Effects of magnetic field, sheared flow and ablative velocity on the Rayleigh-Taylor instability

International Nuclear Information System (INIS)

Li, D.; Zhang, W.L.; Wu, Z.W.

2005-01-01

It is found that magnetic field has a stabilization effect whereas the sheared flow has a destabilization effect on the RT instability in the presence of sharp interface. RT instability only occurs in the long wave region and can be completely suppressed if the stabilizing effect of magnetic field dominates. The RT instability increases with wave number and flow shear, and acts much like a Kelvin-Helmholtz instability when destabilizing effect of sheared flow dominates. It is shown that both of ablation velocity and magnetic filed have stabilization effect on RT instability in the presence of continued interface. The stabilization effect of magnetic field takes place for whole waveband and becomes more significant for the short wavelength. The RT instability can be completely suppressed by the cooperated effect of magnetic field and ablation velocity so that the ICF target shell may be unnecessary to be accelerated to very high speed. The growth rate decreases as the density scale length increases. The stabilization effect of magnetic field is more significant for the short density scale length. (author)

Triclade: influence of a sinuous secondary instability on the Richtmyer-Meshkov instabilities

International Nuclear Information System (INIS)

Boulet, M.; Griffond, J.

2004-01-01

Occurrence of a secondary instability developing after the Richtmyer-Meshkov (primary) instability is emphasized thanks to numerical simulations with the TRICLADE code. We are mainly considering 2D perturbations describes by trigonometric function cosine or [cosine]. However, the 3D case is also tackled. The sinuous secondary instability is characterized by the loss of the symmetries in the direction normal to the interface at its crests. It reduces the late time growing rate of the 'mushrooms' formed by the Richtmyer-Meshkov instability. Related simplified problems, like symmetrical Riemann problems or the Mallier-Maslowe array of counter-rotating vortices, allow us to perform 2D linear stability analysis. Thus, we show that the sinuous secondary instability is not a numerical artifact and that is comes from the continuous incompressible velocity field in the interface region. This instability implies temporal limitations for the validity of single mode simulations; therefore multimode simulations are necessary to study the ]ate-time behaviour of interfaces bitted by shocks. (authors)

Reclosing of field lines and disruptive instability in tokamaks

International Nuclear Information System (INIS)

Kadomtsev, B.B.

The mechanism of field line reclosing is proposed as the most natural explanation of disruptive instability in tokamaks. This mechanism adequately accounts for the internal disruptive instability, assuming that only mode m = 1 develops. It is extended to the presence of two or several modes. When there is a large number of allowed modes, one can speak of free reclosing, which leads to a force-free magnetic field in a diffusion discharge. In a tokamak, B/sub Z/ much greater than B/sub theta/, free reclosing leads to a uniform distribution of the current over the column cross section and to ejection of part of the poloidal flux beyond the confines of the diaphragm. It may be stated that the disruptive instability in a tokamak is an MHD activity that flares up for a short time and is permanently present in a diffusion column. The geometry of magnetic surfaces during reclosing has been analyzed, and qualitative arguments are given to show that disruptive instability begins to develop as a result of the interaction of the mode m = 2 with the inner mode m = 1

Reclosing of field lines and disruptive instability in tokamaks

Energy Technology Data Exchange (ETDEWEB)

Kadomtsev, B. B.

1976-07-01

The mechanism of field line reclosing is proposed as the most natural explanation of disruptive instability in tokamaks. This mechanism adequately accounts for the internal disruptive instability, assuming that only mode m = 1 develops. It is extended to the presence of two or several modes. When there is a large number of allowed modes, one can speak of free reclosing, which leads to a force-free magnetic field in a diffusion discharge. In a tokamak, B/sub Z/ much greater than B/sub theta/, free reclosing leads to a uniform distribution of the current over the column cross section and to ejection of part of the poloidal flux beyond the confines of the diaphragm. It may be stated that the disruptive instability in a tokamak is an MHD activity that flares up for a short time and is permanently present in a diffusion column. The geometry of magnetic surfaces during reclosing has been analyzed, and qualitative arguments are given to show that disruptive instability begins to develop as a result of the interaction of the mode m = 2 with the inner mode m = 1.

Role of electric fields in the MHD evolution of the kink instability

International Nuclear Information System (INIS)

Lapenta, Giovanni; Skender, Marina

2017-01-01

Here, the discovery of electrostatic fields playing a crucial role in establishing plasma motion in the flux conversion and dynamo processes in reversed field pinches is revisited. In order to further elucidate the role of the electrostatic fields, a flux rope configuration susceptible to the kink instability is numerically studied with anMHDcode. Simulated nonlinear evolution of the kink instability is found to confirm the crucial role of the electrostatic fields. Anew insight is gained on the special function of the electrostatic fields: they lead the plasma towards the reconnection site at the mode resonant surface. Without this step the plasma column could not relax to its nonlinear state, since no other agent is present to perform this role. While the inductive field generated directly by the kink instability is the dominant flow driver, the electrostatic field is found to allow the motion in the vicinity of the reconnection region.

The transverse field Richtmyer-Meshkov instability in magnetohydrodynamics

KAUST Repository

Wheatley, V.; Samtaney, Ravi; Pullin, D. I.; Gehre, R. M.

2014-01-01

The magnetohydrodynamic Richtmyer-Meshkov instability is investigated for the case where the initial magnetic field is unperturbed and aligned with the mean interface location. For this initial condition, the magnetic field lines penetrate the perturbed density interface, forbidding a tangential velocity jump and therefore the presence of a vortex sheet. Through simulation, we find that the vorticity distribution present on the interface immediately after the shock acceleration breaks up into waves traveling parallel and anti-parallel to the magnetic field, which transport the vorticity. The interference of these waves as they propagate causes the perturbation amplitude of the interface to oscillate in time. This interface behavior is accurately predicted over a broad range of parameters by an incompressible linearized model derived presently by solving the corresponding impulse driven, linearized initial value problem. Our use of an equilibrium initial condition results in interface motion produced solely by the impulsive acceleration. Nonlinear compressible simulations are used to investigate the behavior of the transverse field magnetohydrodynamic Richtmyer-Meshkov instability, and the performance of the incompressible model, over a range of shock strengths, magnetic field strengths, perturbation amplitudes and Atwood numbers.

The transverse field Richtmyer-Meshkov instability in magnetohydrodynamics

KAUST Repository

Wheatley, V.

2014-01-10

The magnetohydrodynamic Richtmyer-Meshkov instability is investigated for the case where the initial magnetic field is unperturbed and aligned with the mean interface location. For this initial condition, the magnetic field lines penetrate the perturbed density interface, forbidding a tangential velocity jump and therefore the presence of a vortex sheet. Through simulation, we find that the vorticity distribution present on the interface immediately after the shock acceleration breaks up into waves traveling parallel and anti-parallel to the magnetic field, which transport the vorticity. The interference of these waves as they propagate causes the perturbation amplitude of the interface to oscillate in time. This interface behavior is accurately predicted over a broad range of parameters by an incompressible linearized model derived presently by solving the corresponding impulse driven, linearized initial value problem. Our use of an equilibrium initial condition results in interface motion produced solely by the impulsive acceleration. Nonlinear compressible simulations are used to investigate the behavior of the transverse field magnetohydrodynamic Richtmyer-Meshkov instability, and the performance of the incompressible model, over a range of shock strengths, magnetic field strengths, perturbation amplitudes and Atwood numbers.

Thermal instabilities in the edge region of reversed-field pinches

International Nuclear Information System (INIS)

Goedert, J.; Mondt, J.P.

1984-04-01

Thermal stability of the edge region of reversed-field pinch configurations is analyzed within the context of a two-fluid model. Two major sources of instability are identified in combination with a parallel electric field: either an electron temperature gradient and/or a density gradient that leads to rapid growth (of several to many ohmic heating rates) over a region of several millimeters around the mode-rational surfaces in the edge region. The basic signature of both instabilities is electrostatic. In the case of the density gradient mode, the signature relies on the effects of electron compressibility, whereas the temperature gradient mode can be identified as the current-convective instability by taking the limit of zero diamagnetic drift, density gradient, thermal force, drift heat flux, and electron compressibility

Flow instability in laminar jet flames driven by alternating current electric fields

KAUST Repository

Kim, Gyeong Taek

2016-10-13

The effect of electric fields on the instability of laminar nonpremixed jet flames was investigated experimentally by applying the alternating current (AC) to a jet nozzle. We aimed to elucidate the origin of the occurrence of twin-lifted jet flames in laminar jet flow configurations, which occurred when AC electric fields were applied. The results indicated that a twin-lifted jet flame originated from cold jet instability, caused by interactions between negative ions in the jet flow via electron attachment as O +e→O when AC electric fields were applied. This was confirmed by conducting systematic, parametric experiment, which included changing gaseous component in jets and applying different polarity of direct current (DC) to the nozzle. Using two deflection plates installed in parallel with the jet stream, we found that only negative DC on the nozzle could charge oxygen molecules negatively. Meanwhile, the cold jet instability occurred only for oxygen-containing jets. A shedding frequency of jet stream due to AC driven instability showed a good correlation with applied AC frequency exhibiting a frequency doubling. However, for the applied AC frequencies over 80Hz, the jet did not respond to the AC, indicating an existence of a minimum flow induction time in a dynamic response of negative ions to external AC fields. Detailed regime of the instability in terms of jet velocity, AC voltage and frequency was presented and discussed. Hypothesized mechanism to explain the instability was also proposed.

Magneto-Rayleigh-Taylor instability driven by a rotating magnetic field

Science.gov (United States)

Duan, Shuchao; Xie, Weiping; Cao, Jintao; Li, Ding

2018-04-01

In this paper, we analyze theoretically the magneto-Rayleigh-Taylor instability driven by a rotating magnetic field. Slab configurations of finite thickness are treated both with and without using the Wenzel-Kramers-Brillouin approximation. Regardless of the slab thickness, the directional rotation of the driving magnetic field contributes to suppressing these instabilities. The two factors of the finite thickness and directional rotation of the magnetic field cooperate to enhance suppression, with the finite thickness playing a role only when the orientation of the magnetic field is time varying. The suppression becomes stronger as the driving magnetic field rotates faster, and all modes are suppressed, in contrast to the case of a non-rotating magnetic field, for which the vertical mode cannot be suppressed. This implies that the dynamically alternate configuration of a Theta-pinch and a Z-pinch may be applicable to the concept of Theta-Z liner inertial fusion.

Wiebel instability of microwave gas discharge in strong linear and circular pulsed fields

International Nuclear Information System (INIS)

Shokri, B.; Ghorbanalilu, M.

2004-01-01

Being much weaker than the atomic fields, the gas breakdown produced by high-power pulsed microwave fields is investigated in the nonrelativistic case. The distribution function of the electrons produced by the interaction with intense linearly and circularly polarized microwave fields is obtained and it is shown that it is in a nonequilibrium state and anisotropic. The discharge mechanism for the gas atoms is governed by electron-impact avalanche ionization. By analyzing the instability of the system and by finding its growth rate, it is shown that the instability which is governed by the anisotropic property of the distribution function is Wiebel instability

Long-wave theory for a new convective instability with exponential growth normal to the wall.

Science.gov (United States)

Healey, J J

2005-05-15

A linear stability theory is presented for the boundary-layer flow produced by an infinite disc rotating at constant angular velocity in otherwise undisturbed fluid. The theory is developed in the limit of long waves and when the effects of viscosity on the waves can be neglected. This is the parameter regime recently identified by the author in a numerical stability investigation where a curious new type of instability was found in which disturbances propagate and grow exponentially in the direction normal to the disc, (i.e. the growth takes place in a region of zero mean shear). The theory describes the mechanisms controlling the instability, the role and location of critical points, and presents a saddle-point analysis describing the large-time evolution of a wave packet in frames of reference moving normal to the disc. The theory also shows that the previously obtained numerical solutions for numerically large wavelengths do indeed lie in the asymptotic long-wave regime, and so the behaviour and mechanisms described here may apply to a number of cross-flow instability problems.

Proton migration mechanism for the instability of organic field-effect transistors

NARCIS (Netherlands)

Sharma, A.; Mathijssen, S.G.J.; Kemerink, M.; Leeuw, de D.M.; Bobbert, P.A.

2009-01-01

During prolonged application of a gate bias, organic field-effect transistors show an instability involving a gradual shift of the threshold voltage toward the applied gate bias voltage. We propose a model for this instability in p-type transistors with a silicon-dioxide gate dielectric, based on

Nonlinear analysis of generalized cross-field current instability

International Nuclear Information System (INIS)

Yoon, P.H.; Lui, A.T.Y.

1993-01-01

Analysis of the generalized cross-field current instability is carried out in which cross-field drift of both the ions and electrons and their temperatures are permitted to vary in time. The unstable mode under consideration is the electromagnetic generalization of the classical modified-two-stream instability. The generalized instability is made of the modified-two-stream and ion-Weibel modes. The relative importance of the features associated with the ion-Weibel mode and those of the modified-two-stream mode is assessed. Specific applications are made to the Earth's neutral sheet prior to substorm onset and to the Earth's bow shock. The numerical solution indicates that the ion-Weibel mode dominates in the Earth's neutral sheet environment. In contrast, the situation for the bow shock is dominated by the modified-two-stream mode. Notable differences are found between the present calculation and previous results on ion-Weibel mode which restrict the analysis to only parallel propagating waves. However, in the case of Earth's bow shock for which the ion-Weibel mode plays no important role, the inclusion of the electromagnetic ion response is found to differ little from the previous results which treats ions responding only to the electrostatic component of the excited waves

The magnetized electron-acoustic instability driven by a warm, field-aligned electron beam

International Nuclear Information System (INIS)

Sooklal, A.; Mace, R.L.

2004-01-01

The electron-acoustic instability in a magnetized plasma having three electron components, one of which is a field-aligned beam of intermediate temperature, is investigated. When the plasma frequency of the cool electrons exceeds the electron gyrofrequency, the electron-acoustic instability 'bifurcates' at sufficiently large propagation angles with respect to the magnetic field to yield an obliquely propagating, low-frequency electron-acoustic instability and a higher frequency cyclotron-sound instability. Each of these instabilities retains certain wave features of its progenitor, the quasiparallel electron-acoustic instability, but displays also new magnetic qualities through its dependence on the electron gyrofrequency. The obliquely propagating electron-acoustic instability requires a lower threshold beam speed for its excitation than does the cyclotron-sound instability, and for low to intermediate beam speeds has the higher maximum growth rate. When the plasma is sufficiently strongly magnetized that the plasma frequency of the cool electrons is less than the electron gyrofrequency, the only instability in the electron-acoustic frequency range is the strongly magnetized electron-acoustic instability. Its growth rate and real frequency exhibit a monotonic decrease with wave propagation angle and it grows at small to intermediate wave numbers where its parallel phase speed is approximately constant. The relevance of the results to the interpretation of cusp auroral hiss and auroral broadband electrostatic noise is briefly discussed

Mean field instabilities in dissipative heavy ion collisions

International Nuclear Information System (INIS)

Colonna, M.; Guarnera, A.; Istituto Nazionale di Fisica Nucleare, Bologna; Catania Univ.; Di Torro, M.; Catania Univ.

1995-01-01

We discuss new reaction mechanisms that may occur in semi-peripheral heavy ion collisions at intermediate energies. In particular we focus on the dynamics of the overlapping zone, showing the development of neck instabilities, coupled with the possibility of an increasing amount amount of dynamical fluctuations. In a very selected beam energy range between 40 and 70 MeV/u we observe an important interplay between stochastic nucleon exchange and the random nature of nucleon-nucleon collisions. Expected consequences are intermediate mass fragment emissions from the neck region and large variances in the projectile-like and target-like observables. The crucial importance of a time matching between the growth of mean field instabilities and the separation of the interacting system is stressed. Some hints towards the observation of relatively large instability effects in deep inelastic collisions at lower energy are finally suggested. (authors). 29 refs., 5 figs., 2 tabs

Jeans instability of self-gravitating magnetized strongly coupled plasma

International Nuclear Information System (INIS)

Prajapati, R P; Sharma, P K; Sanghvi, R K; Chhajlani, R K

2012-01-01

We investigate the Jeans instability of self-gravitating magnetized strongly coupled plasma. The equations of the problem are formulated using the generalized hydrodynamic model and a general dispersion relation is obtained using the normal mode analysis. This dispersion relation is discussed for transverse and longitudinal mode of propagations. The modified condition of Jeans instability is obtained for magnetized strongly coupled plasma. We find that strong coupling of plasma particles modify the fundamental criterion of Jeans gravitational instability. In transverse mode it is found that Jeans instability criterion gets modified due to the presence of magnetic field, shear viscosity and fluid viscosity but in longitudinal mode it is unaffected due to the presence of magnetic field. From the curves we found that all these parameters have stabilizing influence on the growth rate of Jeans instability.

Hydromagnetic instabilities and magnetic field amplification in core collapse supernovae

Energy Technology Data Exchange (ETDEWEB)

Cerda-Duran, P; Obergaulinger, M; Mueller, E [Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-st. 1, 85748 Garching (Germany); Aloy, M A; Font, J A, E-mail: cerda@mpa-garching.mpg.de [Departamento de Astronomia y Astrofisica, Universidad de Valencia, 46100 Burjassot, Valencia (Spain)

2011-09-22

Some of the most violent events in the universe, the gamma ray burst, could be related to the gravitational collapse of massive stellar cores. The recent association of long GRBs to some class of type Ic supernova seems to support this view. In such scenario fast rotation, strong magnetic fields and general relativistic effects are key ingredients. It is thus important to understand the mechanism that amplifies the magnetic field under that conditions. I present global simulations of the magneto-rotational collapse of stellar cores in general relativity and semi-global simulations of hydromagnetic instabilities under core collapse conditions. I discuss effect of the magneto-rotational instability and the magnetic field amplification during the collapse, the uncertainties in this process and the dynamical effects in the supernova explosion.

SATURATION OF MAGNETOROTATIONAL INSTABILITY THROUGH MAGNETIC FIELD GENERATION

International Nuclear Information System (INIS)

Ebrahimi, F.; Prager, S. C.; Schnack, D. D.

2009-01-01

The saturation mechanism of magnetorotational instability (MRI) is examined through analytical quasi-linear theory and through nonlinear computation of a single mode in a rotating disk. We find that large-scale magnetic field is generated through the α-effect (the correlated product of velocity and magnetic field fluctuations) and causes the MRI mode to saturate. If the large-scale plasma flow is allowed to evolve, the mode can also saturate through its flow relaxation. In astrophysical plasmas, for which the flow cannot relax because of gravitational constraints, the mode saturates through field generation only.

Low-frequency instabilities of a warm plasma in a magnetic field

International Nuclear Information System (INIS)

Smith, D.F.; Hollweg, J.V.

1977-01-01

The marginal stability of a plasma carrying current along the static magnetic field with isotropic Maxwellian ions and isotropic Maxwellian electrons drifting relative to the ions is investigated. The complete electromagnetic dispersion relation is studied using numerical techniques; the electron sums are restricted to three terms which limits the analysis to frequencies much less than the electron gyro-frequency, but includes frequencies somewhat above the ion gyro-frequency. A 'kink-like' instability and an instability of the Alfven mode are found to have the lowest threshold drift velocities in most cases. In fact the threshold drift for the kink-like instability can be significantly less than the ion thermal speed. Electrostatic and electromagnetic ion-cyclotron instabilities are also found as well as the electro-static ion-acoustic instability. No instability of the fast magnetosonic mode was found. The stability analysis provides only threshold drift velocities and gives no information about growth rates. (author)

Effect of magnetic field on Rayleigh-Taylor instability of two superposed fluids

International Nuclear Information System (INIS)

Sharma, P K; Tiwari, Anita; Chhajlani, R K

2012-01-01

The effect of two dimensional magnetic field on the Rayleigh-Taylor (R-T) instability in an incompressible plasma is investigated to include simultaneously the effects of suspended particles and the porosity of the medium. The relevant linearized perturbation equations have been solved. The explicit expression of the linear growth rate is obtained in the presence of fixed boundary conditions. A stability criterion for the medium is derived and discussed the Rayleigh Taylor instabilities in different configurations. It is found that the basic Rayleigh-Taylor instability condition is modified by the presence of magnetic field, suspended particles and porosity of the medium. In case of an unstable R-T configuration, the magnetic field has a stabilizing effect on the system. It is also found that the growth rate of an unstable R-T mode decreases with increasing relaxation frequency thereby showing a stabilizing influence on the R-T configuration.

Estimation of low-dose radiation-responsive proteins in the absence of genomic instability in normal human fibroblast cells.

Science.gov (United States)

Yim, Ji-Hye; Yun, Jung Mi; Kim, Ji Young; Nam, Seon Young; Kim, Cha Soon

2017-11-01

Low-dose radiation has various biological effects such as adaptive responses, low-dose hypersensitivity, as well as beneficial effects. However, little is known about the particular proteins involved in these effects. Here, we sought to identify low-dose radiation-responsive phosphoproteins in normal fibroblast cells. We assessed genomic instability and proliferation of fibroblast cells after γ-irradiation by γ-H2AX foci and micronucleus formation analyses and BrdU incorporation assay, respectively. We screened fibroblast cells 8 h after low-dose (0.05 Gy) γ-irradiation using Phospho Explorer Antibody Microarray and validated two differentially expressed phosphoproteins using Western blotting. Cell proliferation proceeded normally in the absence of genomic instability after low-dose γ-irradiation. Phospho antibody microarray analysis and Western blotting revealed increased expression of two phosphoproteins, phospho-NFκB (Ser536) and phospho-P70S6K (Ser418), 8 h after low-dose radiation. Our findings suggest that low-dose radiation of normal fibroblast cells activates the expression of phospho-NFκB (Ser536) and phospho-P70S6K (Ser418) in the absence of genomic instability. Therefore, these proteins may be involved in DNA damage repair processes.

Self-Field Effects in Magneto-Thermal Instabilities for Nb-Sn Strands

CERN Document Server

Bordini, B; Fehér, S; Rossi, L; Zlobin, A V

2008-01-01

Recent advancements in the critical current density (Jc) of Nb$_{3}$Sn conductors, coupled with a large effective filament size, have drawn attention to the problem of magnetothermal instabilities. At low magnetic fields, the quench current of such high Jc Nb$_{3}$Sn strands is significantly lower than their critical current because of the above-mentioned instabilities. An adiabatic model to calculate the minimum current at which a strand can quench due to magneto-thermal instabilities is developed. The model is based on an 'integral' approach already used elsewhere [1]. The main difference with respect to the previous model is the addition of the self-field effect that allows to describe premature quenches of non-magnetized Nb$_{3}$Sn strands and to better calculate the quench current of strongly magnetized strands. The model is in good agreement with experimental results at 4.2 K obtained at Fermilab using virgin Modified Jelly Roll (MJR) strands with a low Residual Resistivity Ratio (RRR) of the stabilizin...

Cross-field dust acoustic instability in a dusty negative ion plasma

International Nuclear Information System (INIS)

Rosenberg, M

2010-01-01

A cross-field dust acoustic instability in a dusty negative ion plasma in a magnetic field is studied using kinetic theory. The instability is driven by the ExB drifts of the ions. It is assumed that the negative ions are much heavier than the positive ions, and that the dust is negatively charged. The case where the positive ions and electrons are magnetized, the negative ions are marginally unmagnetized, and the dust is unmagnetized is considered. The focus is on a situation where Doppler resonances near harmonics of the positive ion gyrofrequency can affect the spectrum of unstable dust acoustic waves. Application to possible laboratory experimental parameters is discussed.

Linear Analyses of Magnetohydrodynamic Richtmyer-Meshkov Instability in Cylindrical Geometry

KAUST Repository

Bakhsh, Abeer

2018-05-13

We investigate the Richtmyer-Meshkov instability (RMI) that occurs when an incident shock impulsively accelerates the interface between two different fluids. RMI is important in many technological applications such as Inertial Confinement Fusion (ICF) and astrophysical phenomena such as supernovae. We consider RMI in the presence of the magnetic field in converging geometry through both simulations and analytical means in the framework of ideal magnetohydrodynamics (MHD). In this thesis, we perform linear stability analyses via simulations in the cylindrical geometry, which is of relevance to ICF. In converging geometry, RMI is usually followed by the Rayleigh-Taylor instability (RTI). We show that the presence of a magnetic field suppresses the instabilities. We study the influence of the strength of the magnetic field, perturbation wavenumbers and other relevant parameters on the evolution of the RM and RT instabilities. First, we perform linear stability simulations for a single interface between two different fluids in which the magnetic field is normal to the direction of the average motion of the density interface. The suppression of the instabilities is most evident for large wavenumbers and relatively strong magnetic fields strengths. The mechanism of suppression is the transport of vorticity away from the density interface by two Alfv ́en fronts. Second, we examine the case of an azimuthal magnetic field at the density interface. The most evident suppression of the instability at the interface is for large wavenumbers and relatively strong magnetic fields strengths. After the shock interacts with the interface, the emerging vorticity breaks up into waves traveling parallel and anti-parallel to the magnetic field. The interference as these waves propagate with alternating phase causing the perturbation growth rate of the interface to oscillate in time. Finally, we propose incompressible models for MHD RMI in the presence of normal or azimuthal magnetic

Double Arc Instability in the Solar Corona

Energy Technology Data Exchange (ETDEWEB)

Ishiguro, N.; Kusano, K., E-mail: n-ishiguro@isee.nagoya-u.ac.jp [Institute for Space-Earth Environmental Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601 Japan (Japan)

2017-07-10

The stability of the magnetic field in the solar corona is important for understanding the causes of solar eruptions. Although various scenarios have been suggested to date, the tether-cutting reconnection scenario proposed by Moore et al. is one of the widely accepted models to explain the onset process of solar eruptions. Although the tether-cutting reconnection scenario proposes that the sigmoidal field formed by internal reconnection is the magnetic field in the pre-eruptive state, the stability of the sigmoidal field has not yet been investigated quantitatively. In this paper, in order to elucidate the stability problem of the pre-eruptive state, we developed a simple numerical analysis in which the sigmoidal field is modeled by a double arc electric current loop and its stability is analyzed. As a result, we found that the double arc loop is more easily destabilized than the axisymmetric torus, and it becomes unstable even if the external field does not decay with altitude, which is in contrast to the axisymmetric torus instability. This suggests that tether-cutting reconnection may well work as the onset mechanism of solar eruptions, and if so, the critical condition for eruption under a certain geometry may be determined by a new type of instability rather than by the torus instability. Based on them, we propose a new type of instability called double arc instability (DAI). We discuss the critical conditions for DAI and derive a new parameter κ , defined as the product of the magnetic twist and the normalized flux of the tether-cutting reconnection.

Instabilities in inhomogeneous plasma

International Nuclear Information System (INIS)

Mikhailovsky, A.B.

1983-01-01

The plasma inhomogeneity across the magnetic field causes a wide class of instabilities which are called instabilities of an inhomogeneous plasma or gradient instabilities. The instabilities that can be studied in the approximation of a magnetic field with parallel straight field lines are treated first, followed by a discussion of the influence of shear on these instabilities. The instabilities of a weakly inhomogeneous plasma with the Maxwellian velocity distribution of particles caused by the density and temperature gradients are often called drift instabilities, and the corresponding types of perturbations are the drift waves. An elementary theory of drift instabilities is presented, based on the simplest equations of motion of particles in the field of low-frequency and long-wavelength perturbations. Following that is a more complete theory of inhomogeneous collisionless plasma instabilities which uses the permittivity tensor and, in the case of electrostatic perturbations, the scalar of permittivity. The results are used to study the instabilities of a strongly inhomogeneous plasma. The instabilities of a plasma in crossed fields are discussed and the electromagnetic instabilities of plasma with finite and high pressure are described. (Auth.)

Superradiant Instability and Backreaction of Massive Vector Fields around Kerr Black Holes.

Science.gov (United States)

East, William E; Pretorius, Frans

2017-07-28

We study the growth and saturation of the superradiant instability of a complex, massive vector (Proca) field as it extracts energy and angular momentum from a spinning black hole, using numerical solutions of the full Einstein-Proca equations. We concentrate on a rapidly spinning black hole (a=0.99) and the dominant m=1 azimuthal mode of the Proca field, with real and imaginary components of the field chosen to yield an axisymmetric stress-energy tensor and, hence, spacetime. We find that in excess of 9% of the black hole's mass can be transferred into the field. In all cases studied, the superradiant instability smoothly saturates when the black hole's horizon frequency decreases to match the frequency of the Proca cloud that spontaneously forms around the black hole.

Effect of magnetic field on ablatively driven Richtmyer-Meshkov instability induced by interfacial nonlinear structure

International Nuclear Information System (INIS)

Labakanta Mandal; Banerjee, R.; Roy, S.; Khan, M.; Gupta, M.R.

2010-01-01

Complete text of publication follows. In an Inertial Confinement Fusion (ICF) situation, laser driven ablation front of an imploding capsule is subjected to the fluid instabilities like Rayleigh-Taylor (RT), Richtmyer-Meshkov (RM) and Kelvin-Helmholtz (KH) instability. In this case dense core is compressed and accelerated by low density ablating plasma. During this process laser driven shocks interact the interface and hence it becomes unstable due to the formation of nonlinear structure like bubble and spike. The nonlinear structure is called bubble if the lighter fluid pushes inside the heavier fluid and spike, if opposite takes place. R-M instability causes non-uniform compression of ICF fuel pellets and needs to be mitigated. Scientists and researchers are much more interested on RM instability both from theoretical and experimental points of view. In this article, we have presented the analytical expression for the growth rate and velocity for the nonlinear structures due to the effect of magnetic field of fluid using potential flow model. The magnetic field is assumed to be parallel to the plane of two fluid interfaces. If the magnetic field is restricted only to either side of interface the R-M instability can be stabilized or destabilized depending on whether the magnetic pressure on the interface opposes the instability driving shock pressure or acts in the same direction. An interesting result is that if both the fluids are magnetized, interface as well as velocity of bubble and spike will show oscillating stabilization and R-M instability is mitigated. All analytical results are also supported by numerical results. Numerically it is seen that magnetic field above certain minimum value reduces the instability for compression the target in ICF.

Magnetohydrodynamic implosion symmetry and suppression of Richtmyer-Meshkov instability in an octahedrally symmetric field

KAUST Repository

Mostert, W.; Pullin, D. I.; Wheatley, V.; Samtaney, Ravi

2017-01-01

We present numerical simulations of ideal magnetohydrodynamics showing suppression of the Richtmyer-Meshkov instability in spherical implosions in the presence of an octahedrally symmetric magnetic field. This field configuration is of interest owing to its high degree of spherical symmetry in comparison with previously considered dihedrally symmetric fields. The simulations indicate that the octahedral field suppresses the instability comparably to the other previously considered candidate fields for light-heavy interface accelerations while retaining a highly symmetric underlying flow even at high field strengths. With this field, there is a reduction in the root-mean-square perturbation amplitude of up to approximately 50% at representative time under the strongest field tested while maintaining a homogeneous suppression pattern compared to the other candidate fields.

Magnetohydrodynamic implosion symmetry and suppression of Richtmyer-Meshkov instability in an octahedrally symmetric field

KAUST Repository

Mostert, W.

2017-01-27

We present numerical simulations of ideal magnetohydrodynamics showing suppression of the Richtmyer-Meshkov instability in spherical implosions in the presence of an octahedrally symmetric magnetic field. This field configuration is of interest owing to its high degree of spherical symmetry in comparison with previously considered dihedrally symmetric fields. The simulations indicate that the octahedral field suppresses the instability comparably to the other previously considered candidate fields for light-heavy interface accelerations while retaining a highly symmetric underlying flow even at high field strengths. With this field, there is a reduction in the root-mean-square perturbation amplitude of up to approximately 50% at representative time under the strongest field tested while maintaining a homogeneous suppression pattern compared to the other candidate fields.

Genomic instability induced by 60Co γ ray radiation in normal human liver cells

International Nuclear Information System (INIS)

Gen Xiaohua; Guo Xianhua; Zuo Yahui; Wang Xiaoli; Wang Zhongwen

2007-01-01

Objective: To explore the genomic instability induced by 60 Co γ rays. Methods: The cloning efficiency and micronucleus efficiency of normal human liver cell irradiated by 60 Co γ rays were detected, and the method of single cell gel electrophoresis (SCGE) was carried out to measure DNA chains damage. The fast-growing cells were divided into different dose-groups and then irradiated by 60 Co γ rays. After 40 populations doubling, the progenies were secondly irradiated with 2 Gy 60 Co γ rays. Results: The cloning efficiency decreased with the increase of doses after the initial irradiation. After the survival cells were given second irradiation, both results of SCGE and micronucleus frequency showed that the second damage was correlated with the original irradiation doses. Conclusions: 60 Co γ rays can not only induce the immediate biological effects in liver cells, but also lead to the genomic instability in the descendants that leads to an enhanced frequency of genetic changes occurring among the progeny of the original irradiated cell. The expanding effect of second event helps to study the genomic instability. (authors)

Effect of magnetic field and radiative condensation on the Jeans instability of dusty plasma with polarization force

International Nuclear Information System (INIS)

Prajapati, R.P.

2013-01-01

The Jeans instability of self-gravitating dusty plasma with polarization force is investigated considering the effects of magnetic field, dust temperature and radiative condensation. The condition of Jeans instability and expression of critical Jeans wave number are obtained which depend upon polarization force and dust temperature but these are unaffected by the presence of magnetic field. The radiative heat-loss functions also modify the Jeans condition of instability and expression of critical Jeans wave number. It is observed that the polarization force and ratio of radiative heat-loss functions have destabilizing while magnetic field and dust temperature have stabilizing influence on the growth rate of Jeans instability.

Ionization and acoustical instability of a low temperature magnetized plasma in a combined (direct and alternating) electrical field

International Nuclear Information System (INIS)

Andropov, V.G.; Sinkevich, O.A.

1983-01-01

It is shown that the ionization front which moves through a gas along a magnetic field in a combined electrical field, which lies in the plane of the front, may be unstable, as a result of the development of an ionization instability in the plasma behind the front. The criterion of instability of the ionization front does not greatly differ from the criterion of instability of an infinite plasma. The ionization front in the magnetic field is stable only in an electrical field of circular polarization or in a combined field in which the direct and alternating electrical fields are orthogonal and the Joule heat liberation from them is equal. The generation of sound is possible in a magnetized plasma in an alternating electrical field orthogonal to a magnetic due to the parametric acoustical instability at the frequency of the external electrical field. 8 refs

Normal gravity field in relativistic geodesy

Science.gov (United States)

Kopeikin, Sergei; Vlasov, Igor; Han, Wen-Biao

2018-02-01

Modern geodesy is subject to a dramatic change from the Newtonian paradigm to Einstein's theory of general relativity. This is motivated by the ongoing advance in development of quantum sensors for applications in geodesy including quantum gravimeters and gradientometers, atomic clocks and fiber optics for making ultra-precise measurements of the geoid and multipolar structure of the Earth's gravitational field. At the same time, very long baseline interferometry, satellite laser ranging, and global navigation satellite systems have achieved an unprecedented level of accuracy in measuring 3-d coordinates of the reference points of the International Terrestrial Reference Frame and the world height system. The main geodetic reference standard to which gravimetric measurements of the of Earth's gravitational field are referred is a normal gravity field represented in the Newtonian gravity by the field of a uniformly rotating, homogeneous Maclaurin ellipsoid of which mass and quadrupole momentum are equal to the total mass and (tide-free) quadrupole moment of Earth's gravitational field. The present paper extends the concept of the normal gravity field from the Newtonian theory to the realm of general relativity. We focus our attention on the calculation of the post-Newtonian approximation of the normal field that is sufficient for current and near-future practical applications. We show that in general relativity the level surface of homogeneous and uniformly rotating fluid is no longer described by the Maclaurin ellipsoid in the most general case but represents an axisymmetric spheroid of the fourth order with respect to the geodetic Cartesian coordinates. At the same time, admitting a post-Newtonian inhomogeneity of the mass density in the form of concentric elliptical shells allows one to preserve the level surface of the fluid as an exact ellipsoid of rotation. We parametrize the mass density distribution and the level surface with two parameters which are

Ion heating, burnout of the high-frequency field, and ion sound generation under the development of a modulation instability of an intense Langmuir wave in a plasma

Science.gov (United States)

Kirichok, A. V.; Kuklin, V. M.; Pryimak, A. V.; Zagorodny, A. G.

2015-09-01

The development of one-dimensional parametric instabilities of intense long plasma waves is considered in terms of the so-called hybrid models, with electrons being treated as a fluid and ions being regarded as particles. The analysis is performed for both cases when the average plasma field energy is lower (Zakharov's hybrid model—ZHM) or greater (Silin's hybrid model—SHM) than the plasma thermal energy. The efficiency of energy transfer to ions and to ion perturbations under the development of the instability is considered for various values of electron-to-ion mass ratios. The energy of low-frequency oscillations (ion-sound waves) is found to be much lower than the final ion kinetic energy. We also discuss the influence of the changes in the damping rate of the high-frequency (HF) field on the instability development. The decrease of the absorption of the HF field inhibits the HF field burnout within plasma density cavities and gives rise to the broadening of the HF spectrum. At the same time, the ion velocity distribution tends to the normal distribution in both ZHM and SHM.

Baroclinic Instability in the Solar Tachocline for Continuous Vertical Profiles of Rotation, Effective Gravity, and Toroidal Field

Energy Technology Data Exchange (ETDEWEB)

Gilman, Peter A., E-mail: gilman@ucar.edu [High Altitude Observatory, National Center for Atmospheric Research, 3080 Center Green, Boulder, CO 80307-3000 (United States)

2017-06-20

We present results from an MHD model for baroclinic instability in the solar tachocline that includes rotation, effective gravity, and toroidal field that vary continuously with height. We solve the perturbation equations using a shooting method. Without toroidal fields but with an effective gravity declining linearly from a maximum at the bottom to much smaller values at the top, we find instability at all latitudes except at the poles, at the equator, and where the vertical rotation gradient vanishes (32.°3) for longitude wavenumbers m from 1 to >10. High latitudes are much more unstable than low latitudes, but both have e -folding times that are much shorter than a sunspot cycle. The higher the m and the steeper the decline in effective gravity, the closer the unstable mode peak to the top boundary, where the energy available to drive instability is greatest. The effect of the toroidal field is always stabilizing, shrinking the latitude ranges of instability as the toroidal field is increased. The larger the toroidal field, the smaller the longitudinal wavenumber of the most unstable disturbance. All latitudes become stable for a toroidal field exceeding about 4 kG. The results imply that baroclinic instability should occur in the tachocline at latitudes where the toroidal field is weak or is changing sign, but not where the field is strong.

Vacuum instability in scalar field theories

International Nuclear Information System (INIS)

McKane, A.J.

1978-09-01

Scalar field theories with an interaction of the form gphisup(N) have no stable vacuum state for some range of values of their coupling constant, g. This thesis reports calculations of vacuum instability in such theories. Using the idea that the tunnelling out of the vacuum state is described by the instanton solutions of the theory, the imaginary part of the vertex functions is calculated for the massless theory in the one-loop approximation, near the dimension dsub(c) = 2N/N-2, where the theory is just renormalisable. The calculation differs from previous treatments in that dimensional regularisation is used to control the ultra-violet divergences of the theory. In this way previous analytic calculations in conformally invariant field theories are extended to the case where the theory is almost conformally invariant, since it is now defined in dsub(c) - epsilon dimensions (epsilon > 0). (author)

Development of Richtmyer-Meshkov and Rayleigh-Taylor instability in the presence of magnetic field

International Nuclear Information System (INIS)

Khan, Manoranjan; Mandal, Labakanta; Banerjee, Rahul; Roy, Sourav; Gupta, M.R.

2011-01-01

Fluid instabilities like Rayleigh-Taylor (R-T), Richtmyer-Meshkov (R-M) and Kelvin-Helmholtz (K-H) instability can occur in a wide range of physical phenomenon from astrophysical context to Inertial Confinement Fusion (ICF). Using Layzer's potential flow model, we derive the analytical expressions of growth rate of bubble and spike for ideal magnetized fluid in R-T and R-M cases. In the presence of transverse magnetic field, the R-M and R-T instabilities are suppressed or enhanced depending on the direction of magnetic pressure and hydrodynamic pressure. Again the interface of two fluid may oscillate if both the fluids are conducting. However, it is observed that the magnetic field has no effect in linear case.

Robustness of the filamentation instability for asymmetric plasma shells collision in arbitrarily oriented magnetic field

Energy Technology Data Exchange (ETDEWEB)

Bret, A. [ETSI Industriales, Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain and Instituto de Investigaciones Energticas y Aplicaciones Industriales, Campus Universitario de Ciudad Real, 13071 Ciudad Real (Spain)

2013-10-15

The filamentation instability triggered when two counter streaming plasma shells overlap appears to be the main mechanism by which collisionless shocks are generated. It has been known for long that a flow aligned magnetic field can completely suppress this instability. In a recent paper [Phys. Plasmas 18, 080706 (2011)], it was demonstrated in two dimensions that for the case of two cold, symmetric, relativistically colliding shells, such cancellation cannot occur if the field is not perfectly aligned. Here, this result is extended to the case of two asymmetric shells. The filamentation instability appears therefore as an increasingly robust mechanism to generate shocks.

Field-induced magnetic instability within a superconducting condensate

DEFF Research Database (Denmark)

Mazzone, Daniel Gabriel; Raymond, Stephane; Gavilano, Jorge Luis

2017-01-01

The application of magnetic fields, chemical substitution, or hydrostatic pressure to strongly correlated electron materials can stabilize electronic phases with different organizational principles. We present evidence for a fieldinduced quantum phase transition, in superconducting Nd0.05Ce0.95Co...... that the magnetic instability is not magnetically driven, and we propose that it is driven by a modification of superconducting condensate at H*.......In5, that separates two antiferromagnetic phases with identical magnetic symmetry. At zero field, we find a spin-density wave that is suppressed at the critical field mu H-0* = 8 T. For H > H*, a spin-density phase emerges and shares many properties with the Q phase in CeCoIn5. These results suggest...

LONGITUDINAL AND TRANSVERSAL PLASMA WAVE INSTABILITIES IN TWO COUNTERSTREAMING PLASMAS WITHOUT EXTERNAL FIELDS

Energy Technology Data Exchange (ETDEWEB)

Buenemann, D

1963-03-15

Some aspects of the theory of longitudinal and transversal waves in a collisionless nonrelativistic plasma are treated. A dispersion relation for multicomponent plasmas is derived from the linearized Boltzmann-Vlasov equation using the full set of Maxwell's equations without an external field. The velocity distributions of the plasma streams are assumed to be Maxwellian. For the particular case of two counterstreaming plasmas it is shown that there exists transversal instabilities for all counterstreaming velocities whereas the well known two stream instabilities only exist for velocities greater than a critical velocity. Exact solutions for the onset of the instabilities can be given. This kind of instability may occur for any nonisotropic velocity distribution in a collisionless plasma. (auth)

Robustness of the filamentation instability in arbitrarily oriented magnetic field: Full three dimensional calculation

Energy Technology Data Exchange (ETDEWEB)

Bret, A., E-mail: antoineclaude.bret@uclm.es [ETSI Industriales, Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain and Instituto de Investigaciones Energéticas y Aplicaciones Industriales, Campus Universitario de Ciudad Real, 13071 Ciudad Real (Spain)

2014-02-15

The filamentation (Weibel) instability plays a key role in the formation of collisionless shocks which are thought to produce Gamma-Ray-Bursts and High-Energy-Cosmic-Rays in astrophysical environments. While it has been known for long that a flow-aligned magnetic field can completely quench the instability, it was recently proved in 2D that in the cold regime, such cancelation is possible if and only if the field is perfectly aligned. Here, this result is finally extended to a 3D geometry. Calculations are conducted for symmetric and asymmetric counter-streaming relativistic plasma shells. 2D results are retrieved in 3D: the instability can never be completely canceled for an oblique magnetic field. In addition, the maximum growth-rate is always larger for wave vectors lying in the plan defined by the flow and the oblique field. On the one hand, this bears consequences on the orientation of the generated filaments. On the other hand, it certifies 2D simulations of the problem can be performed without missing the most unstable filamentation modes.

Instability of surface electron cyclotron TM-modes influenced by non-monochromatic alternating electric field

International Nuclear Information System (INIS)

Girka, I. O.; Girka, V. O.; Sydora, R. D.; Thumm, M.

2016-01-01

The influence of non-monochromaticity of an external alternating electric field on excitation of TM eigenmodes at harmonics of the electron cyclotron frequency is considered here. These TM-modes propagate along the plasma interface in a metal waveguide. An external static constant magnetic field is oriented perpendicularly to the plasma interface. The problem is solved theoretically using the kinetic Vlasov-Boltzmann equation for description of plasma particles motion and the Maxwell equations for description of the electromagnetic mode fields. The external alternating electric field is supposed to be a superposition of two waves, whose amplitudes are different and their frequencies correlate as 2:1. An infinite set of equations for electric field harmonics of these modes is derived with the aid of nonlinear boundary conditions. This set is solved using the wave packet approach consisting of the main harmonic frequency and two nearest satellite temporal harmonics. Analytical studies of the obtained set of equations allow one to find two different regimes of parametric instability, namely, enhancement and suppression of the instability. Numerical analysis of the instability is carried out for the three first electron cyclotron harmonics.

Renormalization, averaging, conservation laws and AdS (in)stability

International Nuclear Information System (INIS)

Craps, Ben; Evnin, Oleg; Vanhoof, Joris

2015-01-01

We continue our analytic investigations of non-linear spherically symmetric perturbations around the anti-de Sitter background in gravity-scalar field systems, and focus on conservation laws restricting the (perturbatively) slow drift of energy between the different normal modes due to non-linearities. We discover two conservation laws in addition to the energy conservation previously discussed in relation to AdS instability. A similar set of three conservation laws was previously noted for a self-interacting scalar field in a non-dynamical AdS background, and we highlight the similarities of this system to the fully dynamical case of gravitational instability. The nature of these conservation laws is best understood through an appeal to averaging methods which allow one to derive an effective Lagrangian or Hamiltonian description of the slow energy transfer between the normal modes. The conservation laws in question then follow from explicit symmetries of this averaged effective theory.

Ion heating, burnout of the high-frequency field, and ion sound generation under the development of a modulation instability of an intense Langmuir wave in a plasma

Energy Technology Data Exchange (ETDEWEB)

Kirichok, A. V., E-mail: sandyrcs@gmail.com; Kuklin, V. M.; Pryimak, A. V. [Institute for High Technologies, V.N. Karazin Kharkiv National University, 4 Svobody Sq., Kharkiv 61022 (Ukraine); Zagorodny, A. G. [Bogolyubov Institute for Theoretical Physics, 14-b, Metrolohichna str., Kiev 03680 (Ukraine)

2015-09-15

The development of one-dimensional parametric instabilities of intense long plasma waves is considered in terms of the so-called hybrid models, with electrons being treated as a fluid and ions being regarded as particles. The analysis is performed for both cases when the average plasma field energy is lower (Zakharov's hybrid model—ZHM) or greater (Silin's hybrid model—SHM) than the plasma thermal energy. The efficiency of energy transfer to ions and to ion perturbations under the development of the instability is considered for various values of electron-to-ion mass ratios. The energy of low-frequency oscillations (ion-sound waves) is found to be much lower than the final ion kinetic energy. We also discuss the influence of the changes in the damping rate of the high-frequency (HF) field on the instability development. The decrease of the absorption of the HF field inhibits the HF field burnout within plasma density cavities and gives rise to the broadening of the HF spectrum. At the same time, the ion velocity distribution tends to the normal distribution in both ZHM and SHM.

Plasma instabilities multifrequency study in equatorial electrojet

International Nuclear Information System (INIS)

Hanuise, C.

1983-01-01

In this thesis, multifrequential HF coherent radar results are presented, in the field plasma instabilities in equatorial electrojet. In a first part, characteristics of the irregularities observed either at the 3 meter wavelength by VHF radars, either at other wavelengths during pinpoint experiments, or in-situ by probe rockets are recalled. Theoretical studies progressed and are presented, at the same time with these experimental observations: instability linear theory, non linear theories, HF radar specificity, and problems associated to HF waves propagation and refraction in ionosphere. Original experimental results from Ethiopia are gathered in the second part. Plasma instability has been studied in different geophysical conditions and Doppler spectra characteristics are presented for each one of them. These characteristics are completely different according to the various cases; they are also different according to wether observations are made during the day in normal conditions (electric field pointed to the east at the equator) or in counter-electrojet conditions (electric field pointed to the west). The last part is concerned with theoretical interpretation of the previous results. A comprehensive view of the instability physical mechanisms, according to the geophysical conditions encountered, has been allowed by our results, VHF radar measurements at Jicamarca, or in situ probe measurements on the whole. Irregularities study has been limited to the E region [fr

Smoothing and instability with magnetic field in a non-uniformly laser-irradiated planar target

International Nuclear Information System (INIS)

Bell, A.R.; Epperlein, E.M.

1986-01-01

Calculations are presented of the magneto-hydrodynamic response of a planar target to non-uniformities in energy deposition by a laser. The amplitude of the non-uniformities are assumed small and the equations are linearised in small perturbations about the solution for steady planar ablation driven by uniform laser energy deposition. The grad(n)xgrad(T) magnetic field source is included, along with Nernst convection and the Righi-Leduc heat flow. The magnetic field is shown to give a small increase in smoothing. A source term for magnetic field is included to simulate the effects of the Weibel instability. The instability is not strong enough to overcome the smoothing processes under the present assumptions. (author)

Normalization at the field level: fractional counting of citations

OpenAIRE

Leydesdorff, Loet; Opthof, Tobias

2010-01-01

Van Raan et al. (2010; arXiv:1003.2113) have proposed a new indicator (MNCS) for field normalization. Since field normalization is also used in the Leiden Rankings of universities, we elaborate our critique of journal normalization in Opthof & Leydesdorff (2010; arXiv:1002.2769) in this rejoinder concerning field normalization. Fractional citation counting thoroughly solves the issue of normalization for differences in citation behavior among fields. This indicator can also be used to obtain ...

FAST MAGNETIC FIELD AMPLIFICATION IN THE EARLY UNIVERSE: GROWTH OF COLLISIONLESS PLASMA INSTABILITIES IN TURBULENT MEDIA

Energy Technology Data Exchange (ETDEWEB)

Falceta-Gonçalves, D. [SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS (United Kingdom); Kowal, G. [Escola de Artes, Ciências e Humanidades, Universidade de São Paulo, Rua Arlindo Bettio, 1000, São Paulo, SP 03828-000 (Brazil)

2015-07-20

In this work we report on a numerical study of the cosmic magnetic field amplification due to collisionless plasma instabilities. The collisionless magnetohydrodynamic equations derived account for the pressure anisotropy that leads, in specific conditions, to the firehose and mirror instabilities. We study the time evolution of seed fields in turbulence under the influence of such instabilities. An approximate analytical time evolution of the magnetic field is provided. The numerical simulations and the analytical predictions are compared. We found that (i) amplification of the magnetic field was efficient in firehose-unstable turbulent regimes, but not in the mirror-unstable models; (ii) the growth rate of the magnetic energy density is much faster than the turbulent dynamo; and (iii) the efficient amplification occurs at small scales. The analytical prediction for the correlation between the growth timescales and pressure anisotropy is confirmed by the numerical simulations. These results reinforce the idea that pressure anisotropies—driven naturally in a turbulent collisionless medium, e.g., the intergalactic medium, could efficiently amplify the magnetic field in the early universe (post-recombination era), previous to the collapse of the first large-scale gravitational structures. This mechanism, though fast for the small-scale fields (∼kpc scales), is unable to provide relatively strong magnetic fields at large scales. Other mechanisms that were not accounted for here (e.g., collisional turbulence once instabilities are quenched, velocity shear, or gravitationally induced inflows of gas into galaxies and clusters) could operate afterward to build up large-scale coherent field structures in the long time evolution.

Self-field instabilities in high-$J_{c}$ Nb$_{3}$Sn strands the effect of copper RRR

CERN Document Server

Bordini, B

2009-01-01

High critical current density (Jc) Nb$_{3}$Sn conductor is the best candidate for next generation high field (> 10 T) accelerator magnets. Although very promising, state of the art high-Jc Nb$_{3}$Sn strands suffer of magneto-thermal instabilities that can severely limit the strand performance. Recently it has been shown that at 1.9 K the self field instability is the dominating mechanism that limits the performance of strands with a low (<10) Residual Resistivity Ratio (RRR) of the stabilizing copper. At CERN several state of the art high–Jc Nb$_{3}$Sn wires have been tested at 4.2 K and 1.9 K to study the effects on strand self-field instability of: RRR and strand impregnation with stycast. To study the effect of the RRR value on magneto-thermal instabilities, a new 2-D finite element model was also developed at CERN. This model simulates the whole development of the flux jump in the strand cross section also taking into account the heat and current diffusion in the stabilizing copper. In this paper th...

Three-dimensional simulation of the electromagnetic ion/ion beam instability: cross field diffusion

Directory of Open Access Journals (Sweden)

H. Kucharek

2000-01-01

Full Text Available In a system with at least one ignorable spatial dimension charged particles moving in fluctuating fields are tied to the magnetic field lines. Thus, in one-and two-dimensional simulations cross-field diffusion is inhibited and important physics may be lost. We have investigated cross-field diffusion in self-consistent 3-D magnetic turbulence by fully 3-dimensional hybrid simulation (macro-particle ions, massless electron fluid. The turbulence is generated by the electromagnetic ion/ion beam instability. A cold, low density, ion beam with a high velocity stream relative to the background plasma excites the right-hand resonant instability. Such ion beams may be important in the region of the Earth's foreshock. The field turbulence scatters the beam ions parallel as well as perpendicular to the magnetic field. We have determined the parallel and perpendicular diffusion coefficient for the beam ions in the turbulent wave field. The result compares favourably well (within a factor 2 with hard-sphere scattering theory for the cross-field diffusion coefficient. The cross-field diffusion coefficient is larger than that obtained in a static field with a Kolmogorov type spectrum and similar total fluctuation power. This is attributed to the resonant behaviour of the particles in the fluctuating field.

Fluidelastic instability of a flexible tube in a rigid normal square array subjected to uniform two-phase cross-flows

International Nuclear Information System (INIS)

Axisa, F.; Villard, B.; Antunes, J.

1989-01-01

During the last decade several researchers, investigated fluidelastic instability in tube arrays by restricting the problem to a single degree of freedom system. This is a very attractive idea because of obvious theoretical and experimental simplifications. Nevertheless, it has still to be clarified how far such results can be applied to fully flexible arrays. This paper is presenting a few experimental data obtained on a rigid normal square array subjected to uniform air-water cross flows, at various homogeneous void fractions α H from O to 1. Fluidelastic instability was clearly observed in air and in water. However instability was progressively vanishing in two-phase flow, when α H was increased. Such a result is contrasting with those obtained on fully flexible arrays

Non-linear instability of DIII-D to error fields

International Nuclear Information System (INIS)

La Haye, R.J.; Scoville, J.T.

1991-10-01

Otherwise stable DIII-D discharges can become nonlinearly unstable to locked modes and disrupt when subjected to resonant m = 2, n = 1 error field caused by irregular poloidal field coils, i.e. intrinsic field errors. Instability is observed in DIII-D when the magnitude of the radial component of the m = 2, n = 1 error field with respect to the toroidal field is B r21 /B T of about 1.7 x 10 -4 . The locked modes triggered by an external error field are aligned with the static error field and the plasma fluid rotation ceases as a result of the growth of the mode. The triggered locked modes are the precursors of the subsequent plasma disruption. The use of an ''n = 1 coil'' to partially cancel intrinsic errors, or to increase them, results in a significantly expanded, or reduced, stable operating parameter space. Precise error field measurements have allowed the design of an improved correction coil for DIII-D, the ''C-coil'', which could further cancel error fields and help to avoid disruptive locked modes. 6 refs., 4 figs

Wormhole solutions with a complex ghost scalar field and their instability

Science.gov (United States)

Dzhunushaliev, Vladimir; Folomeev, Vladimir; Kleihaus, Burkhard; Kunz, Jutta

2018-01-01

We study compact configurations with a nontrivial wormholelike spacetime topology supported by a complex ghost scalar field with a quartic self-interaction. For this case, we obtain regular asymptotically flat equilibrium solutions possessing reflection symmetry. We then show their instability with respect to linear radial perturbations.

Numerical study and modeling of hydrodynamic instabilities in the context of inertial confinement fusion in the presence of self-generated magnetic fields

International Nuclear Information System (INIS)

Levy, Y.

2012-01-01

In the context of inertial confinement fusion we investigate effects of magnetic fields on the development in the linear regime of two hydrodynamic instabilities: Richtmyer-Meshkov instability using ideal magnetohydrodynamics and ablative Rayleigh-Taylor instability in both acceleration and deceleration stages. Direct numerical simulations with a linear perturbation code enable us to confirm the stabilizing effect of the component of the magnetic field along the perturbations wave vector. The amplitude doesn't grow linearly in time but experiences oscillations instead. The compressibility taken into account in the code does not affect predictions given by an already existing impulsive and incompressible model. As far as Rayleigh-Taylor instability is concerned we study the effects of self-generated magnetic fields that arise from the development of the instability itself. In the acceleration stage we perform two dimensional simulations in planar geometry. We show that magnetic fields of about 1 T can be generated and that the instability growth transits more rapidly into nonlinear growth with the enhancement of the development of the third harmonic. We also propose an adaptation of an existing model that aims at studying thermal conductivity anisotropy effects, to take into account the effects of the self-generated magnetic fields on the Rayleigh-Taylor instability growth rate. Finally, in the deceleration stage, we perform two dimensional simulations in cylindrical geometry that take into account self-generation of magnetic fields due to the instability development. It reveals magnetic fields of about several thousands of Teslas that are not strong enough though to affect the instability behavior. (author) [fr

Cross-Field Current Instabilities in Thin Ionization Layers and the Enhanced Aurora

International Nuclear Information System (INIS)

Johnson, Jay R.; Okuda, Hideo

2008-01-01

Nearly half of the time, auroral displays exhibit thin, bright layers known as 'enhanced aurora'. There is a substantial body of evidence that connects these displays with thin, dense, heavy ion layers in the E-region. Based on the spectral characteristics of the enhanced layers, it is believed that they result when wave-particle interaction heats ambient electrons to energies at or just above the 17 eV ionization energy of N2. While there are several possible instabilities that could produce suprathermal electrons in thin layers, there has been no clear theoretical investigation which examines in detail how wave instabilities in the thin ionization layers could develop and produce the suprathermal electrons. We examine instabilities which would occur in thin, dense, heavy ion layers using extensive analytical analysis combined with particle simulations. We analyze a cross field current instability that is found to be strongly unstable in the heavy ion layers. Electrostatic simulations show that substantial heating of the ambient electrons occurs with energization at or above the N2 ionization energy.

Self-consistent normal ordering of gauge field theories

International Nuclear Information System (INIS)

Ruehl, W.

1987-01-01

Mean-field theories with a real action of unconstrained fields can be self-consistently normal ordered. This leads to a considerable improvement over standard mean-field theory. This concept is applied to lattice gauge theories. First an appropriate real action mean-field theory is constructed. The equations determining the Gaussian kernel necessary for self-consistent normal ordering of this mean-field theory are derived. (author). 4 refs

Flow instability in laminar jet flames driven by alternating current electric fields

KAUST Repository

Kim, Gyeong Taek; Park, Daegeun; Cha, Min; Park, Jeong; Chung, Suk-Ho

2016-01-01

The effect of electric fields on the instability of laminar nonpremixed jet flames was investigated experimentally by applying the alternating current (AC) to a jet nozzle. We aimed to elucidate the origin of the occurrence of twin-lifted jet flames

Parametric instabilities in shallow water magnetohydrodynamics of astrophysical plasma in external magnetic field

Energy Technology Data Exchange (ETDEWEB)

Klimachkov, D.A., E-mail: klimachkovdmitry@gmail.com [Space Research Institute of Russian Academy of Science, 84/32, Profsoyuznaya str., Moscow, 117997 (Russian Federation); Petrosyan, A.S. [Space Research Institute of Russian Academy of Science, 84/32, Profsoyuznaya str., Moscow, 117997 (Russian Federation); Moscow Institute of Physics and Technology (State University), 9 Institutskyi per., Dolgoprudny, Moscow Region, 141700 (Russian Federation)

2017-01-15

This article deals with magnetohydrodynamic (MHD) flows of a thin rotating layer of astrophysical plasma in external magnetic field. We use the shallow water approximation to describe thin rotating plasma layer with a free surface in a vertical external magnetic field. The MHD shallow water equations with external vertical magnetic field are revised by supplementing them with the equations that are consequences of the magnetic field divergence-free conditions and reveal the existence of third component of the magnetic field in such approximation providing its relation with the horizontal magnetic field. It is shown that the presence of a vertical magnetic field significantly changes the dynamics of the wave processes in astrophysical plasma compared to the neutral fluid and plasma layer in a toroidal magnetic field. The equations for the nonlinear wave packets interactions are derived using the asymptotic multiscale method. The equations for three magneto-Poincare waves interactions, for three magnetostrophic waves interactions, for the interactions of two magneto-Poincare waves and for one magnetostrophic wave and two magnetostrophic wave and one magneto-Poincare wave interactions are obtained. The existence of parametric decay and parametric amplifications is predicted. We found following four types of parametric decay instabilities: magneto-Poincare wave decays into two magneto-Poincare waves, magnetostrophic wave decays into two magnetostrophic waves, magneto-Poincare wave decays into one magneto-Poincare wave and one magnetostrophic wave, magnetostrophic wave decays into one magnetostrophic wave and one magneto-Poincare wave. Following mechanisms of parametric amplifications are found: parametric amplification of magneto-Poincare waves, parametric amplification of magnetostrophic waves, magneto-Poincare wave amplification in magnetostrophic wave presence and magnetostrophic wave amplification in magneto-Poincare wave presence. The instabilities growth rates

Non ideal instabilities in field reversed O-pinches

International Nuclear Information System (INIS)

Santiago, M.A.M.; Gomes, A.S.

1987-01-01

Rotational instabilities and resistive tearing modes are the most striking modes observed in high temperature θ-pinches with zero orversed bias field. The configurations which have the effect of a rigid rotation of the plasma column are studied. Some recent experimental data indicate that an m=2 mode appears after the rotation reaches a critical value. It is shown that the growth rate of the m=2 mode may be greater than that of the m=1 resistive kink mode, depending on the experimental conditions. The result are applied to several experimental data in the literature. (author) [pt

Simultaneous density-field visualization and PIV of the Richtmyer-Meshkov instability

Science.gov (United States)

Prestridge, Katherine; Rightley, Paul; Benjamin, Robert; Kurnit, Norman; Boxx, Isaac; Vorobieff, Peter

1999-11-01

We describe a highly-detailed experimental characterization of the Richtmyer-Meshkov instability. A vertical curtain of heavy gas (SF_6) flows into the test section of an air-filled, horizontal shock tube, and the instability evolves after the passage of a Mach 1.2 shock past the curtain. The evolution of the curtain is visualized by seeding the SF6 with small (d ≈ 0.5 μm) glycol/water droplets using a modified theatrical fog generator. Because the event lasts only 1 ms and the initial conditions vary from test to test, rapid and high-resolution (both spatial and temporal) data acquisition is required in order to characterize the initial and dynamic conditions for each experimental event. A customized, frequency-doubled, burst mode Nd:YAG laser and a commercial single-pulse laser are used for the implementation of simultaneous density-field imaging and PIV diagnostics. We have provided data about flow scaling and mixing through image analysis, and PIV data gives us further quantitative physical insight into the evolution of the Richtmyer-Meshkov instability.

Strings, vortex rings, and modes of instability

Directory of Open Access Journals (Sweden)

Steven S. Gubser

2015-03-01

Full Text Available We treat string propagation and interaction in the presence of a background Neveu–Schwarz three-form field strength, suitable for describing vortex rings in a superfluid or low-viscosity normal fluid. A circular vortex ring exhibits instabilities which have been recognized for many years, but whose precise boundaries we determine for the first time analytically in the small core limit. Two circular vortices colliding head-on exhibit stronger instabilities which cause splitting into many small vortices at late times. We provide an approximate analytic treatment of these instabilities and show that the most unstable wavelength is parametrically larger than a dynamically generated length scale which in many hydrodynamic systems is close to the cutoff. We also summarize how the string construction we discuss can be derived from the Gross–Pitaevskii Lagrangian, and also how it compares to the action for giant gravitons.

Excitation of electromagnetic proton cyclotron instability by parallel electric field in the equatorial magnetosphere

International Nuclear Information System (INIS)

Dixit, S.K.; Azif, Z.A.; Gwal, A.K.

1994-01-01

The characteristics of the growth rate of electromagnetic ion cyclotron (EMIC) instability is investigated in a mixture of cold species of ions and warm proton in the presence of weak parallel static electric field. An attempt has been made to explain the excitation of EMIC waves through linear wave-particle (W-P) interaction in the equatorial magnetospheric region. The proton cyclotron instability is modified in presence of weak parallel electric field and the growth rate is computed for equatorial magnetospheric plasma parameters. The results of theoretical investigations of the growth rate are used to explain the excitation mechanism of extremely low frequency/very low frequency (ELF/VLF) waves as observed by satellites. (author). 29 refs., 4 figs

Critical fields and growth rates of the Tayler instability as probed by a columnar gallium experiment

OpenAIRE

Ruediger, Guenther; Gellert, Marcus; Schultz, Manfred; Strassmeier, Klaus G.; Stefani, Frank; Gundrum, Thomas; Seilmayer, Martin; Gerbeth, Gunter

2012-01-01

Many astrophysical phenomena (such as the slow rotation of neutron stars or the rigid rotation of the solar core) can be explained by the action of the Tayler instability of toroidal magnetic fields in the radiative zones of stars. In order to place the theory of this instability on a safe fundament it has been realized in a laboratory experiment measuring the critical field strength, the growth rates as well as the shape of the supercritical modes. A strong electrical current flows through a...

Knockdown of αII spectrin in normal human cells by siRNA leads to chromosomal instability and decreased DNA interstrand cross-link repair

International Nuclear Information System (INIS)

McMahon, Laura W.; Zhang Pan; Sridharan, Deepa M.; Lefferts, Joel A.; Lambert, Muriel W.

2009-01-01

Nonerythroid α-spectrin (αIISp) is a structural protein involved in repair of DNA interstrand cross-links and is deficient in cells from patients with Fanconi anemia (FA), which are defective in ability to repair cross-links. In order to further demonstrate the importance of the role that αIISp plays in normal human cells and in the repair defect in FA, αIISp was knocked down in normal cells using siRNA. Depletion of αIISp in normal cells by siRNA resulted in chromosomal instability and cellular hypersensitivity to DNA interstrand cross-linking agents. An increased number of chromosomal aberrations were observed and, following treatment with a DNA interstrand cross-linking agent, mitomycin C, cells showed decreased cell growth and survival and decreased formation of damage-induced αIISp and XPF nuclear foci. Thus depletion of αIISp in normal cells leads to a number of defects observed in FA cells, such as chromosome instability and a deficiency in cross-link repair.

Instabilities in the flow past localized magnetic fields

International Nuclear Information System (INIS)

Beltran, Alberto; Cuevas, Sergio; Smolentsev, Sergey

2007-01-01

The flow in a shallow layer of an electrically conducting fluid past a localized magnetic field is analyzed numerically. The field occupies only a small fraction of the total flow domain and resemblances the magnetic field created by a permanent magnet located close to the fluid layer. Two different physical cases are considered. In the first one, the fluid layer is free from externally injected electric currents, therefore, only induced currents are present. In the second case, an external electric current is injected to the fluid layer, transversally to the main flow direction. It is shown that the Lorentz force created by the interaction of the electric currents with the non-uniform magnetic field acts as an obstacle for the flow and creates different flow patterns similar to those observed in the flow past bluff bodies. A quasi-two-dimensional model that takes into account the existence of the bottom wall through a linear Hartmann-Rayleigh friction term is considered. When inertial and magnetic forces are strong enough, the wake formed behind the zone of high magnetic field is destabilized and a periodic vortex shedding similar to the classical von Karman street is found. The effect of Hartmann-Rayleigh friction in the emergence of the instability is analyzed

Experimental observation of pulsating instability under acoustic field in downward-propagating flames at large Lewis number

KAUST Repository

Yoon, Sung Hwan

2017-10-12

According to previous theory, pulsating propagation in a premixed flame only appears when the reduced Lewis number, β(Le-1), is larger than a critical value (Sivashinsky criterion: 4(1 +3) ≈ 11), where β represents the Zel\\'dovich number (for general premixed flames, β ≈ 10), which requires Lewis number Le > 2.1. However, few experimental observation have been reported because the critical reduced Lewis number for the onset of pulsating instability is beyond what can be reached in experiments. Furthermore, the coupling with the unavoidable hydrodynamic instability limits the observation of pure pulsating instabilities in flames. Here, we describe a novel method to observe the pulsating instability. We utilize a thermoacoustic field caused by interaction between heat release and acoustic pressure fluctuations of the downward-propagating premixed flames in a tube to enhance conductive heat loss at the tube wall and radiative heat loss at the open end of the tube due to extended flame residence time by diminished flame surface area, i.e., flat flame. The thermoacoustic field allowed pure observation of the pulsating motion since the primary acoustic force suppressed the intrinsic hydrodynamic instability resulting from thermal expansion. By employing this method, we have provided new experimental observations of the pulsating instability for premixed flames. The Lewis number (i.e., Le ≈ 1.86) was less than the critical value suggested previously.

Linear Analysis of Converging Richtmyer-Meshkov Instability in the Presence of an Azimuthal Magnetic Field

KAUST Repository

Bakhsh, Abeer; Samtaney, Ravindra

2017-01-01

We investigate the linear stability of both positive and negative Atwood ratio interfaces accelerated either by a fast magnetosonic or hydrodynamic shock in cylindrical geometry. For the magnetohydrodynamic (MHD) case, we examine the role of an initial seed azimuthal magnetic field on the growth rate of the perturbation. In the absence of a magnetic field, the Richtmyer-Meshkov growth is followed by an exponentially increasing growth associated with the Rayleigh-Taylor instability. In the MHD case, the growth rate of the instability reduces in proportion to the strength of the applied magnetic field. The suppression mechanism is associated with the interference of two waves running parallel and anti-parallel to the interface that transport of vorticity and cause the growth rate to oscillate in time with nearly a zero mean value.

Linear Analysis of Converging Richtmyer-Meshkov Instability in the Presence of an Azimuthal Magnetic Field

KAUST Repository

Bakhsh, Abeer

2017-11-17

We investigate the linear stability of both positive and negative Atwood ratio interfaces accelerated either by a fast magnetosonic or hydrodynamic shock in cylindrical geometry. For the magnetohydrodynamic (MHD) case, we examine the role of an initial seed azimuthal magnetic field on the growth rate of the perturbation. In the absence of a magnetic field, the Richtmyer-Meshkov growth is followed by an exponentially increasing growth associated with the Rayleigh-Taylor instability. In the MHD case, the growth rate of the instability reduces in proportion to the strength of the applied magnetic field. The suppression mechanism is associated with the interference of two waves running parallel and anti-parallel to the interface that transport of vorticity and cause the growth rate to oscillate in time with nearly a zero mean value.

On the kinetic theory of QPEMIC instabilities in weakly ionized plasmas placed in non-parallel fields

International Nuclear Information System (INIS)

Milic, B.S.; Gajic, D.Z.

1994-01-01

Quasi-perpendicular electromagnetic ion-cyclotron (QPEMIC) modes and instabilities are studied, on the ground of linear theory of perturbations and kinetic equations with BGK collision integrals, in weakly ionized, low-β and moderately non-isothermal plasmas placed in non-parallel electric and magnetic fields. The magnetization is assumed to be sufficiently high to cut off the perpendicular steady-state current. Special attention is given to evaluation of magnitudes of the threshold drifts required for the onset of instabilities. It is found that these drifts are smaller than those for the corresponding quasi-perpendicular electrostatic ion-cyclotron (QPESIC) instabilities studied previously for the same type of plasmas. Both QPEMIC and QPESIC threshold drifts exhibit the same behavioural pattern if the order of harmonic, magnetization, non-isothermality or the angle between the fields are varied. An increase of the angle between the fields lowers the threshold drifts, which means that the presence of u perpendicular to (or E perpendicular to ) facilitates the excitation of both QPEMIC and QPESIC instabilities. The QPEMIC threshold drifts are found to depend on the overall gas pressure, and to decrease as the pressure is lowered, which is a feature not found in the QPESIC case. The discrepancies between the QPEMIC and QPESIC threshold drifts increase if the pressure decreases, or if magnetization, degree of ionization or ion charge number increase. (orig.)

Subcritical saturation of the magnetorotational instability through mean magnetic field generation

Science.gov (United States)

Xie, Jin-Han; Julien, Keith; Knobloch, Edgar

2018-03-01

The magnetorotational instability is widely believed to be responsible for outward angular momentum transport in astrophysical accretion discs. The efficiency of this transport depends on the amplitude of this instability in the saturated state. We employ an asymptotic expansion based on an explicit, astrophysically motivated time-scale separation between the orbital period, Alfvén crossing time and viscous or resistive dissipation time-scales, originally proposed by Knobloch and Julien, to formulate a semi-analytical description of the saturated state in an incompressible disc. In our approach a Keplerian shear flow is maintained by the central mass but the instability saturates via the generation of a mean vertical magnetic field. The theory assumes that the time-averaged angular momentum flux and the radial magnetic flux are constant and determines both self-consistently. The results predict that, depending on parameters, steady saturation may be supercritical or subcritical, and in the latter case that the upper (lower) solution branch is always stable (unstable). The angular momentum flux is always outward, consistent with the presence of accretion, and for fixed wavenumber peaks in the subcritical regime. The limit of infinite Reynolds number at large but finite magnetic Reynolds number is also discussed.

Rotational instabilities in field reversed configurations

International Nuclear Information System (INIS)

Santiago, M.A.M.; Tsui, K.H.; Ponciano, B.M.B.; Sakanaka, P.H.

1988-01-01

The rotational instability (n = 2 toroidal mode) in field reversed configurations (FRC) using the ideal MHD equations in cylindrical geometry is studied. These equations are solved using a realistic densite profile, and the influence of some plasma parameters on the growth rate is analysed. The model shows good qualitative results. The growth rate increases rapidly as rotational frequency goes up and the mode m = 2 dominates over the m = 1 mode. With the variation of the density profile, it is observed that the growth rate decreases as the density dip at the center fills up. Calculated value ranges from 1/2 to 1/7 of the rotational frequency Ω whereas the measured value is around Ω/50. The developed analysis is valid for larger machines. The influence of the plasma resistivity on the mode stabilization is also analysed. The resistivity, which is the fundamental factor in the formation of compact torus, tends to decrease the growth rate. (author) [pt

Secular instabilities of Keplerian stellar discs

Science.gov (United States)

Kaur, Karamveer; Kazandjian, Mher V.; Sridhar, S.; Touma, Jihad R.

2018-05-01

We present idealized models of a razor-thin, axisymmetric, Keplerian stellar disc around a massive black hole, and study non-axisymmetric secular instabilities in the absence of either counter-rotation or loss cones. These discs are prograde mono-energetic waterbags, whose phase-space distribution functions are constant for orbits within a range of eccentricities (e) and zero outside this range. The linear normal modes of waterbags are composed of sinusoidal disturbances of the edges of distribution function in phase space. Waterbags that include circular orbits (polarcaps) have one stable linear normal mode for each azimuthal wavenumber m. The m = 1 mode always has positive pattern speed and, for polarcaps consisting of orbits with e normal modes for each m, which can be stable or unstable. We derive analytical expressions for the instability condition, pattern speeds, growth rates, and normal mode structure. Narrow bands are unstable to modes with a wide range in m. Numerical simulations confirm linear theory and follow the non-linear evolution of instabilities. Long-time integration suggests that instabilities of different m grow, interact non-linearly, and relax collisionlessly to a coarse-grained equilibrium with a wide range of eccentricities.

Electroweak vacuum instability and renormalized Higgs field vacuum fluctuations in the inflationary universe

Energy Technology Data Exchange (ETDEWEB)

Kohri, Kazunori [Institute of Particle and Nuclear Studies, KEK, 1-1 Oho, Tsukuba 305-0801 (Japan); Matsui, Hiroki, E-mail: kohri@post.kek.jp, E-mail: matshiro@post.kek.jp [The Graduate University for Advanced Studies (SOKENDAI), 1-1 Oho, Tsukuba 305-0801 (Japan)

2017-08-01

In this work, we investigated the electroweak vacuum instability during or after inflation. In the inflationary Universe, i.e., de Sitter space, the vacuum field fluctuations < δ φ {sup 2} > enlarge in proportion to the Hubble scale H {sup 2}. Therefore, the large inflationary vacuum fluctuations of the Higgs field < δ φ {sup 2} > are potentially catastrophic to trigger the vacuum transition to the negative-energy Planck-scale vacuum state and cause an immediate collapse of the Universe. However, the vacuum field fluctuations < δ φ {sup 2} >, i.e., the vacuum expectation values have an ultraviolet divergence, and therefore a renormalization is necessary to estimate the physical effects of the vacuum transition. Thus, in this paper, we revisit the electroweak vacuum instability from the perspective of quantum field theory (QFT) in curved space-time, and discuss the dynamical behavior of the homogeneous Higgs field φ determined by the effective potential V {sub eff}( φ ) in curved space-time and the renormalized vacuum fluctuations < δ φ {sup 2} >{sub ren} via adiabatic regularization and point-splitting regularization. We simply suppose that the Higgs field only couples the gravity via the non-minimal Higgs-gravity coupling ξ(μ). In this scenario, the electroweak vacuum stability is inevitably threatened by the dynamical behavior of the homogeneous Higgs field φ, or the formations of AdS domains or bubbles unless the Hubble scale is small enough H < Λ {sub I} .

PIC Simulations of Velocity-space Instabilities in a Decreasing Magnetic Field: Viscosity and Thermal Conduction

Science.gov (United States)

Riquelme, Mario; Quataert, Eliot; Verscharen, Daniel

2018-02-01

We use particle-in-cell (PIC) simulations of a collisionless, electron–ion plasma with a decreasing background magnetic field, {\\boldsymbol{B}}, to study the effect of velocity-space instabilities on the viscous heating and thermal conduction of the plasma. If | {\\boldsymbol{B}}| decreases, the adiabatic invariance of the magnetic moment gives rise to pressure anisotropies with {p}| | ,j> {p}\\perp ,j ({p}| | ,j and {p}\\perp ,j represent the pressure of species j (electron or ion) parallel and perpendicular to B ). Linear theory indicates that, for sufficiently large anisotropies, different velocity-space instabilities can be triggered. These instabilities in principle have the ability to pitch-angle scatter the particles, limiting the growth of the anisotropies. Our simulations focus on the nonlinear, saturated regime of the instabilities. This is done through the permanent decrease of | {\\boldsymbol{B}}| by an imposed plasma shear. We show that, in the regime 2≲ {β }j≲ 20 ({β }j\\equiv 8π {p}j/| {\\boldsymbol{B}}{| }2), the saturated ion and electron pressure anisotropies are controlled by the combined effect of the oblique ion firehose and the fast magnetosonic/whistler instabilities. These instabilities grow preferentially on the scale of the ion Larmor radius, and make {{Δ }}{p}e/{p}| | ,e≈ {{Δ }}{p}i/{p}| | ,i (where {{Δ }}{p}j={p}\\perp ,j-{p}| | ,j). We also quantify the thermal conduction of the plasma by directly calculating the mean free path of electrons, {λ }e, along the mean magnetic field, finding that {λ }e depends strongly on whether | {\\boldsymbol{B}}| decreases or increases. Our results can be applied in studies of low-collisionality plasmas such as the solar wind, the intracluster medium, and some accretion disks around black holes.

Bias temperature instability in tunnel field-effect transistors

Science.gov (United States)

Mizubayashi, Wataru; Mori, Takahiro; Fukuda, Koichi; Ishikawa, Yuki; Morita, Yukinori; Migita, Shinji; Ota, Hiroyuki; Liu, Yongxun; O'uchi, Shinichi; Tsukada, Junichi; Yamauchi, Hiromi; Matsukawa, Takashi; Masahara, Meishoku; Endo, Kazuhiko

2017-04-01

We systematically investigated the bias temperature instability (BTI) of tunnel field-effect transistors (TFETs). The positive BTI and negative BTI mechanisms in TFETs are the same as those in metal-oxide-semiconductor FETs (MOSFETs). In TFETs, although traps are generated in high-k gate dielectrics by the bias stress and/or the interface state is degraded at the interfacial layer/channel interface, the threshold voltage (V th) shift due to BTI degradation is caused by the traps and/or the degradation of the interface state locating the band-to-band tunneling (BTBT) region near the source/gate edge. The BTI lifetime in n- and p-type TFETs is improved by applying a drain bias corresponding to the operation conditions.

Kelvin-Helmholtz instability for a bounded plasma flow in a longitudinal magnetic field

International Nuclear Information System (INIS)

Burinskaya, T. M.; Shevelev, M. M.; Rauch, J.-L.

2011-01-01

Kelvin-Helmholtz MHD instability in a plane three-layer plasma is investigated. A general dispersion relation for the case of arbitrarily orientated magnetic fields and flow velocities in the layers is derived, and its solutions for a bounded plasma flow in a longitudinal magnetic field are studied numerically. Analysis of Kelvin-Helmholtz instability for different ion acoustic velocities shows that perturbations with wavelengths on the order of or longer than the flow thickness can grow in an arbitrary direction even at a zero temperature. Oscillations excited at small angles with respect to the magnetic field exist in a limited range of wavenumbers even without allowance for the finite width of the transition region between the flow and the ambient plasma. It is shown that, in a low-temperature plasma, solutions resulting in kink-like deformations of the plasma flow grow at a higher rate than those resulting in quasi-symmetric (sausage-like) deformations. The transverse structure of oscillatory-damped eigenmodes in a low-temperature plasma is analyzed. The results obtained are used to explain mechanisms for the excitation of ultra-low-frequency long-wavelength oscillations propagating along the magnetic field in the plasma sheet boundary layer of the Earth’s magnetotail penetrated by fast plasma flows.

Mean fields and self consistent normal ordering of lattice spin and gauge field theories

International Nuclear Information System (INIS)

Ruehl, W.

1986-01-01

Classical Heisenberg spin models on lattices possess mean field theories that are well defined real field theories on finite lattices. These mean field theories can be self consistently normal ordered. This leads to a considerable improvement over standard mean field theory. This concept is carried over to lattice gauge theories. We construct first an appropriate real mean field theory. The equations determining the Gaussian kernel necessary for self-consistent normal ordering of this mean field theory are derived. (orig.)

Triclade: influence of a sinuous secondary instability on the Richtmyer-Meshkov instabilities; Triclade: influence d'une instabilite sinueuse sur les instabilites de Richtmyer-Meshkov en 2D et 3D

Energy Technology Data Exchange (ETDEWEB)

Boulet, M.; Griffond, J. [CEA Bruyeres-le-Chatel, Dept. Sciences de la Simulation et de l' Information, 91 (France)

2004-07-01

Occurrence of a secondary instability developing after the Richtmyer-Meshkov (primary) instability is emphasized thanks to numerical simulations with the TRICLADE code. We are mainly considering 2D perturbations describes by trigonometric function cosine or [cosine]. However, the 3D case is also tackled. The sinuous secondary instability is characterized by the loss of the symmetries in the direction normal to the interface at its crests. It reduces the late time growing rate of the 'mushrooms' formed by the Richtmyer-Meshkov instability. Related simplified problems, like symmetrical Riemann problems or the Mallier-Maslowe array of counter-rotating vortices, allow us to perform 2D linear stability analysis. Thus, we show that the sinuous secondary instability is not a numerical artifact and that is comes from the continuous incompressible velocity field in the interface region. This instability implies temporal limitations for the validity of single mode simulations; therefore multimode simulations are necessary to study the ]ate-time behaviour of interfaces bitted by shocks. (authors)

Computed tomography for the detection of distal radioulnar joint instability: normal variation and reliability of four CT scoring systems in 46 patients

Energy Technology Data Exchange (ETDEWEB)

Wijffels, Mathieu; Krijnen, Pieta; Schipper, Inger [Leiden University Medical Center, Department of Surgery-Trauma Surgery, P.O. Box 9600, Leiden (Netherlands); Stomp, Wouter; Reijnierse, Monique [Leiden University Medical Center, Department of Radiology, P.O. Box 9600, Leiden (Netherlands)

2016-11-15

The diagnosis of distal radioulnar joint (DRUJ) instability is clinically challenging. Computed tomography (CT) may aid in the diagnosis, but the reliability and normal variation for DRUJ translation on CT have not been established in detail. The aim of this study was to evaluate inter- and intraobserver agreement and normal ranges of CT scoring methods for determination of DRUJ translation in both posttraumatic and uninjured wrists. Patients with a conservatively treated, unilateral distal radius fracture were included. CT scans of both wrists were evaluated independently, by two readers using the radioulnar line method, subluxation ratio method, epicenter method and radioulnar ratio method. The inter- and intraobserver agreement was assessed and normal values were determined based on the uninjured wrists. Ninety-two wrist CTs (mean age: 56.5 years, SD: 17.0, mean follow-up 4.2 years, SD: 0.5) were evaluated. Interobserver agreement was best for the epicenter method [ICC = 0.73, 95 % confidence interval (CI) 0.65-0.79]. Intraobserver agreement was almost perfect for the radioulnar line method (ICC = 0.82, 95 % CI 0.77-0.87). Each method showed a wide normal range for normal DRUJ translation. Normal range for the epicenter method is -0.35 to -0.06 in pronation and -0.11 to 0.19 in supination. DRUJ translation on CT in pro- and supination can be reliably evaluated in both normal and posttraumatic wrists, however with large normal variation. The epicenter method seems the most reliable. Scanning of both wrists might be helpful to prevent the radiological overdiagnosis of instability. (orig.)

Markers of fibrosis and epithelial to mesenchymal transition demonstrate field cancerization in histologically normal tissue adjacent to breast tumors

Science.gov (United States)

Trujillo, Kristina A.; Heaphy, Christopher M.; Mai, Minh; Vargas, Keith M.; Jones, Anna C.; Vo, Phung; Butler, Kimberly S.; Joste, Nancy E.; Bisoffi, Marco; Griffith, Jeffrey K

2011-01-01

Previous studies have shown that a field of genetically altered but histologically normal tissue extends 1 cm or more from the margins of human breast tumors. The extent, composition and biological significance of this field are only partially understood, but the molecular alterations in affected cells could provide mechanisms for limitless replicative capacity, genomic instability and a microenvironment that supports tumor initiation and progression. We demonstrate by microarray, qRT-PCR and immunohistochemistry a signature of differential gene expression that discriminates between patient-matched, tumor-adjacent histologically normal breast tissues located 1 cm and 5 cm from the margins of breast adenocarcinomas (TAHN-1 and TAHN-5, respectively). The signature includes genes involved in extracellular matrix remodeling, wound healing, fibrosis and epithelial to mesenchymal transition (EMT). Myofibroblasts, which are mediators of wound healing and fibrosis, and intra-lobular fibroblasts expressing MMP2, SPARC, TGF-β3, which are inducers of EMT, were both prevalent in TAHN-1 tissues, sparse in TAHN-5 tissues, and absent in normal tissues from reduction mammoplasty. Accordingly, EMT markers S100A4 and vimentin were elevated in both luminal and myoepithelial cells, and EMT markers α-smooth muscle actin and SNAIL were elevated in luminal epithelial cells of TAHN-1 tissues. These results identify cellular processes that are differentially activated between TAHN-1 and TAHN-5 breast tissues, implicate myofibroblasts as likely mediators of these processes, provide evidence that EMT is occurring in histologically normal tissues within the affected field and identify candidate biomarkers to investigate whether or how field cancerization contributes to the development of primary or recurrent breast tumors. PMID:21105047

Ion cyclotron instability saturation and turbulent plasma heating in the presence of ions moving across the magnetic field

International Nuclear Information System (INIS)

Mikhajlenko, V.S.; Stepanov, K.N.

1981-01-01

Ion cyclotron instability saturation is considered in terms of the turbulence theory when there is a beam of heavy ions with large thermal longitudinal velocity spread. The instability excitation is due to a cyclotron interaction with ions of the beam under the anomalous Doppler effect. The instability is shown to be saturated due to an induced plasma ion scattering of ion cyclotron waves when the beam ion charge number Zsub(b) is approximately 1. Decay processes, wave scattering by virtual wave polarization clouds and resonance broadening due to random walk of plasma ions in turbulent instability fields appear to be unimportant. For Zsub(b)>>1 the induced wave scattering by the beam ions is the main process determining the nonlinear stage of the instability. Estimates are given for the oscillation energy density in the instability saturation state and for the turbulent heating rate of plasma and beam ions [ru

Effect of rotation on Jeans instability of magnetized radiative quantum plasma

Science.gov (United States)

Joshi, H.; Pensia, R. K.

2017-03-01

The influence of rotation on the Jeans instability of homogeneous magnetized radiative quantum plasma is investigated. The basic equations of the problem are constructed and linearized by using the Quantum Magnetohydrodynamics (QMHD) model. The general dispersion relation is obtained by using the normal mode analysis technique, which is reduced for both the transverse and the longitudinal mode of propagations and further it is reduced for the axis of rotation parallel and perpendicular to the magnetic field. We found that the stabilizing effects of rotation are decreases for a strong magnetic field which is shown in the graphical representation. We also found that the quantum correction modified the condition of Jeans instability in both modes of propagation. The stabilizing effect of rotation is more increased in the presence of quantum correction.

Vector condensate and AdS soliton instability induced by a magnetic field

International Nuclear Information System (INIS)

Cai, Rong-Gen; Li, Li; Li, Li-Fang; Wu, You

2014-01-01

We continue to study the holographic p-wave superconductor model in the Einstein-Maxwell-complex vector field theory with a non-minimal coupling between the complex vector field and the Maxwell field. In this paper we work in the AdS soliton background which describes a conformal field theory in the confined phase and focus on the probe approximation. We find that an applied magnetic field can lead to the condensate of the vector field and the AdS soliton instability. As a result, a vortex lattice structure forms in the spatial directions perpendicular to the applied magnetic field. As a comparison, we also discuss the vector condensate in the Einstein-SU(2) Yang-Mills theory and find that in the setup of the present paper, the Einstein-Maxwell-complex vector field model is a generalization of the SU(2) model in the sense that the vector field has a general mass and gyromagnetic ratio

Instability of a discharge with a closed EperpendicularH electron drift and a distributed electric field

International Nuclear Information System (INIS)

Kalashnikov, V.K.; Sanochkin, Y.V.

1982-01-01

The stability of a discharge with a closed Hall-current circuit and a distributed electric field is analyzed with respect to long-wave, low-frequency perturbations propagating in the electric drift direction (''low-frequency'' here is with respect to the ion transit time). The analysis is carried out in the linear theory. A dispersion relation derived in the first approximation of the Bubnov--Galerkin method is analyzed numerically. The instability which is found requires a threshold to be attained, which occurs when the neutral density exceeds a certain critical value. An increase in the magnetic field, in contrast, has a stabilizing effect. The instability is oscillatory and develops over wavelengths lying in a finite interval which depends on the dimensions of the device, the magnetic field, and the gas pressure. The wave phase velocity is of order √V/sub i//M, where V/sub i/ is the ionization potential and M is the ion mass. The calculated oscillation frequencies and propagation velocities for the perturbations agree satisfactorily with experimental data. The wave structure is analyzed, and the nature of the instability is determined. Perturbations with an elevated plasma density move in the electric drift direction and correspond to an ionization wave

Electron/electron acoustic instability

International Nuclear Information System (INIS)

Gary, S.P.

1987-01-01

The electron acoustic wave becomes a normal mode of an unmagnetized collisionless plasma in the presence of two electron components with similar densities, but strongly disparate temperatures. The characteristic frequency of this mode is the plasma frequency of the cooler electron component. If these two electron components have a relative drift speed several times the thermal speed of the cooler component, the electron/electron acoustic instability may arise. This paper describes the parametric dependences of the threshold drift speed and maximum growth rate of this instability, and compares these with the same properties of the electron/ion acoustic instability. Under the condition of zero current, the electron/ion acoustic instability typically has the lower threshold drift speed, so that observation of the electron/electron acoustic instability is a strong indication of the presence of an electrical current in the plasma

Universal model of bias-stress-induced instability in inkjet-printed carbon nanotube networks field-effect transistors

Science.gov (United States)

Jung, Haesun; Choi, Sungju; Jang, Jun Tae; Yoon, Jinsu; Lee, Juhee; Lee, Yongwoo; Rhee, Jihyun; Ahn, Geumho; Yu, Hye Ri; Kim, Dong Myong; Choi, Sung-Jin; Kim, Dae Hwan

2018-02-01

We propose a universal model for bias-stress (BS)-induced instability in the inkjet-printed carbon nanotube (CNT) networks used in field-effect transistors (FETs). By combining two experimental methods, i.e., a comparison between air and vacuum BS tests and interface trap extraction, BS instability is explained regardless of either the BS polarity or ambient condition, using a single platform constituted by four key factors: OH- adsorption/desorption followed by a change in carrier concentration, electron concentration in CNT channel corroborated with H2O/O2 molecules in ambient, charge trapping/detrapping, and interface trap generation. Under negative BS (NBS), the negative threshold voltage shift (ΔVT) is dominated by OH- desorption, which is followed by hole trapping in the interface and/or gate insulator. Under positive BS (PBS), the positive ