe crystal. • The laser beam self-focusing lead to increase of intensity of laser radiation at exit surface. • Laser ablation is a result of Te inclusion hydrodynamic expansion. - Abstract: The present paper deals with the laser ablation in CdZnTe crystal irradiated by pulsed infrared laser. Two values of threshold intensities of the laser ablation were determined, namely of about 8.5 and 6.2 MW/cm{sup 2} for the incident and the rear surfaces, correspondingly. Lower intensity of the laser ablation for the rear surface is explained by thermal self-focusing of the laser beam in the CdZnTe crystal due to heating of Te inclusions with a following hydrodynamic expansion.
Can numerical simulations accurately predict hydrodynamic instabilities in liquid films?
Denner, Fabian; Charogiannis, Alexandros; Pradas, Marc; van Wachem, Berend G. M.; Markides, Christos N.; Kalliadasis, Serafim
2014-11-01
Understanding the dynamics of hydrodynamic instabilities in liquid film flows is an active field of research in fluid dynamics and non-linear science in general. Numerical simulations offer a powerful tool to study hydrodynamic instabilities in film flows and can provide deep insights into the underlying physical phenomena. However, the direct comparison of numerical results and experimental results is often hampered by several reasons. For instance, in numerical simulations the interface representation is problematic and the governing equations and boundary conditions may be oversimplified, whereas in experiments it is often difficult to extract accurate information on the fluid and its behavior, e.g. determine the fluid properties when the liquid contains particles for PIV measurements. In this contribution we present the latest results of our on-going, extensive study on hydrodynamic instabilities in liquid film flows, which includes direct numerical simulations, low-dimensional modelling as well as experiments. The major focus is on wave regimes, wave height and wave celerity as a function of Reynolds number and forcing frequency of a falling liquid film. Specific attention is paid to the differences in numerical and experimental results and the reasons for these differences. The authors are grateful to the EPSRC for their financial support (Grant EP/K008595/1).
Three-dimensional single-mode nonlinear ablative Rayleigh-Taylor instability
International Nuclear Information System (INIS)
Yan, R.; Aluie, H.; Betti, R.; Sanz, J.; Liu, B.; Frank, A.
2016-01-01
The nonlinear evolution of the single-mode ablative Rayleigh-Taylor instability is studied in three dimensions. As the mode wavelength approaches the cutoff of the linear spectrum (short-wavelength modes), it is found that the three-dimensional (3D) terminal bubble velocity greatly exceeds both the two-dimensional (2D) value and the classical 3D bubble velocity. Unlike in 2D, the 3D short-wavelength bubble velocity does not saturate. The growing 3D bubble acceleration is driven by the unbounded accumulation of vorticity inside the bubble. The vorticity is transferred by mass ablation from the Rayleigh-Taylor spikes to the ablated plasma filling the bubble volume
Jet-like long spike in nonlinear evolution of ablative Rayleigh-Taylor instability
International Nuclear Information System (INIS)
Ye Wenhua; He Xiantu; Wang Lifeng
2010-01-01
We report the formation of jet-like long spike in the nonlinear evolution of the ablative Rayleigh-Taylor instability (ARTI) experiments by numerical simulations. A preheating model κ(T) = κ SH [1 + f(T)], where κ SH is the Spitzer-Haerm (SH) electron conductivity and f(T) interprets the preheating tongue effect in the cold plasma ahead of the ablative front [Phys. Rev. E 65 (2002) 57401], is introduced in simulations. The simulation results of the nonlinear evolution of the ARTI are in general agreement with the experiment results. It is found that two factors, i.e., the suppressing of ablative Kelvin-Helmholtz instability (AKHI) and the heat flow cone in the spike tips, contribute to the formation of jet-like long spike in the nonlinear evolution of the ARTI. (authors)
Treatment of compounds and alloys in radiation hydrodynamics simulations of ablative laser loading
International Nuclear Information System (INIS)
Swift, Damian C.; Gammel, J. Tinka; Clegg, Samuel M.
2004-01-01
Different methods were compared for constructing models of the behavior of a prototype intermetallic compound, nickel aluminide, for use in radiation hydrodynamics simulations of shock wave generation by ablation induced by laser energy. The models included the equation of state, ionization, and radiation opacity. The methods of construction were evaluated by comparing the results of simulations of an ablatively generated shock wave in a sample of the alloy. The most accurate simulations were obtained using the 'constant number density' mixture model to calculate the equation of state and opacity, and Thomas-Fermi ionization. This model is consistent with that found to be most accurate for simulations of ablatively shocked elements
Numerical simulation of Rayleigh-Taylor instability in ablation driven systems
International Nuclear Information System (INIS)
Verdon, C.P.
1984-01-01
Two-dimensional numerical simulations of ablatively accelerated thin shells subject to Rayleigh-Taylor instability are presented. Results for both single wavelength and multiwavelength perturbations show that the nonlinear effects of the instability are evident mainly in the bubble rather than the spike. Approximate roles for predicting the dominant nonlinear mode-mode interactions, which limit shell performance, are also discussed. The work concludes with a discussion of recommendations for future work in this area
Simulation of instability growth on ICF capsule ablators
Niasse, Nicolas; Chittenden, Jeremy
2014-10-01
It is believed that the ablation-front instabilities are mainly responsible for the hot-spot mix that impacts the performance of ICF capsules. Understanding the formation of these instabilities is therefore a first step towards a better control of the implosion dynamics and the optimization of the fusion yield. Using the Chimera code currently in development at Imperial College, we have performed several spherical wedge simulations of the low and high adiabat ablation phase pre-imposing different single-mode 2D and 3D perturbations on the capsule surface. Synthetic Sc, Fe and V X-ray backlighter images are generated by the Spk code and used to measure the growth of modes 30-160 with initial amplitude <= 3.4 μm PTV. The growth of imposed 2D perturbations is assessed for both low-foot and high-foot radiation pulse shapes on the National Ignition Facility. Results showing the merger of spike and bubble structures in multi-mode perturbations in both 2D and 3D simulations are explored and preliminary assessments of the difference between 2D and 3D non-linear behaviour is discussed. The sensitivity of shock timing to NLTE changes in opacity is also assessed.
International Nuclear Information System (INIS)
Fridman, A M
2008-01-01
The theory and the experimental discovery of extremely strong hydrodynamic instabilities are described, viz. the Kelvin-Helmholtz, centrifugal, and superreflection instabilities. The discovery of the last two instabilities was predicted and the Kelvin-Helmholtz instability in real systems was revised by us. (reviews of topical problems)
Effects of magnetic field, sheared flow and ablative velocity on the Rayleigh-Taylor instability
International Nuclear Information System (INIS)
Li, D.; Zhang, W.L.; Wu, Z.W.
2005-01-01
It is found that magnetic field has a stabilization effect whereas the sheared flow has a destabilization effect on the RT instability in the presence of sharp interface. RT instability only occurs in the long wave region and can be completely suppressed if the stabilizing effect of magnetic field dominates. The RT instability increases with wave number and flow shear, and acts much like a Kelvin-Helmholtz instability when destabilizing effect of sheared flow dominates. It is shown that both of ablation velocity and magnetic filed have stabilization effect on RT instability in the presence of continued interface. The stabilization effect of magnetic field takes place for whole waveband and becomes more significant for the short wavelength. The RT instability can be completely suppressed by the cooperated effect of magnetic field and ablation velocity so that the ICF target shell may be unnecessary to be accelerated to very high speed. The growth rate decreases as the density scale length increases. The stabilization effect of magnetic field is more significant for the short density scale length. (author)
Active control of magneto-hydrodynamic instabilities in hot plasmas
2015-01-01
During the past century, world-wide energy consumption has risen dramatically, which leads to a quest for new energy sources. Fusion of hydrogen atoms in hot plasmas is an attractive approach to solve the energy problem, with abundant fuel, inherent safety and no long-lived radioactivity. However, one of the limits on plasma performance is due to the various classes of magneto-hydrodynamic instabilities that may occur. The physics and control of these instabilities in modern magnetic confinement fusion devices is the subject of this book. Written by foremost experts, the contributions will provide valuable reference and up-to-date research reviews for "old hands" and newcomers alike.
Hydrodynamic cavitation kills prostate cells and ablates benign prostatic hyperplasia tissue.
Itah, Zeynep; Oral, Ozlem; Perk, Osman Yavuz; Sesen, Muhsincan; Demir, Ebru; Erbil, Secil; Dogan-Ekici, A Isin; Ekici, Sinan; Kosar, Ali; Gozuacik, Devrim
2013-11-01
Hydrodynamic cavitation is a physical phenomenon characterized by vaporization and bubble formation in liquids under low local pressures, and their implosion following their release to a higher pressure environment. Collapse of the bubbles releases high energy and may cause damage to exposed surfaces. We recently designed a set-up to exploit the destructive nature of hydrodynamic cavitation for biomedical purposes. We have previously shown that hydrodynamic cavitation could kill leukemia cells and erode kidney stones. In this study, we analyzed the effects of cavitation on prostate cells and benign prostatic hyperplasia (BPH) tissue. We showed that hydrodynamic cavitation could kill prostate cells in a pressure- and time-dependent manner. Cavitation did not lead to programmed cell death, i.e. classical apoptosis or autophagy activation. Following the application of cavitation, we observed no prominent DNA damage and cells did not arrest in the cell cycle. Hence, we concluded that cavitation forces directly damaged the cells, leading to their pulverization. Upon application to BPH tissues from patients, cavitation could lead to a significant level of tissue destruction. Therefore similar to ultrasonic cavitation, we propose that hydrodynamic cavitation has the potential to be exploited and developed as an approach for the ablation of aberrant pathological tissues, including BPH.
Ablative Rayleigh-Taylor instability in the limit of an infinitely large density ratio
International Nuclear Information System (INIS)
Clavin, P.; Almarcha, Ch.
2005-01-01
The instability of ablation fronts strongly accelerated toward the dense medium under the conditions of inertial confinement fusion (ICF) is addressed in the limit of an infinitely large density ratio. The analysis serves to demonstrate that the flow is irrotational to first order, reducing the nonlinear analysis to solve a two-potential flows problem. Vorticity appears at the following orders in the perturbation analysis. This result simplifies greatly the analysis. The possibility for using boundary integral methods opens new perspectives in the nonlinear theory of the ablative Rayleigh-Taylor instability in ICF. A few examples are given at the end of the paper. (authors)
Ma, T; Patel, P K; Izumi, N; Springer, P T; Key, M H; Atherton, L J; Benedetti, L R; Bradley, D K; Callahan, D A; Celliers, P M; Cerjan, C J; Clark, D S; Dewald, E L; Dixit, S N; Döppner, T; Edgell, D H; Epstein, R; Glenn, S; Grim, G; Haan, S W; Hammel, B A; Hicks, D; Hsing, W W; Jones, O S; Khan, S F; Kilkenny, J D; Kline, J L; Kyrala, G A; Landen, O L; Le Pape, S; MacGowan, B J; Mackinnon, A J; MacPhee, A G; Meezan, N B; Moody, J D; Pak, A; Parham, T; Park, H-S; Ralph, J E; Regan, S P; Remington, B A; Robey, H F; Ross, J S; Spears, B K; Smalyuk, V; Suter, L J; Tommasini, R; Town, R P; Weber, S V; Lindl, J D; Edwards, M J; Glenzer, S H; Moses, E I
2013-08-23
Deuterium-tritium inertial confinement fusion implosion experiments on the National Ignition Facility have demonstrated yields ranging from 0.8 to 7×10(14), and record fuel areal densities of 0.7 to 1.3 g/cm2. These implosions use hohlraums irradiated with shaped laser pulses of 1.5-1.9 MJ energy. The laser peak power and duration at peak power were varied, as were the capsule ablator dopant concentrations and shell thicknesses. We quantify the level of hydrodynamic instability mix of the ablator into the hot spot from the measured elevated absolute x-ray emission of the hot spot. We observe that DT neutron yield and ion temperature decrease abruptly as the hot spot mix mass increases above several hundred ng. The comparison with radiation-hydrodynamic modeling indicates that low mode asymmetries and increased ablator surface perturbations may be responsible for the current performance.
Ablative Rayleigh Taylor instability in the limit of an infinitely large density ratio
Clavin, Paul; Almarcha, Christophe
2005-05-01
The instability of ablation fronts strongly accelerated toward the dense medium under the conditions of inertial confinement fusion (ICF) is addressed in the limit of an infinitely large density ratio. The analysis serves to demonstrate that the flow is irrotational to first order, reducing the nonlinear analysis to solve a two-potential flows problem. Vorticity appears at the following orders in the perturbation analysis. This result simplifies greatly the analysis. The possibility for using boundary integral methods opens new perspectives in the nonlinear theory of the ablative RT instability in ICF. A few examples are given at the end of the Note. To cite this article: P. Clavin, C. Almarcha, C. R. Mecanique 333 (2005).
International Nuclear Information System (INIS)
Levy, Y.
2012-01-01
In the context of inertial confinement fusion we investigate effects of magnetic fields on the development in the linear regime of two hydrodynamic instabilities: Richtmyer-Meshkov instability using ideal magnetohydrodynamics and ablative Rayleigh-Taylor instability in both acceleration and deceleration stages. Direct numerical simulations with a linear perturbation code enable us to confirm the stabilizing effect of the component of the magnetic field along the perturbations wave vector. The amplitude doesn't grow linearly in time but experiences oscillations instead. The compressibility taken into account in the code does not affect predictions given by an already existing impulsive and incompressible model. As far as Rayleigh-Taylor instability is concerned we study the effects of self-generated magnetic fields that arise from the development of the instability itself. In the acceleration stage we perform two dimensional simulations in planar geometry. We show that magnetic fields of about 1 T can be generated and that the instability growth transits more rapidly into nonlinear growth with the enhancement of the development of the third harmonic. We also propose an adaptation of an existing model that aims at studying thermal conductivity anisotropy effects, to take into account the effects of the self-generated magnetic fields on the Rayleigh-Taylor instability growth rate. Finally, in the deceleration stage, we perform two dimensional simulations in cylindrical geometry that take into account self-generation of magnetic fields due to the instability development. It reveals magnetic fields of about several thousands of Teslas that are not strong enough though to affect the instability behavior. (author) [fr
Energy Technology Data Exchange (ETDEWEB)
Stephen B. Margolis; Forman A. Williams
1999-03-01
Hydrodynamic (Landau) instability in combustion is typically associated with the onset of wrinkling of a flame surface, corresponding to the formation of steady cellular structures as the stability threshold is crossed. In the context of liquid-propellant combustion, such instability has recently been shown to occur for critical values of the pressure sensitivity of the burning rate and the disturbance wavenumber, significantly generalizing previous classical results for this problem that assumed a constant normal burning rate. Additionally, however, a pulsating form of hydrodynamic instability has been shown to occur as well, corresponding to the onset of temporal oscillations in the location of the liquid/gas interface. In the present work, we consider the realistic influence of a nonzero temperature sensitivity in the local burning rate on both types of stability thresholds. It is found that for sufficiently small values of this parameter, there exists a stable range of pressure sensitivities for steady, planar burning such that the classical cellular form of hydrodynamic instability and the more recent pulsating form of hydrodynamic instability can each occur as the corresponding stability threshold is crossed. For larger thermal sensitivities, however, the pulsating stability boundary evolves into a C-shaped curve in the (disturbance-wavenumber, pressure-sensitivity) plane, indicating loss of stability to pulsating perturbations for all sufficiently large disturbance wavelengths. It is thus concluded, based on characteristic parameter values, that an equally likely form of hydrodynamic instability in liquid-propellant combustion is of a nonsteady, long-wave nature, distinct from the steady, cellular form originally predicted by Landau.
Martinand, Denis; Tilton, Nils
2016-11-01
This study addresses analytically and numerically the coupling between hydrodynamic instabilities and osmotic pressure driven by concentration polarization. The configuration consists of a Taylor-Couette cell filled with a Newtonian fluid carrying a passive scalar. Whereas the concentric inner and outer cylinders are membranes permeable to the solvent, they totally reject the scalar. As a radial in- or outflow of solvent is imposed through both cylinders, a concentration boundary layer develops on the cylinder where the solvent exits, until an equilibrium steady state is reached. In addition, the rotation of the inner cylinder is used to drive centrifugal instabilities in the form of toroidal vortices, which interact with the concentration boundary layer. By means of the osmotic pressure, concentration polarization is found to promote or hinder the hydrodynamic instabilities, depending on capacity of the vortices and diffusion to increase the concentration field at the membrane. The results obtained by analytical stability analysis agree with dedicated Direct Numerical Simulations.
Growth rates of the ablative Rayleigh endash Taylor instability in inertial confinement fusion
International Nuclear Information System (INIS)
Betti, R.; Goncharov, V.N.; McCrory, R.L.; Verdon, C.P.
1998-01-01
A simple procedure is developed to determine the Froude number Fr, the effective power index for thermal conduction ν, the ablation-front thickness L 0 , the ablation velocity V a , and the acceleration g of laser-accelerated ablation fronts. These parameters are determined by fitting the density and pressure profiles obtained from one-dimensional numerical simulations with the analytic isobaric profiles of Kull and Anisimov [Phys. Fluids 29, 2067 (1986)]. These quantities are then used to calculate the growth rate of the ablative Rayleigh endash Taylor instability using the theory developed by Goncharov et al. [Phys. Plasmas 3, 4665 (1996)]. The complicated expression of the growth rate (valid for arbitrary Froude numbers) derived by Goncharov et al. is simplified by using reasonably accurate fitting formulas. copyright 1998 American Institute of Physics
International Nuclear Information System (INIS)
Casner, A.; Masse, L.; Delorme, B.; Jacquet, L.; Liberatore, S.; Smalyuk, V.; Martinez, D.; Seugling, R.; Park, H.S.; Remington, B.A.; Moore, A.; Igumenshev, I.; Chicanne, C.
2013-01-01
In the context of National Ignition Facility Basic Science program we propose to study on the NIF ablative Rayleigh-Taylor (RT) instability in transition from weakly nonlinear to highly nonlinear regimes. Based on the analogy between flame front and ablation front, highly nonlinear RT instability measurements at the ablation front can provide important insights into the initial deflagration stage of thermonuclear supernovae of type Ia. NIF provides a unique platform to study the rich physics of nonlinear and turbulent mixing flows in High Energy Density plasmas because it can accelerate targets over much larger distances and longer time periods than previously achieved on the NOVA and OMEGA lasers. In one shot, growth of RT modulations can be measured from the weakly nonlinear stage near nonlinear saturation levels to the highly nonlinear bubble-competition, bubble-merger regimes and perhaps into a turbulent-like regime. The role of ablation on highly-nonlinear RT instability evolution will be comprehensively studied by varying ablation velocity using indirect and direct-drive platforms. We present a detailed hydro-code design of the indirect-drive platform and discuss the implementation plan for these experiments which only use NIF diagnostics already qualified. (authors)
Energy Technology Data Exchange (ETDEWEB)
Stephen B. Margolis
2000-01-01
A pulsating form of hydrodynamic instability has recently been shown to arise during liquid-propellant deflagration in those parameter regimes where the pressure-dependent burning rate is characterized by a negative pressure sensitivity. This type of instability can coexist with the classical cellular, or Landau, form of hydrodynamic instability, with the occurrence of either dependent on whether the pressure sensitivity is sufficiently large or small in magnitude. For the inviscid problem, it has been shown that when the burning rate is realistically allowed to depend on temperature as well as pressure, that sufficiently large values of the temperature sensitivity relative to the pressure sensitivity causes the pulsating form of hydrodynamic instability to become dominant. In that regime, steady, planar burning becomes intrinsically unstable to pulsating disturbances whose wavenumbers are sufficiently small. In the present work, this analysis is extended to the fully viscous case, where it is shown that although viscosity is stabilizing for intermediate and larger wavenumber perturbations, the intrinsic pulsating instability for small wavenumbers remains. Under these conditions, liquid-propellant combustion is predicted to be characterized by large unsteady cells along the liquid/gas interface.
Power Disturbances Close to Hydrodynamic Instability in Natural Circulation Two-Phase Flow
International Nuclear Information System (INIS)
Mathisen, R.P.; Eklind, O.
1967-07-01
In certain boiling reactor designs high positive void coefficients could exist and under certain circumstances cause instability. Control systems may therefore be desired. In such a controlled reactor there could remain superimposed low frequency power oscillations of some magnitude. The object of the current experiments in SKALVAN was to examine whether or not such slow oscillations could influence the hydrodynamic stability limit of the individual boiling channels. While operating the loop close to the threshold of hydrodynamic instability, the power was pulsed in the boiling channel. The pulse widths had a lower limit of 0.65 sec due to the contactor time constant. The square wave power oscillation amplitude ΔQ/Q was 12.2 %, and the interval T between the pulses was varied in the range 0 0 /T 0 was the mass flow oscillation period. The corresponding mass flow oscillations remained damped for all disturbance periods which were examined. With minimum test section inlet restrictions the power level at instability was much lower than that at burnout conditions. At higher restrictions these phenomena occurred at approximately equivalent power levels. The experiments with minimum inlet restrictions were also performed beyond the instability threshold. In this case it was possible to exceed the nominal burnout point temporarily by 5 per cent or more for periods of the order of magnitude 1 second. Even now the boiling channel conditions were not so severely affected that the burnout detectors tripped, and the power disturbances caused low frequency modulated wave trains
Power Disturbances Close to Hydrodynamic Instability in Natural Circulation Two-Phase Flow
Energy Technology Data Exchange (ETDEWEB)
Mathisen, R P; Eklind, O
1967-07-15
In certain boiling reactor designs high positive void coefficients could exist and under certain circumstances cause instability. Control systems may therefore be desired. In such a controlled reactor there could remain superimposed low frequency power oscillations of some magnitude. The object of the current experiments in SKALVAN was to examine whether or not such slow oscillations could influence the hydrodynamic stability limit of the individual boiling channels. While operating the loop close to the threshold of hydrodynamic instability, the power was pulsed in the boiling channel. The pulse widths had a lower limit of 0.65 sec due to the contactor time constant. The square wave power oscillation amplitude {delta}Q/Q was 12.2 %, and the interval T between the pulses was varied in the range 0 < T{sub 0}/T < 0. 5 where T{sub 0} was the mass flow oscillation period. The corresponding mass flow oscillations remained damped for all disturbance periods which were examined. With minimum test section inlet restrictions the power level at instability was much lower than that at burnout conditions. At higher restrictions these phenomena occurred at approximately equivalent power levels. The experiments with minimum inlet restrictions were also performed beyond the instability threshold. In this case it was possible to exceed the nominal burnout point temporarily by 5 per cent or more for periods of the order of magnitude 1 second. Even now the boiling channel conditions were not so severely affected that the burnout detectors tripped, and the power disturbances caused low frequency modulated wave trains.
Studies in the evolution of hydrodynamic instabilities and their role in inertial confinement fusion
International Nuclear Information System (INIS)
Shvarts, D.; Oron, D.; Sadot, O.
2001-01-01
Hydrodynamic instabilities, such as the Rayleigh-Taylor and Richtmyer-Meshkov instabilities, have a central role when trying to achieve net thermonuclear fusion energy via the method of Inertial Confinement Fusion. We shall review recent theoretical, numerical and experimental work that describes the evolution of two- and three-dimensional perturbations. Finally, the effects of these perturbation on the ignition conditions, using new self-similar solutions for perturbed burn wave propagation will be discussed. (author)
Linear Simulations of the Cylindrical Richtmyer-Meshkov Instability in Hydrodynamics and MHD
Gao, Song
2013-05-01
The Richtmyer-Meshkov instability occurs when density-stratified interfaces are impulsively accelerated, typically by a shock wave. We present a numerical method to simulate the Richtmyer-Meshkov instability in cylindrical geometry. The ideal MHD equations are linearized about a time-dependent base state to yield linear partial differential equations governing the perturbed quantities. Convergence tests demonstrate that second order accuracy is achieved for smooth flows, and the order of accuracy is between first and second order for flows with discontinuities. Numerical results are presented for cases of interfaces with positive Atwood number and purely azimuthal perturbations. In hydrodynamics, the Richtmyer-Meshkov instability growth of perturbations is followed by a Rayleigh-Taylor growth phase. In MHD, numerical results indicate that the perturbations can be suppressed for sufficiently large perturbation wavenumbers and magnetic fields.
Density gradient effects in weakly nonlinear ablative Rayleigh-Taylor instability
International Nuclear Information System (INIS)
Wang, L. F.; Ye, W. H.; He, X. T.
2012-01-01
In this research, density gradient effects (i.e., finite thickness of ablation front effects) in ablative Rayleigh-Taylor instability (ARTI), in the presence of preheating within the weakly nonlinear regime, are investigated numerically. We analyze the weak, medium, and strong ablation surfaces which have different isodensity contours, respectively, to study the influences of finite thickness of ablation front on the weakly nonlinear behaviors of ARTI. Linear growth rates, generation coefficients of the second and the third harmonics, and coefficients of the third-order feedback to the fundamental mode are obtained. It is found that the linear growth rate which has a remarkable maximum, is reduced, especially when the perturbation wavelength λ is short and a cut-off perturbation wavelength λ c appears when the perturbation wavelength λ is sufficiently short, where no higher harmonics exists when λ c . The phenomenon of third-order positive feedback to the fundamental mode near the λ c [J. Sanz et al., Phys. Rev. Lett. 89, 195002 (2002); J. Garnier et al., Phys. Rev. Lett. 90, 185003 (2003); J. Garnier and L. Masse, Phys. Plasmas 12, 062707 (2005)] is confirmed in numerical simulations, and the physical mechanism of the third-order positive feedback is qualitatively discussed. Moreover, it is found that generations and growths of the second and the third harmonics are stabilized (suppressed and reduced) by the ablation effect. Meanwhile, the third-order negative feedback to the fundamental mode is also reduced by the ablation effect, and hence, the linear saturation amplitude (typically ∼0.2λ in our simulations) is increased significantly and therefore exceeds the classical prediction 0.1λ, especially for the strong ablation surface with a small perturbation wavelength. Overall, the ablation effect stabilizes the ARTI in the weakly nonlinear regime. Numerical results obtained are in general agreement with the recent weakly nonlinear theories and simulations
Hydrodynamic scaling of the deceleration-phase Rayleigh–Taylor instability
Energy Technology Data Exchange (ETDEWEB)
Bose, A., E-mail: abos@lle.rochester.edu; Woo, K. M.; Betti, R. [Laboratory of Laser Energetics, Department of Physics, and Fusion Science Center, University of Rochester, 250 East River Road, Rochester, New York 14623-1299 (United States); Nora, R. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
2015-07-15
The scaling of the deceleration phase of inertial fusion direct-drive implosions is investigated for OMEGA and National Ignition Facility (NIF)-size targets. It is shown that the deceleration-phase Rayleigh–Taylor instability (RTI) does not scale hydro-equivalently with implosion size. This is because ablative stabilization resulting from thermal conduction and radiation transport in a spherically converging geometry is different on the two scales. As a consequence, NIF-scale implosions show lower hot-spot density and mass ablation velocity, allowing for higher RTI growth. On the contrary, stabilization resulting from density-gradient enhancement, caused by reabsorption of radiation emitted from the hot spot, is higher on NIF implosions. Since the RTI mitigation related to thermal conduction and radiation transport scale oppositely with implosion size, the degradation of implosion performance caused by the deceleration RTI is similar for NIF and OMEGA targets. It is found that a minimum threshold for the no-α Lawson ignition parameter of χ{sub Ω} ≈ 0.2 at the OMEGA scale is required to demonstrate hydro-equivalent ignition at the NIF scale for symmetric direct-drive implosions.
Hydrodynamic electronic fluid instability in GaAs MESFETs at terahertz frequencies
Li, Kang; Hao, Yue; Jin, Xiaoqi; Lu, Wu
2018-01-01
III-V compound semiconductor field effect transistors (FETs) are potential candidates as solid state THz emitters and detectors due to plasma wave instability in these devices. Using a 2D hydrodynamic model, here we present the numerical studies of electron fluid instability in a FET structure. The model is implemented in a GaAs MESFET structure with a gate length of 0.2 µm as a testbed by taking into account the non-equilibrium transport and multi-valley non-parabolicity energy bands. The results show that the electronic density instability in the channel can produce stable periodic oscillations at THz frequencies. Along with stable oscillations, negative differential resistance in output characteristics is observed. The THz emission energy density increases monotonically with the drain bias. The emission frequency of electron density oscillations can be tuned by both gate and drain biases. The results suggest that III-V FETs can be a kind of versatile THz devices with good tunability on both radiative power and emission frequency.
Observation of hydrodynamic processes of radiation-ablated plasma in a small hole
Energy Technology Data Exchange (ETDEWEB)
Li, Hang; Kuang, Longyu; Jiang, Shaoen, E-mail: jiangshn@vip.sina.com; Ding, Yongkun, E-mail: ding-yk@vip.sina.com [CAS Key Laboratory of Basic Plasma Physics and Department of Modern Physics, University of Science and Technology of China, Hefei 230026 (China); Research Center of Laser Fusion, China Academy of Engineering Physics, P.O. Box 919-986, Mianyang 621900 (China); Song, Tianming; Yang, Jiamin, E-mail: yjm70018@sina.cn; Zhu, Tuo; Lin, Zhiwei; Zheng, Jianhua; Zhang, Haiying; Yu, Ruizhen; Liu, Shenye [Research Center of Laser Fusion, China Academy of Engineering Physics, P.O. Box 919-986, Mianyang 621900 (China); Hu, Guangyue; Zhao, Bin; Zheng, Jian [CAS Key Laboratory of Basic Plasma Physics and Department of Modern Physics, University of Science and Technology of China, Hefei 230026 (China)
2015-07-15
In the hohlraum used in laser indirect-drive inertial confinement fusion experiments, hydrodynamic processes of radiation-ablated high-Z plasma have a great effect on laser injection efficiency, radiation uniformity, and diagnosis of hohlraum radiation field from diagnostic windows (DW). To study plasma filling in the DWs, a laser-irradiated Ti disk was used to generate 2–5 keV narrow energy band X-ray as the intense backlighter source, and laser-produced X-ray in a hohlraum with low-Z foam tamper was used to heat a small hole surrounded by gold wall with 150 μm in diameter and 100 μm deep. The hydrodynamic movement of the gold plasma in the small hole was measured by an X-ray framing camera and the results are analyzed. Quantitative measurement of the plasma areal density distribution and evolution in the small hole can be used to assess the effect of plasma filling on the diagnosis from the DWs.
International Nuclear Information System (INIS)
Labakanta Mandal; Banerjee, R.; Roy, S.; Khan, M.; Gupta, M.R.
2010-01-01
Complete text of publication follows. In an Inertial Confinement Fusion (ICF) situation, laser driven ablation front of an imploding capsule is subjected to the fluid instabilities like Rayleigh-Taylor (RT), Richtmyer-Meshkov (RM) and Kelvin-Helmholtz (KH) instability. In this case dense core is compressed and accelerated by low density ablating plasma. During this process laser driven shocks interact the interface and hence it becomes unstable due to the formation of nonlinear structure like bubble and spike. The nonlinear structure is called bubble if the lighter fluid pushes inside the heavier fluid and spike, if opposite takes place. R-M instability causes non-uniform compression of ICF fuel pellets and needs to be mitigated. Scientists and researchers are much more interested on RM instability both from theoretical and experimental points of view. In this article, we have presented the analytical expression for the growth rate and velocity for the nonlinear structures due to the effect of magnetic field of fluid using potential flow model. The magnetic field is assumed to be parallel to the plane of two fluid interfaces. If the magnetic field is restricted only to either side of interface the R-M instability can be stabilized or destabilized depending on whether the magnetic pressure on the interface opposes the instability driving shock pressure or acts in the same direction. An interesting result is that if both the fluids are magnetized, interface as well as velocity of bubble and spike will show oscillating stabilization and R-M instability is mitigated. All analytical results are also supported by numerical results. Numerically it is seen that magnetic field above certain minimum value reduces the instability for compression the target in ICF.
Lagrangian approach to the problem of the hydrodynamic instabilities of a spheical implosion
International Nuclear Information System (INIS)
Brun, L.; Sitt, B.
For the study of hydrodynamic instabilities of a spherical implosion, a very simple Lagrangian-type formulation is proposed, based on the introduction of a potential of transverse displacements, and on the decomposition of disturbances into spherical harmonics. The different modes are decoupled, and can be studied independently. The development of a numerical code utilizing this formulation can then be considered
Directory of Open Access Journals (Sweden)
Sergey G. Chefranov
2012-11-01
Full Text Available Aims This paper deals with solving of a century-old paradox of linear stability for the Hagen-Poiseuille flow. A new mechanism of dissipative hydrodynamic instability has been established herein, and a basis for the forming of helical structural organization of bloodstream and respective energy effectiveness of the cardiovascular system functioning has been defined by the authors. Materials and methods Theory of hydrodynamic instability, Galerkin’s approximation. Results A new condition Re > Reth-min ≈ 124 of linear (exponential instability of the Hagen-Poisseuille (HP flow with respect to extremely small by magnitude axially-symmetric disturbances of the tangential component of the velocity field is obtained. The disturbances necessarily shall have quasi-periodic longitudinal variability along the pipe axis that corresponds to the observed data. Conclusion We show that the obtained estimate of value of Reth-min corresponds to the condition of independence of the main result (on the linear instability of the HP flow when Re > Reth-min from the procedure of averaging used in the Galerkin approximation. Thus, we obtain the possible natural mechanism for the blood swirling flows formations observed in the aorta and the large blood vessels.
International Nuclear Information System (INIS)
Andronov, V.A.; Zhidov, I.G.; Meskov, E.E.; Nevmerzhitskii, N.V.; Nikiforov, V.V.; Razin, A.N.; Rogatchev, V.G.; Tolshmyakov, A.I.; Yanilkin, Yu.V.
1995-02-01
This report describes an extensive program of investigations conducted at Arzamas-16 in Russia over the past several decades. The focus of the work is on material interface instability and the mixing of two materials. Part 1 of the report discusses analytical and computational studies of hydrodynamic instabilities and turbulent mixing. The EGAK codes are described and results are illustrated for several types of unstable flow. Semiempirical turbulence transport equations are derived for the mixing of two materials, and their capabilities are illustrated for several examples. Part 2 discusses the experimental studies that have been performed to investigate instabilities and turbulent mixing. Shock-tube and jelly techniques are described in considerable detail. Results are presented for many circumstances and configurations
International Nuclear Information System (INIS)
Aglitskiy, Y.; Velikovich, A.L.; Karasik, M.; Serlin, V.; Pawley, C.J.; Schmitt, A.J.; Obenschain, S.P.; Mostovych, A.N.; Gardner, J.H.; Metzler, N.
2002-01-01
Perturbations that seed Rayleigh-Taylor (RT) instability in laser-driven targets form during the early-time period. This time includes a shock wave transit from the front to the rear surface of the target, and a rarefaction wave transit in the opposite direction. During this time interval, areal mass perturbations caused by all sources of nonuniformity (laser imprint, surface ripple) are expected to oscillate. The first direct experimental observations of the areal mass oscillations due to ablative Richtmyer-Meshkov (RM) instability and feedout followed by the RT growth of areal mass modulation are discussed. The experiments were made with 40-99 μm thick planar plastic targets rippled either on the front or on the rear with a sine wave ripple with either 30 or 45 μm wavelength and with 0.5, 1, or 1.5 μm amplitude. Targets were irradiated with 4 ns long Nike KrF laser pulses at ∼50 TW/cm2. The oscillations were observed with our novel diagnostic technique, a monochromatic x-ray imager coupled to a streak camera. For the ablative RM instability (front side ripple), the mass modulation amplitude was typically observed to grow, reach a peak, and then decrease, after which the exponential RT growth started. In some cases, one phase reversal due to the ablative RM instability was observed. For the feedout geometry (rear side ripple), in all cases two phase reversals were observed: a distinct half-oscillation was followed by the onset of the RT growth, resulting in a second phase reversal
International Nuclear Information System (INIS)
Morse, R.L.
1984-01-01
During the last year, the principle activities and accomplishments under this contract have been: (1) detailed examination of steady flow model calculations of ablation driven Taylor instability to determine the specific cause of growth rate reductions at short wavelengths; (2) implementation of the ''piggy back'' type, time-dependent, spherical harmonic, stability code, PANSY, on the Livermore Octopus system, and expansion of the code to treat a wider range of problems; and (3) use of the PANSY stability code to confirm, with this more realistic model, the results of Item 1 above and to begin learning about the phenomenology of Taylor mode growth and propagation, and the phenomenology of the development of the Richtmyer-Meshkov shock instability in compressible shells
International Nuclear Information System (INIS)
Wilkins, M.L.
1979-01-01
Various aspects of hydrodynamics and elastic--plastic flow are introduced for the purpose of defining hydrodynamic terms and explaining what some of the important hydrodynamic concepts are. The first part covers hydrodynamic theory; and discussed fundamental hydrodynamic equations, discontinuities, and shock, detonation, and elastic--plastic waves. The second part deals with applications of hydrodynamic theory to material equations of state, spall, Taylor instabilities, and detonation pressure measurements
International Nuclear Information System (INIS)
Casner, A.; Masse, L.; Liberatore, S.; Delorme, B.; Jacquet, L.; Loiseau, P.; Smalyuk, V. A.; Martinez, D.; Remington, B. A.
2012-01-01
As the control of the development of Rayleigh-Taylor-type hydrodynamic instabilities is crucial to achieve efficient implosions on the Laser Megajoule, and as the complexity of these instabilities requires an experimental validation of theoretical models and of the associated numerical simulations, the authors briefly present a proposition of experiments aimed at studying the strongly non linear Rayleigh-Taylor instability on the National Ignition Facility (NIF). This should allow a regime of competition between bubbles to be achieved for the first time in direct attack. They evoke the first experiment performed in March 2013
Ablation front rayleigh taylor dispersion curve in indirect drive
International Nuclear Information System (INIS)
Budil, K.S.; Lasinski, B.; Edwards, M.J.; Wan, A.S.; Remington, B.A.; Weber, S.V.; Glendinning, S.G.; Suter, L.; Stry, P.
2000-01-01
The Rayleigh-Taylor (RT) instability, which occurs when a lower-density fluid accelerates a higher-density layer, is common in nature. At an ablation front a sharp reduction in the growth rate of the instability at short wave-lengths can occur, in marked contrast to the classical case where growth rates are highest at the shortest wavelengths. Theoretical and numerical investigations of the ablative RT instability are numerous and differ considerably on the level of stabilization expected. We present here the results of a series of laser experiments designed to probe the roll-over and cutoff region of the ablation-front RT dispersion curve in indirect drive. Aluminum foils with imposed sinusoidal perturbations ranging in wavelength from 10 to 70 pm were ablatively accelerated with a radiation drive generated in a gold cylindrical hohlraum. A strong shock wave compresses the package followed by an ∼2 ns period of roughly constant acceleration and the experiment is diagnosed via face-on radiography. Perturbations with wavelengths (ge) 20 (micro)m experienced substantial growth during the acceleration phase while shorter wavelengths showed a sharp drop off in overall growth. These experimental results compared favorably to calculations with a 2-D radiation-hydrodynamics code, however, the growth is significantly affected by the rippled shock launched by the drive. We performed numerical simulations to elucidate the influence of the rippled shock wave on the eventual growth of the perturbations, allowing comparisons to the analytic model developed by Betti et al. This combination of experiments, simulations and analytic modeling illustrates the qualitative simplicity yet quantitative complexity of the compressible RT instability. We have measured the Rayleigh-Taylor (RT) dispersion curve for a radiatively-driven sample in a series of experiments on the Nova laser facility. Planar aluminum foils were ablatively-accelerated and the subsequent perturbation growth was
International Nuclear Information System (INIS)
Aglitskiy, Y.; Karasik, M.; Velikovich, A. L.; Serlin, V.; Weaver, J. L.; Kessler, T. J.; Schmitt, A. J.; Obenschain, S. P.; Nikitin, S. P.; Oh, J.; Metzler, N.
2012-01-01
Experimental study of hydrodynamic perturbation evolution triggered by a laser-driven shock wave breakout at the free rippled rear surface of a plastic target is reported. At sub-megabar shock pressure, planar jets manifesting the development of the Richtmyer-Meshkov-type instability in a non-accelerated target are observed. As the shock pressure exceeds 1 Mbar, an oscillatory rippled expansion wave is observed, followed by the “feedout” of the rear-surface perturbations to the ablation front and the development of the Rayleigh-Taylor instability, which breaks up the accelerated target.
Ma, K. H.; Lefevre, H. J.; Belancourt, P. X.; MacDonald, M. J.; Doeppner, T.; Keiter, P. A.; Kuranz, C. C.; Johnsen, E.
2017-10-01
Recent experiments at the National Ignition Facility studied the effect of radiation on shock-driven hydrodynamic instability growth. X-ray radiography images from these experiments indicate that perturbation growth is lower in highly radiative shocks compared to shocks with negligible radiation flux. The reduction in instability growth is attributed to ablation from higher temperatures in the foam for highly radiative shocks. The proposed design implements the X-ray Thomson Scattering (XRTS) technique in the radiative shock tube platform to measure electron temperatures and densities in the shocked foam. We model these experiments with CRASH, an Eulerian radiation hydrodynamics code with block-adaptive mesh refinement, multi-group radiation transport and electron heat conduction. Simulations are presented with SiO2 and carbon foams for both the high temperature, radiative shock and the low-temperature, hydrodynamic shock cases. Calculations from CRASH give estimations for shock speed, electron temperature, effective ionization, and other quantities necessary for designing the XRTS diagnostic measurement. This work is funded by the LLNL under subcontract B614207, and was performed under the auspices of the U.S. DOE by LLNL under Contract No. DE-AC52-07NA27344.
National Research Council Canada - National Science Library
Aglitskiy, Y; Karasik, M; Velikovich, A. L; Metzler, N; Zalesak, S; Schmitt, A. J; Gardner, J. H; Serlin, V; Weaver, J; Obenschain, S. P
2007-01-01
In inertial confinement fusion (ICF) and high-energy density physics (HEDP), the most important manifestations of the hydrodynamic instabilities and other mixing processes involve lateral motion of the accelerated plasmas...
Martinez, D A; Smalyuk, V A; Kane, J O; Casner, A; Liberatore, S; Masse, L P
2015-05-29
We investigate on the National Ignition Facility the ablative Rayleigh-Taylor instability in the transition from weakly nonlinear to highly nonlinear regimes. A planar plastic package with preimposed two-dimensional broadband modulations is accelerated for up to 12 ns by the x-ray drive of a gas-filled Au radiation cavity with a radiative temperature plateau at 175 eV. This extended tailored drive allows a distance traveled in excess of 1 mm for a 130 μm thick foil. Measurements of the modulation optical density performed by x-ray radiography show that a bubble-merger regime for the Rayleigh-Taylor instability at an ablation front is achieved for the first time in indirect drive. The mutimode modulation amplitudes are in the nonlinear regime, grow beyond the Haan multimode saturation level, evolve toward the longer wavelengths, and show insensitivity to the initial conditions.
International Nuclear Information System (INIS)
Kilkenny, J.D.; Glendinning, S.G.; Haan, S.W.
1993-12-01
It has been recognized for many year's that the most significant limitation of ICF is the Rayleigh-Taylor (R-T) instability. It limits the distance an ablatively driven shell can be moved to several times its initial thickness. Fortunately material flow through the unstable region at velocity v A reduces the growth rate to √ 1+kL / kg -βkv A with β from 2-3. In recent years experiments using both x-ray drive and smoothed laser drive to accelerate foils have confirmed our understanding of the ablative R-T instability in planar geometry. The growth of small initial modulations on the foils is measured for growth factors up to 60 for direct drive and 80 for indirect drive. For x-ray drive large stabilization is evident. After some growth, the instability enters the non-linear phase when mode coupling and saturation are also seen and compare well with modeling. Normalized growth rates for direct drive are measured to be higher, but strategies for reduction by raising the isentrope are being investigated. For direct drive, high spatial frequencies are imprinted from the laser beam and amplified by the R-T instability. Modeling shows an understanding of this ''laser imprinting.''
Radiation hydrodynamical instabilities in cosmological and galactic ionization fronts
Whalen, Daniel J.; Norman, Michael L.
2011-11-01
Ionization fronts, the sharp radiation fronts behind which H/He ionizing photons from massive stars and galaxies propagate through space, were ubiquitous in the universe from its earliest times. The cosmic dark ages ended with the formation of the first primeval stars and galaxies a few hundred Myr after the Big Bang. Numerical simulations suggest that stars in this era were very massive, 25-500 solar masses, with H(II) regions of up to 30,000 light-years in diameter. We present three-dimensional radiation hydrodynamical calculations that reveal that the I-fronts of the first stars and galaxies were prone to violent instabilities, enhancing the escape of UV photons into the early intergalactic medium (IGM) and forming clumpy media in which supernovae later exploded. The enrichment of such clumps with metals by the first supernovae may have led to the prompt formation of a second generation of low-mass stars, profoundly transforming the nature of the first protogalaxies. Cosmological radiation hydrodynamics is unique because ionizing photons coupled strongly to both gas flows and primordial chemistry at early epochs, introducing a hierarchy of disparate characteristic timescales whose relative magnitudes can vary greatly throughout a given calculation. We describe the adaptive multistep integration scheme we have developed for the self-consistent transport of both cosmological and galactic ionization fronts.
Preheating ablation effects on the Rayleigh-Taylor instability in the weakly nonlinear regime
International Nuclear Information System (INIS)
Wang, L. F.; Ye, W. H.; He, X. T.; Sheng, Z. M.; Don, Wai-Sun; Li, Y. J.
2010-01-01
The two-dimensional Rayleigh-Taylor instability (RTI) with and without thermal conduction is investigated by numerical simulation in the weakly nonlinear regime. A preheat model κ(T)=κ SH [1+f(T)] is introduced for the thermal conduction [W. H. Ye, W. Y. Zhang, and X. T. He, Phys. Rev. E 65, 057401 (2002)], where κ SH is the Spitzer-Haerm electron thermal conductivity coefficient and f(T) models the preheating tongue effect in the cold plasma ahead of the ablation front. The preheating ablation effects on the RTI are studied by comparing the RTI with and without thermal conduction with identical density profile relevant to inertial confinement fusion experiments. It is found that the ablation effects strongly influence the mode coupling process, especially with short perturbation wavelength. Overall, the ablation effects stabilize the RTI. First, the linear growth rate is reduced, especially for short perturbation wavelengths and a cutoff wavelength is observed in simulations. Second, the second harmonic generation is reduced for short perturbation wavelengths. Third, the third-order negative feedback to the fundamental mode is strengthened, which plays a stabilization role. Finally, on the contrary, the ablation effects increase the generation of the third harmonic when the perturbation wavelengths are long. Our simulation results indicate that, in the weakly nonlinear regime, the ablation effects are weakened as the perturbation wavelength is increased. Numerical results obtained are in general agreement with the recent weakly nonlinear theories as proposed in [J. Sanz, J. Ramirez, R. Ramis et al., Phys. Rev. Lett. 89, 195002 (2002); J. Garnier, P.-A. Raviart, C. Cherfils-Clerouin et al., Phys. Rev. Lett. 90, 185003 (2003)].
Nonlinear spectrum of the ablative Rayleigh-Taylor instability in laser-accelerated planar plasmas
International Nuclear Information System (INIS)
Keskinen, M. J.; Schmitt, A.
2007-01-01
A model for the nonlinear spectrum of the ablative Rayleigh-Taylor instability in laser-accelerated planar plasmas has been developed for a wide range of Froude numbers and scale sizes. It is found that the spectrum can be characterized by an inverse power law with spectral index of approximately 2 in the limit of small-wavenumber spectrum cutoffs and small-scale density gradient scale lengths. Comparison of the model spectrum with recent experimental observations is made with good agreement
Hydrodynamic instability induced liquid--solid contacts in film boiling
International Nuclear Information System (INIS)
Yao, S.; Henry, R.E.
1976-01-01
The film boiling liquid-solid contacts of saturated ethanol and water to horizontal flat gold plated copper are examined by using electric conductance probe. It is observed that the liquid-solid contacts occur over a wide temperature range, and generally, induced by hydrodynamic instabilities. The area of contact decreases exponentially with interface temperature and is liquid depth dependent. The averaged duration of contacts is strongly influenced by the dominant nucleation process, and thus, depends on the interface temperature and the wettability of the solid during the contact. The frequency of major contacts is about 1.5 times the bubble detaching frequency. It is found that the liquid-solid contacts may account for a large percentage of the film boiling heat transfer near the low temperature end of film boiling and decreases as the interface temperature increases
A survey of pulse shape options for a revised plastic ablator ignition design
Energy Technology Data Exchange (ETDEWEB)
Clark, D. S.; Milovich, J. L.; Hinkel, D. E.; Salmonson, J. D.; Peterson, J. L.; Berzak Hopkins, L. F.; Eder, D. C.; Haan, S. W.; Jones, O. S.; Marinak, M. M.; Robey, H. F.; Smalyuk, V. A.; Weber, C. R. [Lawrence Livermore National Laboratory Livermore, California 94550 (United States)
2014-11-15
Recent experimental results using the “high foot” pulse shape for inertial confinement fusion ignition experiments on the National Ignition Facility (NIF) [Moses et al., Phys. Plasmas 16, 041006 (2009)] have shown encouraging progress compared to earlier “low foot” experiments. These results strongly suggest that controlling ablation front instability growth can significantly improve implosion performance even in the presence of persistent, large, low-mode distortions. Simultaneously, hydrodynamic growth radiography experiments have confirmed that ablation front instability growth is being modeled fairly well in NIF experiments. It is timely then to combine these two results and ask how current ignition pulse shapes could be modified to improve one-dimensional implosion performance while maintaining the stability properties demonstrated with the high foot. This paper presents such a survey of pulse shapes intermediate between the low and high foot extremes in search of an intermediate foot optimum. Of the design space surveyed, it is found that a higher picket version of the low foot pulse shape shows the most promise for improved compression without loss of stability.
Analytic approach to nonlinear hydrodynamic instabilities driven by time-dependent accelerations
Energy Technology Data Exchange (ETDEWEB)
Mikaelian, K O
2009-09-28
We extend our earlier model for Rayleigh-Taylor and Richtmyer-Meshkov instabilities to the more general class of hydrodynamic instabilities driven by a time-dependent acceleration g(t) . Explicit analytic solutions for linear as well as nonlinear amplitudes are obtained for several g(t)'s by solving a Schroedinger-like equation d{sup 2}{eta}/dt{sup 2} - g(t)kA{eta} = 0 where A is the Atwood number and k is the wavenumber of the perturbation amplitude {eta}(t). In our model a simple transformation k {yields} k{sub L} and A {yields} A{sub L} connects the linear to the nonlinear amplitudes: {eta}{sup nonlinear} (k,A) {approx} (1/k{sub L})ln{eta}{sup linear} (k{sub L}, A{sub L}). The model is found to be in very good agreement with direct numerical simulations. Bubble amplitudes for a variety of accelerations are seen to scale with s defined by s = {integral} {radical}g(t)dt, while spike amplitudes prefer scaling with displacement {Delta}x = {integral}[{integral}g(t)dt]dt.
Influence of real gas effects on ablative Rayleigh-Taylor instability in plastic target
International Nuclear Information System (INIS)
Fan Zhengfeng; Xue Chuang; Ye Wenhua; Zhu Shaoping; Wang Lifeng
2011-01-01
In this research, real gas effects on ablative Rayleigh-Taylor instability are investigated in a plastic target. The real gas effects are included by adopting the quotidian equation of state (QEOS) model. Theoretical solutions for both QEOS and ideal gas EOS are obtained and compared, based on a same set of ablation parameters. It is found that when real gas effects are considered, the density gradient becomes less steep than that of ideal gas assumption, even though this cannot be used directly to draw a stabilization conclusion for the real gas effects. Further analysis shows that when real gas effects are considered, lower ∂p/∂T in the dense shell region has the effect of stabilization, whereas the dependence of the internal energy on the density, lower specific heat (at constant volume) in the dense shell region, and higher specific heat in the low-density ablation region contribute to stronger destabilization effects. Overall, when real gas effects are considered, the destabilization effects are dominant for long wavelength perturbations, and the growth rates become much higher than the results of ideal gas assumption. In our specific case, the maximum relative error reaches 18%.
Lefevre, Heath; Ma, Kevin; Belancourt, Patrick; MacDonald, Michael; Doeppner, Tilo; Keiter, Paul; Kuranz, Carolyn
2017-10-01
A recent experiment on the National Ignition Facility (NIF) radiographed the evolution of the Rayleigh-Taylor (RT) instability under high and low drive cases. This experiment showed that under a high drive the growth rate of the RT instability is reduced relative to the low drive case. The high drive launches a radiative shock, increases the temperature of the post-shock region, and ablates the spikes, which reduces the RT growth rate. The plasma parameters must be measured to validate this claim. We present a target design for making X-Ray Thomson Scattering (XRTS) measurements on radiation hydrodynamics experiments on NIF to measure the electron temperature of the shocked region in the above cases. Specifically, we show that a previously fielded NIF radiation hydrodynamics platform can be modified to allow sufficient signal and temperature resolution for XRTS measurements. This work is funded by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, Grant Number DE-NA0002956 and the National Science Foundation through the Basic Plasma Science and Engineering program.
Preparing for an explosion: Hydrodynamic instabilities and turbulence in presupernovae
Energy Technology Data Exchange (ETDEWEB)
Smith, Nathan; Arnett, W. David, E-mail: nathans@as.arizona.edu, E-mail: darnett@as.arizona.edu [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)
2014-04-20
Both observations and numerical simulations are discordant with predictions of conventional stellar evolution codes for the latest stages of a massive star's life before core collapse. The most dramatic example of this disconnect is in the eruptive mass loss occurring in the decade preceding Type IIn supernovae. We outline the key empirical evidence that indicates severe pre-supernova instability in massive stars, and we suggest that the chief reason that these outbursts are absent in stellar evolution models may lie in the treatment of turbulent convection in these codes. The mixing length theory that is used ignores (1) finite amplitude fluctuations in velocity and temperature and (2) their nonlinear interaction with nuclear burning. Including these fluctuations is likely to give rise to hydrodynamic instabilities in the latest burning sequences, which prompts us to discuss a number of far-reaching implications for the fates of massive stars. In particular, we explore connections to enhanced pre-supernova mass loss, unsteady nuclear burning and consequent eruptions, swelling of the stellar radius that may trigger violent interactions with a companion star, and potential modifications to the core structure that could dramatically alter calculations of the core-collapse explosion mechanism itself. These modifications may also impact detailed nucleosynthesis and measured isotopic anomalies in meteorites, as well as the interpretation of young core-collapse supernova remnants. Understanding these critical instabilities in the final stages of evolution may make possible the development of an early warning system for impending core collapse, if we can identify their asteroseismological or eruptive signatures.
Stabilization of ablative Rayleigh-Taylor instability due to change of the Atwood number
International Nuclear Information System (INIS)
Ye Wenhua; He, X.T.; Zhang Weiyan
2002-01-01
Recent experiment [S.G. Glendinning et al., Phys. Rev. Lett. 78, 3318 (1997)] showed that the measured growth rate of laser ablative Rayleigh-Taylor (RT) instability with preheating is about 50% of the classic value and is reduced by about 18% compared with the simulated value obtained with the computer code LASNEX. By changing the temperature variation of the electron thermal conductivity at low temperatures, the density profile from the Bhatnagar-Gross-Krook approximation is recovered in the simulation, and the simulated RT growth rate is in good agreement with the experimental value from Glendinning et al. The preheated density profile on ablative RT stablization is studied numerically. A change of the Atwood number in the preheating case also leads to RT stabilization. The RT growth formula γ=√(Akg/(1+AkL))-2kV a agrees well with experiment and simulation, and is appropriate for the preheating case
Smoothing and instability with magnetic field in a non-uniformly laser-irradiated planar target
International Nuclear Information System (INIS)
Bell, A.R.; Epperlein, E.M.
1986-01-01
Calculations are presented of the magneto-hydrodynamic response of a planar target to non-uniformities in energy deposition by a laser. The amplitude of the non-uniformities are assumed small and the equations are linearised in small perturbations about the solution for steady planar ablation driven by uniform laser energy deposition. The grad(n)xgrad(T) magnetic field source is included, along with Nernst convection and the Righi-Leduc heat flow. The magnetic field is shown to give a small increase in smoothing. A source term for magnetic field is included to simulate the effects of the Weibel instability. The instability is not strong enough to overcome the smoothing processes under the present assumptions. (author)
Hydrodynamic Instability, Integrated Code, Laboratory Astrophysics, and Astrophysics
Takabe, Hideaki
2016-10-01
This is an article for the memorial lecture of Edward Teller Medal and is presented as memorial lecture at the IFSA03 conference held on September 12th, 2003, at Monterey, CA. The author focuses on his main contributions to fusion science and its extension to astrophysics in the field of theory and computation by picking up five topics. The first one is the anomalous resisitivity to hot electrons penetrating over-dense region through the ion wave turbulence driven by the return current compensating the current flow by the hot electrons. It is concluded that almost the same value of potential as the average kinetic energy of the hot electrons is realized to prevent the penetration of the hot electrons. The second is the ablative stabilization of Rayleigh-Taylor instability at ablation front and its dispersion relation so-called Takabe formula. This formula gave a principal guideline for stable target design. The author has developed an integrated code ILESTA (ID & 2D) for analyses and design of laser produced plasma including implosion dynamics. It is also applied to design high gain targets. The third is the development of the integrated code ILESTA. The forth is on Laboratory Astrophysics with intense lasers. This consists of two parts; one is review on its historical background and the other is on how we relate laser plasma to wide-ranging astrophysics and the purposes for promoting such research. In relation to one purpose, I gave a comment on anomalous transport of relativistic electrons in Fast Ignition laser fusion scheme. Finally, I briefly summarize recent activity in relation to application of the author's experience to the development of an integrated code for studying extreme phenomena in astrophysics.
Haan, S. W.; Celliers, P. M.; Collins, G. W.; Orth, C. D.; Clark, D. S.; Amendt, P.; Hammel, B. A.; Robey, H. F.; Huang, H.
2014-10-01
Mix and hydro instability growth are key issues in implosions of ignition targets on NIF. The implosions are designed so that the amplitude of perturbations is thought to be determined by initial seeds to the hydrodynamic instabilities, amplified by an instability growth factor. Experiments have indicated that growth factors can be calculated fairly well, but characterizing the initial seeds is an ongoing effort. Several threads of investigation this year have increased our understanding of growth seeded at the CH/DT interface. These include: more detailed characterization of the CH inner surface; possible other seeds, such as density irregularities either from fabrication defects or arising during the implosion; experiments on the Omega laser measuring velocity modulations on shock fronts shortly after breaking out from the CH, which can seed subsequent growth; and the possible significance of non-hydrodynamic effects such as plasma interpenetration or spall-like ejecta upon shock breakout. This presentation describes these developments, the relationships between them, and their implications for ignition target performance. Work performed under the auspices of the U.S. D.O.E. by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.
Simulating Rayleigh-Taylor (RT) instability using PPM hydrodynamics @scale on Roadrunner (u)
Energy Technology Data Exchange (ETDEWEB)
Woodward, Paul R [Los Alamos National Laboratory; Dimonte, Guy [Los Alamos National Laboratory; Rockefeller, Gabriel M [Los Alamos National Laboratory; Fryer, Christopher L [Los Alamos National Laboratory; Dimonte, Guy [Los Alamos National Laboratory; Dai, W [Los Alamos National Laboratory; Kares, R. J. [Los Alamos National Laboratory
2011-01-05
The effect of initial conditions on the self-similar growth of the RT instability is investigated using a hydrodynamics code based on the piecewise-parabolic-method (PPM). The PPM code was converted to the hybrid architecture of Roadrunner in order to perform the simulations at extremely high speed and spatial resolution. This paper describes the code conversion to the Cell processor, the scaling studies to 12 CU's on Roadrunner and results on the dependence of the RT growth rate on initial conditions. The relevance of the Roadrunner implementation of this PPM code to other existing and anticipated computer architectures is also discussed.
Haan, Steven; Ali, S. J.; Baxamusa, S. H.; Celliers, P. M.; Clark, D. S.; Kritcher, A. L.; Nikroo, A.; Stadermann, M.; Biener, J.; Wallace, R.; Smalyuk, V.; Robey, H.; Weber, C. R.; Huang, H.; Reynolds, H.; Carlson, L.; Rice, N.; Kline, J. L.; Simakov, A. N.; Yi, S. A.
2017-10-01
NIF indirect drive ablators (CH, Be, and high density carbon HDC) show hydrodynamic irregularity beyond that expected from surface features. Characterizing these seeds and estimating their growth is important in projecting performance. The resulting modulations can be measured in x-ray backlit implosions on NIF called Hydro Growth Radiography, and on Omega with 2D velocimetry. This presentation summarizes the experiments for the three ablators, along with simulations thereof and projections of the significance for NIF. For CH, dominant seeds are photo-induced oxidation, which might be mitigated with alumina coating. For Be, perturbations result from Ar and O contamination. For HDC, perturbations are seeded by shock propagation around melt, depend on shock strength, and may constrain the adiabat of future HDC implosions. Work performed under the auspices of the U.S. D.O.E. by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.
Nova experiments to investigate hydrodynamic instabilities in the solid state
International Nuclear Information System (INIS)
Kalantar, D.H.; Remington, B.A.; Chandler, E.A.; Colvin, J.D.; Griswold, D.L.; Turner, R.E.; Weber, S.V.; Wiley, L.G.
1997-01-01
Experiments were done to shock compress and accelerate copper foils at peak presssures of ∼3 Mbar above and below the melt temperature to study the effects of material strength on hydrodynamic instabilities. An x-ray drive generated in a hohlraum target was used to generate the shock wave profiles. The growth of a preimposed perturbation at an embedded interface is diagnosed by x-ray radiography. Results obtained using a high contrastshaped laser pulse show that the growth of the modulation is delayed compared to fluid simulations,which could be due to material strength stabilization. In contrast, when a copper foil is placed above the melt temperature at >3 Mbar with a single shock, it melts upon compression and the modulation growth is consistent with fluid modeling. Experimental results from copper shocked to 3 Mbar both below and above the melt temperature are presented and compared with simulation
A review of the ablative stabilization of the Rayleigh-Taylor instability in regimes relevant to ICF
International Nuclear Information System (INIS)
Kilkenny, J.D.; Glendinning, S.G.; Haan, S.W.; Hammel, B.A.; Lindl, J.D.; Munro, D.; Remington, B.A.; Weber, S.V.; Knauer, J.P.; Verdon, C.P.
1993-12-01
It has been recognized for many years that the most significant limitation of ICF is the Rayleigh-Taylor (R-T) instability. It limits the distance an ablatively driven shell can be moved to several times its initial thickness. Fortunately material flow through the unstable region at velocity v A reduces the growth rate to √ 1+kL / kg -βkv A with β from 2-3. In recent years experiments using both x-ray drive and smoothed laser drive to accelerate foils have confirmed our understanding of the R-T instability. The growth of small initial modulations on the foils is measured for growth factors up to 60 for direct drive and 80 for indirect drive. For x-ray drive large stabilization is evident After some growth, the instability enters the non-linear phase when mode coupling and saturation are also seen and compare well with modeling. Normalized growth rates for direct drive are measured to be higher, but strategies for reduction by raising the isentrope are being investigated. For direct drive, high spatial frequencies are imprinted from the laser beam and amplified by the R-T instability. Modeling shows an understanding of this ''laser imprinting.''
