International Nuclear Information System (INIS)
Brochard, F.; Gravier, E.; Bonhomme, G.
2006-01-01
The spatiotemporal transition scenario of flute instabilities from a regular to a turbulent state is experimentally investigated in the low-β plasma column of a thermionic discharge. The same transition scenario, i.e., the Ruelle-Takens route to turbulence, is found for both the Kelvin-Helmholtz and the Rayleigh-Taylor instabilities. It is demonstrated that the transition can be more or less smooth, according to the discharge mode. In both cases, a strong radial dependence is observed, which is linked to the velocity shear layer in the case of the Kelvin-Helmholtz instability
Finite Larmor radius flute mode theory with end loss
International Nuclear Information System (INIS)
Kotelnikov, I.A.; Berk, H.L.
1993-08-01
The theory of flute mode stability is developed for a two-energy- component plasma partially terminated by a conducting limiter. The formalism is developed as a preliminary study of the effect of end-loss in open-ended mirror machines where large Larmor radius effects are important
Theoretical investigation of flute modes in a magnetic quadrupole
International Nuclear Information System (INIS)
Wu, H.S.
1988-01-01
This research developed theories and conducted numerical investigations of electrostatic flute modes in a plasma confined in a magnetic quadrupole. Chapter I presents the discussion of relevant background. Chapter II contains a brief discussion of the basic flute-mode operator L 0 for intermediate- and low-frequency regimes. Chapter III develops a simple theory for a flute mode with frequency between the electron and ion bounce frequencies in the uniform density and temperature regions of a magnetic quadrupole. The frequency is predicted to be inversely proportional to the wave number. Chapter IV describes the kinetic approach. Chapter V contains the derivation of an eigenvalue equation for electrostatic waves with frequencies below the ion frequency in the private flux region of a magnetic quadrupole. Chapter VI develops a theory for electrostatic waves with frequency below the ion bounce frequency in the shared flux region of a magnetic quadrupole. Chapter VII contains the derivation of a dispersion equation for flute modes with frequencies between the electron and ion bounce frequencies in a plasma confined to a magnetic quadrupole. Chapter VIII presents a summary of the research described
Generation and saturation of large-scale flows in flute turbulence
International Nuclear Information System (INIS)
Sandberg, I.; Isliker, H.; Pavlenko, V. P.; Hizanidis, K.; Vlahos, L.
2005-01-01
The excitation and suppression of large-scale anisotropic modes during the temporal evolution of a magnetic-curvature-driven electrostatic flute instability are numerically investigated. The formation of streamerlike structures is attributed to the linear development of the instability while the subsequent excitation of the zonal modes is the result of the nonlinear coupling between linearly grown flute modes. When the amplitudes of the zonal modes become of the same order as that of the streamer modes, the flute instabilities get suppressed and poloidal (zonal) flows dominate. In the saturated state that follows, the dominant large-scale modes of the potential and the density are self-organized in different ways, depending on the value of the ion temperature
Surface flute modes in the bumpy magnetic field
International Nuclear Information System (INIS)
Girka, I.O.; Girka, V.O.; Lapshin, V.I.
2005-01-01
Surface electromagnetic waves are often determined as the most possible cause of undesirable heating of edge plasma that leads, in turn, to strengthening of plasma - wall interaction in stellarators and increased plasma contamination. The propagation of surface flute modes near the interface of plasma column separated by a vacuum layer from the ring cylindrical ideally conductive metallic chamber is studied. The external steady bumpy magnetic field B-vector 0 = B 0z e-vector z + B 0r e-vector r was considered, B 0z =B 00 [1+ε m (r)cos(k m z)], here ε m '≡dε m /dr, k m =2π/L, L is the period of nonuniformity. non-uniformity of B-vector 0 is planned to be dominant in the confining magnetic field of the modular stellarator Helias, ε m ∼ 0.13. In the bumpy magnetic field the electromagnetic disturbance propagates in the form of the wave envelope, in which one alongside with the fundamental harmonic, proportional to exp[i(mθ±-ωt)], infinite set of satellite spatial harmonics, proportional to exp[i(mθ ± jk m z - ωt)], j=1,2,3..., is present. It is shown, that in the first approximation in the respect to ε m , amplitudes of the fundamental harmonics of the E-wave with the field components E r , E θ , B z do not vary, small satellite harmonics of these fields arise, proportional to exp[i(mθ ± k m z - ωt)]. At the same time due to weak coupling of - and - modes, caused by B-vector 0 nonuniformity and nonzero axial wave number of satellite harmonics, small satellite harmonics of H-wave with the field components E z , B r , B θ also arise. The amplitudes of satellite harmonics of E-wave are shown to be symmetric: E r (+) =E r (-) , E θ (+) =E θ (-) , B z (+) =B z (-) , and the amplitudes of H-wave are antisymmetric: B r (+) =-B r (-) , B θ (+) =- B θ (-) , E z (+) =-E z (-) . In the second approximation in the respect to ε m corrections to the amplitudes of the fundamental harmonic of E-wave arise. The correction to the eigen frequency of the wave
Nonlinear stability of m=1 flute mode in a nonparaxial open plasma device
International Nuclear Information System (INIS)
Lanskij, I.M.; Stupakov, G.V.
1991-01-01
Plasma flute stability as to high shifts under strong effects of ion Larmor finite radius conditions is studied. System consisting of long axisymmetric paraxial mirror device with stabilizing cells at its edges is considered. Variation of plasma energy as to its shift as a whole is calculated. It is shown, that depending on stabilizer type the force bringing plasma back in equilibrium state with shift growth may both increase and decrease
Turbulence and Solar p-Mode Oscillations
Bi, S. L.; Xu, H. Y.
The discrepancy between observed and theoretical mode frequencies can be used to examine the reliability of the standard solar model as a faithful representation of solar real situation. With the help of an improved time-dependent convective model that takes into account contribution of the full spatial and temporal turbulent energy spectrum, we study the influence of turbulent pressure on structure and solar p-mode frequencies. For the radial modes we find that the Reynolds stress produces signification modifications in structure and p-mode spectrum. Compared with an adiabatic approximation, the discrepancy is largely removed by the turbulent correction.
Generation of compressible modes in MHD turbulence
Energy Technology Data Exchange (ETDEWEB)
Cho, Jungyeon [Chungnam National Univ., Daejeon (Korea); Lazarian, A. [Univ. of Wisconsin, Madison, WI (United States)
2005-05-01
Astrophysical turbulence is magnetohydrodynamic (MHD) in nature. We discuss fundamental properties of MHD turbulence and in particular the generation of compressible MHD waves by Alfvenic turbulence and show that this process is inefficient. This allows us to study the evolution of different types of MHD perturbations separately. We describe how to separate MHD fluctuations into three distinct families: Alfven, slow, and fast modes. We find that the degree of suppression of slow and fast modes production by Alfvenic turbulence depends on the strength of the mean field. We review the scaling relations of the modes in strong MHD turbulence. We show that Alfven modes in compressible regime exhibit scalings and anisotropy similar to those in incompressible regime. Slow modes passively mimic Alfven modes. However, fast modes exhibit isotropy and a scaling similar to that of acoustic turbulence both in high and low {beta} plasmas. We show that our findings entail important consequences for star formation theories, cosmic ray propagation, dust dynamics, and gamma ray bursts. We anticipate many more applications of the new insight to MHD turbulence and expect more revisions of the existing paradigms of astrophysical processes as the field matures. (orig.)
Electromagnetic Transport From Microtearing Mode Turbulence
International Nuclear Information System (INIS)
Guttenfelder, W.; Candy, J.; Kaye, S.M.; Nevins, W.M.; Wang, E.; Bell, R.E.; Hammett, G.W.; LeBlanc, B.P.; Mikkelsen, D.R.; Yuh, H.
2011-01-01
This Letter presents non-linear gyrokinetic simulations of microtearing mode turbulence. The simulations include collisional and electromagnetic effects and use experimental parameters from a high beta discharge in the National Spherical Torus Experiment (NSTX). The predicted electron thermal transport is comparable to that given by experimental analysis, and it is dominated by the electromagnetic contribution of electrons free streaming along the resulting stochastic magnetic field line trajectories. Experimental values of flow shear can significantly reduce the predicted transport.
Flute-interchange stability in a hot electron plasma
International Nuclear Information System (INIS)
Dominguez, R.R.
1980-01-01
Several topics in the kinetic stability theory of flute-interchange modes in a hot electron plasma are discussed. The stability analysis of the hot-electron, curvature-driven flute-interchange mode, previously performed in a slab geometry, is extended to a cylindrical plasma. The cold electron concentration necessary for stability differs substantially from previous criteria. The inclusion of a finite temperature background plasma in the stability analysis results in an ion curvature-driven flute-interchange mode which may be stabilized by either hot-electron diamagnetic effects, hot-electron plasma density, or finite (ion) Larmor radius effects
Energy spectrum of tearing mode turbulence in sheared background field
Hu, Di; Bhattacharjee, Amitava; Huang, Yi-Min
2018-06-01
The energy spectrum of tearing mode turbulence in a sheared background magnetic field is studied in this work. We consider the scenario where the nonlinear interaction of overlapping large-scale modes excites a broad spectrum of small-scale modes, generating tearing mode turbulence. The spectrum of such turbulence is of interest since it is relevant to the small-scale back-reaction on the large-scale field. The turbulence we discuss here differs from traditional MHD turbulence mainly in two aspects. One is the existence of many linearly stable small-scale modes which cause an effective damping during the energy cascade. The other is the scale-independent anisotropy induced by the large-scale modes tilting the sheared background field, as opposed to the scale-dependent anisotropy frequently encountered in traditional critically balanced turbulence theories. Due to these two differences, the energy spectrum deviates from a simple power law and takes the form of a power law multiplied by an exponential falloff. Numerical simulations are carried out using visco-resistive MHD equations to verify our theoretical predictions, and a reasonable agreement is found between the numerical results and our model.
Developed Turbulence: From Full Simulations to Full Mode Reductions
Grossmann, Siegfried; Lohse, Detlef; Reeh, Achim
1996-01-01
Developed Navier-Stokes turbulence is simulated with varying wave-vector mode reductions. The flatness and the skewness of the velocity derivative depend on the degree of mode reduction. They show a crossover towards the value of the full numerical simulation when the viscous subrange starts to be
Hyper-resistivity produced by tearing mode turbulence
International Nuclear Information System (INIS)
Strauss, H.R.
1986-01-01
Tearing mode turbulence produces a hyper-resistivity or effective anomalous electron viscosity. The hyper-resistivity is calculated for the mean magnetic field quasilinearly, and for long-wavelength modes using the direct interaction approximation. The hyper-resistivity accounts for current relaxation in reversed-field pinch experiments, and gives a magnetic fluctuation sealing of S -1 /sup // 3 . It causes enhanced tearing mode growth rates in the turbulent phase of tokamak disruptions. In astrophysics, it limits magnetic energy growth due to the dynamo effect, and may explain rapid reconnection phenomena such as solar flares
Equipartition and transport in two-dimensional electrostatic turbulence
DEFF Research Database (Denmark)
Naulin, V.; Nycander, J.; Juul Rasmussen, J.
1998-01-01
Turbulent equipartition is investigated for the nonlinear evolution of pressure driven flute modes of a plasma in an inhomogeneous magnetic field. The Rayleigh-Taylor instability is recovered by linear stability analysis, and occurs when the pressure profile is more peaked than the profile of the...
Zonal flow generation in collisionless trapped electron mode turbulence
International Nuclear Information System (INIS)
Anderson, J; Nordman, H; Singh, R; Weiland, J
2006-01-01
In the present work the generation of zonal flows in collisionless trapped electron mode (TEM) turbulence is studied analytically. A reduced model for TEM turbulence is utilized based on an advanced fluid model for reactive drift waves. An analytical expression for the zonal flow growth rate is derived and compared with the linear TEM growth, and its scaling with plasma parameters is examined for typical tokamak parameter values
Nonlinear simulation of electromagnetic current diffusive interchange mode turbulence
International Nuclear Information System (INIS)
Yagi, M.; Itoh, S.I.; Fukuyama, A.
1998-01-01
The anomalous transport in toroidal plasmas has been investigated extensively. It is pointed out that the nonlinear instability is important in driving the microturbulence[1], i.e., the self-sustained plasma turbulence. This concept is explained as follows; when the electron motion along the magnetic field line is resisted by the background turbulence, it gives rise to the effective resistivity and enhances the level of the turbulence. The nonlinear simulation of the electrostatic current diffusive interchange mode (CDIM) in the two dimensional sheared slab geometry has been performed as an example. The occurrence of the nonlinear instability and the self-sustainment of the plasma turbulence were confirmed by this simulation[2]. On the other hand, the electromagnetic turbulence is sustained in the high pressure limit. The possibility of the self-organization with more variety has been pointed out[3]. It is important to study the electromagnetic turbulence based on the nonlinear simulation. In this paper, the model equation for the electrostatic CDIM turbulence[2] is extended for both electrostatic and electromagnetic turbulence. (1) Not only E x B convective nonlinearity but also the electromagnetic nonlinearity which is related to the parallel flow are incorporated into the model equation. (2) The electron and ion pressure evolution equations are solved separately, making it possible to distinguish the electron and ion thermal diffusivities. The two dimensional nonlinear simulation of the electromagnetic CDIM is performed based on the extended fluid model. This paper is organized as follows. The model equation is explained in section II. The result of simulation is shown in section III. The conclusion and discussion are given in section IV. (author)
A comprehensive spectral theory of zonal-mode dynamics in trapped electron mode turbulence
International Nuclear Information System (INIS)
Terry, P.W.; Gatto, R.; Baver, D.A.; Fernandez, E.
2005-01-01
A comprehensive, self-consistent theory for spectral dynamics in trapped electron mode (TEM) turbulence offers critical new understanding and insights into zonal-mode physics. This theory shows that 1) zonal mode structure, anisotropy, excitation, and temporal behavior arise at and from the interface of nonlinear advection and linear wave properties; 2) waves induce a marked spectral energy-transfer anisotropy that preferentially drives zonal modes relative to non zonal modes; 3) triplet correlations involving density (as opposed to those involving only flow) mediate the dominant energy transfer at long wavelengths; 4) energy transfer becomes inverse in the presence of wave anisotropy, where otherwise it is forward; 5) zonal-mode excitation is accompanied by excitation of a spectrum of damped eigenmodes, making zonal modes nonlinearly damped; and 6) the combination of anisotropic transfer to zonal modes and their nonlinear damping make this the dominant saturation mechanism for TEM turbulence. This accounts for the reduction of turbulence level by zonal modes, not zonal-flow ExB shearing. (author)
Evolutionary pulsational mode dynamics in nonthermal turbulent viscous astrofluids
Karmakar, Pralay Kumar; Dutta, Pranamika
2017-11-01
The pulsational mode of gravitational collapse in a partially ionized self-gravitating inhomogeneous viscous nonthermal nonextensive astrofluid in the presence of turbulence pressure is illustratively analyzed. The constitutive thermal species, lighter electrons and ions, are thermostatistically treated with the nonthermal κ-distribution laws. The inertial species, such as identical heavier neutral and charged dust microspheres, are modelled in the turbulent fluid framework. All the possible linear processes responsible for dust-dust collisions are accounted. The Larson logatropic equations of state relating the dust thermal (linear) and turbulence (nonlinear) pressures with dust densities are included. A regular linear normal perturbation analysis (local) over the complex astrocloud ensues in a generalized quartic dispersion relation with unique nature of plasma-dependent multi-parametric coefficients. A numerical standpoint is provided to showcase the basic mode features in a judicious astronomical paradigm. It is shown that both the kinematic viscosity of the dust fluids and nonthermality parameter (kappa, the power-law tail index) of the thermal species act as stabilizing (damping) agent against the gravity; and so forth. The underlying evolutionary microphysics is explored. The significance of redistributing astrofluid material via waveinduced accretion in dynamic nonhomologic structureless cloud collapse leading to hierarchical astrostructure formation is actualized.
Trapped Electron Mode Turbulence Driven Intrinsic Rotation in Tokamak Plasmas
International Nuclear Information System (INIS)
Wang, W.X.; Hahm, T.S.; Ethier, S.; Zakharov, L.E.
2011-01-01
Recent progress from global gyrokinetic simulations in understanding the origin of intrinsic rotation in toroidal plasmas is reported with emphasis on electron thermal transport dominated regimes. The turbulence driven intrinsic torque associated with nonlinear residual stress generation by the fluctuation intensity and the intensity gradient in the presence of zonal flow shear induced asymmetry in the parallel wavenumber spectrum is shown to scale close to linearly with plasma gradients and the inverse of the plasma current. These results qualitatively reproduce empirical scalings of intrinsic rotation observed in various experiments. The origin of current scaling is found to be due to enhanced kll symmetry breaking induced by the increased radial variation of the safety factor as the current decreases. The physics origin for the linear dependence of intrinsic torque on pressure gradient is that both turbulence intensity and the zonal flow shear, which are two key ingredients for driving residual stress, increase with the strength of turbulence drive, which is R0/LTe and R0/Lne for the trapped electron mode.
Orbital angular momentum mode of Gaussian beam induced by atmospheric turbulence
Cheng, Mingjian; Guo, Lixin; Li, Jiangting; Yan, Xu; Dong, Kangjun
2018-02-01
Superposition theory of the spiral harmonics is employed to numerical study the transmission property of the orbital angular momentum (OAM) mode of Gaussian beam induced by atmospheric turbulence. Results show that Gauss beam does not carry OAM at the source, but various OAM modes appear after affected by atmospheric turbulence. With the increase of atmospheric turbulence strength, the smaller order OAM modes appear firstly, followed by larger order OAM modes. The beam spreading of Gauss beams in the atmosphere enhance with the increasing topological charge of the OAM modes caused by atmospheric turbulence. The mode probability density of the OAM generated by atmospheric turbulence decreases, and peak position gradually deviate from the Gauss beam spot center with the increase of the topological charge. Our results may be useful for improving the performance of long distance laser digital spiral imaging system.
Tokamak fluidlike equations, with applications to turbulence and transport in H mode discharges
International Nuclear Information System (INIS)
Kim, Y.B.; Biglari, H.; Carreras, B.A.; Diamond, P.H.; Groebner, R.J.; Kwon, O.J.; Spong, D.A.; Callen, J.D.; Chang, Z.; Hollenberg, J.B.; Sundaram, A.K.; Terry, P.W.; Wang, J.F.
1990-01-01
Significant progress has been made in developing tokamak fluidlike equations which are valid in all collisionality regimes in toroidal devices, and their applications to turbulence and transport in tokamaks. The areas highlighted in this paper include: the rigorous derivation of tokamak fluidlike equations via a generalized Chapman-Enskog procedure in various collisionality regimes and on various time scales; their application to collisionless and collisional drift wave models in a sheared slab geometry; applications to neoclassical drift wave turbulence; i.e. neoclassical ion-temperature-gradient-driven turbulence and neoclassical electron-drift-wave turbulence; applications to neoclassical bootstrap-current-driven turbulence; numerical simulation of nonlinear bootstrap-current-driven turbulence and tearing mode turbulence; transport in Hot-Ion H mode discharges. 20 refs., 3 figs
Transport due to ion temperature gradient mode vortex turbulence
International Nuclear Information System (INIS)
Pavlenko, V.P.; Weiland, J.
1991-01-01
The ion energy transport due to an ensemble of nonlinear vortices is calculated in the test particle approximation for a strongly turbulent plasma. A diffusion coefficient proportional to the root of the stationary turbulence level is obtained. (au)
A new kinetic description for turbulent collisions including mode-coupling
International Nuclear Information System (INIS)
Misguich, J.H.; Tchen, C.M.
1982-07-01
The usual introduction of higher-order mode-coupling terms in the description of turbulent collisions beyond usual Renormalized Quasi-Linear approximation (RQL) is briefly analyzed. Here new results are derived in the framework of the general kinetic theory, and the equivalence is proved with the long time limit of simple results deduced from the Vlasov equation. The correction to the RQL turbulent collision term is analyzed and a new approximation is proposed. Turbulent collisions are also described by perturbation around the Lagrangian autocorrelation of fluctuating fields. For an homogeneous turbulence, however, the asymptotic integral of this Lagrangian autocorrelation vanishes identically, similarly to what occurs in Brownian motion. For inhomogeneous turbulence this method can nevertheless be used, and higher-order mode-coupling terms can be interpreted as a shielding of elementary Lagrangian turbulent collisions
An Exploration of Physiological Responses to the Native American Flute
Miller, Eric B.; Goss, Clinton F.
2014-01-01
This pilot study explored physiological responses to playing and listening to the Native American flute. Autonomic, electroencephalographic (EEG), and heart rate variability (HRV) metrics were recorded while participants (N = 15) played flutes and listened to several styles of music. Flute playing was accompanied by an 84% increase in HRV (p < .001). EEG theta (4-8 Hz) activity increased while playing flutes (p = .007) and alpha (8-12 Hz) increased while playing lower-pitched flutes (p = .009...
Asahi, Y.; Ishizawa, A.; Watanabe, T.-H.; Tsutsui, H.; Tsuji-Iio, S.
2014-05-01
Turbulent transport caused by electron temperature gradient (ETG) modes was investigated by means of gyrokinetic simulations. It was found that the ETG turbulence can be regulated by meso-scale zonal flows driven by trapped electron modes (TEMs), which are excited with much smaller growth rates than those of ETG modes. The zonal flows of which radial wavelengths are in between the ion and the electron banana widths are not shielded by trapped ions nor electrons, and hence they are effectively driven by the TEMs. It was also shown that an E × B shearing rate of the TEM-driven zonal flows is larger than or comparable to the growth rates of long-wavelength ETG modes and TEMs, which make a main contribution to the turbulent transport before excitation of the zonal flows.
Construction practices in pre-Hispanic flutes
Rawcliffe, Susan
2002-11-01
The ancient cultures of the Americas were separated by thousands of miles and thousand of years. There was a long history of trade over the miles and the years with many shared cultural ideals and artifacts, as evidenced by their musical instruments. Flutes were the most prevalent instruments found throughout the ancient Americas. Some types are unique to the pre-Hispanic world. Although flutes were constructed from a variety of materials, including bone, cane, seed pods, skulls, it is primarily the ceramic ones that survived, and it is ceramic flutes which form the bulk of this writer's work and research. This paper includes musical demonstrations to show how ancient flutemakers could have manipulated timbre during construction. Clay's plasticity enabled the construction of some instruments, and limited the development of others. Pitch jump flutes, certain Veracruzano whistles, and chamberduct flutes and whistles all share the addition of clay flaps or chambers around the aperture, as do hooded pipes. Some instruments exhibit a seemingly cultural predilection for complex tones that are windy, raspy, or animalistic. Simple adjustments of the airduct promote these timbres. Also included will be samples of the original sounds of ancient flutes.
Turbulent edge transport in the Princeton Beta Experiment-Modified high confinement mode
Tynan, G. R.; Schmitz, L.; Blush, L.; Boedo, J. A.; Conn, R. W.; Doerner, R.; Lehmer, R.; Moyer, R.; Kugel, H.; Bell, R.; Kaye, S.; Okabayashi, M.; Sesnic, S.; Sun, Y.
1994-10-01
The first probe measurements of edge turbulence and transport in a neutral beam induced high confinement mode (H-mode) are reported. A strong negative radial electric field is directly observed in H-mode. A transient suppression of normalized ion saturation and floating potential fluctuation levels occurs at the low confinement mode to high confinement mode (L-H) transition, followed by a recovery to near low mode (L-mode) levels. The average poloidal wave number and the poloidal wave-number spectral width are decreased, and the correlation between fluctuating density and potential is reduced. A large-amplitude coherent oscillation, localized to the strong radial electric field region, is observed in H-mode but does not cause transport. In H-mode the effective turbulent diffusion coefficient is reduced by an order of magnitude inside the last closed flux surface and in the scrape-off layer. The results are compared with a heuristic model of turbulence suppression by velocity-shear stabilization.
The impact of pedestal turbulence and electron inertia on edge-localized-mode crashes
Energy Technology Data Exchange (ETDEWEB)
Xi, P. W. [FSC and State Key Lab of Nuclear Physics and Technology, Department of Physics, Peking University, Beijing 100871 (China); Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Xu, X. Q. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Diamond, P. H. [WCI Center for Fusion Theory, National Fusion Research Institute, Daejeon (Korea, Republic of); Center for Astrophysics and Space Sciences and Department of Physics, University of California San Diego, La Jolla, California 92093-0429 (United States)
2014-05-15
We demonstrate that the occurrence of Edge-Localized-Modes (ELM) crashes does not depend only on the linear peeling-ballooning threshold, but also relies on nonlinear processes. Wave-wave interaction constrains the growth time of a mode, thus inducing a shift in the criterion for triggering an ELM crash. An ELM crash requires the P-B growth rate to exceed a critical value γ>γ{sub c}, where γ{sub c} is set by 1/τ{sup ¯}{sub c}, and τ{sup ¯}{sub c} is the averaged mode phase coherence time. For 0<γ<γ{sub c}, P-B turbulence develops but drives enhanced turbulent transport. We also show that electron inertia dramatically changes the instability threshold when density is low. However, P-B turbulence alone cannot generate enough current transport to allow fast reconnection during an ELM crash.
Morowitz, Harold J.
1996-10-01
Harold Morowitz has long been highly regarded both as an eminent scientist and as an accomplished science writer. The essays in The Wine of Life , his first collection, were hailed by C.P. Snow as "some of the wisest, wittiest and best informed I have ever read," and Carl Sagan called them "a delight to read." In later volumes he established a reputation for a wide-ranging intellect, an ability to see unexpected connections and draw striking parallels, and a talent for communicating scientific ideas with optimism and wit. With Entropy and the Magic Flute , Morowitz once again offers an appealing mix of brief reflections on everything from litmus paper to the hippopotamus to the sociology of Palo Alto coffee shops. Many of these pieces are appreciations of scientists that Morowitz holds in high regard, while others focus on health issues, such as America's obsession with cheese toppings. There is also a fascinating piece on the American Type Culture Collection, a zoo or warehouse for microbes that houses some 11,800 strains of bacteria, and over 3,000 specimens of protozoa, algae, plasmids, and oncogenes. Here then are over forty light, graceful essays in which one of our wisest experimental biologists comments on issues of science, technology, society, philosophy, and the arts.
Scaling and interaction of self-similar modes in models of high Reynolds number wall turbulence.
Sharma, A S; Moarref, R; McKeon, B J
2017-03-13
Previous work has established the usefulness of the resolvent operator that maps the terms nonlinear in the turbulent fluctuations to the fluctuations themselves. Further work has described the self-similarity of the resolvent arising from that of the mean velocity profile. The orthogonal modes provided by the resolvent analysis describe the wall-normal coherence of the motions and inherit that self-similarity. In this contribution, we present the implications of this similarity for the nonlinear interaction between modes with different scales and wall-normal locations. By considering the nonlinear interactions between modes, it is shown that much of the turbulence scaling behaviour in the logarithmic region can be determined from a single arbitrarily chosen reference plane. Thus, the geometric scaling of the modes is impressed upon the nonlinear interaction between modes. Implications of these observations on the self-sustaining mechanisms of wall turbulence, modelling and simulation are outlined.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'. © 2017 The Author(s).
POD Mode Robustness for the Turbulent Jet Sampled with PIV
DEFF Research Database (Denmark)
Hodzic, Azur; Meyer, Knud Erik; Velte, Clara Marika
2017-01-01
An important challenge in the description and simulation of turbulence is the large amount of information that is needed to describe even relatively simple flows in detail. The frequent disagreement between Reynolds averaged Navier–Stokes-based simulations and experiments is well known. Albeit, d...... and even high speed volumetric PIV systems providing fully three dimensional velocity fields. Another challenge is how do we verify simulations against experiments and ensure that we indeed have simulated the same flow that we have measured?......An important challenge in the description and simulation of turbulence is the large amount of information that is needed to describe even relatively simple flows in detail. The frequent disagreement between Reynolds averaged Navier–Stokes-based simulations and experiments is well known. Albeit......, direct numerical simulations and in certain cases large eddy simulations tend to agree fairly well with experiments, their practical implementation introduces the problem of data storage. The experimentalist, however, experiences the same problem, using highspeed particle image velocimetry (PIV) systems...
Bifurcation and phase diagram of turbulence constituted from three different scale-length modes
Energy Technology Data Exchange (ETDEWEB)
Itoh, S.-I.; Kitazawa, A.; Yagi, M. [Kyushu Univ., Research Inst. for Applied Mechanics, Kasuga, Fukuoka (Japan); Itoh, K. [National Inst. for Fusion Science, Toki, Gifu (Japan)
2002-04-01
Cases where three kinds of fluctuations having the different typical scale-lengths coexist are analyzed, and the statistical theory of strong turbulence in inhomogeneous plasmas is developed. Statistical nonlinear interactions between fluctuations are kept in the analysis as the renormalized drag, statistical noise and the averaged drive. The nonlinear interplay through them induces a quenching or suppressing effect, even if all the modes are unstable when they are analyzed independently. Variety in mode appearance takes place: one mode quenches the other two modes, or one mode is quenched by the other two modes, etc. The bifurcation of turbulence is analyzed and a phase diagram is drawn. Phase diagrams with cusp type catastrophe and butterfly type catastrophe are obtained. The subcritical bifurcation is possible to occur through the nonlinear interplay, even though each one is supercritical turbulence when analyzed independently. Analysis reveals that the nonlinear stability boundary (marginal point) and the amplitude of each mode may substantially shift from the conventional results of independent analyses. (author)
Abler, M. C.; Mauel, M. E.; Saperstein, A.
2017-12-01
Plasmas confined by a strong dipole field exhibit interchange and entropy mode turbulence, which previous experiments have shown respond locally to active feedback [1]. On the Collisionless Terrella Experiment (CTX), this turbulence is characterized by low frequency, low order, quasi-coherent modes with complex spectral dynamics. We apply bicoherence analysis [2] to study nonlinear phase coupling in a variety of scenarios. First, we study the self-interaction of the naturally occurring interchange turbulence; this analysis is then expanded to include the effects of single or multiple driven modes in the frequency range of the background turbulent oscillations. Initial measurements of coupling coefficients are presented in both cases. Driven low frequency interchange modes are observed to generate multiple harmonics which persist throughout the plasma, becoming weaker as they propagate away from the actuator in the direction of the electron magnetic drift. Future work is also discussed, including application of wavelet bicoherence analysis and applications to planetary magnetospheres. [1] Roberts, Mauel, and Worstell, Phys Plasmas (2015). [2] Grierson, Worstell, and Mauel, Phys Plasmas (2009). Supported by NSF-DOE Partnership for Plasma Science Grants DOE-DE-FG02-00ER54585 and NSF-PHY-1201896.
Multi-scale-nonlinear interactions among macro-MHD mode, micro-turbulence, and zonal flow
International Nuclear Information System (INIS)
Ishizawa, Akihiro; Nakajima, Noriyoshi
2007-01-01
This is the first numerical simulation demonstrating that macro-magnetohydrodynamic (macro-MHD) mode is exited as a result of multi-scale interaction in a quasi-steady equilibrium formed by a balance between zonal flow and micro-turbulence via reduced-two-fluid simulation. Only after obtaining the equilibrium which includes zonal flow and the turbulence caused by kinetic ballooning mode is this simulation of macro-MHD mode, double tearing mode, accomplished. In the quasi-steady equilibrium a macro-fluctuation which has the same helicity as that of double tearing mode is a part of the turbulence until it grows as a macro-MHD mode finally. When the macro-MHD grows it effectively utilize free energy of equilibrium current density gradient because of positive feedback loop between suppression of zonal flow and growth of the macro-fluctuation causing magnetic reconnection. Thus once the macro-MHD grows from the quasi-equilibrium, it does not go back. This simulation is more comparable with experimental observation of growing macro-fluctuation than traditional MHD simulation of linear instabilities in a static equilibrium. (author)
A novel turbulence trigger for neoclassical tearing modes in tokamaks
International Nuclear Information System (INIS)
Itoh, Sanae-I.; Yagi, Masatoshi; Itoh, Kimitaka
2003-07-01
Stochastic trigger by microturbulence for neoclassical tearing mode (NTM) is studied. NTM induces topological change of magnetic structure and has subcritical nature. Transition rate of probability density function for and statistically-averaged amplitude of NTM are obtained. Boundary in the phase diagram is determined as the statistical long time average of the transition conditions. NTM can be excited by crossing this boundary even in the absence of other global instabilities. (author)
International Nuclear Information System (INIS)
Kowal, Grzegorz; Lazarian, A.
2010-01-01
We study compressible magnetohydrodynamic turbulence, which holds the key to many astrophysical processes, including star formation and cosmic-ray propagation. To account for the variations of the magnetic field in the strongly turbulent fluid, we use wavelet decomposition of the turbulent velocity field into Alfven, slow, and fast modes, which presents an extension of the Cho and Lazarian decomposition approach based on Fourier transforms. The wavelets allow us to follow the variations of the local direction of the magnetic field and therefore improve the quality of the decomposition compared to the Fourier transforms, which are done in the mean field reference frame. For each resulting component, we calculate the spectra and two-point statistics such as longitudinal and transverse structure functions as well as higher order intermittency statistics. In addition, we perform a Helmholtz- Hodge decomposition of the velocity field into incompressible and compressible parts and analyze these components. We find that the turbulence intermittency is different for different components, and we show that the intermittency statistics depend on whether the phenomenon was studied in the global reference frame related to the mean magnetic field or in the frame defined by the local magnetic field. The dependencies of the measures we obtained are different for different components of the velocity; for instance, we show that while the Alfven mode intermittency changes marginally with the Mach number, the intermittency of the fast mode is substantially affected by the change.
Turbulent Statistics From Time-Resolved PIV Measurements of a Jet Using Empirical Mode Decomposition
Dahl, Milo D.
2013-01-01
Empirical mode decomposition is an adaptive signal processing method that when applied to a broadband signal, such as that generated by turbulence, acts as a set of band-pass filters. This process was applied to data from time-resolved, particle image velocimetry measurements of subsonic jets prior to computing the second-order, two-point, space-time correlations from which turbulent phase velocities and length and time scales could be determined. The application of this method to large sets of simultaneous time histories is new. In this initial study, the results are relevant to acoustic analogy source models for jet noise prediction. The high frequency portion of the results could provide the turbulent values for subgrid scale models for noise that is missed in large-eddy simulations. The results are also used to infer that the cross-correlations between different components of the decomposed signals at two points in space, neglected in this initial study, are important.
Targeting specific azimuthal modes using wall changes in turbulent pipe flow
van Buren, Tyler; Hellström, Leo; Marusic, Ivan; Smits, Alexander
2017-11-01
We experimentally study turbulent pipe flow at Re =3486 using stereoscopic particle image velocimetry. Using pipe inserts with non-circular geometry to perturb the flow upstream of the measurement location, we excite specific naturally occurring energetic modes. We consider inserts that directly manipulate the flow momentum (vortex generators), and/or induce secondary flows through Reynolds stresses (sinusoidally varying wall shape). These inserts substantially change the mean flow, and produce distinct regions of low and high momentum corresponding to the mode being excited. The inserts add energy in the targeted modes while simultaneously reducing the energy in the non-excited azimuthal modes. In addition, inserts designed to excite two modes simultaneously exhibit non-linear interactions. Supported under ONR Grant N00014-15-1-2402, Program Manager/Director Thomas Fu and the Australian Research Council.
Chen, Mo; Liu, Chao; Xian, Hao
2015-10-10
High-speed free-space optical communication systems using fiber-optic components can greatly improve the stability of the system and simplify the structure. However, propagation through atmospheric turbulence degrades the spatial coherence of the signal beam and limits the single-mode fiber (SMF) coupling efficiency. In this paper, we analyze the influence of the atmospheric turbulence on the SMF coupling efficiency over various turbulences. The results show that the SMF coupling efficiency drops from 81% without phase distortion to 10% when phase root mean square value equals 0.3λ. The simulations of SMF coupling with adaptive optics (AO) indicate that it is inevitable to compensate the high-order aberrations for SMF coupling over relatively strong turbulence. The SMF coupling efficiency experiments, using an AO system with a 137-element deformable mirror and a Hartmann-Shack wavefront sensor, obtain average coupling efficiency increasing from 1.3% in open loop to 46.1% in closed loop under a relatively strong turbulence, D/r0=15.1.
International Nuclear Information System (INIS)
Angelino, P; Bottino, A; Hatzky, R; Jolliet, S; Sauter, O; Tran, T M; Villard, L
2006-01-01
The mutual interactions of ion temperature gradient (ITG) driven modes, zonal flows and geodesic acoustic modes (GAM) in tokamak plasmas are investigated using a global nonlinear gyrokinetic formulation with totally unconstrained evolution of temperature gradient and profile. A series of numerical simulations with the same initial temperature and density profile specifications is performed using a sequence of ideal MHD equilibria differing only in the value of the total plasma current, in particular with identical magnetic shear profiles and shapes of magnetic surfaces. On top of a bursty or quasi-steady state behaviour the zonal flows oscillate at the GAM frequency. The amplitude of these oscillations increases with the value of the safety factor q, resulting in a less effective suppression of ITG turbulence by zonal flows at a lower plasma current. The turbulence-driven volume-averaged radial heat transport is found to scale inversely with the total plasma current
A sparse-mode spectral method for the simulation of turbulent flows
International Nuclear Information System (INIS)
Meneguzzi, M.; Politano, H.; Pouquet, A.; Zolver, M.
1996-01-01
We propose a new algorithm belonging to the family of the sparsemode spectral method to simulate turbulent flows. In this method the number of Fourier modes k increases with k more slowly than k D-1 in dimension D, while retaining the advantage of the fast Fourier transform. Examples of applications of the algorithm are given for the one-dimensional Burger's equation and two-dimensional incompressible MHD flows
International Nuclear Information System (INIS)
Banks, T.M.; Garlick, A.
1982-01-01
Transgranular cleavage is an important mode of crack propagation during stress-corrosion cracking (SCC) of Zircaloy in iodine vapour; and another characteristic feature is the presence of parallel closely spaced ridges. These are often referred to as Y-flutings because each ridge takes the form of an inverted Y when viewed along the direction of crack growth. The flutings are shown here to be formed by localised ductile parting of the Zircaloy near the tips of cleavage cracks; high mechanical constraints in those regions and the limited number of available slip systems result in the formation of a planar array of parallel tunnels. Upon final separation these appear as a pattern of parallel ridges on each fracture face. Striking similarities in morphology have been noted here between Y-flutings in Zircaloy and those produced during tests on unstable fluid interfaces: the direction of motion of the fluid interface can be determined from the Y-morphology and is in agreement with observations from Zircaloy SCC tests. It is further demonstrated that equations governing thermodynamic and kinetic instability of fluid interfaces can be adapted to relate the fluting spacing in Zircaloy to standard fracture mechanics parameters. (author)
Hanson, Frank; Lasher, Mark
2010-06-01
We characterize and compare the effects of turbulence on underwater laser propagation with theory. Measurements of the coupling efficiency of the focused beam into a single-mode fiber are reported. A simple tip-tilt control system, based on the position of the image centroid in the focal plane, was shown to maintain good coupling efficiency for a beam radius equal to the transverse coherence length, r(0). These results are relevant to high bandwidth communication technology that requires good spatial mode quality.
Bailly, Christophe
2015-01-01
This book covers the major problems of turbulence and turbulent processes, including physical phenomena, their modeling and their simulation. After a general introduction in Chapter 1 illustrating many aspects dealing with turbulent flows, averaged equations and kinetic energy budgets are provided in Chapter 2. The concept of turbulent viscosity as a closure of the Reynolds stress is also introduced. Wall-bounded flows are presented in Chapter 3, and aspects specific to boundary layers and channel or pipe flows are also pointed out. Free shear flows, namely free jets and wakes, are considered in Chapter 4. Chapter 5 deals with vortex dynamics. Homogeneous turbulence, isotropy, and dynamics of isotropic turbulence are presented in Chapters 6 and 7. Turbulence is then described both in the physical space and in the wave number space. Time dependent numerical simulations are presented in Chapter 8, where an introduction to large eddy simulation is offered. The last three chapters of the book summarize remarka...
Weak turbulence theory of ion temperature gradient modes for inverted density plasmas
International Nuclear Information System (INIS)
Hahm, T.S.; Tang, W.M.
1989-09-01
Typical profiles measured in H-mode (''high confinement'') discharges from tokamaks such as JET and DIII-D suggest that the ion temperature gradient instability threshold parameter η i (≡dlnT i /dlnn i ) could be negative in many cases. Previous linear theoretical calculations have established the onset conditions for these negative η i -modes and the fact that their growth rate is much smaller than their real frequency over a wide range of negative η i values. This has motivated the present nonlinear weak turbulence analysis to assess the relevance of such instabilities for confinement in H-mode plasmas. The nonlinear eigenmode equation indicates that the 3-wave coupling to shorter wavelength modes is the dominant nonlinear saturation mechanism. It is found that both the saturation level for these fluctuations and the magnitude of the associated ion thermal diffusivity are considerably smaller than the strong turbulence mixing length type estimates for the more conventional positive-η i -instabilities. 19 refs., 3 figs
Effects of Climate Change on Fluted Pumpkin Production and ...
African Journals Online (AJOL)
The importance of fluted pumpkin crop in rural household economy cannot be over emphasized. Farmers in the South South Nigeria depend greatly on fluted pumpkin for its many uses. The production however is beset with a myriad of constraints of which climate change is one of the most outstanding. The study assessed ...
International Nuclear Information System (INIS)
Hahm, T.S.
1990-12-01
Ion temperature gradient turbulence based transport models have difficulties reconciling the recent DIII-D H-mode results where the density profile is flat, but χ e > χ i in the core region. In this work, a nonlinear theory is developed for recently discovered ion temperature gradient trapped electron modes propagating in the electron diamagnetic direction. This instability is predicted to be linearly unstable for L Ti /R approx-lt κ θ ρ s approx-lt (L Ti /R) 1/4 . They are also found to be strongly dispersive even at these long wavelengths, thereby suggesting the importance of the wave-particle-wave interactions in the nonlinear saturation phase. The fluctuation spectrum and anomalous fluxes are calculated. In accordance with the trends observed in DIII-D, the predicted electron thermal diffusivity can be larger than the ion thermal diffusivity. 17 refs., 3 figs
H-Mode Turbulence, Power Threshold, ELM, and Pedestal Studies in NSTX
International Nuclear Information System (INIS)
Maingi, R.; Bush, C.E.; Fredrickson, E.D.; Gates, D.A.; Kaye, S.M.; LeBlanc, B.P.; Menard, J.E.; Meyer, H.; Mueller, D.; Nishino, N.; Roquemore, A.L.; Sabbagh, S.A.; Tritz, K.; Zweben, S.J.; Bell, M.G.; Bell, R.E.; Biewer, T.; Boedo, J.A.; Johnson, D.W.; Kaita, R.; Kugel, H.W.; Maqueda, R.J.; Munsat, T.; Raman, R.; Soukhanovskii, V.A.; Stevenson, T.; Stutman, D.
2004-01-01
High-confinement mode (H-mode) operation plays a crucial role in NSTX [National Spherical Torus Experiment] research, allowing higher beta limits due to reduced plasma pressure peaking, and long-pulse operation due to high bootstrap current fraction. Here, new results are presented in the areas of edge localized modes (ELMs), H-mode pedestal physics, L-H turbulence, and power threshold studies. ELMs of several other types (as observed in conventional aspect ratio tokamaks) are often observed: (1) large, Type I ELMs, (2) ''medium'' Type II/III ELMs, and (3) giant ELMs which can reduce stored energy by up to 30% in certain conditions. In addition, many high-performance discharges in NSTX have tiny ELMs (newly termed Type V), which have some differences as compared with ELM types in the published literature. The H-mode pedestal typically contains between 25-33% of the total stored energy, and the NSTX pedestal energy agrees reasonably well with a recent international multi-machine scaling. We find that the L-H transition occurs on a ∼100 (micro)sec timescale as viewed by a gas puff imaging diagnostic, and that intermittent quiescent periods precede the final transition. A power threshold identity experiment between NSTX and MAST shows comparable loss power at the L-H transition in balanced double-null discharges. Both machines require more power for the L-H transition as the balance is shifted toward lower single null. High field side gas fueling enables more reliable H-mode access, but does not always lead to a lower power threshold e.g., with a reduction of the duration of early heating. Finally the edge plasma parameters just before the L-H transition were compared with theories of the transition. It was found that while some theories can separate well-developed L- and H-mode data, they have little predictive value
Self-sustained turbulence and L-mode confinement in toroidal plasmas
International Nuclear Information System (INIS)
Itoh, K.; Itoh, S.; Fukuyama, A.; Yagi, M.; Azumi, M.
1993-04-01
Theory of the L-mode confinement in toroidal plasmas is developed. The quantitative effect of the anomalous transport, which is caused by microscopic fluctuations, on the pressure-gradient- driven modes is analyzed. The ExB nonlinearity is renormalized in a form of the transport coefficient such as the thermal diffusivity, the ion viscosity and the current diffusivity. The destabilization by the current-diffusivity and the stabilization by the thermal transport and ion viscosity are analyzed. By use of the mean-field approximations, the nonlinear dispersion relation is solved. Growth rate and stability condition are expressed in terms of the renormalized transport coefficients. The transport coefficients in the steady state are obtained by the marginal stability condition for the least stable mode. This method is applied to the microscopic ballooning mode for the toroidal plasma with the magnetic well (such as tokamak). The comparison with experimental observations are made. A good agreement is found in a various aspects of the L-mode plasmas; The typical wavenumber and level of the fluctuations for the self-sustained turbulence is also obtained. The analysis is also made for the plasma with magnetic hill and shear (such as torsatron/Heliotron devices). This method is applied to the interchange modes. Formula of the anomalous transport is obtained. Also investigated is the case of the magnetic well and low magnetic shear (conventional stellarator). The roles of the pressure gradient and the collisionless skin depth in determining the anomalous transport are found to be generic in toroidal plasmas. The difference in the magnetic configuration affects the transport coefficient. These formula explain major experimental observations. (J.P.N.)
Inertial modes and their transition to turbulence in a differentially rotating spherical gap flow
Hoff, Michael; Harlander, Uwe; Andrés Triana, Santiago; Egbers, Christoph
2016-04-01
dominant mode (l,m,ˆω) = (3,2,˜ 0.71) is increasing with increasing |Ro| until a critical Rossby number Rocrit. Accompanying with this is an increase of the zonal mean flow outside the tangent cylinder, leading to enhanced angular momentum transport. At the particular Rocrit, the wave mode, and the entire flow, breaks up into smaller-scale turbulence [6], together with a strong increase of the zonal mean flow inside the tangent cylinder. We found that the critical Rossby number scales approximately with E1/5. References [1] Aldridge, K. D.; Lumb, L. I. (1987): Inertial waves identified in the Earth's fluid outer core. Nature 325 (6103), S. 421-423. DOI: 10.1038/325421a0. [2] Greenspan, H. P. (1968): The theory of rotating fluids. London: Cambridge U.P. (Cambridge monographs on mechanics and applied mathematics). [3] Kelley, D. H.; Triana, S. A.; Zimmerman, D. S.; Lathrop, D. P. (2010): Selection of inertial modes in spherical Couette flow. Phys. Rev. E 81 (2), 26311. DOI: 10.1103/PhysRevE.81.026311. [4] Rieutord, M.; Triana, S. A.; Zimmerman, D. S.; Lathrop, D. P. (2012): Excitation of inertial modes in an experimental spherical Couette flow. Phys. Rev. E 86 (2), 026304. DOI: 10.1103/PhysRevE.86.026304. [5] Hoff, M., Harlander, U., Egbers, C. (2016): Experimental survey of linear and nonlinear inertial waves and wave instabilities in a spherical shell. J. Fluid Mech., (in print) [6] Kerswell, R. R. (1999): Secondary instabilities in rapidly rotating fluids: inertial wave breakdown. Journal of Fluid Mechanics 382, S. 283-306. DOI: 10.1017/S0022112098003954.
DISCOVERY AND RESEARCH ON JIAHU BONE FLUTES IN WUYANG, CHINA.
Energy Technology Data Exchange (ETDEWEB)
JUZHONG, Z.; HARBOTTLE, G.; XINGHUA, X.; CHANGSUI, W.
2000-11-01
The site of Jiahu is located in Jiahu village, Wuyang County, Henan province, on the Western edge of the broad plain of Huanhuaihai. On its north the site borders the Sha River, in the upper reaches of the Huai River; its latitude is 33{degree} 36 minutes North, longitude 113{degree} 40 minutes East, and it is 67.5 meters above sea level. Between 1983 and 1987, the Henan Cultural Relics and Archaeology Institute carried out six campaigns of excavation here, revealing an area of 2400 square meters. Except for the trial excavation in the spring of 1983, Zhang Juzhong has been in charge of all the excavations. In early May 1986, while excavating tomb 78, Zhang Juzhong and Yang Zhenwei first discovered two funerary bone flutes. They soon found other, similar bone flutes in tombs 73, 94 and 121 respectively. Mr. Zhang's attention was instantly focused on these remarkable finds. In the campaign of autumn 1986, one or two more bone flutes were discovered in each of tombs 233,273, 263 and 270. Finally, in the spring of 1987, again one or two bone flutes were found in each of the tombs 282, 363,341,411,344 and 387. Up to the end of excavation in June 1987, altogether 25 bone flutes had been found, of which 17 were complete or almost complete, 6 broken or fragmentary and 2 were half-finished examples. Among the 17 complete bone flutes, there were 14 having seven holes, one five-hole, one six-hole and one eight-hole bone flute. In particular, the bone flute M282:20 was exquisitely made, and complete. Zhang Juzhong, the discoverer of the bone flutes, researcher Pei Mingxiang, the. ex-director of the division, who came to the digging site to see the progress of the work, and their coworkers were all understandably very excited.
International Nuclear Information System (INIS)
Parkin, E. R.; Bicknell, G. V.
2013-01-01
Global three-dimensional magnetohydrodynamic (MHD) simulations of turbulent accretion disks are presented which start from fully equilibrium initial conditions in which the magnetic forces are accounted for and the induction equation is satisfied. The local linear theory of the magnetorotational instability (MRI) is used as a predictor of the growth of magnetic field perturbations in the global simulations. The linear growth estimates and global simulations diverge when nonlinear motions—perhaps triggered by the onset of turbulence—upset the velocity perturbations used to excite the MRI. The saturated state is found to be independent of the initially excited MRI mode, showing that once the disk has expelled the initially net flux field and settled into quasi-periodic oscillations in the toroidal magnetic flux, the dynamo cycle regulates the global saturation stress level. Furthermore, time-averaged measures of converged turbulence, such as the ratio of magnetic energies, are found to be in agreement with previous works. In particular, the globally averaged stress normalized to the gas pressure P >bar = 0.034, with notably higher values achieved for simulations with higher azimuthal resolution. Supplementary tests are performed using different numerical algorithms and resolutions. Convergence with resolution during the initial linear MRI growth phase is found for 23-35 cells per scale height (in the vertical direction).
Nonlinear Simulations of Trapped Electron Mode Turbulence in Low Magnetic Shear Stellarators
Faber, B. J.; Pueschel, M. J.; Terry, P. W.; Hegna, C. C.
2017-10-01
Optimized stellarators, like the Helically Symmetric eXperiment (HSX), often operate with small global magnetic shear to avoid low-order rational surfaces and magnetic islands. Nonlinear, flux-tube gyrokinetic simulations of density-gradient-driven Trapped Electron Mode (TEM) turbulence in HSX shows two distinct spectral fluctuation regions: long-wavelength slab-like TEMs localized by global magnetic shear that extend along field lines and short-wavelength TEMs localized by local magnetic shear to a single helical bad curvature region. The slab-like TEMs require computational domains significantly larger than one poloidal turn and are computationally expensive, making turbulent optimization studies challenging. A computationally more efficient, zero-average-magnetic-shear approximation is shown to sufficiently describe the relevant nonlinear physics and replicate finite-shear computations, and can be exploited in quasilinear models based on linear gyrokinetics as a feasible optimization tool. TEM quasilinear heat fluxes are computed with the zero-shear approximation and compared to experimentally-relevant nonlinear gyrokinetic TEM heat fluxes for HSX. Research supported by U.S. DoE Grants DE-FG02-99ER54546, DE-FG02-93ER54222 and DE-FG02-89ER53291.
On the effective turbulence driving mode of molecular clouds formed in disc galaxies
Jin, Keitaro; Salim, Diane M.; Federrath, Christoph; Tasker, Elizabeth J.; Habe, Asao; Kainulainen, Jouni T.
2017-07-01
We determine the physical properties and turbulence driving mode of molecular clouds formed in numerical simulations of a Milky Way-type disc galaxy with parsec-scale resolution. The clouds form through gravitational fragmentation of the gas, leading to average values for mass, radii and velocity dispersion in good agreement with observations of Milky Way clouds. The driving parameter (b) for the turbulence within each cloud is characterized by the ratio of the density contrast (σ _{ρ /ρ _0}) to the average Mach number (M) within the cloud, b=σ _{ρ /ρ _0}/M. As shown in previous works, b ˜ 1/3 indicates solenoidal (divergence-free) driving and b ˜ 1 indicates compressive (curl-free) driving. We find that the average b value of all the clouds formed in the simulations has a lower limit of b > 0.2. Importantly, we find that b has a broad distribution, covering values from purely solenoidal to purely compressive driving. Tracking the evolution of individual clouds reveals that the b value for each cloud does not vary significantly over their lifetime. Finally, we perform a resolution study with minimum cell sizes of 8, 4, 2 and 1 pc and find that the average b value increases with increasing resolution. Therefore, we conclude that our measured b values are strictly lower limits and that a resolution better than 1 pc is required for convergence. However, regardless of the resolution, we find that b varies by factors of a few in all cases, which means that the effective driving mode alters significantly from cloud to cloud.
Jolivet: Complete Flute Music, Vol. 2 / Guy S. Rickards
Rickards, Guy S.
1996-01-01
Uuest heliplaadist "Jolivet: Complete Flute Music, Vol. 2. Kroumata Percussion Ensemble, Tapiola Sinfonietta, Paavo Järvi". BIS CD 739 (64 minutes: DDD). Item marked from CD630 (6/94), CD272, remainder new to UK
Residual Effect of Chromium on Early Growth of Fluted Pumpkin ...
African Journals Online (AJOL)
Michael Horsfall
some agronomic characters, nutrient content, nutrient uptake and crude protein content of fluted ... Results revealed that the plant height, stem girth, leaf area, number of leaves, dry matter yield, ..... oxygen and this will lead to slow growth and.
Fluid mechanics and heat transfer spirally fluted tubing
Larue, J. C.; Libby, P. A.; Yampolsky, J. S.
1981-08-01
The objective of this program is to develop both a qualitative and a quantitative understanding of the fluid mechanics and heat transfer mechanisms that underlie the measured performance of the spirally fluted tubes under development at General Atomic. The reason for the interest in the spirally fluted tubes is that results to date have indicated three advantages to this tubing concept: The fabrication technique of rolling flutes on strip and subsequently spiralling and simultaneously welding the strip to form tubing results in low fabrication costs, approximately equal to those of commercially welded tubing. The heat transfer coefficient is increased without a concomitant increase of the friction coefficient on the inside of the tube. In single-phase axial flow of water, the helical flutes continuously induce rotation of the flow both within and without the tube as a result of the effect of curvature. An increase in condensation heat transfer on the outside of the tube is achieved. In a vertical orientation with fluid condensing on the outside of the helically fluted tube, the flutes provide a channel for draining the condensed fluid.
Flute instability growth on a magnetized plasma column
International Nuclear Information System (INIS)
Rose, D. V.; Genoni, T. C.; Welch, D. R.; Mehlhorn, T. A.; Porter, J. L.; Ditmire, T.
2006-01-01
The growth of the flute-type instability for a field-aligned plasma column immersed in a uniform magnetic field is studied. Particle-in-cell simulations are compared with a semi-analytic dispersion analysis of the drift cyclotron instability in cylindrical geometry with a Gaussian density profile in the radial direction. For the parameters considered here, the dispersion analysis gives a local maximum for the peak growth rates as a function of R/r i , where R is the Gaussian characteristic radius and r i is the ion gyroradius. The electrostatic and electromagnetic particle-in-cell simulation results give azimuthal and radial mode numbers that are in reasonable agreement with the dispersion analysis. The electrostatic simulations give linear growth rates that are in good agreement with the dispersion analysis results, while the electromagnetic simulations yield growth rate trends that are similar to the dispersion analysis but that are not in quantitative agreement. These differences are ascribed to higher initial field fluctuation levels in the electromagnetic field solver. Overall, the simulations allow the examination of both the linear and nonlinear evolution of the instability in this physical system up to and beyond the point of wave energy saturation
Energy Technology Data Exchange (ETDEWEB)
Wang, G. [University of California, Los Angeles, CA 90095 (United States)]. E-mail: wangg@fusion.gat.com; Peebles, W.A. [University of California, Los Angeles, CA 90095 (United States); Doyle, E.J. [University of California, Los Angeles, CA 90095 (United States); Rhodes, T.L. [University of California, Los Angeles, CA 90095 (United States); Zeng, L. [University of California, Los Angeles, CA 90095 (United States); Nguyen, X. [University of California, Los Angeles, CA 90095 (United States); Osborne, T.H. [General Atomics, San Diego, CA 92186-5608 (United States); Snyder, P.B. [General Atomics, San Diego, CA 92186-5608 (United States); Kramer, G.J. [Princeton Plasma Physics Laboratory, Princeton, NJ 08543 (United States); Nazikian, R. [Princeton Plasma Physics Laboratory, Princeton, NJ 08543 (United States); Groebner, R.J. [General Atomics, San Diego, CA 92186-5608 (United States); Burrell, K.H. [General Atomics, San Diego, CA 92186-5608 (United States); Leonard, A.W. [General Atomics, San Diego, CA 92186-5608 (United States); Fenstermacher, M.E. [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Strait, E.J. [General Atomics, San Diego, CA 92186-5608 (United States)
2007-06-15
High-resolution quadrature reflectometer measurements of density fluctuation levels have been obtained on DIII-D for H-mode edge pedestal studies. Initial results are presented from the L-H transition to the first ELM for two cases: (i) a low pedestal beta discharge, in which density turbulence in the pedestal has little change during the ELM-free phase, and (ii) a high pedestal beta discharge in which both density and magnetic turbulence are observed to increase before the first ELM. These high beta data are consistent with the existence of electromagnetic turbulence suggested by some transport models. During Type-I ELM cycles, when little magnetic turbulence can be observed, pedestal turbulence increases just after an ELM crash and then decreases before next ELM strikes, in contrast to a drop after ELM crash and then it re-grows when strong magnetic turbulence shows similar behavior. Clear ELM precursors are observed on {<=}20% of Type-I ELMs observed to date.
International Nuclear Information System (INIS)
McKee, G.; Gohil, P.; Schlossberg, D.; Boedo, J.; Burrell, K.; deGrassie, J.; Groebner, R.; Makowski, M.; Moyer, R.; Petty, C.; Rhodes, T.; Schmitz, L.; Shafer, M.; Solomon, W.; Umansky, M.; Wang, G.; White, A.; Xu, X.
2008-01-01
The injected power required to induce a transition from L-mode to H-mode plasmas is found to depend strongly on the injected neutral beam torque and consequent plasma toroidal rotation. Edge turbulence and flows, measured near the outboard midplane of the plasma (0.85 < r/a < 1.0) on DIII-D with the high-sensitivity 2D beam emission spectroscopy (BES) system, likewise vary with rotation and suggest a causative connection. The L-H power threshold in plasmas with the ion (del)B drift away from the X-point decreases from 4-6 MW with co-current beam injection, to 2-3 MW with near zero net injected torque, and to <2 MW with counter injection. Plasmas with the ion (del)B drift towards the X-point exhibit a qualitatively similar though less pronounced power threshold dependence on rotation. 2D edge turbulence measurements with BES show an increasing poloidal flow shear as the L-H transition is approached in all conditions. At low rotation, the poloidal flow of turbulent eddies near the edge reverses prior to the L-H transition, generating a significant poloidal flow shear that exceeds the measured turbulence decorrelation rate. This increased poloidal turbulence velocity shear may facilitate the L-H transition. No such reversal is observed in high rotation plasmas. The poloidal turbulence velocity spectrum exhibits a transition from a Geodesic Acoustic Mode zonal flow to a higher-power, lower frequency, zero-mean-frequency zonal flow as rotation varies from co-current to balanced during a torque scan at constant injected neutral beam power, perhaps also facilitating the L-H transition. This reduced power threshold at lower toroidal rotation may benefit inherently low-rotation plasmas such as ITER
Turbulent transport stabilization by ICRH minority fast ions in low rotating JET ILW L-mode plasmas
Bonanomi, N.; Mantica, P.; Di Siena, A.; Delabie, E.; Giroud, C.; Johnson, T.; Lerche, E.; Menmuir, S.; Tsalas, M.; Van Eester, D.; Contributors, JET
2018-05-01
The first experimental demonstration that fast ion induced stabilization of thermal turbulent transport takes place also at low values of plasma toroidal rotation has been obtained in JET ILW (ITER-like wall) L-mode plasmas with high (3He)-D ICRH (ion cyclotron resonance heating) power. A reduction of the gyro-Bohm normalized ion heat flux and higher values of the normalized ion temperature gradient have been observed at high ICRH power and low NBI (neutral beam injection) power and plasma rotation. Gyrokinetic simulations indicate that ITG (ion temperature gradient) turbulence stabilization induced by the presence of high-energetic 3He ions is the key mechanism in order to explain the experimental observations. Two main mechanisms have been identified to be responsible for the turbulence stabilization: a linear electrostatic wave-fast particle resonance mechanism and a nonlinear electromagnetic mechanism. The dependence of the stabilization on the 3He distribution function has also been studied.
International Nuclear Information System (INIS)
Rhodes, T.L.; Leboeuf, J.-N.; Sydora, R.D.; Groebner, R.J.; Doyle, E.J.; McKee, G.R.; Peebles, W.A.; Rettig, C.L.; Zeng, L.; Wang, G.
2002-01-01
Measured turbulence characteristics (correlation lengths, spectra, etc.) in low-confinement (L-mode) and high-performance plasmas in the DIII-D tokamak [Luxon et al., Proceedings Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] show many similarities with the characteristics determined from turbulence simulations. Radial correlation lengths Δr of density fluctuations from L-mode discharges are found to be numerically similar to the ion poloidal gyroradius ρ θ,s , or 5-10 times the ion gyroradius ρ s over the radial region 0.2 θ,s or 5-10 times ρ s , an experiment was performed which modified ρ θs while keeping other plasma parameters approximately fixed. It was found that the experimental Δr did not scale as ρ θ,s , which was similar to low-resolution UCAN simulations. Finally, both experimental measurements and gyrokinetic simulations indicate a significant reduction in the radial correlation length from high-performance quiescent double barrier discharges, as compared to normal L-mode, consistent with reduced transport in these high-performance plasmas
Isliker, H.; Pisokas, Th.; Strintzi, D.; Vlahos, L.
2010-08-01
A new self-organized criticality (SOC) model is introduced in the form of a cellular automaton (CA) for ion temperature gradient (ITG) mode driven turbulence in fusion plasmas. Main characteristics of the model are that it is constructed in terms of the actual physical variable, the ion temperature, and that the temporal evolution of the CA, which necessarily is in the form of rules, mimics actual physical processes as they are considered to be active in the system, i.e., a heating process and a local diffusive process that sets on if a threshold in the normalized ITG R /LT is exceeded. The model reaches the SOC state and yields ion temperature profiles of exponential shape, which exhibit very high stiffness, in that they basically are independent of the loading pattern applied. This implies that there is anomalous heat transport present in the system, despite the fact that diffusion at the local level is imposed to be of a normal kind. The distributions of the heat fluxes in the system and of the heat out-fluxes are of power-law shape. The basic properties of the model are in good qualitative agreement with experimental results.
A study of self organized criticality in ion temperature gradient mode driven gyrokinetic turbulence
Mavridis, M.; Isliker, H.; Vlahos, L.; Görler, T.; Jenko, F.; Told, D.
2014-10-01
An investigation on the characteristics of self organized criticality (Soc) in ITG mode driven turbulence is made, with the use of various statistical tools (histograms, power spectra, Hurst exponents estimated with the rescaled range analysis, and the structure function method). For this purpose, local non-linear gyrokinetic simulations of the cyclone base case scenario are performed with the GENE software package. Although most authors concentrate on global simulations, which seem to be a better choice for such an investigation, we use local simulations in an attempt to study the locally underlying mechanisms of Soc. We also study the structural properties of radially extended structures, with several tools (fractal dimension estimate, cluster analysis, and two dimensional autocorrelation function), in order to explore whether they can be characterized as avalanches. We find that, for large enough driving temperature gradients, the local simulations exhibit most of the features of Soc, with the exception of the probability distribution of observables, which show a tail, yet they are not of power-law form. The radial structures have the same radial extent at all temperature gradients examined; radial motion (transport) though appears only at large temperature gradients, in which case the radial structures can be interpreted as avalanches.
A study of self organized criticality in ion temperature gradient mode driven gyrokinetic turbulence
International Nuclear Information System (INIS)
Mavridis, M.; Isliker, H.; Vlahos, L.; Görler, T.; Jenko, F.; Told, D.
2014-01-01
An investigation on the characteristics of self organized criticality (Soc) in ITG mode driven turbulence is made, with the use of various statistical tools (histograms, power spectra, Hurst exponents estimated with the rescaled range analysis, and the structure function method). For this purpose, local non-linear gyrokinetic simulations of the cyclone base case scenario are performed with the GENE software package. Although most authors concentrate on global simulations, which seem to be a better choice for such an investigation, we use local simulations in an attempt to study the locally underlying mechanisms of Soc. We also study the structural properties of radially extended structures, with several tools (fractal dimension estimate, cluster analysis, and two dimensional autocorrelation function), in order to explore whether they can be characterized as avalanches. We find that, for large enough driving temperature gradients, the local simulations exhibit most of the features of Soc, with the exception of the probability distribution of observables, which show a tail, yet they are not of power-law form. The radial structures have the same radial extent at all temperature gradients examined; radial motion (transport) though appears only at large temperature gradients, in which case the radial structures can be interpreted as avalanches
A study of self organized criticality in ion temperature gradient mode driven gyrokinetic turbulence
Energy Technology Data Exchange (ETDEWEB)
Mavridis, M.; Isliker, H.; Vlahos, L. [Section of Astrophysics, Astronomy and Mechanics, Department of Physics, Aristotle University of Thessaloniki, GR-54124 Thessaloniki (Greece); Görler, T.; Jenko, F.; Told, D. [Max Planck Institute for Plasma Physics, Boltzmannstr. 2, 85748 Garching (Germany)
2014-10-15
An investigation on the characteristics of self organized criticality (Soc) in ITG mode driven turbulence is made, with the use of various statistical tools (histograms, power spectra, Hurst exponents estimated with the rescaled range analysis, and the structure function method). For this purpose, local non-linear gyrokinetic simulations of the cyclone base case scenario are performed with the GENE software package. Although most authors concentrate on global simulations, which seem to be a better choice for such an investigation, we use local simulations in an attempt to study the locally underlying mechanisms of Soc. We also study the structural properties of radially extended structures, with several tools (fractal dimension estimate, cluster analysis, and two dimensional autocorrelation function), in order to explore whether they can be characterized as avalanches. We find that, for large enough driving temperature gradients, the local simulations exhibit most of the features of Soc, with the exception of the probability distribution of observables, which show a tail, yet they are not of power-law form. The radial structures have the same radial extent at all temperature gradients examined; radial motion (transport) though appears only at large temperature gradients, in which case the radial structures can be interpreted as avalanches.
International Nuclear Information System (INIS)
Isliker, H.; Pisokas, Th.; Vlahos, L.; Strintzi, D.
2010-01-01
A new self-organized criticality (SOC) model is introduced in the form of a cellular automaton (CA) for ion temperature gradient (ITG) mode driven turbulence in fusion plasmas. Main characteristics of the model are that it is constructed in terms of the actual physical variable, the ion temperature, and that the temporal evolution of the CA, which necessarily is in the form of rules, mimics actual physical processes as they are considered to be active in the system, i.e., a heating process and a local diffusive process that sets on if a threshold in the normalized ITG R/L T is exceeded. The model reaches the SOC state and yields ion temperature profiles of exponential shape, which exhibit very high stiffness, in that they basically are independent of the loading pattern applied. This implies that there is anomalous heat transport present in the system, despite the fact that diffusion at the local level is imposed to be of a normal kind. The distributions of the heat fluxes in the system and of the heat out-fluxes are of power-law shape. The basic properties of the model are in good qualitative agreement with experimental results.
International Nuclear Information System (INIS)
Terry, P.W.; Ware, A.S.; Newman, D.E.
1994-01-01
A nonlinear frequency shift in dissipative trapped electron mode turbulence is shown to give rise to a relaxation oscillation in the saturated power density spectrum. A simple non-Markovian closure for the coupled evolution of ion momentum and electron density response is developed to describe the oscillations. From solutions of a nonlinear oscillator model based on the closure, it is found that the oscillation is driven by the growth rate, as modified by the amplitude-dependent frequency shift, with inertia provided by the memory of the growth rate of prior amplitudes. This memory arises from time-history integrals common to statistical closures. The memory associated with a finite time of energy transfer between coupled spectrum components does not sustain the oscillation in the simple model. Solutions of the model agree qualitatively with the time-dependent numerical solutions of the original dissipative trapped electron model, yielding oscillations with the proper phase relationship between the fluctuation energy and the frequency shift, the proper evolution of the wave number spectrum shape and particle flux, and a realistic period
A Little Flute Music: Mimicry, Memory, and Narrativity
Directory of Open Access Journals (Sweden)
Vicki Powys
2013-11-01
Full Text Available A lyrebird chick was raised in captivity in the 1920s in Australia’s New England Tablelands, or so the story goes. The bird mimicked the sounds of the household’s flute player, learning two tunes and an ascending scale. When released back into the wild, his flute-like songs and timbre spread throughout the local lyrebird population. We count ourselves among those who admire the sonic achievements of this bioregion’s “flute lyrebirds.” These Superb Lyrebirds (Menura novaehollandiae do indeed deliver an unusual and extraordinarily complex, flute-like territorial song, although often with a musical competence exceeding what a human flutist could achieve. In this paper, we engage with both the living and the dead across a wide-ranging cast of characters, linking up in the here and now and grasping a hand across the span of many years. Memory and narrativity are pertinent to the at times conflicting stories and reminiscences from archival and contemporary sources. Ultimately, accounts of “flute lyrebirds” speak to how meaning evolves in the tensions, boundaries, and interplay between knowledge and imagination. We conclude that this story exceeds containment, dispersed as it is across several fields of inquiry and a number of individual memories that go in and out of sync.
TONE DEVELOPMENT STUDIES WITH A STUDENT DURING FLUTE EDUCATION
Directory of Open Access Journals (Sweden)
Begum Aytemur
2016-12-01
Full Text Available This research investigated the effect of a five stage study program applied by the researcher to one student who had entered university playing the flute, but who had not resolved lip and tone problems in one educational semester through basic long sound studies and scale studies. The participant in the research was a 19 year old student who had completed first year of the music teaching program and had performed in the year-end concert; however she was criticized by listeners and flute teachers for forced and scratchy tone. The research had the basic aim of solving these problems. As a result the “single subject study model”, chosen for research on individuals requesting private training, was chosen for this research model. The findings of the study were collected as video recordings of scale, study and piece work in initial, training and final stages of a six-week education course run every day. To evaluate the obtained recordings, a “Behavior for Quality Flute Tone Scale” was created. The video recordings were investigated by three flute teaching staff, expert in the area, who provided points in accordance with the scale. The obtained points were analyzed using the SPSS 15.0 program. The results showed that the study program created by the researcher provided rapid tonal development of the student. It is considered that the study is important to present an alternative route for flute students experiencing similar problems.
Flux-driven turbulence GDB simulations of the IWL Alcator C-Mod L-mode edge compared with experiment
Francisquez, Manaure; Zhu, Ben; Rogers, Barrett
2017-10-01
Prior to predicting confinement regime transitions in tokamaks one may need an accurate description of L-mode profiles and turbulence properties. These features determine the heat-flux width upon which wall integrity depends, a topic of major interest for research aid to ITER. To this end our work uses the GDB model to simulate the Alcator C-Mod edge and contributes support for its use in studying critical edge phenomena in current and future tokamaks. We carried out 3D electromagnetic flux-driven two-fluid turbulence simulations of inner wall limited (IWL) C-Mod shots spanning closed and open flux surfaces. These simulations are compared with gas puff imaging (GPI) and mirror Langmuir probe (MLP) data, examining global features and statistical properties of turbulent dynamics. GDB reproduces important qualitative aspects of the C-Mod edge regarding global density and temperature profiles, within reasonable margins, and though the turbulence statistics of the simulated turbulence follow similar quantitative trends questions remain about the code's difficulty in exactly predicting quantities like the autocorrelation time A proposed breakpoint in the near SOL pressure and the posited separation between drift and ballooning dynamics it represents are examined This work was supported by DOE-SC-0010508. This research used resources of the National Energy Research Scientific Computing Center (NERSC).
Directory of Open Access Journals (Sweden)
R. A. Treumann
2004-01-01
Full Text Available Mirror mode turbulence is the lowest frequency perpendicular magnetic excitation in magnetized plasma proposed already about half a century ago by Rudakov and Sagdeev (1958 and Chandrasekhar et al. (1958 from fluid theory. Its experimental verification required a relatively long time. It was early recognized that mirror modes for being excited require a transverse pressure (or temperature anisotropy. In principle mirror modes are some version of slow mode waves. Fluid theory, however, does not give a correct physical picture of the mirror mode. The linear infinitesimally small amplitude physics is described correctly only by including the full kinetic theory and is modified by existing spatial gradients of the plasma parameters which attribute a small finite frequency to the mode. In addition, the mode is propagating only very slowly in plasma such that convective transport is the main cause of flow in it. As the lowest frequency mode it can be expected that mirror modes serve as one of the dominant energy inputs into plasma. This is however true only when the mode grows to large amplitude leaving the linear stage. At such low frequencies, on the other hand, quasilinear theory does not apply as a valid saturation mechanism. Probably the dominant processes are related to the generation of gradients in the plasma which serve as the cause of drift modes thus transferring energy to shorter wavelength propagating waves of higher nonzero frequency. This kind of theory has not yet been developed as it has not yet been understood why mirror modes in spite of their slow growth rate usually are of very large amplitudes indeed of the order of |B/B0|2~O(1. It is thus highly reasonable to assume that mirror modes are instrumental for the development of stationary turbulence in high temperature plasma. Moreover, since the magnetic field in mirror turbulence forms extended though slightly oblique magnetic bottles, low parallel energy particles can be trapped
Simulations of drift resistive ballooning L-mode turbulence in the edge plasma of the DIII-D tokamak
Energy Technology Data Exchange (ETDEWEB)
Cohen, B. I.; Umansky, M. V.; Nevins, W. M.; Makowski, M. A. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Boedo, J. A.; Rudakov, D. L. [University of California, San Diego, San Diego, California 92093 (United States); McKee, G. R.; Yan, Z. [University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Groebner, R. J. [General Atomics, P.O. Box 85608, San Diego, California 92186 (United States)
2013-05-15
Results from simulations of electromagnetic drift-resistive ballooning turbulence for tokamak edge turbulence in realistic single-null geometry are reported. The calculations are undertaken with the BOUT three-dimensional fluid code that solves Braginskii-based fluid equations [X. Q. Xu and R. H. Cohen, Contrib. Plasma Phys. 36, 158 (1998)]. The simulation setup models L-mode edge plasma parameters in the actual magnetic geometry of the DIII-D tokamak [J. L. Luxon et al., Fusion Sci. Technol. 48, 807 (2002)]. The computations track the development of drift-resistive ballooning turbulence in the edge region to saturation. Fluctuation amplitudes, fluctuation spectra, and particle and thermal fluxes are compared to experimental data near the outer midplane from Langmuir probe and beam-emission-spectroscopy for a few well-characterized L-mode discharges in DIII-D. The simulations are comprised of a suite of runs in which the physics model is varied to include more fluid fields and physics terms. The simulations yield results for fluctuation amplitudes, correlation lengths, particle and energy fluxes, and diffusivities that agree with measurements within an order of magnitude and within factors of 2 or better for some of the data. The agreement of the simulations with the experimental measurements varies with respect to including more physics in the model equations within the suite of models investigated. The simulations show stabilizing effects of sheared E × B poloidal rotation (imposed zonal flow) and of lower edge electron temperature and density.
Encoding information using Laguerre Gaussian modes over free space turbulence media
CSIR Research Space (South Africa)
Trichili, A
2016-07-01
Full Text Available of the atmospheric turbulence on the proposed communication system. We believe that the proposed technique is promising for high-bit-rate spatial division multiplexing in optical fiber and free space communication systems....
Performance of broiler chickens served heat-treated fluted pumpkin ...
African Journals Online (AJOL)
One hundred and twenty five day-old chicks of Anak 2000 were weighed and randomly distributed to five dietary treatments A, B, C, D and E which contained no FPLE (control), fluted pumpkin leaves (FPL) no heat treatment, FPL immersed in hot water (100°C) for 1, 3 and 5 min, respectively. Each treatment was replicated 3 ...
Growth response of fluted pumpkin (Telfairia occidentalis Hook. F) to ...
African Journals Online (AJOL)
user
2011-10-06
Oct 6, 2011 ... An investigation of the growth response of fluted pumpkin to different combinations of irrigation intervals and spent mushroom ... as vine length, number of leaves, leaf area, number of branches, vine fresh weight and total shoot yield across the treatment variants. ... and physical conditions. Organic fertilizers ...
Microproagation of Fluted pumkin by Enhanced Axilary shoot ...
African Journals Online (AJOL)
In a bid to develop protocols for micropropagation of fluted pumkin (Telfairia occidentalis), single node cuttings of two genotypes, Telfairia occidentalis white and Telfairia occidentalis orange (ToW-1 and ToR-1 respectively) were cultured in Murashige and Skoog medium but with four different combinations of kinetin and ...
Effects of processing on the nutritional composition of fluted pumpkin ...
African Journals Online (AJOL)
Fluted pumpkin seeds were processed into the raw, boiled, fermented, germinated and roasted seeds, dried at 500C, milled and sieved. The seed flours were analyzed for nutritional composition, energy, amino acids and fatty acids of the oils. Processing affected the levels of nutrients in the seed. The energy values ranged ...
Reinvigorating the indigenous flute in African dance performance ...
African Journals Online (AJOL)
In doing this, it attempts to explore the usefulness of flute in encouraging vocational and entrepreneurial skills among the youth, with a view to creating job opportunities. Over the decades, scholars and performing arts practitioners have failed to adequately develop the indigenous musical aerophone instruments such as the ...
Lifecycle1: Flute (piccolo), oboe, clarinet (bass clarinet), bassoon ...
African Journals Online (AJOL)
Lifecycle1: Flute (piccolo), oboe, clarinet (bass clarinet), bassoon, horn, 2 percussionists, 2 violins and cello, Xhosa vocal ensemble and indigenous instruments. J Zaidel-Rudoulph. Abstract. No Abstract Journal for the Musical Arts in Africa Vol. 3 2007: pp. 80-81. Full Text: EMAIL FULL TEXT EMAIL FULL TEXT
Pre-School Children's Encounters with "The Magic Flute"
Nyland, Berenice; Acker, Aleksandra; Ferris, Jill; Deans, Jan
2011-01-01
This article describes a music programme in an Australian early learning centre. Through a repertoire of songs, games and instruments, the children were introduced to music forms, including opera. Mozart's Magic Flute was presented to these children by watching the Metropolitan Opera's latest film performance. Because this opera seized the…
Influence of crude extract of root of Telfairia occidentalis (fluted ...
African Journals Online (AJOL)
The effect of crude extract of root of Telfairia occidentalis (fluted pumpkin) was investigated on the kidney of adult wistar rats. The crude extract of pumpkin root were given both intraperitoneally and orally to rats respectively. The control group received distilled water throughout the duration of experiment. The administration ...
Wang, Wenkang; Pan, Chong; Wang, Jinjun
2018-01-01
The identification and separation of multi-scale coherent structures is a critical task for the study of scale interaction in wall-bounded turbulence. Here, we propose a quasi-bivariate variational mode decomposition (QB-VMD) method to extract structures with various scales from instantaneous two-dimensional (2D) velocity field which has only one primary dimension. This method is developed from the one-dimensional VMD algorithm proposed by Dragomiretskiy and Zosso (IEEE Trans Signal Process 62:531-544, 2014) to cope with a quasi-2D scenario. It poses the feature of length-scale bandwidth constraint along the decomposed dimension, together with the central frequency re-balancing along the non-decomposed dimension. The feasibility of this method is tested on both a synthetic flow field and a turbulent boundary layer at moderate Reynolds number (Re_{τ } = 3458) measured by 2D particle image velocimetry (PIV). Some other popular scale separation tools, including pseudo-bi-dimensional empirical mode decomposition (PB-EMD), bi-dimensional EMD (B-EMD) and proper orthogonal decomposition (POD), are also tested for comparison. Among all these methods, QB-VMD shows advantages in both scale characterization and energy recovery. More importantly, the mode mixing problem, which degrades the performance of EMD-based methods, is avoided or minimized in QB-VMD. Finally, QB-VMD analysis of the wall-parallel plane in the log layer (at y/δ = 0.12) of the studied turbulent boundary layer shows the coexistence of large- or very large-scale motions (LSMs or VLSMs) and inner-scaled structures, which can be fully decomposed in both physical and spectral domains.
DEFF Research Database (Denmark)
Müller, Pavel; De Chiffre, Leonardo
2009-01-01
An investigation on cutting forces and hole quality using carbide 3-flute self-centering drills and 6-flute cermet reamers was performed on 42CrMo4 alloy steel. Different depths of cuts were analyzed with respect to cutting thrust and cutting torque, hole diameter, form and surface integrity. Goo...
International Nuclear Information System (INIS)
Kleva, R.G.
1980-01-01
The first part of this work is concerned with test particle transport in a stochastic magnetic field. In the absence of collisions, the test particle self-diffusion coefficient is given by D = D/sub m/ V (in the zero gyroradius limit), where D/sub m/ is the magnetic diffusion coefficient due to a given spectrum of magnetic fluctuations and V is the particle velocity along a field line. The effect of collisions, either classical or turbulent, on this result is considered. The second part of this work is concerned with the evolution of the collisionless tearing mode in the presence of a stochastic magnetic field. A statistical closure approximation, obtained from the DIA by neglecting a mode-coupling term, is used to derive a nonlinear dispersion relation. For L 0 < L/sub K/ the dominant nonlinear effect is shown to be a turbulent broadening of the perturbed current layer. Saturation occurs when the perturbed current layer broadens to the point where Δ' = 0, where Δ' is the jump in the logarithmic derivative of the vector potential across the perturbed current layer
International Nuclear Information System (INIS)
Guzdar, P.N.; Drake, J.F.
1993-01-01
The generation of shear flow by resistive ballooning modes and resistive interchange modes is compared and contrasted using a 3-D fluid code. The resistive ballooning modes give rise to poloidally asymmetric transport and hence drive poloidal rotation due to the Reynold's Stress as well as the anomalous Stringer/Winsor mechanism. On the other hand the resistive interchange mode can drive shear flow only through the Reynold's Stress. The studies show that if the self-consistent sheared flow is suppressed, the resistive ballooning modes give rise to a larger anomalous transport than produced by the resistive interchange modes. Furthermore the shear flow generated by the resistive ballooning modes is larger than that driven by the resistive interchange modes due to the combined effect of the dual mechanisms stated earlier. As a consequence strong suppression of the fluctuations as well as reduction of the transport occurs for resistive ballooning modes. On the other hand, for the resistive interchange modes the level of fluctuation as well as the anomalous transport is not reduced by the self consistent shear flow generated by the Reynold's Stress. This latter result is in agreement with some earlier 3-D simulation of resistive interchange modes
The Development of the Flute as a Solo Instrument from the Medieval to the Baroque Era
Directory of Open Access Journals (Sweden)
Anna J. Reisenweaver
2011-05-01
Full Text Available As one of the oldest instruments known to mankind, the flute is present in some form in nearly every culture and ethnic group in the world. However, in Western music in particular, the flute has taken its place as an important part of musical culture, both as a solo and an ensemble instrument. The flute has also undergone its most significant technological developments in Western musical culture, moving from the bone keyless flutes of the Prehistoric era to the gold and silver instruments known to performers today. During the Renaissance and Baroque periods in particular, however, the flute rose to popularity as a solo instrument and began to evolve into its modern form. New developments in the design and mechanics of the instrument drove this increased interest, which ultimately gave the flute a prominent position in music that has lasted throughout history.
Feedback effect on flute dynamics in a mirror machine
International Nuclear Information System (INIS)
Be’ery, I; Seemann, O
2015-01-01
The effect of active feedback on flute instability is experimentally studied in a table-top mirror machine. Changing the plasma conditions from mirror-loss dominated to flute-loss dominated, it is demonstrated that while the feedback has no effect on plasma density in the first case, it increases the plasma density by up to 50% in the second case. Measurements of the dependence of instability amplitude on feedback gain show that large gain stimulates high frequency perturbations. The period of these perturbations corresponds to the inherent delay of immersed electrode feedback. Variation of the spatial phase between the input and output of the phase reveals a large asymmetry between positive and negative phase shifts. A simplified model is introduced to explain how a negative phase shift causes positive feedback between the external feedback and the centrifugally driven rotation. (paper)
International Nuclear Information System (INIS)
Burrell, K.H.; Osborne, T.H.; Groebner, R.J.; Rettig, C.L.
1993-01-01
VH-mode plasma exhibit energy confinement times up to 2.4 times the DIII-D/JET H-mode scaling relation and up to 3.9 times the value given by ITER89-P L-mode scaling. If this confinement improvement can be exploited in reactor plasmas, smaller prototype reactors with significantly lower unit cost can be produced. Accordingly, understanding and optimizing the confinement improvement is of significant interest. One of the possible explanations for this bulk confinement improvement is stabilization of turbulence by shear in the radial electric field, similar to the present explanation for the confinement improvement at the extreme plasma edge at the L to H transition. Preliminary measurements have shown that the region of the plasma where the electric field gradient is steepest broadens when the plasma goes from H-mode to VH-mode. More recent measurements have confirmed this broadening and have shown that the change in the electric field gradient occurs prior to the change in the thermal transport. In addition, transport analysis shows that the electric field shear increases in the same region between magnetic flux coordinate p=0.6 and 0.9 where the local thermal transport decreases. Furthermore, far infra-red (FIR) scattering measurements have detected density fluctuations in the region around p=0.8 which could be responsible for enhanced transport and which disappear at the time that the electric shear increases. These fluctuations appear as bursts of density fluctuations in the 0.5 to 1.5 MHz range. The time between bursts increases as the electric field shear increases. Once these bursts disappear, the major change in confinement takes place in most discharges. When isolated bursts occur, the heat and angular momentum pulse connected with the burst are detectable on the plasma profile diagnostics. (author) 13 refs., 4 figs
Active feedback stabilization of the flute instability in a mirror machine using field-aligned coils
International Nuclear Information System (INIS)
Lifshitz, A.; Be'ery, I.; Fisher, A.; Ron, A.; Fruchtman, A.
2012-01-01
A plasma confined in linear mirror machines is unstable even at low β, mainly because of the flute instability. One possible way to stabilize the plasma is to use active feedback to correct the plasma shape in real time. The theoretically investigated apparatus consists of feedback coils aligned with the magnetic field, immersed in a cold plasma around the hot core. When the current through the feedback coils changes, the plasma moves to conserve the magnetic flux via compressional Alfvén waves. An analytical model is used to find a robust feedback algorithm with zero residual currents. It is shown that due to the plasma's rotation, maximal stability is obtained with a large phase angle between the perturbations' modes and the feedback integral-like term. Finally, a two-dimensional MHD simulation implementing the above algorithm in fact shows stabilization of the plasma with zero residual currents. (paper)
Flute instability in the plasma shell of the earth's magnetosphere
International Nuclear Information System (INIS)
Ivanov, V.N.; Pokhotelov, O.A.
1987-01-01
In the plasma shell of the earth's magnetosphere, the surfaces of constant pressure may not coincide with surfaces of constant specific volume. This circumstance forces a reexamination of the theory for the flute instability, in which the pressure has been assumed to remain constant on surfaces of constant specific volume. The MHD equations for flute waves in a curvilinear magnetic field are used to show that an instability of a new type, with a pressure which does not remain constant on surfaces of constant specific volume, can occur in the plasma shell of the magnetosphere. An expression is derived for the growth rate of this instability. Analysis of the equation also shows that perturbations with wavelengths shorter than the ion Larmor radius are stable by virtue of magnetodrift effects. The growth rates of the flute instabilities are calculated for both a dipole magnetic field and an arbitrary magnetic-field configuration. Growth rates calculated for typical values of the characteristics of the earth's plasma shell are reported
Turbulence at the transition to the high density H-mode in Wendelstein 7-AS plasmas
DEFF Research Database (Denmark)
Basse, N.P.; Zoletnik, S.; Baumel, S.
2003-01-01
Recently a new improved confinement regime was found in the Wendelstein 7-AS (W7-AS) stellarator (Renner H. et al 1989 Plasma Phys. Control. Fusion 31 1579). The discovery of this high density high confinement mode (HDH-mode) was facilitated by the installation of divertor modules. In this paper,...
International Nuclear Information System (INIS)
Leconte, M.; Diamond, P.H.; Xu, Y.
2014-01-01
We study the effects of resonant magnetic perturbations (RMPs) on turbulence, flows and confinement in the framework of resistive drift-wave turbulence. This work was motivated, in parts, by experiments reported at the IAEA 2010 conference (Xu et al 2011 Nucl. Fusion 51 062030) which showed a decrease of long-range correlations during the application of RMPs. We derive and apply a zero-dimensional predator–prey model coupling the drift-wave–zonal-mode system (Leconte and Diamond 2012 Phys. Plasmas 19 055903) to the evolution of mean quantities. This model has both density-gradient drive and RMP amplitude as control parameters and predicts a novel type of transport bifurcation in the presence of RMPs. This model allows a description of the full L–H transition evolution with RMPs, including the mean sheared flow evolution. The key results are the following: (i) the L–I and I–H power thresholds both increase with RMP amplitude | b-tilde x |, the relative increase of the L–I threshold scales as ΔP LI ∝| b-tilde x | 2 ν ∗ −2 ρ s −2 , where ν * is edge collisionality and ρ s is the sound gyroradius. (ii) RMPs are predicted to decrease the hysteresis between the forward and back-transition. (iii) Taking into account the mean density evolution, the density profile—sustained by the particle source—has an increased turbulent diffusion compared with the reference case without RMPs which provides one possible explanation for the density pump-out effect. (paper)
Sung, C.; Rhodes, T. L.; Staebler, G. M.; Yan, Z.; McKee, G. R.; Smith, S. P.; Osborne, T. H.; Peebles, W. A.
2018-05-01
For the first time, we report increased edge electron temperature and density turbulence levels ( T˜ e and n˜ e) in Edge Localized Mode free Quiescent H-mode (ELM-free QH-mode) plasmas as compared to the ELMing time period. ELMs can severely damage plasma facing components in fusion plasma devices due to their large transient energy transport, making ELM-free operation a highly sought after goal. The QH-mode is a candidate for this goal as it is ELM-free for times limited only by hardware constraints. It is found that the driving gradients decrease during the QH-mode compared to the ELMing phase, however, a significant decrease in the ExB shearing rate is also observed that taken together is consistent with the increased turbulence. These results are significant as the prediction and control of ELM-free H-mode regimes are crucial for the operation of future fusion devices such as ITER. The changes in the linear growth rates calculated by CGYRO [Candy et al., J. Comput. Phys. 324, 73 (2016)] and the measured ExB shearing rate between ELMing and QH-mode phases are qualitatively consistent with these turbulence changes. Comparison with ELMing and 3D fields ELM suppressed H-mode finds a similar increase in T˜ e and n˜ e, however, with distinctly different origins, the increased driving gradients rather than the changes in the ExB shearing rate in 3D fields ELM suppressed the H-mode. However, linear gyrokinetic calculation results are generally consistent with the increased turbulence in both ELM-controlled discharges.
Profiles of zonal flows and turbulence mode numbers and probe system in the HL-2A tokamak
International Nuclear Information System (INIS)
Hong Wenyu; Zhao Kaijun; Yan Longwen; Dong Jiaqi; Cheng Jun; Qian Jun
2009-01-01
The toroidal and poloidal symmetries (m-0, n-0) of the measured low frequency zonal flows (f=0-5 kHz) and geodesic acoustic mode zonal flow (f=16 kHz) electric potential and radial promulgate features were unambiguously identified with displaced Langmuir probe arrays in the edge plasma of the HL-2A tokamak for the first time. The finite radial wave vector (K r-LF =0.6 cm -1 , K r-GAM =2 cm -1 ) of the flows was simultaneously estimated. The formation mechanism of the flows is identified to be nonlinear three wave coupling between high frequency turbulent fluctuations and the flows. Changes of zonal flow amplitude bring by ECRH power and the boundary safety factors were simply studied. Moreover, change of zonal flow amplitude in radial direction was too observed. (authors)
Effects of diameter and helical angle of flute on the flow evenness of ...
African Journals Online (AJOL)
Jane
2011-10-24
Oct 24, 2011 ... of shaft, flute shape, width of slot and wrapping angle. (Turgut et al., 1995, 1996; ... Figure 1. Technical properties of fluted roller used in this study. average length ... The study was conducted for the ground speed of 1.5 m s-1 ...
2013-09-26
...). The gametogenic cycle (annual cycle in the development of reproductive cells or gametes) of fluted... Cumberland....... Fentress, Morgan, TN Historical and Current. River. Scott. Rock Creek Cumberland...). Live fluted kidneyshell have not been collected in Rock Creek since 1988 (Layzer and Anderson 1992, p...
Low- and high-mode separation of short wavelength turbulence in dithering Wendelstein 7-AS plasmas
DEFF Research Database (Denmark)
Basse, N.P.; Zoletnik, S.; Saffman, M.
2002-01-01
In this article measurements of small scale electron density fluctuations in dithering high confinement (H)-mode plasmas obtained by collective scattering of infrared light are presented. A scan of the fluctuation wavenumber was made in a series of similar discharges in the Wendelstein 7-AS (W7-A...
Dynamic mode decomposition of turbulent cavity flows for self-sustained oscillations
International Nuclear Information System (INIS)
Seena, Abu; Sung, Hyung Jin
2011-01-01
Highlights: ► DMD modes were extracted from two cavity flow data set at Re D = 12,000 and 3000. ► At Re D = 3000, frequencies of boundary layer and shear layer structures coincides. ► Boundary layer structures exceed in size with shear layer structures. ► At Re D = 12,000, structure showed coherence leading to self-sustained oscillations. ► Hydrodynamic resonance occurs if coherence exists in wavenumber and frequency. - Abstract: Self-sustained oscillations in a cavity arise due to the unsteady separation of boundary layers at the leading edge. The dynamic mode decomposition method was employed to analyze the self-sustained oscillations. Two cavity flow data sets, with or without self-sustained oscillations and possessing thin or thick incoming boundary layers (Re D = 12,000 and 3000), were analyzed. The ratios between the cavity depth and the momentum thickness (D/θ) were 40 and 4.5, respectively, and the cavity aspect ratio was L/D = 2. The dynamic modes extracted from the thick boundary layer indicated that the upcoming boundary layer structures and the shear layer structures along the cavity lip line coexisted with coincident frequency space but with different wavenumber space, whereas structures with a thin boundary layer showed complete coherence among the modes to produce self-sustained oscillations. This result suggests that the hydrodynamic resonances that gave rise to the self-sustained oscillations occurred if the upcoming boundary layer structures and the shear layer structures coincided, not only in frequencies, but also in wavenumbers. The influences of the cavity dimensions and incoming momentum thickness on the self-sustained oscillations were examined.
Champagne flutes and brandy snifters: modelling protostellar outflow-cloud chemical interfaces
Rollins, R. P.; Rawlings, J. M. C.; Williams, D. A.; Redman, M. P.
2014-10-01
A rich variety of molecular species has now been observed towards hot cores in star-forming regions and in the interstellar medium. An increasing body of evidence from millimetre interferometers suggests that many of these form at the interfaces between protostellar outflows and their natal molecular clouds. However, current models have remained unable to explain the origin of the observational bias towards wide-angled `brandy snifter' shaped outflows over narrower `champagne flute' shapes in carbon monoxide imaging. Furthermore, these wide-angled systems exhibit unusually high abundances of the molecular ion HCO+. We present results from a chemodynamic model of such regions where a rich chemistry arises naturally as a result of turbulent mixing between cold, dense molecular gas and the hot, ionized outflow material. The injecta drives a rich and rapid ion-neutral chemistry in qualitative and quantitative agreement with the observations. The observational bias towards wide-angled outflows is explained naturally by the geometry-dependent ion injection rate causing rapid dissociation of CO in the younger systems.
Michael, C. A.; Tanaka, K.; Akiyama, T.; Ozaki, T.; Osakabe, M.; Sakakibara, S.; Yamaguchi, H.; Murakami, S.; Yokoyama, M.; Shoji, M.; Vyacheslavov, L. N.; LHD Experimental Group
2018-04-01
In the Large helical device, a change of energetic particle mode is observed as He concentration is varied in ion-ITB type experiments, having constant electron density and input heating power but with a clear increase of central ion temperature in He rich discharges. This activity consists of bursty, but damped energetic interchange modes (EICs, Du et al 2015 Phys. Rev. Lett. 114 155003), whose occurrence rate is dramatically lower in the He-rich discharges. Mechanisms are discussed for the changes in drive and damping of the modes with He concentration. These EIC bursts consist of marked changes in the radial electric field, which is derived from the phase velocity of turbulence measured with the 2D phase contrast imaging (PCI) system. Similar bursts are detected in edge fast ion diagnostics. Ion thermal transport by gyro-Bohm scaling is recognised as a contribution to the change in ion temperature, though fast ion losses by these EIC modes may also contribute to the ion temperature dependence on He concentration, most particularly controlling the height of an ‘edge-pedestal’ in the Ti profile. The steady-state level of fast ions is shown to be larger in helium rich discharges on the basis of a compact neutral particle analyser (CNPA), and the fast-ion component of the diamagnetic stored energy. These events also have an influence on turbulence and transport. The large velocity shear induced produced during these events transiently improves confinement and suppresses turbulence, and has a larger net effect when bursts are more frequent in hydrogen discharges. This exactly offsets the increased gyro-Bohm related turbulence drive in hydrogen which results in the same time-averaged turbulence level in hydrogen as in helium.
Energy Technology Data Exchange (ETDEWEB)
Yang, Q. Q., E-mail: yangqq@ipp.ac.cn; Zhong, F. C., E-mail: gsxu@ipp.ac.cn, E-mail: fczhong@dhu.edu.cn; Jia, M. N. [College of Science, Donghua University, Shanghai 201620 (China); Xu, G. S., E-mail: gsxu@ipp.ac.cn, E-mail: fczhong@dhu.edu.cn; Wang, L.; Wang, H. Q.; Chen, R.; Yan, N.; Liu, S. C.; Chen, L.; Li, Y. L.; Liu, J. B. [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China)
2015-06-15
The power fall-off width in the H-mode scrape-off layer (SOL) in tokamaks shows a strong inverse dependence on the plasma current, which was noticed by both previous multi-machine scaling work [T. Eich et al., Nucl. Fusion 53, 093031 (2013)] and more recent work [L. Wang et al., Nucl. Fusion 54, 114002 (2014)] on the Experimental Advanced Superconducting Tokamak. To understand the underlying physics, probe measurements of three H-mode discharges with different plasma currents have been studied in this work. The results suggest that a higher plasma current is accompanied by a stronger E×B shear and a shorter radial correlation length of turbulence in the SOL, thus resulting in a narrower power fall-off width. A simple model has also been applied to demonstrate the suppression effect of E×B shear on turbulence in the SOL and shows relatively good agreement with the experimental observations.
Surface flute waves in plasmas theory and applications
Girka, Volodymyr; Thumm, Manfred
2014-01-01
The book presents results of a comprehensive study of various features of eigen electromagnetic waves propagating across the axis of plasma filled metal waveguides with cylindrical geometry. The authors collected in one book material on various features of surface flute waves, i. e. impact of waveguide design on wave dispersion, wave damping influenced by various reasons, impact of plasma density and external magnetic field inhomogeneity on the wave, and impact of waveguide corrugation and electric current on the wave. A variety of present surface waves applications and possible future applications is also included. Using the method of successive approximations it is shown how one can solve problems, which concern real experimental devices, starting from simple models. The book applies to both professionals dealing with problems of confined plasmas and to graduate and post-graduate students specializing in the field of plasma physics and related applications.
CFD investigation of flow and heat transfer of nanofluids in isoflux spirally fluted tubes
Salama, Amgad; Azamatov, Abdulaziz Irgashevich; El-Amin, Mohamed; Sun, Shuyu; Huang, Huancong
2012-01-01
In this work, the problem of flow and heat transfer of nanofluids in spirally fluted tubes is investigated numerically using the CFD code Fluent. The tube investigated in this work is characterized by the existence of helical ridging which
La Música Da Vida a Vida: Transverse Flute Music of Otavalo, Ecuador
Vallejo, Jessie M.
2014-01-01
This dissertation introduces an Andean transverse flute tradition of northernEcuador that has been routinely overlooked throughout a long history of scholarship published on the Otavalan region and its Kichwa–speaking inhabitants. Ethnographic data was collected through a variety of methods over the course of eight cumulative months of fieldwork in Ecuador, as well as an additional three and a half years during which I co–produced an album with flute masters from the Hatun Kotama ...
International Nuclear Information System (INIS)
Rhodes, T.L.; Doyle, E.J.; Hillesheim, J.C.; Peebles, W.A.; Schmitz, L.; Holland, C.; Smith, S.P.; Burrell, K.H.; Candy, J.; DeBoo, J.C.; Kinsey, J.E.; Petty, C.C.; Prater, R.; Staebler, G.M.; Waltz, R.E.; White, A.E.; McKee, G.R.; Mikkelsen, D.; Parker, S.; Chen, Y.
2011-01-01
A series of carefully designed experiments on DIII-D have taken advantage of a broad set of turbulence and profile diagnostics to rigorously test gyrokinetic turbulence simulations. In this paper the goals, tools and experiments performed in these validation studies are reviewed and specific examples presented. It is found that predictions of transport and fluctuation levels in the mid-core region (0.4 < ρ < 0.75) are in better agreement with experiment than those in the outer region (ρ ≥ 0.75) where edge coupling effects may become increasingly important and multiscale simulations may also be necessary. Validation studies such as these are crucial in developing confidence in a first-principles based predictive capability for ITER.
Lin, Shih-Yung; Splinter, Scott C.; Tarkenton, Chris; Paddock, David A.; Smeltzer, Stanley S.; Ghose, Sayata; Guzman, Juan C.; Stukus, Donald J.; McCarville, Douglas A.
2013-01-01
The development of durable bonded joint technology for assembling composite structures is an essential component of future space technologies. While NASA is working toward providing an entirely new capability for human space exploration beyond low Earth orbit, the objective of this project is to design, fabricate, analyze, and test a NASA patented durable redundant joint (DRJ) and a NASA/Boeing co-designed fluted-core joint (FCJ). The potential applications include a wide range of sandwich structures for NASA's future launch vehicles. Three types of joints were studied -- splice joint (SJ, as baseline), DRJ, and FCJ. Tests included tension, after-impact tension, and compression. Teflon strips were used at the joint area to increase failure strength by shifting stress concentration to a less sensitive area. Test results were compared to those of pristine coupons fabricated utilizing the same methods. Tensile test results indicated that the DRJ design was stiffer, stronger, and more impact resistant than other designs. The drawbacks of the DRJ design were extra mass and complex fabrication processes. The FCJ was lighter than the DRJ but less impact resistant. With barely visible but detectable impact damages, all three joints showed no sign of tensile strength reduction. No compression test was conducted on any impact-damaged sample due to limited scope and resource. Failure modes and damage propagation were also studied to support progressive damage modeling of the SJ and the DRJ.
International Nuclear Information System (INIS)
Kim, Eun-jin; Diamond, P.H.
2003-01-01
The dynamics of and an interplay among structures (mean shear flows, zonal flows, and generalized Kelvin-Helmholtz modes) are studied in drift wave turbulence. Mean shear flows are found to inhibit the nonlinear generation of zonal flows by weakening the coherent modulation response of the drift wave spectrum. Based on this result, a minimal model for the L→H (low- to high-confinement) transition is proposed, which involves the amplitude of drift waves, zonal flows, and the density gradient. A transition to quiescent H-mode sets in as the profile becomes sufficiently steep to completely damp out drift waves, following an oscillatory transition phase where zonal flows regulate drift wave turbulence. The different roles of mean flows and zonal flows are elucidated. Finally, the effect of poloidally nonaxisymmetric structures (generalized Kelvin-Helmholtz mode) on anomalous transport is investigated, especially in reference to damping of collisionless zonal flows. Results indicate that nonlinear excitation of this structure can be potentially important in enhancing anomalous transport as well as in damping zonal flows
The impact of a modified cutting flute implant design on osseointegration.
Jimbo, R; Tovar, N; Marin, C; Teixeira, H S; Anchieta, R B; Silveira, L M; Janal, M N; Shibli, J A; Coelho, P G
2014-07-01
Information concerning the effects of the implant cutting flute design on initial stability and its influence on osseointegration in vivo is limited. This study evaluated the early effects of implants with a specific cutting flute design placed in the sheep mandible. Forty-eight dental implants with two different macro-geometries (24 with a specific cutting flute design - Blossom group; 24 with a self-tapping design - DT group) were inserted into the mandibular bodies of six sheep; the maximum insertion torque was recorded. Samples were retrieved and processed for histomorphometric analysis after 3 and 6 weeks. The mean insertion torque was lower for Blossom implants (Pimplant contact (BIC) and P=0.52 for bone area fraction occupied (BAFO); at 6 weeks, P=0.55 for BIC and P=0.45 for BAFO. While no histomorphometric differences were observed, ground sections showed different healing patterns between the implants, with better peri-implant bone organization around those with the specific cutting flute design (Blossom group). Implants with the modified cutting flute design had a significantly reduced insertion torque compared to the DT implants with a traditional cutting thread, and resulted in a different healing pattern. Copyright © 2014 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Dewhurst, J.; Hnat, B.; Dudson, B.; Dendy, R. O.; Counsell, G. F.; Kirk, A.
2007-12-01
Almost all astrophysical and magnetically confined fusion plasmas are turbulent. Here, we examine ion saturation current (Isat) measurements of edge plasma turbulence for three MAST L-mode plasmas that differ primarily in their edge magnetic field configurations. First, absolute moments of the coarse grained data are examined to obtain accurate values of scaling exponents. The dual scaling behaviour is identified in all samples, with the temporal scale τ ≍ 40-60 μs separating the two regimes. Strong universality is then identified in the functional form of the probability density function (PDF) for Isat fluctuations, which is well approximated by the Fréchet distribution on temporal scales τ ≤ 40μs. For temporal scales τ > 40μs, the PDFs appear to converge to the Gumbel distribution, which has been previously identified as a universal feature of many other complex phenomena. The optimal fitting parameters k=1.15 for Fréchet and a=1.35 for Gumbel provide a simple quantitative characterisation of the full spectrum of fluctuations. We conclude that, to good approximation, the properties of the edge turbulence are independent of the edge magnetic field configuration.
Development and Performance Evaluation of Fluted Pumpkin Seed Dehulling Machine
Directory of Open Access Journals (Sweden)
M. M. Odewole
2017-08-01
Full Text Available A machine for dehulling fluted pumpkin seed (Telfairia occidentalis was developed. The main objective of developing the machine was to provide a better substitute to traditional methods of dehulling the seed which contains edible oil of high medicinal and nutritional values. Traditional methods are full of drudgery, slow, injury prone and would lead to low and poor outputs in terms of quantity and quality of dehulled products. The machine is made of five major parts: the feed hopper (for holding the seeds to be dehulled before getting into the dehulling chamber, dehulling chamber (the part of the machine that impacts forces on seeds thereby causing fractures and opening of seeds coats for the delivery of the oily kernels, discharge unit (exit for oily kernels and seed coats after dehulling, the frame (for structural support and stability of all parts of the machine and electric motor (power source of the machine.The development process involved design of major components (shaft diameter (20 mm, machine velocity (7.59 m/s, power requirement (3hp single phase electric motor and structural support of mild steel angle iron, selection of construction materials and fabrication. ANSYS R14.5 machine design computer software was used to design the shaft and structural support; while other components were designed with conventional design method of using design equations. The machine works on the principle of centrifugal and impact forces. Performance evaluation was carried out after fabrication and 87.26%, 2.83g/s, 8.9% and 3.84%were obtained for dehulling efficiency, throughput capacity, percentage partially dehulled and percentage undehulled respectively.
Edge energy transport barrier and turbulence in the I-mode regime on Alcator C-Moda)
Hubbard, A. E.; Whyte, D. G.; Churchill, R. M.; Cziegler, I.; Dominguez, A.; Golfinopoulos, T.; Hughes, J. W.; Rice, J. E.; Bespamyatnov, I.; Greenwald, M. J.; Howard, N.; Lipschultz, B.; Marmar, E. S.; Reinke, M. L.; Rowan, W. L.; Terry, J. L.
2011-05-01
We report extended studies of the I-mode regime [Whyte et al., Nucl. Fusion 50, 105005 (2010)] obtained in the Alcator C-Mod tokamak [Marmar et al., Fusion Sci. Technol. 51(3), 3261 (2007)]. This regime, usually accessed with unfavorable ion B × ∇B drift, features an edge thermal transport barrier without a strong particle transport barrier. Steady I-modes have now been obtained with favorable B × ∇B drift, by using specific plasma shapes, as well as with unfavorable drift over a wider range of shapes and plasma parameters. With favorable drift, power thresholds are close to the standard scaling for L-H transitions, while with unfavorable drift they are ˜ 1.5-3 times higher, increasing with Ip. Global energy confinement in both drift configurations is comparable to H-mode scalings, while density profiles and impurity confinement are close to those in L-mode. Transport analysis of the edge region shows a decrease in edge χeff, by typically a factor of 3, between L- and I-mode. The decrease correlates with a drop in mid-frequency fluctuations (f ˜ 50-150 kHz) observed on both density and magnetics diagnostics. Edge fluctuations at higher frequencies often increase above L-mode levels, peaking at f ˜ 250 kHz. This weakly coherent mode is clearest and has narrowest width (Δf/f ˜ 0.45) at low q95 and high Tped, up to 1 keV. The Er well in I-mode is intermediate between L- and H-mode and is dominated by the diamagnetic contribution in the impurity radial force balance, without the Vpol shear typical of H-modes.
Idea Bank: The Native American Flute--A Possibility for Your Classroom
Kacanek, Hal
2011-01-01
The sound of the Native American flute seems to convey care, sadness, loneliness, longing, heartfelt emotion, a sense of the natural world, wisdom, the human spirit, and a sense of culture. It is a sound that competes for attention, dramatically punctuating messages about First Nation peoples on television and in movies. A relatively small group…
Effect of plant spacing on weed suppression and yield of fluted ...
African Journals Online (AJOL)
The field study was conducted to evaluate the effect of plant spacing on weed suppression yield and economic benefit of fluted pumpkin (Telfeiria occidentalis Hook F). The experiment was carried out at the Department of Crop and Soil Science Demonstration Plot, Faculty of Agriculture, University of Port Harcourt, Nigeria ...
The effect of manganese on early growth of fluted pumpkin ( telfairia ...
African Journals Online (AJOL)
The effect of manganese on early growth of fluted pumpkin (telfairia occidentalis hook f) in an ultisol. ER Orhue, CNC Nwaoguala. Abstract. The trials were conducted at the experimental site of University of Benin Teaching and Research Farm to determine the influence of Mn on early growth, nutrient content and uptake by ...
Porkolab, M.; Lin, L.; Edlund, E. M.; Rost, J. C.; Fiore, C. L.; Greenwald, M.; Mikkelsen, D.
2008-11-01
We present recent experimental measurements of turbulence and transport in C-Mod H-Mode plasmas with and without internal transport barriers (ITB) using the phase contrast imaging (PCI) diagnostic and compare the results with GYRO predictions. In plasmas without ITB, the fluctuation above 300 kHz observed by PCI agrees with ITG in GYRO simulation, including the direction of propagation, wavenumber spectrum, and absolute intensity within experimental uncertainly (+/-75%). After transition to ITBs, the observed overall fluctuation intensity increases. GYRO simulation in the core shows that ITG dominates in ITBs but its intensity is lower than the overall experimental measurements which may also include contributions from the plasma edge. These results, as well as the impact of varying ∇Ti, ∇n, and ExB shear on turbulence will be discussed. C.L. Fiore et al., Fusion Sci. Technol., 51, 303 (2007). M. Porkolab et al., IEEE Trans. Plasma Sci. 34, 229 (2006). J. Candy et al., Phys. Rev. Lett., 91, 045001 (2003).
Hnat, B.; Dudson, B. D.; Dendy, R. O.; Counsell, G. F.; Kirk, A.; MAST Team
2008-08-01
Ion saturation current (Isat) measurements of edge plasma turbulence are analysed for six MAST L-mode plasmas that differ primarily in their edge magnetic field configurations. The analysis techniques are designed to capture the strong nonlinearities of the datasets. First, absolute moments of the data are examined to obtain accurate values of scaling exponents. This confirms dual scaling behaviour in all samples, with the temporal scale τ ≈ 40-60 µs separating the two regimes. Strong universality is then identified in the functional form of the probability density function (PDF) for Isat fluctuations, which is well approximated by the Fréchet distribution on temporal scales τ 40 µs, the PDFs appear to converge to the Gumbel distribution, which has been previously identified as a universal feature of many other complex phenomena. The optimal fitting parameters k = 1.15 for Fréchet and a = 1.35 for Gumbel provide a simple quantitative characterization of the full spectrum of fluctuations. It is concluded that, to good approximation, the properties of the edge turbulence are independent of the edge magnetic field configuration.
International Nuclear Information System (INIS)
Mueller, H.W.; Carralero, D.; Birkenmeier, G.; Conway, G.D.; Fischer, R.; Happel, T.; Manz, P.; Suttrop, W.; Wolfrum, E.
2014-01-01
In the tokamak ASDEX Upgrade the influence of a non-axisymmetric n = 2 error field on the turbulence in the far scrape-off layer of a low density L-mode discharge has been studied. There is no density pump-out with the non-axisymmetric perturbation but an increase of the scrape-off layer density at the outer midplane. While the relative ion saturation current fluctuation level in the far scrape-off layer is decreasing, the skewness rises and especially the excess kurtosis grows by a factor of 1.5-3. The frequency of intermittent events (blobs) is increasing by 50 %. Also the poloidal velocity grows with the magnetic perturbation while the typical turbulent structure size becomes smaller by a factor 5-10 about 20-25 mm outside the separatrix. The local spectral density has been calculated from a two-point measurement of the ion saturation current. It is used to derive a dispersion relation. Two poloidal propagation velocities depending on the wave number have been found. One is an upper limit for the bulk E x B velocity and the second one the lower limit of the phase velocity. There is a significant contribution of the phase velocity to the propagation speed in the far scrape-off layer. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
International Nuclear Information System (INIS)
Lao, L.L.; Burrell, K.H.; Casper, T.S.
1996-08-01
The confinement and the stability properties of the DIII-D tokamak high performance discharges are evaluated in terms of rotational and magnetic shear with emphasis on the recent experimental results obtained from the negative central magnetic shear (NCS) experiments. In NCS discharges, a core transport barrier is often observed to form inside the NCS region accompanied by a reduction in core fluctuation amplitudes. Increasing negative magnetic shear contributes to the formation of this core transport barrier, but by itself is not sufficient to fully stabilize the toroidal drift mode (trapped- electron-η i mode) to explain this formation. Comparison of the Doppler shift shear rate to the growth rate of the η i mode suggests that the large core E x B flow shear can stabilize this mode and broaden the region of reduced core transport . Ideal and resistive stability analysis indicates the performance of NCS discharges with strongly peaked pressure profiles is limited by the resistive interchange mode to low Β N < 2.3. This mode is insensitive to the details of the rotational and the magnetic shear profiles. A new class of discharges which has a broad region of weak or slightly negative magnetic shear (WNS) is described. The WNS discharges have broader pressure profiles and higher values than the NCS discharges together with high confinement and high fusion reactivity
International Nuclear Information System (INIS)
He Jiansen; Tu Chuanyi; Marsch, Eckart; Yao Shuo
2012-01-01
To determine the wave modes prevailing in solar wind turbulence at kinetic scales, we study the magnetic polarization of small-scale fluctuations in the plane perpendicular to the data sampling direction (namely, the solar wind flow direction, V SW ) and analyze its orientation with respect to the local background magnetic field B 0,local . As an example, we take only measurements made in an outward magnetic sector. When B 0,local is quasi-perpendicular to V SW , we find that the small-scale magnetic-field fluctuations, which have periods from about 1 to 3 s and are extracted from a wavelet decomposition of the original time series, show a polarization ellipse with right-handed orientation. This is consistent with a positive reduced magnetic helicity, as previously reported. Moreover, for the first time we find that the major axis of the ellipse is perpendicular to B 0,local , a property that is characteristic of an oblique Alfvén wave rather than oblique whistler wave. For an oblique whistler wave, the major axis of the magnetic ellipse is expected to be aligned with B 0,local , thus indicating significant magnetic compressibility, and the polarization turns from right to left handedness as the wave propagation angle (θ kB ) increases toward 90°. Therefore, we conclude that the observation of a right-handed polarization ellipse with orientation perpendicular to B 0,local seems to indicate that oblique Alfvén/ion-cyclotron waves rather than oblique fast-mode/whistler waves dominate in the 'dissipation' range near the break of solar wind turbulence spectra occurring around the proton inertial length.
Tearing instabilities in turbulence
International Nuclear Information System (INIS)
Ishizawa, A.; Nakajima, N.
2009-01-01
Full text: Effects of micro-turbulence on tearing instabilities are investigated by numerically solving a reduced set of two-fluid equations. Micro-turbulence excites both large-scale and small-scale Fourier modes through energy transfer due to nonlinear mode coupling. The energy transfer to large scale mode does not directly excite tearing instability but it gives an initiation of tearing instability. When tearing instability starts to grow, the excited small scale mode plays an important role. The mixing of magnetic flux by micro-turbulence is the dominant factor of non-ideal MHD effect at the resonant surface and it gives rise to magnetic reconnection which causes tearing instability. Tearing instabilities were investigated against static equilibrium or flowing equilibrium so far. On the other hand, the recent progress of computer power allows us to investigate interactions between turbulence and coherent modes such as tearing instabilities in magnetically confined plasmas by means of direct numerical simulations. In order to investigate effects of turbulence on tearing instabilities we consider a situation that tearing mode is destabilized in a quasi-equilibrium including micro-turbulence. We choose an initial equilibrium that is unstable against kinetic ballooning modes and tearing instabilities. Tearing instabilities are current driven modes and thus they are unstable for large scale Fourier modes. On the other hand kinetic ballooning modes are unstable for poloidal Fourier modes that are characterized by ion Larmor radius. The energy of kinetic ballooning modes spreads over wave number space through nonlinear Fourier mode coupling. We present that micro-turbulence affects tearing instabilities in two different ways by three-dimensional numerical simulation of a reduced set of two-fluid equations. One is caused by energy transfer to large scale modes, the other is caused by energy transfer to small scale modes. The former is the excitation of initial
Flute-like musical instruments: A toy model investigated through numerical continuation
Terrien, Soizic; Vergez, Christophe; Fabre, Benoît
2013-07-01
Self-sustained musical instruments (bowed string, woodwind and brass instruments) can be modelled by nonlinear lumped dynamical systems. Among these instruments, flutes and flue organ pipes present the particularity to be modelled as a delay dynamical system. In this paper, such a system, a toy model of flute-like instruments, is studied using numerical continuation. Equilibrium and periodic solutions are explored with respect to the blowing pressure, with focus on amplitude and frequency evolutions along the different solution branches, as well as "jumps" between periodic solution branches. The influence of a second model parameter (namely the inharmonicity) on the behaviour of the system is addressed. It is shown that harmonicity plays a key role in the presence of hysteresis or quasiperiodic regime. Throughout the paper, experimental results on a real instrument are presented to illustrate various phenomena, and allow some qualitative comparisons with numerical results.
Scale separation closure and Alfven wave turbulence
International Nuclear Information System (INIS)
Chen, C.Y.; Mahajan, S.M.
1985-04-01
Based on the concept of scale separation between coherent response function and incoherent source for renormalized turbulence theories, a closure scheme is proposed. A model problem dealing with shear-Alfven wave turbulence is numerically solved; the solution explicitly shows expected turbulence features such as frequency shift from linear modes, band-broadening, and a power law dependence for the turbulence spectrum
Carmen Viejo Llaneza; Ana Laucirica Larrinaga
2016-01-01
Music Performance Anxiety (MPA) is, frequently, one of the problems faced by a musical performer in his or her career. This study observes way in which stage fright affects in musicians, which is a possible factor that may later lead to anxiety in public performances and, furthermore, how we can intervene to mitigate or reduce its effects. An initial interview was conducted with four upper division students of transverse flute. This was followed by some training techniques - relaxation techni...
The Dance of the Dead Rhino: William Kentridge’s Magic Flute
Guarracino, Serena
2010-01-01
The article offers a reading of the staging of The Magic Flute by visual artist William Kentridge, focusing on his introduction of the rhino in the visual landscape of the opera as symbol for the silenced subject of violence. Operatic tradition has always been concerned with the staging of death, in particular with the death of its female protagonists, and recent scholarship has highlighted the complicity of the genre with the ideology of Western patriarchy and colonial violence. In this ligh...
Music Performance Anxiety: Causes, Symptoms and Coping Strategies for Flute Students
Directory of Open Access Journals (Sweden)
Andre Sinico
2013-05-01
Full Text Available This article addresses the causes, symptoms and coping strategies used by undergraduate flute students from three universalities in Brazil to cope with music performance anxiety (MPA during jury recitals. The data collection and analysis procedures used were similar to a study by Siw Nielsen (1999, i.e., recital participant behavioral observation and verbal reports using semi-structured interviews. Both procedures were recorded in audio and video. As a result, the study highlights sixteen causes, nineteen symptoms, and eighteen strategies used by flute students to cope with MPA. Anxiety among the participants was constantly present to a greater or lesser degree. Its main cause was the repertoire for solo flute; nervousness was the symptom most reported by the participants; and positive self-talk was the most used coping strategy. The research concluded that, since anxiety is an inherent emotion in performing music, musicians must use a broad range of strategies—before and during the performance—to thoroughly deal with the causes and symptoms of anxiety. The article also highlights the importance of music professors in knowing the causes of MPA and its symptoms so that they can plan a strategy consistent with the needs of their students that will help them cope with the negative effects of anxiety.
Stirring turbulence with turbulence
Cekli, H.E.; Joosten, R.; van de Water, W.
2015-01-01
We stir wind-tunnel turbulence with an active grid that consists of rods with attached vanes. The time-varying angle of these rods is controlled by random numbers. We study the response of turbulence on the statistical properties of these random numbers. The random numbers are generated by the
Transition from flute modes to drift waves in a magnetized plasma column
International Nuclear Information System (INIS)
Brochard, F.; Gravier, E.; Bonhomme, G.
2005-01-01
Recent experiments performed on the low β plasma device Mirabelle [T. Pierre, G. Leclert, and F. Braun, Rev. Sci. Instrum. 58, 6 (1987)] using a limiter have shown that transitions between various gradient driven instabilities occurred on increasing the magnetic field strength. New thorough measurements allow to identify unambiguously three instability regimes. At low magnetic field the strong ExB velocity shear drives a Kelvin-Helmholtz instability, whereas at high magnetic field drift waves are only observed. A centrifugal (Rayleigh-Taylor) instability is also observed in between when the ExB velocity is shearless and strong enough. A close connection is made between the ratio ρ s /L perpendicular of the drift parameter to the radial density gradient length and each instability regime
The sound of oscillating air jets: Physics, modeling and simulation in flute-like instruments
de La Cuadra, Patricio
Flute-like instruments share a common mechanism that consists of blowing across one open end of a resonator to produce an air jet that is directed towards a sharp edge. Analysis of its operation involves various research fields including fluid dynamics, aero-acoustics, and physics. An effort has been made in this study to extend this description from instruments with fixed geometry like recorders and organ pipes to flutes played by the lips. An analysis of the jet's response to a periodic excitation is the focus of this study, as are the parameters under the player's control in forming the jet. The jet is excited with a controlled excitation consisting of two loudspeakers in opposite phase. A Schlieren system is used to visualize the jet, and image detection algorithms are developed to extract quantitative information from the images. In order to study the behavior of jets observed in different flute-like instruments, several geometries of the excitation and jet shapes are studied. The obtained data is used to propose analytical models that correctly fit the observed measurements and can be used for simulations. The control exerted by the performer on the instrument is of crucial importance in the quality of the sound produced for a number of flute-like instruments. The case of the transverse flute is experimentally studied. An ensemble of control parameters are measured and visualized in order to describe some aspects of the subtle control attained by an experienced flautist. Contrasting data from a novice flautist are compared. As a result, typical values for several non-dimensional parameters that characterize the normal operation of the instrument have been measured, and data to feed simulations has been collected. The information obtained through experimentation is combined with research developed over the last decades to put together a time-domain simulation. The model proposed is one-dimensional and driven by a single physical input. All the variables in the
International Nuclear Information System (INIS)
Jolliet, S.
2009-02-01
The goal of thermonuclear fusion research is to provide power plants, that will be able to produce one gigawatt of electricity. Among the different ways to achieve fusion, the tokamak, based on magnetic confinement, is the most promising one. A gas is heated up to hundreds of millions of degrees and becomes a plasma, which is maintained - or confined - in a toroidal vessel by helical magnetic field lines. Then, deuterium and tritium are injected and fuse to create an α particle and an energetic neutron. In order to have a favorable power balance, the power produced by fusion reactions must exceed the power needed to heat the plasma and the power losses. This can be cast in a very simple expression which stipulates that the product of the density, the temperature and the energy confinement time must exceed some given value. Unfortunately, present-days tokamaks are not able to reach this condition, mostly due to plasma turbulence. The latter phenomenon enhances the heat losses and degrades the energy confinement time, which cannot be predicted by analytical theories such as the so-called neoclassical theory in which the heat losses are caused by Coulomb collisions. Therefore, numerical simulations are being developed to model plasma turbulence, mainly caused by the Ion and Electron Temperature-Gradient and the Trapped-Electron-Mode (TEM) instabilities. The plasma is described by a distribution function which evolves according to the Vlasov equation. The electromagnetic fields created by the particles are self-consistently obtained through Maxwell’s equations. The resulting Vlasov-Maxwell system is greatly simplified by using the gyrokinetic theory, which consists, through an appropriate ordering, of eliminating the fast gyromotion (compared to the typical frequency of instabilities). Nevertheless, it is still extremely difficult to solve this system numerically due to the large range of time and spatial scales to be resolved. In this thesis, the Vlasov
Both, M. A. Adje
2002-11-01
Among the many preserved sound artefacts deposited in the offerings of the Aztec Templo Mayor are a set of ten tubular duct flutes made from clay, dating Late Postclassic Mesoamerica, 1350-1521 AD. The aerophones are completely painted in blue, and characterized by: (1) a short mouthpiece; (2) a framed aperture; (3) a tube with four fingerholes; and (4) an applicated mask with features of the Aztec rain god Tlaloc, basically three rings and a standardized relief structure of two clouds. While all measurements follow the same pattern, one particular organological distinction was made, as five flutes show an exit hole in the middle ring of the mask and five flutes are stopped. Thus, five instruments sound considerably higher, apart from the minimal pitch deviation of each specimen. Both the tonal capacity of each flute and the acoustics of several flutes played simultaneously were recorded and measured. A series of remarkable interference effects could be produced, which were strongly related to the ritual complex reflected in the offering. Taking in consideration the Aztec concept of music, it could be supposed that they were perceived as a principle of the song, or proper voice of Tlaloc.
Flute Teachers’ One-to-One Instructional Strategies at Individual Teaching Stages in Music School
Directory of Open Access Journals (Sweden)
Ana Kavčič Pucihar
2017-12-01
Full Text Available This article focuses on one-to-one studio based instrumental instruction in music schools. Some novelties in the music school woodwind curricula are presented within various contexts. Teacher – student relationship, their interactions, and knowledge transfer are essential in individual instrumental instruction. The learning process is systematically structured within six teaching stages, ranging from new content presentation to learning reviews. We examined music school flute teachers’ beliefs (N=78 about teaching stages in individual studio based instruction. We researched their new content teaching strategies, guided practice and reinforcement, feedback, homework monitoring strategies, formative review and assessment within music studio academic year.
International Nuclear Information System (INIS)
Festa, G; Andreani, C; Pietropaolo, A; Grazzi, F; Scherillo, A; Barzagli, E; Sutton, L F; Bognetti, L; Bini, A; Schooneveld, E
2013-01-01
A metallic 19th century flute was studied by means of integrated and simultaneous neutron-based techniques: neutron diffraction, neutron radiative capture analysis and neutron radiography. This experiment follows benchmark measurements devoted to assessing the effectiveness of a multitask beamline concept for neutron-based investigation on materials. The aim of this study is to show the potential application of the approach using multiple and integrated neutron-based techniques for musical instruments. Such samples, in the broad scenario of cultural heritage, represent an exciting research field. They may represent an interesting link between different disciplines such as nuclear physics, metallurgy and acoustics. (paper)
The Dance of the Dead Rhino: William Kentridge’s Magic Flute
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Serena Guarracino
2010-11-01
Full Text Available The article offers a reading of the staging of The Magic Flute by visual artist William Kentridge, focusing on his introduction of the rhino in the visual landscape of the opera as symbol for the silenced subject of violence. Operatic tradition has always been concerned with the staging of death, in particular with the death of its female protagonists, and recent scholarship has highlighted the complicity of the genre with the ideology of Western patriarchy and colonial violence. In this light, Kentridge's appropriation stages Mozart's opera as both voice of colonial Europe and place of resistance for the postcolonial artist. Kentridge moves the setting of the opera to colonial Africa, and the Flute becomes haunted with the massacre of the Herero people in South West Africa by the German army led by general von Trotha (1904-1907. The African white rhino, a species under the threat of extinction, works in this work as proxy for the missing corpses of the Herero people; in its being subject to humiliation and ruthless murder, it recalls Judith Butler's recent attempt at a different categorization of human life as both a continuous exposure to violence and what can be mourned after death. With its silence among the powerful sounds of Mozart's opera, the body of the dead, dancing rhino stands at the centre of Kentridge's work, which becomes a ceremony of mourning where the Western canon can be made to "resonate differently" (Trinh T. Minh-ha.
Memory effects in turbulent diffusion
International Nuclear Information System (INIS)
Zagorodny, A.G.; Weiland, J.; Wilhelmsson, H.
1993-01-01
A non-Markovian approach is proposed for the derivation of the diffusion coefficient of saturated turbulence. A memory term accounting for nonlocal coherence effects is introduced in a new attempt to describe the transition between weak and strong turbulence. The result compares favourably with recent experiments as well as mode coupling simulations of fusion plasmas. (14 refs.)
Directory of Open Access Journals (Sweden)
MUZÎCA TATIANA
2017-06-01
Full Text Available This article presents the first musicological analysis of Teodor Zgureanu’s concerto for nai (Romanian pan flute and orchestra. The analysis places the concerto within the context of the neofolkloric and polystylistic tradition. Its main focus is to identify the concerto’s dramatic structure and its main means of expression in relation to the modern compositional techniques.
Magnetohydrodynamic turbulence
Biskamp, Dieter
2003-01-01
This book presents an introduction to, and modern account of, magnetohydrodynamic (MHD) turbulence, an active field both in general turbulence theory and in various areas of astrophysics. The book starts by introducing the MHD equations, certain useful approximations and the transition to turbulence. The second part of the book covers incompressible MHD turbulence, the macroscopic aspects connected with the different self-organization processes, the phenomenology of the turbulence spectra, two-point closure theory, and intermittency. The third considers two-dimensional turbulence and compressi
International Nuclear Information System (INIS)
Donnelly, R.J.
1988-01-01
Most flows of fluids, in nature and in technology, are turbulent. Since much of the energy expended by machines and devices that involve fluid flows is spent in overcoming drag caused by turbulence, there is a strong motivation to understand the phenomena. Surprisingly, the peculiar, quantum-mechanical form of turbulence that can form in superfluid helium may turn out to be much simpler to understand that the classical turbulence that forms in normal fluids. It now seems that the study of superfluid turbulence may provide simplified model systems for studying some forms of classical turbulence. There are also practical motivations for studying superfluid turbulence. For example, superfuid helium is often used as a coolant in superconducting machinery. Superfluid turbulence is the primary impediment to the transfer of heat by superfluid helium; an understanding of the phenomena may make it possible to design more efficient methods of refrigeration for superconducting devices. 8 figs
Laguerre Gaussian beam multiplexing through turbulence
CSIR Research Space (South Africa)
Trichili, A
2014-08-17
Full Text Available We analyze the effect of atmospheric turbulence on the propagation of multiplexed Laguerre Gaussian modes. We present a method to multiplex Laguerre Gaussian modes using digital holograms and decompose the resulting field after encountering a...
Leke, Walter N; Khatabi, Behnam; Fondong, Vincent N; Brown, Judith K
2016-08-01
The complete genome sequence was determined and characterized for a previously unreported bipartite begomovirus from fluted pumpkin (Telfairia occidentalis, family Cucurbitaceae) plants displaying mosaic symptoms in Cameroon. The DNA-A and DNA-B components were ~2.7 kb and ~2.6 kb in size, and the arrangement of viral coding regions on the genomic components was like those characteristic of other known bipartite begomoviruses originating in the Old World. While the DNA-A component was more closely related to that of chayote yellow mosaic virus (ChaYMV), at 78 %, the DNA-B component was more closely related to that of soybean chlorotic blotch virus (SbCBV), at 64 %. This newly discovered bipartite Old World virus is herein named telfairia mosaic virus (TelMV).
EuHIT, Collaboration
2015-01-01
As a member of the EuHIT (European High-Performance Infrastructures in Turbulence - see here) consortium, CERN is participating in fundamental research on turbulence phenomena. To this end, the Laboratory provides European researchers with a cryogenic research infrastructure (see here), where the first tests have just been performed.
International Nuclear Information System (INIS)
Horton, W.
1998-07-01
The origin of plasma turbulence from currents and spatial gradients in plasmas is described and shown to lead to the dominant transport mechanism in many plasma regimes. A wide variety of turbulent transport mechanism exists in plasmas. In this survey the authors summarize some of the universally observed plasma transport rates
Energy Technology Data Exchange (ETDEWEB)
Nazarenko, Sergey [Warwick Univ., Coventry (United Kingdom). Mathematics Inst.
2011-07-01
Wave Turbulence refers to the statistical theory of weakly nonlinear dispersive waves. There is a wide and growing spectrum of physical applications, ranging from sea waves, to plasma waves, to superfluid turbulence, to nonlinear optics and Bose-Einstein condensates. Beyond the fundamentals the book thus also covers new developments such as the interaction of random waves with coherent structures (vortices, solitons, wave breaks), inverse cascades leading to condensation and the transitions between weak and strong turbulence, turbulence intermittency as well as finite system size effects, such as ''frozen'' turbulence, discrete wave resonances and avalanche-type energy cascades. This book is an outgrow of several lectures courses held by the author and, as a result, written and structured rather as a graduate text than a monograph, with many exercises and solutions offered along the way. The present compact description primarily addresses students and non-specialist researchers wishing to enter and work in this field. (orig.)
Flute type micropores activated carbon from cotton stalk for high performance supercapacitors
Tian, Xun; Ma, Hongru; Li, Zhe; Yan, Shaocun; Ma, Lei; Yu, Feng; Wang, Gang; Guo, Xuhong; Ma, Yanqing; Wong, Chingping
2017-08-01
Flute type micropores activated carbon (FTMAC) has been successfully obtained from cotton stalk via KOH-chemical activation method. The synthesized carbon material exhibits an ordered pore structure with high specific surface area of 1964.46 m2 g-1 and pore volume of 1.03 m3 g-1. The assembled FTMAC-based electrode delivers a high specific capacitance of 254 F g-1 at a current density of 0.2 A g-1 in 1 M H2SO4 aqueous electrolyte. It still can maintain 221 F g-1at a current density of 10 A g-1, demonstrating a good rate capacity (87% retention), as well as long cyclic stability of 96% capacitance retention after 10000 charging and discharging cycles at current density of 1 A g-1. Moreover, the symmetric supercapacitor can deliver a high energy density of 18.14 W h kg-1 and a power density of 450.37 W kg-1 which is operated in the voltage range of 0-1.8 V.
Experimental investigation of a coherent flute instability using a heavy ion beam probe
International Nuclear Information System (INIS)
Glowienka, J.C.; Jennings, W.C.; Hickok, R.L.
1988-01-01
A coherent, low-frequency instability found in a cylindrical, hollow cathode arc plasma has been investigated by using a heavy ion beam probe (HIBP). The energy density of the plasma was high enough to render it inaccessible to Langmuir probes, but the HIBP was able to provide measurements throughout the plasma cross section. The data clearly show that azimuthal symmetry does not exist. Radial profiles of steady-state density and space potential and of simultaneous n, phi amplitude and phase were obtained to allow detailed comparison between theory and experiment. Predictions from a cylindrically symmetric, small-perturbation theoretical model provide reasonably conclusive identification of the instability as a Kelvin--Helmholtz flute driven by and localized in a region of fluid shear. The most serious discrepancy was with regard to the oscillation frequency, which was consistently predicted to be three to four times lower than that observed experimentally. The reason for the discrepancy is not understood, but it is probably related to inadequacies in the theory caused by assumptions of azimuthal symmetry and of small linear perturbations
Phosphorylation of G Protein-Coupled Receptors: From the Barcode Hypothesis to the Flute Model.
Yang, Zhao; Yang, Fan; Zhang, Daolai; Liu, Zhixin; Lin, Amy; Liu, Chuan; Xiao, Peng; Yu, Xiao; Sun, Jin-Peng
2017-09-01
Seven transmembrane G protein-coupled receptors (GPCRs) are often phosphorylated at the C terminus and on intracellular loops in response to various extracellular stimuli. Phosphorylation of GPCRs by GPCR kinases and certain other kinases can promote the recruitment of arrestin molecules. The arrestins critically regulate GPCR functions not only by mediating receptor desensitization and internalization, but also by redirecting signaling to G protein-independent pathways via interactions with numerous downstream effector molecules. Accumulating evidence over the past decade has given rise to the phospho-barcode hypothesis, which states that ligand-specific phosphorylation patterns of a receptor direct its distinct functional outcomes. Our recent work using unnatural amino acid incorporation and fluorine-19 nuclear magnetic resonance ( 19 F-NMR) spectroscopy led to the flute model, which provides preliminary insight into the receptor phospho-coding mechanism, by which receptor phosphorylation patterns are recognized by an array of phosphate-binding pockets on arrestin and are translated into distinct conformations. These selective conformations are recognized by various effector molecules downstream of arrestin. The phospho-barcoding mechanism enables arrestin to recognize a wide range of phosphorylation patterns of GPCRs, contributing to their diverse functions. Copyright © 2017 by The Author(s).
Optimization for energy consumption in drying section of fluting paper machine
Directory of Open Access Journals (Sweden)
Ghodbanan Shaaban
2017-01-01
Full Text Available Non-linear programming optimization method was used to optimize total steam and air consumption in the dryer section of multi-cylinder fluting paper machine. Equality constraints of the optimization model were obtained from specified process blocks considering mass and energy balance relationships in drying and heat recovery sections. Inequality constraints correspond to process parameters such as production capacity, operating conditions, and other limitations. Using the simulation, the process parameters can be optimized to improve the energy efficiency and heat recovery performance. For a corrugating machine, optimized parameters show the total steam use can be reduced by about 11% due to improvement of the heat recovery performance and optimization of the operating conditions such as inlet web dryness, evaporation rate, and exhaust air humidity, accordingly total steam consumption can be decreased from about 1.71 to 1.53 tonnes steam per tonne paper production. The humidity of the exhaust air should be kept as high as possible to optimize the energy performance and avoid condensation in the pocket dryers and hood exhaust air. So the simulation shows the supply air should be increased by about 10% to achieve optimal humidity level which was determined about 0.152 kgH2O/(kg dry air.
CFD investigation of flow and heat transfer of nanofluids in isoflux spirally fluted tubes
Salama, Amgad
2012-01-01
In this work, the problem of flow and heat transfer of nanofluids in spirally fluted tubes is investigated numerically using the CFD code Fluent. The tube investigated in this work is characterized by the existence of helical ridging which is usually obtained by embossing a smooth tube. A tube of diameter of 15 mm, 1.5 mm groove depth and a single helix with pitch of 64 mm is chosen for simulation. This geometry has been chosen for simulation because it has been investigated experimentally for pure fluids and would, therefore, provide a verification framework with our CFD model. The result of our CFD investigation compares very well with the experimental work conducted on this tube geometry. Interesting patterns are highlighted and investigated including the existence of flow swirl as a result of the existence of the spirally enhanced ridges. This swirl flow enhances heat transfer characteristics of this system as reported in the literatures. This study also shows that further enhancement is achieved if small amount of nanoparticles are introduced to the fluid. These nanoparticles (metallic-based nanoparticles) when introduced to the fluid enhances its heat transfer characteristics.
Directory of Open Access Journals (Sweden)
Syahrul Azwan Sundi
2017-01-01
Full Text Available This paper is a study on full flute (extra-long tool and ground shank end mill wear analysis by utilizing five-axis CNC to implement flank milling strategy on curved shape part. Five-axis machining eases the user to implement variations of strategy such as flank milling. Flank milling is different from point milling. Point milling cuts materials by using the tip of the tool whereas the flank milling uses the cutting tool body to cut material. The type of cutting tool used was end mill 10 mm diameter with High Speed Steel (HSS material. One factor at a time was utilized to analyze the overall data. Feed rate and spindle speed were the two main factors that been set up equally for both full flute and ground shank end mill. At the end of this research, the qualitative analysis based on tool wear between full flute and ground shank end mill is observed. Generally, both types of cutting tools showed almost the same failure indication such as broken edge or chipped off edge, formation of pinned hole on the surface and serration formation or built-up edge (BUE on the primary flute. However, the results obtained from the enlarged images which were captured by Optical Microscope indicated that, the ground shank end mill is better than the full flute end mill.
International Nuclear Information System (INIS)
Lau, Y.T.; Novakovskii, S.V.; Drake, J.F.
1996-01-01
We will present 2D linear and 3D nonlinear studies of resistive-ballooning modes in tokamak edge plasmas which include a closed flux region, as well as a limiter scrape-off layer (SOL) region. These studies therefore go beyond most earlier work, where the stability of the edge in the closed flux region and in the SOL have been considered separately. A 2D linear code, 2D-BALLOON, examines the stability of these curvature driven modes and provides the complete 2D eigenfunction spanning the closed flux surface region as well the open field line region. The sheath boundary condition in the SOL introduces an important new parameter λ = (m e /m i ) 1/2 v ei qR/v Te . This parameter plays a significant role in determining the stability of these modes in both the closed flux and SOL regions because of the radial coupling across the last closed flux surface (LCFS). For small λ the spectrum of unstable modes is broad and extends into the low toroidal mode number exclamation point regime where the spatial structure is flute-like. The amplitude for these modes is larger in the SOL compared to the closed flux region. However when A is increased, the low mode numbers are strongly stabilized and the high mode numbers which are strongly ballooning are the dominant modes. In this regime the radial modes straddle the LCFS. In both these cases, the variation in the plasma density is necessary for the radial localization. In the three-dimensional nonlinear simulations, we have solved a set of fluid equations in a toroidal geometry with both the closed flux region and the SOL. The introduction of the SOL to the twisted tube for the closed flux region, has been a major addition to our 3D code. We find that the turbulent transport in the SOL drops significantly as A is increased, which is consistent with our expectations from the 2D linear code results
Hanratty, Thomas J.
1980-01-01
This paper gives an account of research on the structure of turbulence close to a solid boundary. Included is a method to study the flow close to the wall of a pipe without interferring with it. (Author/JN)
CERN. Geneva. Audiovisual Unit
2005-01-01
Understanding turbulence is vital in astrophysics, geophysics and many engineering applications, with thermal convection playing a central role. I shall describe progress that has recently been made in understanding this ubiquitous phenomenon by making controlled experiments using low-temperature helium, and a brief account of the frontier topic of superfluid turbulence will also be given. CERN might be able to play a unique role in experiments to probe these two problems.
Resistive drift wave turbulence and transport
International Nuclear Information System (INIS)
Wakatani, M.
1986-01-01
Our efforts for studying the properties of resistive drift wave turbulence by using model mode-coupling equations are shown. It may be related to the edge turbulence and the associated anomalous transport in tokamaks or in stellarator/heliotron. (author)
Hot-plasma decoupling condition for long-wavelength modes
International Nuclear Information System (INIS)
Berk, H.L.; Van Dam, J.W.; Spong, D.
1982-10-01
The stability of layer modes is analyzed for z-pinch and bumpy cylinder models. These modes are long wavelength across the layer and flute-like along the field line. The stability condition can be expressed in terms of the ratio of hot to core plasma density. It is shown that to achieve conditions close to the Nelson, Lee-Van Dam core beta limit, one needs a considerably smaller hot to core plasma density than is required to achieve stability at zero core beta
Theory of incremental turbulent transport in tokamaks
International Nuclear Information System (INIS)
Similon, P.L.
1991-01-01
The goal of this research is to understand how the various aspect of turbulent transport operate in tokamaks, in the presence of low frequency fluctuations such as drift waves or trapped electron modes
Recent developments in plasma turbulence and turbulent transport
Energy Technology Data Exchange (ETDEWEB)
Terry, P.W. [Univ. of Wisconsin, Madison, WI (United States)
1997-09-22
This report contains viewgraphs of recent developments in plasma turbulence and turbulent transport. Localized nonlinear structures occur under a variety of circumstances in turbulent, magnetically confined plasmas, arising in both kinetic and fluid descriptions, i.e., in either wave-particle or three-wave coupling interactions. These structures are non wavelike. They cannot be incorporated in the collective wave response, but interact with collective modes through their shielding by the plasma dielectric. These structures are predicted to modify turbulence-driven transport in a way that in consistent with, or in some cases are confirmed by recent experimental observations. In kinetic theory, non wavelike structures are localized perturbations of phase space density. There are two types of structures. Holes are self-trapped, while clumps have a self-potential that is too weak to resist deformation and mixing by ambient potential fluctuations. Clumps remain correlated in turbulence if their spatial extent is smaller than the correlation length of the scattering fields. In magnetic turbulence, clumps travel along stochastic magnetic fields, shielded by the plasma dielectric. A drag on the clump macro-particle is exerted by the shielding, inducing emission into the collective response. The emission in turn damps back on the particle distribution via Landau dampling. The exchange of energy between clumps and particles, as mediated by the collective mode, imposes constraints on transport. For a turbulent spectrum whose mean wavenumber along the equilibrium magnetic field is nonzero, the electron thermal flux is proportional to the ion thermal velocity. Conventional predictions (which account only for collective modes) are larger by the square root of the ion to electron mass ratio. Recent measurements are consistent with the small flux. In fluid plasma,s localized coherent structures can occur as intense vortices.
Tchen, C. M.
1986-01-01
Theoretical and numerical works in atmospheric turbulence have used the Navier-Stokes fluid equations exclusively for describing large-scale motions. Controversy over the existence of an average temperature gradient for the very large eddies in the atmosphere suggested that a new theoretical basis for describing large-scale turbulence was necessary. A new soliton formalism as a fluid analogue that generalizes the Schrodinger equation and the Zakharov equations has been developed. This formalism, processing all the nonlinearities including those from modulation provided by the density fluctuations and from convection due to the emission of finite sound waves by velocity fluctuations, treats large-scale turbulence as coalescing and colliding solitons. The new soliton system describes large-scale instabilities more explicitly than the Navier-Stokes system because it has a nonlinearity of the gradient type, while the Navier-Stokes has a nonlinearity of the non-gradient type. The forced Schrodinger equation for strong fluctuations describes the micro-hydrodynamical state of soliton turbulence and is valid for large-scale turbulence in fluids and plasmas where internal waves can interact with velocity fluctuations.
Electromotive force in strongly compressible magnetohydrodynamic turbulence
Yokoi, N.
2017-12-01
Variable density fluid turbulence is ubiquitous in geo-fluids, not to mention in astrophysics. Depending on the source of density variation, variable density fluid turbulence may be divided into two categories: the weak compressible (entropy mode) turbulence for slow flow and the strong compressible (acoustic mode) turbulence for fast flow. In the strong compressible turbulence, the pressure fluctuation induces a strong density fluctuation ρ ', which is represented by the density variance ( denotes the ensemble average). The turbulent effect on the large-scale magnetic-field B induction is represented by the turbulent electromotive force (EMF) (u': velocity fluctuation, b': magnetic-field fluctuation). In the usual treatment in the dynamo theory, the expression for the EMF has been obtained in the framework of incompressible or weak compressible turbulence, where only the variation of the mean density , if any, is taken into account. We see from the equation of the density fluctuation ρ', the density variance is generated by the large mean density variation ∂ coupled with the turbulent mass flux . This means that in the region where the mean density steeply changes, the density variance effect becomes relevant for the magnetic field evolution. This situation is typically the case for phenomena associated with shocks and compositional discontinuities. With the aid of the analytical theory of inhomogeneous compressible magnetohydrodynamic (MHD) turbulence, the expression for the turbulent electromotive force is investigated. It is shown that, among others, an obliqueness (misalignment) between the mean density gradient ∂ and the mean magnetic field B may contribute to the EMF as ≈χ B×∂ with the turbulent transport coefficient χ proportional to the density variance (χ ). This density variance effect is expected to strongly affect the EMF near the interface, and changes the transport properties of turbulence. In the case of an interface under the MHD slow
Transport barrier fluctuations governed by SOL turbulence spreading
International Nuclear Information System (INIS)
Ghendrih, Ph.; Sarazin, Y.; Ciraolo, G.; Darmet, G.; Garbet, X.; Grangirard, V.; Tamain, P.; Benkadda, S.; Beyer, P.
2007-01-01
Turbulence spreading, namely turbulent transport extending into a stable region is reported both for the flat density profiles in the far SOL and into a modeled H-mode barrier. It is shown that due to turbulence penetration, the pedestal width fluctuates and that its effective width is a factor 2 smaller than the linear predicted width. Turbulence overshooting throughout the pedestal leads to a non-vanishing turbulent transport within the barrier and provides a coupling of core and SOL turbulence despite the transport barrier
International Nuclear Information System (INIS)
Drury, L.O.; Stewart, J.M.
1976-01-01
A generalization of a transformation due to Kurskov and Ozernoi is used to rewrite the usual equations governing subsonic turbulence in Robertson-Walker cosmological models as Navier-Stokes equations with a time-dependent viscosity. This paper first rederives some well-known results in a very simple way by means of this transformation. The main result however is that the establishment of a Kolmogorov spectrum at recombination appears to be incompatible with subsonic turbulence. The conditions after recombination are also discussed briefly. (author)
Directory of Open Access Journals (Sweden)
Gérard Liger-Belair
Full Text Available In champagne tasting, gaseous CO(2 and volatile organic compounds progressively invade the headspace above glasses, thus progressively modifying the chemical space perceived by the consumer. Simultaneous quantification of gaseous CO(2 and ethanol was monitored through micro-gas chromatography (μGC, all along the first 15 minutes following pouring, depending on whether a volume of 100 mL of champagne was served into a flute or into a coupe. The concentration of gaseous CO(2 was found to be significantly higher above the flute than above the coupe. Moreover, a recently developed gaseous CO(2 visualization technique based on infrared imaging was performed, thus confirming this tendency. The influence of champagne temperature was also tested. As could have been expected, lowering the temperature of champagne was found to decrease ethanol vapor concentrations in the headspace of a glass. Nevertheless, and quite surprisingly, this temperature decrease had no impact on the level of gaseous CO(2 found above the glass. Those results were discussed on the basis of a multiparameter model which describes fluxes of gaseous CO(2 escaping the liquid phase into the form of bubbles.
Liger-Belair, Gérard; Bourget, Marielle; Pron, Hervé; Polidori, Guillaume; Cilindre, Clara
2012-01-01
In champagne tasting, gaseous CO(2) and volatile organic compounds progressively invade the headspace above glasses, thus progressively modifying the chemical space perceived by the consumer. Simultaneous quantification of gaseous CO(2) and ethanol was monitored through micro-gas chromatography (μGC), all along the first 15 minutes following pouring, depending on whether a volume of 100 mL of champagne was served into a flute or into a coupe. The concentration of gaseous CO(2) was found to be significantly higher above the flute than above the coupe. Moreover, a recently developed gaseous CO(2) visualization technique based on infrared imaging was performed, thus confirming this tendency. The influence of champagne temperature was also tested. As could have been expected, lowering the temperature of champagne was found to decrease ethanol vapor concentrations in the headspace of a glass. Nevertheless, and quite surprisingly, this temperature decrease had no impact on the level of gaseous CO(2) found above the glass. Those results were discussed on the basis of a multiparameter model which describes fluxes of gaseous CO(2) escaping the liquid phase into the form of bubbles.
Dynamic structure in self-sustained turbulence
International Nuclear Information System (INIS)
Itoh, K.; Itoh, S.; Yagi, M.; Fukuyama, A.
1995-06-01
Dynamical equation for the self-sustained and pressure-driven turbulence in toroidal plasmas is derived. The growth rate of the dressed-test mode, which belongs to the subcritical turbulence, is obtained as a function of the turbulent transport coefficient. In the limit of the low fluctuation level, the mode has the feature of the nonlinear instability and shows the explosive growth. The growth rate vanishes when the driven transport reaches to the stationarily-turbulent level. The stationary solution is thermodynamically stable. The characteristic time, by which the stationary and self-sustained turbulence is established, scales with the ion-sound transit time and is accelerated by the bad magnetic curvature. Influences of the pressure gradient as well as the radial electric field inhomogeneity are quantified. (author)
International Nuclear Information System (INIS)
Imaizumi, Ryota; Morikawa, Koichi; Higuchi, Masamori; Saito, Takayuki
2009-01-01
In this study, the interaction between a bubble swarm and homogeneous isotropic turbulence was experimentally investigated. The objective is to clarify the turbulence modulation induced by interaction between the bubble swarm and the homogeneous isotropic turbulence without mean flow. In order to generate simultaneously ideally homogeneous isotropic turbulence and a sufficiently controlled bubble swarm, we employed both oscillating grid and bubble generators equipped with audio speakers. First, the homogeneous isotropic turbulence was formed by operating the oscillating grid cylindrical acrylic pipe (height: 600 mm, inner diameter: 149 mm) filled with ion-exchanged and degassed water. Second, we stopped the oscillating-grid in arbitrary time after the homogeneous isotropic turbulence was achieved. A few moments later, the controlled bubble swarm (number of bubbles: 3, average equivalent diameter of bubble: 3 mm, bubble Reynolds number: 859, Weber number: 3.48) was launched into the decaying turbulence described above, using the bubble generators. The bubble formation, bubble size and bubble-launch timing are controlled arbitrarily and precisely by this device. In this study, we conducted the following experiments: 1) measurement of the motion of bubbles in rest water and oscillating grid turbulence via high-speed visualization, 2) measurement of the liquid phase motion around the bubbles in rest water via PIV system with LIF method, 3) measurement of the liquid phase motion around the bubbles in oscillating-grid turbulence via PIV system with LIF method. In the vitalization of the liquid-phase motion of both experiments, two high speed video cameras were employed in order to simultaneously film large- and small-scale interrogation areas. The liquid-phase ambient turbulence hastened the change of the bubble motion from zigzag mode to spiral mode. The interaction between the bubble swarm and liquid-phase turbulence increased decay-rate of the turbulence. (author)
DEFF Research Database (Denmark)
Nielsen, Mogens Peter; Shui, Wan; Johansson, Jens
2011-01-01
term with stresses depending linearly on the strain rates. This term takes into account the transfer of linear momentum from one part of the fluid to another. Besides there is another term, which takes into account the transfer of angular momentum. Thus the model implies a new definition of turbulence...
Tearing mode instability due to anomalous resistivity
International Nuclear Information System (INIS)
Furuya, Atsushi; Itoh, Sanae I.; Yagi, Masatoshi
2000-01-01
Tearing mode instability in the presence of microscopic truculence is investigates. The effects of microscopic turbulence on tearing mode are taken as drags which are calculated by one-point renormalization method and mean-field approximation. These effects are reduced to effective diffusivities in reduced MHD equations. Using these equations, the stability analyses of the tearing mode are performed. It is shown that a finite amplitude of fluctuation enhances the growth rate of tearing mode. For very high values of turbulent diffusivities, marginally stable state exists. The effects of each turbulent diffusivity on mode stability are examined near marginal stability boundary. Parameter dependence of the resistive ballooning mode turbulence on tearing mode is analyzed as an example. (author)
Integrated analysis of energy transfers in elastic-wave turbulence.
Yokoyama, Naoto; Takaoka, Masanori
2017-08-01
In elastic-wave turbulence, strong turbulence appears in small wave numbers while weak turbulence does in large wave numbers. Energy transfers in the coexistence of these turbulent states are numerically investigated in both the Fourier space and the real space. An analytical expression of a detailed energy balance reveals from which mode to which mode energy is transferred in the triad interaction. Stretching energy excited by external force is transferred nonlocally and intermittently to large wave numbers as the kinetic energy in the strong turbulence. In the weak turbulence, the resonant interactions according to the weak turbulence theory produce cascading net energy transfer to large wave numbers. Because the system's nonlinearity shows strong temporal intermittency, the energy transfers are investigated at active and moderate phases separately. The nonlocal interactions in the Fourier space are characterized by the intermittent bundles of fibrous structures in the real space.
National Oceanic and Atmospheric Administration, Department of Commerce — Forecast turbulence hazards identified by the Graphical Turbulence Guidance algorithm. The Graphical Turbulence Guidance product depicts mid-level and upper-level...
Graphical Turbulence Guidance - Composite
National Oceanic and Atmospheric Administration, Department of Commerce — Forecast turbulence hazards identified by the Graphical Turbulence Guidance algorithm. The Graphical Turbulence Guidance product depicts mid-level and upper-level...
Magnetohydrodynamic Turbulence
Montgomery, David C.
2004-01-01
Magnetohydrodynamic (MHD) turbulence theory is modeled on neutral fluid (Navier-Stokes) turbulence theory, but with some important differences. There have been essentially no repeatable laboratory MHD experiments wherein the boundary conditions could be controlled or varied and a full set of diagnostics implemented. The equations of MHD are convincingly derivable only in the limit of small ratio of collision mean-free-paths to macroscopic length scales, an inequality that often goes the other way for magnetofluids of interest. Finally, accurate information on the MHD transport coefficients-and thus, the Reynolds-like numbers that order magnetofluid behavior-is largely lacking; indeed, the algebraic expressions used for such ingredients as the viscous stress tensor are often little more than wishful borrowing from fluid mechanics. The one accurate thing that has been done extensively and well is to solve the (strongly nonlinear) MHD equations numerically, usually in the presence of rectangular periodic boundary conditions, and then hope for the best when drawing inferences from the computations for those astrophysical and geophysical MHD systems for which some indisputably turbulent detailed data are available, such as the solar wind or solar prominences. This has led to what is perhaps the first field of physics for which computer simulations are regarded as more central to validating conclusions than is any kind of measurement. Things have evolved in this way due to a mixture of the inevitable and the bureaucratic, but that is the way it is, and those of us who want to work on the subject have to live with it. It is the only game in town, and theories that have promised more-often on the basis of some alleged ``instability''-have turned out to be illusory.
Energy Technology Data Exchange (ETDEWEB)
Smith, D. R.; Fonck, R. J.; McKee, G. R.; Thompson, D. S. [Department of Engineering Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Bell, R. E.; Diallo, A.; Guttenfelder, W.; Kaye, S. M.; LeBlanc, B. P.; Podesta, M. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)
2013-05-15
The spherical torus edge region is among the most challenging regimes for plasma turbulence simulations. Here, we measure the spatial and temporal properties of ion-scale turbulence in the steep gradient region of H-mode pedestals during edge localized mode-free, MHD quiescent periods in the National Spherical Torus Experiment. Poloidal correlation lengths are about 10 ρ{sub i}, and decorrelation times are about 5 a/c{sub s}. Next, we introduce a model aggregation technique to identify parametric dependencies among turbulence quantities and transport-relevant plasma parameters. The parametric dependencies show the most agreement with transport driven by trapped-electron mode, kinetic ballooning mode, and microtearing mode turbulence, and the least agreement with ion temperature gradient turbulence. In addition, the parametric dependencies are consistent with turbulence regulation by flow shear and the empirical relationship between wider pedestals and larger turbulent structures.
Destructive interference of TEM and ITG turbulence
International Nuclear Information System (INIS)
Merz, F.; Jenko, F.
2009-01-01
Full text: Turbulence driven by ion temperature gradient (ITG) modes and trapped electron modes (TEMs) is generally considered the key mechanism for anomalous transport in fusion devices on ion scales. But while pure ITG and, to a lesser extent, also pure TEM turbulence have been studied in detail over the last years, not much is presently known about nonlinear interactions between ITG modes and TEMs, which are often present simultaneously in experimentally relevant situations. This important issue is addressed by means of linear and nonlinear gyrokinetic simulations with the GENE code. To examine the properties of the (linear) TEM and ITG instabilities in the (realistic) transitional regime, the GENE code is run as eigenvalue solver, which allows for a systematic study of dominant and subdominant modes. Corresponding nonlinear initial value computations show that the particle transport of the turbulent system can be completely suppressed if the two driving instabilities are active simultaneously. The direct comparison of the linear modes and the corresponding turbulent system reveals a coexistence of the two microinstabilities in a transitional regime even at the same wave number. The consequences of this dual turbulence drive for transport modeling is discussed. (author)
TEM turbulence optimisation in stellarators
Proll, J. H. E.; Mynick, H. E.; Xanthopoulos, P.; Lazerson, S. A.; Faber, B. J.
2016-01-01
With the advent of neoclassically optimised stellarators, optimising stellarators for turbulent transport is an important next step. The reduction of ion-temperature-gradient-driven turbulence has been achieved via shaping of the magnetic field, and the reduction of trapped-electron mode (TEM) turbulence is addressed in the present paper. Recent analytical and numerical findings suggest TEMs are stabilised when a large fraction of trapped particles experiences favourable bounce-averaged curvature. This is the case for example in Wendelstein 7-X (Beidler et al 1990 Fusion Technol. 17 148) and other Helias-type stellarators. Using this knowledge, a proxy function was designed to estimate the TEM dynamics, allowing optimal configurations for TEM stability to be determined with the STELLOPT (Spong et al 2001 Nucl. Fusion 41 711) code without extensive turbulence simulations. A first proof-of-principle optimised equilibrium stemming from the TEM-dominated stellarator experiment HSX (Anderson et al 1995 Fusion Technol. 27 273) is presented for which a reduction of the linear growth rates is achieved over a broad range of the operational parameter space. As an important consequence of this property, the turbulent heat flux levels are reduced compared with the initial configuration.
Radial propagation of turbulence in tokamaks
International Nuclear Information System (INIS)
Garbet, X.; Laurent, L.; Samain, A.
1993-12-01
It is shown in this paper that a turbulence propagation can be due to toroidal or non linear mode coupling. An analytical analysis indicates that the toroidal coupling acts through a convection while the non linear effects induce a diffusion. Numerical simulations suggest that the toroidal propagation is usually the fastest process, except perhaps in some highly turbulent regimes. The consequence is the possibility of non local effects on the fluctuation level and the associated transport. (authors). 7 figs., 19 refs
Geometry Dependence of Stellarator Turbulence
International Nuclear Information System (INIS)
Mynick, H.E.; Xanthopoulos, P.; Boozer, A.H.
2009-01-01
Using the nonlinear gyrokinetic code package GENE/GIST, we study the turbulent transport in a broad family of stellarator designs, to understand the geometry-dependence of the microturbulence. By using a set of flux tubes on a given flux surface, we construct a picture of the 2D structure of the microturbulence over that surface, and relate this to relevant geometric quantities, such as the curvature, local shear, and effective potential in the Schrodinger-like equation governing linear drift modes
DEFF Research Database (Denmark)
Broholm, Mette Martina; Janniche, Gry Sander; Mosthaf, Klaus
2016-01-01
Characterization of dense non-aqueous phase liquid (DNAPL) source zones in limestone aquifers/bedrock is essential to develop accurate site-specific conceptual models and perform risk assessment. Here innovative field methods were combined to improve determination of source zone architecture......, hydrogeology and contaminant distribution. The FACT™ is a new technology and it was applied and tested at a contaminated site with a limestone aquifer, together with a number of existing methods including wire-line coring with core subsampling, FLUTe® transmissivity profiling and multilevel water sampling...... groundwater sampling (under two flow conditions) and FACT™ sampling and analysis combined with FLUTe® transmissivity profiling and modeling were used to provide a line of evidence for the presence of DNAPL, dissolved and sorbed phase contamination in the limestone fractures and matrix. The combined methods...
International Nuclear Information System (INIS)
Garbet, X.; Mourgues, F.; Samain, A.; Zou, X.
1990-01-01
A serious degradation of confinement with additional heating is commonly observed on most tokamaks. The microtearing modes could provide an explanation for this experimental fact. They are driven linearly unstable by diamagnetism in collisional regimes, but it may be shown that the collisions in non linear regimes provide a small diffusion coefficient which can be only significant at the plasme edge. In the bulk of the plasma, the microtearing turbulence could play a basic role if it is unstable in the collisionless regime. While it is linearly stable without collisions, it could be driven unstable in realistic regimes by the radial diffusion it induces. To study this effect, we have used a model where the non linear action of the modes on a given helicity component is represented by a diffusion operator. They are found unstable for reasonable β p =2μ o nT/B 2 p , with a special radial profile of the potential vector A. The problem arises the validity of this model where non linearities in the trajectories behaviour are replaced by the diffusion which broadens resonances. To test this procedure, we calculate the actual electron distribution function when it is determined by the ergodicity of the field lines. We compute the correlations of the distribution function with the magnetic perturbation and compare them with the analytical expressions derived from the resonance broadening model. (author) 3 refs., 2 figs
Turbulence, Magnetic Reconnection in Turbulent Fluids and Energetic Particle Acceleration
Lazarian, A.; Vlahos, L.; Kowal, G.; Yan, H.; Beresnyak, A.; de Gouveia Dal Pino, E. M.
2012-11-01
Turbulence is ubiquitous in astrophysics. It radically changes many astrophysical phenomena, in particular, the propagation and acceleration of cosmic rays. We present the modern understanding of compressible magnetohydrodynamic (MHD) turbulence, in particular its decomposition into Alfvén, slow and fast modes, discuss the density structure of turbulent subsonic and supersonic media, as well as other relevant regimes of astrophysical turbulence. All this information is essential for understanding the energetic particle acceleration that we discuss further in the review. For instance, we show how fast and slow modes accelerate energetic particles through the second order Fermi acceleration, while density fluctuations generate magnetic fields in pre-shock regions enabling the first order Fermi acceleration of high energy cosmic rays. Very importantly, however, the first order Fermi cosmic ray acceleration is also possible in sites of magnetic reconnection. In the presence of turbulence this reconnection gets fast and we present numerical evidence supporting the predictions of the Lazarian and Vishniac (Astrophys. J. 517:700-718, 1999) model of fast reconnection. The efficiency of this process suggests that magnetic reconnection can release substantial amounts of energy in short periods of time. As the particle tracing numerical simulations show that the particles can be efficiently accelerated during the reconnection, we argue that the process of magnetic reconnection may be much more important for particle acceleration than it is currently accepted. In particular, we discuss the acceleration arising from reconnection as a possible origin of the anomalous cosmic rays measured by Voyagers as well as the origin cosmic ray excess in the direction of Heliotail.
3D fluid simulations of tokamak edge turbulence
International Nuclear Information System (INIS)
Zeiler, A.; Biskamp, D.; Drake, J.F.; Guzdar, P.N.
1995-09-01
3D simulations of drift resistive ballooning turbulence are presented. The turbulence is basically controlled by a parameter α, the ratio of the drift wave frequency to the ideal ballooning growth rate. If this parameters is small (α≤1, corresponding to Ohmic or L-mode plasmas), the system is dominated by ballooning turbulence, which is strongly peaked at the outside of the torus. If it is large (α≥1, corresponding to H-mode plasmas) field line curvature plays a minor role. The turbulence is nonlinearly sustained even if curvature is removed and all modes are linearly stable due to magnetic shear. In the nonlinear regime without curvature the system obeys a different scaling law compared to the low α regime. The transport scaling is discussed in both regimes and the implications for OH-, L-mode and H-mode transport are discussed. (orig.)
Anisotropy effects on curvature-driven flute instabilities in a hot-electron plasma
International Nuclear Information System (INIS)
Spong, D.A.; Berk, H.L.; Van Dam, J.W.; Rosenbluth, M.N.
1982-08-01
The effects of finite parallel temperature are investigated for a hot electron plasma with sufficiently large beta that the magnetic field scale length (Δ/sub B/) is small compared with the vacuum field radius of curvature (R). Numerical and analytical estimates of stability boundaries are obtained for the four possible modes that can be treated in this limit: the conventional hot electron interchange, the high frequency hot electron interchange (ω > ω/sub ci/), the compressional Alfven mode, and the interacting pressure-driven interchange
Li, Xin; Hu, Bin; Miao, Jinbai; Li, Hui
2016-02-01
The aim of this study was to assess the feasibility, efficacy and safety of a modified silicone fluted drain tube after video-assisted thoracic surgery (VATS) lung resection. The prospective randomized study included 50 patients who underwent VATS lung resection between March 2015 and June 2015. Eligible patients were randomized into two groups: experimental group (using the silicone fluted drain tubes for chest drainage) and control group (using standard drain tubes for chest drainage). The volume and characteristics of drainage, postoperative (PO) pain scores and hospital stay were recorded. All patients received standard care during hospital admission. In accordance with the exit criteria, three patients were excluded from study. The remaining 47 patients included in the final analysis were divided into two groups: experiment group (N=24) and control group (N=23). There was no significant difference between the two groups in terms of age, sex, height, weight, clinical diagnosis and type of surgical procedure. There was a trend toward less PO pain in experimental group on postoperative day (POD) 1, with a statistically significant difference. Patients in experimental group had a reduced occurrence of fever [temperature (T) >37.4 °C] compared to the control group. The silicone fluted drain tube is feasible and safe and may relieve patient PO pain and reduce occurrence of fever without the added risk of PO complications.
Hierarchical order in wall-bounded shear turbulence
International Nuclear Information System (INIS)
Carbone, F.; Aubry, N.
1996-01-01
Since turbulence at realistic Reynolds numbers, such as those occurring in the atmosphere or in the ocean, involve a high number of modes that cannot be resolved computationally in the foreseeable future, there is a strong motivation for finding techniques which drastically decrease the number of such required modes, particularly under inhomogeneous conditions. The significance of this work is to show that wall-bounded shear turbulence, in its strongly inhomogeneous direction (normal to the wall), can be decomposed into one (or a few) space endash time mother mode(s), with each mother generating a whole family of modes by stretching symmetry. In other words, the generated modes are similar, dilated copies of their mother. In addition, we show that the nature of all previous modes strongly depends on the symmetry itself. These findings constitute the first scaling theory of inhomogeneous turbulence. copyright 1996 American Institute of Physics
International Nuclear Information System (INIS)
Alademeyin, J. O.; Arawande, J. O.
2016-01-01
This paper reports the physicochemical properties and fatty acid composition of the seed oil extracted from fluted pumpkin (Telfairia occidentalis). The extracted oil was degummed, neutralised and bleached. The oil yield was 42.26±0.20%. The specific gravity (at 25 degree C) of the oil was 0.923±0.003 and the refractive index (at 25 degree C) was 1.475±0.002. Processing of the crude oil resulted in progressive decrease in turbidity, colour, free fatty acid, acid value, peroxide value and saponification value. However, there was increase in smoke point (243.00±0.03 to 253.00±0.03 degree C), flash point (285.00±1.20 to 304.0 1.10 degree C) and fire point (345.001.10 to 358.0 1.55 degree C) as well as iodine value (113.00 to 121.50 g/100 g) and fatty acid composition during the processing of the oil. The fatty acids detected in the oil samples were myristic, palmitic, stearic, oleic, arachidic, behenic, linoleic and linolenic acids. The predominant fatty acid was oleic acid (47.40-47.90%) followed by linoleic acid (26.36-30.44%) while the least fatty acid was linolenic acid (0.01-0.05%). (author)
Study of the plasma edge turbulence in tokamaks
International Nuclear Information System (INIS)
Garbet, X.; Laurent, L.; Mourgues, F.; Roubin, J.P.; Samain, A.
1990-01-01
The plasma edge in tokamaks is known to be very turbulent. We investigate here the non linear stability of a test mode in presence of an helical potential perturbation, i.e. a pump mode, which simulates the plasma turbulence. The particle trajectories in this perturbed equilibrium are derived using an hamiltonian formalism. The electrons appear to have trapped trajectories in the potential well of the pump mode, while the ions experience a large convective motion. These two effects have a large influence on the test mode stability. First, non linearly trapped electrons supply an energy source for the test mode. Second, the ion convective motion introduces a radial scale of the test mode larger than the ion Larmor radius, in agreement with experimental data. These two phenomena allow a bifurcation in the turbulence level and provide therefore an explanation for the L-H transition
Comments on the dispersion equation of a turbulent plasma - an inhomogeneous, magnetoactive case
International Nuclear Information System (INIS)
Ag, A.
1978-03-01
A weakly turbulent, magnetoactive plasma is considered in an inhomogeneous case with anisotropic temperature distribution. The dispersion relation is established following a method developed by Tsytovich and Nekrasov. The correction coefficients are calculated in the three principal scaling modes: (1) the turbulent frequencies predominate, (2) the cyclotronic velocities of the macroinstabilities predominate, (3) the turbulent frequencies are lower. (D.P.)
Images of Edge Turbulence in NSTX
International Nuclear Information System (INIS)
Zweben, S.J.; Bush, C.E.; Maqueda, R.; Munsat, T.; Stotler, D.; Lowrance, J.; Mastracola, V.; Renda, G.
2004-01-01
The 2-D structure of edge plasma turbulence has been measured in the National Spherical Torus Experiment (NSTX) by viewing the emission of the Da spectral line of deuterium. Images have been made at framing rates of up to 250,000 frames/sec using an ultra-high speed CCD camera developed by Princeton Scientific Instruments. A sequence of images showing the transition between L-mode and H-mode states is shown
High Reynolds Number Turbulence
National Research Council Canada - National Science Library
Smits, Alexander J
2007-01-01
The objectives of the grant were to provide a systematic study to fill the gap between existing research on low Reynolds number turbulent flows to the kinds of turbulent flows encountered on full-scale vehicles...
Topics in strong Langmuir turbulence
International Nuclear Information System (INIS)
Skoric, M.M.
1981-01-01
This thesis discusses certain aspects of the turbulence of a fully ionised non-isothermal plasma dominated by the Langmuir mode. Some of the basic properties of strongly turbulent plasmas are reviewed. In particular, interest is focused on the state of Langmuir turbulence, that is the turbulence of a simple externally unmagnetized plasma. The problem of the existence and dynamics of Langmuir collapse is discussed, often met as a non-linear stage of the modulational instability in the framework of the Zakharov equations (i.e. simple time-averaged dynamical equations). Possible macroscopic consequences of such dynamical turbulent models are investigated. In order to study highly non-linear collapse dynamics in its advanced stage, a set of generalized Zakharov equations are derived. Going beyond the original approximation, the author includes the effects of higher electron non-linearities and a breakdown of slow-timescale quasi-neutrality. He investigates how these corrections may influence the collapse stabilisation. Recently, it has been realised that the modulational instability in a Langmuir plasma will be accompanied by the collisionless-generation of a slow-timescale magnetic field. Accordingly, a novel physical situation has emerged which is investigated in detail. The stability of monochromatic Langmuir waves in a self-magnetized Langmuir plasma, is discussed, and the existence of a novel magneto-modulational instability shown. The wave collapse dynamics is investigated and a physical interpretation of the basic results is given. A problem of the transient analysis of an interaction of time-dependent electromagnetic pulses with linear cold plasma media is investigated. (Auth.)
AHP 4: na53 mʑi53 Tibetan Songs, Engagement Chants, and Flute Music
Directory of Open Access Journals (Sweden)
LIBU LAKHI (LI JIANFU 李建富, DAWA TENZIN ཟླ་བ་བསྟན་འཛིན།
2010-06-01
Full Text Available The present study is a straightforward, pragmatic attempt to document the particulars of na53 mi53 song and musical traditions comprising the local 'performance-scape'. The primary researcher, Libu Lakhi, is a native of the community who was trained in a specialized mode of auto-ethnography developed by Charles Kevin Stuart and Gerald Roche at Qinghai Normal University 青海师范大学, Xining City 西宁市, Qinghai Province 青海省. Drawing on ethnomusicology, socio-linguistics, and the 'performance' school of folkloristics, the model is intended to enable local peoples to document and display their own traditions in a form available to scholars and interested persons on a global scale.
DEFF Research Database (Denmark)
Brand, Arno J.; Peinke, Joachim; Mann, Jakob
2011-01-01
The nature of turbulent flow towards, near and behind a wind turbine, the effect of turbulence on the electricity production and the mechanical loading of individual and clustered wind turbines, and some future issues are discussed.......The nature of turbulent flow towards, near and behind a wind turbine, the effect of turbulence on the electricity production and the mechanical loading of individual and clustered wind turbines, and some future issues are discussed....
Pebble Accretion in Turbulent Protoplanetary Disks
Xu, Ziyan; Bai, Xue-Ning; Murray-Clay, Ruth A.
2017-09-01
It has been realized in recent years that the accretion of pebble-sized dust particles onto planetary cores is an important mode of core growth, which enables the formation of giant planets at large distances and assists planet formation in general. The pebble accretion theory is built upon the orbit theory of dust particles in a laminar protoplanetary disk (PPD). For sufficiently large core mass (in the “Hill regime”), essentially all particles of appropriate sizes entering the Hill sphere can be captured. However, the outer regions of PPDs are expected to be weakly turbulent due to the magnetorotational instability (MRI), where turbulent stirring of particle orbits may affect the efficiency of pebble accretion. We conduct shearing-box simulations of pebble accretion with different levels of MRI turbulence (strongly turbulent assuming ideal magnetohydrodynamics, weakly turbulent in the presence of ambipolar diffusion, and laminar) and different core masses to test the efficiency of pebble accretion at a microphysical level. We find that accretion remains efficient for marginally coupled particles (dimensionless stopping time {τ }s˜ 0.1{--}1) even in the presence of strong MRI turbulence. Though more dust particles are brought toward the core by the turbulence, this effect is largely canceled by a reduction in accretion probability. As a result, the overall effect of turbulence on the accretion rate is mainly reflected in the changes in the thickness of the dust layer. On the other hand, we find that the efficiency of pebble accretion for strongly coupled particles (down to {τ }s˜ 0.01) can be modestly reduced by strong turbulence for low-mass cores.
International Nuclear Information System (INIS)
Goldman, M.V.
1984-01-01
After a brief discussion of beam-excited Langmuir turbulence in the solar wind, we explain the criteria for wave-particle, three-wave and strong turbulence interactions. We then present the results of a numerical integration of the Zakharov equations, which describe the strong turbulence saturation of a weak (low-density) high energy, bump-on-tail beam instability. (author)
Poloidal rotation and the evolution of H-mode and VH-mode profiles
International Nuclear Information System (INIS)
Hinton, F.L.; Staebler, G.M.; Kim, Y.B.
1993-12-01
The physics which determines poloidal rotation, and its role in the development of profiles during H- and VH-modes, is discussed. A simple phenomenological transport model, which incorporates the rvec E x rvec B flow shear suppression of turbulence, is shown to predict profile evolution similar to that observed experimentally during H-mode and VH-mode
Progress in turbulence research
International Nuclear Information System (INIS)
Bradshaw, P.
1990-01-01
Recent developments in experiments and eddy simulations, as an introduction to a discussion of turbulence modeling for engineers is reviewed. The most important advances in the last decade rely on computers: microcomputers to control laboratory experiments, especially for multidimensional imaging, and supercomputers to simulate turbulence. These basic studies in turbulence research are leading to genuine breakthroughs in prediction methods for engineers and earth scientists. The three main branches of turbulence research: experiments, simulations (numerically-accurate three-dimensional, time-dependent solutions of the Navier-Stokes equations, with any empiricism confined to the smallest eddies), and modeling (empirical closure of time-averaged equations for turbulent flow) are discussed. 33 refs
Direct numerical simulation of homogeneous stratified rotating turbulence
Energy Technology Data Exchange (ETDEWEB)
Iida, O.; Tsujimura, S.; Nagano, Y. [Nagoya Institute of Technology, Department of Mech. Eng., Nagoya (Japan)
2005-12-01
The effects of the Prandtl number on stratified rotating turbulence have been studied in homogeneous turbulence by using direct numerical simulations and a rapid distortion theory. Fluctuations under strong stable-density stratification can be theoretically divided into the WAVE and the potential vorticity (PV) modes. In low-Prandtl-number fluids, the WAVE mode deteriorates, while the PV mode remains. Imposing rotation on a low-Prandtl-number fluid makes turbulence two-dimensional as well as geostrophic; it is found from the instantaneous turbulent structure that the vortices merge to form a few vertically-elongated vortex columns. During the period toward two-dimensionalization, the vertical vortices become asymmetric in the sense of rotation. (orig.)
Regulation of ETG turbulence by TEM driven zonal flows
Asahi, Yuuichi; Ishizawa, Akihiro; Watanabe, Tomohiko; Tsutsui, Hiroaki; Tsuji-Iio, Shunji
2013-10-01
Anomalous heat transport driven by electron temperature gradient (ETG) turbulence is investigated by means of gyrokinetic simulations. It is found that the ETG turbulence can be suppressed by zonal flows driven by trapped electron modes (TEMs). The TEMs appear in a statistically steady state of ETG turbulence and generate zonal flows, while its growth rate is much smaller than those of ETGs. The TEM-driven zonal flows with lower radial wave numbers are more strongly generated than those driven by ETG modes, because of the higher zonal flow response to a density source term. An ExB shearing rate of the TEM-driven zonal flows is strong enough to suppress the long-wavelength ETG modes which make the main contribution to the turbulent transport.
Turbulent Transport in a Three-dimensional Solar Wind
Energy Technology Data Exchange (ETDEWEB)
Shiota, D. [Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Aichi 464-8601 (Japan); Zank, G. P.; Adhikari, L.; Hunana, P. [Center for Space Plasma and Aeronomic Research (CSPAR), Department of Space Science, University of Alabama in Huntsville, Huntsville, AL 35805 (United States); Telloni, D. [INAF—Astrophysical Observatory of Torino, Via Osservatorio 20, I-10025 Pino Torinese (Italy); Bruno, R., E-mail: shiota@isee.nagoya-u.ac.jp [INAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere 100, I-00133 Roma (Italy)
2017-03-01
Turbulence in the solar wind can play essential roles in the heating of coronal and solar wind plasma and the acceleration of the solar wind and energetic particles. Turbulence sources are not well understood and thought to be partly enhanced by interaction with the large-scale inhomogeneity of the solar wind and the interplanetary magnetic field and/or transported from the solar corona. To investigate the interaction with background inhomogeneity and the turbulence sources, we have developed a new 3D MHD model that includes the transport and dissipation of turbulence using the theoretical model of Zank et al. We solve for the temporal and spatial evolution of three moments or variables, the energy in the forward and backward fluctuating modes and the residual energy and their three corresponding correlation lengths. The transport model is coupled to our 3D model of the inhomogeneous solar wind. We present results of the coupled solar wind-turbulence model assuming a simple tilted dipole magnetic configuration that mimics solar minimum conditions, together with several comparative intermediate cases. By considering eight possible solar wind and turbulence source configurations, we show that the large-scale solar wind and IMF inhomogeneity and the strength of the turbulence sources significantly affect the distribution of turbulence in the heliosphere within 6 au. We compare the predicted turbulence distribution results from a complete solar minimum model with in situ measurements made by the Helios and Ulysses spacecraft, finding that the synthetic profiles of the turbulence intensities show reasonable agreement with observations.
Homogeneous turbulence dynamics
Sagaut, Pierre
2018-01-01
This book provides state-of-the-art results and theories in homogeneous turbulence, including anisotropy and compressibility effects with extension to quantum turbulence, magneto-hydodynamic turbulence and turbulence in non-newtonian fluids. Each chapter is devoted to a given type of interaction (strain, rotation, shear, etc.), and presents and compares experimental data, numerical results, analysis of the Reynolds stress budget equations and advanced multipoint spectral theories. The role of both linear and non-linear mechanisms is emphasized. The link between the statistical properties and the dynamics of coherent structures is also addressed. Despite its restriction to homogeneous turbulence, the book is of interest to all people working in turbulence, since the basic physical mechanisms which are present in all turbulent flows are explained. The reader will find a unified presentation of the results and a clear presentation of existing controversies. Special attention is given to bridge the results obta...
DEFF Research Database (Denmark)
Gilling, Lasse
of resolved inflow turbulence on airfoil simulations in CFD. The detached-eddy simulation technique is used because it can resolve the inflow turbulence without becoming too computationally expensive due to its limited requirements for mesh resolution in the boundary layer. It cannot resolve the turbulence......Wind turbines operate in inflow turbulence whether it originates from the shear in the atmospheric boundary layer or from the wake of other wind turbines. Consequently, the airfoils of the wings experience turbulence in the inflow. The main topic of this thesis is to investigate the effect...... that is formed in attached boundary layers, but the freestream turbulence can penetrate the boundary layer. The idea is that the resolved turbulence from the freestream should mix high momentum flow into the boundary layer and thereby increase the resistance against separation and increase the maximum lift...
Spectral properties of electromagnetic turbulence in plasmas
Directory of Open Access Journals (Sweden)
D. Shaikh
2009-03-01
Full Text Available We report on the nonlinear turbulent processes associated with electromagnetic waves in plasmas. We focus on low-frequency (in comparison with the electron gyrofrequency nonlinearly interacting electron whistlers and nonlinearly interacting Hall-magnetohydrodynamic (H-MHD fluctuations in a magnetized plasma. Nonlinear whistler mode turbulence study in a magnetized plasma involves incompressible electrons and immobile ions. Two-dimensional turbulent interactions and subsequent energy cascades are critically influenced by the electron whisters that behave distinctly for scales smaller and larger than the electron skin depth. It is found that in whistler mode turbulence there results a dual cascade primarily due to the forward spectral migration of energy that coexists with a backward spectral transfer of mean squared magnetic potential. Finally, inclusion of the ion dynamics, resulting from a two fluid description of the H-MHD plasma, leads to several interesting results that are typically observed in the solar wind plasma. Particularly in the solar wind, the high-time-resolution databases identify a spectral break at the end of the MHD inertial range spectrum that corresponds to a high-frequency regime. In the latter, turbulent cascades cannot be explained by the usual MHD model and a finite frequency effect (in comparison with the ion gyrofrequency arising from the ion inertia is essentially included to discern the dynamics of the smaller length scales (in comparison with the ion skin depth. This leads to a nonlinear H-MHD model, which is presented in this paper. With the help of our 3-D H-MHD code, we find that the characteristic turbulent interactions in the high-frequency regime evolve typically on kinetic-Alfvén time-scales. The turbulent fluctuation associated with kinetic-Alfvén interactions are compressive and anisotropic and possess equipartition of the kinetic and magnetic energies.
Scaling, Intermittency and Decay of MHD Turbulence
International Nuclear Information System (INIS)
Lazarian, A.; Cho, Jungyeon
2005-01-01
We discuss a few recent developments that are important for understanding of MHD turbulence. First, MHD turbulence is not so messy as it is usually believed. In fact, the notion of strong non-linear coupling of compressible and incompressible motions along MHD cascade is not tenable. Alfven, slow and fast modes of MHD turbulence follow their own cascades and exhibit degrees of anisotropy consistent with theoretical expectations. Second, the fast decay of turbulence is not related to the compressibility of fluid. Rates of decay of compressible and incompressible motions are very similar. Third, viscosity by neutrals does not suppress MHD turbulence in a partially ionized gas. Instead, MHD turbulence develops magnetic cascade at scales below the scale at which neutrals damp ordinary hydrodynamic motions. Forth, density statistics does not exhibit the universality that the velocity and magnetic field do. For instance, at small Mach numbers the density is anisotropic, but it gets isotropic at high Mach numbers. Fifth, the intermittency of magnetic field and velocity are different. Both depend on whether the measurements are done in a local system of reference oriented along the local magnetic field or in the global system of reference related to the mean magnetic field
Turbulence and anomalous transport in toroidal plasmas
Energy Technology Data Exchange (ETDEWEB)
Nordman, H
1990-12-31
In present-day Tokamak fusion machines, instabilities and turbulence driven by temperature gradients can have a considerable impact on the confinement qualities. This thesis is mainly devoted to analyzing the nonlinear evolution of these instabilities and the associated turbulent transport. A combined analytical and numerical study of the ion temperature gradient driven turbulence is presented. An analytical expression for the ion thermal conductivity is derived and found to be in good agreement with the simulation results. The scaling properties of chi{sub i} are investigated and compared with experimental results. The transport due to the simultaneous presence of a trapped electron mode and an ion temperature gradient mode is analysed. It is found that the coupling of the modes can give rise to inward diffusive fluxes of both particles and energy. The tendency of the system to equilibrate density and temperature scale lengths is compared with recent experimental trends. The nonlinear behaviour of the instabilities is also studied in the context of low dimensional dynamical systems. Here, the relation between the fully nonlinear fluid models and the low dimensional models is discussed. The influence of a high frequency RF-field on the ion temperature gradient driven mode is investigated analytically. The consequences for mode stability and transport are considered. 23 refs.
Turbulence and anomalous transport in toroidal plasmas
International Nuclear Information System (INIS)
Nordman, H.
1989-01-01
In present-day Tokamak fusion machines, instabilities and turbulence driven by temperature gradients can have a considerable impact on the confinement qualities. This thesis is mainly devoted to analyzing the nonlinear evolution of these instabilities and the associated turbulent transport. A combined analytical and numerical study of the ion temperature gradient driven turbulence is presented. An analytical expression for the ion thermal conductivity is derived and found to be in good agreement with the simulation results. The scaling properties of chi i are investigated and compared with experimental results. The transport due to the simultaneous presence of a trapped electron mode and an ion temperature gradient mode is analysed. It is found that the coupling of the modes can give rise to inward diffusive fluxes of both particles and energy. The tendency of the system to equilibrate density and temperature scale lengths is compared with recent experimental trends. The nonlinear behaviour of the instabilities is also studied in the context of low dimensional dynamical systems. Here, the relation between the fully nonlinear fluid models and the low dimensional models is discussed. The influence of a high frequency RF-field on the ion temperature gradient driven mode is investigated analytically. The consequences for mode stability and transport are considered. 23 refs
Kinetic features of interchange turbulence
International Nuclear Information System (INIS)
Sarazin, Y; Grandgirard, V; Fleurence, E; Garbet, X; Ghendrih, Ph; Bertrand, P; Depret, G
2005-01-01
Non-linear gyrokinetic simulations of the interchange instability are discussed. The semi-Lagrangian numerical scheme allows one to address two critical points achieved with simulations lasting several confinement times: an accurate statistical analysis of the fluctuations and the back reaction of the turbulence on equilibrium profiles. Zonal flows are found to quench a 2D + 1D interchange turbulence when one of the species has a vanishing response to zonal modes. Conversely, when streamers dominate, the equilibrium profiles are found to be stiff. In the non-linear regime and steady-state turbulence, the distribution function exhibits a significant departure from a Maxwellian distribution. This property is characterized by an expansion on generalized Laguerre functions with a slow decay of the series of moments. This justifies the use of gyrokinetic simulations since a standard fluid approach, based on a limited number of moments, would certainly require a complex closure so as to take into account the impact of these non-vanishing high order moments
On the bicoherence analysis of plasma turbulence
International Nuclear Information System (INIS)
Itoh, K.; Nagashima, Y.; Fujisawa, A.; Itoh, S.-I.; Yagi, M.; Diamond, P.H.; Fukuyama, A.
2005-10-01
The bicoherence of fluctuations in a system of drift waves and zonal flows is discussed. In strong drift-wave turbulence, where broad-band fluctuations are excited, the bicoherence is examined. A Langevin equation formalism of turbulent interactions allows us to relate the bicoherence coefficient to the projection of nonlinear force onto the test mode. The dependence of the summed bicoherence on the amplitude of zonal flows is clarified. The importance of observing biphase is also stressed. The results provide a basis for measurement of nonlinear interaction in a system of drift waves and zonal flow. (author)
Directory of Open Access Journals (Sweden)
Abdollah barimani
2013-11-01
Full Text Available Location selection for factory competitiveness in the market place plays an important role and should be chosen so that will leads achievement of the strategic advantages compared with other competitors. The objective of this study was determination of the effective criteria for decision making to select the most suitable location for establishing a fluting paper mills from agricultural residues. For this purpose, effective criteria were divided into five major groups: Material and Product, Facilities and limitations of regional (infrastructure, Technical and Human, Economical, Rules & Regulations as well as 33 sub-criteria, after preliminary investigation, preparatory observation, and an interview with some of the paper producers and relevant experts. A hierarchy was designed based on five major groups of criteria and then the priority rates of obtained criteria and sub-criteria were determined by Analytical Hierarchy Process (AHP after compiling expert's opinions via questionnaire. Results have shown that among 33 determined effective criteria in location selection of fluting paper mills from agricultural residues , the sub-criteria of Supply residual amount, Ensure the supply of residual, Cost purchasing of raw material, Cost of transporting raw material have the highest priorities, respectively
Theory of self-sustained turbulence in confined plasmas
International Nuclear Information System (INIS)
Itoh, K.; Itoh, S.-I.; Fukuyama, A.; Yagi, M.
1996-01-01
This article reviews some aspects of recent theoretical activities in Japan on the problem of turbulent transport in confined plasmas. The method of self-sustained turbulence is discussed. The process of the renormalization is shown and the turbulent Prandtl number is introduced. Nonlinear destabilization by the electron momentum diffusion is explained. The nonlinear eigenmode equation is derived for the dressed-test-mode for the inhomogeneous plasma in the shear magnetic field. The eigenvalue equation is solved, and the least stable mode determines the anomalous transport coefficient. The formula of the thermal conductivity is presented for the system of bad average magnetic curvature (current diffusive interchange mode (CDIM) turbulence) and that for the average good magnetic curvature (current diffusive ballooning mode (CDBM) turbulence). The transport coefficient, scale length of fluctuations and fluctuation level are shown to be an increasing function of the pressure gradient. Verification by use of the nonlinear simulation is shown. The bifurcation of the electric field and improved confinement are addressed, in order to explain the H-mode physics. The improved confinement and dynamics such as ELMs are explained. Application to the transport analysis of tokamaks is also presented, including explanations of the L-mode confinement, internal transport barrier, and the role of the current profile control
Tokamak turbulence in self-regulated differentially rotating flow and L-H transition dynamics
International Nuclear Information System (INIS)
Terry, P.W.; Carreras, B.A.; Sidikman, K.
1992-01-01
An analytical study of turbulence in the presence of turbulently generated differentially rotating flow is presented as a paradigm for fluctuation dynamics in L- and H-mode plasmas. Using a drift wave model, the role of both flow shear and flow curvature (second radial derivative of the poloidal ExB flow) is detailed in linear and saturated turbulence phases. In the strong turbulence saturated state, finite amplitude-induced modification of the fluctuation structure near low order rational surfaces strongly inhibits flow shear suppression. Suppression by curvature is not diminished, but it occurs through a frequency shift. A description of L-H mode transition dynamics based on the self-consistent linking of turbulence suppression by differentially rotating flow and generation of flow by turbulent momentum transport is presented. In this model, rising edge temperature triggers a transition characterized by spontaneous generation of differentially rotating flow and decreasing turbulence intensity
From dressed particle to dressed mode in plasmas
Energy Technology Data Exchange (ETDEWEB)
Itoh, Sanae-I. [Kyushu Univ., Research Inst. for Applied Mechanics, Kasuga, Fukuoka (Japan); Itoh, Kimitaka [National Inst. for Fusion Science, Toki, Gifu (Japan)
2002-05-01
A theoretical method to analyze the strong turbulence in far-nonequilibrium plasma is discussed. In this approach, a test mode is treated being dressed with interactions with other modes. Nonlinear dispersion relation of the dressed mode and statistical treatment of turbulence is briefly explained. Analogue to the method of dressed particle, which has given Balescu-Lenard collision operator for inter-particle collisions, is mentioned. (author)
Self-consistent dynamo-like activity in turbulent plasmas
International Nuclear Information System (INIS)
Bhattacharjee, A.; Hameiri, E.
1986-05-01
The evolution of turbulent plasmas is investigated within the framework of resistive magnetohydrodynamics. The functional form of the mean electric field is derived for fluctuations generated by tearing and resistive interchange modes. It is shown that a bath of such local and global modes in pinches causes toroidal field-reversal with finite pressure gradients in the plasma
Statistical characterization of turbulence in the boundary plasma of EAST
DEFF Research Database (Denmark)
Yan, Ning; Nielsen, Anders Henry; Xu, G.S.
2013-01-01
In Ohmic heated low confinement mode (L-mode) discharges, the intermittent statistical characteristics of turbulent fluctuations have been investigated in the edge and the scrape-off layer (SOL) plasma on EAST (the experimental advanced superconducting tokamak) by fast reciprocating Langmuir probe...
Turbulence generation by waves
Energy Technology Data Exchange (ETDEWEB)
Kaftori, D.; Nan, X.S.; Banerjee, S. [Univ. of California, Santa Barbara, CA (United States)
1995-12-31
The interaction between two-dimensional mechanically generated waves, and a turbulent stream was investigated experimentally in a horizontal channel, using a 3-D LDA synchronized with a surface position measuring device and a micro-bubble tracers flow visualization with high speed video. Results show that although the wave induced orbital motion reached all the way to the wall, the characteristics of the turbulence wall structures and the turbulence intensity close to the wall were not altered. Nor was the streaky nature of the wall layer. On the other hand, the mean velocity profile became more uniform and the mean friction velocity was increased. Close to the free surface, the turbulence intensity was substantially increased as well. Even in predominantly laminar flows, the introduction of 2-D waves causes three dimensional turbulence. The turbulence enhancement is found to be proportional to the wave strength.
Plasma Turbulence General Topics
Energy Technology Data Exchange (ETDEWEB)
Kadomtsev, B. B. [Nuclear Energy Institute, Academy of Sciences of the USSR, Moscow, USSR (Russian Federation)
1965-06-15
It is known that under experimental conditions plasma often shows chaotic motion. Such motion, when many degrees of freedom are excited to levels considerably above the thermal level, will be called turbulent. The properties of turbulent plasma in many respects differ from the properties of laminar plasma. It can be said that the appearance of various anomalies in plasma behaviour indicates the presence of turbulence in plasma. In order to verify directly the presence of turbulent motion in plasma we must, however, measure the fluctuation of some microscopic parameters in plasma.
Dynamical eigenfunction decomposition of turbulent channel flow
Ball, K. S.; Sirovich, L.; Keefe, L. R.
1991-01-01
The results of an analysis of low-Reynolds-number turbulent channel flow based on the Karhunen-Loeve (K-L) expansion are presented. The turbulent flow field is generated by a direct numerical simulation of the Navier-Stokes equations at a Reynolds number Re(tau) = 80 (based on the wall shear velocity and channel half-width). The K-L procedure is then applied to determine the eigenvalues and eigenfunctions for this flow. The random coefficients of the K-L expansion are subsequently found by projecting the numerical flow field onto these eigenfunctions. The resulting expansion captures 90 percent of the turbulent energy with significantly fewer modes than the original trigonometric expansion. The eigenfunctions, which appear either as rolls or shearing motions, possess viscous boundary layers at the walls and are much richer in harmonics than the original basis functions.
Toward the Theory of Turbulence in Magnetized Plasmas
International Nuclear Information System (INIS)
Boldyrev, Stanislav
2013-01-01
The goal of the project was to develop a theory of turbulence in magnetized plasmas at large scales, that is, scales larger than the characteristic plasma microscales (ion gyroscale, ion inertial scale, etc.). Collisions of counter-propagating Alfven packets govern the turbulent cascade of energy toward small scales. It has been established that such an energy cascade is intrinsically anisotropic, in that it predominantly supplies energy to the modes with mostly field-perpendicular wave numbers. The resulting energy spectrum of MHD turbulence, and the structure of the fluctuations were studied both analytically and numerically. A new parallel numerical code was developed for simulating reduced MHD equations driven by an external force. The numerical setting was proposed, where the spectral properties of the force could be varied in order to simulate either strong or weak turbulent regimes. It has been found both analytically and numerically that weak MHD turbulence spontaneously generates a 'condensate', that is, concentration of magnetic and kinetic energy at small kllel)). A related topic that was addressed in the project is turbulent dynamo action, that is, generation of magnetic field in a turbulent flow. We were specifically concentrated on the generation of large-scale magnetic field compared to the scales of the turbulent velocity field. We investigate magnetic field amplification in a turbulent velocity field with nonzero helicity, in the framework of the kinematic Kazantsev-Kraichnan model
Reducing Turbulent Transport in Toroidal Configurations via Shaping
International Nuclear Information System (INIS)
Mynick, H.E.; Pomphrey, N.; Xanthopoulos, P.
2011-01-01
Recent progress in reducing turbulent transport in stellarators and tokamaks by 3D shaping using a stellarator optimization code in conjunction with a gyrokinetic code is presented. The original applications of the method focussed on ion temperature gradient transport in a quasi-axisymmetric stellarator design. Here, an examination of both other turbulence channels and other starting configurations is initiated. It is found that the designs evolved for transport from ion temperature gradient turbulence also display reduced transport from other transport channels whose modes are also stabilized by improved curvature, such as electron temperature gradient and ballooning modes. The optimizer is also applied to evolving from a tokamak, finding appreciable turbulence reduction for these devices as well. From these studies, improved understanding is obtained of why the deformations found by the optimizer are beneficial, and these deformations are related to earlier theoretical work in both stellarators and tokamaks.
Overview of edge turbulence and zonal flow studies on TEXTOR
International Nuclear Information System (INIS)
Xu, Y.; Kraemer-Flecken, A.; Reiser, D.
2008-01-01
In the TEXTOR tokamak, the edge turbulence properties and turbulence-associated zonal flows have been systematically investigated both experimentally and theoretically. The experimental results include the investigation of self-organized criticality (SOC) behavior, the intermittent blob transport and the geodesic acoustic mode (GAM) zonal flows. During the Dynamic Ergodic Divertor (DED) operation in TEXTOR, the impact of an ergodized plasma boundary on edge turbulence, turbulent transport and the fluctuation propagation has also been studied in detail. The results show substantial influence by the DED on edge turbulence. The theoretical simulations for TEXTOR parameters show characteristic features of the GAM flows and strong reduction of the blob transport by the DED at the plasma periphery. Moreover, the modelling reveals the importance of the Reynolds stress in driving mean (or zonal) flows at the plasma edge in the ohmic discharge phase in TEXTOR. (author)
PDF Modeling of Turbulent Combustion
National Research Council Canada - National Science Library
Pope, Stephen B
2006-01-01
.... The PDF approach to turbulent combustion has the advantages of fully representing the turbulent fluctuations of species and temperature, and of allowing realistic combustion chemistry to be implemented...
International Nuclear Information System (INIS)
Vorotyntsev, M.A.
1991-01-01
Key problems of turbulent mass transfer at a solid wall are reviewed: closure problem for the concentration field, information on wall turbulence, applications of microelectrodes to study the structure of turbulence, correlation properties of current fluctuations. (author). 26 refs
Gyrokinetic statistical absolute equilibrium and turbulence
International Nuclear Information System (INIS)
Zhu Jianzhou; Hammett, Gregory W.
2010-01-01
A paradigm based on the absolute equilibrium of Galerkin-truncated inviscid systems to aid in understanding turbulence [T.-D. Lee, Q. Appl. Math. 10, 69 (1952)] is taken to study gyrokinetic plasma turbulence: a finite set of Fourier modes of the collisionless gyrokinetic equations are kept and the statistical equilibria are calculated; possible implications for plasma turbulence in various situations are discussed. For the case of two spatial and one velocity dimension, in the calculation with discretization also of velocity v with N grid points (where N+1 quantities are conserved, corresponding to an energy invariant and N entropy-related invariants), the negative temperature states, corresponding to the condensation of the generalized energy into the lowest modes, are found. This indicates a generic feature of inverse energy cascade. Comparisons are made with some classical results, such as those of Charney-Hasegawa-Mima in the cold-ion limit. There is a universal shape for statistical equilibrium of gyrokinetics in three spatial and two velocity dimensions with just one conserved quantity. Possible physical relevance to turbulence, such as ITG zonal flows, and to a critical balance hypothesis are also discussed.
Gyrokinetic Statistical Absolute Equilibrium and Turbulence
International Nuclear Information System (INIS)
Zhu, Jian-Zhou; Hammett, Gregory W.
2011-01-01
A paradigm based on the absolute equilibrium of Galerkin-truncated inviscid systems to aid in understanding turbulence (T.-D. Lee, 'On some statistical properties of hydrodynamical and magnetohydrodynamical fields,' Q. Appl. Math. 10, 69 (1952)) is taken to study gyrokinetic plasma turbulence: A finite set of Fourier modes of the collisionless gyrokinetic equations are kept and the statistical equilibria are calculated; possible implications for plasma turbulence in various situations are discussed. For the case of two spatial and one velocity dimension, in the calculation with discretization also of velocity v with N grid points (where N + 1 quantities are conserved, corresponding to an energy invariant and N entropy-related invariants), the negative temperature states, corresponding to the condensation of the generalized energy into the lowest modes, are found. This indicates a generic feature of inverse energy cascade. Comparisons are made with some classical results, such as those of Charney-Hasegawa-Mima in the cold-ion limit. There is a universal shape for statistical equilibrium of gyrokinetics in three spatial and two velocity dimensions with just one conserved quantity. Possible physical relevance to turbulence, such as ITG zonal flows, and to a critical balance hypothesis are also discussed.
Surface roughness effects on turbulent Couette flow
Lee, Young Mo; Lee, Jae Hwa
2017-11-01
Direct numerical simulation of a turbulent Couette flow with two-dimensional (2-D) rod roughness is performed to examine the effects of the surface roughness. The Reynolds number based on the channel centerline laminar velocity (Uco) and channel half height (h) is Re =7200. The 2-D rods are periodically arranged with a streamwise pitch of λ = 8 k on the bottom wall, and the roughness height is k = 0.12 h. It is shown that the wall-normal extent for the logarithmic layer is significantly shortened in the rough-wall turbulent Couette flow, compared to a turbulent Couette flow with smooth wall. Although the Reynolds stresses are increased in a turbulent channel flow with surface roughness in the outer layer due to large-scale ejection motions produced by the 2-D rods, those of the rough-wall Couette flow are decreased. Isosurfaces of the u-structures averaged in time suggest that the decrease of the turbulent activity near the centerline is associated with weakened large-scale counter-rotating roll modes by the surface roughness. This research was supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2017R1D1A1A09000537) and the Ministry of Science, ICT & Future Planning (NRF-2017R1A5A1015311).
Chaos Synchronization in Navier-Stokes Turbulence
Lalescu, Cristian; Meneveau, Charles; Eyink, Gregory
2013-03-01
Chaos synchronization (CS) has been studied for some time now (Pecora & Carroll 1990), for systems with only a few degrees of freedom as well as for systems described by partial differential equations (Boccaletti et al 2002). CS in general is said to be present in coupled dynamical systems when a specific property of each system has the same time evolution for all, even though the evolution itself is chaotic. The Navier-Stokes (NS) equations describe the velocity for a wide range of fluids, and their solutions are usually called turbulent if fluctuation amplitudes decrease as a power of their wavenumber. There have been some studies of CS for continuous systems (Kocarev et al 1997), but CS for NS turbulence seems not to have been investigated so far. We focus on the synchronization of the small scales of a turbulent flow for which the time history of large scales is prescribed. Our DNS results show that high-wavenumbers in turbulence are fully slaved to modes with wavenumbers up to a critical fraction of the Kolmogorov dissipation wavenumber. The motivation for our work is to study deeply sub-Kolmogorov scales in fully developed turbulence (Schumacher 2007), which we found to be recoverable even at very high Reynolds number from simulations with moderate resolutions. This work is supported by the National Science Foundation's CDI-II program, project CMMI-0941530
Turbulence modelling; Modelisation de la turbulence isotherme
Energy Technology Data Exchange (ETDEWEB)
Laurence, D. [Electricite de France (EDF), Direction des Etudes et Recherches, 92 - Clamart (France)
1997-12-31
This paper is an introduction course in modelling turbulent thermohydraulics, aimed at computational fluid dynamics users. No specific knowledge other than the Navier Stokes equations is required beforehand. Chapter I (which those who are not beginners can skip) provides basic ideas on turbulence physics and is taken up in a textbook prepared by the teaching team of the ENPC (Benque, Viollet). Chapter II describes turbulent viscosity type modelling and the 2k-{epsilon} two equations model. It provides details of the channel flow case and the boundary conditions. Chapter III describes the `standard` (R{sub ij}-{epsilon}) Reynolds tensions transport model and introduces more recent models called `feasible`. A second paper deals with heat transfer and the effects of gravity, and returns to the Reynolds stress transport model. (author). 37 refs.
Nagendra Prakash, Vivek
2013-01-01
This thesis deals with the broad topic of particles in turbulence, which has applications in a diverse number of fields. A vast majority of fluid flows found in nature and in the industry are turbulent and contain dispersed elements. In this thesis, I have focused on light particles (air bubbles in
Dynamic paradigm of turbulence
International Nuclear Information System (INIS)
Mukhamedov, Alfred M.
2006-01-01
In this paper a dynamic paradigm of turbulence is proposed. The basic idea consists in the novel definition of chaotic structure given with the help of Pfaff system of PDE associated with the turbulent dynamics. A methodological analysis of the new and the former paradigm is produced
Chaotic Dynamos Generated by a Turbulent Flow of Liquid Sodium
International Nuclear Information System (INIS)
Ravelet, F.; Monchaux, R.; Aumaitre, S.; Chiffaudel, A.; Daviaud, F.; Dubrulle, B.; Berhanu, M.; Fauve, S.; Mordant, N.; Petrelis, F.; Bourgoin, M.; Odier, Ph.; Plihon, N.; Pinton, J.-F.; Volk, R.
2008-01-01
We report the observation of several dynamical regimes of the magnetic field generated by a turbulent flow of liquid sodium (VKS experiment). Stationary dynamos, transitions to relaxation cycles or to intermittent bursts, and random field reversals occur in a fairly small range of parameters. Large scale dynamics of the magnetic field result from the interactions of a few modes. The low dimensional nature of these dynamics is not smeared out by the very strong turbulent fluctuations of the flow
On Electron-Scale Whistler Turbulence in the Solar Wind
Narita, Y.; Nakamura, R.; Baumjohann, W.; Glassmeier, K.-H.; Motschmann, U.; Giles, B.; Magnes, W.; Fischer, D.; Torbert, R. B.; Russell, C. T.
2016-01-01
For the first time, the dispersion relation for turbulence magnetic field fluctuations in the solar wind is determined directly on small scales of the order of the electron inertial length, using four-point magnetometer observations from the Magnetospheric Multiscale mission. The data are analyzed using the high-resolution adaptive wave telescope technique. Small-scale solar wind turbulence is primarily composed of highly obliquely propagating waves, with dispersion consistent with that of the whistler mode.
Duvvuri, Subrahmanyam; McKeon, Beverley
2017-03-13
Phase relations between specific scales in a turbulent boundary layer are studied here by highlighting the associated nonlinear scale interactions in the flow. This is achieved through an experimental technique that allows for targeted forcing of the flow through the use of a dynamic wall perturbation. Two distinct large-scale modes with well-defined spatial and temporal wavenumbers were simultaneously forced in the boundary layer, and the resulting nonlinear response from their direct interactions was isolated from the turbulence signal for the study. This approach advances the traditional studies of large- and small-scale interactions in wall turbulence by focusing on the direct interactions between scales with triadic wavenumber consistency. The results are discussed in the context of modelling high Reynolds number wall turbulence.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'. © 2017 The Author(s).
Behaviour of turbulence models near a turbulent/non-turbulent interface revisited
International Nuclear Information System (INIS)
Ferrey, P.; Aupoix, B.
2006-01-01
The behaviour of turbulence models near a turbulent/non-turbulent interface is investigated. The analysis holds as well for two-equation as for Reynolds stress turbulence models using Daly and Harlow diffusion model. The behaviour near the interface is shown not to be a power law, as usually considered, but a more complex parametric solution. Why previous works seemed to numerically confirm the power law solution is explained. Constraints for turbulence modelling, i.e., for ensuring that models have a good behaviour near a turbulent/non-turbulent interface so that the solution is not sensitive to small turbulence levels imposed in the irrotational flow, are drawn
Turbulence studies in tokamak boundary plasmas with realistic divertor geometry
International Nuclear Information System (INIS)
Xu, X.Q.; Cohen, R.H.; Porter, G.D.; Rognlien, T.; Ryutov, D.D.; Myra, J.R.; D'Ippolito, D.A.; Moyer, R.; Groebner, R.J.
2001-01-01
Results are presented from the 3D nonlocal electromagnetic turbulence code BOUT and the linearized shooting code BAL for studies of turbulence in tokamak boundary plasmas and its relationship to the L-H transition, in a realistic divertor plasma geometry. The key results include: (1) the identification of the dominant resistive X-point mode in divertor geometry and (2) turbulence suppression in the L-H transition by shear in the ExB drift speed, ion diamagnetism and nite polarization. Based on the simulation results, a parameterization of the transport is given that includes the dependence on the relevant physical parameters. (author)
Turbulence studies in tokamak boundary plasmas with realistic divertor geometry
International Nuclear Information System (INIS)
Xu, X.Q.; Cohen, R.H.; Por, G.D. ter; Rognlien, T.D.; Ryutov, D.D.; Myra, J.R.; D'Ippolito, D.A.; Moyer, R.; Groebner, R.J.
1999-01-01
Results are presented from the 3D nonlocal electromagnetic turbulence code BOUT and the linearized shooting code BAL for studies of turbulence in tokamak boundary plasmas and its relationship to the L-H transition, in a realistic divertor plasma geometry. The key results include: (1) the identification of the dominant resistive X-point mode in divertor geometry and (2) turbulence suppression in the L-H transition by shear in the E x B drift speed, ion diamagnetism and finite polarization. Based on the simulation results, a parameterization of the transport is given that includes the dependence on the relevant physical parameters. (author)
Nonlinear Flow Generation By Electrostatic Turbulence In Tokamaks
International Nuclear Information System (INIS)
Wang, W.X.; Diamond, P.H.; Hahm, T.S.; Ethier, S.; Rewoldt, G.; Tang, W.M.
2010-01-01
Global gyrokinetic simulations have revealed an important nonlinear flow generation process due to the residual stress produced by electrostatic turbulence of ion temperature gradient (ITG) modes and trapped electron modes (TEM). In collisionless TEM (CTEM) turbulence, nonlinear residual stress generation by both the fluctuation intensity and the intensity gradient in the presence of broken symmetry in the parallel wave number spectrum is identified for the first time. Concerning the origin of the symmetry breaking, turbulence self-generated low frequency zonal flow shear has been identified to be a key, universal mechanism in various turbulence regimes. Simulations reported here also indicate the existence of other mechanisms beyond E - B shear. The ITG turbulence driven 'intrinsic' torque associated with residual stress is shown to increase close to linearly with the ion temperature gradient, in qualitative agreement with experimental observations in various devices. In CTEM dominated regimes, a net toroidal rotation is driven in the cocurrent direction by 'intrinsic' torque, consistent with the experimental trend of observed intrinsic rotation. The finding of a 'flow pinch' in CTEM turbulence may offer an interesting new insight into the underlying dynamics governing the radial penetration of modulated flows in perturbation experiments. Finally, simulations also reveal highly distinct phase space structures between CTEM and ITG turbulence driven momentum, energy and particle fluxes, elucidating the roles of resonant and non-resonant particles.
DEFF Research Database (Denmark)
Wang, H.Q.; Xu, G.S.; Guo, H.Y.
2012-01-01
The first high confinement H-mode plasma has been obtained in the Experimental Advanced Superconducting Tokamak (EAST) with about 1 MW lower hybrid current drive after wall conditioning by lithium evaporation and real-time injection of Li powder. Following the L–H transition, a small-amplitude, low...
Pressure gradient turbulent transport and collisionless reconnection
International Nuclear Information System (INIS)
Connor, J.W.
1993-01-01
The scale invariance technique is employed to discuss pressure gradient driven turbulent transport when an Ohm's law with electron inertia, rather than resistivity, is relevant. An expression for thermal diffusivity which has many features appropriate to L-mode transport in tokamaks, is seen to have greater generality than indicated by their particular calculation. The results of applying the technique to a more appropriate collisionless Ohm's law are discussed. (Author)
Broken ergodicity in two-dimensional homogeneous magnetohydrodynamic turbulence
International Nuclear Information System (INIS)
Shebalin, John V.
2010-01-01
Two-dimensional (2D) homogeneous magnetohydrodynamic (MHD) turbulence has many of the same qualitative features as three-dimensional (3D) homogeneous MHD turbulence. These features include several ideal (i.e., nondissipative) invariants along with the phenomenon of broken ergodicity (defined as nonergodic behavior over a very long time). Broken ergodicity appears when certain modes act like random variables with mean values that are large compared to their standard deviations, indicating a coherent structure or dynamo. Recently, the origin of broken ergodicity in 3D MHD turbulence that is manifest in the lowest wavenumbers was found. Here, we study the origin of broken ergodicity in 2D MHD turbulence. It will be seen that broken ergodicity in ideal 2D MHD turbulence can be manifest in the lowest wavenumbers of a finite numerical model for certain initial conditions or in the highest wavenumbers for another set of initial conditions. The origins of broken ergodicity in an ideal 2D homogeneous MHD turbulence are found through an eigenanalysis of the covariance matrices of the probability density function and by an examination of the associated entropy functional. When the values of ideal invariants are kept fixed and grid size increases, it will be shown that the energy in a few large modes remains constant, while the energy in any other mode is inversely proportional to grid size. Also, as grid size increases, we find that broken ergodicity becomes manifest at more and more wavenumbers.
Gyrokinetic simulation of microtearing turbulence
International Nuclear Information System (INIS)
Doerk, Hauke
2013-01-01
radially global implementation of collisions is successfully benchmarked against the PIC code Orb5. Validation of the collision operator is of relevance for microturbulence simulations as well, since collisional effects, for example, play an important role in the instability mechanism of microtearing modes. Considering plasma parameters that are realistic for the fusion experiment ASDEX Upgrade, a standard tokamak device, microtearing modes are found in Gene simulations. These parameters are also relevant for certain ITER scenarios. The most unstable toroidal wavelength lies somewhat above the ion gyroradius, but much finer radial scales are developed. Although this inherent multiscale feature causes nonlinear simulations to be extremely challenging, such gyrokinetic simulations of microtearing turbulence succeed for the first time in the coarse of this work. An outstanding feature of these simulations is that the radial transport of (electron) heat is well described by a simple diffusivity model, as long as the magnetic field fluctuations exceed a certain threshold. The employed Rechester-Rosenbluth type of model crucially relies on magnetic field stochasticity. To show that this condition is fulfilled, the value for the magnetic field diffusivity is computed from the simulation data. Since the resulting transport level is found to be experimentally relevant, our simulations establish microtearing turbulence as an additional candidate to explain enhanced electron thermal transport in standard tokamaks.
Self-regulation of turbulence bursts and transport barriers
International Nuclear Information System (INIS)
Floriani, E; Ciraolo, G; Ghendrih, Ph; Sarazin, Y; Lima, R
2013-01-01
The interplay between turbulent bursts and transport barriers is analyzed with a simplified model of interchange turbulence in magnetically confined plasmas. The turbulent bursts spread into the transport barriers and, depending on the competing magnitude of the burst and stopping capability of the barrier, can burn through. Simulations of two models of transport barriers are presented: a hard barrier where interchange turbulence modes are stable in a prescribed region and a soft barrier with external plasma biasing. The response of the transport barriers to the non-linear perturbations of the turbulent bursts, addressed in a predator–prey approach, indicates that the barriers monitor an amplification factor of the turbulent bursts, with amplification smaller than one for most bursts and, in some cases, amplification factors that can significantly exceed unity. The weak barriers in corrugated profiles and magnetic structures, as well as the standard barriers, are characterized by these transmission properties, which then regulate the turbulent burst transport properties. The interplays of barriers and turbulent bursts are modeled as competing stochastic processes. For different classes of the probability density function (PDF) of these processes, one can predict the heavy tail properties of the bursts downstream from the barrier, either exponential for a leaky barrier, or with power laws for a tight barrier. The intrinsic probing of the transport barriers by the turbulent bursts thus gives access to the properties of the barriers. The main stochastic variables are the barrier width and the spreading distance of the turbulent bursts within the barrier, together with their level of correlation. One finds that in the case of a barrier with volumetric losses, such as radiation or particle losses as addressed in our present simulations, the stochastic model predicts a leaky behavior with an exponential PDF of escaping turbulent bursts in agreement with the simulation
Feedback control of edge turbulence in a tokamak
International Nuclear Information System (INIS)
Kan, Zhai; Yi-zhi, Wen; Chang-xuan, Yu; Wan-dong, Liu; Chao, Wang; Ge, Zhuang; Kan, Zhai; Zhi-Zhan, Yu
1997-01-01
An experiment on feedback control of edge turbulence has been undertaken on the KT-5C tokamak. The results indicate that the edge turbulence could be suppressed or enhanced depending on the phase shift of the feedback network. In a typical case of 90 degree phase shift feedback, the turbulence amplitudes of both T e and n e were reduced by about 25% when the gain of the feedback network was 15. Correspondingly the radial particle flux decreased to about 75% level of the background. Through bispectral analysis it is found that there exists a substantial nonlinear coupling between various modes comprised in edge turbulence, especially in the frequency range from about 10 kHz to 100 kHz, which contains the large part of the edge turbulence energy in KT-5C tokamak. In particular, by actively controlling the turbulence amplitude using feedback, a direct experimental evidence of the link between the nonlinear wave-wave coupling over the whole spectrum in turbulence, the saturated turbulence amplitude, and the radial particle flux was provided. copyright 1997 The American Physical Society
Electron thermal transport in tokamak: ETG or TEM turbulences?
International Nuclear Information System (INIS)
Lin, Z.; Chen, L.; Nishimura, Y.; Qu, H.; Hahm, T.S.; Lewandowski, J.; Rewoldt, G.; Wang, W.X.; Diamond, P.H.; Holland, C.; Zonca, F.; Li, Y.
2005-01-01
This paper reports progress on numerical and theoretical studies of electron transport in tokamak including: (1) electron temperature gradient turbulence; (2) trapped electron mode turbulence; and (3) a new finite element solver for global electromagnetic simulation. In particular, global gyrokinetic particle simulation and nonlinear gyrokinetic theory find that electron temperature gradient (ETG) instability saturates via nonlinear toroidal couplings, which transfer energy successively from unstable modes to damped modes preferably with longer poloidal wavelengths. The electrostatic ETG turbulence is dominated by nonlinearly generated radial streamers. The length of streamers scales with the device size and is much longer than the distance between mode rational surfaces or electron radial excursions. Both fluctuation intensity and transport level are independent of the streamer size. These simulations with realistic plasma parameters find that the electron heat conductivity is much smaller than the experimental value and in contrast with recent findings of flux-tube simulations that ETG turbulence is responsible for the anomalous electron thermal transport in fusion plasmas. The nonlinear toroidal couplings represent a new paradigm for the spectral cascade in plasma turbulence. (author)
Turbulent current drive mechanisms
McDevitt, Christopher J.; Tang, Xian-Zhu; Guo, Zehua
2017-08-01
Mechanisms through which plasma microturbulence can drive a mean electron plasma current are derived. The efficiency through which these turbulent contributions can drive deviations from neoclassical predictions of the electron current profile is computed by employing a linearized Coulomb collision operator. It is found that a non-diffusive contribution to the electron momentum flux as well as an anomalous electron-ion momentum exchange term provide the most efficient means through which turbulence can modify the mean electron current for the cases considered. Such turbulent contributions appear as an effective EMF within Ohm's law and hence provide an ideal means for driving deviations from neoclassical predictions.
Belotserkovskii, OM; Chechetkin, VM
2005-01-01
The authors present the results of numerical experiments carried out to examine the problem of development of turbulence and convection. On the basis of the results, they propose a physical model of the development of turbulence. Numerical algorithms and difference schema for carrying out numerical experiments in hydrodynamics, are proposed. Original algorithms, suitable for calculation of the development of the processes of turbulence and convection in different conditions, even on astrophysical objects, are presented. The results of numerical modelling of several important phenomena having both fundamental and applied importance are described.
Energy Technology Data Exchange (ETDEWEB)
Hoejstrup, J [NEG Micon Project Development A/S, Randers (Denmark); Hansen, K S [Denmarks Technical Univ., Dept. of Energy Engineering, Lyngby (Denmark); Pedersen, B J [VESTAS Wind Systems A/S, Lem (Denmark); Nielsen, M [Risoe National Lab., Wind Energy and Atmospheric Physics, Roskilde (Denmark)
1999-03-01
The pdf`s of atmospheric turbulence have somewhat wider tails than a Gaussian, especially regarding accelerations, whereas velocities are close to Gaussian. This behaviour is being investigated using data from a large WEB-database in order to quantify the amount of non-Gaussianity. Models for non-Gaussian turbulence have been developed, by which artificial turbulence can be generated with specified distributions, spectra and cross-correlations. The artificial time series will then be used in load models and the resulting loads in the Gaussian and the non-Gaussian cases will be compared. (au)
Parallel plasma fluid turbulence calculations
International Nuclear Information System (INIS)
Leboeuf, J.N.; Carreras, B.A.; Charlton, L.A.; Drake, J.B.; Lynch, V.E.; Newman, D.E.; Sidikman, K.L.; Spong, D.A.
1994-01-01
The study of plasma turbulence and transport is a complex problem of critical importance for fusion-relevant plasmas. To this day, the fluid treatment of plasma dynamics is the best approach to realistic physics at the high resolution required for certain experimentally relevant calculations. Core and edge turbulence in a magnetic fusion device have been modeled using state-of-the-art, nonlinear, three-dimensional, initial-value fluid and gyrofluid codes. Parallel implementation of these models on diverse platforms--vector parallel (National Energy Research Supercomputer Center's CRAY Y-MP C90), massively parallel (Intel Paragon XP/S 35), and serial parallel (clusters of high-performance workstations using the Parallel Virtual Machine protocol)--offers a variety of paths to high resolution and significant improvements in real-time efficiency, each with its own advantages. The largest and most efficient calculations have been performed at the 200 Mword memory limit on the C90 in dedicated mode, where an overlap of 12 to 13 out of a maximum of 16 processors has been achieved with a gyrofluid model of core fluctuations. The richness of the physics captured by these calculations is commensurate with the increased resolution and efficiency and is limited only by the ingenuity brought to the analysis of the massive amounts of data generated
Modeling of turbulent chemical reaction
Chen, J.-Y.
1995-01-01
Viewgraphs are presented on modeling turbulent reacting flows, regimes of turbulent combustion, regimes of premixed and regimes of non-premixed turbulent combustion, chemical closure models, flamelet model, conditional moment closure (CMC), NO(x) emissions from turbulent H2 jet flames, probability density function (PDF), departures from chemical equilibrium, mixing models for PDF methods, comparison of predicted and measured H2O mass fractions in turbulent nonpremixed jet flames, experimental evidence of preferential diffusion in turbulent jet flames, and computation of turbulent reacting flows.
Aviation turbulence processes, detection, prediction
Lane, Todd
2016-01-01
Anyone who has experienced turbulence in flight knows that it is usually not pleasant, and may wonder why this is so difficult to avoid. The book includes papers by various aviation turbulence researchers and provides background into the nature and causes of atmospheric turbulence that affect aircraft motion, and contains surveys of the latest techniques for remote and in situ sensing and forecasting of the turbulence phenomenon. It provides updates on the state-of-the-art research since earlier studies in the 1960s on clear-air turbulence, explains recent new understanding into turbulence generation by thunderstorms, and summarizes future challenges in turbulence prediction and avoidance.
Turbulent regimes in the tokamak scrape-off layer
International Nuclear Information System (INIS)
Mosetto, A.
2014-01-01
The tokamak scrape-off layer (SOL) is the plasma region characterized by open field lines that start and end on the vessel walls. The plasma dynamics in the SOL plays a crucial role in determining the overall performance of a tokamak, since it controls the plasma-wall interactions, being responsible of exhausting the tokamak power, it regulates the overall plasma confinement, and it governs the plasma refueling and the removal of fusion ashes. Scrape-off layer physics is intrinsically non-linear and characterized by phenomena that occur on a wide range of spatio-temporal scales. Free energy sources drive a number of unstable modes that develop into turbulence and lead to transport of particles and heat across the magnetic field lines. Depending on the driving instability, different SOL turbulent regimes can be identified. As the SOL turbulent regimes determine the plasma confinement properties and the SOL width (and, consequently, the power flux on the vessel wall, for example), it is of crucial importance to understand which turbulent regimes are active in the SOL, under which conditions they develop, and which are the main properties of the associated turbulent transport. In the present thesis we define the SOL turbulent regimes, and we provide a framework to identify them, given the operational SOL parameters. Our study is based on the drift-reduced Braginskii equations and it is focused on a limited tokamak SOL configuration. We first describe the main SOL linear instabilities, such as the inertial and resistive branches of the drift waves, the resistive, inertial and ideal branches of the ballooning modes, and the ion temperature gradient mode. Then, we find the SOL turbulent regimes depending on the instability driving turbulent transport, assuming that turbulence saturates when the radial gradient associated to the pressure fluctuations is comparable to the equilibrium one. Our methodology for the turbulent regime identification is supported by the analysis
Turbulent buoyant jets and plumes
Rodi, Wolfgang
The Science & Applications of Heat and Mass Transfer: Reports, Reviews, & Computer Programs, Volume 6: Turbulent Buoyant Jets and Plumes focuses on the formation, properties, characteristics, and reactions of turbulent jets and plumes. The selection first offers information on the mechanics of turbulent buoyant jets and plumes and turbulent buoyant jets in shallow fluid layers. Discussions focus on submerged buoyant jets into shallow fluid, horizontal surface or interface jets into shallow layers, fundamental considerations, and turbulent buoyant jets (forced plumes). The manuscript then exami
Saturation mechanism of decaying ion temperature gradient driven turbulence with kinetic electrons
International Nuclear Information System (INIS)
Idomura, Yasuhiro
2016-01-01
We present full-f gyrokinetic simulations of the ion temperature gradient driven (ITG) turbulence including kinetic electrons. By comparing decaying ITG turbulence simulations with adiabatic and kinetic electron models, an impact of kinetic electrons on the ITG turbulence is investigated. It is found that significant electron transport occurs even in the ITG turbulence, and both ion and electron temperature profiles are relaxed. In steady states, both cases show upshifts of nonlinear critical ion temperature gradients from linear ones, while their saturation mechanisms are qualitatively different. In the adiabatic electron case, the ITG mode is stabilized by turbulence driven zonal flows. On the other hand, in the kinetic electron case, passing electrons transport shows fine resonant structures at mode rational surfaces, which generate corrugated density profiles. Such corrugated density profiles lead to fine radial electric fields following the neoclassical force balance relation. The resulting E × B shearing rate greatly exceeds the linear growth rate of the ITG mode. (author)
Warm-ion drift Alfven turbulence and the L-H transition
International Nuclear Information System (INIS)
Scott, B.
1998-01-01
Computations of fluid drift turbulence treating ions and electrons on equal footing, including both temperatures, are conducted in a model toroidal geometry. The resulting 'ion mixing mode' turbulence bears features of both electron drift-Alfven and ion temperature gradient turbulence, and nonlinear sensitivity to the relative strengths of the density and temperature gradients provides a possible route to the bifurcation needed for the L-H transition. (author)
Containerless Ripple Turbulence
Putterman, Seth; Wright, William; Duval, Walter; Panzarella, Charles
2002-11-01
One of the longest standing unsolved problems in physics relates to the behavior of fluids that are driven far from equilibrium such as occurs when they become turbulent due to fast flow through a grid or tidal motions. In turbulent flows the distribution of vortex energy as a function of the inverse length scale [or wavenumber 'k'] of motion is proportional to 1/k5/3 which is the celebrated law of Kolmogorov. Although this law gives a good description of the average motion, fluctuations around the average are huge. This stands in contrast with thermally activated motion where large fluctuations around thermal equilibrium are highly unfavorable. The problem of turbulence is the problem of understanding why large fluctuations are so prevalent which is also called the problem of 'intermittency'. Turbulence is a remarkable problem in that its solution sits simultaneously at the forefront of physics, mathematics, engineering and computer science. A recent conference [March 2002] on 'Statistical Hydrodynamics' organized by the Los Alamos Laboratory Center for Nonlinear Studies brought together researchers in all of these fields. Although turbulence is generally thought to be described by the Navier-Stokes Equations of fluid mechanics the solution as well as its existence has eluded researchers for over 100 years. In fact proof of the existence of such a solution qualifies for a 1 M millennium prize. As part of our NASA funded research we have proposed building a bridge between vortex turbulence and wave turbulence. The latter occurs when high amplitude waves of various wavelengths are allowed to mutually interact in a fluid. In particular we have proposed measuring the interaction of ripples [capillary waves] that run around on the surface of a fluid sphere suspended in a microgravity environment. The problem of ripple turbulence poses similar mathematical challenges to the problem of vortex turbulence. The waves can have a high amplitude and a strong nonlinear
Inflow Turbulence Generation Methods
Wu, Xiaohua
2017-01-01
Research activities on inflow turbulence generation methods have been vigorous over the past quarter century, accompanying advances in eddy-resolving computations of spatially developing turbulent flows with direct numerical simulation, large-eddy simulation (LES), and hybrid Reynolds-averaged Navier-Stokes-LES. The weak recycling method, rooted in scaling arguments on the canonical incompressible boundary layer, has been applied to supersonic boundary layer, rough surface boundary layer, and microscale urban canopy LES coupled with mesoscale numerical weather forecasting. Synthetic methods, originating from analytical approximation to homogeneous isotropic turbulence, have branched out into several robust methods, including the synthetic random Fourier method, synthetic digital filtering method, synthetic coherent eddy method, and synthetic volume forcing method. This article reviews major progress in inflow turbulence generation methods with an emphasis on fundamental ideas, key milestones, representative applications, and critical issues. Directions for future research in the field are also highlighted.
Containerless Ripple Turbulence
Putterman, Seth; Wright, William; Duval, Walter; Panzarella, Charles
2002-01-01
One of the longest standing unsolved problems in physics relates to the behavior of fluids that are driven far from equilibrium such as occurs when they become turbulent due to fast flow through a grid or tidal motions. In turbulent flows the distribution of vortex energy as a function of the inverse length scale [or wavenumber 'k'] of motion is proportional to 1/k(sup 5/3) which is the celebrated law of Kolmogorov. Although this law gives a good description of the average motion, fluctuations around the average are huge. This stands in contrast with thermally activated motion where large fluctuations around thermal equilibrium are highly unfavorable. The problem of turbulence is the problem of understanding why large fluctuations are so prevalent which is also called the problem of 'intermittency'. Turbulence is a remarkable problem in that its solution sits simultaneously at the forefront of physics, mathematics, engineering and computer science. A recent conference [March 2002] on 'Statistical Hydrodynamics' organized by the Los Alamos Laboratory Center for Nonlinear Studies brought together researchers in all of these fields. Although turbulence is generally thought to be described by the Navier-Stokes Equations of fluid mechanics the solution as well as its existence has eluded researchers for over 100 years. In fact proof of the existence of such a solution qualifies for a 1 M$ millennium prize. As part of our NASA funded research we have proposed building a bridge between vortex turbulence and wave turbulence. The latter occurs when high amplitude waves of various wavelengths are allowed to mutually interact in a fluid. In particular we have proposed measuring the interaction of ripples [capillary waves] that run around on the surface of a fluid sphere suspended in a microgravity environment. The problem of ripple turbulence poses similar mathematical challenges to the problem of vortex turbulence. The waves can have a high amplitude and a strong nonlinear
Turbulence Generation in Combustion.
1987-07-22
flame length . This work is summarized in this section. I1.1 Model for Turbulent Burning Velocity For a range of turbulence conditions including...Variable density effects have been added in an approximation, and an expression for the length of jet flames has been developed. The flame length expression...of jet mixing and jet flame length data using fractals, College of Engineering, Energy Report E-86-02, Comell University, Ithaca, NY, 1986. Results
Stochastic tools in turbulence
Lumey, John L
2012-01-01
Stochastic Tools in Turbulence discusses the available mathematical tools to describe stochastic vector fields to solve problems related to these fields. The book deals with the needs of turbulence in relation to stochastic vector fields, particularly, on three-dimensional aspects, linear problems, and stochastic model building. The text describes probability distributions and densities, including Lebesgue integration, conditional probabilities, conditional expectations, statistical independence, lack of correlation. The book also explains the significance of the moments, the properties of the
Magnetohydrodynamic turbulence revisited
International Nuclear Information System (INIS)
Goldreich, P.; Sridhar, S.
1997-01-01
In 1965, Kraichnan proposed that MHD turbulence occurs as a result of collisions between oppositely directed Alfvacute en wave packets. Recent work has generated some controversy over the nature of nonlinear couplings between colliding Alfvacute en waves. We find that the resolution to much of the confusion lies in the existence of a new type of turbulence, intermediate turbulence, in which the cascade of energy in the inertial range exhibits properties intermediate between those of weak and strong turbulent cascades. Some properties of intermediate MHD turbulence are the following: (1) in common with weak turbulent cascades, wave packets belonging to the inertial range are long-lived; (2) however, components of the strain tensor are so large that, similar to the situation in strong turbulence, perturbation theory is not applicable; (3) the breakdown of perturbation theory results from the divergence of neighboring field lines due to wave packets whose perturbations in velocity and magnetic fields are localized, but whose perturbations in displacement are not; (4) three-wave interactions dominate individual collisions between wave packets, but interactions of all orders n≥3 make comparable contributions to the intermediate turbulent energy cascade; (5) successive collisions are correlated since wave packets are distorted as they follow diverging field lines; (6) in common with the weak MHD cascade, there is no parallel cascade of energy, and the cascade to small perpendicular scales strengthens as it reaches higher wavenumbers; (7) for an appropriate weak excitation, there is a natural progression from a weak, through an intermediate, to a strong cascade. copyright 1997 The American Astronomical Society
MULTIFLUID MAGNETOHYDRODYNAMIC TURBULENT DECAY
International Nuclear Information System (INIS)
Downes, T. P.; O'Sullivan, S.
2011-01-01
It is generally believed that turbulence has a significant impact on the dynamics and evolution of molecular clouds and the star formation that occurs within them. Non-ideal magnetohydrodynamic (MHD) effects are known to influence the nature of this turbulence. We present the results of a suite of 512 3 resolution simulations of the decay of initially super-Alfvenic and supersonic fully multifluid MHD turbulence. We find that ambipolar diffusion increases the rate of decay of the turbulence while the Hall effect has virtually no impact. The decay of the kinetic energy can be fitted as a power law in time and the exponent is found to be -1.34 for fully multifluid MHD turbulence. The power spectra of density, velocity, and magnetic field are all steepened significantly by the inclusion of non-ideal terms. The dominant reason for this steepening is ambipolar diffusion with the Hall effect again playing a minimal role except at short length scales where it creates extra structure in the magnetic field. Interestingly we find that, at least at these resolutions, the majority of the physics of multifluid turbulence can be captured by simply introducing fixed (in time and space) resistive terms into the induction equation without the need for a full multifluid MHD treatment. The velocity dispersion is also examined and, in common with previously published results, it is found not to be power law in nature.
Understanding the sub-critical transition to turbulence in wall flows
Indian Academy of Sciences (India)
In contrast with free shear flows presenting velocity profiles with injection points which cascade to turbulence in a relatively mild way, wall bounded flows are deprived of (inertial) instability modes at low Reynolds numbers and become turbulent in a much wilder way, most often marked by the coexistence of laminar and ...
Self-consistency constraints on turbulent magnetic transport and relaxation in collisionless plasma
International Nuclear Information System (INIS)
Terry, P.W.; Diamond, P.H.; Hahm, T.S.
1985-10-01
Novel constraints on collisionless relaxation and transport in drift-Alfven turbulence are reported. These constraints arise due to the consideration of mode coupling and incoherent fluctuations and the proper application of self-consistency conditions. The result that electrostatic fluctuations alone regulate transport in drift-Alfven turbulence follows directly. Quasilinear transport predictions are discussed in light of these constraints
Simulation Of Microtearing Turbulence In NSTX
International Nuclear Information System (INIS)
Guttenfelder, W.; Candy, J.; Kaye, S.M.; Nevins, W.M.; Wanag, E.; Zhang, J.; Bell, R.E.; Crocker, N.A.; Hammett, G.W.; LeBlanc, B.P.; Mikkelsen, D.R.; Ren, Y.; Yuh, H.
2012-01-01
Thermal energy confinement times in NSTX dimensionless parameter scans increase with decreasing collisionality. While ion thermal transport is neoclassical, the source of anomalous electron thermal transport in these discharges remains unclear, leading to considerable uncertainty when extrapolating to future ST devices at much lower collisionality. Linear gyrokinetic simulations find microtearing modes to be unstable in high collisionality discharges. First non-linear gyrokinetic simulations of microtearing turbulence in NSTX show they can yield experimental levels of transport. Magnetic flutter is responsible for almost all the transport (∼98%), perturbed field line trajectories are globally stochastic, and a test particle stochastic transport model agrees to within 25% of the simulated transport. Most significantly, microtearing transport is predicted to increase with electron collisionality, consistent with the observed NSTX confinement scaling. While this suggests microtearing modes may be the source of electron thermal transport, the predictions are also very sensitive to electron temperature gradient, indicating the scaling of the instability threshold is important. In addition, microtearing turbulence is susceptible to suppression via sheared E-B flows as experimental values of E-B shear (comparable to the linear growth rates) dramatically reduce the transport below experimental values. Refinements in numerical resolution and physics model assumptions are expected to minimize the apparent discrepancy. In cases where the predicted transport is strong, calculations suggest that a proposed polarimetry diagnostic may be sensitive to the magnetic perturbations associated with the unique structure of microtearing turbulence.
Interaction of discrete and continuous boundary layer modes to cause transition
International Nuclear Information System (INIS)
Durbin, Paul A.; Zaki, Tamer A.; Liu Yang
2009-01-01
The interaction of discrete and continuous Orr-Sommerfeld modes in a boundary layer is studied by computer simulation. The discrete mode is an unstable Tollmien-Schlichting wave. The continuous modes generate jet-like disturbances inside the boundary layer. Either mode alone does not cause transition to turbulence; however, the interaction between them does. The continuous mode jets distort the discrete modes, producing Λ shaped vortices. Breakdown to turbulence is subsequent. The lateral spacing of the Λ's is sometimes the same as the wavelength of the continuous mode, sometimes it differs, depending on the ratio of wavelength to boundary layer thickness.
Transition in multiple-scale-lengths turbulence in plasmas
Energy Technology Data Exchange (ETDEWEB)
Itoh, S.-I.; Yagi, M.; Kawasaki, M.; Kitazawa, A. [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics; Itoh, K. [National Inst. for Fusion Science, Toki, Gifu (Japan)
2002-02-01
The statistical theory of strong turbulence in inhomogeneous plasmas is developed for the cases where fluctuations with different scale-lengths coexist. Statistical nonlinear interactions between semi-micro and micro modes are first kept in the analysis as the drag, noise and drive. The nonlinear dynamics determines both the fluctuation levels and the cross field turbulent transport for the fixed global parameters. A quenching or suppressing effect is induced by their nonlinear interplay, even if both modes are unstable when analyzed independently. Influence of the inhomogeneous global radial electric field is discussed. A new insight is given for the physics of internal transport barrier. The thermal fluctuation of the scale length of {lambda}{sub D} is assumed to be statistically independent. The hierarchical structure is constructed according to the scale lengths. Transitions in turbulence are found and phase diagrams with cusp type catastrophe are obtained. Dynamics is followed. Statistical properties of the subcritical excitation are discussed. The probability density function (PDF) and transition probability are obtained. Power-laws are obtained in the PDF as well as in the transition probability. Generalization for the case where turbulence is composed of three-classes of modes is also developed. A new catastrophe of turbulent sates is obtained. (author)
Transition in multiple-scale-lengths turbulence in plasmas
International Nuclear Information System (INIS)
Itoh, S.-I.; Yagi, M.; Kawasaki, M.; Kitazawa, A.
2002-02-01
The statistical theory of strong turbulence in inhomogeneous plasmas is developed for the cases where fluctuations with different scale-lengths coexist. Statistical nonlinear interactions between semi-micro and micro modes are first kept in the analysis as the drag, noise and drive. The nonlinear dynamics determines both the fluctuation levels and the cross field turbulent transport for the fixed global parameters. A quenching or suppressing effect is induced by their nonlinear interplay, even if both modes are unstable when analyzed independently. Influence of the inhomogeneous global radial electric field is discussed. A new insight is given for the physics of internal transport barrier. The thermal fluctuation of the scale length of λ D is assumed to be statistically independent. The hierarchical structure is constructed according to the scale lengths. Transitions in turbulence are found and phase diagrams with cusp type catastrophe are obtained. Dynamics is followed. Statistical properties of the subcritical excitation are discussed. The probability density function (PDF) and transition probability are obtained. Power-laws are obtained in the PDF as well as in the transition probability. Generalization for the case where turbulence is composed of three-classes of modes is also developed. A new catastrophe of turbulent sates is obtained. (author)
Compressibility and rotation effects on transport suppression in magnetohydrodynamic turbulence
International Nuclear Information System (INIS)
Yoshizawa, A.
1996-01-01
Compressibility and rotation effects on turbulent transports in magnetohydrodynamic (MHD) flows under arbitrary mean field are investigated using a Markovianized two-scale statistical approach. Some new aspects of MHD turbulence are pointed out in close relation to plasma compressibility. Special attention is paid to the turbulent electromotive force, which plays a central role in the generation of magnetic and velocity fluctuations. In addition to plasma rotation, the interaction between compressibility and magnetic fields is shown to bring a few factors suppressing MHD fluctuations and, eventually, density and temperature transports, even in the presence of steep mean density and temperature gradients. This finding is discussed in the context of the turbulence-suppression mechanism in the tokamak close-quote s high-confinement modes. copyright 1996 American Institute of Physics
Weak turbulence theory for beam-plasma interaction
Yoon, Peter H.
2018-01-01
The kinetic theory of weak plasma turbulence, of which Ronald C. Davidson was an important early pioneer [R. C. Davidson, Methods in Nonlinear Plasma Theory, (Academic Press, New York, 1972)], is a venerable and valid theory that may be applicable to a large number of problems in both laboratory and space plasmas. This paper applies the weak turbulence theory to the problem of gentle beam-plasma interaction and Langmuir turbulence. It is shown that the beam-plasma interaction undergoes various stages of physical processes starting from linear instability, to quasilinear saturation, to mode coupling that takes place after the quasilinear stage, followed by a state of quasi-static "turbulent equilibrium." The long term quasi-equilibrium stage is eventually perturbed by binary collisional effects in order to bring the plasma to a thermodynamic equilibrium with increased entropy.
Linear and nonlinear electrostatic modes in a nonuniform magnetized electron plasma
International Nuclear Information System (INIS)
Vranjes, J.; Shukla, P.K.; Kono, M.; Poedts, S.
2001-01-01
Linear and nonlinear low-frequency modes in a magnetized electron plasma are studied, taking into account a proper description of the equilibrium plasma state that is inhomogeneous. Assuming a homogeneous magnetic field and sheared plasma flows, flute-like perturbations are studied in the presence of density and potential gradients. Linear analysis reveals the presence of a streaming instability and depicts conditions for global linear spiral mode. In the nonlinear domain, a tripolar vortex, which is driven and carried by the flow, is found. Also investigated are the consequences of a magnetic shear as well as nonuniformities along the magnetic field lines, which are shown to be responsible for the possible annulment of the magnetic shear effects. Streaming along the lines of the sheared magnetic field is also studied. A variety of nonlinear structures (viz. global multipolar vortices, local vortex chains, and tripolar vortices) is shown to be the consequence of the simultaneous action of the parallel and perpendicular flows
Turbulence introduction to theory and applications of turbulent flows
Westerweel, Jerry; Nieuwstadt, Frans T M
2016-01-01
This book provides a general introduction to the topic of turbulent flows. Apart from classical topics in turbulence, attention is also paid to modern topics. After studying this work, the reader will have the basic knowledge to follow current topics on turbulence in scientific literature. The theory is illustrated with a number of examples of applications, such as closure models, numerical simulations and turbulent diffusion, and experimental findings. The work also contains a number of illustrative exercises.
Momentum transport in gyrokinetic turbulence
Energy Technology Data Exchange (ETDEWEB)
Buchholz, Rico
2016-07-01
In this thesis, the gyrokinetic-Vlasov code GKW is used to study turbulent transport, with a focus on radial transport of toroidal momentum. To support the studies on turbulent transport an eigenvalue solver has been implemented into GKW. This allows to find, not only the most unstable mode, but also subdominant modes. Furthermore it is possible to follow the modes in parameter scans. Furthermore, two fundamental mechanisms that can generate an intrinsic rotation have been investigated: profile shearing and the velocity nonlinearity. The study of toroidal momentum transport in a tokamak due to profile shearing reveals that the momentum flux can not be accurately described by the gradient in the turbulent intensity. Consequently, a description using the profile variation is used. A linear model has been developed that is able to reproduce the variations in the momentum flux as the profiles of density and temperature vary, reasonably well. It uses, not only the gradient length of density and temperature profile, but also their derivative, i.e. the second derivative of the logarithm of the temperature and the density profile. It is shown that both first as well as second derivatives contribute to the generation of a momentum flux. A difference between the linear and nonlinear simulations has been found with respect to the behaviour of the momentum flux. In linear simulations the momentum flux is independent of the normalized Larmor radius ρ{sub *}, whereas it is linear in ρ{sub *} for nonlinear simulations, provided ρ{sub *} is small enough (≤4.10{sup -3}). Nonlinear simulations reveal that the profile shearing can generate an intrinsic rotation comparable to that of current experiments. Under reactor conditions, however, the intrinsic rotation from the profile shearing is expected to be small due to the small normalized Larmor radius ρ{sub *}
On plasma coupling and turbulence effects in low velocity stopping
Energy Technology Data Exchange (ETDEWEB)
Kurilenkov, Yu K [Unified Institute for High Temperatures of Russian Academy of Sciences, 13/19 Izhorskaya Str., 125412 Moscow (Russian Federation); Maynard, G [Laboratoire de Physique des Gaz et des Plasmas, UMR-8578, Bat. 210, Universite Paris XI, F-91405 Orsay (France); Barriga-Carrasco, M D [Laboratoire de Physique des Gaz et des Plasmas, UMR-8578, Bat. 210, Universite Paris XI, F-91405 Orsay (France); Valuev, A A [Unified Institute for High Temperatures of Russian Academy of Sciences, 13/19 Izhorskaya Str., 125412 Moscow (Russian Federation)
2006-04-28
The problem of stopping power (SP) for projectile ions is analysed in terms of the dielectric function and effective collision frequency for moderately dense and strongly coupled plasmas (SCP). We consider several issues regarding the calculation of stopping power for correlated ensembles of particles and oscillators. In particular, effects of group (few particle) modes, transition from positive to negative dispersion and excitation of collective modes up to suprathermal level at plasma targets are addressed. Linear SP of dense suprathermal (nonlinear) plasma targets at different levels of target plasma turbulence is estimated. The force of suprathermal plasma oscillations on the projectile ions is mostly in the nature of increased frictional drag. The results obtained show the possibility of increasing low velocity stopping (up to 'turbulent' values) in comparison with losses in equilibrium dense plasma targets. Experimental conditions to create specific turbulent targets as well as some connection between stopping phenomena and SCP transport properties are discussed briefly.
On plasma coupling and turbulence effects in low velocity stopping
International Nuclear Information System (INIS)
Kurilenkov, Yu K; Maynard, G; Barriga-Carrasco, M D; Valuev, A A
2006-01-01
The problem of stopping power (SP) for projectile ions is analysed in terms of the dielectric function and effective collision frequency for moderately dense and strongly coupled plasmas (SCP). We consider several issues regarding the calculation of stopping power for correlated ensembles of particles and oscillators. In particular, effects of group (few particle) modes, transition from positive to negative dispersion and excitation of collective modes up to suprathermal level at plasma targets are addressed. Linear SP of dense suprathermal (nonlinear) plasma targets at different levels of target plasma turbulence is estimated. The force of suprathermal plasma oscillations on the projectile ions is mostly in the nature of increased frictional drag. The results obtained show the possibility of increasing low velocity stopping (up to 'turbulent' values) in comparison with losses in equilibrium dense plasma targets. Experimental conditions to create specific turbulent targets as well as some connection between stopping phenomena and SCP transport properties are discussed briefly
Drift wave instability and turbulence in advanced stellarator configurations
International Nuclear Information System (INIS)
Kendl, A.
2001-08-01
In the following chapter, an overview and references on the physics and geometry of helical advanced stellarators is given. On the basis of this configuration, the influence of magnetic field geometry is then discussed in a basic model of drift-Alfven wave turbulence which contains the necessary physics that applies to the plasma edge. By means of linear models, core physics in the form of ITG and dissipative trapped electron modes is further included in our survey. These models are, of course, by far not comprehensive in order to cover the complex physics of plasma turbulence in three-dimensional fusion devices, where a large range of parameter and mode regimes is present. Optimization criteria for a possible systematic minimization of turbulent transport in Helias configurations therefore still have to be regarded as tentative. The results presented here should, however, encourage for more detailed future computations. (orig.)
Yan, Z; McKee, G R; Fonck, R; Gohil, P; Groebner, R J; Osborne, T H
2014-03-28
Comprehensive 2D turbulence and eddy flow velocity measurements on DIII-D demonstrate a rapidly increasing turbulence-driven shear flow that develops ∼100 μs prior to the low-confinement (L mode) to high-confinement (H mode) transition and appears to trigger it. These changes are localized to a narrow layer 1-2 cm inside the magnetic boundary. Increasing heating power increases the Reynolds stress, the energy transfer from turbulence to the poloidal flow, and the edge flow shearing rate that then exceeds the decorrelation rate, suppressing turbulence and triggering the transition.
Implications of Navier-Stokes turbulence theory for plasma turbulence
International Nuclear Information System (INIS)
Montgomery, David
1977-01-01
A brief discussion of Navier-Stokes turbulence theory is given with particular reference to the two dimensional case. The MHD turbulence is introduced with possible applications of techniques developed in Navier-Stokes theory. Turbulence in Vlasov plasma is also discussed from the point of view of the ''direct interaction approximation'' (DIA). (A.K.)
A mathematical model of turbulence for turbulent boundary layers
International Nuclear Information System (INIS)
Pereira Filho, H.D.V.
1977-01-01
Equations to the so called Reynolds stress-tensor (kinetic turbulent energy) and dissipation rate are developed and a turbulence flux approximation used. Our ideia here is to use those equations in order to develop an economical and fast numeircal procedure for computation of turbulent boundary layer. (author) [pt
Gaussian vs non-Gaussian turbulence: impact on wind turbine loads
DEFF Research Database (Denmark)
Berg, Jacob; Natarajan, Anand; Mann, Jakob
2016-01-01
taking into account the safety factor for extreme moments. Other extreme load moments as well as the fatigue loads are not affected because of the use of non-Gaussian turbulent inflow. It is suggested that the turbine thus acts like a low-pass filter that averages out the non-Gaussian behaviour, which......From large-eddy simulations of atmospheric turbulence, a representation of Gaussian turbulence is constructed by randomizing the phases of the individual modes of variability. Time series of Gaussian turbulence are constructed and compared with its non-Gaussian counterpart. Time series from the two...
Yang, Huan; Zimmerman, Aaron; Lehner, Luis
2015-02-27
We demonstrate that rapidly spinning black holes can display a new type of nonlinear parametric instability-which is triggered above a certain perturbation amplitude threshold-akin to the onset of turbulence, with possibly observable consequences. This instability transfers from higher temporal and azimuthal spatial frequencies to lower frequencies-a phenomenon reminiscent of the inverse cascade displayed by (2+1)-dimensional fluids. Our finding provides evidence for the onset of transitory turbulence in astrophysical black holes and predicts observable signatures in black hole binaries with high spins. Furthermore, it gives a gravitational description of this behavior which, through the fluid-gravity duality, can potentially shed new light on the remarkable phenomena of turbulence in fluids.
Energy Technology Data Exchange (ETDEWEB)
Caldas, Ibere L.; Heller, M.V.A.P.; Brasilio, Z.A. [Sao Paulo Univ., SP, RJ (Brazil). Inst. de Fisica
1997-12-31
Full text. In this work we summarize the results from experiments on electrostatic and magnetic fluctuations in tokamak plasmas. Spectral analyses show that these fluctuations are turbulent, having a broad spectrum of wavectors and a broad spectrum of frequencies at each wavector. The electrostatic turbulence induces unexpected anomalous particle transport that deteriorates the plasma confinement. The relationship of these fluctuations to the current state of plasma theory is still unclear. Furthermore, we describe also attempts to control this plasma turbulence with external magnetic perturbations that create chaotic magnetic configurations. Accordingly, the magnetic field lines may become chaotic and then induce a Lagrangian diffusion. Moreover, to discuss nonlinear coupling and intermittency, we present results obtained by using numerical techniques as bi spectral and wavelet analyses. (author)
Energy Technology Data Exchange (ETDEWEB)
Mann, Jakob [Risoe National Lab., Wind Energy and Atmosheric Physics Dept., Roskilde (Denmark)
1999-03-01
The purpose of this work is to develop a model of the spectral velocity-tensor in neutral flow over complex terrain. The resulting equations are implemented in a computer code using the mean flow generated by a linear mean flow model as input. It estimates turbulence structure over hills (except on the lee side if recirculation is present) in the so-called outer layer and also models the changes in turbulence statistics in the vicinity roughness changes. The generated turbulence fields are suitable as input for dynamic load calculations on wind turbines and other tall structures and is under implementation in the collection of programs called WA{sup s}P Engineering. (au) EFP-97; EU-JOULE-3. 15 refs.
Physics of turbulence control and transport barrier formation in DIII-D
International Nuclear Information System (INIS)
Doyle, E.J.; Burrell, K.H.; Carlstrom, T.N.
1996-10-01
This paper describes the physical mechanisms responsible for turbulence control and transport barrier formation on DIII-D as determined from a synthesis of results from different enhanced confinement regimes, including quantitative and qualitative comparisons to theory. A wide range of DIII-D data support the hypothesis that a single underlying physical mechanism, turbulence suppression via E x B shear flow is playing an essential, though not necessarily unique, role in reducing turbulence and transport in all of the following improved confinement regimes: H-mode, VH-mode, high-ell i modes, improved performance counter-injection L-mode discharges and high performance negative central shear (NCS) discharges. DIII-D data also indicate that synergistic effects are important in some cases, as in NCS discharges where negative magnetic shear also plays a role in transport barrier formation. This work indicates that in order to control turbulence and transport it is important to focus on understanding physical mechanisms, such as E x B shear, which can regulate and control entire classes of turbulent modes, and thus control transport. In the highest performance DIII-D discharges, NCS plasmas with a VH-mode like edge, turbulence is suppressed at all radii, resulting in neoclassical levels of ion transport over most of the plasma volume
Low-dimensional chaotic attractors in drift wave turbulence
International Nuclear Information System (INIS)
Persson, M.; Nordman, H.
1991-01-01
Simulation results of toroidal η i -mode turbulence are analyzed using mathematical tools of nonlinear dynamics. Low-dimensional chaotic attractors are found in the strongly nonlinear regime while in the weakly interacting regime the dynamics is high dimensional. In both regimes, the solutions are found to display sensitive dependence on initial conditions, characterized by a positive largest Liapunov exponent. (au)
Turbulence Intensity Scaling: A Fugue
Basse, Nils T.
2018-01-01
We study streamwise turbulence intensity definitions using smooth- and rough-wall pipe flow measurements made in the Princeton Superpipe. Scaling of turbulence intensity with the bulk (and friction) Reynolds number is provided for the definitions. The turbulence intensity is proportional to the square root of the friction factor with the same proportionality constant for smooth- and rough-wall pipe flow. Turbulence intensity definitions providing the best description of the measurements are i...
Turbulent wakes of fractal objects
Staicu, A.D.; Mazzi, B.; Vassilicos, J.C.; Water, van de W.
2003-01-01
Turbulence of a windtunnel flow is stirred using objects that have a fractal structure. The strong turbulent wakes resulting from three such objects which have different fractal dimensions are probed using multiprobe hot-wire anemometry in various configurations. Statistical turbulent quantities are
Plasma turbulence calculations on supercomputers
International Nuclear Information System (INIS)
Carreras, B.A.; Charlton, L.A.; Dominguez, N.; Drake, J.B.; Garcia, L.; Leboeuf, J.N.; Lee, D.K.; Lynch, V.E.; Sidikman, K.
1991-01-01
Although the single-particle picture of magnetic confinement is helpful in understanding some basic physics of plasma confinement, it does not give a full description. Collective effects dominate plasma behavior. Any analysis of plasma confinement requires a self-consistent treatment of the particles and fields. The general picture is further complicated because the plasma, in general, is turbulent. The study of fluid turbulence is a rather complex field by itself. In addition to the difficulties of classical fluid turbulence, plasma turbulence studies face the problems caused by the induced magnetic turbulence, which couples field by itself. In addition to the difficulties of classical fluid turbulence, plasma turbulence studies face the problems caused by the induced magnetic turbulence, which couples back to the fluid. Since the fluid is not a perfect conductor, this turbulence can lead to changes in the topology of the magnetic field structure, causing the magnetic field lines to wander radially. Because the plasma fluid flows along field lines, they carry the particles with them, and this enhances the losses caused by collisions. The changes in topology are critical for the plasma confinement. The study of plasma turbulence and the concomitant transport is a challenging problem. Because of the importance of solving the plasma turbulence problem for controlled thermonuclear research, the high complexity of the problem, and the necessity of attacking the problem with supercomputers, the study of plasma turbulence in magnetic confinement devices is a Grand Challenge problem
Field experiments and laboratory study of plasma turbulence and effects on EM wave propagation
International Nuclear Information System (INIS)
Lee, M.C.; Kuo, S.P.
1990-01-01
Both active experiments in space and laboratory experiments with plasma chambers have been planned to investigate plasma turbulence and effects on electromagnetic wave propagation. Plasma turbulence can be generated by intense waves or occur inherently with the production of plasmas. The turbulence effects to be singled out for investigation include nonlinear mode conversion process and turbulence scattering of electromagnetic waves by plasma density fluctuations. The authors have shown theoretically that plasma density fluctuations can render the nonlinear mode conversion of electromagnetic waves into lower hybrid waves, leading to anomalous absorption of waves in magnetoplasmas. The observed spectral broadening of VLF waves is the evidence of the occurrence of this process. Since the density fluctuations may have a broad range of scale lengths, this process is effective in weakening the electromagnetic waves in a wideband. In addition, plasma density fluctuations can scatter waves and diversify the electromagnetic energy. Schemes of generating plasma turbulence and the diagnoses of plasma effects are discussed
International Nuclear Information System (INIS)
Diamond, P.H.; Biglari, H.; Gang, F.Y.
1991-01-01
Recent advances in the theory of trapped particle pressure gradient driven turbulence are summarized. A novel theory of trapped ion convective cell turbulence is presented. It is shown that non-linear transfer to small scales occurs, and that saturation levels are not unphysically large, as previously thought. As the virulent saturation mechanism of ion Compton scattering is shown to result in weak turbulence at higher frequencies, it is thus likely that trapped ion convective cells are the major agent of tokamak transport. Fluid like trapped electron modes at short wavelengths (k θ ρ i > 1) are shown to drive an inward particle pinch. The characteristics of convective cell turbulence in flat density discharges are described, as is the stability of dissipative trapped electron modes in stellarators, with flexible magnetic field structure. The role of cross-correlations in the dynamics of multifield models of drift wave turbulence is discussed. (author). 32 refs, 8 figs, 1 tab
International Nuclear Information System (INIS)
Eliassen, Lene; Andersen, Søren
2016-01-01
The wind turbine design standards recommend two different methods to generate turbulent wind for design load analysis, the Kaimal spectra combined with an exponential coherence function and the Mann turbulence model. The two turbulence models can give very different estimates of fatigue life, especially for offshore floating wind turbines. In this study the spatial distributions of the two turbulence models are investigated using Proper Orthogonal Decomposition, which is used to characterize large coherent structures. The main focus has been on the structures that contain the most energy, which are the lowest POD modes. The Mann turbulence model generates coherent structures that stretches in the horizontal direction for the longitudinal component, while the structures found in the Kaimal model are more random in their shape. These differences in the coherent structures at lower frequencies for the two turbulence models can be the reason for differences in fatigue life estimates for wind turbines. (paper)
2012-01-01
Dagobert, and C. Franchis . Atmospheric tur- bulence restoration by diffeomorphic image registration and blind deconvolution. In ACIVS, 2008. 1 [4] S...20] V. Tatarskii. Wave Propagation in a Turbulent Medium. McGraw-Hill Books, 1961. 2 [21] Y. Tian and S. Narasimhan. A globally optimal data-driven
van der Veen, Roeland
2016-01-01
In this thesis, several questions related to drop impact and Taylor-Couette turbulence are answered. The deformation of a drop just before impact can cause a bubble to be entrapped. For many applications, such as inkjet printing, it is crucial to control the size of this entrapped bubble. To study
Turbulence and Flying Machines
Indian Academy of Sciences (India)
other to make the aircraft roll. For example, a downward dis- placement of the left aileron causes the airplane to roll to the right. In Figure 4 the elevators have been deflected downwards, giving rise to a 'nose-down' moment about the pitch axis. Delaying Turbulence. In the last few decades, flying machines have proliferated ...
Turbulence and particle acceleration
International Nuclear Information System (INIS)
Scott, J.S.
1975-01-01
A model for the production of high energy particles in the supernova remnant Cas A is considered. The ordered expansion of the fast moving knots produce turbulent cells in the ambient interstellar medium. The turbulent cells act as magnetic scattering centers and charged particles are accelerated to large energies by the second order Fermi mechanism. Model predictions are shown to be consistent with the observed shape and time dependence of the radio spectrum, and with the scale size of magnetic field irregularities. Assuming a galactic supernova rate at 1/50 yr -1 , this mechanism is capable of producing the observed galactic cosmic ray flux and spectrum below 10 16 eV/nucleon. Several observed features of galactic cosmic rays are shown to be consistent with model predictions. A model for the objects known as radio tall galaxies is also presented. Independent blobs of magnetized plasma emerging from an active radio galaxy into an intracluster medium become turbulent due to Rayleigh--Taylor and Kelvin--Helmholz instabilities. The turbulence produces both in situ betatron and 2nd order Fermi accelerations. Predictions of the dependence of spectral index and flux on distance along the tail match observations well. Fitting provides values of physical parameters in the blobs. The relevance of this method of particle acceleration for the problem of the origin of x-ray emission in clusters of galaxies is discussed
Nature of interstellar turbulence
International Nuclear Information System (INIS)
Altunin, V.
1981-01-01
A significant role in producing the pattern of interstellar scintillation observed in discrete radio sources may be played by the magnetoacoustic turbulence that will be generated as shock waves are propagated at velocity V/sub sh/roughly-equal 20--100 km/sec through the interstellar medium, as well as by irregularities in stellar wind emanating from type OB stars
Stochastic modelling of turbulence
DEFF Research Database (Denmark)
Sørensen, Emil Hedevang Lohse
previously been shown to be closely connected to the energy dissipation. The incorporation of the small scale dynamics into the spatial model opens the door to a fully fledged stochastic model of turbulence. Concerning the interaction of wind and wind turbine, a new method is proposed to extract wind turbine...
Nonlinear entropy transfer in ETG-TEM turbulence via TEM driven zonal flows
International Nuclear Information System (INIS)
Asahi, Yuuichi; Tsutsui, Hiroaki; Tsuji-Iio, Shunji; Ishizawa, Akihiro; Sugama, Hideo; Watanabe, Tomohiko
2015-01-01
Nonlinear interplay of the electron temperature gradient (ETG) modes and the trapped electron modes (TEMs) was investigated by means of gyrokinetic simulation. Focusing on the situation where both TEMs and ETG modes are linearly unstable, the effects of TEM-driven zonal flows on ETG turbulence were examined by means of entropy transfer analysis. In a statistically steady turbulence where the TEM driven zonal flows are dominant, it turned out that the zonal flows meditate the entropy transfer of the ETG modes from the low to high radial wavenumber regions. The successive entropy transfer broadens the potential fluctuation spectrum in the radial wavenumber direction. In contrast, in the situation where ETG modes are unstable but TEMs are stable, the pure ETG turbulence does not produce strong zonal flows, leading to a rather narrow spectrum in the radial wavenumber space and a higher transport level. (author)
Shukla-Spatschek diffusion effects on surface plasma waves in astrophysical turbulent plasmas
Lee, Myoung-Jae; Jung, Young-Dae
2017-02-01
The effects of Shukla-Spatschek turbulent diffusion on a temporal mode of surface waves propagating at the interface of an astrophysical turbulent plasma are investigated. The damping rates for high and low modes of surface wave are kinetically derived by employing the Vlasov-Poisson equation and the specular reflection boundary condition. We found that the diffusion caused by the fluctuating electric fields leads to damping for both high and low modes of surface waves. The high-mode damping is enhanced with an increase of the wavenumber and the diffusion coefficient, but suppressed by an increase of electron thermal energy. By contrast, the low-mode damping is suppressed as the wavenumber and the thermal energy increase although it is enhanced as the diffusion increases. The variation of the damping rate due to the Shukla-Spatschek turbulent diffusion is also discussed.
Mean and oscillating plasma flows and turbulence interactions across the L-H confinement transition.
Conway, G D; Angioni, C; Ryter, F; Sauter, P; Vicente, J
2011-02-11
A complex interaction between turbulence driven E × B zonal flow oscillations, i.e., geodesic acoustic modes (GAMs), the turbulence, and mean equilibrium flows is observed during the low to high (L-H) plasma confinement mode transition in the ASDEX Upgrade tokamak. Below the L-H threshold at low densities a limit-cycle oscillation forms with competition between the turbulence level and the GAM flow shearing. At higher densities the cycle is diminished, while in the H mode the cycle duration becomes too short to sustain the GAM, which is replaced by large amplitude broadband flow perturbations. Initially GAM amplitude increases as the H-mode transition is approached, but is then suppressed in the H mode by enhanced mean flow shear.
Analysis of turbulent boundary layers
Cebeci, Tuncer
1974-01-01
Analysis of Turbulent Boundary Layers focuses on turbulent flows meeting the requirements for the boundary-layer or thin-shear-layer approximations. Its approach is devising relatively fundamental, and often subtle, empirical engineering correlations, which are then introduced into various forms of describing equations for final solution. After introducing the topic on turbulence, the book examines the conservation equations for compressible turbulent flows, boundary-layer equations, and general behavior of turbulent boundary layers. The latter chapters describe the CS method for calculati
Magnetosheath electrostatic turbulence
International Nuclear Information System (INIS)
Rodriguez, P.
1979-01-01
By using measurements with the University of Iowa plasma wave experiment on the Imp 6 satellite a study has been conducted of the spectrum of electrostatic plasma waves in the terrestrial magnetosheath. Electrostatic plasma wave turbulence is almost continuously present throughout the magnetosheath with broadband (20 Hz to 70 kHz) rms field intensities typically 0.01--1.0 mV m -1 . Peak intensities of about 1.0 mV m -1 near the electron plasma frequency (30--60 kHz) have been detected occasionally. Two or three components can usually be identified in the spectrum of magnetosheath electrostatic turbulence: a high-frequency (> or =30kHz) component peaking at the electron plasma frequency f/sub p/e, a low-frequency component with a broad intensity maximum below the nominal ion plasma frequency f/sub p/i (approx. f/sub p/e/43), and a less well defined intermediate component in the range f/sub p/i < f< f/sub p/e. The intensity distribution of magnetosheath electrostatic turbulence clearly shows that the low-frequency component is associated with the bow shock, suggesting that the ion heating begun at the shock continues into the downstream magnetosheath. Electrostatic waves below 1 kHz are polarized along the magnetic field direction, a result consistent with the polarization of electrostatic waves at the shock. The high- and intermediate-frequency components are features of the magnetosheath spectrum which are not characteristic of the shock spectrum but are often detected in the upstream solar wind. The intensity distribution of electrostatic turbulence at the magnetosheath plasma frequency has no apparent correlation with the shock, indicating that electron plasma oscillations are a general feature of the magnetosheath. The plasma wave noise shows a tendency to decrease toward the dawn and dusk regions, consistent with a general decrease in turbulence away from the subsolar magnetosheath
Liquid holdup in turbulent contact absorber
International Nuclear Information System (INIS)
Haq, A.; Zaman, M.; Inayat, M.H.; Chughtai, I.R.
2009-01-01
Dynamic liquid holdup in a turbulent contact absorber was obtained through quick shut off valves technique. Experiments were carried out in a Perspex column. Effects of liquid velocity, gas velocity, packing diameter packing density and packing height on dynamic liquid holdup were studied. Hollow spherical high density polyethylene (HDPE) balls were used as inert fluidized packing. Experiments were performed at practical range of liquid and gas velocities. Holdup was calculated on the basis of static bed height. Liquid holdup increases with increasing both liquid and gas velocities both for type 1 and type 2 modes of fluidization. Liquid holdup increases with packing density. No effect of dia was observed on liquid holdup. (author)
A minimal model of self-sustaining turbulence
International Nuclear Information System (INIS)
Thomas, Vaughan L.; Gayme, Dennice F.; Farrell, Brian F.; Ioannou, Petros J.
2015-01-01
In this work, we examine the turbulence maintained in a Restricted Nonlinear (RNL) model of plane Couette flow. This model is a computationally efficient approximation of the second order statistical state dynamics obtained by partitioning the flow into a streamwise averaged mean flow and perturbations about that mean, a closure referred to herein as the RNL ∞ model. The RNL model investigated here employs a single member of the infinite ensemble that comprises the covariance of the RNL ∞ dynamics. The RNL system has previously been shown to support self-sustaining turbulence with a mean flow and structural features that are consistent with direct numerical simulations (DNS). Regardless of the number of streamwise Fourier components used in the simulation, the RNL system’s self-sustaining turbulent state is supported by a small number of streamwise varying modes. Remarkably, further truncation of the RNL system’s support to as few as one streamwise varying mode can suffice to sustain the turbulent state. The close correspondence between RNL simulations and DNS that has been previously demonstrated along with the results presented here suggest that the fundamental mechanisms underlying wall-turbulence can be analyzed using these highly simplified RNL systems
International Nuclear Information System (INIS)
Assis, A.S. de; Silva, C.E. da; Dias Tavares, A. Jr.; Leubner, C.; Kuhn, S.
2001-07-01
We have studied the formation of auroral electron fluxes induced by a field aligned dc electric field in the presence of plasma wave turbulence. The effect of the wave spectral shape on the production rate has been considered. This acceleration scheme was modelled by the weak turbulence approach. The electron fluxes for narrow and broad band spectra, in the case of low and high phase velocities, are calculated, and it is found as a general feature, for all modes, that their enhancement is larger the weaker the background electric field, while for its absolute enhancement it is just the opposite. The electron fluxes are enhanced by many orders of magnitude over that without turbulence. It is also shown that the modes enhance the runaway production rate via their Cherenkov dissipation, and that a synergetic effect occurs in the enhancement when more than one mode turbulent is present in the acceleration region. (author)
Turbulence measurements in fusion plasmas
International Nuclear Information System (INIS)
Conway, G D
2008-01-01
Turbulence measurements in magnetically confined toroidal plasmas have a long history and relevance due to the detrimental role of turbulence induced transport on particle, energy, impurity and momentum confinement. The turbulence-the microscopic random fluctuations in particle density, temperature, potential and magnetic field-is generally driven by radial gradients in the plasma density and temperature. The correlation between the turbulence properties and global confinement, via enhanced diffusion, convection and direct conduction, is now well documented. Theory, together with recent measurements, also indicates that non-linear interactions within the turbulence generate large scale zonal flows and geodesic oscillations, which can feed back onto the turbulence and equilibrium profiles creating a complex interdependence. An overview of the current status and understanding of plasma turbulence measurements in the closed flux surface region of magnetic confinement fusion devices is presented, highlighting some recent developments and outstanding problems.
Destabilizing turbulence in pipe flow
Kühnen, Jakob; Song, Baofang; Scarselli, Davide; Budanur, Nazmi Burak; Riedl, Michael; Willis, Ashley P.; Avila, Marc; Hof, Björn
2018-04-01
Turbulence is the major cause of friction losses in transport processes and it is responsible for a drastic drag increase in flows over bounding surfaces. While much effort is invested into developing ways to control and reduce turbulence intensities1-3, so far no methods exist to altogether eliminate turbulence if velocities are sufficiently large. We demonstrate for pipe flow that appropriate distortions to the velocity profile lead to a complete collapse of turbulence and subsequently friction losses are reduced by as much as 90%. Counterintuitively, the return to laminar motion is accomplished by initially increasing turbulence intensities or by transiently amplifying wall shear. Since neither the Reynolds number nor the shear stresses decrease (the latter often increase), these measures are not indicative of turbulence collapse. Instead, an amplification mechanism4,5 measuring the interaction between eddies and the mean shear is found to set a threshold below which turbulence is suppressed beyond recovery.
Transitional-turbulent spots and turbulent-turbulent spots in boundary layers.
Wu, Xiaohua; Moin, Parviz; Wallace, James M; Skarda, Jinhie; Lozano-Durán, Adrián; Hickey, Jean-Pierre
2017-07-03
Two observations drawn from a thoroughly validated direct numerical simulation of the canonical spatially developing, zero-pressure gradient, smooth, flat-plate boundary layer are presented here. The first is that, for bypass transition in the narrow sense defined herein, we found that the transitional-turbulent spot inception mechanism is analogous to the secondary instability of boundary-layer natural transition, namely a spanwise vortex filament becomes a [Formula: see text] vortex and then, a hairpin packet. Long streak meandering does occur but usually when a streak is infected by a nearby existing transitional-turbulent spot. Streak waviness and breakdown are, therefore, not the mechanisms for the inception of transitional-turbulent spots found here. Rather, they only facilitate the growth and spreading of existing transitional-turbulent spots. The second observation is the discovery, in the inner layer of the developed turbulent boundary layer, of what we call turbulent-turbulent spots. These turbulent-turbulent spots are dense concentrations of small-scale vortices with high swirling strength originating from hairpin packets. Although structurally quite similar to the transitional-turbulent spots, these turbulent-turbulent spots are generated locally in the fully turbulent environment, and they are persistent with a systematic variation of detection threshold level. They exert indentation, segmentation, and termination on the viscous sublayer streaks, and they coincide with local concentrations of high levels of Reynolds shear stress, enstrophy, and temperature fluctuations. The sublayer streaks seem to be passive and are often simply the rims of the indentation pockets arising from the turbulent-turbulent spots.
Gyrokinetic simulations of turbulent transport: size scaling and chaotic behaviour
International Nuclear Information System (INIS)
Villard, L; Brunner, S; Casati, A; Aghdam, S Khosh; Lapillonne, X; McMillan, B F; Bottino, A; Dannert, T; Goerler, T; Hatzky, R; Jenko, F; Merz, F; Chowdhury, J; Ganesh, R; Garbet, X; Grandgirard, V; Latu, G; Sarazin, Y; Idomura, Y; Jolliet, S
2010-01-01
Important steps towards the understanding of turbulent transport have been made with the development of the gyrokinetic framework for describing turbulence and with the emergence of numerical codes able to solve the set of gyrokinetic equations. This paper presents some of the main recent advances in gyrokinetic theory and computing of turbulence. Solving 5D gyrokinetic equations for each species requires state-of-the-art high performance computing techniques involving massively parallel computers and parallel scalable algorithms. The various numerical schemes that have been explored until now, Lagrangian, Eulerian and semi-Lagrangian, each have their advantages and drawbacks. A past controversy regarding the finite size effect (finite ρ * ) in ITG turbulence has now been resolved. It has triggered an intensive benchmarking effort and careful examination of the convergence properties of the different numerical approaches. Now, both Eulerian and Lagrangian global codes are shown to agree and to converge to the flux-tube result in the ρ * → 0 limit. It is found, however, that an appropriate treatment of geometrical terms is necessary: inconsistent approximations that are sometimes used can lead to important discrepancies. Turbulent processes are characterized by a chaotic behaviour, often accompanied by bursts and avalanches. Performing ensemble averages of statistically independent simulations, starting from different initial conditions, is presented as a way to assess the intrinsic variability of turbulent fluxes and obtain reliable estimates of the standard deviation. Further developments concerning non-adiabatic electron dynamics around mode-rational surfaces and electromagnetic effects are discussed.
Ballistic propagation of turbulence front in tokamak edge plasmas
International Nuclear Information System (INIS)
Sugita, Satoru; Itoh, Kimitaka; Itoh, Sanae-I; Yagi, Masatoshi; Fuhr, Guillaume; Beyer, Peter; Benkadda, Sadruddin
2012-01-01
The flux-driven nonlinear simulation of resistive ballooning mode turbulence with tokamak edge geometry is performed to study the non-steady component in the edge turbulence. The large-scale and dynamical events in transport are investigated in a situation where the mean flow is suppressed. Two types of dynamics are observed. One is the radial propagation of the pulse of pressure gradient, the other is the appearance/disappearance of radially elongated global structure of turbulent heat flux. The ballistic propagation is observed in the pulse of pressure gradient, which is associated with the front of turbulent heat flux. We focus on this ballistic propagation phenomenon. Both of the bump of pressure gradient and the front of heat flux propagate inward and outward direction. It is confirmed that the strong fluctuation propagates with the pulse front. It is observed that the number of pulses going outward is close to those going inward. This ballistic phenomenon does not contradict to the turbulence spreading theory. Statistical characteristics of the ballistic propagation of pulses are evaluated and compared with scaling laws which is given by the turbulence spreading theory. It is found that they give qualitatively good agreement. (paper)
Impact of large scale flows on turbulent transport
Energy Technology Data Exchange (ETDEWEB)
Sarazin, Y [Association Euratom-CEA, CEA/DSM/DRFC centre de Cadarache, 13108 St-Paul-Lez-Durance (France); Grandgirard, V [Association Euratom-CEA, CEA/DSM/DRFC centre de Cadarache, 13108 St-Paul-Lez-Durance (France); Dif-Pradalier, G [Association Euratom-CEA, CEA/DSM/DRFC centre de Cadarache, 13108 St-Paul-Lez-Durance (France); Fleurence, E [Association Euratom-CEA, CEA/DSM/DRFC centre de Cadarache, 13108 St-Paul-Lez-Durance (France); Garbet, X [Association Euratom-CEA, CEA/DSM/DRFC centre de Cadarache, 13108 St-Paul-Lez-Durance (France); Ghendrih, Ph [Association Euratom-CEA, CEA/DSM/DRFC centre de Cadarache, 13108 St-Paul-Lez-Durance (France); Bertrand, P [LPMIA-Universite Henri Poincare Nancy I, Boulevard des Aiguillettes BP239, 54506 Vandoe uvre-les-Nancy (France); Besse, N [LPMIA-Universite Henri Poincare Nancy I, Boulevard des Aiguillettes BP239, 54506 Vandoe uvre-les-Nancy (France); Crouseilles, N [IRMA, UMR 7501 CNRS/Universite Louis Pasteur, 7 rue Rene Descartes, 67084 Strasbourg (France); Sonnendruecker, E [IRMA, UMR 7501 CNRS/Universite Louis Pasteur, 7 rue Rene Descartes, 67084 Strasbourg (France); Latu, G [LSIIT, UMR 7005 CNRS/Universite Louis Pasteur, Bd Sebastien Brant BP10413, 67412 Illkirch (France); Violard, E [LSIIT, UMR 7005 CNRS/Universite Louis Pasteur, Bd Sebastien Brant BP10413, 67412 Illkirch (France)
2006-12-15
The impact of large scale flows on turbulent transport in magnetized plasmas is explored by means of various kinetic models. Zonal flows are found to lead to a non-linear upshift of turbulent transport in a 3D kinetic model for interchange turbulence. Such a transition is absent from fluid simulations, performed with the same numerical tool, which also predict a much larger transport. The discrepancy cannot be explained by zonal flows only, despite they being overdamped in fluids. Indeed, some difference remains, although reduced, when they are artificially suppressed. Zonal flows are also reported to trigger transport barriers in a 4D drift-kinetic model for slab ion temperature gradient (ITG) turbulence. The density gradient acts as a source drive for zonal flows, while their curvature back stabilizes the turbulence. Finally, 5D simulations of toroidal ITG modes with the global and full-f GYSELA code require the equilibrium density function to depend on the motion invariants only. If not, the generated strong mean flows can completely quench turbulent transport.
Impact of large scale flows on turbulent transport
International Nuclear Information System (INIS)
Sarazin, Y; Grandgirard, V; Dif-Pradalier, G; Fleurence, E; Garbet, X; Ghendrih, Ph; Bertrand, P; Besse, N; Crouseilles, N; Sonnendruecker, E; Latu, G; Violard, E
2006-01-01
The impact of large scale flows on turbulent transport in magnetized plasmas is explored by means of various kinetic models. Zonal flows are found to lead to a non-linear upshift of turbulent transport in a 3D kinetic model for interchange turbulence. Such a transition is absent from fluid simulations, performed with the same numerical tool, which also predict a much larger transport. The discrepancy cannot be explained by zonal flows only, despite they being overdamped in fluids. Indeed, some difference remains, although reduced, when they are artificially suppressed. Zonal flows are also reported to trigger transport barriers in a 4D drift-kinetic model for slab ion temperature gradient (ITG) turbulence. The density gradient acts as a source drive for zonal flows, while their curvature back stabilizes the turbulence. Finally, 5D simulations of toroidal ITG modes with the global and full-f GYSELA code require the equilibrium density function to depend on the motion invariants only. If not, the generated strong mean flows can completely quench turbulent transport
Airborne Turbulence Detection and Warning ACLAIM Flight Test Results
Hannon, Stephen M.; Bagley, Hal R.; Soreide, Dave C.; Bowdle, David A.; Bogue, Rodney K.; Ehernberger, L. Jack
1999-01-01
The Airborne Coherent Lidar for Advanced Inflight Measurements (ACLAIM) is a NASA/Dryden-lead program to develop and demonstrate a 2 micrometers pulsed Doppler lidar for airborne look-ahead turbulence detection and warning. Advanced warning of approaching turbulence can significantly reduce injuries to passengers and crew aboard commercial airliners. The ACLAIM instrument is a key asset to the ongoing Turbulence component of NASA's Aviation Safety Program, aimed at reducing the accident rate aboard commercial airliners by a factor of five over the next ten years and by a factor of ten over the next twenty years. As well, the advanced turbulence warning capability can prevent "unstarts" in the inlet of supersonic aircraft engines by alerting the flight control computer which then adjusts the engine to operate in a less fuel efficient, and more turbulence tolerant, mode. Initial flight tests of the ACLAIM were completed in March and April of 1998. This paper and presentation gives results from these initial flights, with validated demonstration of Doppler lidar wind turbulence detection several kilometers ahead of the aircraft.
The turbulence structure in an unconfined swirling diffusion flame
International Nuclear Information System (INIS)
Finzenhagen, F.; Doherty, T.O.; Bates, C.; Wirtz, S.; Kremer, H.
1999-01-01
Turbulent swirling flows are used in many practical combustion systems. The swirl improves the flame stability as a result of the formation of a central recirculation zone combined with fast mixing at the boundaries of this zone. Knowledge about swirl flames has increased over the last few decades as a result of practical experience and fundamental research. Some important questions concerning the influence of the turbulence structure on the flame stability and chemical kinetics of the combustion process remain unresolved. The structure of turbulence, especially turbulent scales and time dependent effects, at the outlet zone controls the mixing process and therefore the flame properties. Understanding of these complex phenomena is far from complete. The present work describes the results of an experimental study of the turbulence structure of a swirled diffusion flame using laser-optical measurement techniques, e.g. Laser Doppler Anemometry (LDA) and Particle Image Velocimetry (PW). All the processed information available from the burst-mode Laser Doppler Anemometry (LDA) measurements has been combined and compared with high spatial resolution PIV measurements of the flow. The extensive statistical post processing of the data has enabled the turbulent microstructure to be characterised. (author)
Dubin, D. H. E.
This chapter explores several aspects of the linear electrostatic normal modes of oscillation for a single-species non-neutral plasma in a Penning trap. Linearized fluid equations of motion are developed, assuming the plasma is cold but collisionless, which allow derivation of the cold plasma dielectric tensor and the electrostatic wave equation. Upper hybrid and magnetized plasma waves in an infinite uniform plasma are described. The effect of the plasma surface in a bounded plasma system is considered, and the properties of surface plasma waves are characterized. The normal modes of a cylindrical plasma column are discussed, and finally, modes of spheroidal plasmas, and finite temperature effects on the modes, are briefly described.
Critical Transitions in Thin Layer Turbulence
Benavides, Santiago; Alexakis, Alexandros
2017-11-01
We investigate a model of thin layer turbulence that follows the evolution of the two-dimensional motions u2 D (x , y) along the horizontal directions (x , y) coupled to a single Fourier mode along the vertical direction (z) of the form uq (x , y , z) = [vx (x , y) sin (qz) ,vy (x , y) sin (qz) ,vz (x , y) cos (qz) ] , reducing thus the system to two coupled, two-dimensional equations. Its reduced dimensionality allows a thorough investigation of the transition from a forward to an inverse cascade of energy as the thickness of the layer H = π / q is varied.Starting from a thick layer and reducing its thickness it is shown that two critical heights are met (i) one for which the forward unidirectional cascade (similar to three-dimensional turbulence) transitions to a bidirectional cascade transferring energy to both small and large scales and (ii) one for which the bidirectional cascade transitions to a unidirectional inverse cascade when the layer becomes very thin (similar to two-dimensional turbulence). The two critical heights are shown to have different properties close to criticality that we are able to analyze with numerical simulations for a wide range of Reynolds numbers and aspect ratios. This work was Granted access to the HPC resources of MesoPSL financed by the Region Ile de France and the project Equip@Meso (reference ANR-10-EQPX-29-01).
''Turbulent Equipartition'' Theory of Toroidal Momentum Pinch
International Nuclear Information System (INIS)
Hahm, T.S.; Diamond, P.H.; Gurcan, O.D.; Rewaldt, G.
2008-01-01
The mode-independent part of magnetic curvature driven turbulent convective (TuroCo) pinch of the angular momentum density (Hahm et al., Phys. Plasmas 14,072302 (2007)) which was originally derived from the gyrokinetic equation, can be interpreted in terms of the turbulent equipartition (TEP) theory. It is shown that the previous results can be obtained from the local conservation of 'magnetically weighted angular momentum density', nm i U # parallel# R/B 2 , and its homogenization due to turbulent flows. It is also demonstrated that the magnetic curvature modification of the parallel acceleration in the nonlinear gyrokinetic equation in the laboratory frame, which was shown to be responsible for the TEP part of the TurCo pinch of angular momentum density in the previous work, is closely related to the Coriolis drift coupling to the perturbed electric field. In addition, the origin of the diffusive flux in the rotating frame is highlighted. Finally, it is illustrated that there should be a difference in scalings between the momentum pinch originated from inherently toroidal effects and that coming from other mechanisms which exist in a simpler geometry.
Exact Theory of Compressible Fluid Turbulence
Drivas, Theodore; Eyink, Gregory
2017-11-01
We obtain exact results for compressible turbulence with any equation of state, using coarse-graining/filtering. We find two mechanisms of turbulent kinetic energy dissipation: scale-local energy cascade and ``pressure-work defect'', or pressure-work at viscous scales exceeding that in the inertial-range. Planar shocks in an ideal gas dissipate all kinetic energy by pressure-work defect, but the effect is omitted by standard LES modeling of pressure-dilatation. We also obtain a novel inverse cascade of thermodynamic entropy, injected by microscopic entropy production, cascaded upscale, and removed by large-scale cooling. This nonlinear process is missed by the Kovasznay linear mode decomposition, treating entropy as a passive scalar. For small Mach number we recover the incompressible ``negentropy cascade'' predicted by Obukhov. We derive exact Kolmogorov 4/5th-type laws for energy and entropy cascades, constraining scaling exponents of velocity, density, and internal energy to sub-Kolmogorov values. Although precise exponents and detailed physics are Mach-dependent, our exact results hold at all Mach numbers. Flow realizations at infinite Reynolds are ``dissipative weak solutions'' of compressible Euler equations, similarly as Onsager proposed for incompressible turbulence.
Coherent and turbulent fluctuations in TFTR
International Nuclear Information System (INIS)
McGuire, K.; Arunasalam, V.; Bell, M.G.
1987-04-01
Classification of the sawteeth observed in the TFTR tokamak has been carried out to highlight the differences between the many types observed. Three types of sawteeth are discussed: ''simple,'' ''small,'' and ''compound.'' During the enhanced confinement discharges on TFTR, sawteeth related to q = 1 are usually not present, but a sawtooth-like event is sometimes observed. β approaches the Troyon limit only at low q/sub cyl/ with a clear reduction of achievable β/sub n/ at high q/sub cyl/. This suggests that a β/sub p/ limit, rather than the Troyon-Gruber limit, applies at high q/sub cyl/ in the enhanced confinement discharges. These discharges also reach the stability boundary for n → ∞ ideal MHD ballooning modes. Turbulence measurements in the scrape-off region with Langmuir and magnetic probes show strong edge density turbulence n/n = 0.3 - 0.5, with weak magnetic turbulence B/sub θ/B/sub θ/ > 5 x 10 -6 measured at the wall, but these measurements are very sensitive to local edge conditions
Dynamic Stochastic Superresolution of sparsely observed turbulent systems
International Nuclear Information System (INIS)
Branicki, M.; Majda, A.J.
2013-01-01
Real-time capture of the relevant features of the unresolved turbulent dynamics of complex natural systems from sparse noisy observations and imperfect models is a notoriously difficult problem. The resulting lack of observational resolution and statistical accuracy in estimating the important turbulent processes, which intermittently send significant energy to the large-scale fluctuations, hinders efficient parameterization and real-time prediction using discretized PDE models. This issue is particularly subtle and important when dealing with turbulent geophysical systems with an vast range of interacting spatio-temporal scales and rough energy spectra near the mesh scale of numerical models. Here, we introduce and study a suite of general Dynamic Stochastic Superresolution (DSS) algorithms and show that, by appropriately filtering sparse regular observations with the help of cheap stochastic exactly solvable models, one can derive stochastically ‘superresolved’ velocity fields and gain insight into the important characteristics of the unresolved dynamics, including the detection of the so-called black swans. The DSS algorithms operate in Fourier domain and exploit the fact that the coarse observation network aliases high-wavenumber information into the resolved waveband. It is shown that these cheap algorithms are robust and have significant skill on a test bed of turbulent solutions from realistic nonlinear turbulent spatially extended systems in the presence of a significant model error. In particular, the DSS algorithms are capable of successfully capturing time-localized extreme events in the unresolved modes, and they provide good and robust skill for recovery of the unresolved processes in terms of pattern correlation. Moreover, we show that DSS improves the skill for recovering the primary modes associated with the sparse observation mesh which is equally important in applications. The skill of the various DSS algorithms depends on the energy spectrum
A numerical study of non-isothermal turbulent coaxial jets
Energy Technology Data Exchange (ETDEWEB)
Kriaa, Wassim; Abderrazak, Kamel; Mhiri, Hatem [Ecole Nationale d' Ingenieurs de Monastir, Laboratoire de Mecanique des Fluides et Thermique, Monastir (Tunisia); Palec, Georges le; Bournot, Philippe [Institut de Mecanique de Marseille, Marseille (France)
2008-07-15
In this work, we propose to study non isothermal air-air coaxial jets with two different approaches: parabolic and elliptic approaches. The standard k-{epsilon} model and the RSM model were applied in this study. The numerical resolution of the equations governing this flow type was carried out for: the parabolic approach, by a ''home-made'' CFD code based on a finite difference method, and the elliptic approach by an industrial code (FLUENT) based on a finite volume method. In forced convection mode (Fr={infinity}), the two turbulence models are valid for the prediction of the mean flow. But for turbulent sizes, k-{epsilon} model gives results closer to those achieved in experiments compared to RSM Model. Concerning the limit of validity of the parabolic and elliptic approaches, we showed that for velocities ratio r lower than 1, the results of the two approaches were satisfactory. On the other hand, for r>1, the difference between the results became increasingly significant. In mixed convection mode (Fr{approx_equal}20), the results obtained by the two turbulence models for the mean axial velocity were very different even in the plume region. For the temperature and the turbulent sizes the two models give satisfactory results which agree well with the correlations suggested by the experimenters for X{>=}20. Thus, the second order model with {sigma}{sub t}=0.85 is more effective for a coaxial jet study in a mixed convection mode. (orig.)
Theory of neoclassical resistivity-gradient-driven turbulence
International Nuclear Information System (INIS)
Kwon, O.J.; Diamond, P.H.; Hahm, T.S.
1988-12-01
It is shown that rippling instabilities can tap the density gradient expansion free energy source through the density dependence of the neoclassical resistivity. Linear analyses show that the region where neoclassical rippling modes are significantly excited extends from the edge of the plasma to the region where ν/sub *e/ ≤ 1. Since these modes are non-dispersive, diamagnetic effects are negligible in comparison to the nonlinear decorrelation rate at saturation. Thus, the relevant regime is the 'strong turbulence' regime. The turbulent radial diffusivities of the temperature and the density are obtained as eigenvalues of the renormalized eigenmode equations at steady state. The density gradient acts to enhance the level of turbulence, compared to that driven by the temperature gradient alone. The saturated turbulent state is characterized by: current decoupling, the breakdown of Boltzmann relation, a radial mode scale of density fluctuations exceeding that of temperature fluctuations, implying that density diffusivity exceeds temperature diffusivity, and that density fluctuation levels exceed temperature fluctuation levels. Magnetic fluctuation levels are negligible. 29 refs., 1 fig
Optimization of AMI-MDM-RoFSO under atmospheric turbulence
Directory of Open Access Journals (Sweden)
Chaudhary Sushank
2017-01-01
Full Text Available Radio over Free Space (Ro-FSO is promising candidate for providing ubiquitous digital services especially in rural areas. This work investigates the performance of MDM of two 5Gbps-10GHz data channels over FSO link using LP 01 and LP 02 modes under the effect of atmospheric turbulences. The signal to noise ratio (SNR, total received power, modal decomposition at receiver at the receiver is also reported. The reported result shows the successful transmission of two channels with acceptable SNR over FSO link under atmospheric turbulences.
Shear flow generation and energetics in electromagnetic turbulence
DEFF Research Database (Denmark)
Naulin, V.; Kendl, A.; Garcia, O.E.
2005-01-01
acoustic mode (GAM) transfer in drift-Alfvén turbulence is investigated. By means of numerical computations the energy transfer into zonal flows owing to each of these effects is quantified. The importance of the three driving ingredients in electrostatic and electromagnetic turbulence for conditions...... relevant to the edge of fusion devices is revealed for a broad range of parameters. The Reynolds stress is found to provide a flow drive, while the electromagnetic Maxwell stress is in the cases considered a sink for the flow energy. In the limit of high plasma β, where electromagnetic effects and Alfvén...
Forces on zonal flows in tokamak core turbulence
International Nuclear Information System (INIS)
Hallatschek, K.; Itoh, K.
2005-01-01
The saturation of stationary zonal flows (ZF) in the core of a tokamak has been analyzed in numerical fluid turbulence computer studies. The model was chosen to properly represent the kinetic global plasma flows, i.e., undamped stationary toroidal or poloidal flows and Landau damped geodesic acoustic modes. Reasonable agreement with kinetic simulations in terms of magnitude of transport and occurrence of the Dimits shift was verified. Contrary to common perception, in the final saturated state of turbulence and ZFs, the customary perpendicular Reynolds stress continues to drive the ZFs. The force balance is established by the essentially quasilinear parallel Reynolds stress acting on the parallel return flows required by incompressibility. (author)
The dynamics of interacting nonlinearities governing long wavelength driftwave turbulence
International Nuclear Information System (INIS)
Newman, D.E.
1993-09-01
Because of the ubiquitous nature of turbulence and the vast array of different systems which have turbulent solutions, the study of turbulence is an area of active research. Much present day understanding of turbulence is rooted in the well established properties of homogeneous Navier-Stokes turbulence, which, due to its relative simplicity, allows for approximate analytic solutions. This work examines a group of turbulent systems with marked differences from Navier-Stokes turbulence, and attempts to quantify some of their properties. This group of systems represents a variety of drift wave fluctuations believed to be of fundamental importance in laboratory fusion devices. From extensive simulation of simple local fluid models of long wavelength drift wave turbulence in tokamaks, a reasonably complete picture of the basic properties of spectral transfer and saturation has emerged. These studies indicate that many conventional notions concerning directions of cascades, locality and isotropy of transfer, frequencies of fluctuations, and stationarity of saturation are not valid for moderate to long wavelengths. In particular, spectral energy transfer at long wavelengths is dominated by the E x B nonlinearity, which carries energy to short scale in a manner that is highly nonlocal and anisotropic. In marked contrast to the canonical self-similar cascade dynamics of Kolmogorov, energy is efficiently passed between modes separated by the entire spectrum range in a correlation time. At short wavelengths, transfer is dominated by the polarization drift nonlinearity. While the standard dual cascade applies in this subrange, it is found that finite spectrum size can produce cascades that are reverse directed and are nonconservative in enstrophy and energy similarity ranges. In regions where both nonlinearities are important, cross-coupling between the nolinearities gives rise to large no frequency shifts as well as changes in the spectral dynamics
Anaïs Schaeffer
2015-01-01
As a member of the EuHIT (European High-Performance Infrastructures in Turbulence - see here) consortium, CERN is participating in fundamental research on turbulence phenomena. To this end, the Laboratory provides European researchers with a cryogenic research infrastructure (see here), where the first tests have just been performed. The last day of data collection, tired but satisfied after seven intense days of measurements. Around the cryostat, from left to right: Philippe-E. Roche, Éléonore Rusaouen (CNRS), Olivier Pirotte, Jean-Marc Quetsch (CERN), Nicolas Friedlin (CERN), Vladislav Benda (CERN). Not in the photo: Laurent Le Mao (CERN), Jean-Marc Debernard (CERN), Jean-Paul Lamboy (CERN), Nicolas Guillotin (CERN), Benoit Chabaud (Grenoble Uni), and Gregory Garde (CNRS). CERN has a unique cryogenic facility in hall SM18, consisting of 21 liquid-helium-cooled test stations. While this equipment was, of course, designed for testing parts of CERN's acce...
Thresholds of ion turbulence in tokamaks
International Nuclear Information System (INIS)
Garbet, X.; Laurent, L.; Mourgues, F.; Roubin, J.P.; Samain, A.; Zou, X.L.
1991-01-01
The linear thresholds of ionic turbulence are numerically calculated for the Tokamaks JET and TORE SUPRA. It is proved that the stability domain at η i >0 is determined by trapped ion modes and is characterized by η i ≥1 and a threshold L Ti /R of order (0.2/0.3)/(1+T i /T e ). The latter value is significantly smaller than what has been previously predicted. Experimental temperature profiles in heated discharges are usually marginal with respect to this criterium. It is also shown that the eigenmodes are low frequency, low wavenumber ballooned modes, which may produce a very large transport once the threshold ion temperature gradient is reached
International Nuclear Information System (INIS)
Lin, Z; Rewoldt, G; Ethier, S; Hahm, T S; Lee, W W; Lewandowski, J L V; Nishimura, Y; Wang, W X
2005-01-01
Recent progress in gyrokinetic particle-in-cell simulations of turbulent plasmas using the gyrokinetic toroidal code (GTC) is surveyed. In particular, recent results for electron temperature gradient (ETG) modes and their resulting transport are presented. Also, turbulence spreading, and the effects of the parallel nonlinearity, are described. The GTC code has also been generalized for non-circular plasma cross-section, and initial results are presented. In addition, two distinct methods of generalizing the GTC code to be electromagnetic are described, along with preliminary results. Finally, a related code, GTC-Neo, for calculating neoclassical fluxes, electric fields, and velocities, are described
Homogeneous wave turbulence driven by tidal flows
Favier, B.; Le Reun, T.; Barker, A.; Le Bars, M.
2017-12-01
When a moon orbits around a planet, the rotation of the induced tidal bulge drives a homogeneous, periodic, large-scale flow. The combination of such an excitation with the rotating motion of the planet has been shown to drive parametric resonance of a pair of inertial waves in a mechanism called the elliptical instability. Geophysical fluid layers can also be stratified: this is the case for instance of the Earth's oceans and, as suggested by several studies, of the upper part of the Earth's liquid Outer Core. We thus investigate the stability of a rotating and stratified layer undergoing tidal distortion in the limit where either rotation or stratification is dominant. We show that the periodic tidal flow drives a parametric subharmonic resonance of inertial (resp. internal) waves in the rotating (resp. stratified) case. The instability saturates into a wave turbulence pervading the whole fluid layer. In such a state, the instability mechanism conveys the tidal energy from the large scale tidal flow to the resonant modes, which then feed a succession of triadic resonances also generating small spatial scales. In the rotating case, we observe a kinetic energy spectrum with a k-2 slope for which the Coriolis force is dominant at all spatial scales. In the stratified case, where the timescale separation is increased between the tidal excitation and the Brunt-Väisälä frequencies, the temporal spectrum decays with a ω-2 power law up to the cut-off frequency beyond which waves do not exist. This result is reminiscent of the Garrett and Munk spectrum measured in the oceans and theoretically described as a manifestation of internal wave turbulence. In addition to revealing an instability driving homogeneous turbulence in geophysical fluid layers, our approach is also an efficient numerical tool to investigate the possibly universal properties of wave turbulence in a geophysical context.
International Nuclear Information System (INIS)
Gilmore, Mark Allen
2017-01-01
Turbulence, and turbulence-driven transport are ubiquitous in magnetically confined plasmas, where there is an intimate relationship between turbulence, transport, instability driving mechanisms (such as gradients), plasma flows, and flow shear. Though many of the detailed physics of the interrelationship between turbulence, transport, drive mechanisms, and flow remain unclear, there have been many demonstrations that transport and/or turbulence can be suppressed or reduced via manipulations of plasma flow profiles. This is well known in magnetic fusion plasmas [e.g., high confinement mode (H-mode) and internal transport barriers (ITB's)], and has also been demonstrated in laboratory plasmas. However, it may be that the levels of particle transport obtained in such cases [e.g. H-mode, ITB's] are actually lower than is desirable for a practical fusion device. Ideally, one would be able to actively feedback control the turbulent transport, via manipulation of the flow profiles. The purpose of this research was to investigate the feasibility of using both advanced model-based control algorithms, as well as non-model-based algorithms, to control cross-field turbulence-driven particle transport through appropriate manipulation of radial plasma flow profiles. The University of New Mexico was responsible for the experimental portion of the project, while our collaborators at the University of Montana provided plasma transport modeling, and collaborators at Lehigh University developed and explored control methods.
Polar spacecraft observations of the turbulent outer cusp/magnetopause boundary layer of Earth
Directory of Open Access Journals (Sweden)
J. S. Pickett
1999-01-01
Full Text Available The orbit of the Polar spacecraft has been ideally suited for studying the turbulent region of the cusp that is located near or just outside the magnetopause current sheet at 7-9 RE. The wave data obtained in this region show that electromagnetic turbulence is dominant in the frequency range 1-10 Hz. The waves responsible for this turbulence usually propagate perpendicular to the local magnetic field and have an index of refraction that generally falls between the estimated cold plasma theoretical values of the electromagnetic lower hybrid and whistler modes and may be composed of both modes in concert with kinetic Alfvén waves and/or fast magnetosonic waves. Fourier spectra of the higher frequency wave data also show the electromagnetic turbulence at frequencies up to and near the electron cyclotron frequency. This higher frequency electromagnetic turbulence is most likely associated with whistler mode waves. The lower hybrid drift and current gradient instabilities are suggested as possible mechanisms for producing the turbulence. The plasma and field environment of this turbulent region is examined and found to be extremely complex. Some of the wave activity is associated with processes occurring locally, such as changes in the DC magnetic field, while others are associated with solar wind and interplanetary magnetic field changes.
Polar Spacecraft Observations of the Turbulent Outer Cusp/Magnetopause Boundary Layer of Earth
Pickett, J. S.; Menietti, J. D.; Dowell, J. H.; Gurnett, D. A.; Scudder, J. D.
1999-01-01
The orbit of the Polar spacecraft has been ideally suited for studying the turbulent region of the cusp that is located near or just outside the magnetopause current sheet at 7-9 R(sub E). The wave data obtained in this region show that electromagnetic turbulence is dominant in the frequency range 1-10 Hz. The waves responsible for this turbulence usually propagate perpendicular to the local magnetic field and have an index of refraction that generally falls between the estimated cold plasma theoretical values of the electromagnetic lower hybrid and whistler modes and may be composed of both modes in concert with kinetic Alfven waves and/or fast magnetosonic waves. Fourier spectra of the higher frequency wave data also show the electromagnetic turbulence at frequencies up to and near the electron cyclotron frequency. This higher frequency electromagnetic turbulence is most likely associated with whistler mode waves. The lower hybrid drift and current gradient instabilities are suggested as possible mechanisms for producing the turbulence. The plasma and field environment of this turbulent region is examined and found to be extremely complex. Some of the wave activity is associated with processes occurring locally, such as changes in the DC magnetic field, while others are associated with solar wind and interplanetary magnetic field changes.
Energy Technology Data Exchange (ETDEWEB)
Gilmore, Mark Allen [Univ. of New Mexico, Albuquerque, NM (United States)
2017-02-05
Turbulence, and turbulence-driven transport are ubiquitous in magnetically confined plasmas, where there is an intimate relationship between turbulence, transport, instability driving mechanisms (such as gradients), plasma flows, and flow shear. Though many of the detailed physics of the interrelationship between turbulence, transport, drive mechanisms, and flow remain unclear, there have been many demonstrations that transport and/or turbulence can be suppressed or reduced via manipulations of plasma flow profiles. This is well known in magnetic fusion plasmas [e.g., high confinement mode (H-mode) and internal transport barriers (ITB’s)], and has also been demonstrated in laboratory plasmas. However, it may be that the levels of particle transport obtained in such cases [e.g. H-mode, ITB’s] are actually lower than is desirable for a practical fusion device. Ideally, one would be able to actively feedback control the turbulent transport, via manipulation of the flow profiles. The purpose of this research was to investigate the feasibility of using both advanced model-based control algorithms, as well as non-model-based algorithms, to control cross-field turbulence-driven particle transport through appropriate manipulation of radial plasma flow profiles. The University of New Mexico was responsible for the experimental portion of the project, while our collaborators at the University of Montana provided plasma transport modeling, and collaborators at Lehigh University developed and explored control methods.
Suppression of turbulent resistivity in turbulent Couette flow
Si, Jiahe; Colgate, Stirling A.; Sonnenfeld, Richard G.; Nornberg, Mark D.; Li, Hui; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe
2015-07-01
Turbulent transport in rapidly rotating shear flow very efficiently transports angular momentum, a critical feature of instabilities responsible both for the dynamics of accretion disks and the turbulent power dissipation in a centrifuge. Turbulent mixing can efficiently transport other quantities like heat and even magnetic flux by enhanced diffusion. This enhancement is particularly evident in homogeneous, isotropic turbulent flows of liquid metals. In the New Mexico dynamo experiment, the effective resistivity is measured using both differential rotation and pulsed magnetic field decay to demonstrate that at very high Reynolds number rotating shear flow can be described entirely by mean flow induction with very little contribution from correlated velocity fluctuations.
Suppression of turbulent resistivity in turbulent Couette flow
Energy Technology Data Exchange (ETDEWEB)
Si, Jiahe, E-mail: jsi@nmt.edu; Sonnenfeld, Richard G.; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe [New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801 (United States); Colgate, Stirling A.; Li, Hui [Los Alamos National Laboratory, Los Alamos, New Mexico 87544 (United States); Nornberg, Mark D. [University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)
2015-07-15
Turbulent transport in rapidly rotating shear flow very efficiently transports angular momentum, a critical feature of instabilities responsible both for the dynamics of accretion disks and the turbulent power dissipation in a centrifuge. Turbulent mixing can efficiently transport other quantities like heat and even magnetic flux by enhanced diffusion. This enhancement is particularly evident in homogeneous, isotropic turbulent flows of liquid metals. In the New Mexico dynamo experiment, the effective resistivity is measured using both differential rotation and pulsed magnetic field decay to demonstrate that at very high Reynolds number rotating shear flow can be described entirely by mean flow induction with very little contribution from correlated velocity fluctuations.
Suppression of turbulent resistivity in turbulent Couette flow
International Nuclear Information System (INIS)
Si, Jiahe; Sonnenfeld, Richard G.; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe; Colgate, Stirling A.; Li, Hui; Nornberg, Mark D.
2015-01-01
Turbulent transport in rapidly rotating shear flow very efficiently transports angular momentum, a critical feature of instabilities responsible both for the dynamics of accretion disks and the turbulent power dissipation in a centrifuge. Turbulent mixing can efficiently transport other quantities like heat and even magnetic flux by enhanced diffusion. This enhancement is particularly evident in homogeneous, isotropic turbulent flows of liquid metals. In the New Mexico dynamo experiment, the effective resistivity is measured using both differential rotation and pulsed magnetic field decay to demonstrate that at very high Reynolds number rotating shear flow can be described entirely by mean flow induction with very little contribution from correlated velocity fluctuations
Turbulence and fossil turbulence lead to life in the universe
International Nuclear Information System (INIS)
Gibson, Carl H
2013-01-01
Turbulence is defined as an eddy-like state of fluid motion where the inertial-vortex forces of the eddies are larger than all the other forces that tend to damp the eddies out. Fossil turbulence is a perturbation produced by turbulence that persists after the fluid ceases to be turbulent at the scale of the perturbation. Because vorticity is produced at small scales, turbulence must cascade from small scales to large, providing a consistent physical basis for Kolmogorovian universal similarity laws. Oceanic and astrophysical mixing and diffusion are dominated by fossil turbulence and fossil turbulent waves. Observations from space telescopes show turbulence and vorticity existed in the beginning of the universe and that their fossils persist. Fossils of big bang turbulence include spin and the dark matter of galaxies: clumps of ∼10 12 frozen hydrogen planets that make globular star clusters as seen by infrared and microwave space telescopes. When the planets were hot gas, they hosted the formation of life in a cosmic soup of hot-water oceans as they merged to form the first stars and chemicals. Because spontaneous life formation according to the standard cosmological model is virtually impossible, the existence of life falsifies the standard cosmological model. (paper)
Directory of Open Access Journals (Sweden)
Fausto Borém
2010-12-01
Full Text Available Estudo de caso sobre Cannon de Hermeto Pascoal, obra para flauta, humming na flauta e sons pré-gravados, planejada como uma sessão espírita musical e gravada pelo compositor no disco Slaves Mass (PASCOAL, 1977. A partir do desenho artístico de uma pauta espiralada na capa interna do mesmo LP (PASCOAL e PEREIRA, 1977 e de uma transcrição baseada na faixa gravada, a partitura da obra foi detalhadamente reconstituída e editada (PASCOAL e BORÉM, 2010; incluída neste volume de Per Musi às p.80-82. A combinação das análises formal, escalar e proporcional da partitura e seu cruzamento com a análise espectral da gravação revelam grande unidade e uma íntima relação entre os conteúdos musicais e extra-musicais da obra, na qual elementos opostos dialogam: a improvisação e as camadas de superposição de sons pré-gravados, a sonoridade acústica e os sons manipulados, a performance individual e a coletiva, a estabilidade e a instabilidade modal, as linguagens popular (embolada, jazz modal, free jazz e erudita (música concreta, atonalismo, cadenza, recitativo, os mundos terreno e espiritual. Apresenta também, em primeira mão, a abordagem analítica do "continuum separação-fusão paradoxal" da obra, a partir de ferramenta etnomusicológica criada e realizada por COSTA-LIMA NETO (2009. Inclui uma contextualização do papel da religião na música do "mago" multi-instrumentista, arranjador e compositor da música popular brasileira.Case study on Cannon by Brazilian composer, arranger and multi-instrumentalist Hermeto Pascoal, a work for flute, flute humming and pre-recorded sounds, designed as a musical spiritism session and included in the LP Slaves Mass (PASCOAL, 1977. Departing from an artistic drawing of a music staff spiral included in the internal covers of the same LP (PASCOAL e PEREIRA, 1977 and a transcription based on the listening of the track in the same disc, the score of the work was reconstituted and edited in detail
Comparison between measured and predicted turbulence frequency spectra in ITG and TEM regimes
Citrin, J.; Arnichand, H.; Bernardo, J.; Bourdelle, C.; Garbet, X.; Jenko, F.; Hacquin, S.; Puschel, M. J.; Sabot, R.
2017-01-01
The observation of distinct peaks in tokamak core reflectometry measurements—named quasi-coherent-modes (QCMs)—are identified as a signature of trapped-electron-mode (TEM) turbulence (Arnichand et al 2016 Plasma Phys. Control. Fusion 58 014037). This phenomenon is investigated with detailed linear
Bruno, Roberto
2016-01-01
This book provides an overview of solar wind turbulence from both the theoretical and observational perspective. It argues that the interplanetary medium offers the best opportunity to directly study turbulent fluctuations in collisionless plasmas. In fact, during expansion, the solar wind evolves towards a state characterized by large-amplitude fluctuations in all observed parameters, which resembles, at least at large scales, the well-known hydrodynamic turbulence. This text starts with historical references to past observations and experiments on turbulent flows. It then introduces the Navier-Stokes equations for a magnetized plasma whose low-frequency turbulence evolution is described within the framework of the MHD approximation. It also considers the scaling of plasma and magnetic field fluctuations and the study of nonlinear energy cascades within the same framework. It reports observations of turbulence in the ecliptic and at high latitude, treating Alfvénic and compressive fluctuations separately in...
4th European Turbulence Conference
1993-01-01
The European Turbulence Conferences have been organized under the auspices of the European Mechanics Committee (Euromech) to provide a forum for discussion and exchange of recent and new results in the field of turbulence. The first conference was organized in Lyon in 1986 with 152 participants. The second and third conferences were held in Berlin (1988) and Stockholm (1990) with 165 and 172 participants respectively. The fourth was organized in Delft from 30 June to 3 July 1992 by the J.M. Burgers Centre. There were 214 participants from 22 countries. This steadily growing number of participants demonstrates both the success and need for this type of conference. The main topics of the Fourth European Turbulence Conference were: Dynamical Systems and Transition; Statistical Physics and Turbulence; Experiments and Novel Experimental Techniques; Particles and Bubbles in Turbulence; Simulation Methods; Coherent Structures; Turbulence Modelling and Compressibility Effects. In addition a special session was held o...
Comparison of higher order modes damping techniques for 800 MHz single cell superconducting cavities
Shashkov, Ya. V.; Sobenin, N. P.; Petrushina, I. I.; Zobov, M. M.
2014-12-01
At present, applications of 800 MHz harmonic cavities in both bunch lengthening and shortening regimes are under consideration and discussion in the framework of the High Luminosity LHC project. In this paper we study electromagnetic characteristics of high order modes (HOMs) for a single cell 800 MHz superconducting cavity and arrays of such cavities connected by drifts tubes. Different techniques for the HOMs damping such as beam pipe grooves, coaxial-notch loads, fluted beam pipes etc. are investigated and compared. The influence of the sizes and geometry of the drift tubes on the HOMs damping is analyzed. The problems of a multipacting discharge in the considered structures are discussed and the operating frequency detuning due to the Lorentz force is evaluated.
Comparison of higher order modes damping techniques for 800 MHz single cell superconducting cavities
Energy Technology Data Exchange (ETDEWEB)
Shashkov, Ya.V., E-mail: shashkovyv@mail.ru [National Research Nuclear University MEPhI, Moscow (Russian Federation); Sobenin, N.P.; Petrushina, I.I. [National Research Nuclear University MEPhI, Moscow (Russian Federation); Zobov, M.M. [Laboratori Nazionali di Frascati INFN, Rome (Italy)
2014-12-11
At present, applications of 800 MHz harmonic cavities in both bunch lengthening and shortening regimes are under consideration and discussion in the framework of the High Luminosity LHC project. In this paper we study electromagnetic characteristics of high order modes (HOMs) for a single cell 800 MHz superconducting cavity and arrays of such cavities connected by drifts tubes. Different techniques for the HOMs damping such as beam pipe grooves, coaxial-notch loads, fluted beam pipes etc. are investigated and compared. The influence of the sizes and geometry of the drift tubes on the HOMs damping is analyzed. The problems of a multipacting discharge in the considered structures are discussed and the operating frequency detuning due to the Lorentz force is evaluated.
Turbulence simulations of X point physics on the L-H transitions
International Nuclear Information System (INIS)
Xu, X.Q.; Cohen, R.H.; Nevins, W.M.
2001-01-01
We show that the resistive X-point mode is the dominant mode in boundary plasmas in X-point divertor geometry. The poloidal fluctuation phase velocity from the simulation results of the resistive X-point turbulence shows experimentally measured structure across separatrix in many fusion devices. The fluctuation phase velocity is larger than ExB velocity both in L and H mode phases. We also demonstrate that there is a strong poloidal asymmetry of particle flux in the proximity of the separatrix. Turbulence suppression in the L-H transition results when sources of energy and particles drive sufficient gradients as in the experiments. (author)
International Nuclear Information System (INIS)
Courant, E.D.; Ruth, R.D.; Wang, J.M.
1979-01-01
The name Tacoma refers to the Tacoma Narrows Bridge which collapsed on November 8, 1940 due to massive oscillations caused by high winds. One of the destructive modes was a torsion mode which was excited by transverse wind, a dipole force, and continued until the bridge collapsed. The name is used to refer to a coherent mode of oscillation of a spectrum of oscillators in which the amplitude vs frequency graph contains one node, where the node occurs near the driving frequency and a ω is not symmetric about zero. When this result is applied to vertical instabilities in coasting beams, it implies the existence of a coherent skew quadrupole moment, Q/sub xy/, whenever a coherent dipole oscillation exists
International Nuclear Information System (INIS)
Courant, E.D.; Ruth, R.D.; Wang, J.M.
1979-01-01
The name Tacoma refers to the Tacoma Narrows Bridge which collapsed on November 8, 1940 due to massive oscillations caused by high winds. One of the destructive modes was a torsion mode which was excited by transverse wind, a dipole force, and continued until the bridge collapsed. The name is used to refer to a coherent mode of oscillation of a spectrum of oscillators in which the amplitude vs frequency graph contains one node, where the node occurs near the driving frequency and a(ω) is not symmetric about zero. When this result is applied to vertical instabilities in coasting beams, it implies the existence of a coherent skew quadrupole moment, whenever a coherent dipole oscillation exists
2016-06-23
AFRL-AFOSR-VA-TR-2016-0277 Experimental Investigation of Turbulence-Chemistry Interaction in High- Reynolds -Number Turbulent Partially Premixed...4. TITLE AND SUBTITLE [U] Experimental investigation of turbulence-chemistry interaction in high- Reynolds -number 5a. CONTRACT NUMBER turbulent...for public release Final Report: Experimental investigation of turbulence-chemistry interaction in high- Reynolds -number turbulent partially premixed
Wave turbulence in magnetized plasmas
Directory of Open Access Journals (Sweden)
S. Galtier
2009-02-01
Full Text Available The paper reviews the recent progress on wave turbulence for magnetized plasmas (MHD, Hall MHD and electron MHD in the incompressible and compressible cases. The emphasis is made on homogeneous and anisotropic turbulence which usually provides the best theoretical framework to investigate space and laboratory plasmas. The solar wind and the coronal heating problems are presented as two examples of application of anisotropic wave turbulence. The most important results of wave turbulence are reported and discussed in the context of natural and simulated magnetized plasmas. Important issues and possible spurious interpretations are also discussed.
Direct numerical simulation of turbulent flow with an impedance condition
Olivetti, Simone; Sandberg, Richard D.; Tester, Brian J.
2015-05-01
DNS solutions for a pipe/jet configuration are re-computed with the pipe alone to investigate suppression of previously identified internal noise source(s) with an acoustic liner, using a time domain acoustic liner model developed by Tam and Auriault (AIAA Journal, 34 (1996) 913-917). Liner design parameters are chosen to achieve up to 30 dB attenuation of the broadband pressure field over the pipe length without affecting the velocity field statistics. To understand the effect of the liner on the acoustic and turbulent components of the unsteady wall pressure, an azimuthal/axial Fourier transform is applied and the acoustic and turbulent wavenumber regimes clearly identified. It is found that the spectral component occupying the turbulent wavenumber range is unaffected by the liner whereas the acoustic wavenumber components are strongly attenuated, with individual radial modes being evident as each cuts on with increasing Strouhal number.
Theory of ion-temperature-gradient-driven turbulence in tokamaks
International Nuclear Information System (INIS)
Lee, G.S.; Diamond, P.H.
1986-01-01
An analytic theory of ion-temperature-gradient-driven turbulence in tokamaks is presented. Energy-conserving, renormalized spectrum equations are derived and solved in order to obtain the spectra of stationary ion-temperature-gradient-driven turbulence. Corrections to mixing-length estimates are calculated explicitly. The resulting anomalous ion thermal diffusivity chi/sub i/ = 0.4[(π/2)ln(1 + eta/sub i/)] 2 [(1 + eta/sub i/)/tau] 2 rho/sub s/ 2 c/sub s//L/sub s/ is derived and is found to be consistent with experimentally-deduced thermal diffusivities. The associated electron thermal diffusivity and particle and heat-pinch velocities are also calculated. The effect of impurity gradients on saturated ion-temperature-gradient-driven turbulence is discussed and a related explanation of density profile steepening during Z-mode operation is proposed. 35 refs., 4 figs
Spectra of turbulent static pressure fluctuations in jet mixing layers
Jones, B. G.; Adrian, R. J.; Nithianandan, C. K.; Planchon, H. P., Jr.
1977-01-01
Spectral similarity laws are derived for the power spectra of turbulent static pressure fluctuations by application of dimensional analysis in the limit of large turbulent Reynolds number. The theory predicts that pressure spectra are generated by three distinct types of interaction in the velocity fields: a fourth order interaction between fluctuating velocities, an interaction between the first order mean shear and the third order velocity fluctuations, and an interaction between the second order mean shear rate and the second order fluctuating velocity. Measurements of one-dimensional power spectra of the turbulent static pressure fluctuations in the driven mixing layer of a subsonic, circular jet are presented, and the spectra are examined for evidence of spectral similarity. Spectral similarity is found for the low wavenumber range when the large scale flow on the centerline of the mixing layer is self-preserving. The data are also consistent with the existence of universal inertial subranges for the spectra of each interaction mode.
Laboratory simulation of atmospheric turbulence induced optical wavefront distortion
Taylor, Travis Shane
1999-11-01
Many creative approaches have been taken in the past for simulating the effect that atmospheric turbulence has on optical beams. Most of the experimental architectures have been complicated and consisted of many optical elements as well as moving components. These techniques have shown a modicum of success; however, they are not completely controllable or predictable. A benchtop technique for experimentally producing one important effect that atmospheric turbulence has on optical beams (phase distortion) is presented here. The system is completely controllable and predictable while accurately representing the statistical nature of the problem. Previous experimentation in optical processing through turbulent media has demonstrated that optical wavefront distortions can be produced via spatial light modulating (SLM) devices, and most turbulence models and experimental results indicate that turbulence can be represented as a phase fluctuation. The amplitude distributions in the resulting far field are primarily due to propagation of the phase. Operating a liquid crystal television (LCTV) in the ``phase- mostly'' mode, a phase fluctuation type model for turbulence is utilized in the present investigation, and a real-time experiment for demonstrating the effects was constructed. For an optical system to simulate optical wavefront distortions due to atmospheric turbulence, the following are required: (1)An optical element that modulates the phasefront of an optical beam (2)A model and a technique for generating spatially correlated turbulence simulating distributions (3)Hardware and software for displaying and manipulating the information addressing the optical phase modulation device The LCTV is ideal for this application. When operated in the ``phase-mostly'' mode some LCTVs can modulate the phasefront of an optical beam by as much as 2π and an algorithm for generating spatially correlated phase screens can be constructed via mathematical modeling software such as
DEFF Research Database (Denmark)
Jakobsen, K. P.; Burcharth, H. F.; Ibsen, Lars Bo
1999-01-01
The present appendix contains the derivation of ten different limit state equations divided on three different failure modes. Five of the limit state equations can be used independently of the characteristics of the subsoil, whereas the remaining five can be used for either drained or undrained s...
Directory of Open Access Journals (Sweden)
H. Z. Baumert
2009-03-01
Full Text Available This paper extends a turbulence closure-like model for stably stratified flows into a new dynamic domain in which turbulence is generated by internal gravity waves rather than mean shear. The model turbulent kinetic energy (TKE, K balance, its first equation, incorporates a term for the energy transfer from internal waves to turbulence. This energy source is in addition to the traditional shear production. The second variable of the new two-equation model is the turbulent enstrophy (Ω. Compared to the traditional shear-only case, the Ω-equation is modified to account for the effect of the waves on the turbulence time and space scales. This modification is based on the assumption of a non-zero constant flux Richardson number in the limit of vanishing mean shear when turbulence is produced exclusively by internal waves. This paper is part 1 of a continuing theoretical development. It accounts for mean shear- and internal wave-driven mixing only in the two limits of mean shear and no waves and waves but no mean shear, respectively.
The new model reproduces the wave-turbulence transition analyzed by D'Asaro and Lien (2000b. At small energy density E of the internal wave field, the turbulent dissipation rate (ε scales like ε~E^{2}. This is what is observed in the deep sea. With increasing E, after the wave-turbulence transition has been passed, the scaling changes to ε~E^{1}. This is observed, for example, in the highly energetic tidal flow near a sill in Knight Inlet. The new model further exhibits a turbulent length scale proportional to the Ozmidov scale, as observed in the ocean, and predicts the ratio between the turbulent Thorpe and Ozmidov length scales well within the range observed in the ocean.
Input-output analysis of high-speed turbulent jet noise
Jeun, Jinah; Nichols, Joseph W.
2015-11-01
We apply input-output analysis to predict and understand the aeroacoustics of high-speed isothermal turbulent jets. We consider axisymmetric linear perturbations about Reynolds-averaged Navier-Stokes solutions of ideally expanded turbulent jets with Mach numbers 0 . 6 parabolized stability equations (PSE), and this mode dominates the response. For subsonic jets, however, the singular values indicate that the contributions of suboptimal modes to noise generation are nearly equal to that of the optimal mode, explaining why PSE misses some of the farfield sound in this case. Finally, high-fidelity large eddy simulation (LES) is used to assess the prevalence of suboptimal modes in the unsteady data. By projecting LES data onto the corresponding input modes, the weighted gain of each mode is examined.
Theoretical studies of turbulence and anomalous transport in toroidal confinement devices
International Nuclear Information System (INIS)
Terry, P.W.
1993-01-01
The research performed under this grant has focused on key issues with respect to turbulence and transport in toroidal confinement devices. Progress and publications in these areas are summarized in this report. This work includes analytical and numerical studies of spectral energy transfer and the saturation dynamics and transport of dissipative and collisionless trapped electron turbulence, the role of flow curvature in L-H mode transition physics, fully nonlinear calculations of the anomalous particle transport from the ion mixing mode, and the development of a theory for the drift wave frequency spectrum. Novel aspects of this work include an elucidation of the role of nonlinear frequency shifts in producing nonstationary saturated states, an identification of reverse and non-conserved flows in Hasegawa-Mima turbulence, and a description of the way incoherent emission affects the frequency of turbulent fluctuations
Gyrokinetic Simulations of Solar Wind Turbulence from Ion to Electron Scales
International Nuclear Information System (INIS)
Howes, G. G.; TenBarge, J. M.; Dorland, W.; Numata, R.; Quataert, E.; Schekochihin, A. A.; Tatsuno, T.
2011-01-01
A three-dimensional, nonlinear gyrokinetic simulation of plasma turbulence resolving scales from the ion to electron gyroradius with a realistic mass ratio is presented, where all damping is provided by resolved physical mechanisms. The resulting energy spectra are quantitatively consistent with a magnetic power spectrum scaling of k -2.8 as observed in in situ spacecraft measurements of the 'dissipation range' of solar wind turbulence. Despite the strongly nonlinear nature of the turbulence, the linear kinetic Alfven wave mode quantitatively describes the polarization of the turbulent fluctuations. The collisional ion heating is measured at subion-Larmor radius scales, which provides evidence of the ion entropy cascade in an electromagnetic turbulence simulation.
Zhai, Xiaochun; Wu, Songhua; Liu, Bingyi
2017-06-12
Four field experiments based on Pulsed Coherent Doppler Lidar with different surface roughness have been carried out in 2013-2015 to study the turbulent wind field in the vicinity of operating wind turbine in the onshore and offshore wind parks. The turbulence characteristics in ambient atmosphere and wake area was analyzed using transverse structure function based on Plane Position Indicator scanning mode. An automatic wake processing procedure was developed to determine the wake velocity deficit by considering the effect of ambient velocity disturbance and wake meandering with the mean wind direction. It is found that the turbine wake obviously enhances the atmospheric turbulence mixing, and the difference in the correlation of turbulence parameters under different surface roughness is significant. The dependence of wake parameters including the wake velocity deficit and wake length on wind velocity and turbulence intensity are analyzed and compared with other studies, which validates the empirical model and simulation of a turbine wake for various atmosphere conditions.
Gyrokinetic continuum simulations of turbulence in the Texas Helimak
Bernard, T. N.; Shi, E. L.; Hammett, G. W.; Hakim, A.; Taylor, E. I.
2017-10-01
We have used the Gkeyll code to perform 3x-2v full-f gyrokinetic continuum simulations of electrostatic plasma turbulence in the Texas Helimak. The Helimak is an open field-line experiment with magnetic curvature and shear. It is useful for validating numerical codes due to its extensive diagnostics and simple, helical geometry, which is similar to the scrape-off layer region of tokamaks. Interchange and drift-wave modes are the main turbulence mechanisms in the device, and potential biasing is applied to study the effect of velocity shear on turbulence reduction. With Gkeyll, we varied field-line pitch angle and simulated biased and unbiased cases to study different turbulent regimes and turbulence reduction. These are the first kinetic simulations of the Helimak and resulting plasma profiles agree fairly well with experimental data. This research demonstrates Gkeyll's progress towards 5D simulations of the SOL region of fusion devices. Supported by the U.S. DOE SCGSR program under contract DE-SC0014664, the Max-Planck/Princeton Center for Plasma Physics, the SciDAC Center for the Study of Plasma Microturbulence, and DOE contract DE-AC02-09CH11466.
Effect of free-stream turbulence on boundary layer transition.
Goldstein, M E
2014-07-28
This paper is concerned with the transition to turbulence in flat plate boundary layers due to moderately high levels of free-stream turbulence. The turbulence is assumed to be generated by an (idealized) grid and matched asymptotic expansions are used to analyse the resulting flow over a finite thickness flat plate located in the downstream region. The characteristic Reynolds number Rλ based on the mesh size λ and free-stream velocity is assumed to be large, and the turbulence intensity ε is assumed to be small. The asymptotic flow structure is discussed for the generic case where the turbulence Reynolds number εRλ and the plate thickness and are held fixed (at O(1) and O(λ), respectively) in the limit as [Formula: see text] and ε→0. But various limiting cases are considered in order to explain the relevant transition mechanisms. It is argued that there are two types of streak-like structures that can play a role in the transition process: (i) those that appear in the downstream region and are generated by streamwise vorticity in upstream flow and (ii) those that are concentrated near the leading edge and are generated by plate normal vorticity in upstream flow. The former are relatively unaffected by leading edge geometry and are usually referred to as Klebanoff modes while the latter are strongly affected by leading edge geometry and are more streamwise vortex-like in appearance. © 2014 The Author(s) Published by the Royal Society. All rights reserved.
Excitation mechanisms for Jovian seismic modes
Markham, Steve; Stevenson, Dave
2018-05-01
Recent (2011) results from the Nice Observatory indicate the existence of global seismic modes on Jupiter in the frequency range between 0.7 and 1.5 mHz with amplitudes of tens of cm/s. Currently, the driving force behind these modes is a mystery; the measured amplitudes are many orders of magnitude larger than anticipated based on theory analogous to helioseismology (that is, turbulent convection as a source of stochastic excitation). One of the most promising hypotheses is that these modes are driven by Jovian storms. This work constructs a framework to analytically model the expected equilibrium normal mode amplitudes arising from convective columns in storms. We also place rough constraints on Jupiter's seismic modal quality factor. Using this model, neither meteor strikes, turbulent convection, nor water storms can feasibly excite the order of magnitude of observed amplitudes. Next we speculate about the potential role of rock storms deeper in Jupiter's atmosphere, because the rock storms' expected energy scales make them promising candidates to be the chief source of excitation for Jovian seismic modes, based on simple scaling arguments. We also suggest some general trends in the expected partition of energy between different frequency modes. Finally we supply some commentary on potential applications to gravity, Juno, Cassini and Saturn, and future missions to Uranus and Neptune.
Large Eddy Simulation of turbulence
International Nuclear Information System (INIS)
Poullet, P.; Sancandi, M.
1994-12-01
Results of Large Eddy Simulation of 3D isotropic homogeneous turbulent flows are presented. A computer code developed on Connexion Machine (CM5) has allowed to compare two turbulent viscosity models (Smagorinsky and structure function). The numerical scheme influence on the energy density spectrum is also studied [fr
Advances in compressible turbulent mixing
International Nuclear Information System (INIS)
Dannevik, W.P.; Buckingham, A.C.; Leith, C.E.
1992-01-01
This volume includes some recent additions to original material prepared for the Princeton International Workshop on the Physics of Compressible Turbulent Mixing, held in 1988. Workshop participants were asked to emphasize the physics of the compressible mixing process rather than measurement techniques or computational methods. Actual experimental results and their meaning were given precedence over discussions of new diagnostic developments. Theoretical interpretations and understanding were stressed rather than the exposition of new analytical model developments or advances in numerical procedures. By design, compressibility influences on turbulent mixing were discussed--almost exclusively--from the perspective of supersonic flow field studies. The papers are arranged in three topical categories: Foundations, Vortical Domination, and Strongly Coupled Compressibility. The Foundations category is a collection of seminal studies that connect current study in compressible turbulent mixing with compressible, high-speed turbulent flow research that almost vanished about two decades ago. A number of contributions are included on flow instability initiation, evolution, and transition between the states of unstable flow onset through those descriptive of fully developed turbulence. The Vortical Domination category includes theoretical and experimental studies of coherent structures, vortex pairing, vortex-dynamics-influenced pressure focusing. In the Strongly Coupled Compressibility category the organizers included the high-speed turbulent flow investigations in which the interaction of shock waves could be considered an important source for production of new turbulence or for the enhancement of pre-existing turbulence. Individual papers are processed separately
Interstellar turbulence and shock waves
International Nuclear Information System (INIS)
Bykov, A.M.
1982-01-01
Random deflections of shock fronts propagated through the turbulent interstellar medium can produce the strong electro-density fluctuations on scales l> or approx. =10 13 cm inferred from pulsar radio scintillations. The development of turbulence in the hot-phase ISM is discussed
Conditional Eddies in Plasma Turbulence
DEFF Research Database (Denmark)
Johnsen, Helene; Pécseli, Hans; Trulsen, J.
1986-01-01
Conditional structures, or eddies, in turbulent flows are discussed with special attention to electrostatic turbulence in plasmas. The potential variation of these eddies is obtained by sampling the fluctuations only when a certain condition is satisfied in a reference point. The resulting...
Advances in compressible turbulent mixing
Energy Technology Data Exchange (ETDEWEB)
Dannevik, W.P.; Buckingham, A.C.; Leith, C.E. [eds.
1992-01-01
This volume includes some recent additions to original material prepared for the Princeton International Workshop on the Physics of Compressible Turbulent Mixing, held in 1988. Workshop participants were asked to emphasize the physics of the compressible mixing process rather than measurement techniques or computational methods. Actual experimental results and their meaning were given precedence over discussions of new diagnostic developments. Theoretical interpretations and understanding were stressed rather than the exposition of new analytical model developments or advances in numerical procedures. By design, compressibility influences on turbulent mixing were discussed--almost exclusively--from the perspective of supersonic flow field studies. The papers are arranged in three topical categories: Foundations, Vortical Domination, and Strongly Coupled Compressibility. The Foundations category is a collection of seminal studies that connect current study in compressible turbulent mixing with compressible, high-speed turbulent flow research that almost vanished about two decades ago. A number of contributions are included on flow instability initiation, evolution, and transition between the states of unstable flow onset through those descriptive of fully developed turbulence. The Vortical Domination category includes theoretical and experimental studies of coherent structures, vortex pairing, vortex-dynamics-influenced pressure focusing. In the Strongly Coupled Compressibility category the organizers included the high-speed turbulent flow investigations in which the interaction of shock waves could be considered an important source for production of new turbulence or for the enhancement of pre-existing turbulence. Individual papers are processed separately.
2016-12-29
mixture of salt water aerosols, water soluble aerosols and dust aerosols in a size distribution similar to that shown in Figure 1. ANAM represents...sizes and refractive indices. ANAM mode 0 represents dust particles of continental origin, mode 1 represents water - soluble aerosols, whereas modes 2-4...provide data that may be used to generate a map of the turbulent air flow fields in the vicinity of aircraft and aircraft carriers and to
Large eddy simulation on the effect of free-stream turbulence on bypass transition
International Nuclear Information System (INIS)
Xu, Zhengqian; Zhao, Qingjun; Lin, Qizhao; Xu, Jianzhong
2015-01-01
Highlights: • Low-frequency dominant inflow leads to inner instability. • High-frequency mode is indispensable for inner instability. • Low-frequency mode highly affects the transition onset. • High-frequency mode highly affects the transition rate. • The frequency of laminar streaks is comparable with that of turbulent spot. - Abstract: The effect of free-stream turbulence (FST) on bypass transition in a zero-pressure-gradient boundary layer is investigated by means of Large Eddy Simulation (LES). The broadband turbulent inflow is synthesized to validate the feasibility of LES. Both a zero-thickness plate and one with super-ellipse leading-edge are addressed. The calculated Reynolds-averaged fields are compared with experimental data and decent agreement is achieved. Instantaneous fields show the instability occurs in the lifted low-speed streaks similar to earlier DNS results, which can be ascribed to outer mode. Various inflows with bi-/tri-mode interaction are specified to analyze effects of particular frequency mode on the instability pattern and multifarious transition or non-transition scenarios are obtained. Outer instability is observed in the cases with one low-frequency mode and one high-frequency mode inflow as reported by Zaki and Durbin (2005), and with one more high-frequency mode appended. Inner instability is observed in the case with a low-frequency dominant inflow, while the high-frequency mode is indispensable to induce the secondary instability. Furthermore, the results show that the transition onset is highly sensitive to low-frequency mode while the transition rate is highly sensitive to high-frequency mode. Finally, the formational frequency of turbulent spot (FFTS) is counted and the frequency of laminar streaks is demonstrated by spectral analysis
Nondissipative gravitational turbulence
International Nuclear Information System (INIS)
Gurevich, A.V.; Zybin, K.P.
1988-01-01
The nonlinear stage of development of the Jeans instability in a cold nondissipative gravitating gas is considered. It is shown that for a time exceeding the Jeans time a nondissipative gravitational singularity (NGS) is formed in the vicinity of a local density maximum. The NGS is a stationary dynamic structure, the basis of which is the singularity. The density of the gas at the center of the NGS (for r → 0) tends to infinity, and the field potential and the mean velocity of the trapped gas, possess a power singularity. The turbulent state arises as the result of development of the instability in the case of an irregular initial density distribution. It is an hierarchic structure consisting of nested moving NGS of various sizes, the NGS of smaller dimensions being trapped in the field of a NGS of larger dimensions. The scaling relations for each given NGS in this case hold for both the gas density and density of smaller size trapped NGS. A brief comparison with the observational data shows that the real hierarchic structure of the Universe ranging from scales pertaining to spherical stellar clusters up to those of rich galaxy clusters is apparently a developed gravitational turbulence
Ruan, S; Swaminathan, Nedunchezhian; Darbyshire, O
2014-01-01
This study focuses on the modelling of turbulent lifted jet flames using flamelets and presumed PDF approach with interests on both flame lift-off height and flame brush structure. First, flamelet models used to capture contributions from premixed and non-premixed modes to the partially premixed combustion in the lifted jet flame are assessed using a Direct Numerical Simulation (DNS) data for turbulent lifted hydrogen jet flame. The joint PDFs of mixture fraction, Z, and progress ...
Turbulent transport in the MST reversed-field pinch
International Nuclear Information System (INIS)
Rempel, T.D.; Almagri, A.F.; Assadi, S.; Den Hartog, D.J.; Hokin, S.A.; Prager, S.C.; Sarff, J.S.; Shen, W.; Sidikman, K.L.; Spragins, C.W.; Sprott, J.C.; Stoneking, M.R.; Zita, E.J.
1991-11-01
Measurements of edge turbulence and the associated transport are ongoing in the Madison Symmetric Torus (R = 1.5 m, a = 0.52 m) reversed-field pinch using magnetic and electrostatic probes. Magnetic fluctuations are dominated by m = 1 and n ∼ 2R/a tearing modes. Particle losses induced by magnetic field fluctuations have been found to be ambipolar ( parallel B r > = O). Electrostatic fluctuations are broadband and turbulent, with mode widths δm ∼ 3--7 and δn ∼70--150. Particle, parallel current, and energy transport arising from coherent motion with the fluctuating ExB drift has been measured. Particle transport via this channel is comparable to the total particle loss from MST. Energy transport (from phi >/B o ) due to electrostatic fluctuations is relatively small, and parallel current transport (from parallel E chi >/B o ) may be small as well
International Nuclear Information System (INIS)
Blum, Daniel B; Voth, Greg A; Bewley, Gregory P; Bodenschatz, Eberhard; Gibert, Mathieu; Xu Haitao; Gylfason, Ármann; Mydlarski, Laurent; Yeung, P K
2011-01-01
We present a systematic comparison of conditional structure functions in nine turbulent flows. The flows studied include forced isotropic turbulence simulated on a periodic domain, passive grid wind tunnel turbulence in air and in pressurized SF 6 , active grid wind tunnel turbulence (in both synchronous and random driving modes), the flow between counter-rotating discs, oscillating grid turbulence and the flow in the Lagrangian exploration module (in both constant and random driving modes). We compare longitudinal Eulerian second-order structure functions conditioned on the instantaneous large-scale velocity in each flow to assess the ways in which the large scales affect the small scales in a variety of turbulent flows. Structure functions are shown to have larger values when the large-scale velocity significantly deviates from the mean in most flows, suggesting that dependence on the large scales is typical in many turbulent flows. The effects of the large-scale velocity on the structure functions can be quite strong, with the structure function varying by up to a factor of 2 when the large-scale velocity deviates from the mean by ±2 standard deviations. In several flows, the effects of the large-scale velocity are similar at all the length scales we measured, indicating that the large-scale effects are scale independent. In a few flows, the effects of the large-scale velocity are larger on the smallest length scales. (paper)
Sahraoui, Fouad; Goldstein, Melvyn
2008-01-01
Several observations in space plasmas have reported the presence of coherent structures at different plasma scales. Structure formation is believed to be a direct consequence of nonlinear interactions between the plasma modes, which depend strongly on phase synchronization of those modes. Despite this important role of the phases in turbulence, very limited work has been however devoted to study the phases as a potential tracers of nonlinearities in comparison with the wealth of literature on power spectra of turbulence where phases are totally missed. We present a method based on surrogate data to systematically detect coherent structures in turbulent signals. The new method has been applied successfully to magnetosheath turbulence (Sahraoui, Phys. Rev. E, 2008, in press), where the relationship between the identified phase coherence and intermittency (classically identified as non Gaussian tails of the PDFs) as well as the energy cascade has been studied. Here we review the main results obtained in that study and show further applications to small scale solar wind turbulence. Implications of the results on theoretical modelling of space turbulence (applicability of weak/wave turbulence, its validity limits and its connection to intermittency) will be discussed.
Turbulent premixed flames on fractal-grid-generated turbulence
Energy Technology Data Exchange (ETDEWEB)
Soulopoulos, N; Kerl, J; Sponfeldner, T; Beyrau, F; Hardalupas, Y; Taylor, A M K P [Mechanical Engineering Department, Imperial College London, London SW7 2AZ (United Kingdom); Vassilicos, J C, E-mail: ns6@ic.ac.uk [Department of Aeronautics, Imperial College London, London SW7 2AZ (United Kingdom)
2013-12-15
A space-filling, low blockage fractal grid is used as a novel turbulence generator in a premixed turbulent flame stabilized by a rod. The study compares the flame behaviour with a fractal grid to the behaviour when a standard square mesh grid with the same effective mesh size and solidity as the fractal grid is used. The isothermal gas flow turbulence characteristics, including mean flow velocity and rms of velocity fluctuations and Taylor length, were evaluated from hot-wire measurements. The behaviour of the flames was assessed with direct chemiluminescence emission from the flame and high-speed OH-laser-induced fluorescence. The characteristics of the two flames are considered in terms of turbulent flame thickness, local flame curvature and turbulent flame speed. It is found that, for the same flow rate and stoichiometry and at the same distance downstream of the location of the grid, fractal-grid-generated turbulence leads to a more turbulent flame with enhanced burning rate and increased flame surface area. (paper)
Turbulent Fluid Motion 6: Turbulence, Nonlinear Dynamics, and Deterministic Chaos
Deissler, Robert G.
1996-01-01
Several turbulent and nonturbulent solutions of the Navier-Stokes equations are obtained. The unaveraged equations are used numerically in conjunction with tools and concepts from nonlinear dynamics, including time series, phase portraits, Poincare sections, Liapunov exponents, power spectra, and strange attractors. Initially neighboring solutions for a low-Reynolds-number fully developed turbulence are compared. The turbulence is sustained by a nonrandom time-independent external force. The solutions, on the average, separate exponentially with time, having a positive Liapunov exponent. Thus, the turbulence is characterized as chaotic. In a search for solutions which contrast with the turbulent ones, the Reynolds number (or strength of the forcing) is reduced. Several qualitatively different flows are noted. These are, respectively, fully chaotic, complex periodic, weakly chaotic, simple periodic, and fixed-point. Of these, we classify only the fully chaotic flows as turbulent. Those flows have both a positive Liapunov exponent and Poincare sections without pattern. By contrast, the weakly chaotic flows, although having positive Liapunov exponents, have some pattern in their Poincare sections. The fixed-point and periodic flows are nonturbulent, since turbulence, as generally understood, is both time-dependent and aperiodic.
Faraday Wave Turbulence on a Spherical Liquid Shell
Holt, R. Glynn; Trinh, Eugene H.
1996-01-01
Millimeter-radius liquid shells are acoustically levitated in an ultrasonic field. Capillary waves are observed on the shells. At low energies (minimal acoustic amplitude, thick shell) a resonance is observed between the symmetric and antisymmetric thin film oscillation modes. At high energies (high acoustic pressure, thin shell) the shell becomes fully covered with high-amplitude waves. Temporal spectra of scattered light from the shell in this regime exhibit a power-law decay indicative of turbulence.
Effects of q-profile structure on turbulence spreading: A fluctuation intensity transport analysis
Energy Technology Data Exchange (ETDEWEB)
Yi, S.; Kwon, J. M. [National Fusion Research Institute, Eoeun-dong, Yuseong-gu, Daejeon 305-333 (Korea, Republic of); Diamond, P. H. [National Fusion Research Institute, Eoeun-dong, Yuseong-gu, Daejeon 305-333 (Korea, Republic of); Center for Astrophysics and Space Sciences and Department of Physics, University of California San Diego, La Jolla, California 92093-0429 (United States); Hahm, T. S. [Department of Nuclear Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of)
2014-09-15
This paper studies effects of q-profile structure on turbulence spreading. It reports results of numerical experiments using global gyrokinetic simulations. We examine propagation of turbulence, triggered by an identical linear instability in a source region, into an adjacent, linearly stable region with variable q-profile. The numerical experiments are designed so as to separate the physics of turbulence spreading from that of linear stability. The strength of turbulence spreading is measured by the penetration depth of turbulence. Dynamics of spreading are elucidated by fluctuation intensity balance analysis, using a model intensity evolution equation which retains nonlinear diffusion and damping, and linear growth. It is found that turbulence spreading is strongly affected by magnetic shear s, but is hardly altered by the safety factor q itself. There is an optimal range of modest magnetic shear which maximizes turbulence spreading. For high to modest shear values, the spreading is enhanced by the increase of the mode correlation length with decreasing magnetic shear. However, the efficiency of spreading drops for sufficiently low magnetic shear even though the mode correlation length is comparable to that for the case of optimal magnetic shear. The reduction of spreading is attributed to the increase in time required for the requisite nonlinear mode-mode interactions. The effect of increased interaction time dominates that of increased mode correlation length. Our findings of the reduction of spreading and the increase in interaction time at weak magnetic shear are consistent with the well-known benefit of weak or reversed magnetic shear for core confinement enhancement. Weak shear is shown to promote locality, as well as stability.
Sapsis, Themistoklis P; Majda, Andrew J
2013-08-20
A framework for low-order predictive statistical modeling and uncertainty quantification in turbulent dynamical systems is developed here. These reduced-order, modified quasilinear Gaussian (ROMQG) algorithms apply to turbulent dynamical systems in which there is significant linear instability or linear nonnormal dynamics in the unperturbed system and energy-conserving nonlinear interactions that transfer energy from the unstable modes to the stable modes where dissipation occurs, resulting in a statistical steady state; such turbulent dynamical systems are ubiquitous in geophysical and engineering turbulence. The ROMQG method involves constructing a low-order, nonlinear, dynamical system for the mean and covariance statistics in the reduced subspace that has the unperturbed statistics as a stable fixed point and optimally incorporates the indirect effect of non-Gaussian third-order statistics for the unperturbed system in a systematic calibration stage. This calibration procedure is achieved through information involving only the mean and covariance statistics for the unperturbed equilibrium. The performance of the ROMQG algorithm is assessed on two stringent test cases: the 40-mode Lorenz 96 model mimicking midlatitude atmospheric turbulence and two-layer baroclinic models for high-latitude ocean turbulence with over 125,000 degrees of freedom. In the Lorenz 96 model, the ROMQG algorithm with just a single mode captures the transient response to random or deterministic forcing. For the baroclinic ocean turbulence models, the inexpensive ROMQG algorithm with 252 modes, less than 0.2% of the total, captures the nonlinear response of the energy, the heat flux, and even the one-dimensional energy and heat flux spectra.
International Nuclear Information System (INIS)
Gaarde, C.
1985-01-01
An analysis of spectra of (p,n) reactions showed that they were very selective in exciting spin modes. Charge exchange reactions at intermediate energies give important new understanding of the M1-type of excitations and of the spin structure of continuum p spectra in general. In this paper, the author discusses three charge exchange reactions: (p,n); ( 3 H,t); and (d,2p) at several targets. Low-lying states and the Δ region are discussed separately. Finally, the charge exchange reaction with heavy ion beams is briefly discussed. (G.J.P./Auth.)
COMPREHENSIVE GYROKINETIC SIMULATION OF TOKAMAK TURBULENCE AT FINITE RELATIVE GYRORADIUS
International Nuclear Information System (INIS)
WALTZ, R.E.; CANDY, J.; ROSENBLUTH, M.N.
2002-01-01
OAK B202 COMPREHENSIVE GYROKINETIC SIMULATION OF TOKAMAK TURBULENCE AT FINITE RELATIVE GYRORADIUS. A continuum global gyrokinetic code GYRO has been developed to comprehensively simulate turbulent transport in actual experimental profiles and allow direct quantitative comparisons to the experimental transport flows. GYRO not only treats the now standard ion temperature gradient (ITG) mode turbulence, but also treats trapped and passing electrons with collisions and finite beta, and all in real tokamak geometry. Most importantly the code operates at finite relative gyroradius (ρ*) so as to treat the profile shear stabilization effects which break gyroBohm scaling. The code operates in a cyclic flux tube limit which allows only gyroBohm scaling and a noncyclic radial annulus with physical profile variation. The later requires an adaptive source to maintain equilibrium profiles. Simple ITG simulations demonstrate the broken gyroBohm scaling depends on the actual rotational velocity shear rates competing with mode growth rates, direct comprehensive simulations of the DIII-D ρ*-scaled L-mode experiments are presented as a quantitative test of gyrokinetics and the paradigm
3D Electric Waveforms of Solar Wind Turbulence
Kellogg, P. J.; Goetz, K.; Monson, S. J.
2018-01-01
Electric fields provide the major coupling between the turbulence of the solar wind and particles. A large part of the turbulent spectrum of fluctuations in the solar wind is thought to be kinetic Alfvén waves; however, whistlers have recently been found to be important. In this article, we attempt to determine the mode identification of individual waveforms using the three-dimensional antenna system of the SWaves experiments on the STEREO spacecraft. Samples are chosen using waveforms with an apparent periodic structure, selected visually. The short antennas of STEREO respond to density fluctuations and to electric fields. Measurement of four quantities using only three antennas presents a problem. Methods to overcome or to ignore this difficulty are presented. We attempt to decide whether the waveforms correspond to the whistler mode or the Alfvén mode by using the direction of rotation of the signal. Most of the waveforms are so oblique—nearly linearly polarized—that the direction cannot be determined. However, about one third of the waveforms can be identified, and whistlers and Alfvén waves are present in roughly equal numbers. The selected waveforms are very intense but intermittent and are orders of magnitude stronger than the average, yet their accumulated signal accounts for a large fraction of the average. The average, however, is supposed to be the result of a turbulent mixture of many waves, not short coherent events. This presents a puzzle for future work.
Turbulent/non-turbulent interfaces detected in DNS of incompressible turbulent boundary layers
Watanabe, T.; Zhang, X.; Nagata, K.
2018-03-01
The turbulent/non-turbulent interface (TNTI) detected in direct numerical simulations is studied for incompressible, temporally developing turbulent boundary layers at momentum thickness Reynolds number Reθ ≈ 2000. The outer edge of the TNTI layer is detected as an isosurface of the vorticity magnitude with the threshold determined with the dependence of the turbulent volume on a threshold level. The spanwise vorticity magnitude and passive scalar are shown to be good markers of turbulent fluids, where the conditional statistics on a distance from the outer edge of the TNTI layer are almost identical to the ones obtained with the vorticity magnitude. Significant differences are observed for the conditional statistics between the TNTI detected by the kinetic energy and vorticity magnitude. A widely used grid setting determined solely from the wall unit results in an insufficient resolution in a streamwise direction in the outer region, whose influence is found for the geometry of the TNTI and vorticity jump across the TNTI layer. The present results suggest that the grid spacing should be similar for the streamwise and spanwise directions. Comparison of the TNTI layer among different flows requires appropriate normalization of the conditional statistics. Reference quantities of the turbulence near the TNTI layer are obtained with the average of turbulent fluids in the intermittent region. The conditional statistics normalized by the reference turbulence characteristics show good quantitative agreement for the turbulent boundary layer and planar jet when they are plotted against the distance from the outer edge of the TNTI layer divided by the Kolmogorov scale defined for turbulent fluids in the intermittent region.
Enhanced turbulence during the energy quench of disruptions
International Nuclear Information System (INIS)
Remkes, G.J.J.; Schueller, F.C.
1991-01-01
Enhanced electron density fluctuation levels with frequencies in the megahertz range have been observed during the energy quench phase of minor disruptions in the TORTUR Tokamak. The high frequencies of the phenomena indicate that the enhanced transport during the energy quench is caused by turbulence, and not by the coherent low mode number MHD modes themselves, which initiate the disruptions. Both the growth rate and wavelength of the fluctuations increase to such a level that a corresponding diffusivity would increase by two orders of magnitude. This is in good agreement with the observed temperature redistribution. (author)
Weak turbulence theory for the Gross-Pitaevskii equation
International Nuclear Information System (INIS)
Nazarenko, S.; West, R.; Lvov, Y.
2001-01-01
The goal of this paper is to use the ideas developed for the NLSE to derive a weak turbulence theory for a large set of random waves described by the Gross-Pitaevskii equation. An interesting picture emerges even from a naive application of the results already obtained for the NLSE case. Imagine an arbitrary initial excitation; a superposition of modes with energies somewhere in the middle of the potential well. Because of the nonlinear interaction (''collisions'') there is a redistribution of energy E and particles N among the modes. (orig.)
Turbulent deflagrations, autoignitions, and detonations
Bradley, Derek
2012-09-01
Measurements of turbulent burning velocities in fan-stirred explosion bombs show an initial linear increase with the fan speed and RMS turbulent velocity. The line then bends over to form a plateau of high values around the maximum attainable burning velocity. A further increase in fan speed leads to the eventual complete quenching of the flame due to increasing localised extinctions because of the flame stretch rate. The greater the Markstein number, the more readily does flame quenching occur. Flame propagation along a duct closed at one end, with and without baffles to increase the turbulence, is subjected to a one-dimensional analysis. The flame, initiated at the closed end of the long duct, accelerates by the turbulent feedback mechanism, creating a shock wave ahead of it, until the maximum turbulent burning velocity for the mixture is attained. With the confining walls, the mixture is compressed between the flame and the shock plane up to the point where it might autoignite. This can be followed by a deflagration to detonation transition. The maximum shock intensity occurs with the maximum attainable turbulent burning velocity, and this defines the limit for autoignition of the mixture. For more reactive mixtures, autoignition can occur at turbulent burning velocities that are less than the maximum attainable one. Autoignition can be followed by quasi-detonation or fully developed detonation. The stability of ensuing detonations is discussed, along with the conditions that may lead to their extinction. © 2012 by Pleiades Publishing, Ltd.
Comparison of turbulence mitigation algorithms
Kozacik, Stephen T.; Paolini, Aaron; Sherman, Ariel; Bonnett, James; Kelmelis, Eric
2017-07-01
When capturing imagery over long distances, atmospheric turbulence often degrades the data, especially when observation paths are close to the ground or in hot environments. These issues manifest as time-varying scintillation and warping effects that decrease the effective resolution of the sensor and reduce actionable intelligence. In recent years, several image processing approaches to turbulence mitigation have shown promise. Each of these algorithms has different computational requirements, usability demands, and degrees of independence from camera sensors. They also produce different degrees of enhancement when applied to turbulent imagery. Additionally, some of these algorithms are applicable to real-time operational scenarios while others may only be suitable for postprocessing workflows. EM Photonics has been developing image-processing-based turbulence mitigation technology since 2005. We will compare techniques from the literature with our commercially available, real-time, GPU-accelerated turbulence mitigation software. These comparisons will be made using real (not synthetic), experimentally obtained data for a variety of conditions, including varying optical hardware, imaging range, subjects, and turbulence conditions. Comparison metrics will include image quality, video latency, computational complexity, and potential for real-time operation. Additionally, we will present a technique for quantitatively comparing turbulence mitigation algorithms using real images of radial resolution targets.
International Nuclear Information System (INIS)
Kahn, F.D.
1983-01-01
A relativistic plasma flow can explain many of the observations on the one-sided jets, which are associated with radio sources that show superluminal motions in their cores. The pressure from the ambient medium will communicate across the jet in a relatively short distance, typically 30 kpc. The friction between the jet and the external medium then makes the flow go turbulent. As a result the jet dissipates energy and will be brought to rest within a few hundred kpc, if it does not strike an obstacle before. The mean flow in the jet is strongly sheared and stretches the lines of force of any magnetic field frozen into the plasma. The dominant field direction, as seen from the rest frame of the plasma, is therefore parallel to the length of the jet. Polarization measurements have shown that this is in fact the case. (author)
International Nuclear Information System (INIS)
Pomeau, Y.
1981-07-01
In this work it is reviewed a few known types of transition to turbulence, as the cascade of period doubling and the intermittent transition. This happens in dynamical systems with a few degrees of freedom, as modelled by the iteration of non linear maps. Then it is presented specific transitions for systems with many degrees of freedom. It is condidered first the occurence of a low frequency broadband noise in large cells at the onset of Rayleigh-Benard convection; then the transition by intermittent bursts in parallel flows. In this last case, one is concerned with localized and finite amplitude perturbations. Simple geometric arguments show that these fluctuations, when they are isolated and with a well definite relative speed, exist for a single value of the Reynolds number only [fr
Saturation of the turbulent dynamo.
Schober, J; Schleicher, D R G; Federrath, C; Bovino, S; Klessen, R S
2015-08-01
The origin of strong magnetic fields in the Universe can be explained by amplifying weak seed fields via turbulent motions on small spatial scales and subsequently transporting the magnetic energy to larger scales. This process is known as the turbulent dynamo and depends on the properties of turbulence, i.e., on the hydrodynamical Reynolds number and the compressibility of the gas, and on the magnetic diffusivity. While we know the growth rate of the magnetic energy in the linear regime, the saturation level, i.e., the ratio of magnetic energy to turbulent kinetic energy that can be reached, is not known from analytical calculations. In this paper we present a scale-dependent saturation model based on an effective turbulent resistivity which is determined by the turnover time scale of turbulent eddies and the magnetic energy density. The magnetic resistivity increases compared to the Spitzer value and the effective scale on which the magnetic energy spectrum is at its maximum moves to larger spatial scales. This process ends when the peak reaches a characteristic wave number k☆ which is determined by the critical magnetic Reynolds number. The saturation level of the dynamo also depends on the type of turbulence and differs for the limits of large and small magnetic Prandtl numbers Pm. With our model we find saturation levels between 43.8% and 1.3% for Pm≫1 and between 2.43% and 0.135% for Pm≪1, where the higher values refer to incompressible turbulence and the lower ones to highly compressible turbulence.
Statistical properties of turbulence: An overview
Indian Academy of Sciences (India)
the turbulent advection of passive scalars, turbulence in the one-dimensional Burgers equation, and fluid turbulence in the presence of polymer ... However, it is not easy to state what would consti- tute a solution of the turbulence ...... flow with Lagrangian tracers and use a cubic spline interpolation method to calculate their ...
Strong Turbulence in Low-beta Plasmas
DEFF Research Database (Denmark)
Tchen, C. M.; Pécseli, Hans; Larsen, Søren Ejling
1980-01-01
An investigation of the spectral structure of turbulence in a plasma confined by a strong homogeneous magnetic field was made by means of a fluid description. The turbulent spectrum is divided into subranges. Mean gradients of velocity and density excite turbulent motions, and govern the production......-cathode reflex arc, Stellarator, Zeta discharge, ionospheric plasmas, and auroral plasma turbulence....
Theory of neoclassical ion temperature-gradient-driven turbulence
Kim, Y. B.; Diamond, P. H.; Biglari, H.; Callen, J. D.
1991-02-01
The theory of collisionless fluid ion temperature-gradient-driven turbulence is extended to the collisional banana-plateau regime. Neoclassical ion fluid evolution equations are developed and utilized to investigate linear and nonlinear dynamics of negative compressibility ηi modes (ηi≡d ln Ti/d ln ni). In the low-frequency limit (ωB2p. As a result of these modifications, growth rates are dissipative, rather than sonic, and radial mode widths are broadened [i.e., γ˜k2∥c2s(ηi -(2)/(3) )/μi, Δx˜ρs(Bt/Bp) (1+ηi)1/2, where k∥, cs, and ρs are the parallel wave number, sound velocity, and ion gyroradius, respectively]. In the limit of weak viscous damping, enhanced neoclassical polarization persists and broadens radial mode widths. Linear mixing length estimates and renormalized turbulence theory are used to determine the ion thermal diffusivity in both cases. In both cases, a strong favorable dependence of ion thermal diffusivity on Bp (and hence plasma current) is exhibited. Furthermore, the ion thermal diffusivity for long wavelength modes exhibits favorable density scaling. The possible role of neoclassical ion temperature-gradient-driven modes in edge fluctuations and transport in L-phase discharges and the L to H transition is discussed.
Chen, B.; Xu, X. Q.; Xia, T. Y.; Li, N. M.; Porkolab, M.; Edlund, E.; LaBombard, B.; Terry, J.; Hughes, J. W.; Ye, M. Y.; Wan, Y. X.
2018-05-01
The heat flux distributions on divertor targets in H-mode plasmas are serious concerns for future devices. We seek to simulate the tokamak boundary plasma turbulence and heat transport in the edge localized mode-suppressed regimes. The improved BOUT++ model shows that not only Ip but also the radial electric field Er plays an important role on the turbulence behavior and sets the heat flux width. Instead of calculating Er from the pressure gradient term (diamagnetic Er), it is calculated from the plasma transport equations with the sheath potential in the scrape-off layer and the plasma density and temperature profiles inside the separatrix from the experiment. The simulation results with the new Er model have better agreement with the experiment than using the diamagnetic Er model: (1) The electromagnetic turbulence in enhanced Dα H-mode shows the characteristics of quasi-coherent modes (QCMs) and broadband turbulence. The mode spectra are in agreement with the phase contrast imaging data and almost has no change in comparison to the cases which use the diamagnetic Er model; (2) the self-consistent boundary Er is needed for the turbulence simulations to get the consistent heat flux width with the experiment; (3) the frequencies of the QCMs are proportional to Er, while the divertor heat flux widths are inversely proportional to Er; and (4) the BOUT++ turbulence simulations yield a similar heat flux width to the experimental Eich scaling law and the prediction from the Goldston heuristic drift model.
Effects of premixed flames on turbulence and turbulent scalar transport
Energy Technology Data Exchange (ETDEWEB)
Lipatnikov, A.N.; Chomiak, J. [Department of Applied Mechanics, Chalmers University of Technology, 412 75 Goeteborg (Sweden)
2010-02-15
Experimental data and results of direct numerical simulations are reviewed in order to show that premixed combustion can change the basic characteristics of a fluctuating velocity field (the so-called flame-generated turbulence) and the direction of scalar fluxes (the so-called countergradient or pressure-driven transport) in a turbulent flow. Various approaches to modeling these phenomena are discussed and the lack of a well-elaborated and widely validated predictive approach is emphasized. Relevant basic issues (the transition from gradient to countergradient scalar transport, the role played by flame-generated turbulence in the combustion rate, the characterization of turbulence in premixed flames, etc.) are critically considered and certain widely accepted concepts are disputed. Despite the substantial progress made in understanding the discussed effects over the past decades, these basic issues strongly need further research. (author)
Effect of turbulent collisions on diffusion in stationary plasma turbulence
International Nuclear Information System (INIS)
Xia, H.; Ishihara, O.
1990-01-01
Recently the velocity diffusion process was studied by the generalized Langevin equation derived by the projection operator method. The further study shows that the retarded frictional function plays an important role in suppressing particle diffusion in the velocity space in stronger turbulence as much as the resonance broadening effect. The retarded frictional effect, produced by the effective collisions due to the plasma turbulence is assumed to be a Gaussian, but non-Markovian and non-wide-sense stationary process. The relations between the proposed formulation and the extended resonance broadening theory is discussed. The authors also carry out test particle numerical experiment for Langmuir turbulence to test the theories. In a stronger turbulence a deviation of the diffusion rate from the one predicted by both the quasilinear and the extended resonance theories has been observed and is explained qualitatively by the present formulation
Wind energy impact of turbulence
Hölling, Michae; Ivanell, Stefan
2014-01-01
This book presents the results of the seminar ""Wind Energy and the Impact of Turbulence on the Conversion Process"" which was supported from three societies, namely the EUROMech, EAWE and ERCOFATC and took place in Oldenburg, Germany in spring 2012.The seminar was one of the first scientific meetings devoted to the common topic of wind energy and basic turbulence. The established community of researchers working on the challenging puzzle of turbulence for decades met the quite young community of researchers, who face the upcoming challenges in the fast growing field of wind energy application
Outer scale of atmospheric turbulence
Lukin, Vladimir P.
2005-10-01
In the early 70's, the scientists in Italy (A.Consortini, M.Bertolotti, L.Ronchi), USA (R.Buser, Ochs, S.Clifford) and USSR (V.Pokasov, V.Lukin) almost simultaneously discovered the phenomenon of deviation from the power law and the effect of saturation for the structure phase function. During a period of 35 years we have performed successively the investigations of the effect of low-frequency spectral range of atmospheric turbulence on the optical characteristics. The influence of the turbulence models as well as a outer scale of turbulence on the characteristics of telescopes and systems of laser beam formations has been determined too.
Considerations of ion temperature gradient driven turbulence
International Nuclear Information System (INIS)
Cowley, S.C.; Kulsrud, R.M.
1991-02-01
The ion temperature gradient driven instability is considered in this paper. Physical pictures are presented to clarify the nature of the instability. The saturation of a single eddy is modeled by a simple nonlinear equation. We show that eddies which are elongated in the direction of the temperature gradient are the most unstable and have the highest saturation amplitudes. In a sheared magnetic field, such elongated eddies twist with the field lines. This structure is shown to be alternative to the usual Fourier mode picture in which the mode is localized around the surface where k parallel = 0. We show how these elongated twisting eddies, which are an integral part of the ''ballooning mode'' structure, could survive in a torus. The elongated eddies are shown to be unstable to secondary instabilities that are driven by the large gradients in the long eddy. We argue that this mechanism isotropizes ion temperature gradient turbulence. We further argue that the ''mixing length'' is set by this nonlinear process, not by a linear eigenmode width. 17 refs., 6 figs
Turbulence Modeling and Computation of Turbine Aerodynamics and Heat Transfer
Lakshminarayana, B.; Luo, J.
1996-01-01
The objective of the present research is to develop improved turbulence models for the computation of complex flows through turbomachinery passages, including the effects of streamline curvature, heat transfer and secondary flows. Advanced turbulence models are crucial for accurate prediction of rocket engine flows, due to existance of very large extra strain rates, such as strong streamline curvature. Numerical simulation of the turbulent flows in strongly curved ducts, including two 180-deg ducts, one 90-deg duct and a strongly concave curved turbulent boundary layer have been carried out with Reynolds stress models (RSM) and algebraic Reynolds stress models (ARSM). An improved near-wall pressure-strain correlation has been developed for capturing the anisotropy of turbulence in the concave region. A comparative study of two modes of transition in gas turbine, the by-pass transition and the separation-induced transition, has been carried out with several representative low-Reynolds number (LRN) k-epsilon models. Effects of blade surface pressure gradient, freestream turbulence and Reynolds number on the blade boundary layer development, and particularly the inception of transition are examined in detail. The present study indicates that the turbine blade transition, in the presence of high freestream turbulence, is predicted well with LRN k-epsilon models employed. The three-dimensional Navier-Stokes procedure developed by the present authors has been used to compute the three-dimensional viscous flow through the turbine nozzle passage of a single stage turbine. A low Reynolds number k-epsilon model and a zonal k-epsilon/ARSM (algebraic Reynolds stress model) are utilized for turbulence closure. An assessment of the performance of the turbulence models has been carried out. The two models are found to provide similar predictions for the mean flow parameters, although slight improvement in the prediction of some secondary flow quantities has been obtained by the
Adaptive LES Methodology for Turbulent Flow Simulations
Energy Technology Data Exchange (ETDEWEB)
Oleg V. Vasilyev
2008-06-12
turbulence have recently been completed at the Japanese Earth Simulator (Yokokawa et al. 2002, Kaneda et al. 2003) using a resolution of 40963 (approximately 10{sup 11}) grid points with a Taylor-scale Reynolds number of 1217 (Re {approx} 10{sup 6}). Impressive as these calculations are, performed on one of the world's fastest super computers, more brute computational power would be needed to simulate the flow over the fuselage of a commercial aircraft at cruising speed. Such a calculation would require on the order of 10{sup 16} grid points and would have a Reynolds number in the range of 108. Such a calculation would take several thousand years to simulate one minute of flight time on today's fastest super computers (Moin & Kim 1997). Even using state-of-the-art zonal approaches, which allow DNS calculations that resolve the necessary range of scales within predefined 'zones' in the flow domain, this calculation would take far too long for the result to be of engineering interest when it is finally obtained. Since computing power, memory, and time are all scarce resources, the problem of simulating turbulent flows has become one of how to abstract or simplify the complexity of the physics represented in the full Navier-Stokes (NS) equations in such a way that the 'important' physics of the problem is captured at a lower cost. To do this, a portion of the modes of the turbulent flow field needs to be approximated by a low order model that is cheaper than the full NS calculation. This model can then be used along with a numerical simulation of the 'important' modes of the problem that cannot be well represented by the model. The decision of what part of the physics to model and what kind of model to use has to be based on what physical properties are considered 'important' for the problem. It should be noted that 'nothing is free', so any use of a low order model will by definition lose some information about the
Quantum Turbulence ---Another da Vinci Code---
Tsubota, M.
Quantum turbulence comprises a tangle of quantized vorticeswhich are stable topological defects created by Bose-Einstein condensation, being realized in superfluid helium and atomic Bose-Einstein condensates. In recent years there has been a growing interest in quantum turbulence. One of the important motivations is to understand the relation between quantum and classical turbulence. Quantum turbulence is expected to be much simpler than usual classical turbulence and give a prototype of turbulence. This article reviews shortly the recent research developments on quantum turbulence.
Confinement improvement in H-mode-like plasmas in helical systems
International Nuclear Information System (INIS)
Itoh, K.; Sanuki, H.; Itoh, S.; Fukuyama, A.; Yagi, M.
1993-06-01
The reduction of the anomalous transport due to the inhomogeneous radial electric field is theoretically studied for toroidal helical plasmas. The self-sustained interchange-mode turbulence is analysed for the system with magnetic shear and magnetic hill. For the system with magnetic well like conventional stellarators, the ballooning mode turbulence is studied. Influence of the radial electric field inhomogeneity on the transport coefficients and fluctuations are quantitatively shown. Unified theory of the transport coefficients in the L-mode and H-mode-like plasmas are presented. (author)
International Nuclear Information System (INIS)
Arons, J.; Lea, S.M.
1976-01-01
We describe the results of a linearized hydromagnetic stability analysis of the magnetopause of an accreting neutron star. The magnetosphere is assumed to be slowly rotating, and the plasma just outside of the magnetopause is assumed to be weakly magnetized. The plasma layer is assumed to be bounded above by a shock wave, and to be thin compared with the radius of the magnetosphere. Under these circumstances, the growing modes are shown to be localized in the direction parallel to the zero-order magnetic field. The structure of the modes is still similar to the flute mode, however. The growth rate at each magnetic latitude is lambda given by γ 2 =g/sub n/kα/sub eff/(lambda) tanh [kz/sub s/(lambda)] where g/sub n/ is the magnitude of the gravitational acceleration normal to the surface, kapprox. =vertical-barmvertical-bar/R (lambda)cos lambda, vertical-barmvertical-bar is the azimuthal mode number, R (lambda) is the radius of the magnetosphere, z/sub s/ is the height of the shock above the magnetopause, and α/sub eff/(lambda) <1 is the effective Atwood number which embodies the stabilizing effects of favorable curvature and magnetic tension. We calculate α/sub eff/(lambda), and also discuss the stabilizing effects of viscosity and of aligned flow parallel to the magnetopause
Suppression of plasma turbulence during optimised shear configurations in JET
International Nuclear Information System (INIS)
Conway, G.D.; Borba, D.N.; Alper, B.
1999-08-01
Density turbulence suppression is observed in the internal transport barrier (ITB) region of JET discharges with optimised magnetic shear. The suppression occurs in two stages. First, low frequency turbulence is reduced across the plasma core by a toroidal velocity shear generated by intense auxiliary heating. Then when the ITB forms, high frequency turbulence is reduced locally within the steep pressure gradient region of the ITB, consistent with the effects of enhanced E x B poloidal shear. The turbulence suppression is correlated with reduced plasma transport and improved fusion performance. Much effort has been spent in recent years in developing alternative scenarios for operating tokamak fusion reactors. One particular scenario involves reversing or reducing the central magnetic shear to form an internal transport barrier (ITB). The result is reduced plasma core energy transport and enhanced fusion performance. It is believed that ITBs may be formed through a combination of E x B velocity shear and magnetic shear stabilisation of plasma turbulence and instabilities. In this Letter we present results from JET optimised shear discharges showing that turbulence suppression during ITB formation occurs in two stages. First low frequency turbulence is reduced across the plasma core, coinciding with a region of strong toroidal velocity shear; then high frequency turbulence is locally suppressed around the ITB region, consistent with enhanced pressure gradient driven E x B poloidal shear. The measurements were made using a system of X-mode reflectometers consisting of two, dual-channel toroidal correlation reflectometers at 75 GHz (covering plasma outboard edge) and 105 GHz (core and inboard edge), and a 92-96 GHz swept frequency radial correlation reflectometer (plasma core). Reflectometry is a powerful tool for measuring density fluctuations. The highly localised reflection of the microwave beam gives excellent spatial localisation. Measurements can be made
Constructive modelling of structural turbulence: computational experiment
Energy Technology Data Exchange (ETDEWEB)
Belotserkovskii, O M; Oparin, A M; Troshkin, O V [Institute for Computer Aided Design, Russian Academy of Sciences, Vtoraya Brestskaya st., 19/18, Moscow, 123056 (Russian Federation); Chechetkin, V M [Keldysh Institute for Applied Mathematics, Russian Academy of Sciences, Miusskaya sq., 4, Moscow, 125047 (Russian Federation)], E-mail: o.bel@icad.org.ru, E-mail: a.oparin@icad.org.ru, E-mail: troshkin@icad.org.ru, E-mail: chech@gin@keldysh.ru
2008-12-15
Constructively, the analysis of the phenomenon of turbulence must and can be performed through direct numerical simulations of mechanics supposed to be inherent to secondary flows. This one reveals itself through such instances as large vortices, structural instabilities, vortex cascades and principal modes discussed in this paper. Like fragments of a puzzle, they speak of a motion ordered with its own nuts and bolts, however chaotic it appears at first sight. This opens an opportunity for a multi-oriented approach of which a prime ideology seems to be a rational combination of grid, spectral and statistical methods. An attempt is made to bring together the above instances and produce an alternative point of view on the phenomenon in question when based on the main laws of conservation.
Turbulent response in a stochastic regime
International Nuclear Information System (INIS)
Molvig, K.; Freidberg, J.P.; Potok, R.; Hirshman, S.P.; Whitson, J.C.; Tajima, T.
1981-06-01
The theory for the non-linear, turbulent response in a system with intrinsic stochasticity is considered. It is argued that perturbative Eulerian theories, such as the Direct Interaction Approximation (DIA), are inherently unsuited to describe such a system. The exponentiation property that characterizes stochasticity appears in the Lagrangian picture and cannot even be defined in the Eulerian representation. An approximation for stochastic systems - the Normal Stochastic Approximation - is developed and states that the perturbed orbit functions (Lagrangian fluctuations) behave as normally distributed random variables. This is independent of the Eulerian statistics and, in fact, we treat the Eulerian fluctuations as fixed. A simple model problem (appropriate for the electron response in the drift wave) is subjected to a series of computer experiments. To within numerical noise the results are in agreement with the Normal Stochastic Approximation. The predictions of the DIA for this mode show substantial qualitative and quantitative departures from the observations
Anisoplanatic Imaging through Turbulence
2016-10-07
modes related with one single coefficient of value α=0.3, i.e., = ∙ + (1 − ) ∙ . The reader can notice that the marginal...Laser Science XXV, OSA Optics & Photonics Technical Digest , OSA Technical Digest (CD), 2009. 14. http://www.eso.org/sci/facilities/eelt/science/drm
International Nuclear Information System (INIS)
Kaw, P.K.; Singh, R.; Weiland, J.G.
2001-01-01
Analytical investigations of several linear and nonlinear features of ETG turbulence are reported. The linear theory includes effects such as finite beta induced electromagnetic shielding, coupling to electron magnetohydrodynamic modes like whistlers etc. It is argued that nonlinearly, turbulence and transport are dominated by radially extended modes called 'streamers'. A nonlinear mechanism generating streamers based on a modulational instability theory of the ETG turbulence is also presented. The saturation levels of the streamers using a Kelvin Helmholtz secondary instability mechanism are calculated and levels of the electron thermal transport due to streamers are estimated. (author)
Simulation and analysis of the soot particle size distribution in a turbulent nonpremixed flame
Lucchesi, Marco
2017-02-05
A modeling framework based on Direct Simulation Monte Carlo (DSMC) is employed to simulate the evolution of the soot particle size distribution in turbulent sooting flames. The stochastic reactor describes the evolution of soot in fluid parcels following Lagrangian trajectories in a turbulent flow field. The trajectories are sampled from a Direct Numerical Simulation (DNS) of a n-heptane turbulent nonpremixed flame. The DSMC method is validated against experimentally measured size distributions in laminar premixed flames and found to reproduce quantitatively the experimental results, including the appearance of the second mode at large aggregate sizes and the presence of a trough at mobility diameters in the range 3–8 nm. The model is then applied to the simulation of soot formation and growth in simplified configurations featuring a constant concentration of soot precursors and the evolution of the size distribution in time is found to depend on the intensity of the nucleation rate. Higher nucleation rates lead to a higher peak in number density and to the size distribution attaining its second mode sooner. The ensemble-averaged PSDF in the turbulent flame is computed from individual samples of the PSDF from large sets of Lagrangian trajectories. This statistical measure is equivalent to time-averaged, scanning mobility particle size (SMPS) measurements in turbulent flames. Although individual trajectories display strong bimodality as in laminar flames, the ensemble-average PSDF possesses only one mode and a long, broad tail, which implies significant polydispersity induced by turbulence. Our results agree very well with SMPS measurements available in the literature. Conditioning on key features of the trajectory, such as mixture fraction or radial locations does not reduce the scatter in the size distributions and the ensemble-averaged PSDF remains broad. The results highlight and explain the important role of turbulence in broadening the size distribution of
Suppression of Phase Mixing in Drift-Kinetic Plasma Turbulence
Parker, J. T.; Dellar, P. J.; Schekochihin, A. A.; Highcock, E. G.
2017-12-01
The solar wind and interstellar medium are examples of strongly magnetised, weakly collisional, astrophysical plasmas. Their turbulent fluctuations are strongly anisotropic, with small amplitudes, and frequencies much lower than the Larmor frequency. This regime is described by gyrokinetic theory, a reduced five-dimensional kinetic system describing averages over Larmor orbits. A turbulent plasma may transfer free energy, a measure of fluctuation amplitudes, from injection at large scales, typically by an instability, to dissipation at small physical scales like a turbulent fluid. Alternatively, a turbulent plasma may form fine scale structures in velocity space via phase-mixing, the mechanism that leads to Landau damping in linear plasma theory. Macroscopic plasma properties like heat and momentum transport are affected by both mechanisms. While each is understood in isolation, their interaction is not. We study this interaction using a Hankel-Hermite velocity space representation of gyrokinetic theory. The Hankel transform interacts neatly with the Bessel functions that arise from averaging over Larmor orbits, so the perpendicular velocity space is decoupled for linearized problems. The Hermite transform expresses phase mixing as nearest-neighbor coupling between parallel velocity space scales represented by Hermite mode numbers. We use this representation to study transfer mechanisms in drift-kinetic plasma turbulence, the long wavelength limit of gyrokinetic theory. We show that phase space is divided into two regions, with one transfer mechanism dominating in each. Most energy is contained in the region where the fluid-like nonlinear cascade dominates. Moreover, in that region the nonlinear cascade interferes with phase mixing by exciting an "anti phase mixing" transfer of free energy from small to large velocity space scales. This cancels out the usual phase mixing, and renders the overall behavior fluid-like. These results profoundly change our understanding
Turbulence time series data hole filling using Karhunen-Loeve and ARIMA methods
International Nuclear Information System (INIS)
Chang, M P J L; Nazari, H; Font, C O; Gilbreath, G C; Oh, E
2007-01-01
Measurements of optical turbulence time series data using unattended instruments over long time intervals inevitably lead to data drop-outs or degraded signals. We present a comparison of methods using both Principal Component Analysis, which is also known as the Karhunen-Loeve decomposition, and ARIMA that seek to correct for these event-induced and mechanically-induced signal drop-outs and degradations. We report on the quality of the correction by examining the Intrinsic Mode Functions generated by Empirical Mode Decomposition. The data studied are optical turbulence parameter time series from a commercial long path length optical anemometer/scintillometer, measured over several hundred metres in outdoor environments
Can Venus magnetosheath plasma evolve into turbulence?
Dwivedi, Navin; Schmid, Daniel; Narita, Yasuhito; Volwerk, Martin; Delva, Magda; Voros, Zoltan; Zhang, Tielong
2014-05-01
The present work aims to understand turbulence properties in planetary magnetosheath regions to obtain physical insight on the energy transfer from the larger to smaller scales, in spirit of searching for power-law behaviors in the spectra which is an indication of the energy cascade and wave-wave interaction. We perform a statistical analysis of energy spectra using the Venus Express spacecraft data in the Venusian magnetosheath. The fluxgate magnetometer data (VEXMAG) calibrated down to 1 Hz as well as plasma data from the ion mass analyzer (ASPERA) aboard the spacecraft are used in the years 2006-2009. Ten-minute intervals in the magnetosheath are selected, which is typical time length of observations of quasi-stationary fluctuations avoiding multiple boundaries crossings. The magnetic field data are transformed into the mean-field-aligned (MFA) coordinate system with respect to the large-scale magnetic field direction and the energy spectra are evaluated using a Welch algorithm in the frequency range between 0.008 Hz and 0.5 Hz for 105 time intervals. The averaged energy spectra show a power law upto 0.3 Hz with the approximate slope of -1, which is flatter than the Kolmogorov slope, -5/3. A slight hump in the spectra is found in the compressive component near 0.3 Hz, which could possibly be realization of mirror mode in the magnetosheath. A spectral break (sudden change in slope) accompanies the spectral hump at 0.4 Hz, above which the spectral curve becomes steeper. The overall spectral shape is reminiscent of turbulence. The low-frequency part with the slope -1 is interpreted as realization of the energy containing range, while the high-frequency part with the steepening is interpreted either as the beginning of energy cascade mediated by mirror mode or as the dissipation range due to wave-particle resonance processes. The present research work is fully supported by FP7/STORM (313038).
Turbulence optimisation in stellarator experiments
Energy Technology Data Exchange (ETDEWEB)
Proll, Josefine H.E. [Max-Planck/Princeton Center for Plasma Physics (Germany); Max-Planck-Institut fuer Plasmaphysik, Wendelsteinstr. 1, 17491 Greifswald (Germany); Faber, Benjamin J. [HSX Plasma Laboratory, University of Wisconsin-Madison, Madison, WI 53706 (United States); Helander, Per; Xanthopoulos, Pavlos [Max-Planck/Princeton Center for Plasma Physics (Germany); Lazerson, Samuel A.; Mynick, Harry E. [Plasma Physics Laboratory, Princeton University, P.O. Box 451 Princeton, New Jersey 08543-0451 (United States)
2015-05-01
Stellarators, the twisted siblings of the axisymmetric fusion experiments called tokamaks, have historically suffered from confining the heat of the plasma insufficiently compared with tokamaks and were therefore considered to be less promising candidates for a fusion reactor. This has changed, however, with the advent of stellarators in which the laminar transport is reduced to levels below that of tokamaks by shaping the magnetic field accordingly. As in tokamaks, the turbulent transport remains as the now dominant transport channel. Recent analytical theory suggests that the large configuration space of stellarators allows for an additional optimisation of the magnetic field to also reduce the turbulent transport. In this talk, the idea behind the turbulence optimisation is explained. We also present how an optimised equilibrium is obtained and how it might differ from the equilibrium field of an already existing device, and we compare experimental turbulence measurements in different configurations of the HSX stellarator in order to test the optimisation procedure.
Optimizing Stellarators for Turbulent Transport
International Nuclear Information System (INIS)
Mynick, H.E.; Pomphrey, N.; Xanthopoulos, P.
2010-01-01
Up to now, the term 'transport-optimized' stellarators has meant optimized to minimize neoclassical transport, while the task of also mitigating turbulent transport, usually the dominant transport channel in such designs, has not been addressed, due to the complexity of plasma turbulence in stellarators. Here, we demonstrate that stellarators can also be designed to mitigate their turbulent transport, by making use of two powerful numerical tools not available until recently, namely gyrokinetic codes valid for 3D nonlinear simulations, and stellarator optimization codes. A first proof-of-principle configuration is obtained, reducing the level of ion temperature gradient turbulent transport from the NCSX baseline design by a factor of about 2.5.
Structure and modeling of turbulence
International Nuclear Information System (INIS)
Novikov, E.A.
1995-01-01
The open-quotes vortex stringsclose quotes scale l s ∼ LRe -3/10 (L-external scale, Re - Reynolds number) is suggested as a grid scale for the large-eddy simulation. Various aspects of the structure of turbulence and subgrid modeling are described in terms of conditional averaging, Markov processes with dependent increments and infinitely divisible distributions. The major request from the energy, naval, aerospace and environmental engineering communities to the theory of turbulence is to reduce the enormous number of degrees of freedom in turbulent flows to a level manageable by computer simulations. The vast majority of these degrees of freedom is in the small-scale motion. The study of the structure of turbulence provides a basis for subgrid-scale (SGS) models, which are necessary for the large-eddy simulations (LES)
Modeling Compressed Turbulence with BHR
Israel, Daniel
2011-11-01
Turbulence undergoing compression or expansion occurs in systems ranging from internal combustion engines to supernovae. One common feature in many of these systems is the presence of multiple reacting species. Direct numerical simulation data is available for the single-fluid, low turbulent Mach number case. Wu, et al. (1985) compared their DNS results to several Reynolds-averaged Navier-Stokes models. They also proposed a three-equation k - ɛ - τ model, in conjunction with a Reynolds-stress model. Subsequent researchers have proposed alternative corrections to the standard k - ɛ formulation. Here we investigate three variants of the BHR model (Besnard, 1992). BHR is a model for multi-species variable-density turbulence. The three variants are the linear eddy-viscosity, algebraic-stress, and full Reynolds-stress formulations. We then examine the predictions of the model for the fluctuating density field for the case of variable-density turbulence.
Premixed autoignition in compressible turbulence
Konduri, Aditya; Kolla, Hemanth; Krisman, Alexander; Chen, Jacqueline
2016-11-01
Prediction of chemical ignition delay in an autoignition process is critical in combustion systems like compression ignition engines and gas turbines. Often, ignition delay times measured in simple homogeneous experiments or homogeneous calculations are not representative of actual autoignition processes in complex turbulent flows. This is due the presence of turbulent mixing which results in fluctuations in thermodynamic properties as well as chemical composition. In the present study the effect of fluctuations of thermodynamic variables on the ignition delay is quantified with direct numerical simulations of compressible isotropic turbulence. A premixed syngas-air mixture is used to remove the effects of inhomogeneity in the chemical composition. Preliminary results show a significant spatial variation in the ignition delay time. We analyze the topology of autoignition kernels and identify the influence of extreme events resulting from compressibility and intermittency. The dependence of ignition delay time on Reynolds and turbulent Mach numbers is also quantified. Supported by Basic Energy Sciences, Dept of Energy, United States.
Workshop on Engineering Turbulence Modeling
Povinelli, Louis A. (Editor); Liou, W. W. (Editor); Shabbir, A. (Editor); Shih, T.-H. (Editor)
1992-01-01
Discussed here is the future direction of various levels of engineering turbulence modeling related to computational fluid dynamics (CFD) computations for propulsion. For each level of computation, there are a few turbulence models which represent the state-of-the-art for that level. However, it is important to know their capabilities as well as their deficiencies in order to help engineers select and implement the appropriate models in their real world engineering calculations. This will also help turbulence modelers perceive the future directions for improving turbulence models. The focus is on one-point closure models (i.e., from algebraic models to higher order moment closure schemes and partial differential equation methods) which can be applied to CFD computations. However, other schemes helpful in developing one-point closure models, are also discussed.
Toy models of developed turbulence
Directory of Open Access Journals (Sweden)
M.Hnatich
2005-01-01
Full Text Available We have investigated the advection of a passive scalar quantity by incompressible helical turbulent flow within the framework of extended Kraichnan model. Turbulent fluctuations of velocity field are assumed to have the Gaussian statistics with zero mean and defined noise with finite time-correlation. Actual calculations have been done up to two-loop approximation within the framework of field-theoretic renormalization group approach. It turned out that space parity violation (helicity of turbulent environment does not affect anomalous scaling which is a peculiar attribute of the corresponding model without helicity. However, stability of asymptotic regimes, where anomalous scaling takes place, strongly depends on the amount of helicity. Moreover, helicity gives rise to the turbulent diffusivity, which has been calculated in one-loop approximation.
Stochastic Subspace Modelling of Turbulence
DEFF Research Database (Denmark)
Sichani, Mahdi Teimouri; Pedersen, B. J.; Nielsen, Søren R.K.
2009-01-01
positive definite cross-spectral density matrix a frequency response matrix is constructed which determines the turbulence vector as a linear filtration of Gaussian white noise. Finally, an accurate state space modelling method is proposed which allows selection of an appropriate model order......, and estimation of a state space model for the vector turbulence process incorporating its phase spectrum in one stage, and its results are compared with a conventional ARMA modelling method.......Turbulence of the incoming wind field is of paramount importance to the dynamic response of civil engineering structures. Hence reliable stochastic models of the turbulence should be available from which time series can be generated for dynamic response and structural safety analysis. In the paper...
Turbulence in unmagnetized Vlasov plasmas
International Nuclear Information System (INIS)
Kuo, S.P.
1985-01-01
The classical technique of transformation and characteristics is employed to analyze the problem of strong turbulence in unmagnetized plasmas. The effect of resonance broadening and perturbation expansion are treated simultaneously, without time secularities. The renormalization procedure of Dupree and Tetreault is used in the transformed Vlasov equation to analyze the turbulence and to derive explicitly a diffusion equation. Analyses are extended to inhomogeneous plasmas and the relationship between the transformation and ponderomotive force is obtained. (author)
Turbulent effective absorptivity and refractivity
International Nuclear Information System (INIS)
Rax, J.M.
1984-09-01
The problem of wave propagation in a turbulent magnetized plasma is investigated. Considering small scale, low frequency density fluctuations we solve the Maxwell equations and show that the eikonal approximation remains valid with an effective refractivity and an effective absorptivity taking into account the energy diffusion due to the turbulent motion. Then the result is applied to the problem of lower hybrid waves scattering by drift waves density fluctuations in tokamaks
BOOK REVIEW: Plasma and Fluid Turbulence: Theory and Modelling
Yoshizawa, A.; Itoh, S. I.; Itoh, K.
2003-03-01
in turn suppress the instabilities leading to an intermittent type of dynamics. In chapter 21 the authors finally come to one of their special interests, subcritical, or nonlinear, excitation of turbulence. This is mainly of interest in plasma regimes where there are no strong instabilities or in order to explain magnetic perturbations in situations where only electrostatic modes are linearly unstable. The final part of the book deals mainly with statistical aspects of plasma turbulence, starting with bifurcation and including discussions of the transition from an L-mode (low confinement) to an H-mode (high confinement state) of magnetic confinement of plasmas. This is another area of special expertise of the authors and it is very well written, giving detailed information of the subject area. In conclusion I find the book to be both very pedagogical and very up to date. It can be strongly recommended to researchers who quickly want to reach the research front in plasma turbulence for magnetic confinement starting with only a basic knowledge of plasma or fluid dynamics. It has its main strengths in the fluid and MHD parts, as well as in the statistical descriptions. Jan Weiland
Stochastic catastrophe theory and instabilities in plasma turbulence
International Nuclear Information System (INIS)
Rajkovic, Milan; Skoric, Milos
2009-01-01
Full text: A Langevin equation (LE) describing evolution of turbulence amplitude in plasma is analyzed from the aspect of stochastic catastrophe theory (SCT) so that turbulent plasma is considered as a stochastic gradient system. According to SCT the dynamics of the system is completely determined by the stochastic potential function and the maximum likelihood estimates of stable and unstable equilibria are associated with the modes and anti-modes, respectively, of the system's stationary probability density function. First order phase transitions occur at degenerate equilibrium points and the potential function at these points may be represented in a generic way. Since the diffusion function of plasma LE is not constant the probability density function (pdf) is not a reliable estimator of the number of stable states. We show that the generalized pdf represented as the product of the stationary pdf and the diffusion function is a reliable estimator of the stable states and that it can be evaluated from the zero mean crossing analysis of plasma turbulence signal. Stochastic bifurcations, and particularly the sudden (catastrophic) ones, are recognized from the pdf's obtained by the zero crossing analysis and we illustrate the applications of SCT in plasma turbulence on data obtained from the MAST (Mega Ampere Spherical Tokamak) for low (L), high (H) and unstable dithering (L/H) confinement regimes. The relationship of the transformation invariant zero-crossing function and SCT is shown to provide important information about the nature of edge localized modes (ELMs) and L-H transition. Finally we show that ELMs occur as a result of catastrophic (hard) bifurcations ruling out the self-organized criticality scenario for their origin. (author)
Quantify the complexity of turbulence
Tao, Xingtian; Wu, Huixuan
2017-11-01
Many researchers have used Reynolds stress, power spectrum and Shannon entropy to characterize a turbulent flow, but few of them have measured the complexity of turbulence. Yet as this study shows, conventional turbulence statistics and Shannon entropy have limits when quantifying the flow complexity. Thus, it is necessary to introduce new complexity measures- such as topology complexity and excess information-to describe turbulence. Our test flow is a classic turbulent cylinder wake at Reynolds number 8100. Along the stream-wise direction, the flow becomes more isotropic and the magnitudes of normal Reynolds stresses decrease monotonically. These seem to indicate the flow dynamics becomes simpler downstream. However, the Shannon entropy keeps increasing along the flow direction and the dynamics seems to be more complex, because the large-scale vortices cascade to small eddies, the flow is less correlated and more unpredictable. In fact, these two contradictory observations partially describe the complexity of a turbulent wake. Our measurements (up to 40 diameters downstream the cylinder) show that the flow's degree-of-complexity actually increases firstly and then becomes a constant (or drops slightly) along the stream-wise direction. University of Kansas General Research Fund.
Radial transport in the far scrape-off layer of ASDEX upgrade during L-mode and ELMy H-mode
DEFF Research Database (Denmark)
Ionita, C.; Naulin, Volker; Mehlmann, F.
2013-01-01
The radial turbulent particle flux and the Reynolds stress in the scrape-off layer (SOL) of ASDEX Upgrade were investigated for two limited L-mode (low confinement) and one ELMy H-mode (high confinement) discharge. A fast reciprocating probe was used with a probe head containing five Langmuir...
Zonal flows and turbulence in fluids and plasmas
Parker, Jeffrey Bok-Cheung
In geophysical and plasma contexts, zonal flows are well known to arise out of turbulence. We elucidate the transition from statistically homogeneous turbulence without zonal flows to statistically inhomogeneous turbulence with steady zonal flows. Starting from the Hasegawa--Mima equation, we employ both the quasilinear approximation and a statistical average, which retains a great deal of the qualitative behavior of the full system. Within the resulting framework known as CE2, we extend recent understanding of the symmetry-breaking 'zonostrophic instability'. Zonostrophic instability can be understood in a very general way as the instability of some turbulent background spectrum to a zonally symmetric coherent mode. As a special case, the background spectrum can consist of only a single mode. We find that in this case the dispersion relation of zonostrophic instability from the CE2 formalism reduces exactly to that of the 4-mode truncation of generalized modulational instability. We then show that zonal flows constitute pattern formation amid a turbulent bath. Zonostrophic instability is an example of a Type I s instability of pattern-forming systems. The broken symmetry is statistical homogeneity. Near the bifurcation point, the slow dynamics of CE2 are governed by a well-known amplitude equation, the real Ginzburg-Landau equation. The important features of this amplitude equation, and therefore of the CE2 system, are multiple. First, the zonal flow wavelength is not unique. In an idealized, infinite system, there is a continuous band of zonal flow wavelengths that allow a nonlinear equilibrium. Second, of these wavelengths, only those within a smaller subband are stable. Unstable wavelengths must evolve to reach a stable wavelength; this process manifests as merging jets. These behaviors are shown numerically to hold in the CE2 system, and we calculate a stability diagram. The stability diagram is in agreement with direct numerical simulations of the quasilinear
Bominaar, Jeroen; Pashtrapanska, Mira; Elenbaas, Thijs; Dam, Nico; ter Meulen, Hans; van de Water, Willem
2008-04-01
We describe a scheme of molecular tagging velocimetry in air in which nitric oxide (NO) molecules are created out of O2 and N2 molecules in the focus of a strong laser beam. The NO molecules are visualized a while later by laser-induced fluorescence. The precision of the molecular tagging velocimetry of gas flows is affected by the gradual blurring of the written patterns through molecular diffusion. In the case of turbulent flows, molecular diffusion poses a fundamental limit on the resolution of the smallest scales in the flow. We study the diffusion of written patterns in detail for our tagging scheme which, at short (micros) delay times is slightly anomalous due to local heating by absorption of laser radiation. We show that our experiments agree with a simple convection-diffusion model that allows us to estimate the temperature rise upon writing. Molecular tagging can be a highly nonlinear process, which affects the art of writing. We find that our tagging scheme is (only) quadratic in the intensity of the writing laser.
Theory of anomalous transport in H-mode plasmas
International Nuclear Information System (INIS)
Itoh, S.; Itoh, K.; Fukuyama, A.; Yagi, M.
1993-05-01
Theory of the anomalous transport is developed, and the unified formula for the L- and H-mode plasmas is presented. The self-sustained ballooning-mode turbulence is solved in the presence of the inhomogeneous radial electric field, E r . Reductions in transport coefficients and the amplitude and decorrelation length of fluctuations due to E r ' are quantitatively analyzed. Combined with the E r -bifurcation model, the thickness of the transport barrier is simultaneously determined. (author)
Analysis of current diffusive ballooning mode in tokamaks
International Nuclear Information System (INIS)
Uchida, M.; Fukuyama, A.; Itoh, S.-I.; Yagi, M.
1999-12-01
The effect of finite gyroradius on the current diffusive ballooning mode is examined. Starting from the reduced MHD equations including turbulent transports, coupling with drift motion and finite gyroradius effect of ions, we derive a ballooning mode equation with complex transport coefficients. The eigenfrequency, saturation level and thermal diffusivity are evaluated numerically from the marginal stability condition. Preliminary results of their parameter dependence is presented. (author)
The physics of transport barrier formation in the PBX-M H-mode
International Nuclear Information System (INIS)
Tynan, G.R.; Schmitz, L.; Blush, L.
1994-01-01
Measurements of edge profiles, turbulence, and turbulent-driven transport were made inside the last-closed flux surface (LCFS) and in the scrape-off layer (SOL) of PBX-M L-mode and H-mode plasmas using a fast reciprocating Langmuir probe diagnostic. Direct measurements of the potential profile confirm the generation of a strong inward radial electric field (E r ∼ -100 V/cm) just inside the LCFS in H-mode. Density and potential fluctuations levels are reduced at the L-H transition, resulting in significantly lower turbulent transport. The reduction in turbulent transport occurs across the LCFS and SOL regions and is not localized to the region of strong radial electric field. (author)
Turbulent spots and scalar flashes in pipe transition
Adrian, Ronald; Wu, Xiaohua; Moin, Parviz
2017-11-01
Recent study (Wu et al., PNAS, 1509451112, 2015) demonstrated the feasibility and accuracy of direct computation of the Osborne Reynolds' pipe transition experiment without the unphysical axially periodic boundary condition. Here we use this approach to address three questions: (1) What are the dynamics of turbulent spot generation in pipe transition? (2) How is the succession of scalar flashes, as observed and sketched by Osborne Reynolds, created? (3) What happens to the succession of flashes further downstream? In this study, the inlet disturbance is of radial-mode type imposed through a narrow, three-degree numerical wedge; and the simulation Reynolds number is 6500. Numerical dye is introduced at the inlet plane locally very close to the pipe axis, similar to the needle injection by O. Reynolds. Inception of infant turbulent spots occurs when normal, forward inclined hairpin packets form near the walls from the debris of the inlet perturbations. However, the young and mature turbulent spots consist almost exclusively of reverse, backward leaning hairpin vortices. Scalar flashes appear successively downstream and persist well into the fully-developed turbulent region. Their creation mechanism is addressed. RJA gratefully acknowledges support of the National Science Foundation with NSF Award CBET-0933848.
Relativistic plasma turbulence and its application to pulsar phenomena
International Nuclear Information System (INIS)
Hinata, S.
1976-01-01
A turbulent plasma model of pulsars which has the potential of providing a self-regulatory mechanism for producing an electron-positron plasma over the polar caps, as well as the coherency of the radio wave emission, is analyzed. Turbulent plasma properties including the kinetic and electrostatic energy densities, the wavelength of the most unstable mode, and the effective collision frequency due to the excited electric field, are obtained and applied to the pulsar situation. Since these properties depend on the momentum distribution of the plasma particles, model calculations have been carried out with simple momentum distribution functions. The radio luminosity due to turbulence (bunching or otherwise) turned out to be either insufficient or unclear at the moment for these simple momentum distributions. This indicates that a further investigation of turbulence processes with the self-consistently determined momentum distribution is needed. This is left for future analysis, because entirely different processes (e.g. trapping) are likely to dominate the physics as is demonstrated for one of the model distribution functions. In addition to the above mentioned model, we examine some wave propagation properties in a relativistic electron-positron plasma immersed in a strong magnetic field
The role of zonal flows in disc gravito-turbulence
Vanon, R.
2018-04-01
The work presented here focuses on the role of zonal flows in the self-sustenance of gravito-turbulence in accretion discs. The numerical analysis is conducted using a bespoke pseudo-spectral code in fully compressible, non-linear conditions. The disc in question, which is modelled using the shearing sheet approximation, is assumed to be self-gravitating, viscous, and thermally diffusive; a constant cooling timescale is also considered. Zonal flows are found to emerge at the onset of gravito-turbulence and they remain closely linked to the turbulent state. A cycle of zonal flow formation and destruction is established, mediated by a slow mode instability (which allows zonal flows to grow) and a non-axisymmetric instability (which disrupts the zonal flow), which is found to repeat numerous times. It is in fact the disruptive action of the non-axisymmetric instability to form new leading and trailing shearing waves, allowing energy to be extracted from the background flow and ensuring the self-sustenance of the gravito-turbulent regime.
The role of zonal flows in disc gravito-turbulence
Vanon, R.
2018-07-01
The work presented here focuses on the role of zonal flows in the self-sustenance of gravito-turbulence in accretion discs. The numerical analysis is conducted using a bespoke pseudo-spectral code in fully compressible, non-linear conditions. The disc in question, which is modelled using the shearing sheet approximation, is assumed to be self-gravitating, viscous, and thermally diffusive; a constant cooling time-scale is also considered. Zonal flows are found to emerge at the onset of gravito-turbulence and they remain closely linked to the turbulent state. A cycle of zonal flow formation and destruction is established, mediated by a slow mode instability (which allows zonal flows to grow) and a non-axisymmetric instability (which disrupts the zonal flow), which is found to repeat numerous times. It is in fact the disruptive action of the non-axisymmetric instability to form new leading and trailing shearing waves, allowing energy to be extracted from the background flow and ensuring the self-sustenance of the gravito-turbulent regime.
Comparing simulation of plasma turbulence with experiment
International Nuclear Information System (INIS)
Ross, David W.; Bravenec, Ronald V.; Dorland, William; Beer, Michael A.; Hammett, G. W.; McKee, George R.; Fonck, Raymond J.; Murakami, Masanori; Burrell, Keith H.; Jackson, Gary L.; Staebler, Gary M.
2002-01-01
The direct quantitative correspondence between theoretical predictions and the measured plasma fluctuations and transport is tested by performing nonlinear gyro-Landau-fluid simulations with the GRYFFIN (or ITG) code [W. Dorland and G. W. Hammett, Phys. Fluids B 5, 812 (1993); M. A. Beer and G. W. Hammett, Phys. Plasmas 3, 4046 (1996)]. In an L-mode reference discharge in the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)], which has relatively large fluctuations and transport, the turbulence is dominated by ion temperature gradient (ITG) modes. Trapped electron modes and impurity drift waves also play a role. Density fluctuations are measured by beam emission spectroscopy [R. J. Fonck, P. A. Duperrex, and S. F. Paul, Rev. Sci. Instrum. 61, 3487 (1990)]. Experimental fluxes and corresponding diffusivities are analyzed by the TRANSP code [R. J. Hawryluk, in Physics of Plasmas Close to Thermonuclear Conditions, edited by B. Coppi, G. G. Leotta, D. Pfirsch, R. Pozzoli, and E. Sindoni (Pergamon, Oxford, 1980), Vol. 1, p. 19]. The shape of the simulated wave number spectrum is close to the measured one. The simulated ion thermal transport, corrected for ExB low shear, exceeds the experimental value by a factor of 1.5 to 2.0. The simulation overestimates the density fluctuation level by an even larger factor. On the other hand, the simulation underestimates the electron thermal transport, which may be accounted for by modes that are not accessible to the simulation or to the BES measurement
Turbulence, transport, and zonal flows in the Madison symmetric torus reversed-field pinch
Williams, Z. R.; Pueschel, M. J.; Terry, P. W.; Hauff, T.
2017-12-01
The robustness and the effect of zonal flows in trapped electron mode (TEM) turbulence and Ion Temperature Gradient (ITG) turbulence in the reversed-field pinch (RFP) are investigated from numerical solutions of the gyrokinetic equations with and without magnetic external perturbations introduced to model tearing modes. For simulations without external magnetic field perturbations, zonal flows produce a much larger reduction of transport for the density-gradient-driven TEM turbulence than they do for the ITG turbulence. Zonal flows are studied in detail to understand the nature of their strong excitation in the RFP and to gain insight into the key differences between the TEM- and ITG-driven regimes. The zonal flow residuals are significantly larger in the RFP than in tokamak geometry due to the low safety factor. Collisionality is seen to play a significant role in the TEM zonal flow regulation through the different responses of the linear growth rate and the size of the Dimits shift to collisionality, while affecting the ITG only minimally. A secondary instability analysis reveals that the TEM turbulence drives zonal flows at a rate that is twice that of the ITG turbulence. In addition to interfering with zonal flows, the magnetic perturbations are found to obviate an energy scaling relation for fast particles.
Energy Technology Data Exchange (ETDEWEB)
Scott, F. R.; Jensen, T. H.; Wharton, C. B. [General Atomic Division, General Dynamics Corporation, San Diego, CA (United States)
1966-04-15
A pulsed mirror has been constructed to study the stability of a plasma of modest energy. The 70 eV plasma is piped from a gun to the mirror by a linear octopole guide field. The mirror field is turned on in a plasma transit time. Plasma densities of 10{sup 13} electrons/cm{sup 3} are observed in the central plane of the mirror. Two distinct modes of operation are observed and depend only on conditions established in the guide field. In the first mode the plasma in the mirror appears flute stable, most of the plasma escapes axially, a slow anomalous radial diffusion is observed and microwave emission occurs at the electron cyclotron harmonics ranging from n = 1 to at least n = 19. The microwave emission is not compatible with the electron branch of the Harris instability. The stability of this mode is attributed to line tieing by cold plasma effusing from the guide field region. Densities above 10{sup 11} electrons/cm{sup 3} were observed for 200 {mu}sec in the region between the mirror and the guide field. With the addition of an axially symmetric cylinder in the guide field, this density is decreased. Measurements show plasma densities below 10{sup 11} cm{sup -3} after 40 {mu}sec in this region. The resulting plasma trapped in the mirror exhibits flute instabilities, radial plasma loss, intense erratic microwave emission and rapid density decay. The m = 1 flute is identified and its phase is followed through 4{pi}. The phase velocity is in the direction of the electron B drift. The sign of this phase velocity may be explained by the theory of Krall if the electron energy exceeds the ion energy sufficiently. The addition of conducting plates in the downstream mirror region tempered the violence of the flute instability. This tempering depends only on the surface resistance of these plates. This effect was examined by measuring the frequency spectrum of signals from coated scintillator probes placed near the vacuum envelope. (author) [French] Les auteurs ont
Electrostatic instabilities and turbulence in a toroidal magnetized plasma
International Nuclear Information System (INIS)
Poli, F. M.
2007-06-01
This Thesis aims at characterizing the linear properties of electrostatic drift instabilities arising in a toroidal plasma and the mechanisms leading to their development into turbulence. The experiments are performed on the TORoidal Plasma EXperiment (TORPEX) at CRPP-EPFL, Lausanne. The first part of the Thesis focuses on the identification of the nature of the instabilities observed in TORPEX, using a set of electrostatic probes, designed and built for this purpose. The global features of fluctuations, analyzed for different values of control parameters such as the magnetic field, the neutral gas pressure and the injected microwave power, are qualitatively similar in different experimental scenarios. The maximum of fluctuations is observed on the low field side, where the pressure gradient and the gradient of the magnetic field are co-linear, indicating that the curvature of the magnetic field lines has an important role in the destabilization of the waves. The power spectrum is dominated by electrostatic fluctuations with frequencies much lower than the ion cyclotron frequency. Taking advantage of the extended diagnostics coverage, the spectral properties of fluctuations are measured over the whole poloidal cross-section. Both drift and interchange instabilities develop and propagate on TORPEX, with the stability of both being affected by the curvature of the magnetic field. It is shown that modes of different nature are driven at separate locations over the plasma cross-section and that the wavenumber and frequency spectra, narrow at the location where the instabilities are generated, broaden during convection, suggesting an increase in the degree of turbulence. The transition from coherent to turbulent spectral features and the role of nonlinear coupling between modes in the development of turbulence are treated in the second part of this work. It is found that nonlinear mode-mode coupling is responsible for the redistribution of spectral energy from the
Stability of magnetic modes in tokamaks; Stabilite des modes magnetiques dans les tokamaks
Energy Technology Data Exchange (ETDEWEB)
Zabiego, M
1994-06-01
A theoretical study is carried out concerning two experimental topics: stabilization, by a suprathermal population, of the mode ``m=1, n=1`` which induces the sawtooth effect (modelling the role of suprathermal particles in the stabilization); stability, in the non linear regime, of the magnetic islands involved in magnetic turbulence problems (micro-tearing) and in disruption phenomena (tearing), and the effects of diamagnetism, excitation threshold and saturation levels. 45 figs., 97 refs.
ION-SCALE TURBULENCE IN THE INNER HELIOSPHERE: RADIAL DEPENDENCE
Energy Technology Data Exchange (ETDEWEB)
Comisel, H.; Motschmann, U.; Büchner, J.; Narita, Y.; Nariyuki, Y. [University of Toyama, Faculty of Human Development, 3190, Gofuku, Toyama, 930-8555 (Japan)
2015-10-20
The evolution of the ion-scale plasma turbulence in the inner heliosphere is studied by associating the plasma parameters for hybrid-code turbulence simulations to the radial distance from the Sun via a Solar wind model based mapping procedure. Using a mapping based on a one-dimensional solar wind expansion model, the resulting ion-kinetic scale turbulence is related to the solar wind distance from the Sun. For this purpose the mapping is carried out for various values of ion beta that correspond to the heliocentric distance. It is shown that the relevant normal modes such as ion cyclotron and ion Bernstein modes will occur first at radial distances of about 0.2–0.3 AU, i.e., near the Mercury orbit. This finding can be used as a reference, a prediction to guide the in situ measurements to be performed by the upcoming Solar Orbiter and Solar Probe Plus missions. Furthermore, a radial dependence of the wave-vector anisotropy was obtained. For astrophysical objects this means that the spatial scales of filamentary structures in interstellar media or astrophysical jets can be predicted for photometric observations.
Simulation of microtearing turbulence in national spherical torus experiment
Energy Technology Data Exchange (ETDEWEB)
Guttenfelder, W.; Kaye, S. M.; Bell, R. E.; Hammett, G. W.; LeBlanc, B. P.; Mikkelsen, D. R.; Ren, Y. [Princeton Plasma Physics Laboratory, Princeton New Jersey 08543 (United States); Candy, J. [General Atomics, San Diego, California 92186 (United States); Nevins, W. M.; Wang, E. [Lawrence Livermore National Laboratory, Livermore, California 04551 (United States); Zhang, J.; Crocker, N. A. [University of California Los Angeles, California 90095 (United States); Yuh, H. [Nova Photonics Inc., Princeton, New Jersey 08540 (United States)
2012-05-15
Thermal energy confinement times in National Spherical Torus Experiment (NSTX) dimensionless parameter scans increase with decreasing collisionality. While ion thermal transport is neoclassical, the source of anomalous electron thermal transport in these discharges remains unclear, leading to considerable uncertainty when extrapolating to future spherical tokamak (ST) devices at much lower collisionality. Linear gyrokinetic simulations find microtearing modes to be unstable in high collisionality discharges. First non-linear gyrokinetic simulations of microtearing turbulence in NSTX show they can yield experimental levels of transport. Magnetic flutter is responsible for almost all the transport ({approx}98%), perturbed field line trajectories are globally stochastic, and a test particle stochastic transport model agrees to within 25% of the simulated transport. Most significantly, microtearing transport is predicted to increase with electron collisionality, consistent with the observed NSTX confinement scaling. While this suggests microtearing modes may be the source of electron thermal transport, the predictions are also very sensitive to electron temperature gradient, indicating the scaling of the instability threshold is important. In addition, microtearing turbulence is susceptible to suppression via sheared E Multiplication-Sign B flows as experimental values of E Multiplication-Sign B shear (comparable to the linear growth rates) dramatically reduce the transport below experimental values. Refinements in numerical resolution and physics model assumptions are expected to minimize the apparent discrepancy. In cases where the predicted transport is strong, calculations suggest that a proposed polarimetry diagnostic may be sensitive to the magnetic perturbations associated with the unique structure of microtearing turbulence.
Coherent structures and transport in drift wave plasma turbulence
Energy Technology Data Exchange (ETDEWEB)
Bang Korsholm, S.
2011-12-15
Fusion energy research aims at developing fusion power plants providing safe and clean energy with abundant fuels. Plasma turbulence induced transport of energy and particles is a performance limiting factor for fusion devices. Hence the understanding of plasma turbulence is important for optimization. The present work is a part of the puzzle to understand the basic physics of transport induced by drift wave turbulence in the edge region of a plasma. The basis for the study is the Hasegawa-Wakatani model. Simulation results for 3D periodic and nonperiodic geometries are presented. The Hasegawa-Wakatani model is further expanded to include ion temperature effects. Another expansion of the model is derived from the Braginskii electron temperature equation. The result is a self-consistent set of equations describing the dynamical evolution of the drift wave fluctuations of the electron density, electron temperature and the potential in the presence of density and temperature gradients. 3D simulation results of the models are presented. Finally, the construction and first results from the MAST fluctuation reflectometer is described. The results demonstrate how L- to H-mode transitions as well as edge-localized-modes can be detected by the relatively simple diagnostic system. The present Risoe report is a slightly updated version of my original PhD report which was submitted in April 2002 and defended in August 2002. (Author)
Coherent structures and transport in drift wave plasma turbulence
International Nuclear Information System (INIS)
Bang Korsholm, S.
2011-12-01
Fusion energy research aims at developing fusion power plants providing safe and clean energy with abundant fuels. Plasma turbulence induced transport of energy and particles is a performance limiting factor for fusion devices. Hence the understanding of plasma turbulence is important for optimization. The present work is a part of the puzzle to understand the basic physics of transport induced by drift wave turbulence in the edge region of a plasma. The basis for the study is the Hasegawa-Wakatani model. Simulation results for 3D periodic and nonperiodic geometries are presented. The Hasegawa-Wakatani model is further expanded to include ion temperature effects. Another expansion of the model is derived from the Braginskii electron temperature equation. The result is a self-consistent set of equations describing the dynamical evolution of the drift wave fluctuations of the electron density, electron temperature and the potential in the presence of density and temperature gradients. 3D simulation results of the models are presented. Finally, the construction and first results from the MAST fluctuation reflectometer is described. The results demonstrate how L- to H-mode transitions as well as edge-localized-modes can be detected by the relatively simple diagnostic system. The present Risoe report is a slightly updated version of my original PhD report which was submitted in April 2002 and defended in August 2002. (Author)
International Nuclear Information System (INIS)
Hornsby, W. A.; Peeters, A. G.; Snodin, A. P.; Casson, F. J.; Camenen, Y.; Szepesi, G.; Siccinio, M.; Poli, E.
2010-01-01
The interaction between small scale turbulence (of the order of the ion Larmor radius) and mesoscale magnetic islands is investigated within the gyrokinetic framework. Turbulence, driven by background temperature and density gradients, over nonlinear mode coupling, pumps energy into long wavelength modes, and can result in an electrostatic vortex mode that coincides with the magnetic island. The strength of the vortex is strongly enhanced by the modified plasma flow response connected with the change in topology, and the transport it generates can compete with the parallel motion along the perturbed magnetic field. Despite the stabilizing effect of sheared plasma flows in and around the island, the net effect of the island is a degradation of the confinement. When density and temperature gradients inside the island are below the threshold for turbulence generation, turbulent fluctuations still persist through turbulence convection and spreading. The latter mechanisms then generate a finite transport flux and, consequently, a finite pressure gradient in the island. A finite radial temperature gradient inside the island is also shown to persist due to the trapped particles, which do not move along the field around the island. In the low collisionality regime, the finite gradient in the trapped population leads to the generation of a bootstrap current, which reduces the neoclassical drive.
International Nuclear Information System (INIS)
Johnsen, Eric; Larsson, Johan; Bhagatwala, Ankit V.; Cabot, William H.; Moin, Parviz; Olson, Britton J.; Rawat, Pradeep S.; Shankar, Santhosh K.; Sjoegreen, Bjoern; Yee, H.C.; Zhong Xiaolin; Lele, Sanjiva K.
2010-01-01
Flows in which shock waves and turbulence are present and interact dynamically occur in a wide range of applications, including inertial confinement fusion, supernovae explosion, and scramjet propulsion. Accurate simulations of such problems are challenging because of the contradictory requirements of numerical methods used to simulate turbulence, which must minimize any numerical dissipation that would otherwise overwhelm the small scales, and shock-capturing schemes, which introduce numerical dissipation to stabilize the solution. The objective of the present work is to evaluate the performance of several numerical methods capable of simultaneously handling turbulence and shock waves. A comprehensive range of high-resolution methods (WENO, hybrid WENO/central difference, artificial diffusivity, adaptive characteristic-based filter, and shock fitting) and suite of test cases (Taylor-Green vortex, Shu-Osher problem, shock-vorticity/entropy wave interaction, Noh problem, compressible isotropic turbulence) relevant to problems with shocks and turbulence are considered. The results indicate that the WENO methods provide sharp shock profiles, but overwhelm the physical dissipation. The hybrid method is minimally dissipative and leads to sharp shocks and well-resolved broadband turbulence, but relies on an appropriate shock sensor. Artificial diffusivity methods in which the artificial bulk viscosity is based on the magnitude of the strain-rate tensor resolve vortical structures well but damp dilatational modes in compressible turbulence; dilatation-based artificial bulk viscosity methods significantly improve this behavior. For well-defined shocks, the shock fitting approach yields good results.
Turbulent boundary layer over 2D and 3D large-scale wavy walls
Chamorro, Leonardo P.; Hamed, Ali M.; Castillo, Luciano
2015-11-01
In this work, an experimental investigation of the developing and developed flow over two- and three-dimensional large-scale wavy walls was performed using high-resolution planar particle image velocimetry in a refractive-index-matching flume. The 2D wall is described by a sinusoidal wave in the streamwise direction with amplitude to wavelength ratio a/ λx = 0.05. The 3D wall is defined with an additional wave superimposed on the 2D wall in the spanwise direction with a/ λy = 0.1. The flow was characterized at Reynolds numbers of 4000 and 40000, based on the bulk velocity and the flume half height. Instantaneous velocity fields and time-averaged turbulence quantities reveal strong coupling between large-scale topography and the turbulence dynamics near the wall. Turbulence statistics show the presence of a well-structured shear layer that enhances the turbulence for the 2D wavy wall, whereas the 3D wall exhibits different flow dynamics and significantly lower turbulence levels, particularly for which shows about 30% reduction. The likelihood of recirculation bubbles, levels and spatial distribution of turbulence, and the rate of the turbulent kinetic energy production are shown to be severely affected when a single spanwise mode is superimposed on the 2D wall. POD analysis was also performed to further understand distinctive features of the flow structures due to surface topography.
Intrinsic non-inductive current driven by ETG turbulence in tokamaks
Singh, Rameswar; Kaw, P. K.; Singh, R.; Gürcan, Ã.-. D.
2017-10-01
Motivated by observations and physics understanding of the phenomenon of intrinsic rotation, it is suggested that similar considerations for electron dynamics may result in intrinsic current in tokamaks. We have investigated the possibility of intrinsic non-inductive current in the turbulent plasma of tokamaks. Ohm's law is generalized to include the effect of turbulent fluctuations in the mean field approach. This clearly leads to the identification of sources and the mechanisms of non-inductive current drive by electron temperature gradient turbulence. It is found that a mean parallel electro-motive force and hence a mean parallel current can be generated by (1) the divergence of residual current flux density and (2) a non-flux like turbulent source from the density and parallel electric field correlations. Both residual flux and the non-flux source require parallel wave-number k∥ symmetry breaking for their survival which can be supplied by various means like mean E × B shear, turbulence intensity gradient, etc. Estimates of turbulence driven current are compared with the background bootstrap current in the pedestal region. It is found that turbulence driven current is nearly 10% of the bootstrap current and hence can have a significant influence on the equilibrium current density profiles and current shear driven modes.
Investigation of diocotron modes in toroidally trapped electron plasmas using non-destructive method
Lachhvani, Lavkesh; Pahari, Sambaran; Sengupta, Sudip; Yeole, Yogesh G.; Bajpai, Manu; Chattopadhyay, P. K.
2017-10-01
Experiments with trapped electron plasmas in a SMall Aspect Ratio Toroidal device (SMARTEX-C) have demonstrated a flute-like mode represented by oscillations on capacitive (wall) probes. Although analogous to diocotron mode observed in linear electron traps, the mode evolution in toroids can have interesting consequences due to the presence of in-homogeneous magnetic field. In SMARTEX-C, the probe signals are observed to undergo transition from small, near-sinusoidal oscillations to large amplitude, non-linear "double-peaked" oscillations. To interpret the wall probe signal and bring forth the dynamics, an expression for the induced current on the probe for an oscillating charge is derived, utilizing Green's Reciprocation Theorem. Equilibrium position, poloidal velocity of the charge cloud, and charge content of the cloud, required to compute the induced current, are estimated from the experiments. Signal through capacitive probes is thereby computed numerically for possible charge cloud trajectories. In order to correlate with experiments, starting with an intuitive guess of the trajectory, the model is evolved and tweaked to arrive at a signal consistent with experimentally observed probe signals. A possible vortex like dynamics is predicted, hitherto unexplored in toroidal geometries, for a limited set of experimental observations from SMARTEX-C. Though heuristic, a useful interpretation of capacitive probe data in terms of charge cloud dynamics is obtained.
Modeling of Turbulent Swirling Flows
Shih, Tsan-Hsing; Zhu, Jiang; Liou, William; Chen, Kuo-Huey; Liu, Nan-Suey; Lumley, John L.
1997-01-01
Aircraft engine combustors generally involve turbulent swirling flows in order to enhance fuel-air mixing and flame stabilization. It has long been recognized that eddy viscosity turbulence models are unable to appropriately model swirling flows. Therefore, it has been suggested that, for the modeling of these flows, a second order closure scheme should be considered because of its ability in the modeling of rotational and curvature effects. However, this scheme will require solution of many complicated second moment transport equations (six Reynolds stresses plus other scalar fluxes and variances), which is a difficult task for any CFD implementations. Also, this scheme will require a large amount of computer resources for a general combustor swirling flow. This report is devoted to the development of a cubic Reynolds stress-strain model for turbulent swirling flows, and was inspired by the work of Launder's group at UMIST. Using this type of model, one only needs to solve two turbulence equations, one for the turbulent kinetic energy k and the other for the dissipation rate epsilon. The cubic model developed in this report is based on a general Reynolds stress-strain relationship. Two flows have been chosen for model evaluation. One is a fully developed rotating pipe flow, and the other is a more complex flow with swirl and recirculation.
Advancements in engineering turbulence modeling
Shih, T.-H.
1991-01-01
Some new developments in two-equation models and second order closure models are presented. Two-equation models (k-epsilon models) have been widely used in computational fluid dynamics (CFD) for engineering problems. Most of low-Reynolds number two-equation models contain some wall-distance damping functions to account for the effect of wall on turbulence. However, this often causes the confusion and difficulties in computing flows with complex geometry and also needs an ad hoc treatment near the separation and reattachment points. A set of modified two-equation models is proposed to remove the aforementioned shortcomings. The calculations using various two-equation models are compared with direct numerical simulations of channel flow and flat boundary layers. Development of a second order closure model is also discussed with emphasis on the modeling of pressure related correlation terms and dissipation rates in the second moment equations. All the existing models poorly predict the normal stresses near the wall and fail to predict the 3-D effect of mean flow on the turbulence (e.g. decrease in the shear stress caused by the cross flow in the boundary layer). The newly developed second order near-wall turbulence model is described and is capable of capturing the near-wall behavior of turbulence as well as the effect of 3-D mean flow on the turbulence.
TRIAM-1 turbulent heating experiment
Energy Technology Data Exchange (ETDEWEB)
Nakamura, Yukio; Hiraki, Naoji; Nakamura, Kazuo; Kikuchi, Mitsuru; Nagao, Akihiro [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics
1983-02-01
The experimental studies on the containment of high temperature plasma and turbulent heating using the tokamak device with strong magnetic field (TRIAM-1) started in 1977 have achieved much results up to fiscal 1979, and the anticipated objectives were almost attained. The results of these studies were summarized in the ''Report of the results of strong magnetic field tokamak TRIAM-1 experiment''. In this report, the results obtained by the second stage project of the TRIAM-1 project are summarized. The second stage was the two-year project for fiscal 1980 and 81. In the second stage project, by the complete preparation of measuring instrument and the improvement of the experimental setup, the carefully planned experiment on turbulent heating was performed, in particular, the clarification of the mechanism of turbulent heating was the central theme. As the important results obtained, the detection of ion sound waves at the time of turbulent heating, the formation of high energy ions by wave-particle interaction and the clarification of the process of their energy relaxation, and the verification of the effectiveness of double pulse turbulent heating are enumerated.
TRIAM-1 turbulent heating experiment
International Nuclear Information System (INIS)
Nakamura, Yukio; Hiraki, Naoji; Nakamura, Kazuo; Kikuchi, Mitsuru; Nagao, Akihiro
1983-01-01
The experimental studies on the containment of high temperature plasma and turbulent heating using the tokamak device with strong magnetic field (TRIAM-1) started in 1977 have achieved much results up to fiscal 1979, and the anticipated objectives were almost attained. The results of these studies were summarized in the ''Report of the results of strong magnetic field tokamak TRIAM-1 experiment''. In this report, the results obtained by the second stage project of the TRIAM-1 project are summarized. The second stage was the two-year project for fiscal 1980 and 81. In the second stage project, by the complete preparation of measuring instrument and the improvement of the experimental setup, the carefully planned experiment on turbulent heating was performed, in particular, the clarification of the mechanism of turbulent heating was the central theme. As the important results obtained, the detection of ion sound waves at the time of turbulent heating, the formation of high energy ions by waveparticle interaction and the clarification of the process of their energy relaxation, and the verification of the effectiveness of double pulse turbulent heating are enumerated. (Kako, I.)
PDF turbulence modeling and DNS
Hsu, A. T.
1992-01-01
The problem of time discontinuity (or jump condition) in the coalescence/dispersion (C/D) mixing model is addressed in probability density function (pdf). A C/D mixing model continuous in time is introduced. With the continuous mixing model, the process of chemical reaction can be fully coupled with mixing. In the case of homogeneous turbulence decay, the new model predicts a pdf very close to a Gaussian distribution, with finite higher moments also close to that of a Gaussian distribution. Results from the continuous mixing model are compared with both experimental data and numerical results from conventional C/D models. The effect of Coriolis forces on compressible homogeneous turbulence is studied using direct numerical simulation (DNS). The numerical method used in this study is an eight order compact difference scheme. Contrary to the conclusions reached by previous DNS studies on incompressible isotropic turbulence, the present results show that the Coriolis force increases the dissipation rate of turbulent kinetic energy, and that anisotropy develops as the Coriolis force increases. The Taylor-Proudman theory does apply since the derivatives in the direction of the rotation axis vanishes rapidly. A closer analysis reveals that the dissipation rate of the incompressible component of the turbulent kinetic energy indeed decreases with a higher rotation rate, consistent with incompressible flow simulations (Bardina), while the dissipation rate of the compressible part increases; the net gain is positive. Inertial waves are observed in the simulation results.
Two-dimensional turbulent convection
Mazzino, Andrea
2017-11-01
We present an overview of the most relevant, and sometimes contrasting, theoretical approaches to Rayleigh-Taylor and mean-gradient-forced Rayleigh-Bénard two-dimensional turbulence together with numerical and experimental evidences for their support. The main aim of this overview is to emphasize that, despite the different character of these two systems, especially in relation to their steadiness/unsteadiness, turbulent fluctuations are well described by the same scaling relationships originated from the Bolgiano balance. The latter states that inertial terms and buoyancy terms balance at small scales giving rise to an inverse kinetic energy cascade. The main difference with respect to the inverse energy cascade in hydrodynamic turbulence [R. H. Kraichnan, "Inertial ranges in two-dimensional turbulence," Phys. Fluids 10, 1417 (1967)] is that the rate of cascade of kinetic energy here is not constant along the inertial range of scales. Thanks to the absence of physical boundaries, the two systems here investigated turned out to be a natural physical realization of the Kraichnan scaling regime hitherto associated with the elusive "ultimate state of thermal convection" [R. H. Kraichnan, "Turbulent thermal convection at arbitrary Prandtl number," Phys. Fluids 5, 1374-1389 (1962)].
EFFECT OF ION ∇ B DRIFT DIRECTION ON TURBULENCE FLOW AND FLOW SHEAR
International Nuclear Information System (INIS)
FENZI, C; McKEE, G.R; BURRELL, K.H; CARLSTROM, T.N; FONCK, R.J; GROEBNER, R.J
2003-01-01
The divertor magnetic geometry has a significant effect on the poloidal flow and resulting flow shear of turbulence in the outer region of L-mode tokamak plasmas, as determined via two-dimensional measurements of density fluctuations with Beam Emission Spectroscopy on DIII-D. Plasmas with similar parameters, except that in one case the ion (del)B drift points towards the divertor X-point (lower single-null, LSN), and in the other case, the ion (del)B drift points away from the divertor X-point (upper single-null, USN), are compared. Inside of r/a=0.9, the turbulence characteristics (amplitude, flow direction, correlation lengths) are similar in both cases, while near r/a=0.92, a dramatic reversal of the poloidal flow of turbulence relative to the core flow direction is observed in plasmas with the ion (del)B drift pointing towards the divertor X-point. No such flow reversal is observed in plasmas with the ion (del)B drift pointing away from the divertor X-point. This poloidal flow reversal results in a significantly larger local shear in the poloidal turbulence flow velocity in plasmas with the ion (del)B drift pointing towards the divertor X-point. Additionally, these plasmas locally exhibit significant dispersion, with two distinct and counter-propagating turbulence modes. Likewise, the radial correlation length of the turbulence is reduced in these plasmas, consistent with biorthogonal decomposition measurements of dominant turbulence structures. The naturally occurring turbulence flow shear in these LSN plasmas may facilitate the LH transition that occurs at an input power of roughly one-half to one-third that of corresponding plasmas with the ion (del)B drift pointing away from the X-point
Statistical theory and transition in multiple-scale-lengths turbulence in plasmas
Energy Technology Data Exchange (ETDEWEB)
Itoh, Sanae-I. [Research Institute for Applied Mechanics, Kyushu Univ., Kasuga, Fukuoka (Japan); Itoh, Kimitaka [National Inst. for Fusion Science, Toki, Gifu (Japan)
2001-06-01
The statistical theory of strong turbulence in inhomogeneous plasmas is developed for the cases where fluctuations with different scale-lengths coexist. Nonlinear interactions in the same kind of fluctuations as well as nonlinear interplay between different classes of fluctuations are kept in the analysis. Nonlinear interactions are modelled as turbulent drag, nonlinear noise and nonlinear drive, and a set of Langevin equations is formulated. With the help of an Ansatz of a large number of degrees of freedom with positive Lyapunov number, Langevin equations are solved and the fluctuation dissipation theorem in the presence of strong plasma turbulence has been derived. A case where two driving mechanisms (one for micro mode and the other for semi-micro mode) coexist is investigated. It is found that there are several states of fluctuations: in one state, the micro mode is excited and the semi-micro mode is quenched; in the other state, the semi-micro mode is excited, and the micro mode remains at finite but suppressed level. New type of turbulence transition is obtained, and a cusp type catastrophe is revealed. A phase diagram is drawn for turbulence which is composed of multiple classes of fluctuations. Influence of the inhomogeneous global radial electric field is discussed. A new insight is given for the physics of internal transport barrier. Finally, the nonlocal heat transport due to the long-wave-length fluctuations, which are noise-pumped by shorter-wave-length ones, is analyzed and the impact on transient transport problems is discussed. (author)
On Kinetic Slow Modes, Fluid Slow Modes, and Pressure-balanced Structures in the Solar Wind
Energy Technology Data Exchange (ETDEWEB)
Verscharen, Daniel [Space Science Center and Department of Physics, University of New Hampshire, Durham, NH 03824 (United States); Chen, Christopher H. K. [Department of Physics, Imperial College London, London SW7 2AZ (United Kingdom); Wicks, Robert T., E-mail: daniel.verscharen@unh.edu, E-mail: christopher.chen@imperial.ac.uk, E-mail: r.wicks@ucl.ac.uk [Mullard Space Science Laboratory, University College London, London WC1E 6BT (United Kingdom)
2017-05-10
Observations in the solar wind suggest that the compressive component of inertial-range solar-wind turbulence is dominated by slow modes. The low collisionality of the solar wind allows for nonthermal features to survive, which suggests the requirement of a kinetic plasma description. The least-damped kinetic slow mode is associated with the ion-acoustic (IA) wave and a nonpropagating (NP) mode. We derive analytical expressions for the IA-wave dispersion relation in an anisotropic plasma in the framework of gyrokinetics and then compare them to fully kinetic numerical calculations, results from two-fluid theory, and magnetohydrodynamics (MHD). This comparison shows major discrepancies in the predicted wave phase speeds from MHD and kinetic theory at moderate to high β . MHD and kinetic theory also dictate that all plasma normal modes exhibit a unique signature in terms of their polarization. We quantify the relative amplitude of fluctuations in the three lowest particle velocity moments associated with IA and NP modes in the gyrokinetic limit and compare these predictions with MHD results and in situ observations of the solar-wind turbulence. The agreement between the observations of the wave polarization and our MHD predictions is better than the kinetic predictions, which suggests that the plasma behaves more like a fluid in the solar wind than expected.
On Kinetic Slow Modes, Fluid Slow Modes, and Pressure-balanced Structures in the Solar Wind
International Nuclear Information System (INIS)
Verscharen, Daniel; Chen, Christopher H. K.; Wicks, Robert T.
2017-01-01
Observations in the solar wind suggest that the compressive component of inertial-range solar-wind turbulence is dominated by slow modes. The low collisionality of the solar wind allows for nonthermal features to survive, which suggests the requirement of a kinetic plasma description. The least-damped kinetic slow mode is associated with the ion-acoustic (IA) wave and a nonpropagating (NP) mode. We derive analytical expressions for the IA-wave dispersion relation in an anisotropic plasma in the framework of gyrokinetics and then compare them to fully kinetic numerical calculations, results from two-fluid theory, and magnetohydrodynamics (MHD). This comparison shows major discrepancies in the predicted wave phase speeds from MHD and kinetic theory at moderate to high β . MHD and kinetic theory also dictate that all plasma normal modes exhibit a unique signature in terms of their polarization. We quantify the relative amplitude of fluctuations in the three lowest particle velocity moments associated with IA and NP modes in the gyrokinetic limit and compare these predictions with MHD results and in situ observations of the solar-wind turbulence. The agreement between the observations of the wave polarization and our MHD predictions is better than the kinetic predictions, which suggests that the plasma behaves more like a fluid in the solar wind than expected.
Investigation of small-scale tokamak plasma turbulence by correlative UHR backscattering diagnostics
International Nuclear Information System (INIS)
Gusakov, E Z; Gurchenko, A D; Altukhov, A B; Bulanin, V V; Esipov, L A; Kantor, M Yu; Kouprienko, D V; Lashkul, S I; Petrov, A V; Stepanov, A Yu
2006-01-01
Fine scale turbulence is considered nowadays as a possible candidate for the explanation of anomalous ion and electron energy transport in magnetized fusion plasmas. The unique correlative upper hybrid resonance backscattering (UHR BS) technique is applied at the FT-2 tokamak for investigation of density fluctuations excited in this turbulence. The measurements are carried out in Ohmic discharge at several values of plasma current and density and during current ramp up experiment. The moveable focusing antennas set have been used in experiments allowing probing out of equatorial plane. The radial wave number spectra of the small-scale component of tokamak turbulence are determined from the correlation data with high spatial resolution. Two small-scale modes possessing substantially different phase velocities are observed in plasma under conditions when the threshold for the electron temperature gradient mode excitation is overcome. The possibility of plasma poloidal velocity profile determination using the UHR BS signal is demonstrated
Plasma shaping effects on tokamak scrape-off layer turbulence
Riva, Fabio; Lanti, Emmanuel; Jolliet, Sébastien; Ricci, Paolo
2017-03-01
The impact of plasma shaping on tokamak scrape-off layer (SOL) turbulence is investigated. The drift-reduced Braginskii equations are written for arbitrary magnetic geometries, and an analytical equilibrium model is used to introduce the dependence of turbulence equations on tokamak inverse aspect ratio (ε ), Shafranov’s shift (Δ), elongation (κ), and triangularity (δ). A linear study of plasma shaping effects on the growth rate of resistive ballooning modes (RBMs) and resistive drift waves (RDWs) reveals that RBMs are strongly stabilized by elongation and negative triangularity, while RDWs are only slightly stabilized in non-circular magnetic geometries. Assuming that the linear instabilities saturate due to nonlinear local flattening of the plasma gradient, the equilibrium gradient pressure length {L}p=-{p}e/{{\
Zweben, S. J.; Maqueda, R. J.; Terry, J. L.; Munsat, T.; Myra, J. R.; D'Ippolito, D.; Russell, D. A.; Krommes, J. A.; LeBlanc, B.; Stoltzfus-Dueck, T.; Stotler, D. P.; Williams, K. M.; Bush, C. E.; Maingi, R.; Grulke, O.; Sabbagh, S. A.; White, A. E.
2006-05-01
In this paper we compare the structure and motion of edge turbulence observed in L-mode vs. H-mode plasmas in the National Spherical Torus Experiment (NSTX) [M. Ono, M. G. Bell, R. E. Bell et al., Plasma Phys. Controlled Fusion 45, A335 (2003)]. The radial and poloidal correlation lengths are not significantly different between the L-mode and the H-mode in the cases examined. The poloidal velocity fluctuations are lower and the radial profiles of the poloidal turbulence velocity are somewhat flatter in the H-mode compared with the L-mode plasmas. These results are compared with similar measurements Alcator C-Mod [E. Marmar, B. Bai, R. L. Boivin et al., Nucl. Fusion 43, 1610 (2003)], and with theoretical models.
Non linear self consistency of microtearing modes
International Nuclear Information System (INIS)
Garbet, X.; Mourgues, F.; Samain, A.
1987-01-01
The self consistency of a microtearing turbulence is studied in non linear regimes where the ergodicity of the flux lines determines the electron response. The current which sustains the magnetic perturbation via the Ampere law results from the combines action of the radial electric field in the frame where the island chains are static and of the thermal electron diamagnetism. Numerical calculations show that at usual values of β pol in Tokamaks the turbulence can create a diffusion coefficient of order ν th p 2 i where p i is the ion larmor radius and ν th the electron ion collision frequency. On the other hand, collisionless regimes involving special profiles of each mode near the resonant surface seem possible
Turbulence and transport with spatial-temporal biasing on the scrape-off layer on CASTOR tokamak
International Nuclear Information System (INIS)
Stoeckel, J.
2002-01-01
Experiments with the poloidal ring of 32 plane electrodes were performed on the CASTOR tokamak (R=0.4 m, a=0.06 m, B=1 T) to measure, for the first time, the complete poloidal structure of the electrostatic edge turbulence. In addition, the possibility of active modification of the edge turbulence was checked. The main results are as follows: Quite regular turbulent structures with the pronounced poloidal periodicity are observed by passive measuring signals of the individual electrodes. The dominant poloidal mode number, m=6-8, is approximately of the same value as the edge safety factor. Propagating waves of potential (f=10-40 kHz) with the wave numbers in the range of m=2-8, applied to the ring of the electrodes, modify the edge turbulence significantly due to their interaction with turbulent structures. (author)
Turbulence models in supersonic flows
International Nuclear Information System (INIS)
Shirani, E.; Ahmadikia, H.; Talebi, S.
2001-05-01
The aim of this paper is to evaluate five different turbulence models when used in rather complicated two-dimensional and axisymmetric supersonic flows. They are Baldwin-Lomax, k-l, k-ε, k-ω and k-ζ turbulence models. The compressibility effects, axisymmetric correction terms and some modifications for transition region are used and tested in the models. Two computer codes based on the control volume approach and two flux-splitting methods. Roe and Van Leer, are developed. The codes are used to simulate supersonic mixing layers, flow behind axisymmetric body, under expanded jet, and flow over hollow cylinder flare. The results are compared with experimental data and behavior of the turbulence models is examined. It is shown that both k-l and k-ζ models produce very good results. It is also shown that the compressibility correction in the model is required to obtain more accurate results. (author)
Atmospheric turbulence and diffusion research
International Nuclear Information System (INIS)
Hosker, R.P. Jr.
1993-01-01
The Atmospheric Turbulence and Diffusion Division (well known in the atmospheric dispersion community as the Atmospheric Turbulence and Diffusion Laboratory, ATDL) is one of several field facilities of NOAAs Air Resources Laboratory, headquartered in Silver Spring, Maryland. The laboratory conducts research on matters of atmospheric diffusion and turbulent exchange, concerning air quality. ATDD focuses attention on the physics of the lower atmosphere, with special emphasis on the processes contributing to atmospheric transport, dispersion, deposition, and air-surface exchange, and on the development of predictive capabilities using the results of this research. Research is directed toward issues of national and global importance related to the missions of DOE, to DOE's Oak Ridge Field Office, and to NOAA. The program is divided into four major projects: plume transport and diffusion in the planetary boundary layer, complex topography, canopy micrometeorology, and air-surface exchange
ANISOTROPIC INTERMITTENCY OF MAGNETOHYDRODYNAMIC TURBULENCE
International Nuclear Information System (INIS)
Osman, K. T.; Kiyani, K. H.; Chapman, S. C.; Hnat, B.
2014-01-01
A higher-order multiscale analysis of spatial anisotropy in inertial range magnetohydrodynamic turbulence is presented using measurements from the STEREO spacecraft in fast ambient solar wind. We show for the first time that, when measuring parallel to the local magnetic field direction, the full statistical signature of the magnetic and Elsässer field fluctuations is that of a non-Gaussian globally scale-invariant process. This is distinct from the classic multiexponent statistics observed when the local magnetic field is perpendicular to the flow direction. These observations are interpreted as evidence for the weakness, or absence, of a parallel magnetofluid turbulence energy cascade. As such, these results present strong observational constraints on the statistical nature of intermittency in turbulent plasmas
Resonant quasiparticles in plasma turbulence
International Nuclear Information System (INIS)
Mendonca, J.T.; Bingham, R.; Shukla, P.K.
2003-01-01
A general view is proposed on wave propagation in fluids and plasmas where the resonant interaction of monochromatic waves with quasiparticles is considered. A kinetic equation for quasiparticles is used to describe the broadband turbulence interacting with monochromatic waves. Resonant interactions occur when the phase velocity of the long wavelength monochromatic wave is nearly equal to the group velocity of short wavelength wave packets, or quasiparticles, associated with the turbulent spectrum. It is shown that quasiparticle Landau damping can take place, as well as quasiparticle beam instabilities, thus establishing a direct link between short and large wavelength perturbations of the medium. This link is distinct from the usual picture of direct and inverse energy cascades, and it can be used as a different paradigm for the fluid and plasma turbulence theories
Turbulent breakage of ductile aggregates.
Marchioli, Cristian; Soldati, Alfredo
2015-05-01
In this paper we study breakage rate statistics of small colloidal aggregates in nonhomogeneous anisotropic turbulence. We use pseudospectral direct numerical simulation of turbulent channel flow and Lagrangian tracking to follow the motion of the aggregates, modeled as sub-Kolmogorov massless particles. We focus specifically on the effects produced by ductile rupture: This rupture is initially activated when fluctuating hydrodynamic stresses exceed a critical value, σ>σ(cr), and is brought to completion when the energy absorbed by the aggregate meets the critical breakage value. We show that ductile rupture breakage rates are significantly reduced with respect to the case of instantaneous brittle rupture (i.e., breakage occurs as soon as σ>σ(cr)). These discrepancies are due to the different energy values at play as well as to the statistical features of energy distribution in the anisotropic turbulence case examined.
Orbital-angular-momentum entanglement in turbulence
CSIR Research Space (South Africa)
Hamadou Ibrahim, A
2013-06-01
Full Text Available The turbulence-induced decay of orbital-angular-momentum (OAM) entanglement between two photons is investigated numerically and experimentally. To compare our resultswith previouswork,we simulate the turbulent atmosphere with a single phase screen...
Particle Settling in Low Energy Turbulence
Allen, Rachel; MacVean, Lissa; Tse, Ian; Mazzaro, Laura; Stacey, Mark; Variano, Evan
2014-11-01
Particle settling velocities can be altered by turbulence. In turbulence, dense particles may get trapped in convergent flow regions, and falling particles may be swept towards the downward side of turbulent eddies, resulting in enhanced settling velocities. The degree of velocity enhancement may depend on the Stokes number, the Rouse number, and the turbulent Reynolds number. In a homogeneous, isotropic turbulence tank, we tested the effects of particle size and type, suspended sediment concentration, and level of turbulence on the settling velocities of particles typically found in muddy estuaries. Two Acoustic Doppler Velocimeters (ADVs), separated vertically, measured turbulent velocities and suspended sediment concentrations, which yield condition dependent settling velocities, via ∂/á C ñ ∂ t = -∂/∂ z (ws á C ñ + á w ' C ' ñ) . These results are pertinent to fine sediment transport in estuaries, where high concentrations of suspended material are transported and impacted by low energy turbulence.
PDF methods for turbulent reactive flows
Hsu, Andrew T.
1995-01-01
Viewgraphs are presented on computation of turbulent combustion, governing equations, closure problem, PDF modeling of turbulent reactive flows, validation cases, current projects, and collaboration with industry and technology transfer.
Frontogenesis and turbulent mixing
Zhang, S.; Chen, F.; Shang, Q.
2017-12-01
ageostrophic secondary circulation together with the cross-frontal ageostrophic speed. The mixed characteristic is weak in summer, but the large turbulent dissipation and mixing rate measured in the frontal region, which show that the front promoted exchange of material and energy in the upper ocean.
2D turbulence structure observed by a fast framing camera system in linear magnetized device PANTA
International Nuclear Information System (INIS)
Ohdachi, Satoshi; Inagaki, S.; Kobayashi, T.; Goto, M.
2015-01-01
Mesoscale structure, such as the zonal flow and the streamer plays important role in the drift-wave turbulence. The interaction of the mesoscale structure and the turbulence is not only interesting phenomena but also a key to understand the turbulence driven transport in the magnetically confined plasmas. In the cylindrical magnetized device, PANTA, the interaction of the streamer and the drift wave has been found by the bi-spectrum analysis of the turbulence. In order to study the mesoscale physics directly, the 2D turbulence is studied by a fast-framing visible camera system view from a window located at the end plate of the device. The parameters of the plasma is the following; Te∼3eV, n ∼ 1x10 19 m -3 , Ti∼0.3eV, B=900G, Neutral pressure P n =0.8 mTorr, a∼ 6cm, L=4m, Helicon source (7MHz, 3kW). Fluctuating component of the visible image is decomposed by the Fourier-Bessel expansion method. Several rotating mode is observed simultaneously. From the images, m = 1 (f∼0.7 kHz) and m = 2, 3 (f∼-3.4 kHz) components which rotate in the opposite direction can be easily distinguished. Though the modes rotate constantly in most time, there appear periods where the radially complicated node structure is formed (for example, m=3 component, t = 142.5∼6 in the figure) and coherent mode structures are disturbed. Then, a new rotating period is started again with different phase of the initial rotation until the next event happens. The typical time interval of the event is 0.5 to 1.0 times of the one rotation of the slow m = 1 mode. The wave-wave interaction might be interrupted occasionally. Detailed analysis of the turbulence using imaging technique will be discussed. (author)
Simulations of edge and scrape off layer turbulence in mega ampere spherical tokamak plasmas
DEFF Research Database (Denmark)
Militello, F; Fundamenski, W; Naulin, Volker
2012-01-01
The L-mode interchange turbulence in the edge and scrape-off-layer (SOL) of the tight aspect ratio tokamak MAST is investigated numerically. The dynamics of the boundary plasma are studied using the 2D drift-fluid code ESEL, which has previously shown good agreement with large aspect ratio machin...
International Nuclear Information System (INIS)
Ren, Y.; Kaye, S.M.; Mazzucato, E.; Guttenfelder, W.; Bell, R.E.; Domier, C.W.; LeBlanc, B.P.; Lee, K.C.; Luhmann, N.C. Jr.; Smith, D.R.; Yuh, H.
2011-01-01
In this letter we report the first clear experimental observation of density gradient stabilization of electron temperature gradient driven turbulence in a fusion plasma. It is observed that longer wavelength modes, k (perpendicular) ρ s ∼< 10, are most stabilized by density gradient, and the stabilization is accompanied by about a factor of two decrease in the plasma effective thermal diffusivity.
Experimental studies of edge turbulence and confinement in Alcator C-Moda)
Cziegler, I.; Terry, J. L.; Hughes, J. W.; LaBombard, B.
2010-05-01
The steep gradient edge region and scrape-off-layer (SOL) on the low-field-side of Alcator C-Mod [I. H. Hutchinson, R. Boivin, F. Bombarda et al., Phys. Plasmas 1, 1511 (1994)] tokamak plasmas are studied using gas-puff-imaging diagnostics. In L-mode plasmas, the region extending ˜2 cm inside the magnetic separatrix has fluctuations showing a broad, turbulent spectrum, propagating in the electron diamagnetic drift direction, whereas features in the open field line region propagate in the ion diamagnetic drift direction. This structure is robust against toroidal field strength, poloidal null-point geometry, plasma current, and plasma density. Global parameter dependence of spectral and spatial structure of the turbulence inside the separatrix is explored and characterized, and both the intensity and spectral distributions are found to depend strongly on the plasma density normalized to the tokamak density limit. In H-mode discharges the fluctuations at and inside the magnetic separatrix show fundamentally different trends compared to L-mode, with the electron diamagnetic direction propagating turbulence greatly reduced in ELM-free [F. Wagner et al., Proceedings of the Thirteenth Conference on Plasma Physics and Controlled Nuclear Fusion Research (IAEA, Vienna, 1982), Vol. I, p. 277], and completely dominated by the modelike structure of the quasicoherent mode in enhanced D-alpha regimes [A. E. Hubbard, R. L. Boivin, R. S. Granetz et al., Phys. Plasmas 8, 2033 (2001)], while the normalized SOL turbulence is largely unaffected.
Molecular mixing in turbulent flow
International Nuclear Information System (INIS)
Kerstein, A.R.
1993-01-01
The evolution of a diffusive scalar field subject to turbulent stirring is investigated by comparing two new modeling approaches, the linear-eddy model and the clipped-laminar-profile representation, to results previously obtained by direct numerical simulation (DNS) and by mapping-closure analysis. The comparisons indicate that scalar field evolution is sensitive to the bandwidth of the stirring process, and they suggest that the good agreement between DNS and mapping closure reflects the narrowband character of both. The new models predict qualitatively new behaviors in the wideband stirring regime corresponding to high-Reynolds-number turbulence
Plasma turbulence effects on aurorae
International Nuclear Information System (INIS)
Mishin, E.V.; Telegin, V.A.
1989-01-01
Analysis of modern state of microprocesses physics in plasma of aurorare, initiated by energetic electron flow intrusion, is presented. It is shown that there is a number of phenomena, which cannot be explained under non-collision (collective) mechanisms of interaction are applied. Effects of plasma turbulence in the area of auroral arcs are considered. Introduction of a new structural element to auroral arc - plasma-turbulence (PT) layer is substantiated. Numerical simulation of electron kinetics, changes in neutral composition, as well as generation of IR- and UV-radiation in PT layer has been realized
Ion-acoustic plasma turbulence
International Nuclear Information System (INIS)
Bychenkov, V.Y.; Silin, V.P.
1982-01-01
A theory is developed of the nonlinear state that is established in a plasma as a result of development of ion-acoustic instability. Account is taken simultaneously of the linear induced scattering of the waves by the ions and of the quasilinear relaxation of the electrons by the ion-acoustic pulsations. The distribution of the ion-acoustic turbulence in frequency and in angle is obtained. An Ohm's law is established and expressions are obtained for the electronic heat flux and for the relaxation time of the electron temperature in a turbulent plasma. Anomalously large absorption and scattering of the electromagnetic waves by the ion-acoustic pulsations is predicted
The roles of turbulence on plasma heating
International Nuclear Information System (INIS)
Kawamura, Takaichi; Kawabe, Takaya
1976-01-01
The relation between the heating rate of plasma particles and the thermalization frequency is established, and the important role of plasma turbulence in the fast thermalization process is underlined. This relation can be applied not only in the case of high current turbulent heating but also when turbulent phenomena occur with other heating means. The experimental results on ion and electron heating during the Mach II experiment are presented. The role of turbulence on particle losses accross the magnetic field is analyzed
International Nuclear Information System (INIS)
Garbet, X.; Mourgues, F.; Samain, A.
1987-01-01
Among the various instabilities which could explain the anomalous electron heat transport observed in tokamaks during additional heating, a microtearing turbulence is a reasonable candidate since it affects directly the magnetic topology. This turbulence may be described in a proper frame rotating around the majors axis by a static potential vector. In strong non linear regimes, the flow of electrons along the stochastic field lines induces a current. The point is to know whether this current can sustain the turbulence. The mechanisms of this self-consistency, involving the combined effects of the thermal diamagnetism and of the electric drift are presented here
Testing neoclassical and turbulent effects on poloidal rotation in the core of DIII-D
Energy Technology Data Exchange (ETDEWEB)
Chrystal, C. [University of California San Diego, 9500 Gilman Dr., La Jolla, California 92093-0417 (United States); Burrell, K. H.; Staebler, G. M.; Kinsey, J. E.; Lao, L. L.; Grassie, J. S. de [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Grierson, B. A.; Solomon, W. M.; Wang, W. X. [Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543-0451 (United States); Rhodes, T. L.; Schmitz, L. [University of California Los Angeles, P.O. Box 957099, Los Angeles, California 90095-7099 (United States); Mordijck, S. [College of William and Mary, P.O. Box 8795, Williamsburg, Virginia 23187-8795 (United States); Meneghini, O. [Oak Ridge Associated Universities, 1299 Bethel Valley Rd, Bldg SC-200, Oak Ridge, Tennessee 37830 (United States)
2014-07-15
Experimental tests of ion poloidal rotation theories have been performed on DIII-D using a novel impurity poloidal rotation diagnostic. These tests show significant disagreements with theoretical predictions in various conditions, including L-mode plasmas with internal transport barriers (ITB), H-mode plasmas, and QH-mode plasmas. The theories tested include standard neoclassical theory, turbulence driven Reynolds stress, and fast-ion friction on the thermal ions. Poloidal rotation is observed to spin up at the formation of an ITB and makes a significant contribution to the measurement of the E{sup →}×B{sup →} shear that forms the ITB. In ITB cases, neoclassical theory agrees quantitatively with the experimental measurements only in the steep gradient region. Significant quantitative disagreement with neoclassical predictions is seen in the cores of ITB, QH-, and H-mode plasmas, demonstrating that neoclassical theory is an incomplete description of poloidal rotation. The addition of turbulence driven Reynolds stress does not remedy this disagreement; linear stability calculations and Doppler backscattering measurements show that disagreement increases as turbulence levels decline. Furthermore, the effect of fast-ion friction, by itself, does not lead to improved agreement; in QH-mode plasmas, neoclassical predictions are closest to experimental results in plasmas with the largest fast ion friction. Predictions from a new model that combines all three effects show somewhat better agreement in the H-mode case, but discrepancies well outside the experimental error bars remain.
Testing neoclassical and turbulent effects on poloidal rotation in the core of DIII-D
International Nuclear Information System (INIS)
Chrystal, C.; Burrell, K. H.; Staebler, G. M.; Kinsey, J. E.; Lao, L. L.; Grassie, J. S. de; Grierson, B. A.; Solomon, W. M.; Wang, W. X.; Rhodes, T. L.; Schmitz, L.; Mordijck, S.; Meneghini, O.
2014-01-01
Experimental tests of ion poloidal rotation theories have been performed on DIII-D using a novel impurity poloidal rotation diagnostic. These tests show significant disagreements with theoretical predictions in various conditions, including L-mode plasmas with internal transport barriers (ITB), H-mode plasmas, and QH-mode plasmas. The theories tested include standard neoclassical theory, turbulence driven Reynolds stress, and fast-ion friction on the thermal ions. Poloidal rotation is observed to spin up at the formation of an ITB and makes a significant contribution to the measurement of the E → ×B → shear that forms the ITB. In ITB cases, neoclassical theory agrees quantitatively with the experimental measurements only in the steep gradient region. Significant quantitative disagreement with neoclassical predictions is seen in the cores of ITB, QH-, and H-mode plasmas, demonstrating that neoclassical theory is an incomplete description of poloidal rotation. The addition of turbulence driven Reynolds stress does not remedy this disagreement; linear stability calculations and Doppler backscattering measurements show that disagreement increases as turbulence levels decline. Furthermore, the effect of fast-ion friction, by itself, does not lead to improved agreement; in QH-mode plasmas, neoclassical predictions are closest to experimental results in plasmas with the largest fast ion friction. Predictions from a new model that combines all three effects show somewhat better agreement in the H-mode case, but discrepancies well outside the experimental error bars remain
Exploiting similarity in turbulent shear flows for turbulence modeling
Robinson, David F.; Harris, Julius E.; Hassan, H. A.
1992-01-01
It is well known that current k-epsilon models cannot predict the flow over a flat plate and its wake. In an effort to address this issue and other issues associated with turbulence closure, a new approach for turbulence modeling is proposed which exploits similarities in the flow field. Thus, if we consider the flow over a flat plate and its wake, then in addition to taking advantage of the log-law region, we can exploit the fact that the flow becomes self-similar in the far wake. This latter behavior makes it possible to cast the governing equations as a set of total differential equations. Solutions of this set and comparison with measured shear stress and velocity profiles yields the desired set of model constants. Such a set is, in general, different from other sets of model constants. The rational for such an approach is that if we can correctly model the flow over a flat plate and its far wake, then we can have a better chance of predicting the behavior in between. It is to be noted that the approach does not appeal, in any way, to the decay of homogeneous turbulence. This is because the asymptotic behavior of the flow under consideration is not representative of the decay of homogeneous turbulence.
Exploiting similarity in turbulent shear flows for turbulence modeling
Robinson, David F.; Harris, Julius E.; Hassan, H. A.
1992-12-01
It is well known that current k-epsilon models cannot predict the flow over a flat plate and its wake. In an effort to address this issue and other issues associated with turbulence closure, a new approach for turbulence modeling is proposed which exploits similarities in the flow field. Thus, if we consider the flow over a flat plate and its wake, then in addition to taking advantage of the log-law region, we can exploit the fact that the flow becomes self-similar in the far wake. This latter behavior makes it possible to cast the governing equations as a set of total differential equations. Solutions of this set and comparison with measured shear stress and velocity profiles yields the desired set of model constants. Such a set is, in general, different from other sets of model constants. The rational for such an approach is that if we can correctly model the flow over a flat plate and its far wake, then we can have a better chance of predicting the behavior in between. It is to be noted that the approach does not appeal, in any way, to the decay of homogeneous turbulence. This is because the asymptotic behavior of the flow under consideration is not representative of the decay of homogeneous turbulence.
Holland, Christopher George
Studies of nonlinear couplings and dynamics in plasma turbulence are presented. Particular areas of focus are analytic studies of coherent structure formation in electron temperature gradient turbulence, measurement of nonlinear energy transfer in simulations of plasma turbulence, and bispectral analysis of experimental and computational data. The motivation for these works has been to develop and expand the existing theories of plasma transport, and verify the nonlinear predictions of those theories in simulation and experiment. In Chapter II, we study electromagnetic secondary instabilities of electron temperature gradient turbulence. The growth rate for zonal flow generation via modulational instability of electromagnetic ETG turbulence is calculated, as well as that for zonal (magnetic) field generation. In Chapter III, the stability and saturation of streamers in ETG turbulence is considered, and shown to depend sensitively upon geometry and the damping rates of the Kelvin-Helmholtz mode. Requirements for a credible theory of streamer transport are presented. In addition, a self-consistent model for interactions between ETG and ITG (ion temperature gradient) turbulence is presented. In Chapter IV, the nonlinear transfer of kinetic and internal energy is measured in simulations of plasma turbulence. The regulation of turbulence by radial decorrelation due to zonal flows and generation of zonal flows via the Reynolds stress are explicitly demonstrated, and shown to be symmetric facets of a single nonlinear process. Novel nonlinear saturation mechanisms for zonal flows are discussed. In Chapter V, measurements of fluctuation bicoherence in the edge of the DIII-D tokamak are presented. It is shown that the bicoherence increases transiently before a L-H transition, and decays to its initial value after the barrier has formed. The increase in bicoherence is localized to the region where the transport barrier forms, and shows strong coupling between well
Plasma Soliton Turbulence and Statistical Mechanics
International Nuclear Information System (INIS)
Treumann, R.A.; Pottelette, R.
1999-01-01
Collisionless kinetic plasma turbulence is described approximately in terms of a superposition of non-interacting solitary waves. We discuss the relevance of such a description under astrophysical conditions. Several types of solitary waves may be of interest in this relation as generators of turbulence and turbulent transport. A consistent theory of turbulence can be given only in a few particular cases when the description can be reduced to the Korteweg-de Vries equation or some other simple equation like the Kadomtsev-Petviashvili equation. It turns out that the soliton turbulence is usually energetically harder than the ordinary weakly turbulent plasma description. This implies that interaction of particles with such kinds of turbulence can lead to stronger acceleration than in ordinary turbulence. However, the description in our model is only classical and non-relativistic. Transport in solitary turbulence is most important for drift wave turbulence. Such waves form solitary drift wave vortices which may provide cross-field transport. A more general discussion is given on transport. In a model of Levy flight trapping of particles in solitons (or solitary turbulence) one finds that the residence time of particles in the region of turbulence may be described by a generalized Lorentzian probability distribution. It is shown that under collisionless equilibrium conditions far away from thermal equilibrium such distributions are natural equilibrium distributions. A consistent thermodynamic description of such media can be given in terms of a generalized Lorentzian statistical mechanics and thermodynamics. (author)
Wall roughness induces asymptotic ultimate turbulence
Zhu, Xiaojue; Verschoof, Ruben Adriaan; Bakhuis, Dennis; Huisman, Sander Gerard; Verzicco, Roberto; Sun, Chao; Lohse, Detlef
2018-01-01
Turbulence governs the transport of heat, mass and momentum on multiple scales. In real-world applications, wall-bounded turbulence typically involves surfaces that are rough; however, characterizing and understanding the effects of wall roughness on turbulence remains a challenge. Here, by
Analysis of chaos in plasma turbulence
DEFF Research Database (Denmark)
Pedersen, T.S.; Michelsen, Poul; Juul Rasmussen, J.
1996-01-01
-stationary turbulent state is reached in a finite time, independent of the initial conditions. Different regimes of the turbulent state can be obtained by varying the coupling parameter C, related to the parallel electron dynamics. The turbulence is described by using particle tracking and tools from chaos analysis...
PROTOSTELLAR OUTFLOW EVOLUTION IN TURBULENT ENVIRONMENTS
International Nuclear Information System (INIS)
Cunningham, Andrew J.; Frank, Adam; Carroll, Jonathan; Blackman, Eric G.; Quillen, Alice C.
2009-01-01
The link between turbulence in star-forming environments and protostellar jets remains controversial. To explore issues of turbulence and fossil cavities driven by young stellar outflows, we present a series of numerical simulations tracking the evolution of transient protostellar jets driven into a turbulent medium. Our simulations show both the effect of turbulence on outflow structures and, conversely, the effect of outflows on the ambient turbulence. We demonstrate how turbulence will lead to strong modifications in jet morphology. More importantly, we demonstrate that individual transient outflows have the capacity to re-energize decaying turbulence. Our simulations support a scenario in which the directed energy/momentum associated with cavities is randomized as the cavities are disrupted by dynamical instabilities seeded by the ambient turbulence. Consideration of the energy power spectra of the simulations reveals that the disruption of the cavities powers an energy cascade consistent with Burgers'-type turbulence and produces a driving scale length associated with the cavity propagation length. We conclude that fossil cavities interacting either with a turbulent medium or with other cavities have the capacity to sustain or create turbulent flows in star-forming environments. In the last section, we contrast our work and its conclusions with previous studies which claim that jets cannot be the source of turbulence.
Global Turbulence Decision Support for Aviation
Williams, J.; Sharman, R.; Kessinger, C.; Feltz, W.; Wimmers, A.
2009-09-01
Turbulence is widely recognized as the leading cause of injuries to flight attendants and passengers on commercial air carriers, yet legacy decision support products such as SIGMETs and SIGWX charts provide relatively low spatial- and temporal-resolution assessments and forecasts of turbulence, with limited usefulness for strategic planning and tactical turbulence avoidance. A new effort is underway to develop an automated, rapid-update, gridded global turbulence diagnosis and forecast system that addresses upper-level clear-air turbulence, mountain-wave turbulence, and convectively-induced turbulence. This NASA-funded effort, modeled on the U.S. Federal Aviation Administration's Graphical Turbulence Guidance (GTG) and GTG Nowcast systems, employs NCEP Global Forecast System (GFS) model output and data from NASA and operational satellites to produce quantitative turbulence nowcasts and forecasts. A convective nowcast element based on GFS forecasts and satellite data provides a basis for diagnosing convective turbulence. An operational prototype "Global GTG” system has been running in real-time at the U.S. National Center for Atmospheric Research since the spring of 2009. Initial verification based on data from TRMM, Cloudsat and MODIS (for the convection nowcasting) and AIREPs and AMDAR data (for turbulence) are presented. This product aims to provide the "single authoritative source” for global turbulence information for the U.S. Next Generation Air Transportation System.
The PDF method for turbulent combustion
Pope, S. B.
1991-01-01
Probability Density Function (PDF) methods provide a means of calculating the properties of turbulent reacting flows. They have been successfully applied to many turbulent flames, including some with finite rate kinetic effects. Here the methods are reviewed with an emphasis on computational issues and their application to turbulent combustion.
Sharma, Ati S; Moarref, Rashad; McKeon, Beverley J; Park, Jae Sung; Graham, Michael D; Willis, Ashley P
2016-02-01
We report that many exact invariant solutions of the Navier-Stokes equations for both pipe and channel flows are well represented by just a few modes of the model of McKeon and Sharma [J. Fluid Mech. 658, 336 (2010)]. This model provides modes that act as a basis to decompose the velocity field, ordered by their amplitude of response to forcing arising from the interaction between scales. The model was originally derived from the Navier-Stokes equations to represent turbulent flows and has been used to explain coherent structure and to predict turbulent statistics. This establishes a surprising new link between the two distinct approaches to understanding turbulence.
Nonlinear simulations of particle source effects on edge localized mode
Energy Technology Data Exchange (ETDEWEB)
Huang, J.; Tang, C. J. [College of Physical Science and Technology, Sichuan University, Chengdu 610065 (China); Key Laboratory of High Energy Density Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610064 (China); Chen, S. Y., E-mail: sychen531@163.com [College of Physical Science and Technology, Sichuan University, Chengdu 610065 (China); Key Laboratory of High Energy Density Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610064 (China); Southwestern Institute of Physics, Chengdu 610041 (China); Wang, Z. H. [Southwestern Institute of Physics, Chengdu 610041 (China)
2015-12-15
The effects of particle source (PS) with different intensities and located positions on Edge Localized Mode (ELM) are systematically studied with BOUT++ code. The results show the ELM size strongly decreases with increasing the PS intensity once the PS is located in the middle or bottom of the pedestal. The effects of PS on ELM depend on the located position of PS. When it is located at the top of the pedestal, peeling-ballooning (P-B) modes can extract more free energy from the pressure gradient and grow up to be a large filament at the initial crash phase and the broadening of mode spectrum can be suppressed by PS, which leads to more energy loss. When it is located in the middle or bottom of the pedestal, the extraction of free energy by P-B modes can be suppressed, and a small filament is generated. During the turbulence transport phase, the broader mode spectrum suppresses the turbulence transport when PS is located in the middle, while the zonal flow plays an important role in damping the turbulence transport when PS is located at the bottom.
International Nuclear Information System (INIS)
Roberts, T. M.; Mauel, M. E.; Worstell, M. W.
2015-01-01
Turbulence in plasma confined by a magnetic dipole is dominated by interchange fluctuations with complex dynamics and short spatial coherence. We report the first use of local current-collection feedback to modify, amplify, and suppress these fluctuations. The spatial extent of turbulence regulation is limited to a correlation length near the collector. Changing the gain and phase of collection results in power either extracted from or injected into the turbulence. The measured plasma response shows some agreement with calculations of the linear response of global interchange-like MHD and entropy modes to current-collection feedback
Rippling modes in the edge of a tokamak plasma
International Nuclear Information System (INIS)
Carreras, B.A.; Callen, J.D.; Gaffney, P.W.; Hicks, H.R.
1982-02-01
A promising resistive magnetohydrodynamic candidate for the underlying cause of turbulence in the edge of a tokamak plasma is the rippling instability. In this paper we develop a computational model for these modes in the cylindrical tokamak approximation and explore the linear growth and single-helicity quasi-linear saturation phases of the rippling modes for parameters appropriate to the edge of a tokamak plasma. Large parallel heat conduction does not stabilize these modes; it only reduces their growth rate by a factor scaling as k/sub parallel//sup -4/3/. Nonlinearly, individual rippling modes are found to saturate by quasi-linear flattening of the resistivity profile. The saturated amplitude of the modes scales as m/sup -1/, and the radial extent of these modes grows linearly with time due to radial Vector E x Vector B 0 convection. This evolution is found to be terminated by parallel heat conduction
Rippling modes in the edge of a tokamak plasma
International Nuclear Information System (INIS)
Carreras, B.A.; Gaffney, P.W.; Hicks, H.R.; Callan, J.D.
1982-01-01
A promising resistive magnetohydrodynamic candidate for the underlying cause of turbulence in the edge of a tokamak plasma is the rippling instability. In this paper a computational model for these modes in the cylindrical tokamak approximation was developed and the linear growth and single-helicity quasi-linear saturation phases of the rippling modes for parameters appropriate to the edge of a tokamak plasma were explored. Large parallel heat conduction does not stabilize these modes; it only reduces their growth rate by a factor sacling as K/sup -4/3//sub parallel/. Nonlinearly, individual rippling modes are found to saturate by quasi-linear flattening of the resistivity profile. The saturated amplitude of the modes scales as m -1 , and the radial extent of these modes grows linearly with time due to radial E x B 0 convection. This evolution is found to be terminated by parallel heat conduction
Fully Electromagnetic Nonlinear Gyrokinetic Equations for Tokamak Edge Turbulence
International Nuclear Information System (INIS)
Hahm, T.S.; Wang, Lu; Madsen, J.
2008-01-01
An energy conserving set of the fully electromagnetic nonlinear gyrokinetic Vlasov equation and Maxwell's equations, which is applicable to both L-mode turbulence with large amplitude and H-mode turbulence in the presence of high E x B shear has been derived. The phase-space action variational Lie perturbation method ensures the preservation of the conservation laws of the underlying Vlasov-Maxwell system. Our generalized ordering takes ρ i θi ∼ L E ∼ L p i is the thermal ion Larmor radius and ρ θi = B/B θ ρ i ), as typically observed in the tokamak H-mode edge, with L E and L p being the radial electric field and pressure gradient lengths. We take k # perpendicular# ρ i ∼ 1 for generality, and keep the relative fluctuation amplitudes e(delta)φ/T i ∼ (delta)B/B up to the second order. Extending the electrostatic theory in the presence of high E x B shear [Hahm, Phys. Plasmas 3, 4658 (1996)], contributions of electromagnetic fluctuations to the particle charge density and current are explicitly evaluated via pull-back transformation from the gyrocenter distribution function in the gyrokinetic Maxwell's equation
Comprehensive gyrokinetic simulation of tokamak turbulence at finite relative gyroradius
International Nuclear Information System (INIS)
Waltz, R.E.; Candy, J.; Rosenbluth, M.N.
2003-01-01
A continuum global gyrokinetic code GYRO has been developed to comprehensively simulate turbulent transport in actual experimental profiles and allow direct quantitative comparisons to the experimental transport flows. GYRO not only treats the now standard ion temperature gradient (ITG) mode turbulence, but also treats trapped and passing electrons with collisions and finite beta, and all in real tokamak geometry. Most importantly the code operates at finite relative gyroradius (ρ*) so as to treat the profile shear stabilization effects which break gyro Bohm scaling. The code operates in a cyclic flux tube limit which allows only gyro Bohm scaling and a noncylic radial annulus with physical profile variation. The later requires an adaptive source to maintain equilibrium profiles. Simple ITG simulations demonstrate the broken gyro Bohm scaling paradigm of Garbet and Waltz [Phys. Plasmas 3, 1898 (1996)]. Since broken gyro Bohm scaling depends on the actual rotational velocity shear rates competing with mode growth rates, direct comprehensive simulations of the DIII-D ρ*-scaled L-mode experiments are presented as a quantitative test of gyrokinetics and the paradigm. (author)
5th European Turbulence Conference
1995-01-01
Under the auspices of the Euromech Committee, the Fifth European Turbulence Conference was held in Siena on 5-8 July 1994. Following the previous ETC meeting in Lyon (1986), Berlin (1988), Stockholm (1990) and Delft (1992), the Fifth ETC was aimed at providing a review of the fundamental aspects of turbulence from a theoretical, numerical and experimental point of view. In the magnificent town of Siena, more than 250 scientists from all over the world, spent four days discussing new ideas on turbulence. As a research worker in the field of turbulence, I must say that the works presented at the Conference, on which this book is based, covered almost all areas in this field. I also think that this book provides a major opportunity to have a complete overview of the most recent research works. I am extremely grateful to Prof. C. Cercignani, Dr. M. Loffredo, and Prof. R. Piva who, as members of the local organizing committee, share the success of the Conference. I also want to thank Mrs. Liu' Catena, for her inva...
Stochastic acceleration by hydromagnetic turbulence
International Nuclear Information System (INIS)
Kulsrud, R.M.
1979-03-01
A general theory for particle acceleration by weak hydromagnetic turbulence with a given spectrum of waves is described. Various limiting cases, corresponding to Fermi acceleration and magnetic pumping, are discussed and two numerical examples illustrating them are given. An attempt is made to show that the expression for the rate of Fermi acceleration is valid for finite amplitudes
Topology optimization of turbulent flows
DEFF Research Database (Denmark)
Dilgen, Cetin B.; Dilgen, Sumer B.; Fuhrman, David R.
2018-01-01
The aim of this work is to present a fast and viable approach for taking into account turbulence in topology optimization of complex fluid flow systems, without resorting to any simplifying assumptions in the derivation of discrete adjoints. Topology optimization is an iterative gradient...
Dissipative structures in magnetorotational turbulence
Ross, Johnathan; Latter, Henrik N.
2018-03-01
Via the process of accretion, magnetorotational turbulence removes energy from a disk's orbital motion and transforms it into heat. Turbulent heating is far from uniform and is usually concentrated in small regions of intense dissipation, characterised by abrupt magnetic reconnection and higher temperatures. These regions are of interest because they might generate non-thermal emission, in the form of flares and energetic particles, or thermally process solids in protoplanetary disks. Moreover, the nature of the dissipation bears on the fundamental dynamics of the magnetorotational instability (MRI) itself: local simulations indicate that the large-scale properties of the turbulence (e.g. saturation levels, the stress-pressure relationship) depend on the short dissipative scales. In this paper we undertake a numerical study of how the MRI dissipates and the small-scale dissipative structures it employs to do so. We use the Godunov code RAMSES and unstratified compressible shearing boxes. Our simulations reveal that dissipation is concentrated in ribbons of strong magnetic reconnection that are significantly elongated in azimuth, up to a scale height. Dissipative structures are hence meso-scale objects, and potentially provide a route by which large scales and small scales interact. We go on to show how these ribbons evolve over time — forming, merging, breaking apart, and disappearing. Finally, we reveal important couplings between the large-scale density waves generated by the MRI and the small-scale structures, which may illuminate the stress-pressure relationship in MRI turbulence.