Marenduzzo, D; Orlandini, E; Cates, M E; Yeomans, J M
2007-09-01
We report hybrid lattice Boltzmann (HLB) simulations of the hydrodynamics of an active nematic liquid crystal sandwiched between confining walls with various anchoring conditions. We confirm the existence of a transition between a passive phase and an active phase, in which there is spontaneous flow in the steady state. This transition is attained for sufficiently "extensile" rods, in the case of flow-aligning liquid crystals, and for sufficiently "contractile" ones for flow-tumbling materials. In a quasi-one-dimensional geometry, deep in the active phase of flow-aligning materials, our simulations give evidence of hysteresis and history-dependent steady states, as well as of spontaneous banded flow. Flow-tumbling materials, in contrast, rearrange themselves so that only the two boundary layers flow in steady state. Two-dimensional simulations, with periodic boundary conditions, show additional instabilities, with the spontaneous flow appearing as patterns made up of "convection rolls." These results demonstrate a remarkable richness (including dependence on anchoring conditions) in the steady-state phase behavior of active materials, even in the absence of external forcing; they have no counterpart for passive nematics. Our HLB methodology, which combines lattice Boltzmann for momentum transport with a finite difference scheme for the order parameter dynamics, offers a robust and efficient method for probing the complex hydrodynamic behavior of active nematics.
The analysis of harmonic generation coefficients in the ablative Rayleigh-Taylor instability
Lu, Yan; Fan, Zhengfeng; Lu, Xinpei; Ye, Wenhua; Zou, Changlin; Zhang, Ziyun; Zhang, Wen
2017-10-01
In this research, we use the numerical simulation method to investigate the generation coefficients of the first three harmonics and the zeroth harmonic in the Ablative Rayleigh-Taylor Instability. It is shown that the interface shifts to the low temperature side during the ablation process. In consideration of the third-order perturbation theory, the first three harmonic amplitudes of the weakly nonlinear regime are calculated and then the harmonic generation coefficients are obtained by curve fitting. The simulation results show that the harmonic generation coefficients changed with time and wavelength. Using the higher-order perturbation theory, we find that more and more harmonics are generated in the later weakly nonlinear stage, which is caused by the negative feedback of the later higher harmonics. Furthermore, extending the third-order theory to the fifth-order theory, we find that the second and the third harmonics coefficients linearly depend on the wavelength, while the feedback coefficients are almost constant. Further analysis also shows that when the fifth-order theory is considered, the normalized effective amplitudes of second and third harmonics can reach about 25%-40%, which are only 15%-25% in the frame of the previous third-order theory. Therefore, the third order perturbation theory is needed to be modified by the higher-order theory when ηL reaches about 20% of the perturbation wavelength.
Directory of Open Access Journals (Sweden)
Loomis Eric
2013-11-01
Full Text Available Growth of hydrodynamic instabilities at the interfaces of inertial confinement fusion capsules (ICF due to ablator and fuel non-uniformities are a primary concern for the ICF program. Recently, observed jetting and parasitic mix into the fuel were attributed to isolated defects on the outer surface of the capsule. Strategies for mitigation of these defects exist, however, they require reduced uncertainties in Equation of State (EOS models prior to invoking them. In light of this, we have begun a campaign to measure the growth of isolated defects (bumps due to x-ray ablation Richtmyer-Meshkov in plastic ablators to validate these models. Experiments used hohlraums with radiation temperatures near 70 eV driven by 15 beams from the Omega laser (Laboratory for Laser Energetics, University of Rochester, NY, which sent a ∼1.25Mbar shock into a planar CH target placed over one laser entrance hole. Targets consisted of 2-D arrays of quasi-gaussian bumps (10 microns tall, 34 microns FWHM deposited on the surface facing into the hohlraum. On-axis radiography with a saran (Cl Heα − 2.76keV backlighter was used to measure bump evolution prior to shock breakout. Shock speed measurements were also performed to determine target conditions. Simulations using the LEOS 5310 and SESAME 7592 models required the simulated laser power be turned down to 80 and 88%, respectively to match observed shock speeds. Both LEOS 5310 and SESAME 7592 simulations agreed with measured bump areal densities out to 6 ns where ablative RM oscillations were observed in previous laser-driven experiments, but did not occur in the x-ray driven case. The QEOS model, conversely, over predicted shock speeds and under predicted areal density in the bump.
Kelvin-Helmholtz instability in solar spicules
Directory of Open Access Journals (Sweden)
H Ebadi
2016-12-01
Full Text Available Magneto hydrodynamic waves, propagating along spicules, may become unstable and the expected instability is of Kelvin-Helmholtz type. Such instability can trigger the onset of wave turbulence leading to an effective plasma heating and particle acceleration. In present study, two-dimensional magneto hydrodynamic simulations performed on a Cartesian grid is presented in spicules with different densities, moving at various speeds depending on their environment. Simulations being applied in this study show the onset of Kelvin-Helmholtz type instability and transition to turbulent flow in spicules. Development of Kelvin-Helmholtz instability leads to momentum and energy transport, dissipation, and mixing of fluids. When magnetic fields are involved, field amplification is also possible to take place
Effect of throttling on burnout heat flux and hydrodynamic instability in natural circulation
International Nuclear Information System (INIS)
Mahmoud, S.I.
1980-01-01
Twenty-four experiments were carried out to study the effect of restriction of the flow before inlet of the test section on burnout heat flux and instability of the flow boiling. These experiments were carried out on a 10, 12, 14, 16 mm out diameter stainless steel heated elements, 50 and 75 cms long centered inside a 26 mm inner diameter stainless steel channel forming an annulus through which water followed upwards to give diameter ratios 2.6, 2.17, 1.86 and 1.63 respectively. The parameters are chosen to cover the lack of the literatures for burnout conditions at low pressures, 1.5, 3, 6, 10 atma). These are of great benefit to the designers of high heat flux devices such as boilers and nuclear reactors ...etc. A detail description of the experimental loop is given. Test section, steam separator, condenser, precooler, preheater, throttle valve, flow measurements and safety devices are designed and constructed for an operating pressure up to 10 atma and temperature up to 220 0 C. The results show that 1. The burnout heat flux first increases and then decreases as the restriction of the flow increases; 2. The hydrodynamic instability increases as the restriction of the flow before the test section increases. (author)
Modeling of laser-driven hydrodynamics experiments
di Stefano, Carlos; Doss, Forrest; Rasmus, Alex; Flippo, Kirk; Desjardins, Tiffany; Merritt, Elizabeth; Kline, John; Hager, Jon; Bradley, Paul
2017-10-01
Correct interpretation of hydrodynamics experiments driven by a laser-produced shock depends strongly on an understanding of the time-dependent effect of the irradiation conditions on the flow. In this talk, we discuss the modeling of such experiments using the RAGE radiation-hydrodynamics code. The focus is an instability experiment consisting of a period of relatively-steady shock conditions in which the Richtmyer-Meshkov process dominates, followed by a period of decaying flow conditions, in which the dominant growth process changes to Rayleigh-Taylor instability. The use of a laser model is essential for capturing the transition. also University of Michigan.
Hot-spot mix in ignition-scale inertial confinement fusion targets.
Regan, S P; Epstein, R; Hammel, B A; Suter, L J; Scott, H A; Barrios, M A; Bradley, D K; Callahan, D A; Cerjan, C; Collins, G W; Dixit, S N; Döppner, T; Edwards, M J; Farley, D R; Fournier, K B; Glenn, S; Glenzer, S H; Golovkin, I E; Haan, S W; Hamza, A; Hicks, D G; Izumi, N; Jones, O S; Kilkenny, J D; Kline, J L; Kyrala, G A; Landen, O L; Ma, T; MacFarlane, J J; MacKinnon, A J; Mancini, R C; McCrory, R L; Meezan, N B; Meyerhofer, D D; Nikroo, A; Park, H-S; Ralph, J; Remington, B A; Sangster, T C; Smalyuk, V A; Springer, P T; Town, R P J
2013-07-26
Mixing of plastic ablator material, doped with Cu and Ge dopants, deep into the hot spot of ignition-scale inertial confinement fusion implosions by hydrodynamic instabilities is diagnosed with x-ray spectroscopy on the National Ignition Facility. The amount of hot-spot mix mass is determined from the absolute brightness of the emergent Cu and Ge K-shell emission. The Cu and Ge dopants placed at different radial locations in the plastic ablator show the ablation-front hydrodynamic instability is primarily responsible for hot-spot mix. Low neutron yields and hot-spot mix mass between 34(-13,+50) ng and 4000(-2970,+17 160) ng are observed.
Simple spherical ablative-implosion model
International Nuclear Information System (INIS)
Mayer, F.J.; Steele, J.T.; Larsen, J.T.
1980-01-01
A simple model of the ablative implosion of a high-aspect-ratio (shell radius to shell thickness ratio) spherical shell is described. The model is similar in spirit to Rosenbluth's snowplow model. The scaling of the implosion time was determined in terms of the ablation pressure and the shell parameters such as diameter, wall thickness, and shell density, and compared these to complete hydrodynamic code calculations. The energy transfer efficiency from ablation pressure to shell implosion kinetic energy was examined and found to be very efficient. It may be possible to attach a simple heat-transport calculation to our implosion model to describe the laser-driven ablation-implosion process. The model may be useful for determining other energy driven (e.g., ion beam) implosion scaling
Suppression of the Rayleigh Taylor instability and its implication for the impact ignition
Azechi, H.; Shiraga, H.; Nakai, M.; Shigemori, K.; Fujioka, S.; Sakaiya, T.; Tamari, Y.; Ohtani, K.; Murakami, M.; Sunahara, A.; Nagatomo, H.; Nishihara, K.; Miyanaga, N.; Izawa, Y.
2004-12-01
The Rayleigh Taylor (RT) instability with material ablation through an unstable interface is the key physics that determines the success or failure of inertial fusion energy (IFE) generation, as the RT instability potentially quenches ignition and burn by disintegrating the IFE target. We present two suppression schemes of the RT growth without significant degradation of the target density. The first scheme is to generate a double ablation structure in high-Z doped plastic targets. In addition to the electron ablation surface, a new ablation surface is created by x-ray radiation from the high-Z ions. Contrary to the previous thought, the electron ablation surface is almost completely stabilized by extremely high flow velocity. On the other hand, the RT instability on the radiative ablation surface is significantly moderated. The second is to enhance the nonlocal nature of the electron heat transport by illuminating the target with long wavelength laser light, whereas the high ablation pressure is generated by irradiating with short wavelength laser light. The significant suppression of the RT instability may increase the possibility of impact ignition which uses a high-velocity fuel colliding with a preformed main fuel.
Suppression of the Rayleigh-Taylor instability and its implication for the impact ignition
International Nuclear Information System (INIS)
Azechi, H; Shiraga, H; Nakai, M; Shigemori, K; Fujioka, S; Sakaiya, T; Tamari, Y; Ohtani, K; Murakami, M; Sunahara, A; Nagatomo, H; Nishihara, K; Miyanaga, N; Izawa, Y
2004-01-01
The Rayleigh-Taylor (RT) instability with material ablation through an unstable interface is the key physics that determines the success or failure of inertial fusion energy (IFE) generation, as the RT instability potentially quenches ignition and burn by disintegrating the IFE target. We present two suppression schemes of the RT growth without significant degradation of the target density. The first scheme is to generate a double ablation structure in high-Z doped plastic targets. In addition to the electron ablation surface, a new ablation surface is created by x-ray radiation from the high-Z ions. Contrary to the previous thought, the electron ablation surface is almost completely stabilized by extremely high flow velocity. On the other hand, the RT instability on the radiative ablation surface is significantly moderated. The second is to enhance the nonlocal nature of the electron heat transport by illuminating the target with long wavelength laser light, whereas the high ablation pressure is generated by irradiating with short wavelength laser light. The significant suppression of the RT instability may increase the possibility of impact ignition which uses a high-velocity fuel colliding with a preformed main fuel
Hydrodynamic instabilities in the developing region of an axially rotating pipe flow
Energy Technology Data Exchange (ETDEWEB)
Miranda-Barea, A; Fabrellas-García, C; Parras, L; Pino, C del, E-mail: cpino@uma.es [Universidad de Málaga, Escuela Técnica Superior de Ingeniería Industrial, Ampliación Campus de Teatinos, 29071, Málaga, España (Spain)
2015-06-15
We conduct experiments in a rotating Hagen–Poiseuille flow (RHPF) through flow visualizations when the flow becomes convectively and absolutely unstable at low-to-moderate Reynolds numbers, Re. We characterize periodic patterns at a very high swirl parameter, L, when the flow overcomes the absolutely unstable region. These non-steady helical filaments wrapped around the axis appear in the developing region of the pipe. Experimentally, we compute the onset of these oscillations in the (L, Re)-plane finding that the rotation rate decreases as the Reynolds number increases in the process of achieving the time-dependent state. Additionally, we report information regarding frequencies and wavelengths that appear downstream of the rotating pipe for convectively and absolutely unstable flows, even for very high swirl parameters at which the flow becomes time-dependent in the developing region. We do not observe variations in the trends of these parameters, so these hydrodynamic instabilities in the developing region do not affect the unstable travelling waves downstream of the pipe. (paper)
Energy Technology Data Exchange (ETDEWEB)
Smalyuk, V. A.; Weber, S. V.; Casey, D. T.; Clark, D. S.; Field, J. E.; Haan, S. W.; Hammel, B. A.; Hamza, A. V.; Landen, O. L.; Robey, H. F.; Weber, C. R. [Lawrence Livermore National Laboratory, NIF Directorate, Livermore, California 94550 (United States); Hoover, D. E.; Nikroo, A. [General Atomics, San Diego, California 92186 (United States)
2015-07-15
Hydrodynamic instability growth experiments with three-dimensional (3-D) surface-roughness modulations were performed on plastic (CH) shell spherical implosions at the National Ignition Facility (NIF) [E. M. Campbell, R. Cauble, and B. A. Remington, AIP Conf. Proc. 429, 3 (1998)]. The initial capsule outer-surface roughness was similar to the standard specifications (“native roughness”) used in a majority of implosions on NIF. The experiments included instability growth measurements of the perturbations seeded by the thin membranes (or tents) used to hold the capsules inside the hohlraums. In addition, initial modulations included two divots used as spatial fiducials to determine the convergence in the experiments and to check the accuracy of 3D simulations in calculating growth of known initial perturbations. The instability growth measurements were performed using x-ray, through-foil radiography of one side of the imploding shell, based on time-resolved pinhole imaging. Averaging over 30 similar images significantly increases the signal-to-noise ratio, making possible a comparison with 3-D simulations. At a convergence ratio of ∼3, the measured tent and divot modulations were close to those predicted by 3-D simulations (within ∼15%–20%), while measured 3-D, broadband modulations were ∼3–4 times larger than those simulated based on the growth of the known imposed initial surface modulations. In addition, some of the measured 3-D features in x-ray radiographs did not resemble those characterized on the outer capsule surface before the experiments. One of the hypotheses to explain the results is based on the increased instability amplitudes due to modulations of the oxygen content in the bulk of the capsule. As the target assembly and handling procedures involve exposure to UV light, this can increase the uptake of the oxygen into the capsule, with irregularities in the oxygen seeding hydrodynamic instabilities. These new experimental results have
Xia, Yongfang; Shi, Junrui; Xu, Youning; Ma, Rui
2018-03-01
Filtration combustion (FC) is one style of porous media combustion with inert matrix, in which the combustion wave front propagates, only downstream or reciprocally. In this paper, we investigate the FC flame front inclinational instability of lean methane/air mixtures flowing through a packed bed as a combustion wave front perturbation of the initial preheating temperature non-uniformity is assumed. The predicted results show that the growth rate of the flame front inclinational angle is proportional to the magnitude of the initial preheating temperature difference. Additionally, depending on gas inlet gas velocity and equivalence ratio, it is demonstrated that increase of gas inlet gas velocity accelerates the FC wave front deformation, and the inclinational instability evolves faster at lower equivalence ratio. The development of the flame front inclinational angle may be regarded as a two-staged evolution, which includes rapid increase, and approaching maximum value of inclinational angle due to the quasi-steady condition of the combustion system. The hydrodynamic and thermal mechanisms of the FC inclinational instability are analyzed. Consequently, the local propagation velocity of the FC wave front is non-uniform to result in the development of inclinational angle at the first stage of rapid increase.
Opie, Saul
Hydrodynamic phenomena such as the Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) instabilities can be described by exponential/linear growth of surface perturbations at a bimaterial interface when subjected to constant/impulsive acceleration. A challenge in designing systems to mitigate or exploit these effects is the lack of accurate material models at large dynamic strain rates and pressures. In particular, little stress-strain constitutive information at large strain rates and pressures is available for transient material phases formed at high pressures, and the continuum effect the phase transformation process has on the instability evolution. In this work, a phase-aware isotropic strength model is developed and partially validated with a novel RM-based instability experiment in addition to existing data from the literature. With the validated material model additional simulations are performed to provide insight into to the role that robust material constitutive behavior (e.g., pressure, temperature, rate dependence) has on RM instability and how RM instability experiments can be used to characterize and validated expected material behavior. For phase aware materials, particularly iron in this work, the simulations predict a strong dependence on the Atwood number that single phase materials do not have. At Atwood numbers close to unity, and pressures in the high pressure stability region, the high pressure phase dominates the RM evolution. However, at Atwood numbers close to negative one, the RM evolution is only weakly affected by the high-pressure phase even for shocks well above the phase transformation threshold. In addition to RM evolution this work looks at the closely related shock front perturbation evolution. Existing analytical models for isentropic processes in gases and liquids are modified for metal equation of states and plastic behavior for the first time. It is found that the presence of a volume collapsing phase transformation with increased
Experimental investigation of hydrodynamics of melt layer during laser cutting of steel
Energy Technology Data Exchange (ETDEWEB)
Hirano, Koji; Fabbro, Remy, E-mail: hirano.koji@nsc.co.jp [PIMM Laboratory (Arts et Metiers ParisTech-CNRS), 151 Boulevard de l' Hopital 75013 Paris (France)
2011-03-16
In a laser cutting process, understanding of the hydrodynamics of melt layer is significant, because it is an important factor which controls the final quality. In this work, we observed the hydrodynamics of melt layer on a kerf front in the case of laser cutting of steel with an inert gas. The observation shows that the melt flow on the kerf front exhibits strong instability, depending on cutting velocity. In the intermediate range of velocities, the flow on the central part of the kerf front is continuous, whereas the flow along the sides is discontinuous. It is first confirmed that the instability in the side flow is the cause of striation initiation from the top part of the kerf. The origin of the instability is discussed in terms of instabilities in thermal dynamics and hydrodynamics. The proposed model shows reasonable agreement with experimental results.
Three aspects of critical phenomenons: fundamental, hydrodynamic, conceptual
International Nuclear Information System (INIS)
Beysens, D.
1993-01-01
After a recall of the leading results relative to the universality class of fluids, examples of how well known universal prevision are held in check by fluids specificities, especially hydrodynamics. Applications of critical phenomenons tool to damping, hydrodynamic instabilities, turbulence are described. (A.B.). 11 refs., 7 figs., 1 tab
Studies of thermal-hydrodynamic flow instability, (3)
International Nuclear Information System (INIS)
Suzuoki, Akira
1978-01-01
In the flow system in which large density change occurs midway, sometimes steady flow cannot be maintained according to the conditions, and pulsating flow or the scamper of flow occurs. This phenomenon is called flow instability, and is noticed as one of the causes to obstruct the normal operation in boilers, BWRs and the steam generators for FBRs with parallel evaporating tube system. In the pulsating instability, there are density wave oscillation and pressure wave oscillation. The author has studied the density wave oscillation occurring in the steam generators for FBRs and in this paper, the role played by two-phase flow regarding the occurrence of flow instability, and the effect of the existence of interphase slip on the role played by two-phase flow are reported. The theoretical analysis and the results of the analysis taking a steam generator heated with sodium as the example are described. Regarding flow stability, two-phase flow part generates the variation of weight velocity with different phase in steam single phase part, accepting enthalpy variation in water single phase part. In this action, the effect of interphase slip was observed, and the variation of reverse phase is apt to occur in slip flow as compared with homogeneous flow. Accordingly, flow instability is apt to occur in slip flow. (Kako, I.)
An introduction to astrophysical hydrodynamics
Shore, Steven N
1992-01-01
This book is an introduction to astrophysical hydrodynamics for both astronomy and physics students. It provides a comprehensive and unified view of the general problems associated with fluids in a cosmic context, with a discussion of fluid dynamics and plasma physics. It is the only book on hydrodynamics that addresses the astrophysical context. Researchers and students will find this work to be an exceptional reference. Contents include chapters on irrotational and rotational flows, turbulence, magnetohydrodynamics, and instabilities.
International Nuclear Information System (INIS)
Rahul Banerjee; Khan, M.; Mandal, L.K.; Roy, S.; Gupta, M.R.
2010-01-01
Complete text of publication follows. The Rayleigh-Taylor (R-T) instability and Richtmyer-Meshkov (R-M) instability are well known problems in the formation of some astrophysical structures such as the supernova remnants in the Eagle and Crab nebula. A core collapse supernova is driven by an externally powerful shock, and strong shocks are the breeding ground of hydrodynamic instability such as Rayleigh-Taylor instability or Richtmyer-Meshkov instability. These instabilities are also important issues in the design of targets for inertial confinement fusion (ICF). In an ICF target, a high density fluid is frequently accelerated by the pressure of a low density fluid and after ablation the density quickly decays. So, small ripples at such an interface will grow. Under potential flow model, the perturbed interface between heavier fluid and lighter fluid form bubble and spike like structures. The bubbles are in the form of columns of lighter fluid interleaved by falling spike of heavy fluid. In this paper, we like to presented the effect of viscosity and surface tension on Rayleigh-Taylor instability and Richtmyer-Meshkov instability under the non-linear Layzer's approach and described the displacement curvature, growth and velocity of the tip of the bubble as well as spike. It is seen that, in absence of surface tension the lowering of the asymptotic velocity of the tip of the bubble which is formed when the lighter fluid penetrates into the denser fluid and thus encounters the viscous drag due to the denser fluid, which depends only on the denser fluid's viscosity coefficient. On the other hand the asymptotic velocity of the tip of the spike formed as the denser fluid penetrates into the lighter fluid is reduced by an amount which depends only on the viscosity coefficient of the lighter fluid and the spike is resisted by the viscous drag due to the lighter fluid. However, in presence of surface tension the asymptotic velocity of the tip of the bubble (spike) and
Framing Camera Improvements and hydrodynamic Experiments
National Research Council Canada - National Science Library
Drake, R. P
2007-01-01
.... We also propose to participate in hydrodynamic experiments at NRL whenever they occur, to prepare for an experiment for NIKE to study the onset of turbulence via the Kelvin Helmholtz instability...
Pickworth, Louisa
2017-10-01
Hydrodynamic instabilities and asymmetries are a major obstacle in the quest to achieve ignition as they cause pre-existing capsule perturbations to grow and ultimately quench the fusion burn in experiments at the National Ignition Facility (NIF). This talk will review recent developments of the experimental platforms and techniques to measure high-mode instabilities and low-mode asymmetries in the deceleration phase of implosions. These new platforms provide a natural link between the acceleration-phase experiments and neutron performance of layered deuterium-tritium implosions. In one innovative technique, self-emission from the hot spot was enhanced with argon dopant to ``self-backlight'' the shell in-flight around peak compression. Experiments with pre-imposed 2-D perturbations measured instability growth factors, while experiments with 3-D, ``native-roughness'' perturbations measured shell integrity in the deceleration phase of implosions. In a complimentary technique, the inner surface of the shell, along with its low-mode asymmetries and high-mode perturbations were visualized in implosions using x-ray emission of a high-Z dopant added to the inner surface of the capsule. These new measurements were instrumental in revealing unexpected surprises and providing improved understanding of the role of instabilities and asymmetries on implosion performance. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
X-Ray Laser in an Ablative Capillary Discharge Driven by an m=0 Instability
International Nuclear Information System (INIS)
Kunze, H.J.
2002-01-01
The development of EUV and soft-X ray lasers made great progress during the last decade. In most cases powerful primary lasers in the UV-, visible and near-infrared spectral regions are employed to produce the dense hot plasmas needed as active media for the lasers. Widely spread applications require small table-top systems and here capillary discharges offer an alternative approach and are being studied by several groups. By selecting properly the transient discharge conditions, collisional excitation or three-body recombination are the effective mechanisms to achieve population inversion. At the Ruhr-University a different approach is pursued where charge exchange between different ions in colliding plasmas is utilized. The plasmas are produced in a small ablative capillary discharge made of polyacetal. In the second half cycle an m=O instability develops and results in hot plasmas in the neck regions which stream into the cold plasma outside and create overpopulation of the n=3 level of hydrogenic carbon leading to lasing on the Balmer-alpha line at 18.22 nm. A waved structure of the inner capillary wall induces reliably the instability and pinhole pictures give the clue why not all materials are useful. Double pass experiments using a multilayer mirror give an effective gain-length product of GL=4.3 for a 3 cm long capillary and a life-time of the inversion layers of 400 ps
Coupled Hydrodynamic Instability Growth on Oblique Interfaces with a Reflected Rarefaction
Rasmus, A. M.; Flippo, K. A.; di Stefano, C. A.; Doss, F. W.; Hager, J. D.; Merritt, E. C.; Cardenas, T.; Schmidt, D. W.; Kline, J. L.; Kuranz, C. C.
2017-10-01
Hydrodynamic instabilities play an important role in the evolution of inertial confinement fusion and astrophysical phenomena. Three of the Omega-EP long pulse beams (10 ns square pulse, 14 kJ total energy, 1.1 mm spot size) drive a supported shock across a heavy-to-light, oblique, interface. Single- and double-mode initial conditions seed coupled Richtmyer-Meshkov (RM), Rayleigh-Taylor (RT), and Kelvin-Helmholtz (KH) growth. At early times, growth is dominated by RM and KH, whereas at late times a rarefaction from laser turn-off reaches the interface, leading to decompression and RT growth. The addition of a thirty degree tilt does not alter mix width to within experimental error bars, even while significantly altering spike and bubble morphology. The results of single and double-mode experiments along with simulations using the multi-physics hydro-code RAGE will be presented. This work performed under the auspices of the U.S. Department of Energy by LANL under contract DE-AC52-06NA25396. This work is funded by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, Grant Number DE-NA0002956. This material is partially supported by DOE Office of Science Graduate Student Research (SCGSR) program.
Design of a deuterium and tritium-ablator shock ignition target for the National Ignition Facility
International Nuclear Information System (INIS)
Terry, Matthew R.; Perkins, L. John; Sepke, Scott M.
2012-01-01
Shock ignition presents a viable path to ignition and high gain on the National Ignition Facility (NIF). In this paper, we describe the development of the 1D design of 0.5 MJ class, all-deuterium and tritium (fuel and ablator) shock ignition target that should be reasonably robust to Rayleigh-Taylor fluid instabilities, mistiming, and hot electron preheat. The target assumes “day one” NIF hardware and produces a yield of 31 MJ with reasonable allowances for laser backscatter, absorption efficiency, and polar drive power variation. The energetics of polar drive laser absorption require a beam configuration with half of the NIF quads dedicated to launching the ignitor shock, while the remaining quads drive the target compression. Hydrodynamic scaling of the target suggests that gains of 75 and yields 70 MJ may be possible.
The short circuit instability in protoplanetary disks
DEFF Research Database (Denmark)
Hubbard, A.; McNally, C.P.; Mac Low, M.M.
2013-01-01
We introduce a magneto-hydrodynamic instability which occurs, among other locations, in the inner, hot regions of protoplanetary disks, and which alters the way in which resistive dissipation of magnetic energy into heat proceeds. This instability can be likened to both an electrical short circui...
Soft x-ray driven ablation and its positive use for a new efficient acceleration
International Nuclear Information System (INIS)
Yabe, Takashi; Kiyokawa, Shuji; Mochizuki, Takayasu; Sakabe, Shuji; Yamanaka, Chiyoe
1983-01-01
The ablation process driven by soft X-ray is investigated by one-dimensional hydrodynamic code coupled with LTE, average ion model and multi-group radiation package. The following two major results are obtained: (1) the ablation pressure and mass ablation rate scalings, and (2) a new acceleration scheme which positively uses the unique property of soft X-ray transport. (author)
Application of high-speed photography to hydrodynamic instability research
International Nuclear Information System (INIS)
Chang Lihua; Li Zuoyou; Xiao Zhengfei; Zou Liyong; Liu Jinhong; Xiong Xueshi
2012-01-01
High-speed photography is used to study the Rayleigh-Taylor instability of air-water interface driven by high- pressure exploding gas. Clear images illustrating the instability are obtained, along with the air bubble peak speed and turbulent mixing speed. The RM (Richtmyer-Meshkov) instability of air/SF 6 interface driven by shock wave is also researched by using high-speed Schlieren technique on the horizontal shock tube and primary experimental results are obtained, which show the change of the turbulent mixing region clearly. (authors)
The large density electron beam-plasma Buneman instability
International Nuclear Information System (INIS)
Mantei, T.D.; Doveil, F.; Gresillon, D.
1976-01-01
The threshold conditions and growth rate of the Buneman (electron beam-stationary ion) instability are calculated with kinetic theory, including a stationary electronic population. A criteria on the wave energy sign is used to separate the Buneman hydrodynamic instability from the ion-acoustic kinetic instability. The stationary electron population raises the instability threshold and, for large beam velocities yields a maximum growth rate oblique to the beam. (author)
Designs for highly nonlinear ablative Rayleigh-Taylor experiments on the National Ignition Facility
International Nuclear Information System (INIS)
Casner, A.; Masse, L.; Liberatore, S.; Jacquet, L.; Loiseau, P.; Poujade, O.; Smalyuk, V. A.; Bradley, D. K.; Park, H. S.; Remington, B. A.; Igumenshchev, I.; Chicanne, C.
2012-01-01
We present two designs relevant to ablative Rayleigh-Taylor instability in transition from weakly nonlinear to highly nonlinear regimes at the National Ignition Facility [E. I. Moses, J. Phys.: Conf. Ser. 112, 012003 (2008)]. The sensitivity of nonlinear Rayleigh-Taylor instability physics to ablation velocity is addressed with targets driven by indirect drive, with stronger ablative stabilization, and by direct drive, with weaker ablative stabilization. The indirect drive design demonstrates the potential to reach a two-dimensional bubble-merger regime with a 20 ns duration drive at moderate radiation temperature. The direct drive design achieves a 3 to 5 times increased acceleration distance for the sample in comparison to previous experiments allowing at least 2 more bubble generations when starting from a three-dimensional broadband spectrum.
Designs for highly nonlinear ablative Rayleigh-Taylor experiments on the National Ignition Facility
Energy Technology Data Exchange (ETDEWEB)
Casner, A.; Masse, L.; Liberatore, S.; Jacquet, L.; Loiseau, P.; Poujade, O. [CEA, DAM, DIF, F-91297 Arpajon (France); Smalyuk, V. A.; Bradley, D. K.; Park, H. S.; Remington, B. A. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Igumenshchev, I. [Laboratory of Laser Energetics, University of Rochester, Rochester, New York 14623-1299 (United States); Chicanne, C. [CEA, DAM, VALDUC, F-21120 Is-sur-Tille (France)
2012-08-15
We present two designs relevant to ablative Rayleigh-Taylor instability in transition from weakly nonlinear to highly nonlinear regimes at the National Ignition Facility [E. I. Moses, J. Phys.: Conf. Ser. 112, 012003 (2008)]. The sensitivity of nonlinear Rayleigh-Taylor instability physics to ablation velocity is addressed with targets driven by indirect drive, with stronger ablative stabilization, and by direct drive, with weaker ablative stabilization. The indirect drive design demonstrates the potential to reach a two-dimensional bubble-merger regime with a 20 ns duration drive at moderate radiation temperature. The direct drive design achieves a 3 to 5 times increased acceleration distance for the sample in comparison to previous experiments allowing at least 2 more bubble generations when starting from a three-dimensional broadband spectrum.
Dynamics and stability of radiation-driven double ablation front structures
International Nuclear Information System (INIS)
Drean, V.; Olazabal-Loume, M.; Tikhonchuk, V. T.; Sanz, J.
2010-01-01
The dynamics of double ablation front (DAF) structures is studied for planar targets with moderate atomic number ablators. These structures are obtained in hydrodynamic simulations for various materials and laser intensities and are qualitatively characterized during the acceleration stage of the target. The importance of the radiative transport for the DAF dynamics is then demonstrated. Simulated hydrodynamic profiles are compared with a theoretical model, showing the consistency of the model and the relevant parameters for the dynamics description. The stability of DAF structures with respect to two-dimensional perturbations is studied using two different approaches: one considers the assumptions of the theoretical model and the other one a more complete physics. The numerical simulations performed with both approaches demonstrate good agreement of dispersion curves.
Fragile, P. Chris; Etheridge, Sarina M.; Anninos, Peter; Mishra, Bhupendra; Kluźniak, Włodek
2018-04-01
We present results from two-dimensional, general relativistic, viscous, radiation hydrodynamic numerical simulations of Shakura–Sunyaev thin disks accreting onto stellar-mass Schwarzschild black holes. We consider cases on both the gas- and radiation-pressure-dominated branches of the thermal equilibrium curve, with mass accretion rates spanning the range from \\dot{M}=0.01{L}Edd}/{c}2 to 10L Edd/c 2. The simulations directly test the stability of this standard disk model on the different branches. We find clear evidence of thermal instability for all radiation-pressure-dominated disks, resulting universally in the vertical collapse of the disks, which in some cases then settle onto the stable, gas-pressure-dominated branch. Although these results are consistent with decades-old theoretical predictions, they appear to be in conflict with available observational data from black hole X-ray binaries. We also find evidence for a radiation-pressure-driven instability that breaks the unstable disks up into alternating rings of high and low surface density on a timescale comparable to the thermal collapse. Since radiation is included self-consistently in the simulations, we are able to calculate light curves and power density spectra (PDS). For the most part, we measure radiative efficiencies (ratio of luminosity to mass accretion rate) close to 6%, as expected for a nonrotating black hole. The PDS appear as broken power laws, with a break typically around 100 Hz. There is no evidence of significant excess power at any frequencies, i.e., no quasi-periodic oscillations are observed.
Computational modeling of ultra-short-pulse ablation of enamel
Energy Technology Data Exchange (ETDEWEB)
London, R.A.; Bailey, D.S.; Young, D.A. [and others
1996-02-29
A computational model for the ablation of tooth enamel by ultra-short laser pulses is presented. The role of simulations using this model in designing and understanding laser drilling systems is discussed. Pulses of duration 300 sec and intensity greater than 10{sup 12} W/cm{sup 2} are considered. Laser absorption proceeds via multi-photon initiated plasma mechanism. The hydrodynamic response is calculated with a finite difference method, using an equation of state constructed from thermodynamic functions including electronic, ion motion, and chemical binding terms. Results for the ablation efficiency are presented. An analytic model describing the ablation threshold and ablation depth is presented. Thermal coupling to the remaining tissue and long-time thermal conduction are calculated. Simulation results are compared to experimental measurements of the ablation efficiency. Desired improvements in the model are presented.
Observations of multimode perturbation decay at non-accelerating, soft x-ray driven ablation fronts
Energy Technology Data Exchange (ETDEWEB)
Loomis, E. N.; Batha, S. H. [Los Alamos National Laboratory, Los Alamos, New Mexico 87544 (United States); Braun, D.; Landen, O. L. [Lawrence Livermore National Laboratory, Livermore, California 95281 (United States)
2012-12-15
Minimizing the growth of hydrodynamic instabilities is a fundamental design issue facing the achievement of thermonuclear ignition and burn with Inertial Confinement Fusion (ICF). The thin capsules and extreme accelerations found in ICF make it an inherently unstable system primarily to Rayleigh-Taylor (RT) occurring at the ablation front. A potential mechanism by which perturbations at the outer capsule surface can be reduced lies in the already present ablative Richtmyer-Meshkov (RM) effect, which operates during the first shock transit of the ablator. At present, the available Equation of State (EOS) models predict a wide range of behavior for the ablative RM oscillations of multimode isolated defects on plastic (CH) capsules. To resolve these differences, we conducted experiments at the OMEGA Laser Facility [T. R. Boehly et al., Optics Comm. 133 (1997)] that measured the evolution of gaussian-shaped bumps driven by soft x-ray ablation from a halfraum. Shock speeds in the CH target were measured to reach 15 {mu}m/ns for halfraum radiation temperatures of 70 eV lasting for up to 7 ns. The evolution of gaussian-shaped bumps of different widths and heights were measured using on-axis x-ray radiography at up to 37 Multiplication-Sign magnification. Bumps with initial widths of 34 and 44 {mu}m FWHM were found to grow by 3 Multiplication-Sign their initial areal density and then saturate out to 6 ns due to lateral compression of the bump characteristic of the formation of a rippled shock front propagating into the solid target. Narrower 17 {mu}m FWHM bumps, on the other hand, grew by roughly 2 Multiplication-Sign followed immediately by a decrease back to initial values of areal density out to 7 ns, which largely agrees with both LEOS 5310 and SESAME 7592 EOS predictions. The difference in observed behavior suggests that high spatial frequency modes found in narrower bumps are needed to significantly affect the ablation front profile on shorter time scales.
Onset of Darrieus-Landau Instability in Expanding Flames
Mohan, Shikhar; Matalon, Moshe
2017-11-01
The effect of small amplitude perturbations on the propagation of circular flames in unconfined domains is investigated, computationally and analytically, within the context of the hydrodynamic theory. The flame, treated as a surface of density discontinuity separating fresh combustible mixture from the burnt gas, propagates at a speed dependent upon local curvature and hydrodynamic strain. For mixtures with Lewis numbers above criticality, thermodiffusive effects have stabilizing influences which largely affect the flame at small radii. The amplitude of these disturbances initially decay and only begin to grow once a critical radius is reached. This instability is hydrodynamic in nature and is a consequence of thermal expansion. Through linear stability analysis, predictions of critical flame radius at the onset of instability are obtained as functions of Markstein length and thermal expansion coefficients. The flame evolution is also examined numerically where the motion of the interface is tracked via a level-set method. Consistent with linear stability results, simulations show the flame initially remaining stable and the existence of a particular mode that will be first to grow and later determine the cellular structure observed experimentally at the onset of instability.
Energy Technology Data Exchange (ETDEWEB)
Okamoto, Kazuhisa [Nagoya University, Department of Physics, Nagoya (Japan); Nonaka, Chiho [Nagoya University, Department of Physics, Nagoya (Japan); Nagoya University, Kobayashi-Maskawa Institute for the Origin of Particles and the Universe (KMI), Nagoya (Japan); Duke University, Department of Physics, Durham, NC (United States)
2017-06-15
We construct a new relativistic viscous hydrodynamics code optimized in the Milne coordinates. We split the conservation equations into an ideal part and a viscous part, using the Strang spitting method. In the code a Riemann solver based on the two-shock approximation is utilized for the ideal part and the Piecewise Exact Solution (PES) method is applied for the viscous part. We check the validity of our numerical calculations by comparing analytical solutions, the viscous Bjorken's flow and the Israel-Stewart theory in Gubser flow regime. Using the code, we discuss possible development of the Kelvin-Helmholtz instability in high-energy heavy-ion collisions. (orig.)
Okamoto, Kazuhisa; Nonaka, Chiho
2017-06-01
We construct a new relativistic viscous hydrodynamics code optimized in the Milne coordinates. We split the conservation equations into an ideal part and a viscous part, using the Strang spitting method. In the code a Riemann solver based on the two-shock approximation is utilized for the ideal part and the Piecewise Exact Solution (PES) method is applied for the viscous part. We check the validity of our numerical calculations by comparing analytical solutions, the viscous Bjorken's flow and the Israel-Stewart theory in Gubser flow regime. Using the code, we discuss possible development of the Kelvin-Helmholtz instability in high-energy heavy-ion collisions.
Suppression of the Rayleigh-Taylor instability due to self-radiation in a multiablation target
International Nuclear Information System (INIS)
Fujioka, Shinsuke; Sunahara, Atsushi; Nishihara, Katsunobu; Johzaki, Tomoyuki; Shiraga, Hiroyuki; Shigemori, Keisuke; Nakai, Mitsuo; Ikegawa, Tadashi; Murakami, Masakatsu; Nagai, Keiji; Norimatsu, Takayoshi; Azechi, Hiroshi; Yamanaka, Tatsuhiko; Ohnishi, Naofumi
2004-01-01
A scheme to suppress the Rayleigh-Taylor instability has been investigated for a direct-drive inertial fusion target. In a high-Z doped-plastic target, two ablation surfaces are formed separately--one driven by thermal radiation and the other driven by electron conduction. The growth of the Rayleigh-Taylor instability is significantly suppressed on the radiation-driven ablation surface inside the target due to the large ablation velocity and long density scale length. A significant reduction of the growth rate was observed in simulations and experiments using a brominated plastic target. A new direct-drive pellet was designed using this scheme
International Nuclear Information System (INIS)
Hu, S. X.; Michel, D. T.; Edgell, D. H.; Froula, D. H.; Follett, R. K.; Goncharov, V. N.; Myatt, J. F.; Skupsky, S.; Yaakobi, B.
2013-01-01
Direct-drive–ignition designs with plastic CH ablators create plasmas of long density scale lengths (L n ≥ 500 μm) at the quarter-critical density (N qc ) region of the driving laser. The two-plasmon–decay (TPD) instability can exceed its threshold in such long-scale-length plasmas (LSPs). To investigate the scaling of TPD-induced hot electrons to laser intensity and plasma conditions, a series of planar experiments have been conducted at the Omega Laser Facility with 2-ns square pulses at the maximum laser energies available on OMEGA and OMEGA EP. Radiation–hydrodynamic simulations have been performed for these LSP experiments using the two-dimensional hydrocode draco. The simulated hydrodynamic evolution of such long-scale-length plasmas has been validated with the time-resolved full-aperture backscattering and Thomson-scattering measurements. draco simulations for CH ablator indicate that (1) ignition-relevant long-scale-length plasmas of L n approaching ∼400 μm have been created; (2) the density scale length at N qc scales as L n (μm)≃(R DPP ×I 1/4 /2); and (3) the electron temperature T e at N qc scales as T e (keV)≃0.95×√(I), with the incident intensity (I) measured in 10 14 W/cm 2 for plasmas created on both OMEGA and OMEGA EP configurations with different-sized (R DPP ) distributed phase plates. These intensity scalings are in good agreement with the self-similar model predictions. The measured conversion fraction of laser energy into hot electrons f hot is found to have a similar behavior for both configurations: a rapid growth [f hot ≃f c ×(G c /4) 6 for G c hot ≃f c ×(G c /4) 1.2 for G c ≥ 4, with the common wave gain is defined as G c =3 × 10 −2 ×I qc L n λ 0 /T e , where the laser intensity contributing to common-wave gain I qc , L n , T e at N qc , and the laser wavelength λ 0 are, respectively, measured in [10 14 W/cm 2 ], [μm], [keV], and [μm]. The saturation level f c is observed to be f c ≃ 10 –2 at around
Magnetically-Driven Convergent Instability Growth platform on Z.
Energy Technology Data Exchange (ETDEWEB)
Knapp, Patrick [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Mattsson, Thomas [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Martin, Matthew [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Benage, John F. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Jenkins, James [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Albright, Brian James [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2017-09-01
Hydrodynamic instability growth is a fundamentally limiting process in many applications. In High Energy Density Physics (HEDP) systems such as inertial confinement fusion implosions and stellar explosions, hydro instabilities can dominate the evolution of the object and largely determine the final state achievable. Of particular interest is the process by which instabilities cause perturbations at a density or material interface to grow nonlinearly, introducing vorticity and eventually causing the two species to mix across the interface. Although quantifying instabilities has been the subject of many investigations in planar geometry, few have been done in converging geometry. During FY17, the team executed six convergent geometry instability experiments. Based on earlier results, the platform was redesigned and improved with respect to load centering at installation making the installation reproducible and development of a new 7.2 keV, Co He-a backlighter system to better penetrate the liner. Together, the improvements yielded significantly improved experimental results. The results in FY17 demonstrate the viability of using experiments on Z to quantify instability growth in cylindrically convergent geometry. Going forward, we will continue the partnership with staff and management at LANL to analyze the past experiments, compare to hydrodynamics growth models, and design future experiments.
Kinetic simulations of Rayleigh-Taylor instabilities
International Nuclear Information System (INIS)
Sagert, Irina; Bauer, Wolfgang; Colbry, Dirk; Howell, Jim; Staber, Alec; Strother, Terrance
2014-01-01
We report on an ongoing project to develop a large scale Direct Simulation Monte Carlo code. The code is primarily aimed towards applications in astrophysics such as simulations of core-collapse supernovae. It has been tested on shock wave phenomena in the continuum limit and for matter out of equilibrium. In the current work we focus on the study of fluid instabilities. Like shock waves these are routinely used as test-cases for hydrodynamic codes and are discussed to play an important role in the explosion mechanism of core-collapse supernovae. As a first test we study the evolution of a single-mode Rayleigh-Taylor instability at the interface of a light and a heavy fluid in the presence of a gravitational acceleration. To suppress small-wavelength instabilities caused by the irregularity in the separation layer we use a large particle mean free path. The latter leads to the development of a diffusion layer as particles propagate from one fluid into the other. For small amplitudes, when the instability is in the linear regime, we compare its position and shape to the analytic prediction. Despite the broadening of the fluid interface we see a good agreement with the analytic solution. At later times we observe the development of a mushroom like shape caused by secondary Kelvin-Helmholtz instabilities as seen in hydrodynamic simulations and consistent with experimental observations.
Jorajuria, Corentin; Machicoane, Nathanael; Osuna, Rodrigo; Aliseda, Alberto
2017-11-01
Break-up of a liquid jet by a high speed coaxial gas jet is a frequently-used configuration to generate a high quality spray. Despite its extended use in engineering and natural processes, the instabilities that control the liquid droplet size and their spatio-temporal distribution in the spray are not completely understood. We present an experimental measurements of the near field in a canonical coaxial gas-liquid atomizer. The liquid Reynolds number is constant at 103, while the gas jet Reynolds number is varied from 104-106. The liquid injection rate and the swirl ratio are harmonically modulated to understand the effect of unsteadiness on the interfacial instability that triggers primary break-up. The gas velocity is measured using a combination of hot-wire anemometry and 3D PIV, resolving the gas boundary layer and the three-dimensionality of the flow, particularly in the cases with swirl. The development of the hydrodynamic instabilities on the liquid-gas interface is quantified using high speed visualizations at the exit of the nozzle and related to the frequency and growth rates predicted by stability analysis of this boundary layer flow. The resulting droplet size distribution is measured at the end of the break-up process via Particle Phase Doppler Anemometry and compared to stability analysis predictions statistics.
Transient effects in unstable ablation fronts and mixing layers in HEDP
International Nuclear Information System (INIS)
Clarisse, J-M; Gauthier, S; Dastugue, L; Vallet, A; Schneider, N
2016-01-01
We report results obtained for two elementary unstable flow configurations relevant to high energy density physics: the ablation front instability and the Rayleigh–Taylor -instability induced mixing layer. These two flows are characterized by a transience of their perturbation dynamics. In the ablative flow case, this perturbation dynamics transience takes the form of finite-durations of successive linear-perturbation evolution phases until reaching regimes of decaying oscillations. This behaviour is observed in various regimes: weakly or strongly accelerated ablation fronts, irradiation asymmetries or initial external-surface defects, and is a result of the mean-flow unsteadiness and stretching. In the case of the Rayleigh–Taylor-instability induced mixing layer, perturbation dynamics transience manifests itself through the extinction of turbulence and mixing as the flow reaches a stable state made of two stably stratified layers of pure fluids separated by an unstratified mixing layer. A second feature, also due to compressibility, takes the form of an intense acoustic wave production, mainly localized in the heavy fluid. Finally, we point out that a systematic short-term linear-perturbation dynamics analysis should be undertaken within the framework of non-normal stability theory. (paper)
International Nuclear Information System (INIS)
Krafft, G.A.; Mark, J.W.K.; Wang, T.S.F.
1983-01-01
In an earlier paper, closed hydrodynamic equations were derived with possible application to the simulation of beam plasmas relevant to designs of heavy ion accelerators for inertial confinement fusion energy applications. The closure equations involved a novel feature of anisotropic stresses even transverse to the beam. A related hydrodynamic model is used in this paper to examine further the boundaries of validity of such hydrodynamic approximations. It is also proposed as a useful tool to provide an economic means for searching the large parameter space relevant to three-dimensional stability problems involving coupling of longitudinal and transverse motions in the presence of wall impedance
Measuring the iron spectral opacity in solar conditions using a double ablation front scheme
Energy Technology Data Exchange (ETDEWEB)
Colaitis, A. [Centre Lasers Intenses et Applications, Talence (France); CEA/DRF/IRFU/DAp, CEA Saclay (France); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Univ. of Rochester, NY (United States). Lab. for Laser Energetics; Ducret, J. E. [Centre Lasers Intenses et Applications, Talence (France); CEA/DRF/IRFU/DAp, CEA Saclay (France); Turck-Chieze, S [CEA/DRF/IRFU/DAp, CEA Saclay (France); Pennec, M L [CEA/DRF/IRFU/DAp, CEA Saclay (France); CEA/DIF, Arpajon (France); Blancard, C [CEA/DIF, Arpajon (France)
2018-01-22
We propose a new method to achieve hydrodynamic conditions relevant for the investigation of the radiation transport properties of the plasma at the base of the solar convection zone. The method is designed in the framework of opacity measurements with high-power lasers and exploits the temporal and spatial stability of hydrodynamic parameters in counter-propagating Double Ablation Front (DAF) structures.
Bugli, M.; Guilet, J.; Müller, E.; Del Zanna, L.; Bucciantini, N.; Montero, P. J.
2018-03-01
Geometrically thick tori with constant specific angular momentum have been widely used in the last decades to construct numerical models of accretion flows on to black holes. Such discs are prone to a global non-axisymmetric hydrodynamic instability, known as Papaloizou-Pringle instability (PPI), which can redistribute angular momentum and also lead to an emission of gravitational waves. It is, however, not clear yet how the development of the PPI is affected by the presence of a magnetic field and by the concurrent development of the magnetorotational instability (MRI). We present a numerical analysis using three-dimensional GRMHD simulations of the interplay between the PPI and the MRI considering, for the first time, an analytical magnetized equilibrium solution as initial condition. In the purely hydrodynamic case, the PPI selects as expected the large-scale m = 1 azimuthal mode as the fastest growing and non-linearly dominant mode. However, when the torus is threaded by a weak toroidal magnetic field, the development of the MRI leads to the suppression of large-scale modes and redistributes power across smaller scales. If the system starts with a significantly excited m = 1 mode, the PPI can be dominant in a transient phase, before being ultimately quenched by the MRI. Such dynamics may well be important in compact star mergers and tidal disruption events.
Energy Technology Data Exchange (ETDEWEB)
Zupanic, Franc [University of Maribor, Faculty of Mechanical Engineering, University Centre for Electron Microscopy, Smetanova 17, SI-2000 Maribor (Slovenia)], E-mail: franc.zupanic@uni-mb.si; Boncina, Tonica [University of Maribor, Faculty of Mechanical Engineering, University Centre for Electron Microscopy, Smetanova 17, SI-2000 Maribor (Slovenia); Pipic, Davor; Henc-Bartolic, Visnja [University of Zagreb, Faculty of Electrical Engineering and Computing, Department of Applied Physics, Unska 3, 10000 Zagreb (Croatia)
2008-10-06
A Cu-Sn-Zn-Pb alloy was irradiated by ultraviolet nitrogen laser pulses (N{sub 2} laser, wavelength 337 nm, pulse duration 6 ns, frequency 1 Hz, power 0.5 MW and average power density 0.67 GW/m{sup 2}). The surface topography and microstructure were mainly studied by scanning electron microscopy, and a focused ion beam. The non-homogenized spatial beam profile resulted in the activation of several ablative mechanisms, the main being phase explosion and hydrodynamic instability. They caused a crater to be formed, surrounded by a raised rim and wavelike structure in a halo. FIB cross-sectioning and imaging showed a shallow (few micrometers) molten and resolidified surface layer. Streaks were observed in the heat-affected zone beneath the molten layer, indicating partial recrystallization of initially cold-worked material.
Eckhaus and Benjamin-Feir instabilities near a weakly inverted bifurcation
International Nuclear Information System (INIS)
Brand, H.R.; Deissler, R.J.
1992-01-01
We investigate how the criteria for two prototype instabilities in one-dimensional pattern-forming systems, namely for the Eckhaus instability and for the Benjamin-Feir instability, change as one goes from a continuous bifurcation to a spatially periodic or spatially and/or time-periodic state to the corresponding weakly inverted, i.e., hysteretic, cases. We also give the generalization to two-dimensional patterns in systems with anisotropy as they arise, for example, for hydrodynamic instabilities in nematic liquid crystals
Energy Technology Data Exchange (ETDEWEB)
Bauder, W. [Argonne National Laboratory, Physics Division, 9600 S. Cass Ave, Lemont, IL 60439 (United States); University of Notre Dame, Nuclear Science Laboratory, 124 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Pardo, R.C.; Kondev, F.G.; Kondrashev, S.; Nair, C.; Nusair, O. [Argonne National Laboratory, Physics Division, 9600 S. Cass Ave, Lemont, IL 60439 (United States); Palchan, T. [Hebrew University, Racah Institute of Physics, Jerusalem 91904 (Israel); Scott, R.; Seweryniak, D.; Vondrasek, R. [Argonne National Laboratory, Physics Division, 9600 S. Cass Ave, Lemont, IL 60439 (United States); Collon, P. [University of Notre Dame, Nuclear Science Laboratory, 124 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Paul, M. [Hebrew University, Racah Institute of Physics, Jerusalem 91904 (Israel)
2015-10-15
A laser ablation material injection system has been developed at the ATLAS electron cyclotron resonance (ECR) ion source for use in accelerator mass spectrometry experiments. Beam production with laser ablation initially suffered from instabilities due to fluctuations in laser energy and cratering on the sample surface by the laser. However, these instabilities were rectified by applying feedback correction for the laser energy and rastering the laser across the sample surface. An initial experiment successfully produced and accelerated low intensity actinide beams with up to 1000 counts per second. With continued development, laser ablation shows promise as an alternative material injection scheme for ECR ion sources and may help substantially reduce cross talk in the source.
On the instability of a modified cup-burner flame in the infrared spectral region
Directory of Open Access Journals (Sweden)
Petr Bitala
2016-03-01
Full Text Available This study describes the modification of a standardised cup-burner apparatus. The replacement of the original glass chimney is performed by shielding a nitrogen co-flow enabled measurement at a wavelength of 3.9 μm. This modification, together with a special arrangement of the measuring system (spectral filtering, data acquisition and post-processing, permitted the observation of various types of hydrodynamic instabilities, including transition states. The advantages of our arrangement are demonstrated with an ethylene non-premixed flame with high sooting tendency. Two known modes of hydrodynamic instability (varicose and sinuous that occur in buoyant flames were studied and described quantitatively. Based on the intensity of the infrared emissions, we identified and qualitatively described the modes of periodic hydrodynamic instability that are accompanied by flame tip opening, which has not been observed for this type of flame.
Numerical investigations of Z-pinch plasma instabilities
International Nuclear Information System (INIS)
Duan Yaoyong; Guo Yonghui; Wang Wensheng; Qiu Aici
2004-01-01
A two-dimensional, radiation magneto-hydrodynamics model is applied to the simulation of Z-pinch plasma sausage instability. Different implosion mechanisms in the cases of the existence and the non-existence of instability are analyzed, and the effects of various initial density perturbation levels on the x-ray power and energy are investigated. Numerical results show that x-ray energy output is not susceptive to sausage instabilities in a certain extent but x-ray power versus time is evidently dependent on the instabilities. In addition, this paper also studies the effects of numerical treatment of extreme low density in Z-pinch simulations on numerical results
Radiation loss driven instabilities in laser heated plasmas
International Nuclear Information System (INIS)
Evans, R.G.
1985-01-01
Any plasma in which a significant part of the power balance is due to optically thin radiative losses may be subject to a radiation cooling instability. A simple analytical model gives the dispersion relation for the instability and inclusion of a realistic radiation loss term in a two dimensional hydrodynamic simulation shows that ''jet'' like features form in moderate to high Z plasmas
International Nuclear Information System (INIS)
Berland, T.; Joessang, T.; Feder, J.
1986-04-01
The laser doppler velocimetry technique has been used to measure the radial flow velocity in the Taylor vortex flow at several Taylor numbers close to and above the critical value. The first four harmonics of the flow field have been analyzed using a model described by Davey. The analysis demonstrates that the amplitude of the first harmonic of the super-critical flow field can be regarded as the ''order parameter'' of the transition from the laminar Couette flow to the Taylor vortex flow. This transition is described by a generalized Landau theory for classical second order mean-field phase transitions. The analysis of the results of carefully performed experiments not only confirms the findings of earlier experimental work, but in addition all the significant parameters of the full Davey model for this hydrodynamic instability are determied
International Nuclear Information System (INIS)
Boehly, T.R.; Goncharov, V.N.; Gotchev, O.; Knauer, J.P.; Meyerhofer, D.D.; Oron, D.; Regan, S.P.; Srebro, Y.; Seka, W.; Shvarts, D.; Skupsky, S.; Smalyuk, V.A.
2001-01-01
The creation of a plasma atmosphere in laser-target interactions increases the distance between the regions of laser absorption and hydrodynamic instability (ablation front), thus allowing thermal smoothing and a reduction of laser-imprinted modulations that reach the unstable ablation region. The total laser imprinting is reduced with pulse shapes that produce a plasma atmosphere more rapidly and by the implementation of temporal beam smoothing. These effects are measured and found to be consistent with models for the hydrodynamics and optical smoothing by spectral dispersion (SSD). Imprinting is reduced as the laser bandwidth is increased from 0.2 to 1.0 THz
Impact of hydrodynamic stresses on bacterial flagella
Das, Debasish; Riley, Emily; Lauga, Eric
2017-11-01
The locomotion of bacteria powered by helical filaments, such as Escherichia coli, critically involves the generation of flows and hydrodynamic stresses which lead to forces and moments balanced by the moment applied by the bacterial rotary motor (which is embedded in the cell wall) and the deformation of the short flexible hook. In this talk we use numerical computations to accurately compute these hydrodynamic stresses, to show how they critically lead to fluid-structure instabilities at the whole-cell level, and enquire if they can be used to rationalise experimental measurements of bacterial motor torques. ERC Consolidator Grant.
Evaporation as a diagnostic test for hydrodynamic cooling of laser-ablated clusters
International Nuclear Information System (INIS)
Klots, C.E.
1991-01-01
The properties of materials laser-ablated from a surface are of considerable interest. The interrogation of these properties inevitably occurs at a point some distance from the surface. One might then ask what processes have occurred in the intervening path length. Immediately, for example, one wonders whether the material was released as such from the surface or was formed as a result of collisions at a distant point. Similarly, one might ask if an observed ''temperature'' of the materials is characteristic of the ablation process of of subsequent events. We will indicate here how measurements of metastable evaporation rates can provide clues which are pertinent to these questions. 7 refs
RINGED ACCRETION DISKS: INSTABILITIES
Energy Technology Data Exchange (ETDEWEB)
Pugliese, D.; Stuchlík, Z., E-mail: d.pugliese.physics@gmail.com, E-mail: zdenek.stuchlik@physics.cz [Institute of Physics and Research Centre of Theoretical Physics and Astrophysics, Faculty of Philosophy and Science, Silesian University in Opava, Bezručovo náměstí 13, CZ-74601 Opava (Czech Republic)
2016-04-01
We analyze the possibility that several instability points may be formed, due to the Paczyński mechanism of violation of mechanical equilibrium, in the orbiting matter around a supermassive Kerr black hole. We consider a recently proposed model of a ringed accretion disk, made up by several tori (rings) that can be corotating or counter-rotating relative to the Kerr attractor due to the history of the accretion process. Each torus is governed by the general relativistic hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. We prove that the number of the instability points is generally limited and depends on the dimensionless spin of the rotating attractor.
Self-organized pattern formation upon femtosecond laser ablation by circularly polarized light
International Nuclear Information System (INIS)
Varlamova, Olga; Costache, Florenta; Reif, Juergen; Bestehorn, Michael
2006-01-01
Surface ripples generation upon femtosecond laser ablation is attributed to self-organized structure formation from instability. We report that linear arrangements are observed not only for linearly polarized light but also for ablation with circularly polarized light. Long ordered chains of spherical nanoparticles, reminding of bead-strings are almost parallel but exhibit typical non-linear dynamics features such as bifurcations. In a first attempt to understand the self-assembly, we rely on models recently developed for the description of similar structures upon ion beam erosion and for the simulation of instabilities in thin liquid films. Our picture describes an unstable surface layer, non-uniformly eroded through Coulomb repulsion between individual positive charges
Sarkar, N; Basu, A
2012-11-01
We construct a coarse-grained effective two-dimensional (2d hydrodynamic theory as a theoretical model for a coupled system of a fluid membrane and a thin layer of a polar active fluid in its ordered state that is anchored to the membrane. We show that such a system is prone to generic instabilities through the interplay of nonequilibrium drive, polar order and membrane fluctuation. We use our model equations to calculate diffusion coefficients of an inclusion in the membrane and show that their values depend strongly on the system size, in contrast to their equilibrium values. Our work extends the work of S. Sankararaman and S. Ramaswamy (Phys. Rev. Lett., 102, 118107 (2009)) to a coupled system of a fluid membrane and an ordered active fluid layer. Our model is broadly inspired by and should be useful as a starting point for theoretical descriptions of the coupled dynamics of a cell membrane and a cortical actin layer anchored to it.
High-order hydrodynamic algorithms for exascale computing
Energy Technology Data Exchange (ETDEWEB)
Morgan, Nathaniel Ray [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2016-02-05
Hydrodynamic algorithms are at the core of many laboratory missions ranging from simulating ICF implosions to climate modeling. The hydrodynamic algorithms commonly employed at the laboratory and in industry (1) typically lack requisite accuracy for complex multi- material vortical flows and (2) are not well suited for exascale computing due to poor data locality and poor FLOP/memory ratios. Exascale computing requires advances in both computer science and numerical algorithms. We propose to research the second requirement and create a new high-order hydrodynamic algorithm that has superior accuracy, excellent data locality, and excellent FLOP/memory ratios. This proposal will impact a broad range of research areas including numerical theory, discrete mathematics, vorticity evolution, gas dynamics, interface instability evolution, turbulent flows, fluid dynamics and shock driven flows. If successful, the proposed research has the potential to radically transform simulation capabilities and help position the laboratory for computing at the exascale.
The Rayleigh-Taylor instability in inertial fusion, astrophysical plasma and flames
International Nuclear Information System (INIS)
Bychkov, V; Modestov, M; Akkerman, V; Eriksson, L-E
2007-01-01
Previous results are reviewed and new results are presented on the Rayleigh-Taylor instability in inertial confined fusion, flames and supernovae including gravitational and thermonuclear explosion mechanisms. The instability couples micro-scale plasma effects to large-scale hydrodynamic phenomena. In inertial fusion the instability reduces target compression. In supernovae the instability produces large-scale convection, which determines the fate of the star. The instability is often accompanied by mass flux through the unstable interface, which may have either a stabilizing or a destabilizing influence. Destabilization happens due to the Darrieus-Landau instability of a deflagration front. Still, it is unclear whether the instabilities lead to well-organized large-scale structures (bubbles) or to relatively isotropic turbulence (mixing layer)
Nanosecond laser ablation of target Al in a gaseous medium: explosive boiling
Mazhukin, V. I.; Mazhukin, A. V.; Demin, M. M.; Shapranov, A. V.
2018-03-01
An approximate mathematical description of the processes of homogeneous nucleation and homogeneous evaporation (explosive boiling) of a metal target (Al) under the influence of ns laser radiation is proposed in the framework of the hydrodynamic model. Within the continuum approach, a multi-phase, multi-front hydrodynamic model and a computational algorithm are designed to simulate nanosecond laser ablation of the metal targets immersed in gaseous media. The proposed approach is intended for modeling and detailed analysis of the mechanisms of heterogeneous and homogeneous evaporation and their interaction with each other. It is shown that the proposed model and computational algorithm allow modeling of interrelated mechanisms of heterogeneous and homogeneous evaporation of metals, manifested in the form of pulsating explosive boiling. Modeling has shown that explosive evaporation in metals is due to the presence of a near-surface temperature maximum. It has been established that in nanosecond pulsed laser ablation, such exposure regimes can be implemented in which phase explosion is the main mechanism of material removal.
On the existence of hydrodynamic instability in single diffusive ...
Indian Academy of Sciences (India)
bottom heavy systems with permeable boundaries. A K GUPTA1, ... Abstract. We utilize the reformulated equations of the classical theory, as derived by ... of gravity-dominated thermal instability in a horizontal liquid layer heated underside (or.
Annual Report: Hydrodynamics and Radiative Hydrodynamics with Astrophysical Applications
Energy Technology Data Exchange (ETDEWEB)
R. Paul Drake
2005-12-01
We report the ongoing work of our group in hydrodynamics and radiative hydrodynamics with astrophysical applications. During the period of the existing grant, we have carried out two types of experiments at the Omega laser. One set of experiments has studied radiatively collapsing shocks, obtaining high-quality scaling data using a backlit pinhole and obtaining the first (ever, anywhere) Thomson-scattering data from a radiative shock. Other experiments have studied the deeply nonlinear development of the Rayleigh-Taylor (RT) instability from complex initial conditions, obtaining the first (ever, anywhere) dual-axis radiographic data using backlit pinholes and ungated detectors. All these experiments have applications to astrophysics, discussed in the corresponding papers either in print or in preparation. We also have obtained preliminary radiographs of experimental targets using our x-ray source. The targets for the experiments have been assembled at Michigan, where we also prepare many of the simple components. The above activities, in addition to a variety of data analysis and design projects, provide good experience for graduate and undergraduates students. In the process of doing this research we have built a research group that uses such work to train junior scientists.
Warm dense mater: another application for pulsed power hydrodynamics
Energy Technology Data Exchange (ETDEWEB)
Reinovsky, Robert Emil [Los Alamos National Laboratory
2009-01-01
Pulsed Power Hydrodynamics (PPH) is an application of low-impedance pulsed power, and high magnetic field technology to the study of advanced hydrodynamic problems, instabilities, turbulence, and material properties. PPH can potentially be applied to the study of the properties of warm dense matter (WDM) as well. Exploration of the properties of warm dense matter such as equation of state, viscosity, conductivity is an emerging area of study focused on the behavior of matter at density near solid density (from 10% of solid density to slightly above solid density) and modest temperatures ({approx}1-10 eV). Conditions characteristic of WDM are difficult to obtain, and even more difficult to diagnose. One approach to producing WDM uses laser or particle beam heating of very small quantities of matter on timescales short compared to the subsequent hydrodynamic expansion timescales (isochoric heating) and a vigorous community of researchers are applying these techniques. Pulsed power hydrodynamic techniques, such as large convergence liner compression of a large volume, modest density, low temperature plasma to densities approaching solid density or through multiple shock compression and heating of normal density material between a massive, high density, energetic liner and a high density central 'anvil' are possible ways to reach relevant conditions. Another avenue to WDM conditions is through the explosion and subsequent expansion of a conductor (wire) against a high pressure (density) gas background (isobaric expansion) techniques. However, both techniques demand substantial energy, proper power conditioning and delivery, and an understanding of the hydrodynamic and instability processes that limit each technique. In this paper we will examine the challenges to pulsed power technology and to pulsed power systems presented by the opportunity to explore this interesting region of parameter space.
Rayleigh-Taylor/gravitational instability in dense magnetoplasmas
Energy Technology Data Exchange (ETDEWEB)
Ali, S., E-mail: shahid.ali@ncp.edu.p [National Centre for Physics, Quaid-i-Azam University Campus, Islamabad (Pakistan); IPFN, Instituto Superior Tecnico, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Ahmed, Z. [COMSATS Institute of Information Technology, Department of Physics, Wah Campus (Pakistan); Mirza, Arshad M. [Theoretical Plasma Physics Group, Physics Department, Quaid-i-Azam University, Islamabad 45320 (Pakistan); Ahmad, I. [COMSATS Institute of Information Technology, Department of Physics, Islamabad Campus (Pakistan)
2009-08-10
The Rayleigh-Taylor instability is investigated in a nonuniform dense quantum magnetoplasma. For this purpose, a quantum hydrodynamical model is used for the electrons whereas the ions are assumed to be cold and classical. The dispersion relation for the Rayleigh-Taylor instability becomes modified with the quantum corrections associated with the Fermi pressure law and the quantum Bohm potential force. Numerically, it is found that the quantum speed and density gradient significantly modify the growth rate of RT instability. In a dense quantum magnetoplasma case, the linear growth rate of RT instability becomes significantly higher than its classical value and the modes are found to be highly localized. The present investigation should be useful in the studies of dense astrophysical magnetoplasmas as well as in laser-produced plasmas.
Rayleigh-Taylor/gravitational instability in dense magnetoplasmas
International Nuclear Information System (INIS)
Ali, S.; Ahmed, Z.; Mirza, Arshad M.; Ahmad, I.
2009-01-01
The Rayleigh-Taylor instability is investigated in a nonuniform dense quantum magnetoplasma. For this purpose, a quantum hydrodynamical model is used for the electrons whereas the ions are assumed to be cold and classical. The dispersion relation for the Rayleigh-Taylor instability becomes modified with the quantum corrections associated with the Fermi pressure law and the quantum Bohm potential force. Numerically, it is found that the quantum speed and density gradient significantly modify the growth rate of RT instability. In a dense quantum magnetoplasma case, the linear growth rate of RT instability becomes significantly higher than its classical value and the modes are found to be highly localized. The present investigation should be useful in the studies of dense astrophysical magnetoplasmas as well as in laser-produced plasmas.
International Nuclear Information System (INIS)
Lockett, R D
2006-01-01
Flame instabilities, cellular structures and soot formed in high pressure, rich, spherically expanding iso-octane-air flames have been studied experimentally using high speed Schlieren cinematography, OH fluorescence, Mie scattering and laser induced incandescence. Cellular structures with two wavelength ranges developed on the flame surface. The larger wavelength cellular structure was produced by the Landau-Darrieus hydrodynamic instability, while the short wavelength cellular structure was produced by the thermal-diffusive instability. Large negative curvature in the short wavelength cusps caused local flame quenching and fracture of the flame surface. In rich flames with equivalence ratio φ > 1.8, soot was formed in a honeycomb-like structure behind flame cracks associated with the large wavelength cellular structure induced by the hydrodynamic instability. The formation of soot precursors through low temperature pyrolysis was suggested as a suitable mechanism for the initiation of soot formation behind the large wavelength flame cracks
Energy Technology Data Exchange (ETDEWEB)
Lockett, R D [School of Engineering and Mathematical Sciences, City University, Northampton Square, London EC1V OHB (United Kingdom)
2006-07-15
Flame instabilities, cellular structures and soot formed in high pressure, rich, spherically expanding iso-octane-air flames have been studied experimentally using high speed Schlieren cinematography, OH fluorescence, Mie scattering and laser induced incandescence. Cellular structures with two wavelength ranges developed on the flame surface. The larger wavelength cellular structure was produced by the Landau-Darrieus hydrodynamic instability, while the short wavelength cellular structure was produced by the thermal-diffusive instability. Large negative curvature in the short wavelength cusps caused local flame quenching and fracture of the flame surface. In rich flames with equivalence ratio {phi} > 1.8, soot was formed in a honeycomb-like structure behind flame cracks associated with the large wavelength cellular structure induced by the hydrodynamic instability. The formation of soot precursors through low temperature pyrolysis was suggested as a suitable mechanism for the initiation of soot formation behind the large wavelength flame cracks.
Energy Technology Data Exchange (ETDEWEB)
Becker, Kurt M; Jahnberg, S; Haga, I; Hansson, P T; Mathisen, R P
1964-09-15
A theoretical model for predicting the threshold of instability for two phase flow in a natural circulation loop is presented. The model calculates the flow transient caused by a step disturbance of the heat input, and is based upon the conservation laws of mass, momentum and energy in one dimensional form. Empirical correlations are used in the model for estimating the void fractions and the two-phase flow pressure drops. The equations are solved numerically in a finite difference approximation coded for a digital computer. An experimental study of the hydrodynamic instability and dynamic burnout in two-phase flow has been performed in a natural circulation loop in the pressure range from 10 to 70 atg. The test sections were round ducts of 20, 30 and 36 mm inner diameter and 4890 mm heated length. The experimental results showed that within the ranges tested, the stability of the flow increases with increasing pressure and increasing throttling before the test section, but decreases with increasing Inlet subcooling and increasing throttling after the test section. Comparing the natural circulation burnout steam qualities with corresponding forced circulation data shoved that the former data were low by a factor up to 2.5. However, by applying inlet throttling of the flow the burnout values approached and finally coincided with the forced circulation data. The present experimental results as well as data available from other sources have been compared with the stability thresholds obtained with the theoretical model. The comparisons included circular, annular and rod cluster geometries, and the agreement between the experimental and theoretical stability limits was good. Finally the application of the experimental and theoretical results on the assessment of boiling heavy water reactor design is discussed.
International Nuclear Information System (INIS)
Becker, Kurt M.; Jahnberg, S.; Haga, I.; Hansson, P.T.; Mathisen, R.P.
1964-09-01
A theoretical model for predicting the threshold of instability for two phase flow in a natural circulation loop is presented. The model calculates the flow transient caused by a step disturbance of the heat input, and is based upon the conservation laws of mass, momentum and energy in one dimensional form. Empirical correlations are used in the model for estimating the void fractions and the two-phase flow pressure drops. The equations are solved numerically in a finite difference approximation coded for a digital computer. An experimental study of the hydrodynamic instability and dynamic burnout in two-phase flow has been performed in a natural circulation loop in the pressure range from 10 to 70 atg. The test sections were round ducts of 20, 30 and 36 mm inner diameter and 4890 mm heated length. The experimental results showed that within the ranges tested, the stability of the flow increases with increasing pressure and increasing throttling before the test section, but decreases with increasing Inlet subcooling and increasing throttling after the test section. Comparing the natural circulation burnout steam qualities with corresponding forced circulation data shoved that the former data were low by a factor up to 2.5. However, by applying inlet throttling of the flow the burnout values approached and finally coincided with the forced circulation data. The present experimental results as well as data available from other sources have been compared with the stability thresholds obtained with the theoretical model. The comparisons included circular, annular and rod cluster geometries, and the agreement between the experimental and theoretical stability limits was good. Finally the application of the experimental and theoretical results on the assessment of boiling heavy water reactor design is discussed
Energy balance of a laser ablation plume expanding in a background gas
DEFF Research Database (Denmark)
Amoruso, Salvatore; Schou, Jørgen; Lunney, James G.
2010-01-01
The energy balance of a laser ablation plume in an ambient gas for nanosecond pulses has been investigated on the basis of the model of Predtechensky and Mayorov (PM), which provides a relatively simple and clear description of the essential hydrodynamics. This approach also leads to an insightfu...
Modeling and simulations of radiative blast wave driven Rayleigh-Taylor instability experiments
Shimony, Assaf; Huntington, Channing M.; Trantham, Matthew; Malamud, Guy; Elbaz, Yonatan; Kuranz, Carolyn C.; Drake, R. Paul; Shvarts, Dov
2017-10-01
Recent experiments at the National Ignition Facility measured the growth of Rayleigh-Taylor RT instabilities driven by radiative blast waves, relevant to astrophysics and other HEDP systems. We constructed a new Buoyancy-Drag (BD) model, which accounts for the ablation effect on both bubble and spike. This ablation effect is accounted for by using the potential flow model ]Oron et al PoP 1998], adding another term to the classical BD formalism: βDuA / u , where β the Takabe constant, D the drag term, uA the ablation velocity and uthe instability growth velocity. The model results are compared with the results of experiments and 2D simulations using the CRASH code, with nominal radiation or reduced foam opacity (by a factor of 1000). The ablation constant of the model, βb / s, for the bubble and for the spike fronts, are calibrated using the results of the radiative shock experiments. This work is funded by the Lawrence Livermore National Laboratory under subcontract B614207, and was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.
The Nike KrF laser facility: Performance and initial target experiments
International Nuclear Information System (INIS)
Obenschain, S.P.; Bodner, S.E.; Colombant, D.; Gerber, K.; Lehmberg, R.H.; McLean, E.A.; Mostovych, A.N.; Pronko, M.S.; Pawley, C.J.; Schmitt, A.J.; Sethian, J.D.; Serlin, V.; Stamper, J.A.; Sullivan, C.A.; Dahlburg, J.P.; Gardner, J.H.; Chan, Y.; Deniz, A.V.; Hardgrove, J.; Lehecka, T.; Klapisch, M.
1996-01-01
Krypton-fluoride (KrF) lasers are of interest to laser fusion because they have both the large bandwidth capability (approx-gt THz) desired for rapid beam smoothing and the short laser wavelength (1/4 μm) needed for good laser endash target coupling. Nike is a recently completed 56-beam KrF laser and target facility at the Naval Research Laboratory. Because of its bandwidth of 1 THz FWHM (full width at half-maximum), Nike produces more uniform focal distributions than any other high-energy ultraviolet laser. Nike was designed to study the hydrodynamic instability of ablatively accelerated planar targets. First results show that Nike has spatially uniform ablation pressures (Δp/p<2%). Targets have been accelerated for distances sufficient to study hydrodynamic instability while maintaining good planarity. In this review we present the performance of the Nike laser in producing uniform illumination, and its performance in correspondingly uniform acceleration of targets. copyright 1996 American Institute of Physics
Hydrodynamick instabilities on ICF capsules
International Nuclear Information System (INIS)
Haan, S.W.
1991-01-01
This article summarizes our current understanding of hydrodynamic instabilities as relevant to ICF. First we discuss classical, single mode Rayleigh-Taylor instability, and nonlinear effects in the evolution of a single mode. Then we discuss multimode systems, considering: (1) the onset of nonlinearity; (2) a second order mode coupling theory for weakly nonlinear effects, and (3) the fully nonlinear regime. Two stabilization mechanisms relevant to ICF are described next: gradient scale length and convective stabilization. Then we describe a model which is meant to estimate the weakly nonlinear evolution of multi-mode systems as relevant to ICF, given the short-wavelength stabilization. Finally, we discuss the relevant code simulation capability, and experiments. At this time we are quite optimistic about our ability to estimate instability growth on ICF capsules, but further experiments and simulations are needed to verify the modeling. 52 refs
Instability of a planar expansion wave
International Nuclear Information System (INIS)
Velikovich, A.L.; Zalesak, S.T.; Metzler, N.; Wouchuk, J.G.
2005-01-01
An expansion wave is produced when an incident shock wave interacts with a surface separating a fluid from a vacuum. Such an interaction starts the feedout process that transfers perturbations from the rippled inner (rear) to the outer (front) surface of a target in inertial confinement fusion. Being essentially a standing sonic wave superimposed on a centered expansion wave, a rippled expansion wave in an ideal gas, like a rippled shock wave, typically produces decaying oscillations of all fluid variables. Its behavior, however, is different at large and small values of the adiabatic exponent γ. At γ>3, the mass modulation amplitude δm in a rippled expansion wave exhibits a power-law growth with time ∝t β , where β=(γ-3)/(γ-1). This is the only example of a hydrodynamic instability whose law of growth, dependent on the equation of state, is expressed in a closed analytical form. The growth is shown to be driven by a physical mechanism similar to that of a classical Richtmyer-Meshkov instability. In the opposite extreme γ-1 -1/2 , and then starts to decrease. The mechanism driving the growth is the same as that of Vishniac's instability of a blast wave in a gas with low γ. Exact analytical expressions for the growth rates are derived for both cases and favorably compared to hydrodynamic simulation results
International Nuclear Information System (INIS)
Betti, R.; Umansky, M.; Lobatchev, V.; Goncharov, V.N.; McCrory, R.L.
2001-01-01
A model for the deceleration phase of imploding inertial confinement fusion capsules is derived by solving the conservation equations for the hot spot. It is found that heat flux leaving the hot spot goes back in the form of internal energy and pdV work of the material ablated off the inner shell surface. Though the hot-spot temperature is reduced by the heat conduction losses, the hot-spot density increases due to the ablated material in such a way that the hot-spot pressure is approximately independent of heat conduction. For direct-drive National Ignition Facility-like capsules, the ablation velocity off the shell inner surface is of the order of tens μm/ns, the deceleration of the order of thousands μm/ns2, and the density-gradient scale length of the order a few μm. Using the well-established theory of the ablative Rayleigh-Taylor instability, it is shown that the growth rates of the deceleration phase instability are significantly reduced by the finite ablative flow and the unstable spectrum exhibits a cutoff for mode numbers of about l≅90
Laser-solid interaction and dynamics of the laser-ablated materials
International Nuclear Information System (INIS)
Chen, K.R.; Leboeuf, J.N.; Geohegan, D.B.; Wood, R.F.; Donato, J.M.; Liu, C.L.; Puretzky, A.A.
1995-01-01
Rapid transformations through the liquid and vapor phases induced by laser-solid interactions are described by the authors' thermal model with the Clausius-Clapeyron equation to determine the vaporization temperature under different surface pressure condition. Hydrodynamic behavior of the vapor during and after ablation is described by gas dynamic equations. These two models are coupled. Modeling results show that lower background pressure results lower laser energy density threshold for vaporization. The ablation rate and the amount of materials removed are proportional to the laser energy density above its threshold. The authors also demonstrate a dynamic source effect that accelerates the unsteady expansion of laser-ablated material in the direction perpendicular to the solid. A dynamic partial ionization effect is studied as well. A self-similar theory shows that the maximum expansion velocity is proportional to c s α, where 1 - α is the slope of the velocity profile. Numerical hydrodynamic modeling is in good agreement with the theory. With these effects, α is reduced. Therefore, the expansion front velocity is significantly higher than that from conventional models. The results are consistent with experiments. They further study how the plume propagates in high background gas condition. Under appropriate conditions, the plume is slowed down, separates with the background, is backward moving, and hits the solid surface. Then, it splits into two parts when it rebounds from the surface. The results from the modeling will be compared with experimental observations where possible
International Nuclear Information System (INIS)
Lindl, J.D.; Mead, W.C.
1975-01-01
LASNEX calculations with a modified electron conductivity show the existence of a firepolishing stabilization effect. By modifying the thermal conductivity so that K α T/sup n//rho/sup m/, one is able to construct a situation in which the electrons deposit their energy in a thin layer at the ablation surface and closely match the zero order solutions assumed earlier. The firepolishing effect appears to require that a significant fraction of the total pressure be due to the ablation process itself rather than the thermal pressure in the corona gas. It also requires KL approximately 1 where L is the scale height for decay of thermal perturbations generated at the ablation surface. For classical electron conductivity, because the thermal flux depends linearly on the grams/cm 2 necessary to stop the electrons, (1/rho) nabla rho approximately (1/T) nabla T near the ablation surface so that the pressure is nearly constant across the ablation surface. Hence there is no ablation pressure as such and no firepolishing effect for electron-driven implosions
Hydrodynamic instability of elastic-plastic solid plates at the early stage of acceleration.
Piriz, A R; Sun, Y B; Tahir, N A
2015-03-01
A model is presented for the linear Rayleigh-Taylor instability taking place at the early stage of acceleration of an elastic-plastic solid, when the shock wave is still running into the solid and is driven by a time varying pressure on the interface. When the the shock is formed sufficiently close to the interface, this stage is considered to follow a previous initial phase controlled by the Ritchmyer-Meshkov instability that settles new initial conditions. The model reproduces the behavior of the instability observed in former numerical simulation results and provides a relatively simpler physical picture than the currently existing one for this stage of the instability evolution.
Jeans instability of self-gravitating magnetized strongly coupled plasma
International Nuclear Information System (INIS)
Prajapati, R P; Sharma, P K; Sanghvi, R K; Chhajlani, R K
2012-01-01
We investigate the Jeans instability of self-gravitating magnetized strongly coupled plasma. The equations of the problem are formulated using the generalized hydrodynamic model and a general dispersion relation is obtained using the normal mode analysis. This dispersion relation is discussed for transverse and longitudinal mode of propagations. The modified condition of Jeans instability is obtained for magnetized strongly coupled plasma. We find that strong coupling of plasma particles modify the fundamental criterion of Jeans gravitational instability. In transverse mode it is found that Jeans instability criterion gets modified due to the presence of magnetic field, shear viscosity and fluid viscosity but in longitudinal mode it is unaffected due to the presence of magnetic field. From the curves we found that all these parameters have stabilizing influence on the growth rate of Jeans instability.
Fluid Instabilities of Magnetar-Powered Supernovae
Chen, Ke-Jung
2017-05-01
Magnetar-powered supernova explosions are competitive models for explaining very luminous optical transits. Until recently, these explosion models were mainly calculated in 1D. Radiation emitted from the magnetar snowplows into the previous supernovae ejecta and causes a nonphysical dense shell (spike) found in previous 1D studies. This suggests that strong fluid instabilities may have developed within the magnetar-powered supernovae. Such fluid instabilities emerge at the region where luminous transits later occur, so they can affect the consequent observational signatures. We examine the magnetar-powered supernovae with 2D hydrodynamics simulations and find that the 1D dense shell transforms into the development of Rayleigh-Taylor and thin shell instabilities in 2D. The resulting mixing is able to fragment the entire shell and break the spherical symmetry of supernovae ejecta.
Faraday instability in deformable domains
International Nuclear Information System (INIS)
Pucci, G.
2013-01-01
Hydrodynamical instabilities are usually studied either in bounded regions or free to grow in space. In this article we review the experimental results of an intermediate situation, in which an instability develops in deformable domains. The Faraday instability, which consists in the formation of surface waves on a liquid experiencing a vertical forcing, is triggered in floating liquid lenses playing the role of deformable domains. Faraday waves deform the lenses from the initial circular shape and the mutual adaptation of instability patterns with the lens boundary is observed. Two archetypes of behaviour have been found. In the first archetype a stable elongated shape is reached, the wave vector being parallel to the direction of elongation. In the second archetype the waves exceed the response of the lens border and no equilibrium shape is reached. The lens stretches and eventually breaks into fragments that have a complex dynamics. The difference between the two archetypes is explained by the competition between the radiation pressure the waves exert on the lens border and its response due to surface tension.
Biomedical device prototype based on small scale hydrodynamic cavitation
Ghorbani, Morteza; Sozer, Canberk; Alcan, Gokhan; Unel, Mustafa; Ekici, Sinan; Uvet, Huseyin; Koşar, Ali
2018-03-01
This study presents a biomedical device prototype based on small scale hydrodynamic cavitation. The application of small scale hydrodynamic cavitation and its integration to a biomedical device prototype is offered as an important alternative to other techniques, such as ultrasound therapy, and thus constitutes a local, cheap, and energy-efficient solution, for urinary stone therapy and abnormal tissue ablation (e.g., benign prostate hyperplasia (BPH)). The destructive nature of bubbly, cavitating, flows was exploited, and the potential of the prototype was assessed and characterized. Bubbles generated in a small flow restrictive element (micro-orifice) based on hydrodynamic cavitation were utilized for this purpose. The small bubbly, cavitating, flow generator (micro-orifice) was fitted to a small flexible probe, which was actuated with a micromanipulator using fine control. This probe also houses an imaging device for visualization so that the emerging cavitating flow could be locally targeted to the desired spot. In this study, the feasibility of this alternative treatment method and its integration to a device prototype were successfully accomplished.
Biomedical device prototype based on small scale hydrodynamic cavitation
Directory of Open Access Journals (Sweden)
Morteza Ghorbani
2018-03-01
Full Text Available This study presents a biomedical device prototype based on small scale hydrodynamic cavitation. The application of small scale hydrodynamic cavitation and its integration to a biomedical device prototype is offered as an important alternative to other techniques, such as ultrasound therapy, and thus constitutes a local, cheap, and energy-efficient solution, for urinary stone therapy and abnormal tissue ablation (e.g., benign prostate hyperplasia (BPH. The destructive nature of bubbly, cavitating, flows was exploited, and the potential of the prototype was assessed and characterized. Bubbles generated in a small flow restrictive element (micro-orifice based on hydrodynamic cavitation were utilized for this purpose. The small bubbly, cavitating, flow generator (micro-orifice was fitted to a small flexible probe, which was actuated with a micromanipulator using fine control. This probe also houses an imaging device for visualization so that the emerging cavitating flow could be locally targeted to the desired spot. In this study, the feasibility of this alternative treatment method and its integration to a device prototype were successfully accomplished.
Pellet-plasma interaction: Local disturbances caused by pellet ablation in tokamaks
International Nuclear Information System (INIS)
Lengyel, L.L.
1989-01-01
The local disturbance amplitudes caused by ablating pellets in tokamaks are computed in the framework of a magnetohydrodynamic model supplemented by the neutral gas plasma shielding ablation model. The model computes, for a given number of pellet particles locally deposited, the time histories of the ablatant cloud parameters, such as cloud radius, cloud length, electron density, temperature and cloud beta, at a succession of magnetic flux surfaces. The cloud radius thus determined may be fed back into the ablation model, thus adjusting the effect of the shielding cloud on the ablation rate. The model is applied to typical plasma parameter ranges of existing and planned tokamaks. The results show that the ablating pellets may cause massive local disturbances in tokamaks, depending upon the number of particles locally deposited. The peaks of these disturbances are of a spike nature, lasting only a few microseconds (Alfven time-scale). The characteristic decay time of the 'quasi-steady' disturbance values that characterize the after-spike period is of the order of several milliseconds (hydrodynamic time-scale). The peak electron density values may be as high as 10 23 to 10 25 m -3 , with the associated beta peaks exceeding unity. The 'quasi-steady' values of the electron density and the ablatant beta may be of the order of 10 22 to 10 24 m -3 and unity, respectively. Furthermore, the results show the strong dependence of the ablation rate on the dynamic characteristics of the ablatant cloud surrounding the pellet. (author). 25 refs, 6 figs, 2 tabs
Effects of Thin High-z Layers on the Hydrodynamics of Laser-Accelerated Plastic Targets
National Research Council Canada - National Science Library
Obenschain, S. P; Colombant, D; Karasik, M; Pawley, C. J; Serlin, V; Schmitt, A. J; Gardner, J. H; Phillips, L; Aglitskly, Y; Chan, Y
2002-01-01
.... This pulse shape simulates the generic shape needed for high-gain fusion implosions. Imprint of laser nonuniformity during start up of the low intensity foot is a well-known seed for hydrodynamic instability...
Instability of a planar expansion wave.
Velikovich, A L; Zalesak, S T; Metzler, N; Wouchuk, J G
2005-10-01
An expansion wave is produced when an incident shock wave interacts with a surface separating a fluid from a vacuum. Such an interaction starts the feedout process that transfers perturbations from the rippled inner (rear) to the outer (front) surface of a target in inertial confinement fusion. Being essentially a standing sonic wave superimposed on a centered expansion wave, a rippled expansion wave in an ideal gas, like a rippled shock wave, typically produces decaying oscillations of all fluid variables. Its behavior, however, is different at large and small values of the adiabatic exponent gamma. At gamma > 3, the mass modulation amplitude delta(m) in a rippled expansion wave exhibits a power-law growth with time alpha(t)beta, where beta = (gamma - 3)/(gamma - 1). This is the only example of a hydrodynamic instability whose law of growth, dependent on the equation of state, is expressed in a closed analytical form. The growth is shown to be driven by a physical mechanism similar to that of a classical Richtmyer-Meshkov instability. In the opposite extreme gamma - 1 gas with low . Exact analytical expressions for the growth rates are derived for both cases and favorably compared to hydrodynamic simulation results.
Energy Technology Data Exchange (ETDEWEB)
Smitherman, D.P.
1998-04-01
Eight beams carrying a shaped pulse from the NOVA laser were focused into a hohlraum with a total energy of about 25 kJ. A planar foil was placed on the side of the hohlraum with perturbations facing away from the hohlraum. All perturbations were 4 {micro}m in amplitude and 50 {micro}m in wavelength. Three foils of pure aluminum were shot with thicknesses and pulse lengths respectively of 86 {micro}m and 2. 2 ns, 50 {micro}m and 4.5 ns, and 35 {micro}m with both 2.2 ns and 4. 5 ns pulses. Two composite foils constructed respectively of 32 and 84 {micro}m aluminum on the ablative side and 10 {micro}m beryllium on the cold surface were also shot using the 2.2 ns pulse. X-ray framing cameras recorded perturbation growth using both face- and side-on radiography. The LASNEX code was used to model the experiments. A shock wave interacted with the perturbation on the cold surface generating growth from a Richtmyer-Meshkov instability and a strong acoustic mode. The cold surface perturbation fed-out to the Rayleigh-Taylor unstable ablation surface, both by differential acceleration and interface coupling, where it grew. A density jump did not appear to have a large effect on feed-out from interface coupling. The Rayleigh-Taylor instability`s vortex pairs overtook and reversed the direction of flow of the Richtmyer-Meshkov vortices, resulting in the foil moving from a sinuous to a bubble and spike configuration. The Rayleigh-Taylor instability may have acted as an ablative instability on the hot surface, and as a classical instability on the cold surface, on which grew second and third order harmonics.
Temporal dependence of the mass ablation rate in uv irradiated spherical targets
International Nuclear Information System (INIS)
Delettrez, J.; Jaanimagi, P.A.; Henke, B.L.; Richardson, M.C.
1985-01-01
In this talk, measurements of thermal transport in spherical geometry using time-resolved x-ray spectroscopy are presented. The time dependence of the mass ablation rate (m) is determined by following the progress of the ablation surface through thin layers of material embedded at various depths below the surface of the target. These measurements made with 6, 12 and 24 uv (351 nm) beams from OMEGA are compared to previous thermal transport data and are in qualitative agreement with detailed LILAC hydrodynamic code simulations which predict a sharp decrease in m after the peak of the laser pulse. Viewgraphs of the talk comprise the report
Hot spot mix in ICF implosions on the NIF
Ma, Tammy
2016-10-01
In the quest to achieve ignition through the inertial confinement fusion scheme, one of the critical challenges is to drive a symmetric implosion at high velocity without hydrodynamic instabilities becoming detrimental. These instabilities, primarily at the ablation front and the fuel-ablator interface, can cause mix of the higher-Z shell into the hot spot, resulting in increased radiation loss and thus reduced temperature and neutron yield. To quantify the level of mix, we developed a model that infers the level of hot spot contamination using the ratio of the enhanced x-ray production relative to the neutron yield. Applying this methodology to the full ensemble of indirect-drive National Ignition Facility (NIF) cryogenically layered DT implosions provides insight on the sensitivity of performance to the level of ablator-hot spot mix. In particular, the improvement seen with the High Foot design can be primarily attributed to a reduction in ablation-front instability mix that enabled the implosions to be pushed to higher velocity and performance. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, Lawrence Livermore National Security, LLC.
International Nuclear Information System (INIS)
Fletcher, D.F.
1984-03-01
A review of the literature on Rayleigh-Taylor, Kelvin-Helmholtz and capillary instability is presented. The concept of Weber breakup is examined and found to involve a combination of the above instabilities. Sample calculations are given which show how these instabilities may contribute to the mixing of melt and coolant in a molten fuel coolant interaction. It is concluded that Rayleigh-Taylor instability is likely to be important as the melt falls into the coolant and that Kelvin-Helmholtz instability is likely to develop when significant vapour velocities occur. (author)
Edge instability in incompressible planar active fluids
Nesbitt, David; Pruessner, Gunnar; Lee, Chiu Fan
2017-12-01
Interfacial instability is highly relevant to many important biological processes. A key example arises in wound healing experiments, which observe that an epithelial layer with an initially straight edge does not heal uniformly. We consider the phenomenon in the context of active fluids. Improving upon the approximation used by Zimmermann, Basan, and Levine [Eur. Phys. J.: Spec. Top. 223, 1259 (2014), 10.1140/epjst/e2014-02189-7], we perform a linear stability analysis on a two-dimensional incompressible hydrodynamic model of an active fluid with an open interface. We categorize the stability of the model and find that for experimentally relevant parameters, fingering instability is always absent in this minimal model. Our results point to the crucial role of density variation in the fingering instability in tissue regeneration.
Linear study of the precessional fishbone instability
Idouakass, M.; Faganello, M.; Berk, H. L.; Garbet, X.; Benkadda, S.
2016-10-01
The precessional fishbone instability is an m = n = 1 internal kink mode destabilized by a population of trapped energetic particles. The linear phase of this instability is studied here, analytically and numerically, with a simplified model. This model uses the reduced magneto-hydrodynamics equations for the bulk plasma and the Vlasov equation for a population of energetic particles with a radially decreasing density. A threshold condition for the instability is found, as well as a linear growth rate and frequency. It is shown that the mode frequency is given by the precession frequency of the deeply trapped energetic particles at the position of strongest radial gradient. The growth rate is shown to scale with the energetic particle density and particle energy while it is decreased by continuum damping.
Inertial effects in laser-driven ablation
International Nuclear Information System (INIS)
Harrach, R.J.; Szeoke, A.; Howard, W.M.
1983-01-01
The gasdynamic partial differential equations (PDE's) governing the motion of an ablatively accelerated target (rocket) contain an inertial force term that arises from acceleration of the reference frame in which the PDE's are written. We give a simple, intuitive description of this effect, and estimate its magnitude and parametric dependences by means of approximate analytical formulas inferred from our computer hydrocode calculations. Often this inertial term is negligible, but for problems in the areas of laser fusion and laser equation of state studies we find that it can substantially reduce the attainable hydrodynamic efficiency of acceleration and implosion
Richtmyer-Meshkov instability in elastic-plastic media
Piriz, Antonio R.; López Cela, Juan J.; Tahir, Naeem A.; Hoffmann, Dieter H. H.
2008-04-01
Hydrodynamic instabilities are of great importance in the LAPLAS (Laboratory of Planetary Sciences) experiment that is being designed for the study of high energy density states of matter in the framework of the FAIR projectDuring the implosion of the LAPLAS cylindrical target Richtmyer-Meshkov (RM) instability occurs when a shock is launched into a material pusher with elastic and plastic properties that determines the physics of the instability evolution. We have studied the evolution of the interface from which the shock is launched as a consequence of the RM instability. For this we have developed an analytical model and we have performed two-dimensional numerical simulations in order to validate the model. Model and simulations show the asymptotic stability state in which the interface oscillates elastically around a mean value higher than the initial perturbation amplitude. Such a mean value is determined by an initial plastic phase. Applications to the measurement of the yield strength of materials under extreme conditions are foreseen.
Energy Technology Data Exchange (ETDEWEB)
Milovich, J. L., E-mail: milovich1@llnl.gov; Robey, H. F.; Clark, D. S.; Baker, K. L.; Casey, D. T.; Cerjan, C.; Field, J.; MacPhee, A. G.; Pak, A.; Patel, P. K.; Peterson, J. L.; Smalyuk, V. A.; Weber, C. R. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
2015-12-15
Experimental results from indirectly driven ignition implosions during the National Ignition Campaign (NIC) [M. J. Edwards et al., Phys. Plasmas 20, 070501 (2013)] achieved a record compression of the central deuterium-tritium fuel layer with measured areal densities up to 1.2 g/cm{sup 2}, but with significantly lower total neutron yields (between 1.5 × 10{sup 14} and 5.5 × 10{sup 14}) than predicted, approximately 10% of the 2D simulated yield. An order of magnitude improvement in the neutron yield was subsequently obtained in the “high-foot” experiments [O. A. Hurricane et al., Nature 506, 343 (2014)]. However, this yield was obtained at the expense of fuel compression due to deliberately higher fuel adiabat. In this paper, the design of an adiabat-shaped implosion is presented, in which the laser pulse is tailored to achieve similar resistance to ablation-front instability growth, but with a low fuel adiabat to achieve high compression. Comparison with measured performance shows a factor of 3–10× improvement in the neutron yield (>40% of predicted simulated yield) over similar NIC implosions, while maintaining a reasonable fuel compression of >1 g/cm{sup 2}. Extension of these designs to higher laser power and energy is discussed to further explore the trade-off between increased implosion velocity and the deleterious effects of hydrodynamic instabilities.
A generalized transport-velocity formulation for smoothed particle hydrodynamics
Energy Technology Data Exchange (ETDEWEB)
Zhang, Chi; Hu, Xiangyu Y., E-mail: xiangyu.hu@tum.de; Adams, Nikolaus A.
2017-05-15
The standard smoothed particle hydrodynamics (SPH) method suffers from tensile instability. In fluid-dynamics simulations this instability leads to particle clumping and void regions when negative pressure occurs. In solid-dynamics simulations, it results in unphysical structure fragmentation. In this work the transport-velocity formulation of Adami et al. (2013) is generalized for providing a solution of this long-standing problem. Other than imposing a global background pressure, a variable background pressure is used to modify the particle transport velocity and eliminate the tensile instability completely. Furthermore, such a modification is localized by defining a shortened smoothing length. The generalized formulation is suitable for fluid and solid materials with and without free surfaces. The results of extensive numerical tests on both fluid and solid dynamics problems indicate that the new method provides a unified approach for multi-physics SPH simulations.
Acoustic-hydrodynamic-flame coupling—A new perspective for zero and low Mach number flows
Pulikkottil, V. V.; Sujith, R. I.
2017-04-01
A combustion chamber has a hydrodynamic field that convects the incoming fuel and oxidizer into the chamber, thereby causing the mixture to react and produce heat energy. This heat energy can, in turn, modify the hydrodynamic and acoustic fields by acting as a source and thereby, establish a positive feedback loop. Subsequent growth in the amplitude of the acoustic field variables and their eventual saturation to a limit cycle is generally known as thermo-acoustic instability. Mathematical representation of these phenomena, by a set of equations, is the subject of this paper. In contrast to the ad hoc models, an explanation of the flame-acoustic-hydrodynamic coupling, based on fundamental laws of conservation of mass, momentum, and energy, is presented in this paper. In this paper, we use a convection reaction diffusion equation, which, in turn, is derived from the fundamental laws of conservation to explain the flame-acoustic coupling. The advantage of this approach is that the physical variables such as hydrodynamic velocity and heat release rate are coupled based on the conservation of energy and not based on an ad hoc model. Our approach shows that the acoustic-hydrodynamic interaction arises from the convection of acoustic velocity fluctuations by the hydrodynamic field and vice versa. This is a linear mechanism, mathematically represented as a convection operator. This mechanism resembles the non-normal mechanism studied in hydrodynamic theory. We propose that this mechanism could relate the instability mechanisms of hydrodynamic and thermo-acoustic systems. Furthermore, the acoustic-hydrodynamic interaction is shown to be responsible for the convection of entropy disturbances from the inlet of the chamber. The theory proposed in this paper also unifies the observations in the fields of low Mach number flows and zero Mach number flows. In contrast to the previous findings, where compressibility is shown to be causing different physics for zero and low Mach
Desorption/ablation of lithium fluoride induced by extreme ultraviolet laser radiation
Directory of Open Access Journals (Sweden)
Blejchař Tomáš
2016-06-01
Full Text Available The availability of reliable modeling tools and input data required for the prediction of surface removal rate from the lithium fluoride targets irradiated by the intense photon beams is essential for many practical aspects. This study is motivated by the practical implementation of soft X-ray (SXR or extreme ultraviolet (XUV lasers for the pulsed ablation and thin film deposition. Specifically, it is focused on quantitative description of XUV laser-induced desorption/ablation from lithium fluoride, which is a reference large band-gap dielectric material with ionic crystalline structure. Computational framework was proposed and employed here for the reconstruction of plume expansion dynamics induced by the irradiation of lithium fluoride targets. The morphology of experimentally observed desorption/ablation craters were reproduced using idealized representation (two-zone approximation of the laser fluence profile. The calculation of desorption/ablation rate was performed using one-dimensional thermomechanic model (XUV-ABLATOR code taking into account laser heating and surface evaporation of the lithium fluoride target occurring on a nanosecond timescale. This step was followed by the application of two-dimensional hydrodynamic solver for description of laser-produced plasma plume expansion dynamics. The calculated plume lengths determined by numerical simulations were compared with a simple adiabatic expansion (blast-wave model.
Non-hydrodynamic model of plasma focus structure
International Nuclear Information System (INIS)
Imshennik, V.S.; Zueva, N.M.; Lokutsievskij, O.V.; Mikhajlova, M.S.
1985-01-01
Experimental and theoretical plasma focus study has resulted in the necessity of creating a non-hydrodynamic plasma focus structure model (MKHD model). This model describes the final stage of plasma focus, which starts immediately after maximum plasma compression. It is related to a very limited space near the neck of the sausage instability. The MKHD model is two-dimensional, axially symmetric and collisionless with respect to the ions and magnetohydrodynamic with respect to the electrons; it accounts for the pinch instability of the sausage type (m=0 mode). The MKHD model, first of all, explains the long time of the plasma focus existence and non-thermonuclear peculiarities in the neutron yield. The initial and boundary conditions are formulated in accordance with the experiments and the results of computations in the 2D MHD model. A non-stationary process of plasma focus dynamics is studied numerically for a relatively long time - about 20 ns; this time is, in principle, not restricted. The computations show that the external edge of the neck expands rather slowly (at a speed that is lower than the thermal ion velocity, by an order of magnitude), and the magnetic field energy is converted to the kinetic energy of the chaotic ion motion (which is doubled for the time of computation). A 'supra-thermal' tail (with the deuterium ion energy higher than 10 keV) forms slowly at the ion distribution function; this tail determines a substantial part of the total neutron yield. The formation of stable vortices, which actually determine the structure of the plasma flow during the developed non-hydrodynamic stage of the plasma focus, is also found in the computations. These properties of the development of the sausage instability, as found in the numerical experiment with the MKHD plasma focus model, are in qualitative agreement with the behaviour of an instability of the same type in the MHD models of the Z-pinch
International Nuclear Information System (INIS)
Montierth, L.; Morse, R.
1984-01-01
This chapter discusses small amplitude growth of the outside surface instability and modes of failure resulting from nonlinear development of the inside surface instability. It is demonstrated that pellets with initial pellet aspect ratio, A /SUB p/ >5 may have difficulty with Rayleigh-Taylor instability and that shells with A /SUB p/ greater than or equal to10 will probably demand stringent smoothness specification in order not to experience failure in the final implosion. The linear amplification of the outside surface instability can easily exceed 10 3 for A /SUB p/ and resulting A values in the range of programmatic interest. Amplifications of this order, starting from attainable surface finishes, can then penetrate to the inside shell surface, producing perturbations there which approach the nonlinear development amplitude and at the start of the final deceleration. It is shown that such inside surface perturbations can be amplified to large amplitude by the inside instability and cause failure through reduction of the maximum fuel temperature achieved. Insight into the scaling of failure mechanisms is offered
Fluctuations and instabilities of a holographic metal
Jokela, Niko; Järvinen, Matti; Lippert, Matthew
2013-02-01
We analyze the quasinormal modes of the D2-D8' model of 2+1-dimensional, strongly-coupled, charged fermions in a background magnetic field and at non-zero density. The model is known to include a quantum Hall phase with integer filling fraction. As expected, we find a hydrodynamical diffusion mode at small momentum and the nonzero-temperature holographic zero sound, which becomes massive above a critical magnetic field. We confirm the previously-known thermodynamic instability. In addition, we discover an instability at low temperature, large mass, and in a charge density and magnetic field range near the quantum Hall phase to an inhomogeneous striped phase.
Thermoacoustic instability of a laminar premixed flame in Rijke tube with a hydrodynamic region
Zhao, Dan; Chow, Z. H.
2013-07-01
In this work, a Rijke tube with a hydrodynamic region confined is considered to investigate its non-normality and the effect of the hydrodynamic region on the system stability behaviors. Experiments are first conducted on Rijke tubes with different lengths. It is found that the fundamental mode frequency is decreased and then increased, as the flame is placed at different axial positions at the bottom half of the tube. This trend agrees well with the prediction from the thermoacoustic model developed, of which the hydrodynamic region is modelled as an oscillating 'airplug' and the flame dynamics is captured by using classical G-equation. In addition, the flame as measured is found to respond differently to oncoming acoustic disturbances. Modal and non-modal stability analyses are then conducted to determine the eigenmode growth rate and the transient one of acoustic disturbances. The 'safest' and most 'dangerous' flame locations as defined as those corresponding to extreme eigenmode and transient growth rate are estimated, and compared with those from the model without the hydrodynamic region. In order to mitigate such detrimental oscillations, identification and mitigation algorithms are experimentally implemented on the Rijke tube. The sound pressure level is reduced by approximately 50 dB. To gain insights on the thermoacoustic system, transfer function of the actuated Rijke tube system is measured by injecting a broad-band white noise. Compared with the estimation from our model, good agreement is observed. Finally, the marginal stability regions are estimated.
Nonlinear instability and convection in a vertically vibrated granular bed
Shukla, P.; Ansari, I.H.; van der Meer, Roger M.; Lohse, Detlef; Alam, M.
2014-01-01
The nonlinear instability of the density-inverted granular Leidenfrost state and the resulting convective motion in strongly shaken granular matter are analysed via a weakly nonlinear analysis of the hydrodynamic equations. The base state is assumed to be quasi-steady and the effect of harmonic
Evidence of Rayleigh-Taylor instabilities in tri-layer targets
International Nuclear Information System (INIS)
Galmiche, D.; Holstein, P.A.; Meyer, B.; Rostaing, M.; Wilke, N.
1988-01-01
The results of the experiments carried out on a laser system are reported. The work is performed in order to investigate the problem of target instability under ablative acceleration and to get direct evidence of Rayleigh-Taylor instabilities. Tri-layer experiments assert the validity of X-ray spectroscopy measurements as experimental method to investigate the problem. A mixing zone is evidenced and general trends of mixing development versus target acceleration are coherent with numerical simulations. Results obtained with optical smoothing demonstrate that the apparent mixing is not due to large scale illumination non uniformities. Numerical simulations confirm that Rayleigh-Taylor instability seems to be the dominant process responsible for the mixing. Benefit of time resolved spectroscopy appears attractive and gives a real knowledge of the mixing layer
A pulsed power hydrodynamics approach to exploring properties of warm dense matter
Energy Technology Data Exchange (ETDEWEB)
Reinovsky, Robert Emil [Los Alamos National Laboratory
2008-01-01
Pulsed Power Hydrodynamics, as an application of low-impedance, pulsed power, and high magnetic field technology developed over the last decade to study advanced hydrodynamic problems, instabilities, turbulence, and material properties, can potentially be applied to the study of the behavior and properties of warm dense matter (WDM) as well. Exploration of the properties, such as equation of state and conductivity, of warm dense matter is an emerging area of study focused on the behavior of matter at density near solid density (from 10% of solid density to a few times solid density) and modest temperatures ({approx}1-10 eV). Warm dense matter conditions can be achieved by laser or particle beam heating of very small quantities of matter on timescales short compared to the subsequent hydrodynamic expansion timescales (isochoric heating) and a vigorous community of researchers is applying these techniques using petawatt scale laser systems, but the microscopic size scale of the WDM produced in this way limits access to some physics phenomena. Pulsed power hydrodynamics techniques, either through high convergence liner compression of a large volume, modest density, low temperature plasma to densities approaching solid density or through the explosion and subsequent expansion of a conductor (wire) against a high pressure (density) gas background (isobaric expansion) techniques both offer the prospect for producing warm dense matter in macroscopic quantities. However, both techniques demand substantial energy, proper power conditioning and delivery, and an understanding of the hydrodynamic and instability processes that limit each technique. Similarly, liner compression of normal density material, perhaps using multiple reflected shocks can provide access to the challenging region above normal density -- again with the requirement of very large amounts of driving energy. In this paper we will provide an introduction to techniques that might be applied to explore this
Mishra, Gaurav; Ghosh, Karabi; Ray, Aditi; Gupta, N. K.
2018-06-01
Radiation hydrodynamic (RHD) simulations for four different potential high-Z hohlraum materials, namely Tungsten (W), Gold (Au), Lead (Pb), and Uranium (U) are performed in order to investigate their performance with respect to x-ray absorption, re-emission and ablation properties, when irradiated by constant temperature drives. A universal functional form is derived for estimating time dependent wall albedo for high-Z materials. Among the high-Z materials studied, it is observed that for a fixed simulation time the albedo is maximum for Au below 250 eV, whereas it is maximum for U above 250 eV. New scaling laws for shock speed vs drive temperature, applicable over a wide temperature range of 100 eV to 500 eV, are proposed based on the physics of x-ray driven stationary ablation. The resulting scaling relation for a reference material Aluminium (Al), shows good agreement with that of Kauffman's power law for temperatures ranging from 100 eV to 275 eV. New scaling relations are also obtained for temperature dependent mass ablation rate and ablation pressure, through RHD simulation. Finally, our study reveals that for temperatures above 250 eV, U serves as a better hohlraum material since it offers maximum re-emission for x-rays along with comparable mass ablation rate. Nevertheless, traditional choice, Au works well for temperatures below 250 eV. Besides inertial confinement fusion (ICF), the new scaling relations may find its application in view-factor codes, which generally ignore atomic physics calculations of opacities and emissivities, details of laser-plasma interaction and hydrodynamic motions.
Hihath, Sahar; Santala, Melissa K.; Cen, Xi; Campbell, Geoffrey; van Benthem, Klaus
2016-03-01
Obliteration of matter by pulsed laser beams is not only prevalent in science fiction movies, but finds numerous technological applications ranging from additive manufacturing over machining of micro- and nanostructured features to health care. Pulse lengths ranging from femtoseconds to nanoseconds are utilized at varying laser beam energies and pulse lengths, and enable the removal of nanometric volumes of material. While the mechanisms for removal of material by laser irradiation, i.e., laser ablation, are well understood on the micrometer length scale, it was previously impossible to directly observe obliteration processes on smaller scales due to experimental limitations for the combination of nanometer spatial and nanosecond temporal resolution. Here, we report the direct observation of metal thin film ablation from a solid substrate through dynamic transmission electron microscopy. Quantitative analysis reveals liquid-phase dewetting of the thin-film, followed by hydrodynamic sputtering of nano- to submicron sized metal droplets. We discovered unexpected fracturing of the substrate due to evolving thermal stresses. This study confirms that hydrodynamic sputtering remains a valid mechanism for droplet expulsion on the nanoscale, while irradiation induced stress fields represent limit laser processing of nanostructured materials. Our results allow for improved safety during laser ablation in manufacturing and medical applications.
International Nuclear Information System (INIS)
Bud'ko, A.B.; Liberman, M.A.; Bondarenko, E.A.
1992-01-01
Since development of the RT modes in the ablatively accelerated plasma of laser targets imposes crucial limitations on symmetry of spherical implosions and hence on energy cumulation, it has been the subject of intensive numerical and analytical analysis in the recent years, particularly in the context of inertial confinement fusion. Recent thin-foil ablative-acceleration experiments as well as the results of 2D numerical simulations demonstrated substantial reduction of the instability growth rates compared with the classical theory predictions up to the total stabilization in the short-wavelength limit. The numerical results indicated that the main stabilization mechanism is convection. To derive the scaling laws for the RT growth rates and cut-off wavenumbers in the wide range of flow parameters, analytical solutions attract special interest. The analytical approach based on the discontinuity model was developed to analyze the reduction of the RT growth rates by the plasma convective flow and the thermal conductivity effects. The following major problem arises in the discontinuity approximation, which leaves the solution undetermined: the number of the boundary conditions on the perturbed ablation surface is not sufficient to derive the dispersion equation. One needs additional boundary conditions not associated with the conservation laws on the discontinuity surface to close the system of linearized equations for small perturbations. The stabilization effect of highly structured hydrodynamic profiles was studied by Mikaelian and Munro for a stationary plasma. Nevertheless, no reasonable analytical model was constructed taking into account the combined convective, thermal conductivity and density gradient reduction of the RT growth rates. In this report we develop the analytical approach based on the WKB approximation to analyze the stabilization of the RT modes in plasma with smooth density and velocity gradients. (author) 9 refs., 1 fig
Direct-drive laser-fusion in the US
International Nuclear Information System (INIS)
McCrory, R.L.; Soures, J.M.; Audebert, P.
1986-01-01
Direct-drive experiments at the University of Rochester's Laboratory for Laser Energetics (LLE) and the Naval Research Laboratory (NRL) are presently addressing issues in pellet compression and heating: efficiency of coupling of laser energy to the target and the coupling of absorbed energy to the fuel, drive uniformity, hydrodynamic stability, preheat arising from laser plasma instabilities and x-rays, and target diagnostics. The 24-beam, 2500-Joule, 351 nm OMEGA laser system at LLE has been used in an experimental effort to achieve high compressed DT fuel densities. Detailed hydrodynamic computer simulations at NRL predict that the growth rate of the ablative Rayleigh-Taylor instability is less than the classical values. Recent Rayleigh-Taylor experiments ar NRL are testing these predictions
Numerical study of jets secondary instabilities
International Nuclear Information System (INIS)
Brancher, Pierre
1996-01-01
The work presented in this dissertation is a contribution to the study of the transition to turbulence in open shear flows. Results from direct numerical simulations are interpreted within the framework of hydrodynamic stability theory. The first chapter is an introduction to the primary and secondary instabilities observed in jets and mixing layers. The numerical method used in the present study is detailed in the second chapter. The dynamics of homogeneous circular jets subjected to stream wise and azimuthal perturbations are investigated in the third chapter. A complete scenario describing the evolution of the jet is proposed with emphasis on the dynamics of vorticity within the flow. In the fourth chapter a parametric study reveals a three-dimensional secondary instability mainly controlled in the linear regime by the Strouhal number of the primary instability. In the nonlinear regime the dynamics of the azimuthal harmonies are described by means of model equations and are linked to the formation of stream wise vortices in the braid. The fifth chapter is dedicated to the convective or absolute nature of the secondary instabilities in plane shear layers. It is shown that there are flow configurations for which the two-dimensional secondary instability (pairing) is absolute even though the primary instability (Kelvin-Helmholtz) is convective. Some preliminary results concerning the three-dimensional secondary instabilities arc presented at the end of this chapter. The last chapter summarizes the main results and examines possible extensions of this work. (author) [fr
Comparison of plastic, high density carbon, and beryllium as indirect drive NIF ablators
Kritcher, A. L.; Clark, D.; Haan, S.; Yi, S. A.; Zylstra, A. B.; Callahan, D. A.; Hinkel, D. E.; Berzak Hopkins, L. F.; Hurricane, O. A.; Landen, O. L.; MacLaren, S. A.; Meezan, N. B.; Patel, P. K.; Ralph, J.; Thomas, C. A.; Town, R.; Edwards, M. J.
2018-05-01
Detailed radiation hydrodynamic simulations calibrated to experimental data have been used to compare the relative strengths and weaknesses of three candidate indirect drive ablator materials now tested at the NIF: plastic, high density carbon or diamond, and beryllium. We apply a common simulation methodology to several currently fielded ablator platforms to benchmark the model and extrapolate designs to the full NIF envelope to compare on a more equal footing. This paper focuses on modeling of the hohlraum energetics which accurately reproduced measured changes in symmetry when changes to the hohlraum environment were made within a given platform. Calculations suggest that all three ablator materials can achieve a symmetric implosion at a capsule outer radius of ˜1100 μm, a laser energy of 1.8 MJ, and a DT ice mass of 185 μg. However, there is more uncertainty in the symmetry predictions for the plastic and beryllium designs. Scaled diamond designs had the most calculated margin for achieving symmetry and the highest fuel absorbed energy at the same scale compared to plastic or beryllium. A comparison of the relative hydrodynamic stability was made using ultra-high resolution capsule simulations and the two dimensional radiation fluxes described in this work [Clark et al., Phys. Plasmas 25, 032703 (2018)]. These simulations, which include low and high mode perturbations, suggest that diamond is currently the most promising for achieving higher yields in the near future followed by plastic, and more data are required to understand beryllium.
Energy Technology Data Exchange (ETDEWEB)
Ferraro, A [Consiglio Nazionale delle Ricerche, Turin (Italy). Lab. di Cosmo-Geofisica; Max-Planck-Institut fuer Extraterrestrische Physik, Garching (Germany, F.R.)); Massaglia, S [Turin Univ. (Italy). Ist. di Fisica; Trussoni, E [Consiglio Nazionale delle Ricerche, Turin (Italy). Lab. di Cosmo-Geofisica
1982-03-01
In this paper a discussion is presented on Kelvin-Helmholtz instabilities in pressure-confined two-dimensional flows (slabs) delimited by boundary layers with velocity and density gradients. It is found that the fastest growing modes in supersonic flows are produced by perturbations reflecting at the boundaries and have wavelengths of the order of the slab width; this peak of instability is even more evident than in the case of vortex-sheet cylindrical flows, discussed in a previous paper. From a comparison of the results for the two-dimensional slab and three-dimensional cylinder it is concluded that a two-dimensional treatment provides an adequate description of instabilities in fluid flows. In this analogy, symmetric and antisymmetric modes in the slab correspond to pinching and helical modes in the cylinder. In the final section a comparison is attempted of the results obtained with morphologies in collimated jets in extragalactic radio sources; general characteristics appear to be classifiable in terms of scale-lengths of the velocity and density gradients in the boundary layers.
Energy distribution of ions produced by laser ablation of silver in vacuum
International Nuclear Information System (INIS)
Toftmann, B.; Schou, J.; Canulescu, S.
2013-01-01
The ion energy in a silver ablation plume for fluence in the range of 0.6–2.4 J cm −2 , typical for a pulsed laser deposition (PLD) experiment has been investigated. In this fluence range the ion fraction of the ablated particles becomes gradually dominant and can be utilized to characterize the ablation process. A silver target in vacuum was irradiated with a Nd:YAG laser at a wavelength of 355 nm and detailed measurements of the time-resolved angular distribution of plume ions were made. In contrast to earlier work, the beam spot was circular such that any flip-over effect of the plume is avoided. The angular energy distribution of ions in forward direction exceeds values of 500 eV, while at large angles the ion energy tail is below 100 eV. The maximum for the time-of-flight distributions agrees consistently with the prediction of Anisimov's model in the low fluence range, in which hydrodynamic motion prevails.
International Nuclear Information System (INIS)
Jain, Shweta; Sharma, Prerana; Chhajlani, R. K.
2015-01-01
The Jeans instability of self-gravitating quantum plasma is examined considering the effects of viscosity, finite Larmor radius (FLR) corrections and rotation. The analysis is done by normal mode analysis theory with the help of relevant linearized perturbation equations of the problem. The general dispersion relation is obtained using the quantum magneto hydrodynamic model. The modified condition of Jeans instability is obtained and the numerical calculations have been performed to show the effects of various parameters on the growth rate of Jeans instability
Strings, vortex rings, and modes of instability
Directory of Open Access Journals (Sweden)
Steven S. Gubser
2015-03-01
Full Text Available We treat string propagation and interaction in the presence of a background Neveu–Schwarz three-form field strength, suitable for describing vortex rings in a superfluid or low-viscosity normal fluid. A circular vortex ring exhibits instabilities which have been recognized for many years, but whose precise boundaries we determine for the first time analytically in the small core limit. Two circular vortices colliding head-on exhibit stronger instabilities which cause splitting into many small vortices at late times. We provide an approximate analytic treatment of these instabilities and show that the most unstable wavelength is parametrically larger than a dynamically generated length scale which in many hydrodynamic systems is close to the cutoff. We also summarize how the string construction we discuss can be derived from the Gross–Pitaevskii Lagrangian, and also how it compares to the action for giant gravitons.
Jeans instability with exchange effects in quantum dusty magnetoplasmas
International Nuclear Information System (INIS)
Jamil, M.; Rasheed, A.; Rozina, Ch.; Jung, Y.-D.; Salimullah, M.
2015-01-01
Jeans instability is examined in magnetized quantum dusty plasmas using the quantum hydrodynamic model. The quantum effects are considered via exchange-correlation potential, recoil effect, and Fermi degenerate pressure, in addition to thermal effects of plasma species. It is found that the electron exchange and correlation potential have significant effects over the threshold value of wave vector and Jeans instability. The presence of electron exchange and correlation effect shortens the time of dust sound that comparatively stabilizes the self gravitational collapse. The results at quantum scale are helpful in understanding the collapse of the self-gravitating dusty plasma systems
Lower bound on the electroweak wall velocity from hydrodynamic instability
Energy Technology Data Exchange (ETDEWEB)
Mégevand, Ariel; Membiela, Federico Agustín; Sánchez, Alejandro D., E-mail: megevand@mdp.edu.ar, E-mail: membiela@mdp.edu.ar, E-mail: sanchez@mdp.edu.ar [IFIMAR (CONICET-UNMdP), Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata, Deán Funes (7600) 3350 Mar del Plata (Argentina)
2015-03-01
The subsonic expansion of bubbles in a strongly first-order electroweak phase transition is a convenient scenario for electroweak baryogenesis. For most extensions of the Standard Model, stationary subsonic solutions (i.e., deflagrations) exist for the propagation of phase transition fronts. However, deflagrations are known to be hydrodynamically unstable for wall velocities below a certain critical value. We calculate this critical velocity for several extensions of the Standard Model and compare with an estimation of the wall velocity. In general, we find a region in parameter space which gives stable deflagrations as well as favorable conditions for electroweak baryogenesis.
Lower bound on the electroweak wall velocity from hydrodynamic instability
International Nuclear Information System (INIS)
Mégevand, Ariel; Membiela, Federico Agustín; Sánchez, Alejandro D.
2015-01-01
The subsonic expansion of bubbles in a strongly first-order electroweak phase transition is a convenient scenario for electroweak baryogenesis. For most extensions of the Standard Model, stationary subsonic solutions (i.e., deflagrations) exist for the propagation of phase transition fronts. However, deflagrations are known to be hydrodynamically unstable for wall velocities below a certain critical value. We calculate this critical velocity for several extensions of the Standard Model and compare with an estimation of the wall velocity. In general, we find a region in parameter space which gives stable deflagrations as well as favorable conditions for electroweak baryogenesis
Lower bound on the electroweak wall velocity from hydrodynamic instability
Energy Technology Data Exchange (ETDEWEB)
Mégevand, Ariel; Membiela, Federico Agustín; Sánchez, Alejandro D. [IFIMAR (CONICET-UNMdP), Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata, Deán Funes (7600) 3350 Mar del Plata (Argentina)
2015-03-27
The subsonic expansion of bubbles in a strongly first-order electroweak phase transition is a convenient scenario for electroweak baryogenesis. For most extensions of the Standard Model, stationary subsonic solutions (i.e., deflagrations) exist for the propagation of phase transition fronts. However, deflagrations are known to be hydrodynamically unstable for wall velocities below a certain critical value. We calculate this critical velocity for several extensions of the Standard Model and compare with an estimation of the wall velocity. In general, we find a region in parameter space which gives stable deflagrations as well as favorable conditions for electroweak baryogenesis.
Fluid instabilities and wakes in a soap-film tunnel
International Nuclear Information System (INIS)
Vorobieff, P.; Ecke, R.E.
1999-01-01
We present a compact, low-budget two-dimensional hydrodynamic flow visualization system based on a tilted, gravity-driven soap film tunnel. This system is suitable for demonstrations and studies of a variety of fluid mechanics problems, including turbulent wakes past bluff bodies and lifting surfaces, Kelvin - Helmholtz instability, and grid turbulence. copyright 1999 American Association of Physics Teachers
Kiciński, Jan
2018-01-01
The paper presents the results of the analysis of the dynamic performance of the rotor being a component of the ORC turbine set with the net electrical output of 100 kW and the nominal speed of 9000 rpm. The research was conducted using tools capable of performing the necessary simulation of the system operating under highly unstable conditions, i.e., in a strongly nonlinear regime. In this regard, the author of the paper followed the subsequent phases of whirl/whip formation manifested in the fluid film. Constructional solutions within the scope of the bearing were examined with non-conventional lubricating mediums (low boiling mediums). On the basis of those scientific studies, the decision to build a working prototype of the machine was taken. Such a prototype has already been manufactured, having regard to the outcome of the conducted analyses. The research presented herein produced interesting results showing that, under the conditions of hydrodynamic instability, the phenomena taking place inside the lubricating gap of the slide bearing are not recurrent for each individual rotor revolution, notwithstanding the fact that the external excitation forces acting on the system are fully repeatable. The research tools were presented that allow a detailed qualitative and quantitative description of such phenomena.
On the instability of convective flow in cylinder and possible secondary regimes
Energy Technology Data Exchange (ETDEWEB)
Bekezhanova, V B; Andreev, V K, E-mail: bekezhanova@mail.ru, E-mail: andr@icm.krasn.ru [Institute of Computational Modelling SB RAS, Akademgorodok, 50/44, Krasnoyarsk, Institute of Mathematics and Fundamental Informatics, Siberian Federal University, Svobodny, 79, Krasnoyarsk, 660041 (Russian Federation)
2014-08-01
A new exact solution of equations of free convection is constructed in the framework of the Oberbeck–Boussinesq approximation. The solution contains an independent parameter and describes the flow of a viscous heat-conducting liquid in the vertical cylinder with large radius. Complex rheology and radiative heating are taken into account. The considered problem reduces to the operator equation with strongly nonlinear operator. The solvability of the operator problem is proved. The iterative procedure for finding the free parameter is suggested. Three different classes of solution are obtained with the help of the procedure. The linear stability of all classes of solutions is studied numerically. Critical thermal mode is isolated. Evolution of oscillatory mode depending on Prandtl number is investigated. It is shown that under small Prandtl numbers oscillatory modes decay. If Prandtl numbers are not small a new instability type appears. This instability is connected with growing thermal disturbances. Another instability mechanism is discovered in the short waves domain. In this case the crisis is attributed to growing hydrodynamical disturbances. Secondary regimes arising in the hydrodynamical mechanism of the stability loss are calculated. (paper)
Effect of FLR correction on Rayleigh -Taylor instability of quantum and stratified plasma
International Nuclear Information System (INIS)
Sharma, P.K.; Tiwari, Anita; Argal, Shraddha; Chhajlani, R.K.
2013-01-01
The Rayleigh Taylor instability of stratified incompressible fluids is studied in presence of FLR Correction and quantum effects in bounded medium. The Quantum magneto hydrodynamic equations of the problem are solved by using normal mode analysis method. A dispersion relation is carried out for the case where plasma is bounded by two rigid planes z = 0 and z = h. The dispersion relation is obtained in dimensionless form to discuss the growth rate of Rayleigh Taylor instability in presence of FLR Correction and quantum effects. The stabilizing or destabilizing behavior of quantum effect and FLR correction on the Rayleigh Taylor instability is analyzed. (author)
Energy Technology Data Exchange (ETDEWEB)
Tong Huifeng; Yuan Hong [Institute of Fluid Physics, Chinese Academy of Engineering Physics, P.O. Box 919-101, Mianyang, Sichuan 621900 (China); Tang Zhiping [CAS Key Laboratory for Mechanical Behavior and Design of Materials, Department of Mechanics and Mechanical Engineering, University of Science and Technology of China, Hefei 230026 (China)
2013-01-28
When an intense laser beam irradiates on a solid target, ambient air ionizes and becomes plasma, while part of the target rises in temperature, melts, vaporizes, ionizes, and yet becomes plasma. A general Godunov finite difference scheme WENO (Weighted Essentially Non-Oscillatory Scheme) with fifth-order accuracy is used to simulate 2-dimensional axis symmetrical laser-supported plasma flow field in the process of laser ablation. The model of the calculation of ionization degree of plasma and the interaction between laser beam and plasma are considered in the simulation. The numerical simulations obtain the profiles of temperature, density, and velocity at different times which show the evolvement of the ablative plasma. The simulated results show that the laser energy is strongly absorbed by plasma on target surface and that the velocity of laser supported detonation (LSD) wave is half of the ideal LSD value derived from Chapman-Jouguet detonation theory.
Rayleigh-Taylor and Kelvin-Helmholtz instabilities in targets accelerated by laser ablation
International Nuclear Information System (INIS)
Emery, M.H.; Gardner, J.H.; Boris, J.P.
1982-01-01
With use of the fast2d laser-shell model, the acceleration of a 20-μm-thick plastic foil up to 160 km/s has been simulated. It is possible to follow the Rayleigh-Taylor bubble-and-spike development far into the nonlinear regime and beyond the point of foil fragmentation. Strong shear flow develops which evolves into the Kelvin-Helmholtz instability. The Kelvin-Helmholtz instability causes the tips of the spikes to widen and as a result reduce their rate of ''fall.''
Effect of Compliant Walls on Secondary Instabilities in Boundary-Layer Transition
Joslin, Ronald D.; Morris, Philip J.
1991-01-01
For aerodynamic and hydrodynamic vehicles, it is highly desirable to reduce drag and noise levels. A reduction in drag leads to fuel savings. In particular for submersible vehicles, a decrease in noise levels inhibits detection. A suggested means to obtain these reduction goals is by delaying the transition from laminar to turbulent flow in external boundary layers. For hydrodynamic applications, a passive device which shows promise for transition delays is the compliant coating. In previous studies with a simple mechanical model representing the compliant wall, coatings were found that provided transition delays as predicted from the semi-empirical e(sup n) method. Those studies were concerned with the linear stage of transition where the instability of concern is referred to as the primary instability. For the flat-plate boundary layer, the Tollmien-Schlichting (TS) wave is the primary instability. In one of those studies, it was shown that three-dimensional (3-D) primary instabilities, or oblique waves, could dominate transition over the coatings considered. From the primary instability, the stretching and tilting of vorticity in the shear flow leads to a secondary instability mechanism. This has been theoretical described by Herbert based on Floquet theory. In the present study, Herbert's theory is used to predict the development of secondary instabilities over isotropic and non-isotropic compliant walls. Since oblique waves may be dominant over compliant walls, a secondary theory extention is made to allow for these 3-D primary instabilities. The effect of variations in primary amplitude, spanwise wavenumber, and Reynolds number on the secondary instabilities are examined. As in the rigid wall case, over compliant walls the subharmonic mode of secondary instability dominates for low-amplitude primary disturbances. Both isotropic and non-isotropic compliant walls lead to reduced secondary growth rates compared to the rigid wall results. For high frequencies
Sixth International Symposium on Bifurcations and Instabilities in Fluid Dynamics (BIFD2015)
DEFF Research Database (Denmark)
Bar-Yoseph, P. Z.; Brøns, Morten; Gelfgat, A.
2016-01-01
dynamics and remain a challenge for experimental, theoretical and computational studies. Examples of prototypical hydrodynamic instabilities are the Rayleigh–Bénard, Taylor–Couette, Bénard–Marangoni, Rayleigh–Taylor, and Kelvin–Helmholtz instabilities. A fundamental understanding of bifurcation patterns...... diseases, such as atherosclerotic and vulnerable plaques, abdominal aortic aneurisms, carotid artery disease, and pulmonary embolisms and implications for vascular interventions such as grafting and stenting. The collection of papers in this issue is a selection of the presentations given at the Sixth...
Progress on the physics of ignition for radiation driven inertial confinement fusion (ICF) targets
International Nuclear Information System (INIS)
Lindl, J.D.; Marinak, M.M.
1996-09-01
Extensive modeling of proposed National Ignition Facility (NIF) ignition targets has resulted in a variety of targets using different materials in the fuel shell, using driving temperatures which range from 250-300 eV, and requiring energies from 15 W/cm 2 for this type of hohlraum. The symmetry in Nova gas- filled hohlraums is affected by the gas fill. A large body of evidence now exists which indicates that this effect is due to laser beam filamentation which can be largely controlled by beam smoothing. We present here the firs 3-D simulations of hydrodynamic instability for the NIF point design capsule. These simulations, with the HYDRA radiation hydrodynamics code, indicate that spikes can penetrate up to 10 μm into the 30μm radius hot spot before ignition is quenched. Using capsules whose surface is modified by laser ablation, Nova experiments have been used to quantify the degradation of implosions subject to near NIF levels of hydrodynamic instability
Rayleigh-Taylor instabilities in indirect laser drive with rugby-shaped hohlraums
International Nuclear Information System (INIS)
Casner, A.; Galmiche, D.; Huser, G.; Jadaud, J.P.; Richard, A.; Liberatore, S.; Vandenboomgaerde, M.
2009-01-01
The mastering of the development of hydrodynamic instabilities like Rayleigh-Taylor instabilities is an important milestone on the way to perform efficient laser implosions. The complexity of these instabilities implies an experimental validation of the theoretical models and their computer simulations. An experimental platform involving the Omega laser has allowed us to perform indirect drive with rugby-shaped hohlraums. The experiments have validated the growth of 2- and 3-dimensional initial defects as predicted by theory. We have shown that the 3-dimensional defect saturates for an higher amplitude than the 2-dimensional one does. The experiments have been made by using a plastic shell doped with Germanium (CH:Ge). (A.C.)
Annual Report 2006 for Hydrodynamics and Radiation Hydrodynamics with Astrophysical Applications
Energy Technology Data Exchange (ETDEWEB)
R. Paul Drake
2007-04-05
We report the ongoing work of our group in hydrodynamics and radiation hydrodynamics with astrophysical applications. During the period of the existing grant, we have carried out two types of experiments at the Omega laser. One set of experiments has studied radiatively collapsing shocks, obtaining data using a backlit pinhole with a 100 ps backlighter and beginning to develop the ability to look into the shock tube with optical or x-ray diagnostics. Other experiments have studied the deeply nonlinear development of the Rayleigh-Taylor (RT) instability from complex initial conditions, using dual-axis radiographic data with backlit pinholes and ungated detectors to complete the data set for a Ph.D. student. We lead a team that is developing a proposal for experiments at the National Ignition Facility and are involved in experiments at NIKE and LIL. All these experiments have applications to astrophysics, discussed in the corresponding papers. We assemble the targets for the experiments at Michigan, where we also prepare many of the simple components. We also have several projects underway in our laboratory involving our x-ray source. The above activities, in addition to a variety of data analysis and design projects, provide good experience for graduate and undergraduates students. In the process of doing this research we have built a research group that uses such work to train junior scientists.
International Nuclear Information System (INIS)
Nobile, A.; Balkey, M.M.; Bartos, J.J.; Batha, S.H.; Day, R.D.; Elliott, J.E.; Elliott, N.E.; Gomez, V.M.; Hatch, D.J.; Lanier, N.E.; Fincke, J.R.; Manzanares, R.; Pierce, T.H.; Sandoval, D.L.; Schmidt, D.W.; Steckle, W.P.
2004-01-01
Experimental campaigns are being conducted at the 60 beam OMEGA laser at the University of Rochester's Laboratory for Laser Energetics to acquire data to validate hydrodynamic models in the high energy-density regime. This paper describes targets that have been developed and constructed for these experimental campaigns. Targets are 860 μm inner diameter by 2.2 mm length cylinders with 70 μm thick polymer ablator. On the ablator inner surface and located halfway along the axis of the cylinder is a 500 μm wide Al marker band. Band thicknesses in the range 8-16 microns are used. CH foam with densities in the range 30-90 mg/cc fills the inside of the cylinder. While these targets have been fabricated for years, several new improvements and features have recently been developed. Improvements include the use of epoxy instead of polystyrene for the ablator, and the use of electrodeposited Al for the marker band. A critical feature of the target is the surface feature that is placed on the marker band. Experiments are aimed at understanding the hydrodynamic behavior of imploding cylinders as a function of this surface feature. Recent development work has focused on production of engineered surface features on the target marker band. Using a fast tool servo on a diamond turning lathe, a wide range of specified surface features have been produced. This paper will address improvements to the cylinder targets as well as current development efforts
Modeling and analysis of hydrodynamic instabilities in two-phase flow using two-fluid model
International Nuclear Information System (INIS)
Zhou, J.; Podowski, M.Z.
2001-01-01
Because of the practical importance of two-phase flow instabilities, especially in boiling water nuclear reactor technology, substantial efforts have been made to date to understand the physical phenomena governing such instabilities and to develop computational tools to model the dynamics of marginally-stable/unstable boiling systems. The purpose of this paper is to present an integrated methodology for the analysis of flow-induced instabilities in boiling channels and systems. The major novel aspects of the proposed approach are: (a) it is based on the combined frequency-domain and time-domain methods, the former used to quantify stability margins and to determine the onset of instability conditions, the latter to study the nonlinear system response outside the stability boundaries identified using the nearly-exact results of the frequency-domain analysis; (b) the two-fluid model of two-phase flow has been used for the first time to analytically derive the boiling channel transfer functions for the parallel-channel and channel-to-channel instability modes. In this way, the major characteristics of a boiling system, including the onset-of-instability conditions, can be readily evaluated by using the qualitative frequency-domain approach, whereas the explicit time-domain integration is performed, if necessary, only for the operating conditions that have already been identified as unstable. Both methods use the same physical two-fluid model that, in one case, is linearized and used to derive a rigorous analytical solution in the complex domain, and, in the other case, is solved numerically using an algorithm developed especially for this purpose. The results using both methods have been compared against each other and extensively tested. The testing and validation of the new model included comparisons of the predicted steady-state distributions of major parameters and of the transient channel response against experimental data
Thermo-hydrodynamic lubrication in hydrodynamic bearings
Bonneau, Dominique; Souchet, Dominique
2014-01-01
This Series provides the necessary elements to the development and validation of numerical prediction models for hydrodynamic bearings. This book describes the thermo-hydrodynamic and the thermo-elasto-hydrodynamic lubrication. The algorithms are methodically detailed and each section is thoroughly illustrated.
Predictability of Rayleigh-Taylor instability
International Nuclear Information System (INIS)
Viecelli, J.A.
1986-01-01
Numerical experiments modeling the Rayleigh Taylor instability are carried out using a two-dimensional incompressible Eulerian hydrodynamic code VFTS. The method of integrating the Navier-Stokes equations including the viscous terms is similar to that described in Kim and Moin, except that Lagrange particles have been added and provision for body forces is given. The Eulerian method is 2nd order accurate in both space and time, and the Poisson equation for the effective pressure field is solved exactly at each time step using a cyclic reduction method. 3 refs., 3 figs
Numerical Simulation of Doped Targets for ICF
Phillips, Lee; Gardner, John H.; Bodner, Stephen E.; Colombant, Denis; Klapisch, Marcel; Bar-Shalom, Avraham
1997-11-01
The ablative Rayleigh-Taylor (RT) instability can be reduced by preheating the ablator, thereby reducing the peak density and increasing the mass ablation velocity. The ablator can be preheated with radiation from higher Z dopants.(Gardner, J.H., Bodner, S.E., Dahlburg, J.P., Phys. Fluids 3), 1070 (1991) Dopants also reduce the density gradient at the ablator, which provides a second mechanism to reduce the RT growth rate. We have recently developed a more sophisticated and detailed radiation package that uses opacities generated by an STA code, with non-LTE radiation transport based on the Busquet method. This radiation package has been incorporated into NRL's FAST2D radiation hydrodynamics code, which has been used to evaluate and optimize the use of various dopants that can provide interesting levels of preheat for an ICF target.
Nonlinear evolution of single spike in Richtmyer-Meshkov instability
International Nuclear Information System (INIS)
Fukuda, Y.; Nishihara, K.; Wouchuk, J.G.
2000-01-01
Nonlinear evolution of single spike structure and vortex in the Richtmyer-Meshkov instability is investigated with the use of a two-dimensional hydrodynamic code. It is shown that singularity appears in the vorticity left by transmitted and reflected shocks at a corrugated interface. This singularity results in opposite sign of vorticity along the interface that causes double spiral structure of the spike. (authors)
Sedimentation and gravitational instability of Escherichia coli Suspension
Salin, Dominique; Douarche, Carine
2017-11-01
The successive runs and tumbles of Escherichia coli bacteria provide an active matter suspension of rod-like particles with a large swimming, Brownian like, diffusion. As opposed to inactive elongated particles, this diffusion prevents clustering of the particles and hence instability in the gravity field. We measure the time dependent E . coli concentration profile during their sedimentation. After some hours, due to the dioxygen consumption, a motile / non-motile front forms leading to a Rayleigh-Taylor type gravitational instability. Analysing both sedimentation and instability in the framework of active particle suspensions, we can measure the relevant bacteria hydrodynamic characteristics such as its single particle sedimentation velocity and its hindrance volume. Comparing these quantities to the ones of equivalent passive particles (ellipsoid, rod) we tentatively infer the effective shape and size of the bacteria involved in its buoyancy induced advection and diffusion. Laboratoire FAST University Paris Saclay France.
Effects of fluid instabilities on laser fusion pellets
International Nuclear Information System (INIS)
Mead, W.C.; Lindl, J.D.
1975-01-01
A direct two-dimensional simulation method for fluid flow and plasma physics was used. The computer code LASNEX models the plasma phenomena of laser light absorption by inverse bremsstrahlung and plasma instabilities; energy transport and partition, using flux-limited diffusion and separate ion, electron, and radiation temperatures; and, optionally, effects of multigroup photon and particle transport and magnetic field physics. The fluid dynamics itself is Lagrangian, with an equation of state used to determine pressure, energy, and opacity as a function of density and temperature. Thermonuclear burn of compressed matter is included to permit evaluation of output to input energy ratios. The code tests with anomalies are described. Current understanding of fluid instability in the presence of ablation is discussed. (U.S.)
Yoon, Sung Hwan
2017-10-12
According to previous theory, pulsating propagation in a premixed flame only appears when the reduced Lewis number, β(Le-1), is larger than a critical value (Sivashinsky criterion: 4(1 +3) ≈ 11), where β represents the Zel\\'dovich number (for general premixed flames, β ≈ 10), which requires Lewis number Le > 2.1. However, few experimental observation have been reported because the critical reduced Lewis number for the onset of pulsating instability is beyond what can be reached in experiments. Furthermore, the coupling with the unavoidable hydrodynamic instability limits the observation of pure pulsating instabilities in flames. Here, we describe a novel method to observe the pulsating instability. We utilize a thermoacoustic field caused by interaction between heat release and acoustic pressure fluctuations of the downward-propagating premixed flames in a tube to enhance conductive heat loss at the tube wall and radiative heat loss at the open end of the tube due to extended flame residence time by diminished flame surface area, i.e., flat flame. The thermoacoustic field allowed pure observation of the pulsating motion since the primary acoustic force suppressed the intrinsic hydrodynamic instability resulting from thermal expansion. By employing this method, we have provided new experimental observations of the pulsating instability for premixed flames. The Lewis number (i.e., Le ≈ 1.86) was less than the critical value suggested previously.
Gaseous laser targets and optical diagnostics for studying compressible hydrodynamic instabilities
International Nuclear Information System (INIS)
Edwards, J M; Robey, H; Mackinnon, A
2001-01-01
Explore the combination of optical diagnostics and gaseous targets to obtain important information about compressible turbulent flows that cannot be derived from traditional laser experiments for the purposes of V and V of hydrodynamics models and understanding scaling. First year objectives: Develop and characterize blast wave-gas jet test bed; Perform single pulse shadowgraphy of blast wave interaction with turbulent gas jet as a function of blast wave Mach number; Explore double pulse shadowgraphy and image correlation for extracting velocity spectra in the shock-turbulent flow interaction; and Explore the use/adaptation of advanced diagnostics
Pellet ablation and ablation model development
International Nuclear Information System (INIS)
Houlberg, W.A.
1989-01-01
A broad survey of pellet ablation is given, based primarily on information presented at this meeting. The implications of various experimental observations for ablation theory are derived from qualitative arguments of the physics involved. The major elements of a more complete ablation theory are then outlined in terms of these observations. This is followed by a few suggestions on improving the connections between theory and experimental results through examination of ablation data. Although this is a rather aggressive undertaking for such a brief (and undoubtedly incomplete) assessment, some of the discussion may help us advance the understanding of pellet ablation. 17 refs
Nonlinear evolution of the sausage instability
International Nuclear Information System (INIS)
Book, D.L.; Ott, E.; Lampe, M.
1976-01-01
Sausage instabilities of an incompressible, uniform, perfectly conducting Z pinch are studied in the nonlinear regime. In the long wavelength limit (analogous to the ''shallow water theory'' of hydrodynamics), a simplified set of universal fluid equations is derived, with no radial dependence, and with all parameters scaled out. Analytic and numerical solutions of these one-dimensional equations show that an initially sinusoidal perturbation grows into a ''spindle'' or cylindrical ''spike and bubble'' shape, with sharp radial maxima. In the short wavelength limit, the problem is shown to be mathematically equivalent to the planar semi-infinite Rayleigh--Taylor instability, which also grows into a spike-and-bubble shape. Since the spindle shape is common to both limits, it is concluded that it probably obtains in all cases. The results are in agreement with dense plasma focus experiments
International Nuclear Information System (INIS)
R. Paul Drake
2007-01-01
We report the ongoing work of our group in hydrodynamics and radiation hydrodynamics with astrophysical applications. During the period of the existing grant, we have carried out two types of experiments at the Omega laser. One set of experiments has studied radiatively collapsing shocks, obtaining data using a backlit pinhole with a 100 ps backlighter and beginning to develop the ability to look into the shock tube with optical or x-ray diagnostics. Other experiments have studied the deeply nonlinear development of the Rayleigh-Taylor (RT) instability from complex initial conditions, using dual-axis radiographic data with backlit pinholes and ungated detectors to complete the data set for a Ph.D. student. We lead a team that is developing a proposal for experiments at the National Ignition Facility and are involved in experiments at NIKE and LIL. All these experiments have applications to astrophysics, discussed in the corresponding papers. We assemble the targets for the experiments at Michigan, where we also prepare many of the simple components. We also have several projects underway in our laboratory involving our x-ray source. The above activities, in addition to a variety of data analysis and design projects, provide good experience for graduate and undergraduates students. In the process of doing this research we have built a research group that uses such work to train junior scientists
EFFECTS OF DIFFERENT NUMERICAL INTERFACE METHODS ON HYDRODYNAMICS INSTABILITY
Energy Technology Data Exchange (ETDEWEB)
FRANCOIS, MARIANNE M. [Los Alamos National Laboratory; DENDY, EDWARD D. [Los Alamos National Laboratory; LOWRIE, ROBERT B. [Los Alamos National Laboratory; LIVESCU, DANIEL [Los Alamos National Laboratory; STEINKAMP, MICHAEL J. [Los Alamos National Laboratory
2007-01-11
The authors compare the effects of different numerical schemes for the advection and material interface treatments on the single-mode Rayleigh-Taylor instability, using the RAGE hydro-code. The interface growth and its surface density (interfacial area) versus time are investigated. The surface density metric shows to be better suited to characterize the difference in the flow, than the conventional interface growth metric. They have found that Van Leer's limiter combined to no interface treatment leads to the largest surface area. Finally, to quantify the difference between the numerical methods they have estimated the numerical viscosity in the linear-regime at different scales.
Hydrodynamic simulations of microjetting from shock-loaded grooves
Roland, C.; de Rességuier, T.; Sollier, A.; Lescoute, E.; Soulard, L.; Loison, D.
2017-01-01
The interaction of a shock wave with a free surface which has geometrical defects, such as cavities or grooves, may lead to the ejection of micrometric debris at velocities of km/s. This process can be involved in many applications, like pyrotechnics or industrial safety. Recent laser shock experiments reported elsewhere in this conference have provided some insight into jet formation as well as jet tip velocities for various groove angles and shock pressures. Here, we present hydrodynamic simulations of these experiments, in both 2D and 3D geometries, using both finite element method and smoothed particle hydrodynamics. Numerical results are compared to several theoretical predictions including the Richtmyer-Meshkov instabilities. The role of the elastic-plastic behavior on jet formation is illustrated. Finally, the possibility to simulate the late stage of jet expansion and fragmentation is explored, to evaluate the mass distribution of the ejecta and their ballistic properties, still essentially unknown in the experiments.
Indirect drive ablative Rayleigh-Taylor experiments with rugby hohlraums on OMEGA
International Nuclear Information System (INIS)
Casner, A.; Galmiche, D.; Huser, G.; Jadaud, J.-P.; Liberatore, S.; Vandenboomgaerde, M.
2009-01-01
Results of ablative Rayleigh-Taylor instability growth experiments performed in indirect drive on the OMEGA laser facility [T. R. Boehly, D. L. Brown, S. Craxton et al., Opt. Commun. 133, 495 (1997)] are reported. These experiments aim at benchmarking hydrocodes simulations and ablator instabilities growth in conditions relevant to ignition in the framework of the Laser MegaJoule [C. Cavailler, Plasma Phys. Controlled Fusion 47, 389 (2005)]. The modulated samples under study were made of germanium-doped plastic (CHGe), which is the nominal ablator for future ignition experiments. The incident x-ray drive was provided using rugby-shaped hohlraums [M. Vandenboomgaerde, J. Bastian, A. Casner et al., Phys. Rev. Lett. 99, 065004 (2007)] and was characterized by means of absolute time-resolved soft x-ray power measurements through a dedicated diagnostic hole, shock breakout data and one-dimensional and two-dimensional (2D) side-on radiographies. All these independent x-ray drive diagnostics lead to an actual on-foil flux that is about 50% smaller than laser-entrance-hole measurements. The experimentally inferred flux is used to simulate experimental optical depths obtained from face-on radiographies for an extensive set of initial conditions: front-side single-mode (wavelength λ=35, 50, and 70 μm) and two-mode perturbations (wavelength λ=35 and 70 μm, in phase or in opposite phase). Three-dimensional pattern growth is also compared with the 2D case. Finally the case of the feedthrough mechanism is addressed with rear-side modulated foils.
Indirect drive ablative Rayleigh-Taylor experiments with rugby hohlraums on OMEGA
Casner, A.; Galmiche, D.; Huser, G.; Jadaud, J.-P.; Liberatore, S.; Vandenboomgaerde, M.
2009-09-01
Results of ablative Rayleigh-Taylor instability growth experiments performed in indirect drive on the OMEGA laser facility [T. R. Boehly, D. L. Brown, S. Craxton et al., Opt. Commun. 133, 495 (1997)] are reported. These experiments aim at benchmarking hydrocodes simulations and ablator instabilities growth in conditions relevant to ignition in the framework of the Laser MégaJoule [C. Cavailler, Plasma Phys. Controlled Fusion 47, 389 (2005)]. The modulated samples under study were made of germanium-doped plastic (CHGe), which is the nominal ablator for future ignition experiments. The incident x-ray drive was provided using rugby-shaped hohlraums [M. Vandenboomgaerde, J. Bastian, A. Casner et al., Phys. Rev. Lett. 99, 065004 (2007)] and was characterized by means of absolute time-resolved soft x-ray power measurements through a dedicated diagnostic hole, shock breakout data and one-dimensional and two-dimensional (2D) side-on radiographies. All these independent x-ray drive diagnostics lead to an actual on-foil flux that is about 50% smaller than laser-entrance-hole measurements. The experimentally inferred flux is used to simulate experimental optical depths obtained from face-on radiographies for an extensive set of initial conditions: front-side single-mode (wavelength λ =35, 50, and 70 μm) and two-mode perturbations (wavelength λ =35 and 70 μm, in phase or in opposite phase). Three-dimensional pattern growth is also compared with the 2D case. Finally the case of the feedthrough mechanism is addressed with rear-side modulated foils.
Wall ablation of heated compound-materials into non-equilibrium discharge plasmas
Wang, Weizong; Kong, Linghan; Geng, Jinyue; Wei, Fuzhi; Xia, Guangqing
2017-02-01
The discharge properties of the plasma bulk flow near the surface of heated compound-materials strongly affects the kinetic layer parameters modeled and manifested in the Knudsen layer. This paper extends the widely used two-layer kinetic ablation model to the ablation controlled non-equilibrium discharge due to the fact that the local thermodynamic equilibrium (LTE) approximation is often violated as a result of the interaction between the plasma and solid walls. Modifications to the governing set of equations, to account for this effect, are derived and presented by assuming that the temperature of the electrons deviates from that of the heavy particles. The ablation characteristics of one typical material, polytetrafluoroethylene (PTFE) are calculated with this improved model. The internal degrees of freedom as well as the average particle mass and specific heat ratio of the polyatomic vapor, which strongly depends on the temperature, pressure and plasma non-equilibrium degree and plays a crucial role in the accurate determination of the ablation behavior by this model, are also taken into account. Our assessment showed the significance of including such modifications related to the non-equilibrium effect in the study of vaporization of heated compound materials in ablation controlled arcs. Additionally, a two-temperature magneto-hydrodynamic (MHD) model accounting for the thermal non-equilibrium occurring near the wall surface is developed and applied into an ablation-dominated discharge for an electro-thermal chemical launch device. Special attention is paid to the interaction between the non-equilibrium plasma and the solid propellant surface. Both the mass exchange process caused by the wall ablation and plasma species deposition as well as the associated momentum and energy exchange processes are taken into account. A detailed comparison of the results of the non-equilibrium model with those of an equilibrium model is presented. The non-equilibrium results
Theoretical and experimental research on nonlinear hydrodynamic stability and transition is presented. Bifurcations, amplitude equations, pattern in experiments, and shear flows are considered. Particular attention is given to bifurcations of plane viscous fluid flow and transition to turbulence, chaotic traveling wave covection, chaotic behavior of parametrically excited surface waves in square geometry, amplitude analysis of the Swift-Hohenberg equation, traveling wave convection in finite containers, focus instability in axisymmetric Rayleigh-Benard convection, scaling and pattern formation in flowing sand, dynamical behavior of instabilities in spherical gap flows, and nonlinear short-wavelength Taylor vortices. Also discussed are stability of a flow past a two-dimensional grid, inertia wave breakdown in a precessing fluid, flow-induced instabilities in directional solidification, structure and dynamical properties of convection in binary fluid mixtures, and instability competition for convecting superfluid mixtures.
Richtmyer–Meshkov instability of a thermal interface in a two-fluid plasma
Bond, D.
2017-11-03
We computationally investigate the Richtmyer–Meshkov instability of a density interface with a single-mode perturbation in a two-fluid, ion–electron plasma with no initial magnetic field. Self-generated magnetic fields arise subsequently. We study the case where the density jump across the initial interface is due to a thermal discontinuity, and select plasma parameters for which two-fluid plasma effects are expected to be significant in order to elucidate how they alter the instability. The instability is driven via a Riemann problem generated precursor electron shock that impacts the density interface ahead of the ion shock. The resultant charge separation and motion generates electromagnetic fields that cause the electron shock to degenerate and periodically accelerate the electron and ion interfaces, driving Rayleigh–Taylor instability. This generates small-scale structures and substantially increases interfacial growth over the hydrodynamic case.
Basic Hydrodynamics of Richtmyer-Meshkov-type Growth and Oscillations in the ICF-Relevant Conditions
2010-01-01
Washington, DC 20375 3ARTEP Inc ., Ellicott City, Maryland 21042 4Department of Mechanical Engineering, Ben Gurion University, Beer Sheva, Israel...the 56-beam Nike KrF laser facility at the Naval Research Laboratory (3 kJ in 0.248 μm, see Obenschain et al. 1996). Basic hydrodynamics of Richtmyer...2000 Nike (NRL) 0.248 8-13 4 400 40 30, 45 1.85 Si monochrom. Ablative RMI, feedout, classical RMI, impulsive loading, re- shock
SIMULATIONS OF HIGH-VELOCITY CLOUDS. I. HYDRODYNAMICS AND HIGH-VELOCITY HIGH IONS
International Nuclear Information System (INIS)
Kwak, Kyujin; Henley, David B.; Shelton, Robin L.
2011-01-01
We present hydrodynamic simulations of high-velocity clouds (HVCs) traveling through the hot, tenuous medium in the Galactic halo. A suite of models was created using the FLASH hydrodynamics code, sampling various cloud sizes, densities, and velocities. In all cases, the cloud-halo interaction ablates material from the clouds. The ablated material falls behind the clouds where it mixes with the ambient medium to produce intermediate-temperature gas, some of which radiatively cools to less than 10,000 K. Using a non-equilibrium ionization algorithm, we track the ionization levels of carbon, nitrogen, and oxygen in the gas throughout the simulation period. We present observation-related predictions, including the expected H I and high ion (C IV, N V, and O VI) column densities on sightlines through the clouds as functions of evolutionary time and off-center distance. The predicted column densities overlap those observed for Complex C. The observations are best matched by clouds that have interacted with the Galactic environment for tens to hundreds of megayears. Given the large distances across which the clouds would travel during such time, our results are consistent with Complex C having an extragalactic origin. The destruction of HVCs is also of interest; the smallest cloud (initial mass ∼ 120 M sun ) lost most of its mass during the simulation period (60 Myr), while the largest cloud (initial mass ∼ 4 x 10 5 M sun ) remained largely intact, although deformed, during its simulation period (240 Myr).
Richtmyer-Meshkov instability in shock-flame interactions
Massa, Luca; Pallav Jha Collaboration
2011-11-01
Shock-flame interactions occur in supersonic mixing and detonation formation. Therefore, their analysis is important to explosion safety, internal combustion engine performance, and supersonic combustor design. The fundamental process at the basis of the interaction is the Richtmyer-Meshkov instability supported by the density difference between burnt and fresh mixtures. In the present study we analyze the effect of reactivity on the Richtmyer- Meshkov instability with particular emphasis on combustion lengths that typify the scaling between perturbation growth and induction. The results of the present linear analysis study show that reactivity changes the perturbation growth rate by developing a non-zero pressure gradient at the flame surface. The baroclinic torque based on the density gradient across the flame acts to slow down the instability growth for high wave numbers. A non-hydrodynamic flame representation leads to the definition of an additional scaling Peclet number, the effects of which are investigated. It is found that an increased flame-contact separation destabilizes the contact discontinuity by augmenting the tangential shear.
Ignition target and laser-plasma instabilities
International Nuclear Information System (INIS)
Laffite, S.; Loiseau, P.
2010-01-01
For the first time indirect drive ignition targets have been designed with the constraint of limiting laser-plasma instabilities. The amplification of these instabilities is directly proportional to the luminous flux density, it means to the sizes of the focal spots too. This study shows that increasing the sizes of the focal spots does not reduce linear amplification gains in a proportional way because the global optimization of the target implies changes in hydrodynamical conditions that in turn have an impact on the value of the amplification gain. The design of the target is a 2-step approach: the first step aims at assuring a uniform irradiation and compression of the target. The first step requires information concerning the laser focusing spots, the dimensions of the hohlraum, the inert gas contained in it, the materials of the wall. The second step is an optimization approach whose aim is to reduce the risk of laser-plasmas instabilities. This optimization is made through simulations of the amplification gains of stimulated Raman and Brillouin backscattering. This method has allowed us to design an optimized target for a rugby-shaped hohlraum. (A.C.)
Progress toward Kelvin-Helmholtz instabilities in a High-Energy-Density Plasma on the Nike laser
Harding, E. C.; Drake, R. P.; Gillespie, R. S.; Grosskopf, M. J.; Huntington, C. M.; Aglitskiy, Y.; Weaver, J. L.; Velikovich, A. L.; Plewa, T.; Dwarkadas, V. V.
2008-04-01
In the realm of high-energy-density (HED) plasmas, there exist three primary hydrodynamic instabilities of concern: Rayleigh-Taylor (RT), Richtmyer-Meshkov (RM), and Kelvin-Helmholtz (KH). Although the RT and the RM instabilities have been readily observed and diagnosed in the laboratory, the KH instability remains relatively unexplored in HED plasmas. Unlike the RT and RM instabilities, the KH instability is driven by a lifting force generated by a strong velocity gradient in a stratified fluid. Understanding the KH instability mechanism in HED plasmas will provide essential insight into oblique shock systems, jets, mass stripping, and detailed RT-spike development. In addition, our KH experiment will help provide the groundwork for future transition to turbulence experiments. We present 2D FLASH simulations and experimental data from our initial attempts to create a pure KH system using the Nike laser at the Naval Research Laboratory.
International Nuclear Information System (INIS)
Andre, M.; Coutant, J.; Dautray, R.; Decoster, A.; Decroisette, M.; Duborgel, B.; Ouvry, J.; Ovadia, J.; Watteau, J.P.
1990-01-01
The principal objective of the CEL-V laser program is to realize high performances ablative implosions. The indirect drive approach has been chosen to reach the high degree of uniformity required. In relation to this objective, the radiation transfer and the development of hydrodynamics instabilities are widely studied. Besides, efforts have been developed in the field of diagnostics, and of laser technology with optical smoothing and high damage level coatings studies
A technique to remove the tensile instability in weakly compressible SPH
Xu, Xiaoyang; Yu, Peng
2018-01-01
When smoothed particle hydrodynamics (SPH) is directly applied for the numerical simulations of transient viscoelastic free surface flows, a numerical problem called tensile instability arises. In this paper, we develop an optimized particle shifting technique to remove the tensile instability in SPH. The basic equations governing free surface flow of an Oldroyd-B fluid are considered, and approximated by an improved SPH scheme. This includes the implementations of the correction of kernel gradient and the introduction of Rusanov flux into the continuity equation. To verify the effectiveness of the optimized particle shifting technique in removing the tensile instability, the impacting drop, the injection molding of a C-shaped cavity, and the extrudate swell, are conducted. The numerical results obtained are compared with those simulated by other numerical methods. A comparison among different numerical techniques (e.g., the artificial stress) to remove the tensile instability is further performed. All numerical results agree well with the available data.
Abstracts of 4. IAEA technical meeting on the theory of plasma instabilities
International Nuclear Information System (INIS)
2009-05-01
The Fourth IAEA-TM on Theory of Plasma Instabilities provided a forum for open discussion on theoretical and computational physics issues relevant to burning plasma. The meeting covered linear and non-linear theory and simulation of plasma instabilities, including core/edge turbulence, magneto-hydrodynamic (MHD) process, high energy particle driven dynamics and their effects on plasma confinement. Special attention was paid to the multi-scale interaction dynamics in better understanding the burning plasma and also to the modeling of such complex physical processes. The meeting also organized a panel session to discuss the prospect of plasma theory and simulation for future fusion research for the ITER ERA. Young scientists were enthusiastically encouraged to enjoy this session which may stimulate the research for the future. The meeting covered the following topics: (1) Overview: State of the art and importance of multi-scale physics for understanding burning plasmas; (2) Linear and nonlinear instabilities and their theoretical/computational methodologies including critical gradient problem and comparison with experiments; (3) Core/edge turbulent transport including momentum transport, turbulence-profile interaction and barrier formation, etc and their theoretical/ computational understandings; (4) Magneto-hydrodynamic (MHD) instability including energetic particle physics and their impact on confinement in burning plasmas; (5) Physics and modeling of multi-scale interactions and their impact on the plasma performance and control. Those topics were discussed with close relevance to key experimental results. A panel session 'Theoretical Plasma Physics for the ITER ERA' was organized under interdisciplinary aspects with other fields such as astrophysics and fluid dynamics. Each of the abstracts available has been indexed separately
International Nuclear Information System (INIS)
Scott, K.; Huntley, J.M.; Phillips, W.A.
1993-01-01
The luminous plume formed by laser ablation of the high-temperature superconductor YBa 2 Cu 3 O 7-δ has been investigated using high-speed framing photography. Variation of the background oxygen pressure was found to significantly influence the velocity distribution of the ablated species, leading in particular to shock wave formation and instabilities on the shock front at higher pressures. Spectral characteristics of the plume were studied using optical interference filters, and two distinct regions of emission were identified. (orig.)
Hydrodynamic fluctuations from a weakly coupled scalar field
Jackson, G.; Laine, M.
2018-04-01
Studies of non-equilibrium dynamics of first-order cosmological phase transitions may involve a scalar field interacting weakly with the energy-momentum tensor of a thermal plasma. At late times, when the scalar field is approaching equilibrium, it experiences both damping and thermal fluctuations. We show that thermal fluctuations induce a shear viscosity and a gravitational wave production rate, and propose that including this tunable contribution may help in calibrating the measurement of the gravitational wave production rate in hydrodynamic simulations. Furthermore it may enrich their physical scope, permitting in particular for a study of the instability of growing bubbles.
Shvarts, Dov
2017-10-01
Hydrodynamic instabilities, and the mixing that they cause, are of crucial importance in describing many phenomena, from very large scales such as stellar explosions (supernovae) to very small scales, such as inertial confinement fusion (ICF) implosions. Such mixing causes the ejection of stellar core material in supernovae, and impedes attempts at ICF ignition. The Rayleigh-Taylor instability (RTI) occurs at an accelerated interface between two fluids with the lower density accelerating the higher density fluid. The Richtmyer-Meshkov (RM) instability occurs when a shock wave passes an interface between the two fluids of different density. In the RTI, buoyancy causes ``bubbles'' of the light fluid to rise through (penetrate) the denser fluid, while ``spikes'' of the heavy fluid sink through (penetrate) the lighter fluid. With realistic multi-mode initial conditions, in the deep nonlinear regime, the mixing zone width, H, and its internal structure, progress through an inverse cascade of spatial scales, reaching an asymptotic self-similar evolution: hRT =αRT Agt2 for RT and hRM =αRM tθ for RM. While this characteristic behavior has been known for years, the self-similar parameters αRT and θRM and their dependence on dimensionality and density ratio have continued to be intensively studied and a relatively wide distribution of those values have emerged. This talk will describe recent theoretical advances in the description of this turbulent mixing evolution that sheds light on the spread in αRT and θRM. Results of new and specially designed experiments, done by scientists from several laboratories, were performed recently using NIF, the only facility that is powerful enough to reach the self-similar regime, for quantitative testing of this theoretical advance, will be presented.
Accelerated expansion of laser-ablated materials near a solid surface
International Nuclear Information System (INIS)
Chen, K.R.; Leboeuf, J.N.; Wood, R.F.; Geohegan, D.B.; Donato, J.M.; Liu, C.L.; Puretzky, A.A.
1995-01-01
A dynamic source effect that accelerates the expansion of laser-ablated material in the direction perpendicular to the target is demonstrated. A self-similar theory shows that the maximum expansion velocity is proportional to c s /α, where 1-α is the slope of the velocity profile and c s is the sound speed. Numerical hydrodynamic modeling is in good agreement with the theory. A dynamic partial ionization effect is also studied. With these effects, α is reduced and the maximum expansion velocity is significantly increased over that found from conventional models. copyright 1995 The American Physical Society
Energy Technology Data Exchange (ETDEWEB)
Fokin, Vladimir B.; Povarnitsyn, Mikhail E., E-mail: povar@ihed.ras; Levashov, Pavel R.
2017-02-28
Highlights: • We model double-pulse laser ablation of aluminum using microscopic and macroscopic approaches. • Both methods show decrease in depth of crater with increasing delay between pulses. • Both methods reveal the plume temperature growth with the increasing delay. • Good agreement between results is a step towards the development of combined model. - Abstract: We elaborated two numerical methods, two-temperature hydrodynamics and hybrid two-temperature molecular dynamics, which take into account basic mechanisms of a metal target response to ultrashort laser irradiation. The model used for the description of the electronic subsystem is identical for both approaches, while the ionic part is defined by an equation of state in hydrodynamics and by an interatomic potential in molecular dynamics. Since the phase diagram of the equation of state and corresponding potential match reasonably well, the dynamics of laser ablation obtained by both methods is quite similar. This correspondence can be considered as a first step towards the development of a self-consistent combined model. Two important processes are highlighted in simulations of double-pulse ablation: (1) the crater depth decrease as a result of recoil flux formation in the nascent plume when the delay between the pulses increases; (2) the plume reheating by the second pulse that gives rise to two- three-fold growth of the electron temperature with the delay varying from 0 to 200 ps.
Laser ablation of titanium in liquid in external electric field
Energy Technology Data Exchange (ETDEWEB)
Serkov, A.A. [Wave Research Center of A.M. Prokhorov General Physics Institute of the Russian Academy of Sciences, 38, Vavilov Street, 119991 Moscow (Russian Federation); The Federal State Educational Institution of Higher Professional Education, “Moscow Institute of Physics and Technology (State University)”, 9 Institutskiy per., 141700, Dolgoprudny, Moscow Region (Russian Federation); Barmina, E.V., E-mail: barminaev@gmail.com [Wave Research Center of A.M. Prokhorov General Physics Institute of the Russian Academy of Sciences, 38, Vavilov Street, 119991 Moscow (Russian Federation); Shafeev, G.A. [Wave Research Center of A.M. Prokhorov General Physics Institute of the Russian Academy of Sciences, 38, Vavilov Street, 119991 Moscow (Russian Federation); National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), 31, Kashirskoye Highway, 115409 Moscow (Russian Federation); Voronov, V.V. [A.M. Prokhorov General Physics Institute of the Russian Academy of Sciences, 38, Vavilov Street, 119991 Moscow (Russian Federation)
2015-09-01
Highlights: • Ablation of a bulk Ti target by 10 ps laser pulses in liquid is experimentally studied in external DC electric field. • Applied cathodic bias leads to increase in average size of self-organized nanostructures formed upon ablation of titanium target. • Laser ablation of Ti target in external electric field results in generation of elongated titanium oxide nanoparticles. - Abstract: Ablation of a bulk Ti target by 10 ps laser pulses in water is experimentally studied in external DC electric field. It is demonstrated that both lateral size of nanostructures (NS) on Ti surface and their density depend on the electric field applied to the target. Scanning Electron Microscopy of NS reveals the shift of their size distribution function toward larger sizes with applied field (cathodic bias, 25 V DC). Density of mushroom-like NS with applied electric field amounts to 10{sup 10} cm{sup −2}. X-ray diffraction of generated nanoparticles (NPs) shows difference in the crystallographic structure of NPs of non-stoichiometric Ti oxides generated with and without electric field. This conclusion is corroborated with the optical absorption spectroscopy of obtained colloids. Transmission Electron Microscopy of NPs also shows difference in morphology of particles produced with and without cathodic bias. The results are interpreted on the basis of instability of the melt on Ti surface in the electric field.
Development of Richtmyer-Meshkov and Rayleigh-Taylor instability in the presence of magnetic field
International Nuclear Information System (INIS)
Khan, Manoranjan; Mandal, Labakanta; Banerjee, Rahul; Roy, Sourav; Gupta, M.R.
2011-01-01
Fluid instabilities like Rayleigh-Taylor (R-T), Richtmyer-Meshkov (R-M) and Kelvin-Helmholtz (K-H) instability can occur in a wide range of physical phenomenon from astrophysical context to Inertial Confinement Fusion (ICF). Using Layzer's potential flow model, we derive the analytical expressions of growth rate of bubble and spike for ideal magnetized fluid in R-T and R-M cases. In the presence of transverse magnetic field, the R-M and R-T instabilities are suppressed or enhanced depending on the direction of magnetic pressure and hydrodynamic pressure. Again the interface of two fluid may oscillate if both the fluids are conducting. However, it is observed that the magnetic field has no effect in linear case.
Comparison of plastic, high-density carbon, and beryllium as NIF ablators
Kritcher, Andrea
2017-10-01
An effort is underway to compare the three principal ablators for National Ignition Facility (NIF) implosions: plastic (CH), High Density Carbon (HDC), and beryllium (Be). This presentation will summarize the comparison and discuss in more detail the issues pertaining to hohlraum performance and symmetry. Several aspects of the hohlraum design are affected by the ablator properties, as the ablator constrains the first shock and determines the overall pulse length. HDC targets can utilize shorter pulse lengths due to the thinner, higher density shell, and should be less susceptible to late time wall motion. However, HDC requires a larger picket energy to ensure adequate melt, leading to increased late time wall movement. Be is intermediate to CH and HDC in both these regards, and has more ablated material in the hohlraum. These tradeoffs as well as other design choices for currently fielded campaigns are assessed in this work. To assess consistently the radiation drive and symmetry, integrated postshot simulations of the hohlraum and capsule were done for each design using the same methodology. The simulation results are compared to experimental data. Using this post-shot model, we make a projection of the relative plausible performance that can be achieved, while maintaining adequate symmetry, using the full NIF laser, i.e. 1.8 MJ/500 TW Full NIF Equivalent (FNE). The hydrodynamic stability of the different ablators is also an important consideration and will be presented for the current platforms and projection to FNE. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
NONLINEAR EVOLUTION OF GLOBAL HYDRODYNAMIC SHALLOW-WATER INSTABILITY IN THE SOLAR TACHOCLINE
International Nuclear Information System (INIS)
Dikpati, Mausumi
2012-01-01
We present a fully nonlinear hydrodynamic 'shallow-water' model of the solar tachocline. The model consists of a global spherical shell of differentially rotating fluid, which has a deformable top, thus allowing motions in radial directions along with latitudinal and longitudinal directions. When the system is perturbed, in the course of its nonlinear evolution it can generate unstable low-frequency shallow-water shear modes from the differential rotation, high-frequency gravity waves, and their interactions. Radiative and overshoot tachoclines are characterized in this model by high and low effective gravity values, respectively. Building a semi-implicit spectral scheme containing very low numerical diffusion, we perform nonlinear evolution of shallow-water modes. Our first results show that (1) high-latitude jets or polar spin-up occurs due to nonlinear evolution of unstable hydrodynamic shallow-water disturbances and differential rotation, (2) Reynolds stresses in the disturbances together with changing shell thickness and meridional flow are responsible for the evolution of differential rotation, (3) disturbance energy primarily remains concentrated in the lowest longitudinal wavenumbers, (4) an oscillation in energy between perturbed and unperturbed states occurs due to evolution of these modes in a nearly dissipation-free system, and (5) disturbances are geostrophic, but occasional nonadjustment in geostrophic balance can occur, particularly in the case of high effective gravity, leading to generation of gravity waves. We also find that a linearly stable differential rotation profile remains nonlinearly stable.
Energy Technology Data Exchange (ETDEWEB)
Simakov, Andrei N., E-mail: simakov@lanl.gov; Wilson, Douglas C.; Yi, Sunghwan A.; Kline, John L.; Batha, Steven H. [Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, New Mexico 87545 (United States); Clark, Daniel S.; Milovich, Jose L.; Salmonson, Jay D. [Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551 (United States)
2014-02-15
For indirect drive inertial confinement fusion, Beryllium (Be) ablators offer a number of important advantages as compared with other ablator materials, e.g., plastic and high density carbon. In particular, the low opacity and relatively high density of Be lead to higher rocket efficiencies giving a higher fuel implosion velocity for a given X-ray drive; and to higher ablation velocities providing more ablative stabilization and reducing the effect of hydrodynamic instabilities on the implosion performance. Be ablator advantages provide a larger target design optimization space and can significantly improve the National Ignition Facility (NIF) [J. D. Lindl et al., Phys. Plasmas 11, 339 (2004)] ignition margin. Herein, we summarize the Be advantages, briefly review NIF Be target history, and present a modern, optimized, low adiabat, Revision 6 NIF Be target design. This design takes advantage of knowledge gained from recent NIF experiments, including more realistic levels of laser-plasma energy backscatter, degraded hohlraum-capsule coupling, and the presence of cross-beam energy transfer.
International Nuclear Information System (INIS)
Liu, C.L.; LeBoeuf, J.N.; Wood, R.F.; Geohegan, D.B.; Donato, J.M.; Chen, K.R.; Puretzky, A.A.
1994-11-01
Various physical processes during laser ablation of solids for pulsed-laser deposition (PLD) are studied using a variety of computational techniques. In the course of the authors combined theoretical and experimental effort, they have been trying to work on as many aspects of PLD processes as possible, but with special focus on the following areas: (a) the effects of collisional interactions between the particles in the plume and in the background on the evolving flow field and on thin film growth, (b) interactions between the energetic particles and the growing thin films and their effects on film quality, (c) rapid phase transformations through the liquid and vapor phases under possibly nonequilibrium thermodynamic conditions induced by laser-solid interactions, (d) breakdown of the vapor into a plasma in the early stages of ablation through both electronic and photoionization processes, (c) hydrodynamic behavior of the vapor/plasma during and after ablation. The computational techniques used include finite difference (FD) methods, particle-in-cell model, and atomistic simulations using molecular dynamics (MD) techniques
Direct measurement of the image displacement instability in a linear induction accelerator
Burris-Mog, T. J.; Ekdahl, C. A.; Moir, D. C.
2017-06-01
The image displacement instability (IDI) has been measured on the 20 MeV Axis I of the dual axis radiographic hydrodynamic test facility and compared to theory. A 0.23 kA electron beam was accelerated across 64 gaps in a low solenoid focusing field, and the position of the beam centroid was measured to 34.3 meters downstream from the cathode. One beam dynamics code was used to model the IDI from first principles, while another code characterized the effects of the resistive wall instability and the beam break-up (BBU) instability. Although the BBU instability was not found to influence the IDI, it appears that the IDI influences the BBU. Because the BBU theory does not fully account for the dependence on beam position for coupling to cavity transverse magnetic modes, the effect of the IDI is missing from the BBU theory. This becomes of particular concern to users of linear induction accelerators operating in or near low magnetic guide fields tunes.
Conservative ground of qualification BRU-A VVER-1000 in modes of instability of diphasic environment
International Nuclear Information System (INIS)
Skalozubov, V.I.; Klyuchnikov, A.A.; Haj Farajallah Dabbach
2010-01-01
The article first presents grounds and conditions of origin of hydraulic shocks in the VVER system of safety relief valves, caused interchannel heat hydrodynamic instability of biphasic medium. It is supposed conservatively that origin of hydraulic shocks caused instability of biphasic stream determines the unavailability to close of safety relief valves. It is established that the modes of hydraulic shocks in safety relief valves of VVER 1000 (B-320) at the fully opened valves are not typical for the conditions of accidents with intercontour leakages.
Intense harmonic generation from various ablation media
International Nuclear Information System (INIS)
Ozaki, T.; Elouga, L.; Suzuki, M.; Kuroda, H.; Ganeev, R.A.
2006-01-01
lens (f = 680 nm). The high-order harmonics were spectrally resolved using a flat-field grazing-incidence XUV spectrometer with a Hitachi 1200-grooves/mm grating. The XUV spectrum was detected by a microchannel plate with phosphor screen and recorded by a CCD camera. Ablation harmonic experiments were performed with silver and indium targets. We selected silver because of its high conversion efficiency, and indium for its peculiar intensity enhancement effects of the 13 th harmonics. Due to the high intensities of the ablation harmonics, all harmonic spectra were obtained in a single shot. Experiments reveal that the pre-pulse condition for maximum harmonic generation is distinctly different for the two targets. Hydrodynamic simulations using the HYADES code show that the high density of the ablation medium results in strong absorption of the generated harmonics. Therefore, the trade-off between high harmonic efficiency and high absorption is especially important in the present scheme, which can change significantly with the pre-plasma condition. Results with indium targets also reveal a distinct change in the ratio between the 13 th and 15 th harmonic intensity when varying the main pump intensity. This phenomenon is attributed to the change in the resonance conditions of the 13 th harmonic with a strong radiative transition of the In + ion, due to the AC-Stark effect. We will also present new results on ablation harmonics using tin targets.
International Nuclear Information System (INIS)
R Paul Drake
2004-01-01
OAK-B135 This is the final report from the project Hydrodynamics by High-Energy-Density Plasma Flow and Hydrodynamics and Radiation Hydrodynamics with Astrophysical Applications. This project supported a group at the University of Michigan in the invention, design, performance, and analysis of experiments using high-energy-density research facilities. The experiments explored compressible nonlinear hydrodynamics, in particular at decelerating interfaces, and the radiation hydrodynamics of strong shock waves. It has application to supernovae, astrophysical jets, shock-cloud interactions, and radiative shock waves
Pair-instability Supernova Simulations: Progenitor Evolution, Explosion, and Light Curves
Energy Technology Data Exchange (ETDEWEB)
Gilmer, Matthew S.; Fröhlich, Carla [Department of Physics, North Carolina State University, Raleigh, NC 27695 (United States); Kozyreva, Alexandra [The Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978 (Israel); Hirschi, Raphael [Astrophysics group, School of Chemical and Physical Sciences, Keele University, Keele, Staffordshire ST5 5BG (United Kingdom); Yusof, Norhasliza, E-mail: msgilmer@ncsu.edu [Department of Physics, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia)
2017-09-10
In recent years, the viability of the pair-instability supernova (PISN) scenario for explaining superluminous supernovae has all but disappeared except for a few slowly-evolving examples. However, PISNe are not predicted to be superluminous throughout the bulk of their mass range. In fact, it is more likely that the first PISN we see (if we have not seen one already) will not be superluminous. Here, we present hydrodynamic simulations of PISNe for four stellar models with unique envelope properties spanning the PISN mass range. In addition, we compute synthetic light curves (LCs) for comparison with current and future observations. We also investigate, in the context of our most massive model, the prospect of mixing in the supernova ejecta, alleviating discrepancies between current PISN models and the remaining superluminous candidate events. To this end, we present the first published 3D hydrodynamic simulations of PISNe. After achieving convergence between 1D, 2D, and 3D simulations, we examine mixing in the supernova ejecta and its affect on the bolometric LC. We observe slight deviations from spherical symmetry, which increase with the number of dimensions. We find no significant effects on the bolometric LC; however, we conclude that mixing between the silicon and oxygen rich layers caused by the Rayleigh–Taylor instability may affect spectra.
Investigation of the Rayleigh-Taylor and Richtmyer-Meshkov instabilities
International Nuclear Information System (INIS)
Riccardo Bonazza
2006-01-01
The present research program is centered on the experimental and numerical study of two instabilities that develop at the interface between two different fluids when the interface experiences an impulsive or a constant acceleration. The instabilities, called the Richtmyer-Meshkov and Rayleigh-Taylor instability, respectively (RMI and RTI), adversely affect target implosion in experiments aimed at the achievement of nuclear fusion by inertial confinement by causing the nuclear fuel contained in a target and the ablated shell material to mix, leading to contamination of the fuel, yield reduction or no ignition at all. Specifically, our work is articulated in three main directions: study of impulsively accelerated spherical gas inhomogeneities; study of impulsively accelerated 2-D interfaces; study of a liquid interface under the action of gravity. The objectives common to all three activities are to learn some physics directly from our experiments and calculations; and to develop a database at previously untested conditions to be used to calibrate and verify some of the computational tools being developed within the RTI/RMI community at the national laboratories and the ASCI centers
Linear simulations of the cylindrical Richtmyer-Meshkov instability in magnetohydrodynamics
Bakhsh, Abeer
2016-03-09
Numerical simulations and analysis indicate that the Richtmyer-Meshkov instability(RMI) is suppressed in ideal magnetohydrodynamics(MHD) in Cartesian slab geometry. Motivated by the presence of hydrodynamic instabilities in inertial confinement fusion and suppression by means of a magnetic field, we investigate the RMI via linear MHD simulations in cylindrical geometry. The physical setup is that of a Chisnell-type converging shock interacting with a density interface with either axial or azimuthal (2D) perturbations. The linear stability is examined in the context of an initial value problem (with a time-varying base state) wherein the linearized ideal MHD equations are solved with an upwind numerical method. Linear simulations in the absence of a magnetic field indicate that RMI growth rate during the early time period is similar to that observed in Cartesian geometry. However, this RMI phase is short-lived and followed by a Rayleigh-Taylor instability phase with an accompanied exponential increase in the perturbation amplitude. We examine several strengths of the magnetic field (characterized by β=2p/B^2_r) and observe a significant suppression of the instability for β ≤ 4. The suppression of the instability is attributed to the transport of vorticity away from the interface by Alfvén fronts.
Effects of thin high-Z layers on the hydrodynamics of laser-accelerated plastic targets
International Nuclear Information System (INIS)
Obenschain, S.P.; Colombant, D.G.; Karasik, M.; Pawley, C.J.; Serlin, V.; Schmitt, A.J.; Weaver, J.L.; Gardner, J.H.; Phillips, L.; Aglitskiy, Y.; Chan, Y.; Dahlburg, J.P.; Klapisch, M.
2002-01-01
Experimental results and simulations that study the effects of thin metallic layers with high atomic number (high-Z) on the hydrodynamics of laser accelerated plastic targets are presented. These experiments employ a laser pulse with a low-intensity foot that rises into a high-intensity main pulse. This pulse shape simulates the generic shape needed for high-gain fusion implosions. Imprint of laser nonuniformity during start up of the low intensity foot is a well-known seed for hydrodynamic instability. Large reductions are observed in hydrodynamic instability seeded by laser imprint when certain minimum thickness gold or palladium layers are applied to the laser-illuminated surface of the targets. The experiment indicates that the reduction in imprint is at least as large as that obtained by a 6 times improvement in the laser uniformity. Simulations supported by experiments are presented showing that during the low intensity foot the laser light can be nearly completely absorbed by the high-Z layer. X rays originating from the high-Z layer heat the underlying lower-Z plastic target material and cause large buffering plasma to form between the layer and the accelerated target. This long-scale plasma apparently isolates the target from laser nonuniformity and accounts for the observed large reduction in laser imprint. With onset of the higher intensity main pulse, the high-Z layer expands and the laser light is transmitted. This technique will be useful in reducing laser imprint in pellet implosions and thereby allow the design of more robust targets for high-gain laser fusion
Instabilities and chaos in a kinetic equation for active nematics
International Nuclear Information System (INIS)
Shi, Xia-qing; Ma, Yu-qiang; Chaté, Hugues
2014-01-01
We study dry active nematics at the kinetic equation level, stressing the differences with the well-known Doi theory for non-active rods near thermal equilibrium. By deriving hydrodynamic equations from the kinetic equation, we show analytically that these two description levels share the same qualitative phase diagram, as defined by the linear instability limits of spatially-homogeneous solutions. In particular, we show that the ordered, homogeneous state is unstable in a region bordering the linear onset of nematic order, and is only linearly stable deeper in the ordered phase. Direct simulations of the kinetic equation reveal that its solutions are chaotic in the region of linear instability of the ordered homogeneous state. The local mechanisms for this large-scale chaos are discussed. (paper)
Effects of thermal conduction and compressibility on Rayleigh-Taylor instability
International Nuclear Information System (INIS)
Takabe, Hideaki; Mima, Kunioki.
1980-01-01
In order to study the stability of the ablation front in laser driven implosion, the thermal conduction and compressibility effects on the Rayleigh-Taylor instability are considered. It is found that the thermal conduction effect cannot stabilize the Rayleigh-Taylor mode, but reduce the growth rate in the short wavelength case. But, the growth rate is found not to differ from the classical value √gk in the long wavelength limit, where the compressibility is essential. (author)
Lesion size in relation to ablation site during radiofrequency ablation
DEFF Research Database (Denmark)
Petersen, H H; Chen, X; Pietersen, A
1998-01-01
This study was designed to investigate the effect of the convective cooling of the tip of the ablation electrode during temperature controlled radiofrequency ablation. In vivo two different application sites in the left ventricle of anaesthetised pigs were ablated and in vitro ablation was perfor......This study was designed to investigate the effect of the convective cooling of the tip of the ablation electrode during temperature controlled radiofrequency ablation. In vivo two different application sites in the left ventricle of anaesthetised pigs were ablated and in vitro ablation...... was performed during two different flow-velocities in a tissue bath, while electrode contact pressure and position were unchanged. Target temperature was 80 degrees C. Obtained tip temperature, power consumption and lesion dimensions were measured. In vivo lesion volume, depth and width were found significantly.......61 in vitro). We conclude that during temperature controlled radiofrequency ablation lesion size differs for septal and apical left ventricular applications. Differences in convective cooling might play an important role in this respect. This is supported by our in vitro experiments, where increased...
Star formation, using 3-D explicit Eulerian hydrodynamics
International Nuclear Information System (INIS)
Williams, H.A.
1988-01-01
Evolutions of rapidly rotating, self-gravitating objects initially in axisymmetric equilibrium have been studied using a 3-D Newtonian hydrodynamic computer code with an eye toward understanding angular momentum transport in dynamically evolving protostars. First, a number of evolutions have been modeled using an existing explicit, Eulerian, finite difference code that is accurate to first-order in its spatial differences. The bar-mode dynamic instability has been explored by considering several models with different degrees of compressibility. This instability occurs in models with different degrees of comprresibility. This instability occurs in models having β > β d ≡ 0.27, where β is the ratio of the rotational to the gravitational potential energy. A two-armed spiral, with a well-defined pattern speed and growth rate that match the pattern speed and growth rate predicted by linear theory, develops from each of the axisymmetric equilibria. The models with greater compressibility exhibit spirals which are more tightly wound. As the nonaxisymmetric distortion become large in an extended evolution, the object does not undergo binary fission as had been thought earlier. Instead, the spiral elongates and then wraps up on itself, forming a central pulsating triaxial object surrounded by a more diffuse ring-like disk. Angular momentum and mass are dynamically redistributed by gravitational torques during the evolution, and β is reduced below β d . Since this gravitational-rotational dynamic instability is a general feature of gaseous systems, this study may have application to theta galaxies and to rapidly rotating neutron stars, as well as to protostars
Directory of Open Access Journals (Sweden)
Kelly Ratheal
2016-01-01
Full Text Available Cardiac ablation is a procedure that uses either radiofrequency or cryothermal energy to destroy cells in the heart to terminate and/or prevent arrhythmias. The indications for cardiac catheter ablation include refractory, symptomatic arrhythmias, with more specific guidelines for atrial fibrillation in particular. The ablation procedure itself involves mapping the arrhythmia and destruction of the aberrant pathway in an effort to permanently prevent the arrhythmia. There are many types of arrhythmias, and they require individualized approaches to ablation based on their innately different electrical pathways. Ablation of arrhythmias, such as Wolff-Parkinson-White syndrome, AV nodal reentrant tachycardia, and atrial-fibrillation, is discussed in this review. Ablation has a high success rate overall and minimal complication rates, leading to improved quality of life in many patients.
Wienkers, A. F.; Ogilvie, G. I.
2018-04-01
Non-linear evolution of the parametric instability of inertial waves inherent to eccentric discs is studied by way of a new local numerical model. Mode coupling of tidal deformation with the disc eccentricity is known to produce exponentially growing eccentricities at certain mean-motion resonances. However, the details of an efficient saturation mechanism balancing this growth still are not fully understood. This paper develops a local numerical model for an eccentric quasi-axisymmetric shearing box which generalises the often-used cartesian shearing box model. The numerical method is an overall second order well-balanced finite volume method which maintains the stratified and oscillatory steady-state solution by construction. This implementation is employed to study the non-linear outcome of the parametric instability in eccentric discs with vertical structure. Stratification is found to constrain the perturbation energy near the mid-plane and localise the effective region of inertial wave breaking that sources turbulence. A saturated marginally sonic turbulent state results from the non-linear breaking of inertial waves and is subsequently unstable to large-scale axisymmetric zonal flow structures. This resulting limit-cycle behaviour reduces access to the eccentric energy source and prevents substantial transport of angular momentum radially through the disc. Still, the saturation of this parametric instability of inertial waves is shown to damp eccentricity on a time-scale of a thousand orbital periods. It may thus be a promising mechanism for intermittently regaining balance with the exponential growth of eccentricity from the eccentric Lindblad resonances and may also help explain the occurrence of "bursty" dynamics such as the superhump phenomenon.
Laser plasma instability experiments with KrF lasers
International Nuclear Information System (INIS)
Weaver, J. L.; Karasik, M.; Serlin, V.; Obenschain, S.; Chan, L-Y.; Kehne, D.; Schmitt, A. J.; Colombant, D.; Velikovich, A.; Oh, J.; Lehmberg, R. H.; Afeyan, B.; Phillips, L.; Seely, J.; Brown, C.; Feldman, U.; Aglitskiy, Y.; Mostovych, A. N.; Holland, G.
2007-01-01
Deleterious effects of laser-plasma instability (LPI) may limit the maximum laser irradiation that can be used for inertial confinement fusion. The short wavelength (248 nm), large bandwidth, and very uniform illumination available with krypton-fluoride (KrF) lasers should increase the maximum usable intensity by suppressing LPI. The concomitant increase in ablation pressure would allow implosion of low-aspect-ratio pellets to ignition with substantial gain (>20) at much reduced laser energy. The proposed KrF-laser-based Fusion Test Facility (FTF) would exploit this strategy to achieve significant fusion power (150 MW) with a rep-rate system that has a per pulse laser energy well below 1 MJ. Measurements of LPI using the Nike KrF laser are presented at and above intensities needed for the FTF (I∼2x10 15 W/cm 2 ). The results to date indicate that LPI is indeed suppressed. With overlapped beam intensity above the planar, single beam intensity threshold for the two-plasmon decay instability, no evidence of instability was observed via measurements of (3/2)ω o and (1/2)ω o harmonic emissions
Predictions of the microstructural contribution to instability seeding in beryllium ICF capsules
International Nuclear Information System (INIS)
Hoffman, Nelson M.; Swift, Damian C.
2004-01-01
The constitutive properties of beryllium are anisotropic. During the implosion of an inertial confinement fusion capsule, it is possible for instabilities to be seeded from the microstructure. We are using experiment and theory to place constraints on the microstructure and loading history. The relation between surface roughness and amplitude of ablative Rayleigh-Taylor instabilities has been characterized well. Here we present a method of relating the microstructure to an equivalent surface roughness, using continuum mechanical simulations of shock waves in polycrystalline beryllium. Beryllium was treated using a single-crystal plasticity model developed using ab initio quantum mechanics for the equation of state and elasticity, and laser-driven shock wave measurements to calibrate representations of dislocation and disclination dynamics
From the advective-acoustic instability to the asymmetric explosions of Core Collapse Supernovae
International Nuclear Information System (INIS)
Galletti, Pascal
2005-01-01
The advective-acoustic cycle is a hydrodynamical mechanism fed by the coupling between advected waves (entropy, vorticity) and an acoustic feedback. Already studied in physics (rumble instability in ramjet, whistling tea kettle), it was introduced in astrophysics in the frame of the instability of the Bondi-Hoyle-Lyttleton accretion flow. In this thesis, we propose this cycle as an explanation for the asymmetry of the explosion of Core Collapse Supernovae. The evaluation of Eigenmodes for the classical accretion above a solid surface (white dwarfs, neutron stars) and the use of a toy-model reveal the importance of the advective-acoustic cycle in such an instable accretion flow. Following these results and the comparison with numerical simulations, a modelization of the flow when the shock stalls during a Core Collapse Supernova, shows that the advective-acoustic cycle is a natural mechanism to explain the non-spherical instability of the shock. The domination of l = 1 modes may be responsible for the observed pulsar kicks. (author) [fr
International Nuclear Information System (INIS)
Chen, K.R.; King, T.C.; Hes, J.H.; Leboeuf, J.N.; Geohegan, D.B.; Wood, R.F.; Puretzky, A.A.; Donato, J.M.
1999-01-01
A self-similar theory and numerical hydrodynamic modeling is developed to investigate the effects of dynamic source and partial ionization on the acceleration of the unsteady expansion of laser-ablated material near a solid target surface. The dynamic source effect accelerates the expansion in the direction perpendicular to the target surface, while the dynamic partial ionization effect accelerates the expansion in all directions. The vaporized material during laser ablation provides a nonadiabatic dynamic source at the target surface into the unsteady expanding fluid. For studying the dynamic source effect, the self-similar theory begins with an assumed profile of plume velocity, u=v/v m =α+(1-α)ξ, where v m is the maximum expansion velocity, α is a constant, and ξ=x/v m t. The resultant profiles of plume density and plume temperature are derived. The relations obtained from the conservations of mass, momentum, and energy, respectively, all show that the maximum expansion velocity is inversely proportional to α, where 1-α is the slope of plume velocity profile. The numerical hydrodynamic simulation is performed with the Rusanov method and the Newton Raphson method. The profiles and scalings obtained from numerical hydrodynamic modeling are in good agreement with the theory. The dynamic partial ionization requires ionization energy from the heat at the expansion front, and thus reduces the increase of front temperature. The reduction of thermal motion would increase the flow velocity to conserve the momentum. This dynamic partial ionization effect is studied with the numerical hydrodynamic simulation including the Saha equation. With these effects, α is reduced from its value of conventional free expansion. This reduction on α increases the flow velocity slope, decreases the flow velocity near the surface, and reduces the thermal motion of plume, such that the maximum expansion velocity is significantly increased over that found from conventional models
Directory of Open Access Journals (Sweden)
Lei Zhang
Full Text Available The aim of this study was to investigate the therapeutic efficacy of percutaneous radiofrequency (RF ablation versus microwave (MW ablation for hepatocellular carcinoma (HCC measuring ≤ 5 cm in greatest diameter. From January 2006 to December 2006, 78 patients had undergone RF ablation whereas 77 had undergone MW ablation. Complete ablation (CA, local tumour progression (LTP and distant recurrence (DR were compared. The overall survival curves were calculated with the Kaplan-Meier technique and compared with the log-rank test. The CA rate was 83.4% (78/93 for RF ablation and 86.7%(91/105 for MW ablation. The LTP rate was 11.8% (11/93 for RF ablation and 10.5% (11/105 for MW ablation. DR was found in 51 (65.4% in the RF ablation and 62 (80.5% in the MW ablation. There was no significant difference in the 1-, 3-, and 5-year overall survival rates (P = 0.780 and the 1-, 3-, and 5-year disease-free survival rates (P = 0.123 between RF and MW ablation. At subgroup analyses, for patients with tumors ≤ 3.0 cm, there was no significant difference in the 1-, 3-, and 5-year overall survival rates (P = 0.067 and the corresponding disease-free survival rates(P = 0.849. For patients with tumor diameters of 3.1-5.0 cm, the 1-, 3-, and 5-year overall survival rates were 87.1%, 61.3%, and 40.1% for RF ablation and 85.4%, 36.6%, and 22% for MW ablation, with no significant difference (P = 0.068. The corresponding disease-free survival rates were 74.2%, 54.8%, and 45.2% for the RF ablation group and 53.3%, 26.8%, and 17.1% for the MW ablation group. The disease-free survival curve for the RF ablation group was significantly better than that for the MW ablation group (P = 0.018. RF ablation and MW ablation are both effective methods in treating hepatocellular carcinomas, with no significant differences in CA, LTP, DR, and overall survival.
International Nuclear Information System (INIS)
Sharma, P.K.; Tiwari, Anita; Argal, Shraddha; Chhajlani, R.K.
2013-01-01
This paper is devoted to an investigation of Quantum effects and magnetic field effects on the Rayleigh Taylor instability of two superposed incompressible fluids in bounded porous medium. The Quantum magneto hydrodynamic equations are solved by using normal mode method and a dispersion relation is obtained. The dispersion relation is derived for the case where plasma is bounded by two rigid planes z = 0 and z = h. The Rayleigh Taylor instability growth rate and stability condition of the medium is discussed in the presence of quantum effect, magnetic field, porosity and permeability. It is found that the magnetic field and medium porosity have stabilizing influence while permeability has destabilizing influence on the Rayleigh Taylor instability. (author)
Bifurcation theory for toroidal MHD instabilities
International Nuclear Information System (INIS)
Maschke, E.K.; Morros Tosas, J.; Urquijo, G.
1992-01-01
Using a general representation of magneto-hydrodynamics in terms of stream functions and potentials, proposed earlier, a set of reduced MHD equations for the case of toroidal geometry had been derived by an appropriate ordering with respect to the inverse aspect ratio. When all dissipative terms are neglected in this reduced system, it has the same linear stability limits as the full ideal MHD equations, to the order considered. When including resistivity, thermal conductivity and viscosity, we can apply bifurcation theory to investigate nonlinear stationary solution branches related to various instabilities. In particular, we show that a stationary solution of the internal kink type can be found
International Nuclear Information System (INIS)
Willi, O.; Pasley, J.; Iwase, A.; Nazarov, W.; Rose, S.J.
2000-01-01
The Rayleigh-Taylor instability was studied in the short wavelength regime using single mode targets that were driven by hohlraum radiation allowing the Takabe-Morse roll-over due to ablative stabilisation to be investigated. A temporally shaped soft x-ray drive was generated by focusing one of the PHEBUS laser beams into a gold hohlraum with a maximum radiation temperature of about 120 eV. Thin plastic foils with sinusoidal modulations with wavelengths between 12 and 50 μm, and a perturbation amplitude of about 10% of the wavelength, were used. A low density 50 mg/cc tri-acrylate foam 150 μm in length facing the hohlraum was attached to the modulated foam target. The targets were radiographed face-on at an x-ray energy of about 1.3 keV with a spatial resolution of about 5 μm using a Wolter-like x-ray microscope coupled to an x-ray streak camera with a temporal resolution of 50 ps. The acceleration was obtained from side-on radiography. 2-D hydrodynamic code simulations have been carried out to compare the experimental results with the simulations. (authors)
Irradiation instability at the inner edges of accretion disks
Energy Technology Data Exchange (ETDEWEB)
Fung, Jeffrey; Artymowicz, Pawel, E-mail: fung@astro.utoronto.ca [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada)
2014-07-20
An instability can potentially operate in highly irradiated disks where the disk sharply transitions from being radially transparent to opaque (the 'transition region'). Such conditions may exist at the inner edges of transitional disks around T Tauri stars and accretion disks around active galactic nuclei. We derive the criterion for this instability, which we term the 'irradiation instability', or IRI. We also present the linear growth rate as a function of β, the ratio between radiation force and gravity, and c{sub s}, the sound speed of the disk, obtained using two methods: a semi-analytic analysis of the linearized equations and a numerical simulation using the GPU-accelerated hydrodynamical code PEnGUIn. In particular, we find that IRI occurs at β ∼ 0.1 if the transition region extends as wide as ∼0.05r, and at higher β values if it is wider. This threshold value applies to c{sub s} ranging from 3% of the Keplerian orbital speed to 5%, and becomes higher if c{sub s} is lower. Furthermore, in the nonlinear evolution of the instability, disks with a large β and small c{sub s} exhibit 'clumping', extreme local surface density enhancements that can reach over 10 times the initial disk surface density.
Radiofrequency thermal ablation of malignant hepatic tumors: post-ablation syndrome
International Nuclear Information System (INIS)
Choi, Jung Bin; Rhim, Hyunchul; Kim, Yongsoo; Koh, Byung Hee; Cho, On Koo; Seo, Heung Suk; Lee, Seung Ro
2000-01-01
To evaluate post-ablation syndrome after radiofrequency thermal ablation of malignant hepatic tumors. Forty-two patients with primary (n=3D29) or secondary (n=3D13) hepatic tumors underwent radiofrequency thermal ablation. A total of 65 nodules ranging in size from 1.1 to 5.0 (mean, 3.1) cm were treated percutaneously using a 50W RF generator with 15G expandable needle electrodes. We retrospectively evaluated the spectrum of post-ablation syndrome including pain, fever (≥3D 38 deg C), nausea, vomiting, right shoulder pain, and chest discomfort according to frequency, intensity and duration, and the findings were correlated with tumor location and number of ablations. We also evaluated changes in pre-/post-ablation serum aminotransferase (ALT/AST) and prothrombin time, and correlated these findings with the number of ablations. Post-ablation syndrome was noted in 29 of 42 patients (69.0%), and most symptoms improved with conservative treatment. The most important of these were abdominal plan (n=3D20, 47.6%), fever (n=3D8, 19.0%), and nausea (n=3D7, 16.7%), and four of 42 (9.5%) patients complained of severe pain. The abdominal pain lasted from 3 hours to 5.5 days (mean; 20.4 hours), the fever from 6 hours to 5 days (mean; 63.0 hours). And the nausea from 1 hours to 4 days (mean; 21.0 hours). Other symptoms were right shoulder pain (n=3D6, 14.3%), chest discomfort (n=3D3, 7.1%), and headache (n=3D3, 7.1%). Seventeen of 20 patients (85%) with abdominal pain had subcapsular tumor of the liver. There was significant correlation between pain, location of the tumor, and a number of ablations. After ablation, ALT/AST was elevated more than two-fold in 52.6%/73.7% of patients, respectively but there was no significant correlation with the number of ablation. Post-ablation syndrome is a frequent and tolerable post-procedural process after radiofrequency thermal ablation. The spectrum of this syndrome provides a useful guideline for the post-ablation management. (author)
Direct measurement of the image displacement instability in a linear induction accelerator
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T. J. Burris-Mog
2017-06-01
Full Text Available The image displacement instability (IDI has been measured on the 20 MeV Axis I of the dual axis radiographic hydrodynamic test facility and compared to theory. A 0.23 kA electron beam was accelerated across 64 gaps in a low solenoid focusing field, and the position of the beam centroid was measured to 34.3 meters downstream from the cathode. One beam dynamics code was used to model the IDI from first principles, while another code characterized the effects of the resistive wall instability and the beam break-up (BBU instability. Although the BBU instability was not found to influence the IDI, it appears that the IDI influences the BBU. Because the BBU theory does not fully account for the dependence on beam position for coupling to cavity transverse magnetic modes, the effect of the IDI is missing from the BBU theory. This becomes of particular concern to users of linear induction accelerators operating in or near low magnetic guide fields tunes.
International Nuclear Information System (INIS)
Vandenboomgaerde, M; Liberatore, S; Galmiche, D; Casner, A; Huser, G; Jadaud, J P; Villette, B
2008-01-01
Implosion of inertial confinement fusion (ICF) capsule is very sensitive to the growth of sphericity perturbations. The control of the feeding of such perturbations and their transport ('feedthrough') through the ablator is a key point to reach ignition. Since 2002, experiments have been designed and performed on the Omega laser facility in order to study these phenomena in planar geometry. A new 'rugby shaped' hohlraum was used. We present experimental results and comparisons with numerical simulations
Two-component Superfluid Hydrodynamics of Neutron Star Cores
Energy Technology Data Exchange (ETDEWEB)
Kobyakov, D. N. [Institute of Applied Physics of the Russian Academy of Sciences, 603950 Nizhny Novgorod (Russian Federation); Pethick, C. J., E-mail: dmitry.kobyakov@appl.sci-nnov.ru, E-mail: pethick@nbi.dk [The Niels Bohr International Academy, The Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, DK-2100 Copenhagen Ø (Denmark)
2017-02-20
We consider the hydrodynamics of the outer core of a neutron star under conditions when both neutrons and protons are superfluid. Starting from the equation of motion for the phases of the wave functions of the condensates of neutron pairs and proton pairs, we derive the generalization of the Euler equation for a one-component fluid. These equations are supplemented by the conditions for conservation of neutron number and proton number. Of particular interest is the effect of entrainment, the fact that the current of one nucleon species depends on the momenta per nucleon of both condensates. We find that the nonlinear terms in the Euler-like equation contain contributions that have not always been taken into account in previous applications of superfluid hydrodynamics. We apply the formalism to determine the frequency of oscillations about a state with stationary condensates and states with a spatially uniform counterflow of neutrons and protons. The velocities of the coupled sound-like modes of neutrons and protons are calculated from properties of uniform neutron star matter evaluated on the basis of chiral effective field theory. We also derive the condition for the two-stream instability to occur.
Supernova Hydrodynamics on the Omega Laser. Final report
International Nuclear Information System (INIS)
Drake, R. Paul
2004-01-01
(B204)The fundamental motivation for our work is that supernovae are not well understood. Recent observations have clarified the depth of our ignorance, by producing observed phenomena that current theory and computer simulations cannot reproduce. Such theories and simulations involve, however, a number of physical mechanisms that have never been studied in isolation. We perform experiments, in compressible hydrodynamics and radiation hydrodynamics, relevant to supernovae and supernova remnants. These experiments produce phenomena in the laboratory that are believed, based on simulations, to be important to astrophysics but that have not been directly observed in either the laboratory or in an astrophysical system. During the period of this grant, we have focused on the scaling of an astrophysically relevant, radiative-precursor shock, on preliminary studies of collapsing radiative shocks, and on the multimode behavior and the three-dimensional, deeply nonlinear evolution of the Rayleigh-Taylor (RT) instability at a decelerating, embedded interface. These experiments required strong compression and decompression, strong shocks (Mach ∼10 or greater), flexible geometries, and very smooth laser beams, which means that the 60-beam Omega laser is the only facility capable of carrying out this program
Theory of the corrugation instability of a piston-driven shock wave.
Bates, J W
2015-01-01
We analyze the two-dimensional stability of a shock wave driven by a steadily moving corrugated piston in an inviscid fluid with an arbitrary equation of state. For h≤-1 or h>h(c), where h is the D'yakov parameter and h(c) is the Kontorovich limit, we find that small perturbations on the shock front are unstable and grow--at first quadratically and later linearly--with time. Such instabilities are associated with nonequilibrium fluid states and imply a nonunique solution to the hydrodynamic equations. The above criteria are consistent with instability limits observed in shock-tube experiments involving ionizing and dissociating gases and may have important implications for driven shocks in laser-fusion, astrophysical, and/or detonation studies.
Hydrodynamic simulations of light ion beam-matter interactions: ablative acceleration of thin foils
International Nuclear Information System (INIS)
Devore, C.R.; Gardner, J.H.; Boris, J.P.; Mosher, D.
1984-01-01
A one-dimensional model is used to study the hydrodynamic response of thin foils to bombardment by an intense proton beam. The beam targets are single- and multilayer planar foils of gold and polystyrene. The main conclusion is that the efficiency of conversion of incident beam energy to directed kinetic energy of the target is maximized by using a multilayer design. For beam parameters associated with the Gamble II device at the Naval Research Laboratory, the simulations yield payload velocities of over 5 cm/μs and energy conversion efficiencies of over 30%. The implications of these results for inertial confinement fusion research are discussed. (author)
Energy Technology Data Exchange (ETDEWEB)
Vandenboomgaerde, M; Liberatore, S; Galmiche, D; Casner, A; Huser, G; Jadaud, J P; Villette, B [Commissariat a l' Energie Atomique, CEA/DAM-Ile de France, BP 12, 91680 Bruyeres-Le-Chatel (France)
2008-05-15
Implosion of inertial confinement fusion (ICF) capsule is very sensitive to the growth of sphericity perturbations. The control of the feeding of such perturbations and their transport ('feedthrough') through the ablator is a key point to reach ignition. Since 2002, experiments have been designed and performed on the Omega laser facility in order to study these phenomena in planar geometry. A new 'rugby shaped' hohlraum was used. We present experimental results and comparisons with numerical simulations.
Effects on Implosion Characteristics of High-Z Dopant Profiles in ICF Ignition Capsule Ablators
Li, Yongsheng; Wang, Min; Gu, Jianfa; Zou, Shiyang; Kang, Dongguo; Ye, Wenhua; Zhang, Weiyan
2012-10-01
For ignition target design (ITD) of indirect drive ICF [J. Lindl, PoP 2, 3933(1995)], high-Z dopants in capsule ablators were used to prevent preheat of DTadjacentablators by Au M-band flux in laser-driven gold Hohlraums, therefore to restrain the growth of high-mode hydro-instabilities and to improve the targetrobustness.Based on NIC's Rev. 5 ITD[S. W. Haan et al., PoP 18, 051001(2011)], we investigated the effect of thickness and dopant concentration of doped layers on implosion characteristics, including the Atwood number (AWN) of fuel-ablator interface, the density gradient scale length (DGSL) of ablation front and the implosion velocity (VIM); all three variables decrease with increment of dopant dosage, and increase with dopant concentration while keeping dosage constant. Since a smaller AWN, a larger DGSL, and a faster VIM always characterize a more robust ITD, one should make tradeoff among them by adjusting the dopant profiles in ablators.A Gaussian spectrum (GS) was used to imitate the Au M-band flux [Y. S. Li et al., PoP 18, 022701(2011)], and the impact of GScenter on implosion characteristics of Rev. 5 ITD was studied while moving the GScenter towards higher energy, the ablatorpreheat got severe, AWN got larger, DGSL got larger, and VIM got faster.
Narayanan, Kiran; Samtaney, Ravi
2018-04-01
We obtain numerical solutions of the two-fluid fluctuating compressible Navier-Stokes (FCNS) equations, which consistently account for thermal fluctuations from meso- to macroscales, in order to study the effect of such fluctuations on the mixing behavior in the Richtmyer-Meshkov instability (RMI). The numerical method used was successfully verified in two stages: for the deterministic fluxes by comparison against air-SF6 RMI experiment, and for the stochastic terms by comparison against the direct simulation Monte Carlo results for He-Ar RMI. We present results from fluctuating hydrodynamic RMI simulations for three He-Ar systems having length scales with decreasing order of magnitude that span from macroscopic to mesoscopic, with different levels of thermal fluctuations characterized by a nondimensional Boltzmann number (Bo). For a multidimensional FCNS system on a regular Cartesian grid, when using a discretization of a space-time stochastic flux Z (x ,t ) of the form Z (x ,t ) →1 /√{h ▵ t }N (i h ,n Δ t ) for spatial interval h , time interval Δ t , h , and Gaussian noise N should be greater than h0, with h0 corresponding to a cell volume that contains a sufficient number of molecules of the fluid such that the fluctuations are physically meaningful and produce the right equilibrium spectrum. For the mesoscale RMI systems simulated, it was desirable to use a cell size smaller than this limit in order to resolve the viscous shock. This was achieved by using a modified regularization of the noise term via Z (h3,h03)>x ,t →1 /√ ▵ t max(i h ,n Δ t ) , with h0=ξ h ∀h mixing behavior emerges as the ensemble-averaged behavior of several fluctuating instances, whereas when Bo≈1 , a deviation from deterministic behavior is observed. For all cases, the FCNS solution provides bounds on the growth rate of the amplitude of the mixing layer.
Narayanan, Kiran
2018-04-19
We obtain numerical solutions of the two-fluid fluctuating compressible Navier-Stokes (FCNS) equations, which consistently account for thermal fluctuations from meso- to macroscales, in order to study the effect of such fluctuations on the mixing behavior in the Richtmyer-Meshkov instability (RMI). The numerical method used was successfully verified in two stages: for the deterministic fluxes by comparison against air-SF6 RMI experiment, and for the stochastic terms by comparison against the direct simulation Monte Carlo results for He-Ar RMI. We present results from fluctuating hydrodynamic RMI simulations for three He-Ar systems having length scales with decreasing order of magnitude that span from macroscopic to mesoscopic, with different levels of thermal fluctuations characterized by a nondimensional Boltzmann number (Bo). For a multidimensional FCNS system on a regular Cartesian grid, when using a discretization of a space-time stochastic flux Z(x,t) of the form Z(x,t)→1/-tN(ih,nΔt) for spatial interval h, time interval Δt, h, and Gaussian noise N should be greater than h0, with h0 corresponding to a cell volume that contains a sufficient number of molecules of the fluid such that the fluctuations are physically meaningful and produce the right equilibrium spectrum. For the mesoscale RMI systems simulated, it was desirable to use a cell size smaller than this limit in order to resolve the viscous shock. This was achieved by using a modified regularization of the noise term via Zx,t→1/-tmaxh3,h03Nih,nΔt, with h0=ξh
Narayanan, Kiran; Samtaney, Ravi
2018-01-01
We obtain numerical solutions of the two-fluid fluctuating compressible Navier-Stokes (FCNS) equations, which consistently account for thermal fluctuations from meso- to macroscales, in order to study the effect of such fluctuations on the mixing behavior in the Richtmyer-Meshkov instability (RMI). The numerical method used was successfully verified in two stages: for the deterministic fluxes by comparison against air-SF6 RMI experiment, and for the stochastic terms by comparison against the direct simulation Monte Carlo results for He-Ar RMI. We present results from fluctuating hydrodynamic RMI simulations for three He-Ar systems having length scales with decreasing order of magnitude that span from macroscopic to mesoscopic, with different levels of thermal fluctuations characterized by a nondimensional Boltzmann number (Bo). For a multidimensional FCNS system on a regular Cartesian grid, when using a discretization of a space-time stochastic flux Z(x,t) of the form Z(x,t)→1/-tN(ih,nΔt) for spatial interval h, time interval Δt, h, and Gaussian noise N should be greater than h0, with h0 corresponding to a cell volume that contains a sufficient number of molecules of the fluid such that the fluctuations are physically meaningful and produce the right equilibrium spectrum. For the mesoscale RMI systems simulated, it was desirable to use a cell size smaller than this limit in order to resolve the viscous shock. This was achieved by using a modified regularization of the noise term via Zx,t→1/-tmaxh3,h03Nih,nΔt, with h0=ξh
Laser-induced hydrodynamic instability and pattern formation in metallic nanofilms
Sureshkumar, R.; Trice, J.; Favazza, C.; Kalyanaraman, R.
2007-11-01
Cost effective methodologies for the robust generation of nanoscale patterns in thin films and at interfaces are crucial in photonic, opto-electronic and solar energy harvesting applications. When ultrathin metal films are exposed to a series of short (ns) laser pulses, spontaneous pattern formation results with spatio-temporal scales that depend on the film height and thermo-physical properties of the film/substrate bilayer. Various self-organization mechanisms have been identified, including a dewetting instability due to a competition between surface tension and dispersion forces, and intrinsic and/or extrinsic thermocapillary effects. We will discuss these mechanisms as well as the evolution of surface perturbations which have been explored using experiments, linear stability analysis and nonlinear dynamical simulations (Trice et al. Phys. Rev. B, 75, 235439 (2007); Favazza et al. Appl. Phys. Lett., 91, 043105 (2007); 88, 153118 (2006)).
International Nuclear Information System (INIS)
Lee, Jeong Min; Han, Joon Koo; Kim, Se Hyung; Lee, Jae Young; Park, Hee Sun; Hur, Hurn; Choi, Byung Ihn; Shin, Kyung Sook
2004-01-01
We wished to compare the in-vitro efficiency of wet radiofrequency (RF) ablation with the efficiency of dry RF ablation and RF ablation with preinjection of NaCl solutions using excised bovine liver. Radiofrequency was applied to excised bovine livers in a monopolar mode for 10 minutes using a 200 W generator and a perfused-cooled electrode with or without injection or slow infusion of NaCl solutions. After placing the perfused-cooled electrode in the explanted liver, 50 ablation zones were created with five different regimens: group A; standard dry RF ablation, group B; RF ablation with 11 mL of 5% NaCl solution preinjection, group C; RF ablation with infusion of 11 mL of 5% NaCl solution at a rate of 1 mL/min, group D; RFA with 6 mL of 36% NaCl solution preinjection, group E; RF ablation with infusion of 6 mL of 36% NaCl solution at a rate of 0.5 mL/min. In groups C and E, infusion of the NaCl solutions was started 1 min before RF ablation and then maintained during RF ablation (wet RF ablation). During RF ablation, we measured the tissue temperature at 15 mm from the electrode. The dimensions of the ablation zones and changes in impedance, current and liver temperature during RF ablation were then compared between the groups. With injection or infusion of NaCl solutions, the mean initial tissue impedance prior to RF ablation was significantly less in groups B, C, D, and E (43-75 Ω) than for group A (80 Ω) (ρ 3 in group A; 12.4 ± 3.8 cm 3 in group B; 80.9 ± 9.9 cm 3 in group C; 45.3 ± 11.3 cm 3 in group D and 81.6 ± 8.6 cm 3 in group E. The tissue temperature measured at 15 mm from the electrode was higher in groups C, D and E than other groups (ρ < 0.05): 53 ± 12 .deg. C in group A, 42 ± 2 .deg. C in group B, 93 ± 8 .deg. C in group C; 79 ± 12 .deg. C in group D and 83 ± 8 .deg.C in group E. Wet RF ablation with 5% or 36% NaCl solutions shows better efficiency in creating a large ablation zone than does dry RF ablation or RF ablation with
Contribution to study of interfaces instabilities in plane, cylindrical and spherical geometry
Toque, Nathalie
1996-12-01
This thesis proposes several experiments of hydrodynamical instabilities which are studied, numerically and theoretically. The experiments are in plane and cylindrical geometry. Their X-ray radiographies show the evolution of an interface between two solid media crossed by a detonation wave. These materials are initially solid. They become liquide under shock wave or stay between two phases, solid and liquid. The numerical study aims at simulating with the codes EAD and Ouranos, the interfaces instabilities which appear in the experiments. The experimental radiographies and the numerical pictures are in quite good agreement. The theoretical study suggests to modelise a spatio-temporal part of the experiments to obtain the quantitative development of perturbations at the interfaces and in the flows. The models are linear and in plane, cylindrical and spherical geometry. They preceed the inoming study of transition between linear and non linear development of instabilities in multifluids flows crossed by shock waves.
Hydrodynamic simulations of accretion disks in cataclysmic variables
International Nuclear Information System (INIS)
Hirose, Masahito; Osaki, Yoji
1990-01-01
The tidal effects of secondary stars on accretion disks in cataclysmic variables are studied by two-dimensional hydrodynamical simulations. The time evolution of an accretion disk under a constant mass supply rate from the secondary is followed until it reaches a quasi-steady state. We have examined various cases of different mass ratios of binary systems. It is found that the accretion disk settles into a steady state of an elongated disk fixed in the rotating frame of the binary in a binary system with comparable masses of component stars. On the other hand, in the case of a low-mass secondary, the accretion disk develops a non-axisymmetric (eccentric) structure and finally settles into a periodically oscillating state in which a non-axisymmetric eccentric disk rotates in the opposite direction to the orbital motion of the binary in the rotating frame of the binary. The period of oscillation is a few percent longer than the orbital period of the binary, and it offers a natural explanation for the ''superhump'' periodicity of SU UMa stars. Our results thus confirm basically those of Whitehurst (1988, AAA 45.064.032) who discovered the tidal instability of an accretion disk in the case of a low-mass secondary. We then discuss the cause of the tidal instability. It is shown that the tidal instability of accretion disks is caused by a parametric resonance between particle orbits and an orbiting secondary star with a 1:3 period ratio. (author)
Role of Bénard-Marangoni instabilities during solvent evaporation in polymer surface corrugations.
Bassou, N; Rharbi, Y
2009-01-06
Film formation through the drying of polymer solutions is a widely used process in laboratories and in many industrial applications such as coatings. One of the main goals of these applications is to control the film surface morphology. In many cases, evaporation has been found to yield corrugated patterns on the free surface of films. This has been interpreted in terms of either mechanical or hydrodynamic instabilities. In this article, we present experimental results where mesoscale 2D well-ordered surface corrugation patterns are formed during solvent evaporation from polystyrene/toluene solutions. The transformation of Benard-Marangoni instabilities into surface corrugation is studied during the entire drying process using particle tracking, 3D morphology analyses, etc. We show that the corrugation wavelength is controlled by the Benard-Marangoni instability, whereas the corrugation amplitude is controlled by a mechanism that involves a high evaporation rate.
Femtosecond laser fluence based nanostructuring of W and Mo in ethanol
Bashir, Shazia; Rafique, Muhammad Shahid; Nathala, Chandra Sekher; Ajami, Ali Asghar; Husinsky, Wolfgang
2017-05-01
The effect of femtosecond laser fluence on nanostructuring of Tungsten (W) and Molybdenum (Mo) has been investigated after ablation in ethanol environment. A Ti: Sapphire laser (800 nm, 30 fs) at fluences ranging from 0.6 to 5.7 J cm-2 was employed to ablate targets. The growth of structures on the surface of irradiated targets is investigated by Field Emission Scanning Electron Microscope (FESEM) analysis. The SEM was performed for both central as well as the peripheral ablated regions. It is observed that both the development and shape of nanoscale features is dependent upon deposited energies to the target surface as well as nature of material. Nanostructures grown on Mo are more distinct and well defined as compared to W. At central ablated areas of W, unorganized Laser Induced Periodic Surface Structures (LIPSS) are grown at low fluences, whereas, nonuniform melting along with cracking is observed at higher fluences. In case of Mo, well-defined and organized LIPSS are observed for low fluences. With increasing fluence, LIPSS become unorganized and broken with an appearance of cracks and are completely vanished with the formation of nanoscale cavities and conical structures. In case of peripheral ablated areas broken and bifurcated LIPSS are grown for all fluences for both materials. The, ablated diameter, ablation depth, ablation rate and the dependence of periodicity of LIPSS on the laser fluence are also estimated for both W and Mo. Parametric instabilities of laser-induced plasma along with generation and scattering of surface plasmons is considered as a possible cause for the formation of LIPSS. For ethanol assisted ablation, the role of bubble cavitation, precipitation, confinement and the convective flow is considered to be responsible for inducing increased hydrodynamic instabilities at the liquid-solid interface.
Femtosecond laser fluence based nanostructuring of W and Mo in ethanol
Energy Technology Data Exchange (ETDEWEB)
Bashir, Shazia, E-mail: shaziabashir@gcu.edu.pk [Institute of Applied Physics, Vienna University of Technology, Vienna (Austria); Centre for Advanced Studies in Physics, Government College University Lahore (Pakistan); Rafique, Muhammad Shahid [Institute of Applied Physics, Vienna University of Technology, Vienna (Austria); Department of Physics, University of Engineering and Technology Lahore (Pakistan); Nathala, Chandra Sekher [Institute of Applied Physics, Vienna University of Technology, Vienna (Austria); Ajami, Ali Asghar [Institute of Applied Physics, Vienna University of Technology, Vienna (Austria); Faculty of Physics, Semnan University, Semnan (Iran, Islamic Republic of); Husinsky, Wolfgang [Institute of Applied Physics, Vienna University of Technology, Vienna (Austria)
2017-05-15
The effect of femtosecond laser fluence on nanostructuring of Tungsten (W) and Molybdenum (Mo) has been investigated after ablation in ethanol environment. A Ti: Sapphire laser (800 nm, 30 fs) at fluences ranging from 0.6 to 5.7 J cm{sup −2} was employed to ablate targets. The growth of structures on the surface of irradiated targets is investigated by Field Emission Scanning Electron Microscope (FESEM) analysis. The SEM was performed for both central as well as the peripheral ablated regions. It is observed that both the development and shape of nanoscale features is dependent upon deposited energies to the target surface as well as nature of material. Nanostructures grown on Mo are more distinct and well defined as compared to W. At central ablated areas of W, unorganized Laser Induced Periodic Surface Structures (LIPSS) are grown at low fluences, whereas, nonuniform melting along with cracking is observed at higher fluences. In case of Mo, well-defined and organized LIPSS are observed for low fluences. With increasing fluence, LIPSS become unorganized and broken with an appearance of cracks and are completely vanished with the formation of nanoscale cavities and conical structures. In case of peripheral ablated areas broken and bifurcated LIPSS are grown for all fluences for both materials. The, ablated diameter, ablation depth, ablation rate and the dependence of periodicity of LIPSS on the laser fluence are also estimated for both W and Mo. Parametric instabilities of laser-induced plasma along with generation and scattering of surface plasmons is considered as a possible cause for the formation of LIPSS. For ethanol assisted ablation, the role of bubble cavitation, precipitation, confinement and the convective flow is considered to be responsible for inducing increased hydrodynamic instabilities at the liquid-solid interface.
Ramaswamy, Sriram
2007-03-01
Collections of self-driven or ``active'' particles are now recognised as a distinct kind of nonequilibrium matter, and an understanding of their phases, hydrodynamics, mechanical response, and correlations is a vital and rapidly developing part of the statistical physics of soft-matter systems far from equilibrium. My talk will review our recent results, from theory, simulation and experiment, on order, fluctuations, and flow instabilities in collections of active particles, in suspension or on a solid surface. Our work, which began by adapting theories of flocking to include the hydrodynamics of the ambient fluid, provides the theoretical framework for understanding active matter in all its diversity: contractile filaments in cell extracts, crawling or dividing cells, collectively swimming bacteria, fish schools, and agitated monolayers of orientable granular particles.
Search for Rayleigh-Taylor instability in laser irradiated layered thin foil targets
International Nuclear Information System (INIS)
Kilkenny, J.D.; Hares, J.D.; Rumsby, P.T.
1980-01-01
An experiment to measure the Rayleigh-Taylor instability at the vacuum-ablation surface of laser irradiated layered targets by time resolved x-ray spectroscopy is described. The time taken to burn through a layer of material is measured to be the same for massive targets as for thin foil accelerating targets. It is inferred that the thin foil targets might be Rayleigh-Taylor stable despite the values of γtauapproximately equal to15 calculated from classical theory. (author)
Modeling and experiments of x-ray ablation of National Ignition Facility first wall materials
International Nuclear Information System (INIS)
Anderson, A.T.; Burnham, A.K.; Tobin, M.T.; Peterson, P.F.
1996-01-01
This paper discusses results of modeling and experiments on the x-ray response of selected materials relevant to NIF target chamber design. X-ray energy deposition occurs in such small characteristic depths (on the order of a micron) that thermal conduction and hydrodynamic motion significantly affect the material response, even during the typical 10-ns pulses. The finite-difference ablation model integrates four separate processes: x-ray energy deposition, heat conduction, hydrodynamics, and surface vaporization. Experiments have been conducted at the Nova laser facility in Livermore on response of various materials to NIF-relevant x-ray fluences. Fused silica, Si nitride, B carbide, B, Si carbide, C, Al2O3, and Al were tested. Response was diagnosed using post-shot examinations of the surfaces with SEM and atomic force microscopes. Judgements were made about the dominant removal mechanisms for each material; relative importances of these processes were also studied with the x-ray response model
An experimental study of simultaneous ablation with dual probes in radiofrequency thermal ablation
International Nuclear Information System (INIS)
Jang, Il Soo; Rhim, Hyun Chul; Koh, Byung Hee; Cho, On Koo; Seo, Heung Suk; Kim, Yong Soo; Kim, Young Sun; Heo, Jeong Nam
2003-01-01
To determine the differences between sequential ablation with a single probe and simultaneous ablation with dual probes. Using two 14-gauge expandable probes (nine internal prongs with 4-cm deployment), radiofrequency was applied sequentially (n=8) or simultaneously (n=8) to ten ex-vivo cow livers. Before starting ablation, two RF probes with an inter-probe space of 2 cm (n=8) or 3 cm (n=8) were inserted. In the sequential group, switching the connecting cable to an RF generator permitted ablation with the second probe just after ablation with the first probe had finished. In the simultaneous group, single ablation was performed only after connecting the shafts of both RF probes using a connection device. Each ablation lasted 7 minutes at a target temperature of 105-110 .deg. C. The size and shape of the ablated area, and total ablation time were then compared between the two groups. With 2-cm spacing, the group, mean length and overlapping width of ablated lesions were, respectively, 5.20 and 5.05 cm in the sequential group (n=4), and 5.81 and 5.65 cm in the simultaneous group (n=4). With 3-cm spacing, the corresponding figures were 4.99 and 5.60 cm in the sequential group (n=4), and 6.04 and 6.78 cm in the simultaneous group (n=4). With 2-cm spacing, the mean depth of the proximal waist was 0.58 cm in the sequential (group and 0.28 cm in the simultaneous group, while with 3-cm spacing, the corresponding figures were 1.65 and 1.48 cm. In neither group was there a distal waist. Mean total ablation time was 23.4 minutes in the sequential group and 14 minutes in the simultaneous group. In terms of ablation size and ablation time, simultaneous radiofrequency ablation with dual probes is superior to sequential ablation with a single probe. A simultaneous approach will enable an operator to overcome difficulty in probe repositioning during overlapping ablation, resulting in complete ablation with a successful safety margin
Flock, Mario; Nelson, Richard P.; Turner, Neal J.; Bertrang, Gesa H.-M.; Carrasco-González, Carlos; Henning, Thomas; Lyra, Wladimir; Teague, Richard
2017-12-01
Planets are born in protostellar disks, which are now observed with enough resolution to address questions about internal gas flows. Magnetic forces are possibly drivers of the flows, but ionization state estimates suggest that much of the gas mass decouples from magnetic fields. Thus, hydrodynamical instabilities could play a major role. We investigate disk dynamics under conditions typical for a T Tauri system, using global 3D radiation-hydrodynamics simulations with embedded particles and a resolution of 70 cells per scale height. Stellar irradiation heating is included with realistic dust opacities. The disk starts in joint radiative balance and hydrostatic equilibrium. The vertical shear instability (VSI) develops into turbulence that persists up to at least 1600 inner orbits (143 outer orbits). Turbulent speeds are a few percent of the local sound speed at the midplane, increasing to 20%, or 100 m s-1, in the corona. These are consistent with recent upper limits on turbulent speeds from optically thin and thick molecular line observations of TW Hya and HD 163296. The predominantly vertical motions induced by the VSI efficiently lift particles upward. Grains 0.1 and 1 mm in size achieve scale heights greater than expected in isotropic turbulence. We conclude that while kinematic constraints from molecular line emission do not directly discriminate between magnetic and nonmagnetic disk models, the small dust scale heights measured in HL Tau and HD 163296 favor turbulent magnetic models, which reach lower ratios of the vertical kinetic energy density to the accretion stress.
International Nuclear Information System (INIS)
Schneider, V.; Rentzsch, T.; Maruhn, J.
1988-04-01
In this report we describe a two-dimensional hydrodynamic code applicable to the problems stated. In section II we describe the algorithm solving the hydrodynamic equations. In section III we present test calculations involving the propagation of shocks and contact discontinuities as well as the growth of a Rayleigh-Taylor Instability (RTI). Section IV includes all the modifications and supplements required to use the code to investigate the interaction of intense HI beams with matter. Numcerical simulations of experiments using the RFQ facility and the planned SIS-ESR at GSI are finally discussed in section V. (orig./HSI)
Ablation mass features in multi-pulses femtosecond laser ablate molybdenum target
Zhao, Dongye; Gierse, Niels; Wegner, Julian; Pretzler, Georg; Oelmann, Jannis; Brezinsek, Sebastijan; Liang, Yunfeng; Neubauer, Olaf; Rasinski, Marcin; Linsmeier, Christian; Ding, Hongbin
2018-03-01
In this study, the ablation mass features related to reflectivity of bulk Molybdenum (Mo) were investigated by a Ti: Sa 6 fs laser pulse at central wavelength 790 nm. The ablated mass removal was determined using Confocal Microscopy (CM) technique. The surface reflectivity was calibrated and measured by a Lambda 950 spectrophotometer as well as a CCD camera during laser ablation. The ablation mass loss per pulse increase with the increasing of laser shots, meanwhile the surface reflectivity decrease. The multi-pulses (100 shots) ablation threshold of Mo was determined to be 0.15 J/cm2. The incubation coefficient was estimated as 0.835. The reflectivity change of the Mo target surface following multi-pulses laser ablation were studied as a function of laser ablation shots at various laser fluences from 1.07 J/cm2 to 36.23 J/cm2. The results of measured reflectivity indicate that surface reflectivity of Mo target has a significant decline in the first 3-laser pulses at the various fluences. These results are important for developing a quantitative analysis model for laser induced ablation and laser induced breakdown spectroscopy for the first wall diagnosis of EAST tokamak.
Plasma wave instability and amplification of terahertz radiation in field-effect-transistor arrays
International Nuclear Information System (INIS)
Popov, V V; Tsymbalov, G M; Shur, M S
2008-01-01
We show that the strong amplification of terahertz radiation takes place in an array of field-effect transistors at small DC drain currents due to hydrodynamic plasmon instability of the collective plasmon mode. Planar designs compatible with standard integrated circuit fabrication processes and strong coupling of terahertz radiation to plasmon modes in FET arrays make such arrays very attractive for potential applications in solid-state terahertz amplifiers and emitters
Dynamic stabilization of the imploding-shell Rayleigh-Taylor instability
International Nuclear Information System (INIS)
Boris, J.P.
1977-01-01
A method for dynamic stabilization of the Rayleigh-Taylor (R-T) instability on the surface of an imploding fusion pellet is discussed. The driving laser beams are modulated in intensity so the ablation layer is subject to a rapidly and strongly oscillating acceleration. A substantial band of the Rayleigh-Taylor instability spectrum can be stabilized by this oscillation even though the time average acceleration vector lies in the destabilizing direction. By adjusting the frequency, structure, and amplitude of the modulation, the band of dynamically stabilized modes can be made to include the most unstable and dangerous modes. Thus considerably higher aspect ratio shells (i.e., thinner shells) could implode successfully than had been previously considered stable enough. Both theory and numerical simulations support this conclusion for the case of laser-driven pellet implosions. Similar modulation via transverse beam oscillations or parallel bunching should also work to stabilize the most dangerous surface Rayleigh-Taylor modes in relativistic electron-, ion- and heavy ion-pellet fusion schemes. (U.K.)
MHD Kelvin-Helmholtz instability in non-hydrostatic equilibrium
International Nuclear Information System (INIS)
Laghouati, Y; Bouabdallah, A; Zizi, M; Alemany, A
2007-01-01
The present work deals with the linear stability of a magnetohydrodynamic shear flow so that a stratified inviscid fluid rotating about a vertical axis when a uniform magnetic field is applied in the direction of the streaming or zonal flow. In geophysical flow, the stability of the flow is determined by taking into account the nonhydrostatic condition depending on Richardson number R i and the deviation δ from hydrostatic equilibrium. According to Stone (Stone P H 1971 J. Fluid. Mech. 45 659), it is shown that such deviation δ decreases the growth rates of three kinds of instability which can appear as geostrophic (G), symmetric (S) and Kelvin-Helmholtz (K-H) instabilities. To be specific, the evolution of the flow is therefore considered in the light of the influence of magnetic field, particularly, on K-H instability. The results of this study are presented by the linear stability of a magnetohydrodynamic, with horizontal free-shear flow of stratified fluid, subject to rotation about the vertical axis and uniform magnetic field in the zonal direction. Results are discussed and compared to previous works as Chandrasekhar (Chandrasekhar S 1961 Hydrodynamic and hydromagnetic stability (Oxford: Clarendon Press) chapter 11 pp 481-513) and Stone
Elasto-hydrodynamic lubrication
Dowson, D; Hopkins, D W
1977-01-01
Elasto-Hydrodynamic Lubrication deals with the mechanism of elasto-hydrodynamic lubrication, that is, the lubrication regime in operation over the small areas where machine components are in nominal point or line contact. The lubrication of rigid contacts is discussed, along with the effects of high pressure on the lubricant and bounding solids. The governing equations for the solution of elasto-hydrodynamic problems are presented.Comprised of 13 chapters, this volume begins with an overview of elasto-hydrodynamic lubrication and representation of contacts by cylinders, followed by a discussio
Elementary classical hydrodynamics
Chirgwin, B H; Langford, W J; Maxwell, E A; Plumpton, C
1967-01-01
Elementary Classical Hydrodynamics deals with the fundamental principles of elementary classical hydrodynamics, with emphasis on the mechanics of inviscid fluids. Topics covered by this book include direct use of the equations of hydrodynamics, potential flows, two-dimensional fluid motion, waves in liquids, and compressible flows. Some general theorems such as Bernoulli's equation are also considered. This book is comprised of six chapters and begins by introducing the reader to the fundamental principles of fluid hydrodynamics, with emphasis on ways of studying the motion of a fluid. Basic c
Thin shell, high velocity inertial confinement fusion implosions on the national ignition facility.
Ma, T; Hurricane, O A; Callahan, D A; Barrios, M A; Casey, D T; Dewald, E L; Dittrich, T R; Döppner, T; Haan, S W; Hinkel, D E; Berzak Hopkins, L F; Le Pape, S; MacPhee, A G; Pak, A; Park, H-S; Patel, P K; Remington, B A; Robey, H F; Salmonson, J D; Springer, P T; Tommasini, R; Benedetti, L R; Bionta, R; Bond, E; Bradley, D K; Caggiano, J; Celliers, P; Cerjan, C J; Church, J A; Dixit, S; Dylla-Spears, R; Edgell, D; Edwards, M J; Field, J; Fittinghoff, D N; Frenje, J A; Gatu Johnson, M; Grim, G; Guler, N; Hatarik, R; Herrmann, H W; Hsing, W W; Izumi, N; Jones, O S; Khan, S F; Kilkenny, J D; Knauer, J; Kohut, T; Kozioziemski, B; Kritcher, A; Kyrala, G; Landen, O L; MacGowan, B J; Mackinnon, A J; Meezan, N B; Merrill, F E; Moody, J D; Nagel, S R; Nikroo, A; Parham, T; Ralph, J E; Rosen, M D; Rygg, J R; Sater, J; Sayre, D; Schneider, M B; Shaughnessy, D; Spears, B K; Town, R P J; Volegov, P L; Wan, A; Widmann, K; Wilde, C H; Yeamans, C
2015-04-10
Experiments have recently been conducted at the National Ignition Facility utilizing inertial confinement fusion capsule ablators that are 175 and 165 μm in thickness, 10% and 15% thinner, respectively, than the nominal thickness capsule used throughout the high foot and most of the National Ignition Campaign. These three-shock, high-adiabat, high-foot implosions have demonstrated good performance, with higher velocity and better symmetry control at lower laser powers and energies than their nominal thickness ablator counterparts. Little to no hydrodynamic mix into the DT hot spot has been observed despite the higher velocities and reduced depth for possible instability feedthrough. Early results have shown good repeatability, with up to 1/2 the neutron yield coming from α-particle self-heating.
The Nike KrF laser facility: Performance and initial target experiments
Obenschain, S. P.; Bodner, S. E.; Colombant, D.; Gerber, K.; Lehmberg, R. H.; McLean, E. A.; Mostovych, A. N.; Pronko, M. S.; Pawley, C. J.; Schmitt, A. J.; Sethian, J. D.; Serlin, V.; Stamper, J. A.; Sullivan, C. A.; Dahlburg, J. P.; Gardner, J. H.; Chan, Y.; Deniz, A. V.; Hardgrove, J.; Lehecka, T.; Klapisch, M.
1996-05-01
Krypton-fluoride (KrF) lasers are of interest to laser fusion because they have both the large bandwidth capability (≳THz) desired for rapid beam smoothing and the short laser wavelength (1/4 μm) needed for good laser-target coupling. Nike is a recently completed 56-beam KrF laser and target facility at the Naval Research Laboratory. Because of its bandwidth of 1 THz FWHM (full width at half-maximum), Nike produces more uniform focal distributions than any other high-energy ultraviolet laser. Nike was designed to study the hydrodynamic instability of ablatively accelerated planar targets. First results show that Nike has spatially uniform ablation pressures (Δp/pNike laser in producing uniform illumination, and its performance in correspondingly uniform acceleration of targets.
International Nuclear Information System (INIS)
Bud'ko, A.B.; Velikovich, A.L.; Liberman, M.A.; Felber, F.S.
1989-01-01
A solution is derived for the problem of the initial, linear stage of the growth of small perturbations in the course of the cylindrically symmetric compression and expansion of a plasma liner and a Z-pinch with a sharp boundary. In these systems, Rayleigh-Taylor instabilities localized near the plasma boundaries are the most dangerous. Bulk convective instabilities develop in addition to these Rayleigh-Taylor instabilities. The various instability modes, including local and global Rayleigh-Taylor modes, which grown in an accelerated plasma with distributed profiles of hydrodynamic variables, are classified. The spectra of the instability growth rates are calculated for plasma liners and Z-pinches. The shape of these spectra reveals an explanation of the stratification and filamentation of the plasma observed experimentally in pinches and liners. The imposition of a longitudinal magnetic field gives rise to a stability window in the space of the flow parameters. In this window, the Rayleigh-Taylor modes are suppressed completely by magnetic shear, while the bulk convective modes are suppressed to a significant extent
Mind the gap: a flow instability controlled by particle-surface distance
Driscoll, Michelle; Delmotte, Blaise; Youssef, Mena; Sacanna, Stefano; Donev, Aleksandar; Chaikin, Paul
2016-11-01
Does a rotating particle always spin in place? Not if that particle is near a surface: rolling leads to translational motion, as well as very strong flows around the particle, even quite far away. These large advective flows strongly couple the motion of neighboring particles, giving rise to strong collective effects in groups of rolling particles. Using a model experimental system, weakly magnetic colloids driven by a rotating magnetic field, we observe that driving a compact group of microrollers leads to a new kind of flow instability. First, an initially uniformly-distributed strip of particles evolves into a shock structure, and then it becomes unstable, emitting fingers with a well-defined wavelength. Using 3D large-scale simulations in tandem with our experiments, we find that the instability wavelength is controlled not by the driving torque or the fluid viscosity, but a geometric parameter: the microroller's distance above the container floor. Furthermore, we find that the instability dynamics can be reproduced using only one ingredient: hydrodynamic interactions near a no-slip boundary.
The structure and composition of lithium fluoride films grown by off-axis pulsed laser ablation
International Nuclear Information System (INIS)
Henley, S.J.; Ashfold, M.N.R.; Pearce, S.R.J.
2003-01-01
Alkali halide coatings have been reported to act as effective dipole layers to lower the surface work function and induce a negative electron affinity of diamond surfaces. Here, the results of the analysis of films grown on silicon and quartz substrates by 193 nm pulsed laser ablation from a commercially available sintered disk of LiF are reported. The morphology, composition and crystallinity of films grown are examined and suitable deposition parameters for optimising the growth are suggested. The ablation was shown to be very efficient at removing a large amount of material from the target, even at relatively low fluence. The morphology of the films produced was poor, however, with a high density of asperities categorised as either particulates produced by exfoliation, or as droplets produced by hydrodynamic sputtering. An improved morphology with smaller droplets and fewer particulates could be produced by mounting the substrate at an angle of 65 deg. to the axis of the ablation plume and using a fluence close to the measured ablation threshold of 1.2±0.1 J/cm 2 . The elemental composition of the films was shown to be indistinguishable from that of bulk LiF, despite evidence for significant recondensation of Li back onto the target. Films containing crystal grains oriented with the direction normal to the substrate surface were observed at substrate temperatures in excess of 300 deg. C. An improved extent of orientation was observed on the quartz substrates
Influence of non-LTE radiation ablation on imploding neutron yield
International Nuclear Information System (INIS)
Sheng Jiatian; Li Yunsheng; Gao Yaomin; Li Meng; Feng Tinggui; Zhang Lifa; Zeng Xiancai; Mou Wenyong; Feng Jie; Chen Jiabin
2005-01-01
The process of radiative ablation and neutron yields of DD-capsule with CH shell implosion driven by Plank spectrum and nonequilibrium spectrum radiation fields was numerically studied using 1-D RDMG code of multigroup-nonequilibrium radiation hydrodynamics. The simulation results were compared with the experimental results. The results of the simulation show that the nonequilibrium of energy spectrum distribution of the hohlraum radiation source, especially the M-band of it, will preheat DD in the capsule obviously, decrease the compressing ratio, electron and ion temperatures of DD gas, and therefore decrease the neutron yields markedly. The simulation results also show that the law of decreasing of neutron yields with increasing of the CH-sell thickness is in agreement with the experiment basically. (authors)
Energy Technology Data Exchange (ETDEWEB)
Doss, F. W., E-mail: fdoss@lanl.gov; Kline, J. L.; Flippo, K. A.; Perry, T. S.; DeVolder, B. G.; Tregillis, I.; Loomis, E. N.; Merritt, E. C.; Murphy, T. J.; Welser-Sherrill, L.; Fincke, J. R. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
2015-05-15
An indirectly-driven shock tube experiment fielded on the National Ignition Facility (NIF) was used to create a high-energy-density hydrodynamics platform at unprecedented scale. Scaling up a shear-induced mixing experiment previously fielded at OMEGA, the NIF shear platform drives 130 μm/ns shocks into a CH foam-filled shock tube (∼ 60 mg/cc) with interior dimensions of 1.5 mm diameter and 5 mm length. The pulse-shaping capabilities of the NIF are used to extend the drive for >10 ns, and the large interior tube volumes are used to isolate physics-altering edge effects from the region of interest. The scaling of the experiment to the NIF allows for considerable improvement in maximum driving time of hydrodynamics, in fidelity of physics under examination, and in diagnostic clarity. Details of the experimental platform and post-shot simulations used in the analysis of the platform-qualifying data are presented. Hydrodynamic scaling is used to compare shear data from OMEGA with that from NIF, suggesting a possible change in the dimensionality of the instability at late times from one platform to the other.
Radiofrequency Ablation of Lung Tumors
... News Physician Resources Professions Site Index A-Z Radiofrequency Ablation (RFA) / Microwave Ablation (MWA) of Lung Tumors ... and Microwave Ablation of Lung Tumors? What are Radiofrequency and Microwave Ablation of Lung Tumors? Radiofrequency ablation, ...
Neutrino-driven supernovae: An accretion instability in a nuclear physics controlled environment
International Nuclear Information System (INIS)
Janka, H.-T.; Buras, R.; Kitaura Joyanes, F.S.; Marek, A.; Rampp, M.; Scheck, L.
2005-01-01
New simulations demonstrate that low-mode, nonradial hydrodynamic instabilities of the accretion shock help starting hot-bubble convection in supernovae and thus support explosions by the neutrino-heating mechanism. The prevailing conditions depend on the high-density equation of state which governs stellar core collapse, core bounce, and neutron star formation. Tests of this sensitivity to nuclear physics variations are shown for spherically symmetric models. Implications of current explosion models for r-process nucleosynthesis are addressed
The fragmentation of proto-globular clusters. I. Thermal instabilities
International Nuclear Information System (INIS)
Murray, S.D.; Lin, D.N.C.
1989-01-01
The metal abundances among the stars within a typical globular cluster are remarkably homogeneous. This indicates that star formation in these systems was a globally coordinated event which occurred over a time span less than or comparable to the collapse time scale of the cluster. This issue is addressed by assuming that the fragmentation of a proto-globular cluster cloud proceeded in two steps. In the first step, thermal instability led to the rapid growth of initial fluctuations. This led to a large contrast in the dynamical time scales between the perturbations and the parent cloud, and the perturbations then underwent gravitational instabilities on short time scales. This process is modeled using one-dimensional hydrodynamic simulations of clouds both with and without external heat sources and self-gravity. The models include the effects of a non-equilibrium H2 abundance. The results indicate that fragmentation can occur on time scales significantly less than the dynamical time scale of the parent cloud. 21 refs
Visco-instability of shear viscoelastic collisional dusty plasma systems
Mahdavi-Gharavi, M.; Hajisharifi, K.; Mehidan, H.
2018-04-01
In this paper, the stability of Newtonian and non-Newtonian viscoelastic collisional shear-velocity dusty plasmas is studied, using the framework of a generalized hydrodynamic (GH) model. Motivated by Banerjee et al.'s work (Banerjee et al., New J. Phys., vol. 12 (12), 2010, p. 123031), employing linear perturbation theory as well as the local approximation method in the inhomogeneous direction, the dispersion relations of the Fourier modes are obtained for Newtonian and non-Newtonian dusty plasma systems in the presence of a dust-neutral friction term. The analysis of the obtained dispersion relation in the non-Newtonian case shows that the inhomogeneous viscosity force depending on the velocity shear profile can be the genesis of a free energy source which leads the shear system to be unstable. Study of the dust-neutral friction effect on the instability of the considered systems using numerical analysis of the dispersion relation in the Newtonian case demonstrates that the maximum growth rate decreases considerably by increasing the collision frequency in the hydrodynamic regime, while this reduction can be neglected in the kinetic regime. Results show a more significant stabilization role of the dust-neutral friction term in the non-Newtonian cases, through decreasing the maximum growth rate at any fixed wavenumber and construction of the instable wavenumber region. The results of the present investigation will greatly contribute to study of the time evolution of viscoelastic laboratory environments with externally applied shear; where in these experiments the dust-neutral friction process can play a considerable role.
International Nuclear Information System (INIS)
Bose, A.; Betti, R.; Shvarts, D.; Woo, K. M.
2017-01-01
To achieve ignition with inertial confinement fusion (ICF), it is important to under- stand the effect of asymmetries on the hydrodynamics and energetics of the compres- sion. This paper describes a theoretical model for the compression of distorted hot spots, and quantitative estimates using hydrodynamic simulations. The asymmetries are categorized into low (Ι < 6) and intermediate (Ι < A < 40) modes by comparison of the wavelength with the thermal-diffusion scale length. Long-wavelength modes introduce substantial nonradial motion, whereas intermediate-wavelength modes in- volve more cooling by thermal ablation. We discover that for distorted hot spots, the measured neutron-averaged properties can be very different from the real hydro- dynamic conditions. This is because mass ablation driven my thermal conduction introduces flows in the Rayleigh–Taylor bubbles, this results in pressure variation, in addition to temperature variation between the bubbles and the neutron-producing region (~1 keV for intermediate modes). The differences are less pronounced for long-wavelength asymmetries since the bubbles are relatively hot and sustain fusion reactions. The yield degradation− with respect to the symmetric− results primarily from a reduction in the hot-spot pressure for low modes and from a reduction in burn volume for intermediate modes. It is shown that the degradation in internal energy of the hot-spot is equivalent for both categories, and is equal to the total residual energy in the shell including the bubbles. This quantity is correlated with the shell residual kinetic energy for low-modes, and includes the kinetic energy in the bubbles for mid-modes.
Droplet and multiphase effects in a shock-driven hydrodynamic instability with reshock
Middlebrooks, John B.; Avgoustopoulos, Constantine G.; Black, Wolfgang J.; Allen, Roy C.; McFarland, Jacob A.
2018-06-01
Shock-driven multiphase instabilities (SDMI) are unique physical phenomena that have far-reaching applications in engineering and science such as high energy explosions, scramjet combustors, and supernovae events. The SDMI arises when a multiphase field is impulsively accelerated by a shock wave and evolves as a result of gradients in particle-gas momentum transfer. A new shock tube facility has been constructed to study the SDMI. Experiments were conducted to investigate liquid particle and multiphase effects in the SDMI. A multiphase cylindrical interface was created with water droplet laden air in our horizontal shock tube facility. The interface was accelerated by a Mach 1.66 shock wave, and its reflection from the end wall. The interface development was captured using laser illumination and a high-resolution CCD camera. Laser interferometry was used to determine the droplet size distribution. A particle filtration technique was used to determine mass loading within an interface and verify particle size distribution. The effects of particle number density, particle size, and a secondary acceleration (reshock) of the interface were noted. Particle number density effects were found comparable to Atwood number effects in the Richtmyer-Meshkov instability for small (˜ 1.7 {μ }m) droplets. Evaporation was observed to alter droplet sizes and number density, markedly after reshock. For large diameter droplets (˜ 10.7 {μ }m), diminished development was observed with larger droplets lagging far behind the interface. These lagging droplets were also observed to breakup after reshock into structured clusters of smaller droplets. Mixing width values were reported to quantify mixing effects seen in images.
Tensile Instability and Artificial Stresses in Impact Problems in SPH
International Nuclear Information System (INIS)
Mehra, Vishal; Sijoy C D; Mishra, Vinayak; Chaturvedi, Shashank
2012-01-01
The smooth particle hydrodynamics (SPH) is a meshless computational technique that is popular in the modeling of impact and penetration problems. However, SPH is liable to a tensile instability that manifests itself as a bunching of nodes and formation of artificial voids and no generally accepted formulation exists to counter this instability. We examine the performance of two methods that have been proposed to deal with the tensile instability— the Monaghan artificial stresses and the Godunov-type SPH. The impact and penetration of 0.5 cm radii steel spheres on 2 mm thick aluminium plate at 3.1 km/s is chosen for comparison. We show that the artificial void formation in St-Al impact is suppressed but not eliminated by using Monaghan stresses while the void formation is entirely eliminated by using Godunov-type formulation of SPH that was proposed by Parshikov and Medin.
Combined effect of viscosity and vorticity on single mode Rayleigh-Taylor instability bubble growth
International Nuclear Information System (INIS)
Banerjee, Rahul; Mandal, Labakanta; Roy, S.; Khan, M.; Gupta, M. R.
2011-01-01
The combined effect of viscosity and vorticity on the growth rate of the bubble associated with single mode Rayleigh-Taylor instability is investigated. It is shown that the effect of viscosity on the motion of the lighter fluid associated with vorticity accumulated inside the bubble due to mass ablation may be such as to reduce the net viscous drag on the bubble exerted by the upper heavier fluid as the former rises through it.
Dynamics of laser ablation at the early stage during and after ultrashort pulse
International Nuclear Information System (INIS)
Ilnitsky, D K; Zhakhovsky, V V; Migdal, K P; Inogamov, N A; Khokhlov, V A; Petrov, Yu V
2016-01-01
Study of material flow in two-temperature states is needed for a fundamental understanding the physics of femtosecond laser ablation. To explore phenomena at a very early stage of laser action on a metallic target our in-house two-temperature hydrodynamics code is used here. The early stage covers duration of laser pulse with next first few picoseconds. We draw attention to the difference in behavior at this stage between the cases: (i) of an ultrathin film (thickness of order of skin depth d skin or less), (ii) thin films (thickness of a film is 4-7 of d skin for gold), and (iii) bulk targets (more than 10 d skin for gold). We demonstrate that these differences follow from a competition among conductive cooling of laser excited electrons in a skin layer, electron-ion coupling, and hydrodynamics of unloading caused by excess of pressure of excited free electrons. Conductive cooling of the skin needs a heat sink, which is performed by the cold material outside the skin. Such sink is unavailable in the ultrathin films. (paper)
Particle force model effects in a shock-driven multiphase instability
Black, W. J.; Denissen, N.; McFarland, J. A.
2018-05-01
This work presents simulations on a shock-driven multiphase instability (SDMI) at an initial particle volume fraction of 1% with the addition of a suite of particle force models applicable in dense flows. These models include pressure-gradient, added-mass, and interparticle force terms in an effort to capture the effects neighboring particles have in non-dilute flow regimes. Two studies are presented here: the first seeks to investigate the individual contributions of the force models, while the second study focuses on examining the effect of these force models on the hydrodynamic evolution of a SDMI with various particle relaxation times (particle sizes). In the force study, it was found that the pressure gradient and interparticle forces have little effect on the instability under the conditions examined, while the added-mass force decreases the vorticity deposition and alters the morphology of the instability. The relaxation-time study likewise showed a decrease in metrics associated with the evolution of the SDMI for all sizes when the particle force models were included. The inclusion of these models showed significant morphological differences in both the particle and carrier species fields, which increased as particle relaxation times increased.
Energy Technology Data Exchange (ETDEWEB)
Tang, Jun [Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China); Xie, Zhiyong [Shanghai Institute of Laser Plasma, Shanghai 201800 (China); Du, Ai [Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China); Ye, Junjian [Shanghai Institute of Laser Plasma, Shanghai 201800 (China); Zhang, Zhihua; Shen, Jun [Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China); Zhou, Bin, E-mail: zhoubin863@tongji.edu.cn [Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China)
2014-04-15
Highlights: • Sinusoidal perturbed Al foil was prepared by single-point diamond turning. • Perturbed Al foil was measured by surface profiler and white light interferometer. • Perturbed Al foil and CH layer adhered with each other via a hot-press process. • Parameters and cross-section of the CH–Al perturbation target was characterized. - Abstract: A polystyrene (CH)/aluminum (Al) dual-layer perturbation target for hydrodynamic instability experiments in inertial confinement fusion (ICF) was designed and fabricated. The target was composed of a perturbed 40 μm Al foil and a CH layer. The detailed fabrication method consisted of four steps. The 40 μm Al foil was first prepared by roll and polish process; the perturbation patterns were then introduced on the surface of the Al foil by the single-point diamond turning (SPDT) technology; the CH layer was prepared via a simple method which called spin-coating process; finally, the CH layer was directly coated on the perturbation surface of Al foil by a hot-press process to avoid the use of a sticker and to eliminate the gaps between the CH layer and the Al foil. The parameters of the target, such as the perturbation wavelength (T) and perturbation amplitude (A), were characterized by a QC-5000 tool microscope, an alpha-step 500 surface profiler and a NT1100 white light interferometer. The results showed that T and A of the target were about 52 μm and 7.34 μm, respectively. Thickness of the Al foil (H1), thickness of the CH layer (H2), and cross-section of the dual-layer target were characterized by a QC-5000 tool microscope and a scanning electron microscope (SEM). H1 and H2 were about 40 μm and 15 μm, respectively, the cross-sectional photographs of the target showed that the CH layer and the Al foil adhered perfectly with each other.
Applications of pulsed energy sources and hydrodynamic response to materials science
International Nuclear Information System (INIS)
Perry, F.; Nelson, W.
1993-01-01
The dynamic response of materials to pulsed, relativistic electron beams was studied for materials science applications over two decades ago. Presently, intense light ion beams are being explored for materials science applications. These include the Ion Beam Surface Treatment (IBEST) of materials for producing stronger and more corrosion-resistant materials and the evaporative deposition of polycrystalline thin films. Laser sources are also being extensively utilized as pulsed energy sources in medical science and in clinical applications. In particular, laser-tissue interactions are being investigated for laser angioplasty and surgery as well as cancer therapy. The understanding of the energy deposition and hydrodynamic response of a wide range of materials is essential to the success of these applications. In order to address these materials science applications, the authors are utilizing and developing high quality, energy deposition-hydrodynamic code techniques which can aid in the design and interpretation of experiments. Consequently, the authors strongly encourage the development of 3-dimensional, species-selective diagnostic techniques, e.g. Resonant Holographic Interferometry Spectroscopy (RHIS), to be used in analyzing the ablation plume in the thin film deposition experiments. In this presentation they show the results and discuss the limitations of calculations for these materials applications. They also discuss the status of the RHIS diagnostic
Mode coupling in nonlinear Rayleigh--Taylor instability
International Nuclear Information System (INIS)
Ofer, D.; Shvarts, D.; Zinamon, Z.; Orszag, S.A.
1992-01-01
This paper studies the interaction of a small number of modes in the two-fluid Rayleigh--Taylor instability at relatively late stages of development, i.e., the nonlinear regime, using a two-dimensional hydrodynamic code incorporating a front-tracking scheme. It is found that the interaction of modes can greatly affect the amount of mixing and may even reduce the width of the mixing region. This interaction is both relatively long range in wave-number space and also acts in both directions, i.e., short wavelengths affect long wavelengths and vice versa. Three distinct stages of interaction have been identified, including substantial interaction among modes some of which may still be in their classical (single mode) ''linear'' phase
Sassa, S.
2017-12-01
This presentation shows some recent research advances on tsunami-seabed-structure interaction following the 2011 Tohoku Earthquake Tsunami, Japan. It presents a concise summary and discussion of utilizing a geotechnical centrifuge and a large-scale hydro flume for the modelling of tsunami-seabed-structure interaction. I highlight here the role of tsunami-induced seepage in piping/boiling, erosion and bearing capacity decrease and failure of the rubble/seabed foundation. A comparison and discussion are made on the stability assessment for the design of tsunami-resistant structures on the basis of the results from both geo-centrifuge and large-scale hydrodynamic experiments. The concurrent processes of the instability involving the scour of the mound/sandy seabed, bearing capacity failure and flow of the foundation and the failure of caisson breakwaters under tsunami overflow and seepage coupling are made clear in this presentation. Three series of experiments were conducted under fifty gravities. The first series of experiments targeted the instability of the mounds themselves, and the second series of experiments clarified how the mound scour would affect the overall stability of the caissons. The third series of experiments examined the effect of a countermeasure on the basis of the results from the two series of experiments. The experimental results first demonstrated that the coupled overflow-seepage actions promoted the development of the mound scour significantly, and caused bearing capacity failure of the mound, resulting in the total failure of the caisson breakwater, which otherwise remained stable without the coupling effect. The velocity vectors obtained from the high-resolution image analysis illustrated the series of such concurrent scour/bearing-capacity-failure/flow processes leading to the instability of the breakwater. The stability of the breakwaters was significantly improved with decreasing hydraulic gradient underneath the caissons due to an
Steiner, Adam; Yager-Elorriaga, David; Patel, Sonal; Jordan, Nicholas; Gilgenbach, Ronald; Lau, Y. Y.
2015-11-01
The electrothermal instability (ETI) and magneto-Rayleigh Taylor instability (MRT) are important in the implosion of metallic liners, such as magnetized liner implosion fusion (MagLIF). The MAIZE linear transformer driver (LTD) at the University of Michigan generates 200 ns risetime-current pulses of 500 to 600 kA into Al foil liners to study plasma instabilities and implosion dynamics, most recently MRT growth on imploding cylindrical liners. A full circuit model of MAIZE, along with I-V measurements, yields time-resolved load inductance. This has enabled measurements of an effective current-carrying radius to determine implosion velocity and plasma-vacuum interface acceleration. Measurements are also compared to implosion data from 4-time-frame laser shadowgraphy. Improved resolution measurements on the laser shadowgraph system have been used to examine the liner interface early in the shot to examine surface perturbations resulting from ETI for various seeding conditions. Fourier analysis examines the growth rates of wavelength bands of these structures to examine the transition from ETI to MRT. This work was supported by the U.S. DoE through award DE-SC0012328. S.G. Patel is supported by Sandia National Labs. D.A. Yager is supported by NSF fellowship grant DGE 1256260.
Effect of ablatant composition on the ablation of a fuelling pellet
International Nuclear Information System (INIS)
Chang, C.T.; Thomsen, K.; Piret, S.
1988-01-01
The single species neutral-shielding model for the ablation of a hydrogenic pellet is extended by considering the ablatant as a mixture of four species: molecular and atomic hydrogen, protons and electrons. Compared with the results of the frozen flow, (i.e. the single species molecular hydrogen gas model), results of the analysis showed that the presence of dissociation and ionization effects caused a marked difference of the ablatant state. The attenuations of the incoming electron energy and energy flux, however, are very much similar irrespective of whether the ablated flow is in a frozen or an equilibrium state. The scaling law of the pellet ablation rate with respect to the plasma state of Te, ne and the pellet radius remains the same; the ablation rate is reduced by approximately 15%. To examine the possible existence of a spherical shell around the pellet where most of the incoming electron energy is absorbed, acodmparison is made between the local electron collisional mean free path and the electron Larmor radius. A critical field at the ionization radius is evaluated. An effective spherical energyabsorbing region exists when the local field strength is below the critical value. For a plasma state of low Te and ne, (where the ablatant is hardly ionized), and for one near the thermonuclear condition (where a highly dense ablatant exists near the pellet), the effective energy absorption region is nearly spherical. 20 refs. (author)
Pak, Arthur; Benedetti, L. R.; Berzak Hopkins, L. F.; Clark, D.; Divol, L.; Dewald, E. L.; Fittinghoff, D.; Izumi, N.; Khan, S. F.; Landen, O.; Lepape, S.; Ma, T.; Marley, E.; Nagel, S.; Volegov, P.; Weber, C.; Bradley, D. K.; Callahan, D.; Grim, G.; Hurricane, O. A.; Patel, P.; Schneider, M. B.; Edwards, M. J.
2017-10-01
In recent inertial confinement implosion experiments conducted at the National Ignition Facility, bright and spatially localized x-ray emission within the hot spot at stagnation has been observed. This emission is associated with higher Z ablator material that is injected into the hot spot by the hydrodynamic perturbation induced by the 5-10 um diameter capsule fill tube. The reactivity of the DT fuel and subsequent yield of the implosion are strongly dependent on the density, temperature, and confinement time achieved throughout the stagnation of the implosion. Radiative losses from higher Z ablator material that mixes into the hot spot as well as non-uniformities in the compression and confinement induced by the fill tube perturbation can degrade the yield of the implosion. This work will examine the impact to conditions at stagnation that results from the fill tube perturbation. This assessment will be based from a pair of experiments conducted with a high density carbon ablator where the only deliberate change was reduction in fill tube diameter from 10 to 5 um. An estimate of the radiative losses and impact on performance from ablator mix injected into the hot spot by the fill tube perturbation will be presented. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
International Nuclear Information System (INIS)
Mahmood, S.; Rawat, R. S.; Wang, Y.; Lee, S.; Tan, T. L.; Springham, S. V.; Lee, P.; Zakaullah, M.
2012-01-01
The effect of laser energy fluence on the onset and growth of Rayleigh–Taylor (RT) instabilities in laser induced Fe plasma is investigated using time-resolved fast gated imaging. The snow plow and shock wave models are fitted to the experimental results and used to estimate the ablation parameters and the density of gas atoms that interact with the ablated species. It is observed that RT instability develops during the interface deceleration stage and grows for a considerable time for higher laser energy fluence. The effects of RT instabilities formation on the surface topography of the Fe thin films grown in pulsed laser deposition system are investigated (i) using different laser energy fluences for the same wavelength of laser radiation and (ii) using different laser wavelengths keeping the energy fluence fixed. It is concluded that the deposition achieved under turbulent condition leads to less smooth deposition surfaces with bigger sized particle agglomerates or network.
International Nuclear Information System (INIS)
Gupta, N.K.
2002-01-01
The effects of radiation transport on hydrodynamic parameters of laser produced plasmas are studied. LTE and non-LTE atomic models are used to calculate multi group opacities and emissivities. Screened hydrogenic atom model is used to calculate the energy levels. The population densities of neutral to fully ionized ions are obtained by solving the steady state rate equations. Radiation transport is treated in multi-group diffusion or Sn method. A comparison is made between 1 and 100 group radiation transport and LTE and non-LTE models. For aluminium, multi group radiation transport leads to much higher mass ablation as compared to the 1 group and no radiation transport cases. This in turn leads to higher ablation pressures. However, for gold gray approximation gives higher mass ablation as compared to multi group simulations. LTE conversion efficiency of laser light into x-rays is more than the non-LTE estimates. For LTE as well as non-LTE cases, the one group approximation over-predicts the conversion efficiency Multi group non-LTE simulations predict that the conversion efficiency increases with laser intensity up to a maximum and then it decreases. (author)
Laser ablation principles and applications
1994-01-01
Laser Ablation provides a broad picture of the current understanding of laser ablation and its many applications, from the views of key contributors to the field. Discussed are in detail the electronic processes in laser ablation of semiconductors and insulators, the post-ionization of laser-desorbed biomolecules, Fourier-transform mass spectroscopy, the interaction of laser radiation with organic polymers, laser ablation and optical surface damage, laser desorption/ablation with laser detection, and laser ablation of superconducting thin films.
Zhou, Yufeng; Gao, Xiaobin Wilson
2016-09-01
High-intensity focused ultrasound (HIFU) is emerging as an effective therapeutic modality in clinics. Besides the thermal ablation, tissue disintegration is also possible because of the interaction between the distorted HIFU bursts and either bubble cloud or boiling bubble. Hydrodynamic cavitation is another type of cavitation and has been employed widely in industry, but its role in mechanical erosion to tissue is not clearly known. In this study, the bubble dynamics immediately after the termination of HIFU exposure in the transparent gel phantom was captured by high-speed photography, from which the bubble displacement towards the transducer and the changes of bubble size was quantitatively determined. The characteristics of hydrodynamic cavitation due to the release of the acoustic radiation force and relaxation of compressed surrounding medium were found to associate with the number of pulses delivered and HIFU parameters (i.e. pulse duration and pulse repetition frequency). Because of the initial big bubble (~1 mm), large bubble expansion (up to 1.76 folds), and quick bubble motion (up to ~1 m s-1) hydrodynamic cavitation is significant after HIFU exposure and may lead to mechanical erosion. The shielding effect of residual tiny bubbles would reduce the acoustic energy delivered to the pre-existing bubble at the focus and, subsequently, the hydrodynamic cavitation effect. Tadpole shape of mechanical erosion in ex vivo porcine kidney samples was similar to the contour of bubble dynamics in the gel. Liquefied tissue was observed to emit towards the transducer through the punctured tissue after HIFU exposure in the sonography. In summary, the release of HIFU exposure-induced hydrodynamic cavitation produces significant bubble expansion and motion, which may be another important mechanism of tissue erosion. Understanding its mechanism and optimizing the outcome would broaden and enhance HIFU applications.
Zhou, Yufeng; Gao, Xiaobin Wilson
2016-09-21
High-intensity focused ultrasound (HIFU) is emerging as an effective therapeutic modality in clinics. Besides the thermal ablation, tissue disintegration is also possible because of the interaction between the distorted HIFU bursts and either bubble cloud or boiling bubble. Hydrodynamic cavitation is another type of cavitation and has been employed widely in industry, but its role in mechanical erosion to tissue is not clearly known. In this study, the bubble dynamics immediately after the termination of HIFU exposure in the transparent gel phantom was captured by high-speed photography, from which the bubble displacement towards the transducer and the changes of bubble size was quantitatively determined. The characteristics of hydrodynamic cavitation due to the release of the acoustic radiation force and relaxation of compressed surrounding medium were found to associate with the number of pulses delivered and HIFU parameters (i.e. pulse duration and pulse repetition frequency). Because of the initial big bubble (~1 mm), large bubble expansion (up to 1.76 folds), and quick bubble motion (up to ~1 m s -1 ) hydrodynamic cavitation is significant after HIFU exposure and may lead to mechanical erosion. The shielding effect of residual tiny bubbles would reduce the acoustic energy delivered to the pre-existing bubble at the focus and, subsequently, the hydrodynamic cavitation effect. Tadpole shape of mechanical erosion in ex vivo porcine kidney samples was similar to the contour of bubble dynamics in the gel. Liquefied tissue was observed to emit towards the transducer through the punctured tissue after HIFU exposure in the sonography. In summary, the release of HIFU exposure-induced hydrodynamic cavitation produces significant bubble expansion and motion, which may be another important mechanism of tissue erosion. Understanding its mechanism and optimizing the outcome would broaden and enhance HIFU applications.
International Nuclear Information System (INIS)
Tanaka, Toshihiro; Westphal, Saskia; Isfort, Peter; Braunschweig, Till; Penzkofer, Tobias; Bruners, Philipp; Kichikawa, Kimihiko; Schmitz-Rode, Thomas; Mahnken, Andreas H.
2012-01-01
Purpose: To compare the effectiveness of microwave (MW) ablation with radiofrequency (RF) ablation for treating breast tissue in a nonperfused ex vivo model of healthy bovine udder tissue. Materials and Methods: MW ablations were performed at power outputs of 25W, 35W, and 45W using a 915-MHz frequency generator and a 2-cm active tip antenna. RF ablations were performed with a bipolar RF system with 2- and 3-cm active tip electrodes. Tissue temperatures were continuously monitored during ablation. Results: The mean short-axis diameters of the coagulation zones were 1.34 ± 0.14, 1.45 ± 0.13, and 1.74 ± 0.11 cm for MW ablation at outputs of 25W, 35W, and 45W. For RF ablation, the corresponding values were 1.16 ± 0.09 and 1.26 ± 0.14 cm with electrodes having 2- and 3-cm active tips, respectively. The mean coagulation volumes were 2.27 ± 0.65, 2.85 ± 0.72, and 4.45 ± 0.47 cm 3 for MW ablation at outputs of 25W, 35W, and 45W and 1.18 ± 0.30 and 2.29 ± 0.55 cm 3 got RF ablation with 2- and 3-cm electrodes, respectively. MW ablations at 35W and 45W achieved significantly longer short-axis diameters than RF ablations (P < 0.05). The highest tissue temperature was achieved with MW ablation at 45W (P < 0.05). On histological examination, the extent of the ablation zone in MW ablations was less affected by tissue heterogeneity than that in RF ablations. Conclusion: MW ablation appears to be advantageous with respect to the volume of ablation and the shape of the margin of necrosis compared with RF ablation in an ex vivo bovine udder.
X-ray ablation measurements and modeling for ICF applications
International Nuclear Information System (INIS)
Anderson, A.T.
1996-09-01
X-ray ablation of material from the first wall and other components of an ICF (Inertial Confinement Fusion) chamber is a major threat to the laser final optics. Material condensing on these optics after a shot may cause damage with subsequent laser shots. To ensure the successful operation of the ICF facility, removal rates must be predicted accurately. The goal for this dissertation is to develop an experimentally validated x-ray response model, with particular application to the National Ignition Facility (NIF). Accurate knowledge of the x-ray and debris emissions from ICF targets is a critical first step in the process of predicting the performance of the target chamber system. A number of 1-D numerical simulations of NIF targets have been run to characterize target output in terms of energy, angular distribution, spectrum, and pulse shape. Scaling of output characteristics with variations of both target yield and hohlraum wall thickness are also described. Experiments have been conducted at the Nova laser on the effects of relevant x-ray fluences on various materials. The response was diagnosed using post-shot examinations of the surfaces with scanning electron microscope and atomic force microscope instruments. Judgments were made about the dominant removal mechanisms for each material. Measurements of removal depths were made to provide data for the modeling. The finite difference ablation code developed here (ABLATOR) combines the thermomechanical response of materials to x-rays with models of various removal mechanisms. The former aspect refers to energy deposition in such small characteristic depths (∼ micron) that thermal conduction and hydrodynamic motion are significant effects on the nanosecond time scale. The material removal models use the resulting time histories of temperature and pressure-profiles, along with ancillary local conditions, to predict rates of surface vaporization and the onset of conditions that would lead to spallation
Oddo, Silvia; Balestra, Margherita; Vera, Lara; Giusti, Massimo
2018-05-11
Radiofrequency ablation and laser ablation are safe and effective techniques for reducing thyroid nodule volume, neck symptoms, and cosmetic complaints. Therapeutic success is defined as a nodule reduction > 50% between 6 and 12 months after the procedure, but a percentage of nodules inexplicably do not respond to thermal ablation. We describe the case of a young Caucasian woman with a solid benign thyroid nodule who refused surgery and who had undergone radiofrequency ablation in 2013. The nodule did not respond in terms of either volume reduction or improvement in neck symptoms. After 2 years, given the patient's continued refusal of thyroidectomy, we proposed laser ablation. The nodule displayed a significant volume reduction (- 50% from radiofrequency ablation baseline volume, - 57% from laser ablation baseline), and the patient reported a significant improvement in neck symptoms (from 6/10 to 1/10 on a visual analogue scale). We conjecture that some benign thyroid nodules may be intrinsically resistant to necrosis when one specific ablation technique is used, but may respond to another technique. To the best of our knowledge, this is the first description of the effect of performing a different percutaneous ablation technique in a nodule that does not respond to radiofrequency ablation.
International Nuclear Information System (INIS)
Ferapontov, E.V.
2002-01-01
Hydrodynamic surfaces are solutions of hydrodynamic-type systems viewed as non-parametrized submanifolds of the hodograph space. We propose an invariant differential-geometric characterization of hydrodynamic surfaces by expressing the curvature form of the characteristic web in terms of the reciprocal invariants. (author)
Energy Technology Data Exchange (ETDEWEB)
Vandenboomgaerde, M.; Bonnefille, M.; Gauthier, P. [CEA, DAM, DIF, F-91297 Arpajon (France)
2016-05-15
Highly resolved radiation-hydrodynamics FCI2 simulations have been performed to model laser experiments on the National Ignition Facility. In these experiments, cylindrical gas-filled hohlraums with gold walls are driven by a 20 ns laser pulse. For the first time, simulations show the appearance of Kelvin-Helmholtz (KH) vortices at the interface between the expanding wall material and the gas fill. In this paper, we determine the mechanisms which generate this instability: the increase of the gas pressure around the expanding gold plasma leads to the aggregation of an over-dense gold layer simultaneously with shear flows. At the surface of this layer, all the conditions are met for a KH instability to grow. Later on, as the interface decelerates, the Rayleigh-Taylor instability also comes into play. A potential scenario for the generation of a mixing zone at the gold-gas interface due to the KH instability is presented. Our estimates of the Reynolds number and the plasma diffusion width at the interface support the possibility of such a mix. The key role of the first nanosecond of the laser pulse in the instability occurrence is also underlined.
Kele, Petra G.; de Jong, Koert P.; van der Jagt, Eric J.
Purpose: To test the hypothesis that volume changes of ablation zones (AZs) on successive computed tomography (CT) scans could predict ablation site recurrences (ASRs) in patients with colorectal liver metastases treated by radiofrequency (RF) ablation. Materials and Methods: RF ablation was
Longitudinal waves and a beam instability in a relativistic anisotropic plasma
International Nuclear Information System (INIS)
Onishchenko, O.G.
1981-01-01
Dispersion relations are derived for longitudinal waves in a relativistic plasma with an arbitrary anisotropic particle distribution function. Longitudinal waves with phase velocity lower than the speed of light are shown to exist in such a plasma. The damping rate of longitudinal waves due to the Cerenkov interaction with plasma particles is derived for such a plasma. The instability of a beam of high-energy particles in such a plasma is studied. As the anisotropy of an ultrarelativistic plasma becomes less pronounced, the maximum hydrodynamic growth rate decreases
Finding the first cosmic explosions. III. Pulsational pair-instability supernovae
International Nuclear Information System (INIS)
Whalen, Daniel J.; Smidt, Joseph; Even, Wesley; Fryer, Chris L.; Woosley, S. E.; Heger, Alexander; Stiavelli, Massimo
2014-01-01
Population III supernovae have been the focus of growing attention because of their potential to directly probe the properties of the first stars, particularly the most energetic events that can be seen at the edge of the observable universe. But until now pulsational pair-instability supernovae, in which explosive thermonuclear burning in massive stars fails to unbind them but can eject their outer layers into space, have been overlooked as cosmic beacons at the earliest redshifts. These shells can later collide and, like Type IIn supernovae, produce superluminous events in the UV at high redshifts that could be detected in the near infrared today. We present numerical simulations of a 110 M ☉ pulsational pair-instability explosion done with the Los Alamos radiation hydrodynamics code Radiation Adaptive Grid Eulerian. We find that collisions between consecutive pulsations are visible in the near infrared out to z ∼ 15-20 and can probe the earliest stellar populations at cosmic dawn.
Laser induced ablatively driven interfacial nonlinear fluid instabilities in multilayer targets
International Nuclear Information System (INIS)
Manoranjan Khan; Gupta, M.R.; Mandal, L.K.; Roy, S.; Banerjee, R.
2010-01-01
Complete text of publication follows. High power laser driven shock waves in condensed matter have important application for studying equation of state (EOS) and high pressure physics. This is an important phenomenon in fuel compression for Inertial Confinement Fusion (ICF) experiments where multilayer targets of differing shock impedance are interacted by laser induced shocks. The interface between the two fluid becomes unstable when driven by the impulsive force (Richtmyer-Meshkov) due to such a shock wave or a continuously acting force e.g., gravity (Rayleigh-Taylor). In the nonlinear stage, the fluid interface is found to develop structures having finger-like shapes. The structures resemble a bubble (spike) accordingly as a lighter (heavier) fluid pushes in a heavier (lighter) fluid. These effects need to be mitigated for efficient compression in ICF experiment. We have studied the effect of density variation on R-T and R-M instability on the temporal development of nonlinear two fluid interfacial structures like bubble and spike. It is shown that the velocity of bubble or spike decreases leading to stabilization if the density of the fluids leads to lowering of the Atwood number. The Atwood number A = ρ a -ρ b / ρ a +ρ b changes to A* = ρ a *ρ b */ ρ a *ρ b * where ρ* m = ρ m (1-1/γ m ), m = [a,b], assuming ρ a > ρ b . It has been seen that the stabilization or destabilization (depending on the algebraic sign of the gradient) will be proportional to the pressure p 0 at the interface. The set of equation describing the dynamics of the bubbles and spikes in presence of fluid density variation are not analytically integrable in closed form. All the results are derived by numerical methods and are represented and interpreted. Analytical calculations are performed (not presented here) to modify the dynamical boundary condition between the two fluids and we have finally arrived at the following expression for the asymptotic bubble velocity ν b 2 = 2(r
Voltage and pace-capture mapping of linear ablation lesions overestimates chronic ablation gap size.
O'Neill, Louisa; Harrison, James; Chubb, Henry; Whitaker, John; Mukherjee, Rahul K; Bloch, Lars Ølgaard; Andersen, Niels Peter; Dam, Høgni; Jensen, Henrik K; Niederer, Steven; Wright, Matthew; O'Neill, Mark; Williams, Steven E
2018-04-26
Conducting gaps in lesion sets are a major reason for failure of ablation procedures. Voltage mapping and pace-capture have been proposed for intra-procedural identification of gaps. We aimed to compare gap size measured acutely and chronically post-ablation to macroscopic gap size in a porcine model. Intercaval linear ablation was performed in eight Göttingen minipigs with a deliberate gap of ∼5 mm left in the ablation line. Gap size was measured by interpolating ablation contact force values between ablation tags and thresholding at a low force cut-off of 5 g. Bipolar voltage mapping and pace-capture mapping along the length of the line were performed immediately, and at 2 months, post-ablation. Animals were euthanized and gap sizes were measured macroscopically. Voltage thresholds to define scar were determined by receiver operating characteristic analysis as voltage, pace-capture, and ablation contact force maps. All modalities overestimated chronic gap size, by 1.4 ± 2.0 mm (ablation contact force map), 5.1 ± 3.4 mm (pace-capture), and 9.5 ± 3.8 mm (voltage mapping). Error on ablation contact force map gap measurements were significantly less than for voltage mapping (P = 0.003, Tukey's multiple comparisons test). Chronically, voltage mapping and pace-capture mapping overestimated macroscopic gap size by 11.9 ± 3.7 and 9.8 ± 3.5 mm, respectively. Bipolar voltage and pace-capture mapping overestimate the size of chronic gap formation in linear ablation lesions. The most accurate estimation of chronic gap size was achieved by analysis of catheter-myocardium contact force during ablation.
Radiofrequency and microwave tumor ablation in patients with implanted cardiac devices: Is it safe?
Energy Technology Data Exchange (ETDEWEB)
Skonieczki, Brendan D., E-mail: bskonieczki@lifespan.org [Department of Diagnostic Imaging, Warren Alpert Medical School of Brown University/Rhode Island Hospital, 593 Eddy Street, Providence, RI 02903 (United States); Wells, Catherine, E-mail: cwells1@bidmc.harvard.edu [Department of Radiology, Harvard Medical School/Beth Israel Deaconess Medical Center, 330 Brookline Avenue, Boston, MA 02215 (United States); Wasser, Elliot J., E-mail: ewasser@lifespan.org [Department of Diagnostic Imaging, Warren Alpert Medical School of Brown University/Rhode Island Hospital, 593 Eddy Street, Providence, RI 02903 (United States); Dupuy, Damian E., E-mail: ddupuy@lifespan.org [Department of Diagnostic Imaging, Warren Alpert Medical School of Brown University/Rhode Island Hospital, 593 Eddy Street, Providence, RI 02903 (United States)
2011-09-15
Purpose: To identify malfunction of implanted cardiac devices during or after thermal ablation of tumors in lung, kidney, liver or bone, using radiofrequency (RF) or microwave (MW) energy. Materials and methods: After providing written consent, 19 patients (15 men and 4 women; mean age 78 years) with pacemakers or pacemaker/defibrillators underwent 22 CT image-guided percutaneous RF or MW ablation of a variety of tumors. Before and after each procedure, cardiac devices were interrogated and reprogrammed by a trained cardiac electrophysiology fellow. Possible pacer malfunctions included abnormalities on electrocardiographic (EKG) monitoring and alterations in device settings. Our institutional review board approved this Health Insurance Portability and Accountability Act-compliant study. Informed consent for participation in this retrospective study was deemed unnecessary by our review board. Results: During 20 of 22 sessions, no abnormalities were identified in continuous, EKG tracings or pacemaker functions. However, in two sessions significant changes, occurred in pacemaker parameters: inhibition of pacing during RF application in one, session and resetting of mode by RF energy in another session. These changes did not, result in hemodynamic instability of either patient. MW ablation was not associated with, any malfunction. In all 22 sessions, pacemakers were undamaged and successfully reset to original parameters. Conclusion: RF or MW ablation of tumors in liver, kidney, bone and lung can be performed safely in patients with permanent intra-cardiac devices, but careful planning between radiology and cardiology is essential to avoid adverse outcomes.
International Nuclear Information System (INIS)
Barrios, M. A.; Suter, L. J.; Glenn, S.; Benedetti, L. R.; Bradley, D. K.; Collins, G. W.; Hammel, B. A.; Izumi, N.; Ma, T.; Scott, H.; Smalyuk, V. A.; Regan, S. P.; Epstein, R.; Kyrala, G. A.
2013-01-01
Bright spots in the hot spot intensity profile of gated x-ray images of ignition-scale implosions at the National Ignition Facility [G. H. Miller et al., Opt. Eng. 443, (2004)] are observed. X-ray images of cryogenically layered deuterium-tritium (DT) and tritium-hydrogen-deuterium (THD) ice capsules, and gas filled plastic shell capsules (Symcap) were recorded along the hohlraum symmetry axis. Heterogeneous mixing of ablator material and fuel into the hot spot (i.e., hot-spot mix) by hydrodynamic instabilities causes the bright spots. Hot-spot mix increases the radiative cooling of the hot spot. Fourier analysis of the x-ray images is used to quantify the evolution of bright spots in both x- and k-space. Bright spot images were azimuthally binned to characterize bright spot location relative to known isolated defects on the capsule surface. A strong correlation is observed between bright spot location and the fill tube for both Symcap and cryogenically layered DT and THD ice targets, indicating the fill tube is a significant seed for the ablation front instability causing hot-spot mix. The fill tube is the predominant seed for Symcaps, while other capsule non-uniformities are dominant seeds for the cryogenically layered DT and THD ice targets. A comparison of the bright spot power observed for Si- and Ge-doped ablator targets shows heterogeneous mix in Symcap targets is mostly material from the doped ablator layer
Laser-Driven Hydrodynamic Experiments in the Turbulent Plasma Regime: from OMEGA to NIF
International Nuclear Information System (INIS)
Robey, H F; Miles, A R; Hansen, J F; Blue, B E; Drake, R P
2003-01-01
There is a great deal of interest in studying the evolution of hydrodynamic phenomena in high energy density plasmas that have transitioned beyond the initial phases of instability into an Ely developed turbulent state. Motivation for this study arises both in fusion plasmas as well as in numerous astrophysical applications where the understanding of turbulent mixing is essential. Double-shell ignition targets, for example, are subject to large growth of short wavelength perturbations on both surfaces of the high-Z inner shell. These perturbations, initiated by Richtmyer-Meshkov and Rayleigh-Taylor instabilities, can transition to a turbulent state and will lead to deleterious mixing of the cooler shell material with the hot burning fuel. In astrophysical plasmas, due to the extremely large scale, turbulent hydrodynamic mixing is also of wide-spread interest. The radial mixing that occurs in the explosion phase of core-collapse supernovae is an example that has received much attention in recent years and yet remains only poorly understood. In all of these cases, numerical simulation of the flow field is very difficult due to the large Reynolds number and corresponding wide range of spatial scales characterizing the plasma. Laboratory experiments on high energy density facilities that can access this regime are therefore of great interest. Experiments exploring the transition to turbulence that are currently being conducted on the Omega laser will be described. We will also discuss experiments being planned for the initial commissioning phases of the NIF as well as the enhanced experimental parameter space that will become available, as additional quads are made operational
Roberton, Benjamin J; Liu, David; Power, Mark; Wan, John M C; Stuart, Sam; Klass, Darren; Yee, John
2014-05-01
Percutaneous image-guided thermal ablation is safe and efficacious in achieving local control and improving outcome in the treatment of both early stage non-small-cell lung cancer and pulmonary metastatic disease, in which surgical treatment is precluded by comorbidity, poor cardiorespiratory reserve, or unfavorable disease distribution. Radiofrequency ablation is the most established technology, but new thermal ablation technologies such as microwave ablation and cryoablation may offer some advantages. The use of advanced techniques, such as induced pneumothorax and the popsicle stick technique, or combining thermal ablation with radiotherapy, widens the treatment options available to the multidisciplinary team. The intent of this article is to provide the reader with a practical knowledge base of pulmonary ablation by concentrating on indications, techniques, and follow-up. Copyright © 2014 Canadian Association of Radiologists. Published by Elsevier Inc. All rights reserved.
Kovasznay modes in the linear stability analysis of self-similar ablation flows
International Nuclear Information System (INIS)
Lombard, V.
2008-12-01
Exact self-similar solutions of gas dynamics equations with nonlinear heat conduction for semi-infinite slabs of perfect gases are used for studying the stability of ablative flows in inertial confinement fusion, when a shock wave propagates in front of a thermal front. Both the similarity solutions and their linear perturbations are numerically computed with a dynamical multi-domain Chebyshev pseudo-spectral method. Laser-imprint results, showing that maximum amplification occurs for a laser-intensity modulation of zero transverse wavenumber have thus been obtained (Abeguile et al. (2006); Clarisse et al. (2008)). Here we pursue this approach by proceeding for the first time to an analysis of perturbations in terms of Kovasznay modes. Based on the analysis of two compressible and incompressible flows, evolution equations of vorticity, acoustic and entropy modes are proposed for each flow region and mode couplings are assessed. For short times, perturbations are transferred from the external surface to the ablation front by diffusion and propagate as acoustic waves up to the shock wave. For long times, the shock region is governed by the free propagation of acoustic waves. A study of perturbations and associated sources allows us to identify strong mode couplings in the conduction and ablation regions. Moreover, the maximum instability depends on compressibility. Finally, a comparison with experiments of flows subjected to initial surface defects is initiated. (author)
Reshocks, rarefactions, and the generalized Layzer model for hydrodynamic instabilities
International Nuclear Information System (INIS)
Mikaelian, K.O.
2008-01-01
We report numerical simulations and analytic modeling of shock tube experiments on Rayleigh-Taylor and Richtmyer-Meshkov instabilities. We examine single interfaces of the type A/B where the incident shock is initiated in A and the transmitted shock proceeds into B. Examples are He/air and air/He. In addition, we study finite-thickness or double-interface A/B/A configurations like air/SF 6 /air gas-curtain experiments. We first consider conventional shock tubes that have a 'fixed' boundary: A solid endwall which reflects the transmitted shock and reshocks the interface(s). Then we focus on new experiments with a 'free' boundary--a membrane disrupted mechanically or by the transmitted shock, sending back a rarefaction towards the interface(s). Complex acceleration histories are achieved, relevant for Inertial Confinement Fusion implosions. We compare our simulation results with a generalized Layzer model for two fluids with time-dependent densities, and derive a new freeze-out condition whereby accelerating and compressive forces cancel each other out. Except for the recently reported failures of the Layzer model, the generalized Layzer model and hydrocode simulations for reshocks and rarefactions agree well with each other, and remain to be verified experimentally
Long-duration planar direct-drive hydrodynamics experiments on the NIF
Casner, A.; Mailliet, C.; Khan, S. F.; Martinez, D.; Izumi, N.; Kalantar, D.; Di Nicola, P.; Di Nicola, J. M.; Le Bel, E.; Igumenshchev, I.; Tikhonchuk, V. T.; Remington, B. A.; Masse, L.; Smalyuk, V. A.
2018-01-01
The advent of high-power lasers facilities such as the National Ignition Facility (NIF) and the laser megajoule provide unique platforms to study the physics of turbulent mixing flows in high energy density plasmas. We report here on the commissioning of a novel planar direct-drive platform on the NIF, which allows the acceleration of targets during 30 ns. Planar plastic samples were directly irradiated by 300-450 kJ of UV laser light (351 nm) and a very good planarity of the laser drive is demonstrated. No detrimental effect of imprint is observed in the case of these thick plastic targets (300 μm), which is beneficial for future academic experiments requesting similar irradiation conditions. The long-duration direct-drive (DD) platform is thereafter harnessed to study the ablative Rayleigh-Taylor instability (RTI) in DD. The growth of two-dimensional pre-imposed perturbations is quantified through time-resolved face-on x-ray radiography and used as a benchmark for radiative hydrocode simulations. The ablative RTI is then quantified in its highly nonlinear stage starting from intentionally large 3D imprinted broadband modulations. Two generations of bubble mergers is observed for the first time in DD, as a result of the unprecedented long laser acceleration.
Experimental demonstration of laser imprint reduction using underdense foams
International Nuclear Information System (INIS)
Delorme, B.; Casner, A.; Olazabal-Loumé, M.; Nicolaï, Ph.; Breil, J.; Tikhonchuk, V. T.; Michel, D. T.; Seka, W.; Froula, D. H.; Goncharov, V.; Riazuelo, G.; Borisenko, N.; Orekhov, A.; Fujioka, S.; Sunahara, A.; Grech, M.
2016-01-01
Reducing the detrimental effect of the Rayleigh-Taylor (RT) instability on the target performance is a critical challenge. In this purpose, the use of targets coated with low density foams is a promising approach to reduce the laser imprint. This article presents results of ablative RT instability growth measurements, performed on the OMEGA laser facility in direct-drive for plastic foils coated with underdense foams. The laser beam smoothing is explained by the parametric instabilities developing in the foam and reducing the laser imprint on the plastic (CH) foil. The initial perturbation pre-imposed by the means of a specific phase plate was shown to be smoothed using different foam characteristics. Numerical simulations of the laser beam smoothing in the foam and of the RT growth are performed with a suite of paraxial electromagnetic and radiation hydrodynamic codes. They confirmed the foam smoothing effect in the experimental conditions.
Experimental demonstration of laser imprint reduction using underdense foams
Energy Technology Data Exchange (ETDEWEB)
Delorme, B.; Casner, A. [CEA, DAM, DIF, F-91297 Arpajon (France); CELIA, University of Bordeaux-CNRS-CEA, F-33400 Talence (France); Olazabal-Loumé, M. [CEA, DAM, CESTA, 15 Avenue des Sablières, F-33114 Le Barp (France); CELIA, University of Bordeaux-CNRS-CEA, F-33400 Talence (France); Nicolaï, Ph.; Breil, J.; Tikhonchuk, V. T. [CELIA, University of Bordeaux-CNRS-CEA, F-33400 Talence (France); Michel, D. T.; Seka, W.; Froula, D. H.; Goncharov, V. [Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623 (United States); Riazuelo, G. [CEA, DAM, DIF, F-91297 Arpajon (France); Borisenko, N.; Orekhov, A. [P. N. Lebedev Physical Institute, RAS, 53 Leninskii Prospect, Moscow 119991 (Russian Federation); Fujioka, S.; Sunahara, A. [Institute of Laser Engineering, Osaka University, Suita, Osaka 565 (Japan); Grech, M. [LULI, Ecole Polytechnique, CNRS, CEA, UPMC, 91128 Palaiseau (France)
2016-04-15
Reducing the detrimental effect of the Rayleigh-Taylor (RT) instability on the target performance is a critical challenge. In this purpose, the use of targets coated with low density foams is a promising approach to reduce the laser imprint. This article presents results of ablative RT instability growth measurements, performed on the OMEGA laser facility in direct-drive for plastic foils coated with underdense foams. The laser beam smoothing is explained by the parametric instabilities developing in the foam and reducing the laser imprint on the plastic (CH) foil. The initial perturbation pre-imposed by the means of a specific phase plate was shown to be smoothed using different foam characteristics. Numerical simulations of the laser beam smoothing in the foam and of the RT growth are performed with a suite of paraxial electromagnetic and radiation hydrodynamic codes. They confirmed the foam smoothing effect in the experimental conditions.
International Nuclear Information System (INIS)
Cunha, F.R.; Couto, H.L.G.
2011-01-01
Magnetostatic attraction may lead to formation of aggregates in stable colloidal magnetic suspensions and magneto-rheological suspensions. The aggregation problem of magnetic composites under differential sedimentation is a key problem in the control of the instability of non-Brownian suspensions. Against these attractive forces are the electrostatic repulsion and the hydrodynamic interactions acting as stabilizing effects to the suspension. This work concerns an investigation of the pairwise interaction of magnetic particles in a dilute sedimenting suspension. We focus attention on suspensions where the Peclet number is large (negligible Brownian motion) and where the Reynolds number (negligible inertia) is small. The suspension is composed of magnetic micro-spheres of different radius and density immersed in a Newtonian fluid moving under the action of gravity. The theoretical calculations are based on direct computations of the hydrodynamic and the magnetic interactions among the rigid spheres in the regime of low particle Reynolds number. From the limiting trajectory in which aggregation occurs, we calculate the collision efficiency, representing the dimensionless rate at which aggregates are formed. The numerical results show clear evidence that the hydrodynamic interactions are of fundamental relevance in the process of magnetic particle aggregation. We compare the stabilizing effects between electrostatic repulsion and hydrodynamic interactions.
Energy Technology Data Exchange (ETDEWEB)
Cunha, F.R., E-mail: frcunha@unb.b [Universidade de Brasilia, Faculdade de Tecnologia, Depto. de Engenharia Mecanica, Grupo de Mecanica dos Fluidos de Escoamentos Complexos - VORTEX, Campus Universitario Darcy Ribeiro, 70910-900, Brasilia, DF (Brazil); Couto, H.L.G. [Universidade de Brasilia, Faculdade de Tecnologia, Depto. de Engenharia Mecanica, Grupo de Mecanica dos Fluidos de Escoamentos Complexos - VORTEX, Campus Universitario Darcy Ribeiro, 70910-900, Brasilia, DF (Brazil)
2011-01-15
Magnetostatic attraction may lead to formation of aggregates in stable colloidal magnetic suspensions and magneto-rheological suspensions. The aggregation problem of magnetic composites under differential sedimentation is a key problem in the control of the instability of non-Brownian suspensions. Against these attractive forces are the electrostatic repulsion and the hydrodynamic interactions acting as stabilizing effects to the suspension. This work concerns an investigation of the pairwise interaction of magnetic particles in a dilute sedimenting suspension. We focus attention on suspensions where the Peclet number is large (negligible Brownian motion) and where the Reynolds number (negligible inertia) is small. The suspension is composed of magnetic micro-spheres of different radius and density immersed in a Newtonian fluid moving under the action of gravity. The theoretical calculations are based on direct computations of the hydrodynamic and the magnetic interactions among the rigid spheres in the regime of low particle Reynolds number. From the limiting trajectory in which aggregation occurs, we calculate the collision efficiency, representing the dimensionless rate at which aggregates are formed. The numerical results show clear evidence that the hydrodynamic interactions are of fundamental relevance in the process of magnetic particle aggregation. We compare the stabilizing effects between electrostatic repulsion and hydrodynamic interactions.
Direct numerical simulations of type Ia supernovae flames II: The Rayleigh-Taylor instability
International Nuclear Information System (INIS)
Bell, J.B.; Day, M.S.; Rendleman, C.A.; Woosley, S.E.; Zingale, M.
2004-01-01
A Type Ia supernova explosion likely begins as a nuclear runaway near the center of a carbon-oxygen white dwarf. The outward propagating flame is unstable to the Landau-Darrieus, Rayleigh-Taylor, and Kelvin-Helmholtz instabilities, which serve to accelerate it to a large fraction of the speed of sound. We investigate the Rayleigh-Taylor unstable flame at the transition from the flamelet regime to the distributed-burning regime, around densities of 10e7 gm/cc, through detailed, fully resolved simulations. A low Mach number, adaptive mesh hydrodynamics code is used to achieve the necessary resolution and long time scales. As the density is varied, we see a fundamental change in the character of the burning--at the low end of the density range the Rayleigh-Taylor instability dominates the burning, whereas at the high end the burning suppresses the instability. In all cases, significant acceleration of the flame is observed, limited only by the size of the domain we are able to study. We discuss the implications of these results on the potential for a deflagration to detonation transition
Directory of Open Access Journals (Sweden)
Nathan Elie Frenk
Full Text Available OBJECTIVES: To evaluate the safety and long-term efficacy of computed tomography-guided percutaneous ethanol ablation for benign primary and secondary hyperfunctioning adrenal disorders. METHOD: We retrospectively evaluated the long-term results of nine patients treated with computed tomography-guided percutaneous ethanol ablation: eight subjects who presented with primary adrenal disorders, such as pheochromocytoma, primary macronodular adrenal hyperplasia and aldosterone-producing adenoma, and one subject with Cushing disease refractory to conventional treatment. Eleven sessions were performed for the nine patients. The patient data were reviewed for the clinical outcome and procedure-related complications over ten years. RESULTS: Patients with aldosterone-producing adenoma had clinical improvement: symptoms recurred in one case 96 months after ethanol ablation, and the other patient was still in remission 110 months later. All patients with pheochromocytoma had clinical improvement but were eventually submitted to surgery for complete remission. No significant clinical improvement was seen in patients with hypercortisolism due to primary macronodular adrenal hyperplasia or Cushing disease. Major complications were seen in five of the eleven procedures and included cardiovascular instability and myocardial infarction. Minor complications attributed to sedation were seen in two patients. CONCLUSION: Computed tomography-guided ethanol ablation does not appear to be suitable for the long-term treatment of hyperfunctioning adrenal disorders and is not without risks.
Hydrodynamics of soft active matter
Marchetti, M. C.; Joanny, J. F.; Ramaswamy, S.; Liverpool, T. B.; Prost, J.; Rao, Madan; Simha, R. Aditi
2013-07-01
This review summarizes theoretical progress in the field of active matter, placing it in the context of recent experiments. This approach offers a unified framework for the mechanical and statistical properties of living matter: biofilaments and molecular motors in vitro or in vivo, collections of motile microorganisms, animal flocks, and chemical or mechanical imitations. A major goal of this review is to integrate several approaches proposed in the literature, from semimicroscopic to phenomenological. In particular, first considered are “dry” systems, defined as those where momentum is not conserved due to friction with a substrate or an embedding porous medium. The differences and similarities between two types of orientationally ordered states, the nematic and the polar, are clarified. Next, the active hydrodynamics of suspensions or “wet” systems is discussed and the relation with and difference from the dry case, as well as various large-scale instabilities of these nonequilibrium states of matter, are highlighted. Further highlighted are various large-scale instabilities of these nonequilibrium states of matter. Various semimicroscopic derivations of the continuum theory are discussed and connected, highlighting the unifying and generic nature of the continuum model. Throughout the review, the experimental relevance of these theories for describing bacterial swarms and suspensions, the cytoskeleton of living cells, and vibrated granular material is discussed. Promising extensions toward greater realism in specific contexts from cell biology to animal behavior are suggested, and remarks are given on some exotic active-matter analogs. Last, the outlook for a quantitative understanding of active matter, through the interplay of detailed theory with controlled experiments on simplified systems, with living or artificial constituents, is summarized.
Langmuir instability in partially spin polarized bounded degenerate plasma
Iqbal, Z.; Jamil, M.; Murtaza, G.
2018-04-01
Some new features of waves inside the cylindrical waveguide on employing the separated spin evolution quantum hydrodynamic model are evoked. Primarily, the instability of Langmuir wave due to the electron beam in a partially spin polarized degenerate plasma considering a nano-cylindrical geometry is discussed. Besides, the evolution of a new spin-dependent wave (spin electron acoustic wave) due to electron spin polarization effects in the real wave spectrum is elaborated. Analyzing the growth rate, it is found that in the absence of Bohm potential, the electron spin effects or exchange interaction reduce the growth rate as well as k-domain but the inclusion of Bohm potential increases both the growth rate and k-domain. Further, we investigate the geometry effects expressed by R and pon and find that they have opposite effects on the growth rate and k-domain of the instability. Additionally, how the other parameters like electron beam density or streaming speed of beam electrons influence the growth rate is also investigated. This study may find its applications for the signal analysis in solid state devices at nanoscales.
Directory of Open Access Journals (Sweden)
Da Liu
2017-09-01
Full Text Available Riverbank vegetation is of high importance both for preserving the form (morphology and function (ecology of natural river systems. Revegetation of riverbanks is commonly used as a means of stream rehabilitation and management of bank instability and erosion. In this experimental study, the effect of different riverbank vegetation densities on flow hydrodynamics across the channel, including the riparian zone, are reported and discussed. The configuration of vegetation elements follows either linear or staggered arrangements as vegetation density is progressively increased, within a representative range of vegetation densities found in nature. Hydrodynamic measurements including mean streamwise velocity and turbulent intensity flow profiles are recorded via acoustic Doppler velocimetry (ADV—both at the main channel and within the riverbank. These results show that for the main channel and the toe of riverbank, turbulence intensity for the low densities (λ ≈ 0 to 0.12 m−1 can increase up to 40% compared the case of high densities (λ = 0.94 to 1.9 m−1. Further analysis of these data allowed the estimation of bed-shear stresses, demonstrating 86% and 71% increase at the main channel and near the toe region, for increasing densities (λ = 0 to 1.9 m−1. Quantifying these hydrodynamic effects is important for assessing the contribution of physically representative ranges of riparian vegetation densities on hydrogeomorphologic feedback.
Energy Technology Data Exchange (ETDEWEB)
Xu, H.-X.; Xie, X.-Y.; Lu, M.-D. E-mail: lumd@21cn.com; Chen, J.-W.; Yin, X.-Y.; Xu, Z.-F.; Liu, G.-J
2004-01-01
AIM: To investigate the therapeutic efficacy of thermal ablation for treatment of hepatocellular carcinoma (HCC) using microwave and radiofrequency (RF) energy application. MATERIALS AND METHODS: A total of 190 nodules in 97 patients (84 male, 13 female; mean age 53.4 years, range 24-74 years) with HCC were treated with microwave or RF ablation in the last 4 years. The applicators were introduced into the tumours under conscious analgesic sedation by intravenous administration of fentanyl citrate and droperidol and local anaesthesia in both thermal ablation procedures. The patients were then followed up with contrast-enhanced computed tomography (CT) to evaluate treatment response. Survival was analysed using the Kaplan-Meier method. RESULTS: Complete ablation was obtained in 92.6% (176/190) nodules. The complete ablation rates were 94.6% (106/112) in microwave ablation and 89.7% (70/78) in RF ablation. The complete ablation rates in tumours{<=}2.0, 2.1-3.9 and {>=}4.0 cm were 93.1, 93.8 and 86.4%, respectively. Local recurrence was found in 9.5% nodules and the rates in tumours{<=}2.0, 2.1-3.9 and {>=}4.0 cm in diameter were 3.4, 9.9 and 31.8%, respectively. In the follow-up period, 7.1% nodules ablated by microwave and 12.8% by RF presented local recurrence. The 1, 2 and 3-year distant recurrence-free survivals were 47.2, 34.9 and 31.0%, respectively. Estimated mean survival was 32 months, and 1, 2 and 3-year cumulative survivals were 75.6, 58.5, and 50.0%, respectively. One and 2 years survivals of Child-Pugh class A, B and C patients were 83.8 and 70.4%, 78.2 and 53.2%, 36.3 and 27.3%, respectively. CONCLUSION: Thermal ablation therapy by means of microwave and RF energy application is an effective and safe therapeutic technique for hepatocellular carcinoma. Large tumours can be completely ablated, but have a significantly higher risk of local recurrence at follow-up.
International Nuclear Information System (INIS)
Xu, H.-X.; Xie, X.-Y.; Lu, M.-D.; Chen, J.-W.; Yin, X.-Y.; Xu, Z.-F.; Liu, G.-J.
2004-01-01
AIM: To investigate the therapeutic efficacy of thermal ablation for treatment of hepatocellular carcinoma (HCC) using microwave and radiofrequency (RF) energy application. MATERIALS AND METHODS: A total of 190 nodules in 97 patients (84 male, 13 female; mean age 53.4 years, range 24-74 years) with HCC were treated with microwave or RF ablation in the last 4 years. The applicators were introduced into the tumours under conscious analgesic sedation by intravenous administration of fentanyl citrate and droperidol and local anaesthesia in both thermal ablation procedures. The patients were then followed up with contrast-enhanced computed tomography (CT) to evaluate treatment response. Survival was analysed using the Kaplan-Meier method. RESULTS: Complete ablation was obtained in 92.6% (176/190) nodules. The complete ablation rates were 94.6% (106/112) in microwave ablation and 89.7% (70/78) in RF ablation. The complete ablation rates in tumours≤2.0, 2.1-3.9 and ≥4.0 cm were 93.1, 93.8 and 86.4%, respectively. Local recurrence was found in 9.5% nodules and the rates in tumours≤2.0, 2.1-3.9 and ≥4.0 cm in diameter were 3.4, 9.9 and 31.8%, respectively. In the follow-up period, 7.1% nodules ablated by microwave and 12.8% by RF presented local recurrence. The 1, 2 and 3-year distant recurrence-free survivals were 47.2, 34.9 and 31.0%, respectively. Estimated mean survival was 32 months, and 1, 2 and 3-year cumulative survivals were 75.6, 58.5, and 50.0%, respectively. One and 2 years survivals of Child-Pugh class A, B and C patients were 83.8 and 70.4%, 78.2 and 53.2%, 36.3 and 27.3%, respectively. CONCLUSION: Thermal ablation therapy by means of microwave and RF energy application is an effective and safe therapeutic technique for hepatocellular carcinoma. Large tumours can be completely ablated, but have a significantly higher risk of local recurrence at follow-up
Ablation threshold and ablation mechanism transition of polyoxymethylene irradiated by CO2 laser.
Li, Gan; Cheng, Mousen; Li, Xiaokang
2016-09-01
Polyoxymethylene (POM) decomposes gradually as it is heated up by the irradiation of CO2 laser; the long-chain molecules of POM are broken into short chains, which leads to the lowering of the melting point and the critical temperature of the ablation products. When the product temperature is above the melting point, ablation comes up in the way of vaporization; when the product temperature is higher than the critical temperature, all liquid products are transformed into gas instantly and the ablation mechanism is changed. The laser fluence at which significant ablation is observed is defined as the ablation threshold, and the fluence corresponding to the ablation mechanism changing is denoted as the flyover threshold. In this paper, random pyrolysis is adopted to describe the pyrolytic decomposition of POM, and consequently, the components of the pyrolysis products under different pyrolysis rates are acquired. The Group Contribution method is used to count the thermodynamic properties of the pyrolysis products, and the melting point and the critical temperature of the product mixture are obtained by the Mixing Law. The Knudsen layer relationship is employed to evaluate the ablation mass removal when the product temperature is below the critical temperature. The gas dynamics conservation laws associated with the Jouguet condition are used to calculate the mass removal when the product temperature is higher than the critical temperature. Based on the model, a set of simulations for various laser intensities and lengths are carried out to generalize the relationships between the thresholds and the laser parameters. Besides the ablated mass areal density, which fits the experimental data quite well, the ablation temperature, pyrolysis rate, and product components are also discussed for a better understanding of the ablation mechanism of POM.
Atrial fibrillation ablation using a closed irrigation radiofrequency ablation catheter.
Golden, Keith; Mounsey, John Paul; Chung, Eugene; Roomiani, Pahresah; Morse, Michael Andew; Patel, Ankit; Gehi, Anil
2012-05-01
Catheter ablation is an effective therapy for symptomatic, medically refractory atrial fibrillation (AF). Open-irrigated radiofrequency (RF) ablation catheters produce transmural lesions at the cost of increased fluid delivery. In vivo models suggest closed-irrigated RF catheters create equivalent lesions, but clinical outcomes are limited. A cohort of 195 sequential patients with symptomatic AF underwent stepwise AF ablation (AFA) using a closed-irrigation ablation catheter. Recurrence of AF was monitored and outcomes were evaluated using Kaplan-Meier survival analysis and Cox proportional hazards models. Mean age was 59.0 years, 74.9% were male, 56.4% of patients were paroxysmal and mean duration of AF was 5.4 years. Patients had multiple comorbidities including hypertension (76.4%), tobacco abuse (42.1%), diabetes (17.4%), and obesity (mean body mass index 30.8). The median follow-up was 55.8 weeks. Overall event-free survival was 73.6% with one ablation and 77.4% after reablation (reablation rate was 8.7%). Median time to recurrence was 26.9 weeks. AF was more likely to recur in patients being treated with antiarrhythmic therapy at the time of last follow-up (recurrence rate 30.3% with antiarrhythmic drugs, 13.2% without antiarrhythmic drugs; hazard ratio [HR] 2.2, 95% confidence interval [CI] 1.1-4.4, P = 0.024) and in those with a history of AF greater than 2 years duration (HR 2.7, 95% CI 1.1-6.9, P = 0.038). Our study represents the largest cohort of patients receiving AFA with closed-irrigation ablation catheters. We demonstrate comparable outcomes to those previously reported in studies of open-irrigation ablation catheters. Given the theoretical benefits of a closed-irrigation system, a large head-to-head comparison using this catheter is warranted. ©2012, The Authors. Journal compilation ©2012 Wiley Periodicals, Inc.
Hydrodynamics and phases of flocks
International Nuclear Information System (INIS)
Toner, John; Tu Yuhai; Ramaswamy, Sriram
2005-01-01
actually grow with the number of organisms faster than the N 'law of large numbers' obeyed by virtually all other known systems. As for equilibrium systems, the hydrodynamic behavior of any phase of flocks is radically modified by additional conservation laws. One such law is conservation of momentum of the background fluid through which many flocks move, which gives rise to the 'hydrodynamic backflow' induced by the motion of a large flock through a fluid. We review the theoretical work on the effect of such background hydrodynamics on three phases of flocks-the ferromagnetic and nematic phases described above, and the disordered phase in which there is no order in the motion of the organisms. The most surprising prediction in this case is that 'ferromagnetic' motion is always unstable for low Reynolds-number suspensions. Experiments appear to have seen this instability, but a quantitative comparison is awaited. We conclude by suggesting further theoretical and experimental work to be done
Equation of state study of Laser Megajoule capsules ablator materials
International Nuclear Information System (INIS)
Colin-Lalu, Pierre
2016-01-01
This PhD thesis enters the field of inertial confinement fusion studies. In particular, it focuses on the equation of state tables of ablator materials synthesized on LMJ capsules. This work is indeed aims at improving the theoretical models introduced into the equation of state tables. We focused in the Mbar-eV pressure-temperature range because it can be access on kJ-scale laser facilities.In order to achieve this, we used the QEOS model, which is simple to use, configurable, and easily modifiable.First, quantum molecular dynamics (QMD) simulations were performed to generate cold compression curve as well as shock compression curves along the principal Hugoniot. Simulations were compared to QEOS model and showed that atomic bond dissociation has an effect on the compressibility. Results from these simulations are then used to parametrize the Grueneisen parameter in order to generate a tabulated equation of state that includes dissociation. It allowed us to show its influence on shock timing in a hydrodynamic simulation.Second, thermodynamic states along the Hugoniot were measured during three experimental campaigns upon the LULI2000 and GEKKO XII laser facilities. Experimental data confirm QMD simulations.This study was performed on two ablator materials which are an undoped polymer CHO, and a silicon-doped polymer CHOSi. Results showed universal shock compression properties. (author) [fr
Growth of Rayleigh-Taylor and bulk convective instabilities in dynamics of plasma liners and pinches
International Nuclear Information System (INIS)
Bud'ko, A.B.; Velikovich, A.L.; Liberman, M.A.; Felber, F.S.
1989-01-01
Perturbation growth is studied for the initial, linear stage of an instability development in the course of a cylindrically-symmetric compression and expansion of plasma liners and Z-pinches with a sharp boundary. The hydrodynamic instabilities are Rayleigh-Taylor and bulk convective ones, the former being the most dengerous. Classification of the instability modes developing in accelerated plasmas, inclusing the local and global Rayleigh-Taylor modes, is given. The spectra of the instability growth rates are calculated for plasma liners and Z-pinches. The properties of the spectra appear to explain the filamentation and stratification of plasmas observed in the experiments with liners and Z-pinches. An axial magnetic field is shown to create a window of stability in the space of the flow parameters, where th Rayleigh-Taylor modes are fully suppressed by the magnetic shear, and the bulk convective ones - to a considerable extent. The axial magnetic field required to stabilize the implosion of a liner is estimated as B z0 =(10-30 kG)I(MA)/R 0 (cm), where I is the average current, R 0 - the initial radius of the liner
Energy Technology Data Exchange (ETDEWEB)
Weaver, J. L.; Kehne, D.; Brown, C. M.; Obenschain, S. P.; Serlin, V.; Schmitt, A. J. [U.S. Naval Research Laboratory, Washington DC 20375 (United States); Oh, J.; Lehmberg, R. H.; Mclean, E.; Manka, C. [Research Support Instruments, Lanham, Maryland 20905 (United States); Phillips, L. [Alogus Research Corporation, McLean, Virginia 22101 (United States); Afeyan, B. [Polymath Research, Inc., Pleasanton, California 94566 (United States); Seely, J.; Feldman, U. [Berkeley Research Associates, Inc., Beltsville, Maryland 20705 (United States)
2013-02-15
The krypton-fluoride (KrF) laser is an attractive choice for inertial confinement fusion due to its combination of short wavelength ({lambda}=248 nm), large bandwidth (up to 3 THz), and superior beam smoothing by induced spatial incoherence. These qualities improve the overall hydrodynamics of directly driven pellet implosions and should allow use of increased laser intensity due to higher thresholds for laser plasma instabilities when compared to frequency tripled Nd:glass lasers ({lambda}=351 nm). Here, we report the first observations of the two-plasmon decay instability using a KrF laser. The experiments utilized the Nike laser facility to irradiate solid plastic planar targets over a range of pulse lengths (0.35 ns{<=}{tau}{<=}1.25 ns) and intensities (up to 2 Multiplication-Sign 10{sup 15} W/cm{sup 2}). Variation of the laser pulse created different combinations of electron temperature and electron density scale length. The observed onset of instability growth was consistent with the expected scaling that KrF lasers have a higher intensity threshold for instabilities in the quarter critical density region.
International Nuclear Information System (INIS)
Weaver, J. L.; Kehne, D.; Brown, C. M.; Obenschain, S. P.; Serlin, V.; Schmitt, A. J.; Oh, J.; Lehmberg, R. H.; Mclean, E.; Manka, C.; Phillips, L.; Afeyan, B.; Seely, J.; Feldman, U.
2013-01-01
The krypton-fluoride (KrF) laser is an attractive choice for inertial confinement fusion due to its combination of short wavelength (λ=248 nm), large bandwidth (up to 3 THz), and superior beam smoothing by induced spatial incoherence. These qualities improve the overall hydrodynamics of directly driven pellet implosions and should allow use of increased laser intensity due to higher thresholds for laser plasma instabilities when compared to frequency tripled Nd:glass lasers (λ=351 nm). Here, we report the first observations of the two-plasmon decay instability using a KrF laser. The experiments utilized the Nike laser facility to irradiate solid plastic planar targets over a range of pulse lengths (0.35 ns≤τ≤1.25 ns) and intensities (up to 2×10 15 W/cm 2 ). Variation of the laser pulse created different combinations of electron temperature and electron density scale length. The observed onset of instability growth was consistent with the expected scaling that KrF lasers have a higher intensity threshold for instabilities in the quarter critical density region.
Weaver, J. L.; Oh, J.; Phillips, L.; Afeyan, B.; Seely, J.; Kehne, D.; Brown, C. M.; Obenschain, S. P.; Serlin, V.; Schmitt, A. J.; Feldman, U.; Lehmberg, R. H.; Mclean, E.; Manka, C.
2013-02-01
The krypton-fluoride (KrF) laser is an attractive choice for inertial confinement fusion due to its combination of short wavelength (λ =248 nm), large bandwidth (up to 3 THz), and superior beam smoothing by induced spatial incoherence. These qualities improve the overall hydrodynamics of directly driven pellet implosions and should allow use of increased laser intensity due to higher thresholds for laser plasma instabilities when compared to frequency tripled Nd:glass lasers (λ =351 nm). Here, we report the first observations of the two-plasmon decay instability using a KrF laser. The experiments utilized the Nike laser facility to irradiate solid plastic planar targets over a range of pulse lengths (0.35 ns≤τ≤1.25 ns) and intensities (up to 2×1015 W/cm2). Variation of the laser pulse created different combinations of electron temperature and electron density scale length. The observed onset of instability growth was consistent with the expected scaling that KrF lasers have a higher intensity threshold for instabilities in the quarter critical density region.
Reshocks, rarefactions, and the generalized Layzer model for hydrodynamic instabilities
Energy Technology Data Exchange (ETDEWEB)
Mikaelian, K O
2008-06-10
We report numerical simulations and analytic modeling of shock tube experiments on Rayleigh-Taylor and Richtmyer-Meshkov instabilities. We examine single interfaces of the type A/B where the incident shock is initiated in A and the transmitted shock proceeds into B. Examples are He/air and air/He. In addition, we study finite-thickness or double-interface A/B/A configurations like air/SF{sub 6}/air gas-curtain experiments. We first consider conventional shock tubes that have a 'fixed' boundary: A solid endwall which reflects the transmitted shock and reshocks the interface(s). Then we focus on new experiments with a 'free' boundary--a membrane disrupted mechanically or by the transmitted shock, sending back a rarefaction towards the interface(s). Complex acceleration histories are achieved, relevant for Inertial Confinement Fusion implosions. We compare our simulation results with a generalized Layzer model for two fluids with time-dependent densities, and derive a new freeze-out condition whereby accelerating and compressive forces cancel each other out. Except for the recently reported failures of the Layzer model, the generalized Layzer model and hydrocode simulations for reshocks and rarefactions agree well with each other, and remain to be verified experimentally.
Radiofrequency ablation of pulmonary tumors
Energy Technology Data Exchange (ETDEWEB)
Crocetti, Laura, E-mail: l.crocetti@med.unipi.i [Division of Diagnostic Imaging and Intervention, Department of Liver Transplants, Hepatology and Infectious Diseases, Pisa University School of Medicine (Italy); Lencioni, Riccardo [Division of Diagnostic Imaging and Intervention, Department of Liver Transplants, Hepatology and Infectious Diseases, Pisa University School of Medicine (Italy)
2010-07-15
The development of image-guided percutaneous techniques for local tumor ablation has been one of the major advances in the treatment of solid tumors. Among these methods, radiofrequency (RF) ablation is currently established as the primary ablative modality at most institutions. RF ablation is accepted as the best therapeutic choice for patients with early-stage hepatocellular carcinoma when liver transplantation or surgical resection are not suitable options and is considered as a viable alternate to surgery for inoperable patients with limited hepatic metastatic disease, especially from colorectal cancer. Recently, RF ablation has been demonstrated to be a safe and valuable treatment option for patients with unresectable or medically inoperable lung malignancies. Resection should remain the standard therapy for non-small cell lung cancer (NSCLC) but RF ablation may be better than conventional external-beam radiation for the treatment of the high-risk individual with NSCLC. Initial favourable outcomes encourage combining radiotherapy and RF ablation, especially for treating larger tumors. In the setting of colorectal cancer lung metastases, survival rates provided by RF ablation in selected patients, are substantially higher than those obtained with any chemotherapy regimens and provide indirect evidence that RF ablation therapy improves survival in patients with limited lung metastatic disease.
Dynamo generated by the centrifugal instability
Marcotte, Florence; Gissinger, Christophe
2016-10-01
We present a scenario for magnetic field amplification where an electrically conducting fluid is confined in a differentially rotating, spherical shell with thin aspect ratio. When the angular momentum sufficiently decreases outwards, a hydrodynamic instability develops in the equatorial region, characterized by pairs of counter-rotating toroidal vortices similar to those observed in cylindrical Couette flow. These spherical Taylor-Couette vortices generate a subcritical dynamo magnetic field dominated by nonaxisymmetric components. We show that the critical magnetic Reynolds number seems to reach a constant value at large Reynolds number and that the global rotation can strongly decrease the dynamo onset. Our numerical results are understood within the framework of a simple dynamical system, and we propose a low-dimensional model for subcritical dynamo bifurcations. Implications for both laboratory dynamos and astrophysical magnetic fields are finally discussed.
Agrawal, Nidhi; Smith, Greg; Heffelfinger, Ryan
2014-02-01
Ablative laser resurfacing has evolved as a safe and effective treatment for skin rejuvenation. Although traditional lasers were associated with significant thermal damage and lengthy recovery, advances in laser technology have improved safety profiles and reduced social downtime. CO2 lasers remain the gold standard of treatment, and fractional ablative devices capable of achieving remarkable clinical improvement with fewer side effects and shorter recovery times have made it a more practical option for patients. Although ablative resurfacing has become safer, careful patient selection and choice of suitable laser parameters are essential to minimize complications and optimize outcomes. This article describes the current modalities used in ablative laser skin resurfacing and examines their efficacy, indications, and possible side effects. Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.
International Nuclear Information System (INIS)
Frenk, Nathan Elie; Sebastianes, Fernando; Lerario, Antonio Marcondes; Fragoso, Maria Candida Barisson Villares; Mendonca, Berenice Bilharinho
2016-01-01
Objectives: To evaluate the safety and long-term efficacy of computed tomography-guided percutaneous ethanol ablation for benign primary and secondary hyper functioning adrenal disorders. Method: We retrospectively evaluated the long-term results of nine patients treated with computed tomography guided percutaneous ethanol ablation: eight subjects who presented with primary adrenal disorders, such as pheochromocytoma, primary macro nodular adrenal hyperplasia and aldosterone-producing adenoma, and one subject with Cushing disease refractory to conventional treatment. Eleven sessions were performed for the nine patients. The patient data were reviewed for the clinical outcome and procedure-related complications over ten years. Results: Patients with aldosterone-producing adenoma had clinical improvement: symptoms recurred in one case 96 months after ethanol ablation, and the other patient was still in remission 110 months later. All patients with pheochromocytoma had clinical improvement but were eventually submitted to surgery for complete remission. No significant clinical improvement was seen in patients with hypercortisolism due to primary macro nodular adrenal hyperplasia or Cushing disease. Major complications were seen in five of the eleven procedures and included cardiovascular instability and myocardial infarction. Minor complications attributed to sedation were seen in two patients. Conclusion: Computed tomography-guided ethanol ablation does not appear to be suitable for the long-term treatment of hyper functioning adrenal disorders and is not without risks. (author)
Energy Technology Data Exchange (ETDEWEB)
Frenk, Nathan Elie; Sebastianes, Fernando; Lerario, Antonio Marcondes; Fragoso, Maria Candida Barisson Villares; Mendonca, Berenice Bilharinho [Universidade de Sao Paulo (USP), SP (Brazil). Faculdade de Medicina; Menezes, Marcos Roberto de, E-mail: menezesmr@gmail.com [Instituto do Cancer do Estado de Sao Paulo, SP (Brazil)
2016-10-15
Objectives: To evaluate the safety and long-term efficacy of computed tomography-guided percutaneous ethanol ablation for benign primary and secondary hyper functioning adrenal disorders. Method: We retrospectively evaluated the long-term results of nine patients treated with computed tomography guided percutaneous ethanol ablation: eight subjects who presented with primary adrenal disorders, such as pheochromocytoma, primary macro nodular adrenal hyperplasia and aldosterone-producing adenoma, and one subject with Cushing disease refractory to conventional treatment. Eleven sessions were performed for the nine patients. The patient data were reviewed for the clinical outcome and procedure-related complications over ten years. Results: Patients with aldosterone-producing adenoma had clinical improvement: symptoms recurred in one case 96 months after ethanol ablation, and the other patient was still in remission 110 months later. All patients with pheochromocytoma had clinical improvement but were eventually submitted to surgery for complete remission. No significant clinical improvement was seen in patients with hypercortisolism due to primary macro nodular adrenal hyperplasia or Cushing disease. Major complications were seen in five of the eleven procedures and included cardiovascular instability and myocardial infarction. Minor complications attributed to sedation were seen in two patients. Conclusion: Computed tomography-guided ethanol ablation does not appear to be suitable for the long-term treatment of hyper functioning adrenal disorders and is not without risks. (author)
Measurement of the Rayleigh-Taylor instability in targets driven by optically smoothed laser beams
International Nuclear Information System (INIS)
Desselberger, M.; Willi, O.; Savage, M.; Lamb, M.J.
1990-01-01
Growth rates of the Rayleigh-Taylor instability were measured in targets with imposed sinusoidal modulations irradiated by optically smoothed 0.53-μm laser beams. A hybrid optical smoothing technique utilizing induced-spatial-incoherence and random-phase-plate technology was used for the first time. The wave-number dependence and the nonlinear behavior of Rayleigh-Taylor growth were investigated by using targets with a range of modulation periodicities and depths. The results are compared to 2D hydrodynamic-code simulations
Energy Technology Data Exchange (ETDEWEB)
Casner, A.; Galmiche, D.; Huser, G.; Jadaud, J.P.; Richard, A.; Liberatore, S.; Vandenboomgaerde, M. [CEA Bruyeres-le-Chatel, 91 (France)
2009-07-01
The mastering of the development of hydrodynamic instabilities like Rayleigh-Taylor instabilities is an important milestone on the way to perform efficient laser implosions. The complexity of these instabilities implies an experimental validation of the theoretical models and their computer simulations. An experimental platform involving the Omega laser has allowed us to perform indirect drive with rugby-shaped hohlraums. The experiments have validated the growth of 2- and 3-dimensional initial defects as predicted by theory. We have shown that the 3-dimensional defect saturates for an higher amplitude than the 2-dimensional one does. The experiments have been made by using a plastic shell doped with Germanium (CH:Ge). (A.C.)
Contact Line Instability Caused by Air Rim Formation under Nonsplashing Droplets.
Pack, Min; Kaneelil, Paul; Kim, Hyoungsoo; Sun, Ying
2018-05-01
Drop impact is fundamental to various natural and industrial processes such as rain-induced soil erosion and spray-coating technologies. The recent discovery of the role of air entrainment between the droplet and the impacting surface has produced numerous works, uncovering the unique physics that correlates the air film dynamics with the drop impact outcomes. In this study, we focus on the post-failure air entrainment dynamics for We numbers well below the splash threshold under different ambient pressures and elucidate the interfacial instabilities formed by air entrainment at the wetting front of impacting droplets on perfectly smooth, viscous films of constant thickness. A high-speed total internal reflection microscopy technique accounting for the Fresnel reflection at the drop-air interface allows for in situ measurements of an entrained air rim at the wetting front. The presence of an air rim is found to be a prerequisite to the interfacial instability which is formed when the capillary pressure in the vicinity of the contact line can no longer balance the increasing gas pressure near the wetting front. A critical capillary number for the air rim formation is experimentally identified above which the wetting front becomes unstable where this critical capillary number inversely scales with the ambient pressure. The contact line instabilities at relatively low We numbers ( We ∼ O(10)) observed in this study provide insight into the conventional understanding of hydrodynamic instabilities under drop impact which usually require We ≫ 10.
Fermi-Pasta-Ulam recurrence and modulation instability
Kuznetsov, E. A.
2017-01-01
We give a qualitative conceptual explanation of the Fermi-Pasta-Ulam (FPU) like recurrence in the onedimensional focusing nonlinear Schrodinger equation (NLSE). The recurrence can be considered as a result of the nonlinear development of the modulation instability. All known exact localized solitary wave solutions describing propagation on the background of the modulationally unstable condensate show the recurrence to the condensate state after its interaction with solitons. The condensate state locally recovers its original form with the same amplitude but a different phase after soliton leave its initial region. Based on the integrability of the NLSE, we demonstrate that the FPU recurrence takes place not only for condensate, but also for a more general solution in the form of the cnoidal wave. This solution is periodic in space and can be represented as a solitonic lattice. That lattice reduces to isolated soliton solution in the limit of large distance between solitons. The lattice transforms into the condensate in the opposite limit of dense soliton packing. The cnoidal wave is also modulationally unstable due to soliton overlapping. The recurrence happens at the nonlinear stage of the modulation instability. Due to generic nature of the underlying mathematical model, the proposed concept can be applied across disciplines and nonlinear systems, ranging from optical communications to hydrodynamics.
Experimental study of the hydrodynamic instabilities occurring in boiling-water reactors
International Nuclear Information System (INIS)
Fabreca, S.
1964-10-01
The subjects is an experimental out-of pile loop study of the hydrodynamic oscillations occurring in boiling-water reactors. The study was carried out at atmospheric pressure and at pressure of about 8 atmospheres, in channels heated electrically by a constant and uniform specified current. In the test at 8 atmospheres the channel was a round tube of approximately 6 mm interior diameter. At 1 atmosphere a ring-section channel was used, 10 * 20 mm in diameter, with an inner heating tube and an outer tube of pyrex. It was possible to operate with natural convection and also with forced convection with test-channel by-pass. The study consists of 3 parts: 1. Preliminary determination of the laws governing pressure-drop during boiling. 2. Determination of the fronts at which oscillation appears, within a wide range of the parameters involved. 3. A descriptive study of the oscillations and measurement of the periods. The report gives the oscillation fronts with natural and forced convection for various values of the singular pressure drop at the channel inlet and for various riser lengths. The results are presented in non-dimensional form, which is available, in first approximation, for all geometric scales and for all fluids. Besides the following points were observed: - the wall (nature and thickness) can be an important factor ; - oscillation can occur in a horizontal channel. (author) [fr
Kinetic theory of the sausage instability of a z-pinch
International Nuclear Information System (INIS)
Isichenko, M.B.; Kulyabin, K.L.; Yan'kov, V.V.
1989-01-01
A linear problem of z-pinch sausage development is considered taking into account the influence of kinetic effects for ideal scanning current. Plasma electrons are considered to be cold and ions - collisionless. It is also supposed that the magnetic field inside a pinch doesn't affect the motion of ions, which are reflected like in a mirror from a jump of an electric potential arising on the plasma boundary. In case of long-wave perturbations ka >1 the acount of kinetics leads to considerable decrease of the increment [(ka) 1/2 times] in comparison with the hydrodynamic description, that permits to explain the increased instability of z-pinches observed in experiments
A hybrid-drive nonisobaric-ignition scheme for inertial confinement fusion
Energy Technology Data Exchange (ETDEWEB)
He, X. T., E-mail: xthe@iapcm.ac.cn [Institute of Applied Physics and Computational Mathematics, P. O. Box 8009, Beijing 100094 (China); Center for Applied Physics and Technology, HEDPS, Peking University, Beijing 100871 (China); IFSA Collaborative Innovation Center of MoE, Shanghai Jiao-Tong University, Shanghai 200240 (China); Institute of Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027 (China); Li, J. W.; Wang, L. F.; Liu, J.; Lan, K.; Ye, W. H. [Institute of Applied Physics and Computational Mathematics, P. O. Box 8009, Beijing 100094 (China); Center for Applied Physics and Technology, HEDPS, Peking University, Beijing 100871 (China); IFSA Collaborative Innovation Center of MoE, Shanghai Jiao-Tong University, Shanghai 200240 (China); Fan, Z. F.; Wu, J. F. [Institute of Applied Physics and Computational Mathematics, P. O. Box 8009, Beijing 100094 (China)
2016-08-15
A new hybrid-drive (HD) nonisobaric ignition scheme of inertial confinement fusion (ICF) is proposed, in which a HD pressure to drive implosion dynamics increases via increasing density rather than temperature in the conventional indirect drive (ID) and direct drive (DD) approaches. In this HD (combination of ID and DD) scheme, an assembled target of a spherical hohlraum and a layered deuterium-tritium capsule inside is used. The ID lasers first drive the shock to perform a spherical symmetry implosion and produce a large-scale corona plasma. Then, the DD lasers, whose critical surface in ID corona plasma is far from the radiation ablation front, drive a supersonic electron thermal wave, which slows down to a high-pressure electron compression wave, like a snowplow, piling up the corona plasma into high density and forming a HD pressurized plateau with a large width. The HD pressure is several times the conventional ID and DD ablation pressure and launches an enhanced precursor shock and a continuous compression wave, which give rise to the HD capsule implosion dynamics in a large implosion velocity. The hydrodynamic instabilities at imploding capsule interfaces are suppressed, and the continuous HD compression wave provides main pdV work large enough to hotspot, resulting in the HD nonisobaric ignition. The ignition condition and target design based on this scheme are given theoretically and by numerical simulations. It shows that the novel scheme can significantly suppress implosion asymmetry and hydrodynamic instabilities of current isobaric hotspot ignition design, and a high-gain ICF is promising.
Energy Technology Data Exchange (ETDEWEB)
Vu, Tran Manh; Park, Jeong; Kwon, Oh Boong; Bae, Dae Seok [School of Mechanical Engineering, Pukyong National University, San 100, Yongdang-dong, Nam-gu, Busan 608-739 (Korea); Yun, Jin Han; Keel, Sang In [Environment and Energy Research Division, Korea Institute of Machinery and Materials, 171 Jang-dong, Yuseong-gu, Daejeon 305-343 (Korea)
2010-04-15
Experiments were conducted in a constant pressure combustion chamber using schlieren system to investigate the effects of carbon dioxide-nitrogen-helium diluents on cellular instabilities of syngas-air premixed flames at room temperature and elevated pressures. The cellular instabilities for the diluted syngas-air flames were interpreted and evaluated in the viewpoint of the hydrodynamic and diffusional-thermal instabilities. Laminar burning velocities and Markstein lengths were calculated by analyzing high-speed schlieren images at various diluent concentrations and equivalence ratios. The measured unstretched laminar burning velocities were compared with the predicted results computed using the PREMIX code with the kinetic mechanism developed by Sun et al. Also, experimentally measured Peclet numbers were compared with the predicted results for fuel-lean flames. Experimental results showed substantial reduction of the laminar burning velocities and of the Markstein lengths with the diluent additions in the fuel blends. Effective Lewis numbers of helium-diluted syngas-air flames increased but those of carbon dioxide- and nitrogen-diluted syngas-air flames decreased in increase of diluents in the reactant mixtures. With helium diluent, the propensity for cells formation was significantly diminished, whereas the cellular instabilities for carbon dioxide- and nitrogen-diluted syngas-air flames were not suppressed. (author)
Metal shell technology based upon hollow jet instability
International Nuclear Information System (INIS)
Kendall, J.M.; Lee, M.C.; Wang, T.G.
1982-01-01
Spherical shells of submillimeter size are sought as ICF targets. Such shells must be dimensionally precise, smooth, of high strength, and composed of a high atomic number material. We describe a technology for the production of shells based upon the hydrodynamic instability of an annular jet of molten metal. We have produced shells in the 0.7--2.0 mm size range using tin as a test material. Specimens exhibit good sphericity, fair concentricity, and excellent finish over most of the surface. Work involving a gold--lead--antimony alloy is in progress. Droplets of this are amorphous and possess superior surface finish. The flow of tin models that of the alloy well; experiments on both metals show that the technique holds considerable promise
Exciting an Initially Cold Asteroid Belt Through a Planetary Instability
Deienno, Rogerio; Izidoro, Andre; Morbidelli, Alessandro; Gomes, Rodney; Nesvorny, David; Raymond, Sean N.
2018-04-01
The main asteroid belt (MB) is low in mass but dynamically excited, with much larger eccentricities and inclinations than the planets. In recent years, the Grand Tack model has been the predominant model capable of reconciling the formation of the terrestrial planets with a depleted but excited MB. Despite this success, the Grand Tack is still not generally accepted because of uncertainties in orbital migration. It was recently proposed that chaotic early evolution of Jupiter and Saturn could excite the initially cold MB. However, hydrodynamical simulations predict that the giant planets should generally emerge from the gas disk phase on orbits characterized by resonant and regular motion. Here we propose a new mechanism to excite the MB during the giant planets' ('Nice model') instability, which is expected to have included repeated close encounters between Jupiter and one or more ice giants ('Jumping Jupiter' -- JJ). We show that when Jupiter temporarily reaches a high enough level of excitation, both in eccentricity and inclination, it induces strong forced vectors of eccentricity and inclination within the MB region. Because during the JJ instability Jupiter's orbit 'jumps' around, forced vectors keep changing both in magnitude and phase throughout the whole MB region. The entire cold primordial MB can thus be excited as a natural outcome of the JJ instability. Furthermore, we show that the subsequent evolution of the Solar System is capable of reshaping the resultant MB to its present day orbital state, and that a strong mass depletion is always associated to the JJ instability phase.
Bakhsh, Abeer; Samtaney, Ravindra
2017-01-01
We investigate the linear stability of both positive and negative Atwood ratio interfaces accelerated either by a fast magnetosonic or hydrodynamic shock in cylindrical geometry. For the magnetohydrodynamic (MHD) case, we examine the role of an initial seed azimuthal magnetic field on the growth rate of the perturbation. In the absence of a magnetic field, the Richtmyer-Meshkov growth is followed by an exponentially increasing growth associated with the Rayleigh-Taylor instability. In the MHD case, the growth rate of the instability reduces in proportion to the strength of the applied magnetic field. The suppression mechanism is associated with the interference of two waves running parallel and anti-parallel to the interface that transport of vorticity and cause the growth rate to oscillate in time with nearly a zero mean value.
Bakhsh, Abeer
2017-11-17
We investigate the linear stability of both positive and negative Atwood ratio interfaces accelerated either by a fast magnetosonic or hydrodynamic shock in cylindrical geometry. For the magnetohydrodynamic (MHD) case, we examine the role of an initial seed azimuthal magnetic field on the growth rate of the perturbation. In the absence of a magnetic field, the Richtmyer-Meshkov growth is followed by an exponentially increasing growth associated with the Rayleigh-Taylor instability. In the MHD case, the growth rate of the instability reduces in proportion to the strength of the applied magnetic field. The suppression mechanism is associated with the interference of two waves running parallel and anti-parallel to the interface that transport of vorticity and cause the growth rate to oscillate in time with nearly a zero mean value.
SELF-DESTRUCTING SPIRAL WAVES: GLOBAL SIMULATIONS OF A SPIRAL-WAVE INSTABILITY IN ACCRETION DISKS
International Nuclear Information System (INIS)
Bae, Jaehan; Hartmann, Lee; Nelson, Richard P.; Richard, Samuel
2016-01-01
We present results from a suite of three-dimensional global hydrodynamic simulations that shows that spiral density waves propagating in circumstellar disks are unstable to the growth of a parametric instability that leads to break down of the flow into turbulence. This spiral wave instability (SWI) arises from a resonant interaction between pairs of inertial waves, or inertial-gravity waves, and the background spiral wave. The development of the instability in the linear regime involves the growth of a broad spectrum of inertial modes, with growth rates on the order of the orbital time, and results in a nonlinear saturated state in which turbulent velocity perturbations are of a similar magnitude to those induced by the spiral wave. The turbulence induces angular momentum transport and vertical mixing at a rate that depends locally on the amplitude of the spiral wave (we obtain a stress parameter α ∼ 5 × 10 −4 in our reference model). The instability is found to operate in a wide range of disk models, including those with isothermal or adiabatic equations of state, and in viscous disks where the dimensionless kinematic viscosity ν ≤ 10 −5 . This robustness suggests that the instability will have applications to a broad range of astrophysical disk-related phenomena, including those in close binary systems, planets embedded in protoplanetary disks (including Jupiter in our own solar system) and FU Orionis outburst models. Further work is required to determine the nature of the instability and to evaluate its observational consequences in physically more complete disk models than we have considered in this paper.
Dissipative relativistic hydrodynamics
International Nuclear Information System (INIS)
Imshennik, V.S.; Morozov, Yu.I.
1989-01-01
Using the comoving reference frame in the general non-inertial case, the relativistic hydrodynamics equations are derived with an account for dissipative effects in the matter. From the entropy production equation, the exact from for the dissipative tensor components is obtained. As a result, the closed system of equations of dissipative relativistic hydrodynamics is obtained in the comoving reference frame as a relativistic generalization of the known Navier-Stokes equations for Lagrange coordinates. Equations of relativistic hydrodynamics with account for dissipative effects in the matter are derived using the assocoated reference system in general non-inertial case. True form of the dissipative tensor components is obtained from entropy production equation. Closed system of equations for dissipative relativistic hydrodynamics is obtained as a result in the assocoated reference system (ARS) - relativistic generalization of well-known Navier-Stokes equations for Lagrange coordinates. Equation system, obtained in this paper for ARS, may be effectively used in numerical models of explosive processes with 10 51 erg energy releases which are characteristic for flashes of supernovae, if white dwarf type compact target suggested as presupernova
Shock wave, fluid instability and implosion studies with a kinetic particle approach
Sagert, Irina; Even, Wesley P.; Strother, Terrance T.
2016-10-01
Many problems in laboratory plasma physics are subject to flows that move between the continuum and the kinetic regime. The correct description of these flows is crucial in order to capture their impact on the system's dynamical evolution. Examples are capsule implosions in inertial confinement fusion (ICF). Although their dynamics is predominantly shaped by shock waves and fluid instabilities, non-equilibrium flows in form of deuterium/tritium ions have been shown to play a significant role. We present recent studies with our Monte Carlo kinetic particle code that is designed to capture continuum and kinetic flows in large physical systems with possible applications in ICF studies. Discussed results will include standard shock wave and fluid instability tests and simulations that are adapted towards future ICF studies with comparisons to hydrodynamic simulations. This work used the Wolf TriLAB Capacity Cluster at LANL. I.S. acknowledges support through a Director's fellowship (20150741PRD3) from Los Alamos National Laboratory.
Fluid-Elastic Instability of U-Tube Bundle in Air-Water Two-Phase Flow
International Nuclear Information System (INIS)
Chu, In Cheol; Lee, Chang Hee; Yun, Young Jung; Chung, Heung June
2007-03-01
Using steam generator U-tube flow-induced vibration test facility, the flow-induced vibration characteristics of U-tube in row 34-44 and line 71-77 were investigated. Air and water at room temperature and near atmospheric pressure were used as working fluids. In the present experiments, followings were evaluated under two-phase cross-flow condition: the fundamental vibration responses and the critical gap velocity for a fluid-elastic instability of U-tubes, the damping ratio and hydrodynamic mass of U-tubes. In addition, the fluid-elastic instability factor, K, was preliminary assessed using Connors' relation. In the case of the U-tubes which are not supported by partial egg-crate in OPR100 steam generator, it has been found that the vibration displacement of those U-tubes are highly possible to exceed the design limit even by a turbulent excitation mechanism. The damping ratio of U-tubes measured in the present experiments was significantly higher than the OPR1000 steam generator design value. The fluid-elastic instability factor of U-tube bundle obtained in the present experiments were preliminary evaluated to be mostly in the range of 6.5-10.5
Percutaneous thermal ablation of renal neoplasms
International Nuclear Information System (INIS)
Tacke, J.; Mahnken, A.H.; Guenther, R.W.
2005-01-01
Due to modern examination techniques such as multidetector computed tomography and high-field magnetic resonance imaging, the detection rate of renal neoplasms is continually increasing. Even though tumors exceeding 4 cm in diameter rarely metastasize, all renal lesions that are possible neoplasms should be treated. Traditional treatment techniques include radical nephrectomy or nephron-sparing resection, which are increasingly performed laparoscopically. Modern thermal ablation techniques such as hyperthermal techniques like radiofrequency ablation RFA, laser induced thermal ablation LITT, focused ultrasound FUS and microwave therapy MW, as well as hypothermal techniques (cryotherapy) may be a useful treatment option for patients who are unfit for or refuse surgical resection. Cryotherapy is the oldest and best known thermal ablation technique and can be performed laparoscopically or percutaneously. Since subzero temperatures have no antistyptic effect, additional maneuvers must be performed to control bleeding. Percutaneous cryotherapy of renal tumors is a new and interesting method, but experience with it is still limited. Radiofrequency ablation is the most frequently used method. Modern probe design allows volumes between 2 and 5 cm in diameter to be ablated. Due to hyperthermal tract ablation, the procedure is deemed to be safe and has a low complication rate. Although there are no randomized comparative studies to open resection, the preliminary results for renal RFA are promising and show RFA to be superior to other thermal ablation techniques. Clinical success rates are over 90% for both, cryo- and radiofrequency ablation. Whereas laser induced thermal therapy is established in hepatic ablation, experience is minimal with respect to renal application. For lesions of more than 2 cm in diameter, additional cooling catheters are required. MR thermometry offers temperature control during ablation. Microwave ablation is characterized by small ablation volumes
Luciano, Rezzolla
2013-01-01
Relativistic hydrodynamics is a very successful theoretical framework to describe the dynamics of matter from scales as small as those of colliding elementary particles, up to the largest scales in the universe. This book provides an up-to-date, lively, and approachable introduction to the mathematical formalism, numerical techniques, and applications of relativistic hydrodynamics. The topic is typically covered either by very formal or by very phenomenological books, but is instead presented here in a form that will be appreciated both by students and researchers in the field. The topics covered in the book are the results of work carried out over the last 40 years, which can be found in rather technical research articles with dissimilar notations and styles. The book is not just a collection of scattered information, but a well-organized description of relativistic hydrodynamics, from the basic principles of statistical kinetic theory, down to the technical aspects of numerical methods devised for the solut...
Theoretical and numerical study of Rayleigh-Taylor instabilities in magnetized plasmas
International Nuclear Information System (INIS)
Andrei, A. Ivanov
2001-06-01
In this thesis we're studying both the general case of the 'classic' Rayleigh-Taylor instability (in incompressible fluids) and more specific cases of the instabilities of Rayleigh-Taylor type in magnetized plasmas, in the liners or wire array implosions etc. We have studied the influence of the Hall diffusion of magnetic field on the growth rate of the instability. We have obtained in this work a self-similar solution for the widening of the initial profile of the magnetic field and for the wave of the penetration of magnetic field. After that the subsequent evolution of the magnetic field in plasma opening switches (POS) has been examined. We have shown the possibility of the existence of a strong rarefaction wave for collisional and non-collisional cases. This wave can explain the phenomenon of the opening of POS. The effect of the suppression of Rayleigh-Taylor instability by forced oscillations of the boundary between two fluids permits us to propose some ideas for the experiments of inertial fusion. We have considered the general case of the instability, in other words - two incompressible viscous superposed fluids in a gravitational field. We have obtained an exact analytical expression for the growth rate and then we have analyzed the influence of the parameters of external 'pumping' on the instability. These results can be applied to a wide range of systems, starting from classic hydrodynamics and up to astrophysical plasmas. The scheme of wire arrays has become recently a very popular method to obtain a high power X-radiation or for a high quality implosion in Z-pinches. The experimental studies have demonstrated that the results of implosion are much better for the case of multiple thin wires situated cylindrically than in a usual liner scheme. We have examined the problem modeling the stabilization of Rayleigh-Taylor instability for a wire array system. The reason for instability suppression is the regular spatial modulation of the surface plasma
Laboratory Simulations of Micrometeoroid Ablation
Thomas, Evan Williamson
Each day, several tons of meteoric material enters Earth's atmosphere, the majority of which consist of small dust particles (micrometeoroids) that completely ablate at high altitudes. The dust input has been suggested to play a role in a variety of phenomena including: layers of metal atoms and ions, nucleation of noctilucent clouds, effects on stratospheric aerosols and ozone chemistry, and the fertilization of the ocean with bio-available iron. Furthermore, a correct understanding of the dust input to the Earth provides constraints on inner solar system dust models. Various methods are used to measure the dust input to the Earth including satellite detectors, radar, lidar, rocket-borne detectors, ice core and deep-sea sediment analysis. However, the best way to interpret each of these measurements is uncertain, which leads to large uncertainties in the total dust input. To better understand the ablation process, and thereby reduce uncertainties in micrometeoroid ablation measurements, a facility has been developed to simulate the ablation of micrometeoroids in laboratory conditions. An electrostatic dust accelerator is used to accelerate iron particles to relevant meteoric velocities (10-70 km/s). The particles are then introduced into a chamber pressurized with a target gas, and they partially or completely ablate over a short distance. An array of diagnostics then measure, with timing and spatial resolution, the charge and light that is generated in the ablation process. In this thesis, we present results from the newly developed ablation facility. The ionization coefficient, an important parameter for interpreting meteor radar measurements, is measured for various target gases. Furthermore, experimental ablation measurements are compared to predictions from commonly used ablation models. In light of these measurements, implications to the broader context of meteor ablation are discussed.
Recent development of hydrodynamic modeling
Hirano, Tetsufumi
2014-09-01
In this talk, I give an overview of recent development in hydrodynamic modeling of high-energy nuclear collisions. First, I briefly discuss about current situation of hydrodynamic modeling by showing results from the integrated dynamical approach in which Monte-Carlo calculation of initial conditions, quark-gluon fluid dynamics and hadronic cascading are combined. In particular, I focus on rescattering effects of strange hadrons on final observables. Next I highlight three topics in recent development in hydrodynamic modeling. These include (1) medium response to jet propagation in di-jet asymmetric events, (2) causal hydrodynamic fluctuation and its application to Bjorken expansion and (3) chiral magnetic wave from anomalous hydrodynamic simulations. (1) Recent CMS data suggest the existence of QGP response to propagation of jets. To investigate this phenomenon, we solve hydrodynamic equations with source term which exhibits deposition of energy and momentum from jets. We find a large number of low momentum particles are emitted at large angle from jet axis. This gives a novel interpretation of the CMS data. (2) It has been claimed that a matter created even in p-p/p-A collisions may behave like a fluid. However, fluctuation effects would be important in such a small system. We formulate relativistic fluctuating hydrodynamics and apply it to Bjorken expansion. We found the final multiplicity fluctuates around the mean value even if initial condition is fixed. This effect is relatively important in peripheral A-A collisions and p-p/p-A collisions. (3) Anomalous transport of the quark-gluon fluid is predicted when extremely high magnetic field is applied. We investigate this possibility by solving anomalous hydrodynamic equations. We found the difference of the elliptic flow parameter between positive and negative particles appears due to the chiral magnetic wave. Finally, I provide some personal perspective of hydrodynamic modeling of high energy nuclear collisions
Squara, F; Theodore, G; Scarlatti, D; Ferrari, E
2017-02-01
We report the case of an 82-year-old man presenting with ventricular fibrillation (VF) occurring acutely after atrioventricular node (AVN) ablation. This patient had severe valvular cardiomyopathy, chronic atrial fibrillation (AF), and underwent prior to the AVN ablation a biventricular implantable cardiac defibrillator positioning. The VF was successfully cardioverted with one external electrical shock. What makes this presentation original is that the pre-ablation spontaneous heart rate in AF was slow (84 bpm), and that VF occurred after ablation despite a minimal heart rate drop of only 14 bpm. VF is the most feared complication of AVN ablation, but it had previously only been described in case of acute heart rate drop after ablation of at least 30 bpm (and more frequently>50 bpm). This case report highlights the fact that VF may occur after AVN ablation regardless of the heart rate drop, rendering temporary fast ventricular pacing mandatory whatever the pre-ablation heart rate. Copyright © 2016 Elsevier Masson SAS. All rights reserved.
Zhou, Wenhui; Arellano, Ronald S
2018-04-06
To evaluate perioperative outcomes of thermal ablation with microwave (MW), radiofrequency (RF), and cryoablation for stage T1c renal cell carcinoma (RCC). A retrospective analysis of 384 patients (mean age, 71 y; range, 22-88 y) was performed between October 2006 and October 2016. Mean radius, exophytic/endophytic, nearness to collecting system or sinus, anterior/posterior, and location relative to polar lines; preoperative aspects and dimensions used for anatomic classification; and centrality index scores were 6.3, 7.9, and 2.7, respectively. Assessment of pre- and postablation serum blood urea nitrogen, creatinine, and estimated glomerular filtration rate was performed to assess functional outcomes. Linear regression analyses were performed to compare sedation medication dosages among the three treatment cohorts. Univariable and multivariable logistic regression analyses were performed to compare rates of residual disease and complications among treatment modalities. A total of 437 clinical stage T1N0M0 biopsy-proven RCCs measuring 1.2-6.9 cm were treated with computed tomography (CT)-guided MW ablation (n = 44; 10%), RF ablation (n = 347; 79%), or cryoablation (n = 46; 11%). There were no significant differences in patient demographic or tumor characteristics among cohorts. Complication rates and immediate renal function changes were similar among the three ablation modalities (P = .46 and P = .08, respectively). MW ablation was associated with significantly decreased ablation time (P < .05), procedural time (P < .05), and dosage of sedative medication (P < .05) compared with RF ablation and cryoablation. CT-guided percutaneous MW ablation is comparable to RF ablation or cryoablation for the treatment of stage T1N0M0 RCC with regard to treatment response and is associated with shorter treatment times and less sedation than RF ablation or cryoablation. In addition, the safety profile of CT-guided MW ablation is noninferior to those of RF ablation or
Salvetti, Maria
2017-01-01
The book provides a detailed approach to the physics, fluid dynamics, modeling, experimentation and numerical simulation of cavitation phenomena, with special emphasis on cavitation-induced instabilities and their implications on the design and operation of high performance turbopumps and hydraulic turbines. The first part covers the fundamentals (nucleation, dynamics, thermodynamic effects, erosion) and forms of cavitation (attached cavitation, cloud cavitation, supercavitation, vortex cavitation) relevant to hydraulic turbomachinery, illustrates modern experimental techniques for the characterization, visualization and analysis of cavitating flows, and introduces the main aspects of the hydrodynamic design and performance of axial inducers, centrifugal turbopumps and hydo-turbines. The second part focuses on the theoretical modeling, experimental analysis, and practical control of cavitation-induced fluid-dynamic and rotordynamic instabilities of hydraulic turbomachinery, with special emphasis on cavitating...
Perioral Rejuvenation With Ablative Erbium Resurfacing.
Cohen, Joel L
2015-11-01
Since the introduction of the scanning full-field erbium laser, misconceptions regarding ablative erbium resurfacing have resulted in its being largely overshadowed by ablative fractional resurfacing. This case report illustrates the appropriateness of full-field erbium ablation for perioral resurfacing. A patient with profoundly severe perioral photodamage etched-in lines underwent full-field ablative perioral resurfacing with an erbium laser (Contour TRL, Sciton Inc., Palo Alto, CA) that allows separate control of ablation and coagulation. The pre-procedure consultations included evaluation of the severity of etched-in lines, and discussion of patient goals, expectations, and appropriate treatment options, as well as a review of patient photos and post-treatment care required. The author generally avoids full-field erbium ablation in patients with Fitzpatrick type IV and above. For each of 2 treatment sessions (separated by approximately 4 months), the patient received (12 cc plain 2% lidodaine) sulcus blocks before undergoing 4 passes with the erbium laser at 150 μ ablation, no coagulation, and then some very focal 30 μ ablation to areas of residual lines still visualized through the pinpoint bleeding. Similarly, full-field ablative resurfacing can be very reliable for significant wrinkles and creping in the lower eyelid skin--where often a single treatment of 80 μ ablation, 50 μ coagulation can lead to a nice improvement. Standardized digital imaging revealed significant improvement in deeply etched rhytides without significant adverse events. For appropriately selected patients requiring perioral (or periorbital) rejuvenation, full-field ablative erbium resurfacing is safe, efficacious and merits consideration.
Analysis of weakly nonlinear three-dimensional Rayleigh--Taylor instability growth
International Nuclear Information System (INIS)
Dunning, M.J.; Haan, S.W.
1995-01-01
Understanding the Rayleigh--Taylor instability, which develops at an interface where a low density fluid pushes and accelerates a higher density fluid, is important to the design, analysis, and ultimate performance of inertial confinement fusion targets. Existing experimental results measuring the growth of two-dimensional (2-D) perturbations (perturbations translationally invariant in one transverse direction) are adequately modeled using the 2-D hydrodynamic code LASNEX [G. B. Zimmerman and W. L. Kruer, Comments Plasma Phys. Controlled Fusion 11, 51 (1975)]. However, of ultimate interest is the growth of three-dimensional (3-D) perturbations such as those initiated by surface imperfections or illumination nonuniformities. Direct simulation of such 3-D experiments with all the significant physical processes included and with sufficient resolution is very difficult. This paper addresses how such experiments might be modeled. A model is considered that couples 2-D linear regime hydrodynamic code results with an analytic model to allow modeling of 3-D Rayleigh--Taylor growth through the linear regime and into the weakly nonlinear regime. The model is evaluated in 2-D by comparison with LASNEX results. Finally the model is applied to estimate the dynamics of a hypothetical 3-D foil
Hydrodynamic optical soliton tunneling
Sprenger, P.; Hoefer, M. A.; El, G. A.
2018-03-01
A notion of hydrodynamic optical soliton tunneling is introduced in which a dark soliton is incident upon an evolving, broad potential barrier that arises from an appropriate variation of the input signal. The barriers considered include smooth rarefaction waves and highly oscillatory dispersive shock waves. Both the soliton and the barrier satisfy the same one-dimensional defocusing nonlinear Schrödinger (NLS) equation, which admits a convenient dispersive hydrodynamic interpretation. Under the scale separation assumption of nonlinear wave (Whitham) modulation theory, the highly nontrivial nonlinear interaction between the soliton and the evolving hydrodynamic barrier is described in terms of self-similar, simple wave solutions to an asymptotic reduction of the Whitham-NLS partial differential equations. One of the Riemann invariants of the reduced modulation system determines the characteristics of a soliton interacting with a mean flow that results in soliton tunneling or trapping. Another Riemann invariant yields the tunneled soliton's phase shift due to hydrodynamic interaction. Soliton interaction with hydrodynamic barriers gives rise to effects that include reversal of the soliton propagation direction and spontaneous soliton cavitation, which further suggest possible methods of dark soliton control in optical fibers.
Hydrodynamic cavitation for sonochemical effects.
Moholkar, V S; Kumar, P S; Pandit, A B
1999-03-01
A comparative study of hydrodynamic and acoustic cavitation has been made on the basis of numerical solutions of the Rayleigh-Plesset equation. The bubble/cavity behaviour has been studied under both acoustic and hydrodynamic cavitation conditions. The effect of varying pressure fields on the collapse of the cavity (sinusoidal for acoustic and linear for hydrodynamic) and also on the latter's dynamic behaviour has been studied. The variations of parameters such as initial cavity size, intensity of the acoustic field and irradiation frequency in the case of acoustic cavitation, and initial cavity size, final recovery pressure and time for pressure recovery in the case of hydrodynamic cavitation, have been found to have significant effects on cavity/bubble dynamics. The simulations reveal that the bubble/cavity collapsing behaviour in the case of hydrodynamic cavitation is accompanied by a large number of pressure pulses of relatively smaller magnitude, compared with just one or two pulses under acoustic cavitation. It has been shown that hydrodynamic cavitation offers greater control over operating parameters and the resultant cavitation intensity. Finally, a brief summary of the experimental results on the oxidation of aqueous KI solution with a hydrodynamic cavitation set-up is given which supports the conclusion of this numerical study. The methodology presented allows one to manipulate and optimise of specific process, either physical or chemical.
Solitonic Dispersive Hydrodynamics: Theory and Observation
Maiden, Michelle D.; Anderson, Dalton V.; Franco, Nevil A.; El, Gennady A.; Hoefer, Mark A.
2018-04-01
Ubiquitous nonlinear waves in dispersive media include localized solitons and extended hydrodynamic states such as dispersive shock waves. Despite their physical prominence and the development of thorough theoretical and experimental investigations of each separately, experiments and a unified theory of solitons and dispersive hydrodynamics are lacking. Here, a general soliton-mean field theory is introduced and used to describe the propagation of solitons in macroscopic hydrodynamic flows. Two universal adiabatic invariants of motion are identified that predict trapping or transmission of solitons by hydrodynamic states. The result of solitons incident upon smooth expansion waves or compressive, rapidly oscillating dispersive shock waves is the same, an effect termed hydrodynamic reciprocity. Experiments on viscous fluid conduits quantitatively confirm the soliton-mean field theory with broader implications for nonlinear optics, superfluids, geophysical fluids, and other dispersive hydrodynamic media.
Energy Technology Data Exchange (ETDEWEB)
Sommer, C. M., E-mail: christof.sommer@med.uni-heidelberg.de [University Hospital Heidelberg, INF 110, Department of Diagnostic and Interventional Radiology (Germany); Lemm, G.; Hohenstein, E. [Minimally Invasive Therapies and Nuclear Medicine, SLK Kliniken Heilbronn GmbH, Clinic for Radiology (Germany); Bellemann, N.; Stampfl, U. [University Hospital Heidelberg, INF 110, Department of Diagnostic and Interventional Radiology (Germany); Goezen, A. S.; Rassweiler, J. [Clinic for Urology, SLK Kliniken Heilbronn GmbH (Germany); Kauczor, H. U.; Radeleff, B. A. [University Hospital Heidelberg, INF 110, Department of Diagnostic and Interventional Radiology (Germany); Pereira, P. L. [Minimally Invasive Therapies and Nuclear Medicine, SLK Kliniken Heilbronn GmbH, Clinic for Radiology (Germany)
2013-06-15
Purpose. This study was designed to evaluate the clinical efficacy of CT-guided bipolar and multipolar radiofrequency ablation (RF ablation) of renal cell carcinoma (RCC) and to analyze specific technical aspects between both technologies. Methods. We included 22 consecutive patients (3 women; age 74.2 {+-} 8.6 years) after 28 CT-guided bipolar or multipolar RF ablations of 28 RCCs (diameter 2.5 {+-} 0.8 cm). Procedures were performed with a commercially available RF system (Celon AG Olympus, Berlin, Germany). Technical aspects of RF ablation procedures (ablation mode [bipolar or multipolar], number of applicators and ablation cycles, overall ablation time and deployed energy, and technical success rate) were analyzed. Clinical results (local recurrence-free survival and local tumor control rate, renal function [glomerular filtration rate (GFR)]) and complication rates were evaluated. Results. Bipolar RF ablation was performed in 12 procedures and multipolar RF ablation in 16 procedures (2 applicators in 14 procedures and 3 applicators in 2 procedures). One ablation cycle was performed in 15 procedures and two ablation cycles in 13 procedures. Overall ablation time and deployed energy were 35.0 {+-} 13.6 min and 43.7 {+-} 17.9 kJ. Technical success rate was 100 %. Major and minor complication rates were 4 and 14 %. At an imaging follow-up of 15.2 {+-} 8.8 months, local recurrence-free survival was 14.4 {+-} 8.8 months and local tumor control rate was 93 %. GFR did not deteriorate after RF ablation (50.8 {+-} 16.6 ml/min/1.73 m{sup 2} before RF ablation vs. 47.2 {+-} 11.9 ml/min/1.73 m{sup 2} after RF ablation; not significant). Conclusions. CT-guided bipolar and multipolar RF ablation of RCC has a high rate of clinical success and low complication rates. At short-term follow-up, clinical efficacy is high without deterioration of the renal function.
Dhiman, Joginder Singh; Sharma, Rajni
2017-12-01
The effects of nonuniform rotation and magnetic field on the instability of a self gravitating infinitely extending axisymmetric cylinder of viscoelastic ferromagnetic medium have been studied using the Generalised Hydrodynamic (GH) model. The non-uniform magnetic field and rotation are acting along the axial direction of the cylinder and the propagation of the wave is considered along the radial direction, while the ferrofluid magnetization is taken collinear with the magnetic field. A general dispersion relation representing magnetization, magnetic permeability and viscoelastic relaxation time parameters is obtained using the normal mode analysis method in the linearized perturbation equation system. Jeans criteria which represent the onset of instability of self gravitating medium are obtained under the limits; when the medium behaves like a viscous liquid (strongly coupled limit) and a Newtonian liquid (weakly coupled limit). The effects of various parameters on the Jeans instability criteria and on the growth rate of self gravitating viscoelastic ferromagnetic medium have been discussed. It is found that the magnetic polarizability due to ferromagnetization of medium marginalizes the effect of non-uniform magnetic field on the Jeans instability, whereas the viscoelasticity of the medium has the usual stabilizing effect on the instability of the system. Further, it is found that the cylindrical geometry is more stable than the Cartesian one. The variation of growth rate against the wave number and radial distance has been depicted graphically.
Doyon, Benjamin; Dubail, Jérôme; Konik, Robert; Yoshimura, Takato
2017-11-01
The theory of generalized hydrodynamics (GHD) was recently developed as a new tool for the study of inhomogeneous time evolution in many-body interacting systems with infinitely many conserved charges. In this Letter, we show that it supersedes the widely used conventional hydrodynamics (CHD) of one-dimensional Bose gases. We illustrate this by studying "nonlinear sound waves" emanating from initial density accumulations in the Lieb-Liniger model. We show that, at zero temperature and in the absence of shocks, GHD reduces to CHD, thus for the first time justifying its use from purely hydrodynamic principles. We show that sharp profiles, which appear in finite times in CHD, immediately dissolve into a higher hierarchy of reductions of GHD, with no sustained shock. CHD thereon fails to capture the correct hydrodynamics. We establish the correct hydrodynamic equations, which are finite-dimensional reductions of GHD characterized by multiple, disjoint Fermi seas. We further verify that at nonzero temperature, CHD fails at all nonzero times. Finally, we numerically confirm the emergence of hydrodynamics at zero temperature by comparing its predictions with a full quantum simulation performed using the NRG-TSA-abacus algorithm. The analysis is performed in the full interaction range, and is not restricted to either weak- or strong-repulsion regimes.
Water spray assisted ultrashort laser pulse ablation
International Nuclear Information System (INIS)
Silvennoinen, M.; Kaakkunen, J.J.J.; Paivasaari, K.; Vahimaa, P.
2013-01-01
Highlights: ► We show the novel method to use multibeam processing with ultrashort pulses efficiently. ► Sprayed thin water layer on ablation zone enhances ablation rate and quality. ► In some cases this method also enables ablation of the deeper and straighter holes compared to ones made without the water layer. ► Method also makes possible to directly write features without the self-organizing structures. - Abstract: We have studied femtosecond ablation under sprayed thin water film and its influence and benefits compared with ablation in the air atmosphere. These have been studied in case of the hole and the groove ablation using IR femtosecond laser. Water enhances the ablation rate and in some situations it makes possible to ablate the holes with a higher aspect ratio. While ablating the grooves, the water spray allows using the high fluences without the generation of the self-organized structures.
Hydrodynamic escape from planetary atmospheres
Tian, Feng
Hydrodynamic escape is an important process in the formation and evolution of planetary atmospheres. Due to the existence of a singularity point near the transonic point, it is difficult to find transonic steady state solutions by solving the time-independent hydrodynamic equations. In addition to that, most previous works assume that all energy driving the escape flow is deposited in one narrow layer. This assumption not only results in less accurate solutions to the hydrodynamic escape problem, but also makes it difficult to include other chemical and physical processes in the hydrodynamic escape models. In this work, a numerical model describing the transonic hydrodynamic escape from planetary atmospheres is developed. A robust solution technique is used to solve the time dependent hydrodynamic equations. The method has been validated in an isothermal atmosphere where an analytical solution is available. The hydrodynamic model is applied to 3 cases: hydrogen escape from small orbit extrasolar planets, hydrogen escape from a hydrogen rich early Earth's atmosphere, and nitrogen/methane escape from Pluto's atmosphere. Results of simulations on extrasolar planets are in good agreement with the observations of the transiting extrasolar planet HD209458b. Hydrodynamic escape of hydrogen from other hypothetical close-in extrasolar planets are simulated and the influence of hydrogen escape on the long-term evolution of these extrasolar planets are discussed. Simulations on early Earth suggest that hydrodynamic escape of hydrogen from a hydrogen rich early Earth's atmosphere is about two orders magnitude slower than the diffusion limited escape rate. A hydrogen rich early Earth's atmosphere could have been maintained by the balance between the hydrogen escape and the supply of hydrogen into the atmosphere by volcanic outgassing. Origin of life may have occurred in the organic soup ocean created by the efficient formation of prebiotic molecules in the hydrogen rich early
International Nuclear Information System (INIS)
Kim, Young Sun; Rhim, Hyun Chul; Koh, Byung Hee; Cho, On Koo; Seo, Heung Suk; Kim, Yong Soo; Joo, Kyoung Bin
2001-01-01
To assess the effect of ethanol infusion on the size of ablated lesion during radiofrequency (RF) thermal ablation. We performed an ex vivo experimental study using a total of 15 pig livers. Three groups were designed: 1)normal control (n=10), 2) saline infusion (n=10) 3) ethanol infusion (n=10). Two radiofrequency ablations were done using a 50 watt RF generator and a 15 guage expandable elections with four prongs in each liver. During ablation for 8 minutes, continuous infusion of fluid at a rate of 0.5 ml/min through the side arm of electrode was performed. We checked the frequency of the 'impeded-out' phenomenon due to abrupt increase of impedance during ablation. Size of ablated lesion was measured according to length, width, height, and subsequently volume after the ablations. The sizes of the ablated lesions were compared between the three groups. 'Impeded-out' phenomenon during ablation was noted 4 times in control group, although that never happened in saline or ethanol infusion groups. There were significant differences in the volumes of ablated lesions between control group (10.62 ± 1.45 cm 3 ) and saline infusion group (15.33 ± 2.47 cm 3 ), and saline infusion group and ethanol infusion group (18.78 ± 3.58 cm 3 ) (p<0.05). Fluid infusion during radiofrequency thermal ablation decrease a chance of charming and increase the volume of the ablated lesion. Ethanol infusion during ablation may induce larger volume of ablated lesion than saline infusion.
Instability of the cored barotropic disc: the linear eigenvalue formulation
Polyachenko, E. V.
2018-05-01
Gaseous rotating razor-thin discs are a testing ground for theories of spiral structure that try to explain appearance and diversity of disc galaxy patterns. These patterns are believed to arise spontaneously under the action of gravitational instability, but calculations of its characteristics in the gas are mostly obscured. The paper suggests a new method for finding the spiral patterns based on an expansion of small amplitude perturbations over Lagrange polynomials in small radial elements. The final matrix equation is extracted from the original hydrodynamical equations without the use of an approximate theory and has a form of the linear algebraic eigenvalue problem. The method is applied to a galactic model with the cored exponential density profile.
Squire, Jonathan; Hopkins, Philip F.
2018-04-01
We identify and study a number of new, rapidly growing instabilities of dust grains in protoplanetary disks, which may be important for planetesimal formation. The study is based on the recognition that dust-gas mixtures are generically unstable to a Resonant Drag Instability (RDI), whenever the gas, absent dust, supports undamped linear modes. We show that the "streaming instability" is an RDI associated with epicyclic oscillations; this provides simple interpretations for its mechanisms and accurate analytic expressions for its growth rates and fastest-growing wavelengths. We extend this analysis to more general dust streaming motions and other waves, including buoyancy and magnetohydrodynamic oscillations, finding various new instabilities. Most importantly, we identify the disk "settling instability," which occurs as dust settles vertically into the midplane of a rotating disk. For small grains, this instability grows many orders of magnitude faster than the standard streaming instability, with a growth rate that is independent of grain size. Growth timescales for realistic dust-to-gas ratios are comparable to the disk orbital period, and the characteristic wavelengths are more than an order of magnitude larger than the streaming instability (allowing the instability to concentrate larger masses). This suggests that in the process of settling, dust will band into rings then filaments or clumps, potentially seeding dust traps, high-metallicity regions that in turn seed the streaming instability, or even overdensities that coagulate or directly collapse to planetesimals.
A hydrodynamic formalism for Brownian systems
International Nuclear Information System (INIS)
Pina, E.; Rosales, M.A.
1981-01-01
A formal hydrodynamic approach to Brownian motion is presented and the corresponding equations are derived. Hydrodynamic quantities are expressed in terms of the physical variables characterizing the Brownian systems. Contact is made with the hydrodynamic model of Quantum Mechanics. (author)
SELF-DESTRUCTING SPIRAL WAVES: GLOBAL SIMULATIONS OF A SPIRAL-WAVE INSTABILITY IN ACCRETION DISKS
Energy Technology Data Exchange (ETDEWEB)
Bae, Jaehan; Hartmann, Lee [Department of Astronomy, University of Michigan, 1085 S. University Ave., Ann Arbor, MI 48109 (United States); Nelson, Richard P.; Richard, Samuel, E-mail: jaehbae@umich.edu, E-mail: lhartm@umich.edu, E-mail: r.p.nelson@qmul.ac.uk, E-mail: samuel.richard@qmul.ac.uk [Astronomy Unit, Queen Mary University of London, Mile End Road, London E1 4NS (United Kingdom)
2016-09-20
We present results from a suite of three-dimensional global hydrodynamic simulations that shows that spiral density waves propagating in circumstellar disks are unstable to the growth of a parametric instability that leads to break down of the flow into turbulence. This spiral wave instability (SWI) arises from a resonant interaction between pairs of inertial waves, or inertial-gravity waves, and the background spiral wave. The development of the instability in the linear regime involves the growth of a broad spectrum of inertial modes, with growth rates on the order of the orbital time, and results in a nonlinear saturated state in which turbulent velocity perturbations are of a similar magnitude to those induced by the spiral wave. The turbulence induces angular momentum transport and vertical mixing at a rate that depends locally on the amplitude of the spiral wave (we obtain a stress parameter α ∼ 5 × 10{sup −4} in our reference model). The instability is found to operate in a wide range of disk models, including those with isothermal or adiabatic equations of state, and in viscous disks where the dimensionless kinematic viscosity ν ≤ 10{sup −5}. This robustness suggests that the instability will have applications to a broad range of astrophysical disk-related phenomena, including those in close binary systems, planets embedded in protoplanetary disks (including Jupiter in our own solar system) and FU Orionis outburst models. Further work is required to determine the nature of the instability and to evaluate its observational consequences in physically more complete disk models than we have considered in this paper.
Energy Technology Data Exchange (ETDEWEB)
Peralta, Pedro [Arizona State Univ., Tempe, AZ (United States); Fortin, Elizabeth [Arizona State Univ., Tempe, AZ (United States); Opie, Saul [Arizona State Univ., Tempe, AZ (United States); Gautam, Sudrishti [Arizona State Univ., Tempe, AZ (United States); Gopalakrishnan, Ashish [Arizona State Univ., Tempe, AZ (United States); Lynch, Jenna [Arizona State Univ., Tempe, AZ (United States); Chen, Yan [Arizona State Univ., Tempe, AZ (United States); Loomis, Eric [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2017-03-01
Activities for this grant included: 1) Development of dynamic impact experiments to probe strength and phase transition influence on dynamic deformation, 2) development of modern strength and phase aware simulation capabilities, 3) and post-processing of experimental data with simulation and closed form analytical techniques. Two different dynamic experiments were developed to probe material strengths in solid metals (largely copper and iron in this effort). In the first experiment a flyer plate impacts a flat target with an opposite rippled surface that is partially supported by a weaker window material. Post mortem analysis of the target sample showed a strong and repeatable residual plastic deformation dependence on grain orientation. Yield strengths for strain rates near 10^{5} s^{-1} and plastic strains near ~50% were estimated to be around 180 to 240 MPa, varying in this range with grain orientation. Unfortunately dynamic real-time measurements were difficult with this setup due to diagnostic laser scattering; hence, an additional experimental setup was developed to complement these results. In the second set of experiments a rippled surface was ablated by a controlled laser pulsed, which launched a rippled shock front to an opposite initially flat diagnostic surface that was monitored in real-time with spatially resolved velocimetry techniques, e.g., line VISAR in addition to Transient Imaging Displacement Interferometry (TIDI) displacement measurements. This setup limited the displacements at the diagnostic surface to a reasonable level for TIDI measurements (~ less than one micrometer). These experiments coupled with analytical and numerical solutions provided evidence that viscous and elastic deviatoric strength affect shock front perturbation evolution in clearly different ways. Particularly, normalized shock front perturbation amplitudes evolve with viscosity (η) and perturbation wavelength (λ) as η/λ, such that increasing viscosity
Ablation of Solid Hydrogen in a Plasma
DEFF Research Database (Denmark)
Jørgensen, L. W.; Sillesen, Alfred Hegaard
1979-01-01
Several hydrogen pellet ablation models based on the formation of a shielding neutral cloud have been reported by different authors. The predicted ablation rates are shown to follow almost the same scaling law and this is used to explain the authors' ablation experiment.......Several hydrogen pellet ablation models based on the formation of a shielding neutral cloud have been reported by different authors. The predicted ablation rates are shown to follow almost the same scaling law and this is used to explain the authors' ablation experiment....
International Nuclear Information System (INIS)
Sommer, C. M.; Lemm, G.; Hohenstein, E.; Bellemann, N.; Stampfl, U.; Goezen, A. S.; Rassweiler, J.; Kauczor, H. U.; Radeleff, B. A.; Pereira, P. L.
2013-01-01
Purpose. This study was designed to evaluate the clinical efficacy of CT-guided bipolar and multipolar radiofrequency ablation (RF ablation) of renal cell carcinoma (RCC) and to analyze specific technical aspects between both technologies. Methods. We included 22 consecutive patients (3 women; age 74.2 ± 8.6 years) after 28 CT-guided bipolar or multipolar RF ablations of 28 RCCs (diameter 2.5 ± 0.8 cm). Procedures were performed with a commercially available RF system (Celon AG Olympus, Berlin, Germany). Technical aspects of RF ablation procedures (ablation mode [bipolar or multipolar], number of applicators and ablation cycles, overall ablation time and deployed energy, and technical success rate) were analyzed. Clinical results (local recurrence-free survival and local tumor control rate, renal function [glomerular filtration rate (GFR)]) and complication rates were evaluated. Results. Bipolar RF ablation was performed in 12 procedures and multipolar RF ablation in 16 procedures (2 applicators in 14 procedures and 3 applicators in 2 procedures). One ablation cycle was performed in 15 procedures and two ablation cycles in 13 procedures. Overall ablation time and deployed energy were 35.0 ± 13.6 min and 43.7 ± 17.9 kJ. Technical success rate was 100 %. Major and minor complication rates were 4 and 14 %. At an imaging follow-up of 15.2 ± 8.8 months, local recurrence-free survival was 14.4 ± 8.8 months and local tumor control rate was 93 %. GFR did not deteriorate after RF ablation (50.8 ± 16.6 ml/min/1.73 m 2 before RF ablation vs. 47.2 ± 11.9 ml/min/1.73 m 2 after RF ablation; not significant). Conclusions. CT-guided bipolar and multipolar RF ablation of RCC has a high rate of clinical success and low complication rates. At short-term follow-up, clinical efficacy is high without deterioration of the renal function.
Influence of ablation wavelength and time on optical properties of laser ablated carbon dots
Isnaeni, Hanna, M. Yusrul; Pambudi, A. A.; Murdaka, F. H.
2017-01-01
Carbon dots, which are unique and applicable materials, have been produced using many techniques. In this work, we have fabricated carbon dots made of coconut fiber using laser ablation technique. The purpose of this work is to evaluate two ablation parameters, which are ablation wavelength and ablation time. We used pulsed laser from Nd:YAG laser with emit wavelength at 355 nm, 532 nm and 1064 nm. We varied ablation time one hour and two hours. Photoluminescence and time-resolved photoluminescence setup were used to study the optical properties of fabricated carbon dots. In general, fabricated carbon dots emit bluish green color emission upon excitation by blue laser. We found that carbon dots fabricated using 1064 nm laser produced the highest carbon dots emission among other samples. The peak wavelength of carbon dots emission is between 495 nm until 505 nm, which gives bluish green color emission. Two hours fabricated carbon dots gave four times higher emission than one hour fabricated carbon dot. More emission intensity of carbon dots means more carbon dots nanoparticles were fabricated during laser ablation process. In addition, we also measured electron dynamics of carbon dots using time-resolved photoluminescence. We found that sample with higher emission has longer electron decay time. Our finding gives optimum condition of carbon dots fabrication from coconut fiber using laser ablation technique. Moreover, fabricated carbon dots are non-toxic nanoparticles that can be applied for health, bio-tagging and medical applications.
International Nuclear Information System (INIS)
Baladi, Arash; Sarraf Mamoory, Rasoul
2010-01-01
Aluminum nanoparticles were synthesized by pulsed laser ablation of Al targets in ethanol, acetone, and ethylene glycol. Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM) images, Particle size distribution diagram from Laser Particle Size Analyzer (LPSA), UV-visible absorption spectra, and weight changes of targets were used for the characterization and comparison of products. The experiments demonstrated that ablation efficiency in ethylene glycol is too low, in ethanol is higher, and in acetone is highest. Comparison between ethanol and acetone clarified that acetone medium leads to finer nanoparticles (mean diameter of 30 nm) with narrower size distribution (from 10 to 100 nm). However, thin carbon layer coats some of them, which was not observed in ethanol medium. It was also revealed that higher ablation time resulted in higher ablated mass, but lower ablation rate. Finer nanoparticles, moreover, were synthesized in higher ablation times.
Energy Technology Data Exchange (ETDEWEB)
Baladi, Arash [Materials Engineering Department, Tarbiat Modares University, Jalal Al Ahmad, P.O. Box 14115-143, Tehran (Iran, Islamic Republic of); Sarraf Mamoory, Rasoul, E-mail: rsarrafm@modares.ac.ir [Materials Engineering Department, Tarbiat Modares University, Jalal Al Ahmad, P.O. Box 14115-143, Tehran (Iran, Islamic Republic of)
2010-10-01
Aluminum nanoparticles were synthesized by pulsed laser ablation of Al targets in ethanol, acetone, and ethylene glycol. Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM) images, Particle size distribution diagram from Laser Particle Size Analyzer (LPSA), UV-visible absorption spectra, and weight changes of targets were used for the characterization and comparison of products. The experiments demonstrated that ablation efficiency in ethylene glycol is too low, in ethanol is higher, and in acetone is highest. Comparison between ethanol and acetone clarified that acetone medium leads to finer nanoparticles (mean diameter of 30 nm) with narrower size distribution (from 10 to 100 nm). However, thin carbon layer coats some of them, which was not observed in ethanol medium. It was also revealed that higher ablation time resulted in higher ablated mass, but lower ablation rate. Finer nanoparticles, moreover, were synthesized in higher ablation times.
Energy Technology Data Exchange (ETDEWEB)
McEachen, James C., E-mail: james.mceachen2@gmail.com [Mayo Clinic, Division of Preventive, Occupational, and Aerospace Medicine (United States); Leng, Shuai; Atwell, Thomas D. [Mayo Clinic, Department of Radiology (United States); Tollefson, Matthew K. [Mayo Clinic, Department of Urology (United States); Friese, Jeremy L. [Mayo Clinic, Department of Radiology (United States); Wang, Zhen; Murad, M. Hassan [Mayo Clinic, Division of Preventive, Occupational, and Aerospace Medicine (United States); Schmit, Grant D. [Mayo Clinic, Department of Radiology (United States)
2016-02-15
IntroductionOnce reserved solely for non-surgical cases, percutaneous ablation is becoming an increasingly popular treatment option for a wider array of patients with small renal masses and the radiation risk needs to be better defined as this transition continues.Materials and MethodsRetrospective review of our renal tumor ablation database revealed 425 patients who underwent percutaneous ablation for treatment of 455 renal tumors over a 5-year time period. Imparted radiation dose information was reviewed for each procedure and converted to effective patient dose and skin dose using established techniques. Statistical analysis was performed with each ablative technique.ResultsFor the 331 cryoablation procedures, the mean DLP was 6987 mGycm (SD = 2861) resulting in a mean effective dose of 104.7 mSv (SD = 43.5) and the mean CTDI{sub vol} was 558 mGy (SD = 439) resulting in a mean skin dose of 563.2 mGy (SD = 344.1). For the 124 RFA procedures, the mean DLP was 3485 mGycm (SD = 1630) resulting in a mean effective dose of 50.3 mSv (SD = 24.0) and the mean CTDI{sub vol} was 232 mGy (SD = 149) resulting in a mean skin dose of 233.2 mGy (SD = 117.4). The difference in patient radiation exposure between the two renal ablation techniques was statistically significant (p < 0.001).ConclusionBoth cryoablation and RFA imparted an average skin dose that was well below the 2 Gy deterministic threshold for appreciable sequela. Renal tumor cryoablation resulted in a mean skin and effective radiation dose more than twice that for RFA. The radiation exposure for both renal tumor ablation techniques was at the high end of the medical imaging radiation dose spectrum.
Energy Technology Data Exchange (ETDEWEB)
Barrios, M. A.; Liedahl, D. A.; Schneider, M. B.; Jones, O.; Brown, G. V.; Fournier, K. B.; Moore, A. S.; Ross, J. S.; Landen, O.; Kauffman, R. L.; Nikroo, A.; Kroll, J.; Callahan, D. A.; Hinkel, D. E.; Bradley, D.; Moody, J. D. [Lawrence Livermore National Laboratory, Livermore, California 94551 (United States); Regan, S. P. [Laboratory for Laser Energetics, Rochester, New York 14623 (United States); Jaquez, J.; Huang, H. [General Atomics, San Diego, California 92121 (United States); Hansen, S. B. [Sandia National Laboratories, Albuquerque, New Mexico 87123 (United States)
2016-05-15
The first measurement of the electron temperature (T{sub e}) inside a National Ignition Facility hohlraum is obtained using temporally resolved K-shell X-ray spectroscopy of a mid-Z tracer dot. Both isoelectronic- and interstage-line ratios are used to calculate the local T{sub e} via the collisional–radiative atomic physics code SCRAM [Hansen et al., High Energy Density Phys 3, 109 (2007)]. The trajectory of the mid-Z dot as it is ablated from the capsule surface and moves toward the laser entrance hole (LEH) is measured using side-on x-ray imaging, characterizing the plasma flow of the ablating capsule. Data show that the measured dot location is farther away from the LEH in comparison to the radiation-hydrodynamics simulation prediction using HYDRA [Marinak et al., Phys. Plasmas 3, 2070 (1996)]. To account for this discrepancy, the predicted simulation T{sub e} is evaluated at the measured dot trajectory. The peak T{sub e}, measured to be 4.2 keV ± 0.2 keV, is ∼0.5 keV hotter than the simulation prediction.
Xie, Beibei; Yang, Dong; Xie, Haiyan; Nie, Xin; Liu, Wanyu
2016-08-01
In order to expand the study on flow instability of supercritical circulating fluidized bed (CFB) boiler, a new numerical computational model considering the heat storage of the tube wall metal was presented in this paper. The lumped parameter method was proposed for wall temperature calculation and the single channel model was adopted for the analysis of flow instability. Based on the time-domain method, a new numerical computational program suitable for the analysis of flow instability in the water wall of supercritical CFB boiler with annular furnace was established. To verify the code, calculation results were respectively compared with data of commercial software. According to the comparisons, the new code was proved to be reasonable and accurate for practical engineering application in analysis of flow instability. Based on the new program, the flow instability of supercritical CFB boiler with annular furnace was simulated by time-domain method. When 1.2 times heat load disturbance was applied on the loop, results showed that the inlet flow rate, outlet flow rate and wall temperature fluctuated with time eventually remained at constant values, suggesting that the hydrodynamic flow was stable. The results also showed that in the case of considering the heat storage, the flow in the water wall is easier to return to stable state than without considering heat storage.
How to fake hydrodynamic signals
Energy Technology Data Exchange (ETDEWEB)
Romatschke, Paul [Department of Physics, 390 UCB, University of Colorado at Boulder, Boulder, CO (United States); Center for Theory of Quantum Matter, University of Colorado, Boulder, CO 80309 (United States)
2016-12-15
Flow signatures in experimental data from relativistic ion collisions, are usually interpreted as a fingerprint of the presence of a hydrodynamic phase during the evolution of these systems. I review some theoretical ideas to ‘fake’ this hydrodynamic behavior in p+A and A+A collisions. I find that transverse flow and femtoscopic measurements can easily be forged through non-hydrodynamic evolution, while large elliptic flow requires some non-vanishing interactions in the hot phase.
International Nuclear Information System (INIS)
Boss, Alan P.
2009-01-01
The disk instability mechanism for giant planet formation is based on the formation of clumps in a marginally gravitationally unstable protoplanetary disk, which must lose thermal energy through a combination of convection and radiative cooling if they are to survive and contract to become giant protoplanets. While there is good observational support for forming at least some giant planets by disk instability, the mechanism has become theoretically contentious, with different three-dimensional radiative hydrodynamics codes often yielding different results. Rigorous code testing is required to make further progress. Here we present two new analytical solutions for radiative transfer in spherical coordinates, suitable for testing the code employed in all of the Boss disk instability calculations. The testing shows that the Boss code radiative transfer routines do an excellent job of relaxing to and maintaining the analytical results for the radial temperature and radiative flux profiles for a spherical cloud with high or moderate optical depths, including the transition from optically thick to optically thin regions. These radial test results are independent of whether the Eddington approximation, diffusion approximation, or flux-limited diffusion approximation routines are employed. The Boss code does an equally excellent job of relaxing to and maintaining the analytical results for the vertical (θ) temperature and radiative flux profiles for a disk with a height proportional to the radial distance. These tests strongly support the disk instability mechanism for forming giant planets.
International Nuclear Information System (INIS)
Amanifard, N.; Haghighat Namini, V.
2012-01-01
In this study a Modified Compressible Smoothed Particle Hydrodynamics method is introduced which is applicable in problems involving shock wave structures and elastic-plastic deformations of solids. As a matter of fact, algorithm of the method is based on an approach which descritizes the momentum equation into three parts and solves each part separately and calculates their effects on the velocity field and displacement of particles. The most exclusive feature of the method is exactly removing artificial viscosity of the formulations and representing good compatibility with other reasonable numerical methods without any rigorous numerical fractures or tensile instabilities while Modified Compressible Smoothed Particle Hydrodynamics does not use any extra modifications. Two types of problems involving elastic-plastic deformations and shock waves are presented here to demonstrate the capability of Modified Compressible Smoothed Particle Hydrodynamics in simulation of such problems and its ability to capture shock. The problems that are proposed here are low and high velocity impacts between aluminum projectiles and semi infinite aluminum beams. Elastic-perfectly plastic model is chosen for constitutive model of the aluminum and the results of simulations are compared with other reasonable studies in these cases.
SECULAR GRAVITATIONAL INSTABILITY OF A DUST LAYER IN SHEAR TURBULENCE
International Nuclear Information System (INIS)
Michikoshi, Shugo; Kokubo, Eiichiro; Inutsuka, Shu-ichiro
2012-01-01
We perform a linear stability analysis of a dust layer in a turbulent gas disk. Youdin investigated the secular gravitational instability (GI) of a dust layer using hydrodynamic equations with a turbulent diffusion term. We obtain essentially the same result independently of Youdin. In the present analysis, we restrict the area of interest to small dust particles, while investigating the secular GI in a more rigorous manner. We discuss the time evolution of the dust surface density distribution using a stochastic model and derive the advection-diffusion equation. The validity of the analysis by Youdin is confirmed in the strong drag limit. We demonstrate quantitatively that the finite thickness of a dust layer weakens the secular GI and that the density-dependent diffusion coefficient changes the growth rate. We apply the results obtained to the turbulence driven by the shear instability and find that the secular GI is faster than the radial drift when the gas density is three times as large as that in the minimum-mass disk model. If the dust particles are larger than chondrules, the secular GI grows within the lifetime of a protoplanetary disk.
Energy Technology Data Exchange (ETDEWEB)
El-Tantawy, S.A., E-mail: samireltantawy@yahoo.com
2017-02-26
Progress is reported on the modulational instability (MI) of ion-acoustic waves (IAWs) and dissipative rogue waves (RWs) in ultracold neutral plasmas (UNPs). The UNPs consist of inertial ions fluid and Maxwellian inertialess hot electrons, and the presence of an ion kinematic viscosity is allowed. For this purpose, a modified nonlinear Schrödinger equation (NLSE) is derived and then solved analytically to show the occurrence of MI. It is found that the (in)stability regions of the wavepacks are dependent on time due to of the existence of the dissipative term. The existing regions of the MI of the IAWs are inventoried precisely. After that, we use a suitable transformation to convert the modified NLSE into the normal NLSE whose analytical solutions for rogue waves are known. The rogue wave propagation condition and its behavior are discussed. The impact of the relevant physical parameters on the profile of the RWs is examined. - Highlights: • UNPs are modeled by the phenomenological generalized hydrodynamic equations. • The derivative expansion method has been employed in order to derive a modified-NLSE. • A suitable transformation is used to transform the modified-NLSE into the standard NLSE. • The effect of the ion viscosity on the modulational instability and rogue waves is investigated.
Jeans instability and antiscreening in the system of matter-antimatter with antigravitation
International Nuclear Information System (INIS)
Trigger, S A; Gribov, I A
2015-01-01
The hypothesis of antigravitational interaction of elementary particles and antiparticles is applied to the simple two-component hydrodynamic model Λ-CDM (Lambda cold-dark matter) with gravitational repulsion and attraction. An increase in the Jeans instability rate, the presence of antiscreening, and the dominant role of the gravitational repulsion as a possible mechanism of spatial separation of matter and antimatter in the Universe are shown, as well as the observable acceleration of far galaxies. The sound wave is found for the two-component gravitational-antigravitational system. The suggested approach permits to reestablish the idea about baryon symmetry of the Universe, causing its steady large-scale flatness and accelerated Universe expansion. (paper)
Hydrodynamical description of collective flow
Huovinen, Pasi
2003-01-01
I review how hydrodynamical flow is related to the observed flow in ultrarelativistic heavy ion collisions and how initial conditions, equation of state and freeze-out temperature affect flow in hydrodynamical models.
Catheter ablation of epicardial ventricular tachycardia
Directory of Open Access Journals (Sweden)
Takumi Yamada, MD, PhD
2014-08-01
Full Text Available Ventricular tachycardias (VTs can usually be treated by endocardial catheter ablation. However, some VTs can arise from the epicardial surface, and their substrate can be altered only by epicardial catheter ablation. There are two approaches to epicardial catheter ablation: transvenous and transthoracic. The transvenous approach through the coronary venous system (CVS has been commonly used because it is easily accessible. However, this approach may be limited by the distribution of the CVS and insufficient radiofrequency energy delivery. Transthoracic epicardial catheter ablation has been developed to overcome these limitations of the transvenous approach. It is a useful supplemental or even preferred strategy to eliminate epicardial VTs in the electrophysiology laboratory. This technique has been applied for scar-related VTs secondary to often non-ischemic cardiomyopathy and sometimes ischemic cardiomyopathy, and idiopathic VTs as the epicardial substrates of these VTs have become increasingly recognized. When endocardial ablation and epicardial ablation through the CVS are unsuccessful, transthoracic epicardial ablation should be the next option. Intrapericardial access is usually obtained through a subxiphoidal pericardial puncture. This approach might not be possible in patients with pericardial adhesions caused by prior cardiac surgery or pericarditis. In such cases, a hybrid procedure involving surgical access with a subxiphoid pericardial window and a limited anterior or lateral thoracotomy might be a feasible and safe method of performing an epicardial catheter ablation in the electrophysiology laboratory. Potential complications associated with this technique include bleeding and collateral damage to the coronary arteries and phrenic nerve. Although the risk of these complications is low, electrophysiologists who attempt epicardial catheter ablation should know the complications associated with this technique, how to minimize their
Dynamic behavior of plasma-facing materials during plasma instabilities in tokamak reactors
International Nuclear Information System (INIS)
Hassanein, A.; Konkashbaev, I.
1997-01-01
Damage to plasma-facing and nearby components due to plasma instabilities remains a major obstacle to a successful tokamak concept. The high energy deposited on facing materials during plasma instabilities can cause severe erosion, plasma contamination, and structural failure of these components. Erosion damage can take various forms such as surface vaporization, spallation, and liquid ejection of metallic materials. Comprehensive thermodynamic and radiation hydrodynamic codes have been developed, integrated, and used to evaluate the extent of various damage to plasma-facing and nearby components. The eroded and splashed materials will be transported and then redeposited elsewhere on other plasma-facing components. Detailed physics of plasma/solid-liquid/vapor interaction in a strong magnetic field have been developed, optimized, and implemented in a self-consistent model. The plasma energy deposited in the evolving divertor debris is quickly and intensely reradiated, which may cause severe erosion and melting of other nearby components. Factors that influence and reduce vapor-shielding efficiency such as vapor diffusion and turbulence are also discussed and evaluated
[Radiofrequency ablation of hepatocellular carcinoma].
Widmann, Gerlig; Schullian, Peter; Bale, Reto
2013-03-01
Percutaneous radiofrequency ablation (RFA) is well established in the treatment of hepatocellular carcinoma (HCC). Due to its curative potential, it is the method of choice for non resectable BCLC (Barcelona Liver Clinic) 0 and A. RFA challenges surgical resection for small HCC and is the method of choice in bridging for transplantation and recurrence after resection or transplantation. The technical feasibility of RFA depends on the size and location of the HCC and the availability of ablation techniques (one needle techniques, multi-needle techniques). More recently, stereotactic multi-needle techniques with 3D trajectory planning and guided needle placement substantially improve the spectrum of treatable lesions including large volume tumors. Treatment success depends on the realization of ablations with large intentional margins of tumor free tissue (A0 ablation in analogy to R0 resection), which has to be documented by fusion of post- with pre-ablation images, and confirmed during follow-up imaging.
A spectral analysis of ablating meteors
Bloxam, K.; Campbell-Brown, M.
2017-09-01
Meteor ablation features in the spectral lines occurring at 394, 436, 520, and 589 nm were observed using a four-camera spectral system between September and December 2015. In conjunction with this multi-camera system the Canadian Automated Meteor Observatory was used to observe the orbital parameters and fragmentation of these meteors. In total, 95 light curves with complete data in the 520 and 589 nm filters were analyzed; some also had partial or complete data in the 394 nm filter, but no usable data was collected with the 436 nm filter. Of the 95 events, 70 exhibited some degree of differential ablation, and in all except 3 of these 70 events the 589 nm filter started or ended sooner compared with the 520 nm filter, indicating early ablation at the 589 nm wavelength. In the majority of cases the meteor showed evidence of fragmentation regardless of the type of ablation (differential or uniform). A surprising result was the lack of correlation found concerning the KB parameter, linked to meteoroid strength, and differential ablation. In addition, 22 shower-associated meteors were observed; Geminids showed mainly slight differential ablation, while Taurids were more likely to ablate uniformly.
Energy Technology Data Exchange (ETDEWEB)
Smalyuk, V. A.; Robey, H. F.; Döppner, T.; Jones, O. S.; Milovich, J. L.; Bachmann, B.; Baker, K. L.; Berzak Hopkins, L. F.; Bond, E.; Callahan, D. A.; Casey, D. T.; Celliers, P. M.; Cerjan, C.; Clark, D. S.; Dixit, S. N.; Edwards, M. J.; Haan, S. W.; Hamza, A. V.; Hurricane, O. A.; Jancaitis, K. S. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); and others
2015-08-15
Radiation-driven, layered deuterium-tritium plastic capsule implosions were carried out using a new, 3-shock “adiabat-shaped” drive on the National Ignition Facility. The purpose of adiabat shaping is to use a stronger first shock, reducing hydrodynamic instability growth in the ablator. The shock can decay before reaching the deuterium-tritium fuel leaving it on a low adiabat and allowing higher fuel compression. The fuel areal density was improved by ∼25% with this new drive compared to similar “high-foot” implosions, while neutron yield was improved by more than 4 times, compared to “low-foot” implosions driven at the same compression and implosion velocity.
Theoretical and numerical studies of Rayleigh-Taylor instabilities in magnetized plasmas
International Nuclear Information System (INIS)
Ivanov, A.A.
2001-06-01
. These results can be applied to a wide range of systems, starting from classic hydrodynamics and up to astrophysical plasmas. The scheme of wire arrays has become recently a very popular method to obtain a high power X-radiation or for a high quality implosion in Z-pinches. The experimental studies have demonstrated that the results of implosion are much better for the case of multiple thin wires situated cylindrically than in a usual liner scheme. We have examined the problem modeling the stabilization of Rayleigh-Taylor instability for a wire array system. The reason for instability suppression is the regular spatial modulation of the surface plasma-magnetic field (in the vacuum). This modulation is created by the explosions of solid wires and by subsequent plasma evolution. We have also examined the coupling of the instability modes that takes place in the presence of the magnetic field and this study shows that the spatial surface modulation can effectively diminish the growth rate of the considered instability. (author)
Measurements of Magneto-Rayleigh-Taylor instability growth in solid liners on the 20 MA Z facility
International Nuclear Information System (INIS)
Bigman, Verle; Vesey, Roger Alan; Shores, Jonathon; Herrmann, Mark C.; Stamm, Robert; Killebrew, Korbie; Holt, Randy; Blue, Brent; Nakhleh, Charlie; McBride, Ryan D.; Leifeste, Gordon T.; Smith, Ian Craig; Stygar, William A.; Porter, John Larry Jr.; Cuneo, Michael Edward; Bennett, Guy R.; Schroen, Diana Grace; Sinars, Daniel Brian; Lopez, Mike R.; Slutz, Stephen A.; Atherton, Briggs W.; Tomlinson, Kurt; Edens, Aaron D.; Savage, Mark Edward; Peterson, Kyle J.
2010-01-01
The magneto-Rayleigh-Taylor (MRT) instability is the most important instability for determining whether a cylindrical liner can be compressed to its axis in a relatively intact form, a requirement for achieving the high pressures needed for inertial confinement fusion (ICF) and other high energy-density physics applications. While there are many published RT studies, there are a handful of well-characterized MRT experiments at time scales >1 (micro)s and none for 100 ns z-pinch implosions. Experiments used solid Al liners with outer radii of 3.16 mm and thicknesses of 292 (micro)m, dimensions similar to magnetically-driven ICF target designs (1). In most tests the MRT instability was seeded with sinusoidal perturbations (λ = 200, 400 (micro)m, peak-to-valley amplitudes of 10, 20 (micro)m, respectively), wavelengths similar to those predicted to dominate near stagnation. Radiographs show the evolution of the MRT instability and the effects of current-induced ablation of mass from the liner surface. Additional Al liner tests used 25-200 (micro)m wavelengths and flat surfaces. Codes being used to design magnetized liner ICF loads (1) match the features seen except at the smallest scales (<50 (micro)m). Recent experiments used Be liners to enable penetrating radiography using the same 6.151 keV diagnostics and provide an in-flight measurement of the liner density profile.
Hydrodynamics and stellar winds an introduction
Maciel, Walter J
2014-01-01
Stellar winds are a common phenomenon in the life of stars, from the dwarfs like the Sun to the red giants and hot supergiants, constituting one of the basic aspects of modern astrophysics. Stellar winds are a hydrodynamic phenomenon in which circumstellar gases expand towards the interstellar medium. This book presents an elementary introduction to the fundamentals of hydrodynamics with an application to the study of stellar winds. The principles of hydrodynamics have many other applications, so that the book can be used as an introduction to hydrodynamics for students of physics, astrophysics and other related areas.
CT-guided radiofrequency tumor ablation in children
International Nuclear Information System (INIS)
Botsa, Evanthia; Poulou, Loukia S.; Koundouraki, Antonia; Thanos, Loukas; Koutsogiannis, Ioannis; Ziakas, Panayiotis D.; Alexopoulou, Efthimia
2014-01-01
Image-guided radiofrequency ablation is a well-accepted technique of interventional oncology in adults. To evaluate the efficacy and safety of CT-guided radiofrequency ablation as a minimally invasive treatment for metastatic neoplasms in children. A total of 15 radiofrequency ablation sessions were performed in 12 children and young adults (median age 9.5; range 5-18 years) with metastatic malignancies. Seven children and young adults had secondary hepatic lesions, three had pulmonary and two had bone lesions. Radiofrequency ablation was performed under conscious sedation. The median lesion size was 1.7 cm (range 1.3-2.8 cm). The median time for ablation was 8 min (range 7-10 min). Radiofrequency procedures were technically successful in all tumors. Postablation imaging immediately after, and 1 month and 3 months after radiofrequency ablation showed total necrosis in all patients. At 6-month follow-up, three patients (all with lesion size >2 cm) had local recurrence and underwent a second radiofrequency ablation session. At 2-year follow-up no patient had recurrence of the treated tumor. Post-ablation syndrome occurred in four children. No major complication occurred. CT-guided radiofrequency tumor ablation was safe and efficient for palliative treatment in our cohort of patients. (orig.)
CT-guided radiofrequency tumor ablation in children
Energy Technology Data Exchange (ETDEWEB)
Botsa, Evanthia [National and Kapodistrian University of Athens, First Pediatric Clinic, Agia Sofia Children' s Hospital, Athens (Greece); Poulou, Loukia S.; Koundouraki, Antonia; Thanos, Loukas [Sotiria General Hospital for Chest Diseases, Department of Medical Imaging and Interventional Radiology, Athens (Greece); Koutsogiannis, Ioannis [General Military Hospital NIMTS, Department of Medical Imaging, Athens (Greece); Ziakas, Panayiotis D. [Warren Alpert Medical School of Brown University Rhode Island Hospital, Division of Infectious Diseases, Providence, RI (United States); Alexopoulou, Efthimia [Attikon University Hospital, Second Department of Radiology, Athens University School of Medicine, Athens (Greece)
2014-11-15
Image-guided radiofrequency ablation is a well-accepted technique of interventional oncology in adults. To evaluate the efficacy and safety of CT-guided radiofrequency ablation as a minimally invasive treatment for metastatic neoplasms in children. A total of 15 radiofrequency ablation sessions were performed in 12 children and young adults (median age 9.5; range 5-18 years) with metastatic malignancies. Seven children and young adults had secondary hepatic lesions, three had pulmonary and two had bone lesions. Radiofrequency ablation was performed under conscious sedation. The median lesion size was 1.7 cm (range 1.3-2.8 cm). The median time for ablation was 8 min (range 7-10 min). Radiofrequency procedures were technically successful in all tumors. Postablation imaging immediately after, and 1 month and 3 months after radiofrequency ablation showed total necrosis in all patients. At 6-month follow-up, three patients (all with lesion size >2 cm) had local recurrence and underwent a second radiofrequency ablation session. At 2-year follow-up no patient had recurrence of the treated tumor. Post-ablation syndrome occurred in four children. No major complication occurred. CT-guided radiofrequency tumor ablation was safe and efficient for palliative treatment in our cohort of patients. (orig.)
Advances in laser ablation of materials
International Nuclear Information System (INIS)
Singh, R.K.; Lowndes, D.H.; Chrisey, D.B.; Fogarassy, E.; Narayan, J.
1998-01-01
The symposium, Advances in Laser Ablation of Materials, was held at the 1998 MRS Spring Meeting in San Francisco, California. The papers in this symposium illustrate the advances in pulsed laser ablation for a wide variety of applications involving semiconductors, superconductors, metals, ceramics, and polymers. In particular, advances in the deposition of oxides and related materials are featured. Papers dealing with both fundamentals and the applications of laser ablation are presented. Topical areas include: fundamentals of ablation and growth; in situ diagnostics and nanoscale synthesis advances in laser ablation techniques; laser surface processing; pulsed laser deposition of ferroelectric, magnetic, superconducting and optoelectronic thin films; and pulsed laser deposition of carbon-based and polymeric materials. Sixty papers have been processed separately for inclusion on the data base
Choi, In Young; Kim, Pyo Nyun; Lee, Sung Gu; Won, Hyung Jin; Shin, Yong Moon
2017-10-01
To evaluate the safety and efficacy of radiofrequency (RF) ablation for treatment of focal hepatic lesions adjacent to the gallbladder with electrode relocation and ablation time reduction. Thirty-nine patients who underwent RF ablation for focal hepatic lesions adjacent to the gallbladder (≤ 10 mm) were evaluated retrospectively from January 2011 to December 2014 (30 men and 9 women; age range, 51-85 y; mean age, 65 y). Of 36 patients with hepatocellular carcinoma, 3 had a second treatment for recurrence (mean tumor size, 15 mm ± 6). Patients were divided into 2 subgroups based on lesion distance from the gallbladder: nonabutting (> 5 mm; n = 19) and abutting (≤ 5 mm; n = 20). Electrodes were inserted parallel to the gallbladder through the center of a tumor in the nonabutting group and through the center of the expected ablation zone between a 5-mm safety zone on the liver side and the gallbladder in the abutting group. Ablation time was decreased in proportion to the transverse diameter of the expected ablation zone. Technical success and technical effectiveness rates were 89.7% and 97.4%, respectively, with no significant differences between groups (P = 1.00). Local tumor progression was observed in 3 patients (1 in the nonabutting group and 2 in the abutting group; P = 1.00). There were no major complications. The gallbladder was thickened in 10 patients, with no significant difference between groups (P = .72). Biloma occurred in 1 patient in the nonabutting group. RF ablation with electrode relocation and reduction of ablation time can be a safe and effective treatment for focal hepatic lesions adjacent to the gallbladder. Copyright © 2017 SIR. Published by Elsevier Inc. All rights reserved.
Characterization of tracked radiofrequency ablation in phantom
International Nuclear Information System (INIS)
Chen, Chun-Cheng R.; Miga, Michael I.; Galloway, Robert L.
2007-01-01
In radiofrequency ablation (RFA), successful therapy requires accurate, image-guided placement of the ablation device in a location selected by a predictive treatment plan. Current planning methods rely on geometric models of ablations that are not sensitive to underlying physical processes in RFA. Implementing plans based on computational models of RFA with image-guided techniques, however, has not been well characterized. To study the use of computational models of RFA in planning needle placement, this work compared ablations performed with an optically tracked RFA device with corresponding models of the ablations. The calibration of the tracked device allowed the positions of distal features of the device, particularly the tips of the needle electrodes, to be determined to within 1.4±0.6 mm of uncertainty. Ablations were then performed using the tracked device in a phantom system based on an agarose-albumin mixture. Images of the sliced phantom obtained from the ablation experiments were then compared with the predictions of a bioheat transfer model of RFA, which used the positional data of the tracked device obtained during ablation. The model was demonstrated to predict 90% of imaged pixels classified as being ablated. The discrepancies between model predictions and observations were analyzed and attributed to needle tracking inaccuracy as well as to uncertainties in model parameters. The results suggest the feasibility of using finite element modeling to plan ablations with predictable outcomes when implemented using tracked RFA
Anisotropic gravitational instability
International Nuclear Information System (INIS)
Polyachenko, V.L.; Fridman, A.M.
1988-01-01
Exact solutions of stability problems are obtained for two anisotropic gravitational systems of different geometries - a layer of finite thickness at rest and a rotating cylinder of finite radius. It is shown that the anisotropic gravitational instability which develops in both cases is of Jeans type. However, in contrast to the classical aperiodic Jeans instability, this instability is oscillatory. The physics of the anisotropic gravitational instability is investigated. It is shown that in a gravitating layer this instability is due, in particular, to excitation of previously unknown interchange-Jeans modes. In the cylinder, the oscillatory Jeans instability is associated with excitation of a rotational branch, this also being responsible for the beam gravitational instability. This is the reason why this instability and the anisotropic gravitational instability have so much in common
Field enhancement induced laser ablation
DEFF Research Database (Denmark)
Fiutowski, Jacek; Maibohm, Christian; Kjelstrup-Hansen, Jakob
Sub-diffraction spatially resolved, quantitative mapping of strongly localized field intensity enhancement on gold nanostructures via laser ablation of polymer thin films is reported. Illumination using a femtosecond laser scanning microscope excites surface plasmons in the nanostructures....... The accompanying field enhancement substantially lowers the ablation threshold of the polymer film and thus creates local ablation spots and corresponding topographic modifications of the polymer film. Such modifications are quantified straightforwardly via scanning electron and atomic force microscopy. Thickness...
Radiofrequency ablation in dermatology
Directory of Open Access Journals (Sweden)
Sachdeva Silonie
2007-01-01
Full Text Available Radiofreqeuency ablation is a versatile dermatosurgical procedure used for surgical management of skin lesions by using various forms of alternating current at an ultra high frequency. The major modalities in radiofrequency are electrosection, electrocoagulation, electrodessication and fulguration. The use of radiofrequency ablation in dermatosurgical practice has gained importance in recent years as it can be used to treat most of the skin lesions with ease in less time with clean surgical field due to adequate hemostasis and with minimal side effects and complications. This article focuses on the major tissue effects and factors influencing radiofrequency ablation and its application for various dermatological conditions.
Percutaneous Microwave Ablation of Renal Angiomyolipomas
Energy Technology Data Exchange (ETDEWEB)
Cristescu, Mircea, E-mail: mcristescu@uwhealth.org [University of Wisconsin, Department of Radiology (United States); Abel, E. Jason, E-mail: abel@urology.wisc.edu [University of Wisconsin, Department of Urology (United States); Wells, Shane, E-mail: swells@uwhealth.org; Ziemlewicz, Timothy J., E-mail: tziemlewicz@uwhealth.org [University of Wisconsin, Department of Radiology (United States); Hedican, Sean P., E-mail: hedican@surgery.wisc.edu [University of Wisconsin, Department of Urology (United States); Lubner, Megan G., E-mail: mlubner@uwhealth.org; Hinshaw, J. Louis, E-mail: jhinshaw@uwhealth.org; Brace, Christopher L., E-mail: cbrace@uwhealth.org; Lee, Fred T., E-mail: flee@uwhealth.org [University of Wisconsin, Department of Radiology (United States)
2016-03-15
PurposeTo evaluate the safety and efficacy of US-guided percutaneous microwave (MW) ablation in the treatment of renal angiomyolipoma (AML).Materials and MethodsFrom January 2011 to April 2014, seven patients (5 females and 2 males; mean age 51.4) with 11 renal AMLs (9 sporadic type and 2 tuberous sclerosis associated) with a mean size of 3.4 ± 0.7 cm (range 2.4–4.9 cm) were treated with high-powered, gas-cooled percutaneous MW ablation under US guidance. Tumoral diameter, volume, and CT/MR enhancement were measured on pre-treatment, immediate post-ablation, and delayed post-ablation imaging. Clinical symptoms and creatinine were assessed on follow-up visits.ResultsAll ablations were technically successful and no major complications were encountered. Mean ablation parameters were ablation power of 65 W (range 60–70 W), using 456 mL of hydrodissection fluid per patient, over 4.7 min (range 3–8 min). Immediate post-ablation imaging demonstrated mean tumor diameter and volume decreases of 1.8 % (3.4–3.3 cm) and 1.7 % (27.5–26.3 cm{sup 3}), respectively. Delayed imaging follow-up obtained at a mean interval of 23.1 months (median 17.6; range 9–47) demonstrated mean tumor diameter and volume decreases of 29 % (3.4–2.4 cm) and 47 % (27.5–12.1 cm{sup 3}), respectively. Tumoral enhancement decreased on immediate post-procedure and delayed imaging by CT/MR parameters, indicating decreased tumor vascularity. No patients required additional intervention and no patients experienced spontaneous bleeding post-ablation.ConclusionOur early experience with high-powered, gas-cooled percutaneous MW ablation demonstrates it to be a safe and effective modality to devascularize and decrease the size of renal AMLs.
Watanabe, Ken; Uchiyama, Mayuki; Fukuda, Kunihiko
2017-09-01
This article examines the outcome of radioactive iodine ablation therapy for thyroid cancer in high-risk patients and investigates background factors influencing ablation failure. We included 91 patients in this retrospective analysis and evaluated the ablation success rate. Successful ablation was defined as the absence of visible iodine-131 (I-131) accumulation in the thyroid bed after whole-body scans and thyroglobulin levels sex, I-131 dose, pathology, resection stump findings, tumor T category and thyroglobulin levels, which could affect ablation outcome. Successful ablation was achieved in only 14 patients (15.4%). Pre-ablation serum thyroglobulin levels were significantly higher in the ablation failure group than in the success group (P 10 ng/ml were significantly related to ablation failure after multivariate analysis (odds ratio 27.2; 95% confidence interval 2.469-299.7; P = 0.007). The ablation success rate was very low because of high thyroglobulin levels, even with high-dose I-131. High-risk patients, especially those with high thyroglobulin levels (>10 ng/ml), are unlikely to reach levels low enough to meet successful ablation criteria.
Impact of Relativistic Electron Beam on Hole Acoustic Instability in Quantum Semiconductor Plasmas
Siddique, M.; Jamil, M.; Rasheed, A.; Areeb, F.; Javed, Asif; Sumera, P.
2018-01-01
We studied the influence of the classical relativistic beam of electrons on the hole acoustic wave (HAW) instability exciting in the semiconductor quantum plasmas. We conducted this study by using the quantum-hydrodynamic model of dense plasmas, incorporating the quantum effects of semiconductor plasma species which include degeneracy pressure, exchange-correlation potential and Bohm potential. Analysis of the quantum characteristics of semiconductor plasma species along with relativistic effect of beam electrons on the dispersion relation of the HAW is given in detail qualitatively and quantitatively by plotting them numerically. It is worth mentioning that the relativistic electron beam (REB) stabilises the HAWs exciting in semiconductor (GaAs) degenerate plasma.
Temperature-controlled irrigated tip radiofrequency catheter ablation
DEFF Research Database (Denmark)
Petersen, H H; Chen, X; Pietersen, Adrian
1998-01-01
INTRODUCTION: In patients with ventricular tachycardias due to structural heart disease, catheter ablation cures radiofrequency ablation. Irrigated tip radiofrequency ablation using power control and high infusion rates enlarges lesion......: We conclude that temperature-controlled radiofrequency ablation with irrigated tip catheters using low target temperature and low infusion rate enlarges lesion size without increasing the incidence of cratering and reduces coagulum formation of the tip....
Micrometeoroid ablation simulated in the laboratory
Sternovsky, Zoltan; Thomas, Evan W.; DeLuca, Michael; Horanyi, Mihaly; Janches, Diego; Munsat, Tobin L.; Plane, John M. C.
2016-04-01
A facility is developed to simulate the ablation of micrometeoroids in laboratory conditions, which also allows measuring the ionization probability of the ablated material. An electrostatic dust accelerator is used to generate iron and meteoric analog particles with velocities 10-50 km/s. The particles are then introduced into a cell filled with nitrogen, air or carbon dioxide gas with pressures adjustable in the 0.02 - 0.5 Torr range, where the partial or complete ablation of the particle occurs over a short distance. An array of biased electrodes is used to collect the ionized products with spatial resolution along the ablating particles' path, allowing thus the study of the temporal resolution of the process. A simple ablation model is used to match the observations. For completely ablated particles the total collected charge directly yields the ionization efficiency for. The measurements using iron particles in N2 and air are in relatively good agreement with earlier data. The measurements with CO2 and He gases, however, are significantly different from the expectations.
Fundamental Insights into Combustion Instability Predictions in Aerospace Propulsion
Huang, Cheng
Integrated multi-fidelity modeling has been performed for combustion instability in aerospace propulsion, which includes two levels of analysis: first, computational fluid dynamics (CFD) using hybrid RANS/LES simulations for underlying physics investigations (high-fidelity modeling); second, modal decomposition techniques for diagnostics (analysis & validation); third, development of flame response model using model reduction techniques for practical design applications (low-order model). For the high-fidelity modeling, the relevant CFD code development work is moving towards combustion instability prediction for liquid propulsion system. A laboratory-scale single-element lean direct injection (LDI) gas turbine combustor is used for configuration that produces self-excited combustion instability. The model gas turbine combustor is featured with an air inlet section, air plenum, swirler-venturi-injector assembly, combustion chamber, and exit nozzle. The combustor uses liquid fuel (Jet-A/FT-SPK) and heated air up to 800K. Combustion dynamics investigations are performed with the same geometry and operating conditions concurrently between the experiment and computation at both high (φ=0.6) and low (φ=0.36) equivalence ratios. The simulation is able to reach reasonable agreement with experiment measurements in terms of the pressure signal. Computational analyses are also performed using an acoustically-open geometry to investigate the characteristic hydrodynamics in the combustor with both constant and perturbed inlet mass flow rates. Two hydrodynamic modes are identified by using Dynamic Mode Decomposition (DMD) analysis: Vortex Breakdown Bubble (VBB) and swirling modes. Following that, the closed geometry simulation results are analyzed in three steps. In step one, a detailed cycle analysis shows two physically important couplings in the combustor: first, the acoustic compression enhances the spray drop breakup and vaporization, and generates more gaseous fuel for
International Nuclear Information System (INIS)
Watanabe, Ken; Uchiyama, Mayuki; Fukuda, Kunihiko
2017-01-01
This article examines the outcome of radioactive iodine ablation therapy for thyroid cancer in nigh-risk patients and investigates background factors influencing ablation failure. We included 91 patients in this retrospective analysis and evaluated the ablation success rate. Successful ablation was defined as the absence of visible iodine-131 (I-131) accumulation in the thyroid bed after whole-body scans and thyroglobulin levels <2 ng/ml in a TSH-stimulated state after ablation. We extracted data on patients' age, sex, I-131 dose, pathology, resection stump findings, tumor T category and thyroglobulin levels, which could affect ablation outcome. Successful ablation was achieved in only 14 patients (15.4%). Pre-ablation serum thyroglobulin levels were significantly higher in the ablation failure group than in the success group (P < 0.001), while no significant differences were found for other factors between the groups. Furthermore, thyroglobulin levels >10 ng/ml were significantly related to ablation failure after multivariate analysis (odds ratio 27.2; 95% confidence interval 2.469-299.7; P = 0.007). The ablation success rate was very low because of high thyroglobulin levels, even with high-dose I-131. High-risk patients, especially those with high thyroglobulin levels (>10 ng/ml), are unlikely to reach levels low enough to meet successful ablation criteria. (author)
Hydrodynamics of electrons in graphene
Lucas, Andrew; Chung Fong, Kin
2018-02-01
Generic interacting many-body quantum systems are believed to behave as classical fluids on long time and length scales. Due to rapid progress in growing exceptionally pure crystals, we are now able to experimentally observe this collective motion of electrons in solid-state systems, including graphene. We present a review of recent progress in understanding the hydrodynamic limit of electronic motion in graphene, written for physicists from diverse communities. We begin by discussing the ‘phase diagram’ of graphene, and the inevitable presence of impurities and phonons in experimental systems. We derive hydrodynamics, both from a phenomenological perspective and using kinetic theory. We then describe how hydrodynamic electron flow is visible in electronic transport measurements. Although we focus on graphene in this review, the broader framework naturally generalizes to other materials. We assume only basic knowledge of condensed matter physics, and no prior knowledge of hydrodynamics.
Cryoballoon Ablation for Atrial Fibrillation
Directory of Open Access Journals (Sweden)
Jason G. Andrade, MD
2012-03-01
Full Text Available Focal point-by-point radiofrequency catheter ablation has shown considerable success in the treatment of paroxysmal atrial fibrillation. However, it is not without limitations. Recent clinical and preclinical studies have demonstrated that cryothermal ablation using a balloon catheter (Artic Front©, Medtronic CryoCath LP provides an effective alternative strategy to treating atrial fibrillation. The objective of this article is to review efficacy and safety data surrounding cryoballoon ablation for paroxysmal and persistent atrial fibrillation. In addition, a practical step-by-step approach to cryoballoon ablation is presented, while highlighting relevant literature regarding: 1 the rationale for adjunctive imaging, 2 selection of an appropriate cryoballoon size, 3 predictors of efficacy, 4 advanced trouble-shooting techniques, and 5 strategies to reduce procedural complications, such as phrenic nerve palsy.
Gill, Kanwar Rupinder S.; Gross, Seth A.; Greenwald, Bruce D.; Hemminger, Lois L.; Wolfsen, Herbert C.
2009-06-01
Background: There are few data available comparing endoscopic ablation methods for Barrett's esophagus with high-grade dysplasia (BE-HGD). Objective: To determine differences in symptoms and complications associated with endoscopic ablation. Design: Prospective observational study. Setting: Two tertiary care centers in USA. Patients: Consecutive patients with BE-HGD Interventions: In this pilot study, symptoms profile data were collected for BE-HGD patients among 3 endoscopic ablation methods: porfimer sodium photodynamic therapy, radiofrequency ablation and low-pressure liquid nitrogen spray cryotherapy. Main Outcome Measurements: Symptom profiles and complications from the procedures were assessed 1-8 weeks after treatment. Results: Ten BE-HGD patients were treated with each ablation modality (30 patients total; 25 men, median age: 69 years (range 53-81). All procedures were performed in the clinic setting and none required subsequent hospitalization. The most common symptoms among all therapies were chest pain, dysphagia and odynophagia. More patients (n=8) in the porfimer sodium photodynamic therapy group reported weight loss compared to radio-frequency ablactation (n=2) and cryotherapy (n=0). Four patients in the porfimer sodium photodynamic therapy group developed phototoxicity requiring medical treatment. Strictures, each requiring a single dilation, were found in radiofrequency ablactation (n=1) and porfimer sodium photodynamic therapy (n=2) patients. Limitations: Small sample size, non-randomized study. Conclusions: These three endoscopic therapies are associated with different types and severity of post-ablation symptoms and complications.
Enhanced Radiofrequency Ablation With Magnetically Directed Metallic Nanoparticles.
Nguyen, Duy T; Tzou, Wendy S; Zheng, Lijun; Barham, Waseem; Schuller, Joseph L; Shillinglaw, Benjamin; Quaife, Robert A; Sauer, William H
2016-05-01
Remote heating of metal located near a radiofrequency ablation source has been previously demonstrated. Therefore, ablation of cardiac tissue treated with metallic nanoparticles may improve local radiofrequency heating and lead to larger ablation lesions. We sought to evaluate the effect of magnetic nanoparticles on tissue sensitivity to radiofrequency energy. Ablation was performed using an ablation catheter positioned with 10 g of force over prepared ex vivo specimens. Tissue temperatures were measured and lesion volumes were acquired. An in vivo porcine thigh model was used to study systemically delivered magnetically guided iron oxide (FeO) nanoparticles during radiofrequency application. Magnetic resonance imaging and histological staining of ablated tissue were subsequently performed as a part of ablation lesion analysis. Ablation of ex vivo myocardial tissue treated with metallic nanoparticles resulted in significantly larger lesions with greater impedance changes and evidence of increased thermal conductivity within the tissue. Magnet-guided localization of FeO nanoparticles within porcine thigh preps was demonstrated by magnetic resonance imaging and iron staining. Irrigated ablation in the regions with greater FeO, after FeO infusion and magnetic guidance, created larger lesions without a greater incidence of steam pops. Metal nanoparticle infiltration resulted in significantly larger ablation lesions with altered electric and thermal conductivity. In vivo magnetic guidance of FeO nanoparticles allowed for facilitated radiofrequency ablation without direct infiltration into the targeted tissue. Further research is needed to assess the clinical applicability of this ablation strategy using metallic nanoparticles for the treatment of cardiac arrhythmias. © 2016 American Heart Association, Inc.
Lee, Bo Ram; Clark, S. E.; Hoffmann, D. H. H.; Niemann, C.
2014-10-01
The Raptor kJ class 1053 nm Nd:Glass laser in the Phoenix laser laboratory at University of California, Los Angeles, is used to ablate a dense debris plasma from a graphite or plastic target embedded in a tenuous, uniform, and quiescent ambient magnetized plasma in the Large Plasma Device (LAPD) which provides a peak plasma density of ni ~ 1013 cm-3. Its background magnetic field can vary between 200 and 1200 G. Debris ions from laser produced plasma expand out conically with super-Alfvénic speed (MA ~ 2) and expel the background magnetic field and ambient ions to form a diamagnetic bubble. The debris plasma interacts with the ambient plasma and the magnetic field and acts as a piston which can create collisionless shocks. Flute-type instabilities, which are probably large Larmor radius Rayleigh Taylor instabilities or lower hybrid drift instabilities, are developed at the bubble edge and also observed in the experiment. The amplitude and wavelength dependence of the instabilities, which might be a strong function of debris to ambient mass to charge ratio, is studied and the experimental results are compared to the two dimensional hybrid simulations. the Deutsche Forschungsgemeinschaft in the framework of the Excellence Initiative Darmstadt Graduate School of Energy Science and Engineering (GSC1070).
International Nuclear Information System (INIS)
Garnier, Josselin; Cherfils, Catherine
2005-01-01
This paper is devoted to the study of the deceleration phase of inertial confinement capsules. First the self-similar flow exhibited by Betti et al. [Phys. Plasmas 8, 5257 (2001)] is proved to be an attractor in the sense that arbitrary initial conditions converge towards this solution. The convergence rate depends on the ablation process and heat conductivity and it is shown to be a power law of the increase rate of the hotspot mass. Second the thin layer that separates the hotspot from the cold shell is described and it is shown that it also converges to a locally self-similar profile. By using and generalizing a shell model introduced by Betti et al. [Phys. Plasmas 9, 2277 (2002)] a closed system of ordinary differential equations for the main hydrodynamic variables is derived. Finally the linear growth rates of the deceleration phase Rayleigh-Taylor instabilities are computed taking into account ablation and spherical convergence. Significant differences are exhibited between directly and indirectly driven capsules
Black brane entropy and hydrodynamics
Booth, I.; Heller, M.P.; Spaliński, M.
2010-01-01
A generalization of entropy to near-equilibrium phenomena is provided by the notion of a hydrodynamic entropy current. Recent advances in holography have lead to the formulation of fluid-gravity duality, a remarkable connection between the hydrodynamics of certain strongly coupled media and dynamics
Black brane entropy and hydrodynamics
Booth, I.; Heller, M.P.; Spaliński, M.
2011-01-01
A generalization of entropy to near-equilibrium phenomena is provided by the notion of a hydrodynamic entropy current. Recent advances in holography have lead to the formulation of fluid-gravity duality, a remarkable connection between the hydrodynamics of certain strongly coupled media and dynamics
Nonlinear evolution of single spike structure and vortex in Richtmeyer-Meshkov instability
International Nuclear Information System (INIS)
Fukuda, Yuko O.; Nishihara, Katsunobu; Okamoto, Masayo; Nagatomo, Hideo; Matsuoka, Chihiro; Ishizaki, Ryuichi; Sakagami, Hitoshi
1999-01-01
Nonlinear evolution of single spike structure and vortex in the Richtmyer-Meshkov instability is investigated for two dimensional case, and axial symmetric and non axial symmetric cases with the use of a three-dimensional hydrodynamic code. It is shown that singularity appears in the vorticity left by transmitted and reflected shocks at a corrugated interface. This singularity results in opposite sign of vorticity along the interface that causes double spiral structure of the spike. Difference of nonlinear growth rate and double spiral structure among three cases is also discussed by visualization of simulation data. In a case that there is no slip-off of initial spike axis, vorticity ring is relatively stable, but phase rotation occurs. (author)
International Nuclear Information System (INIS)
Sommer, C. M.; Arnegger, F.; Koch, V.; Pap, B.; Holzschuh, M.; Bellemann, N.; Gehrig, T.; Senft, J.; Nickel, F.; Mogler, C.; Zelzer, S.; Meinzer, H. P.; Stampfl, U.; Kauczor, H. U.; Radeleff, B. A.
2012-01-01
Purpose: This study was designed to analyze the effect of two different ablation modes (“temperature control” and “power control”) of a microwave system on procedural outcome in porcine kidneys in vivo. Methods: A comme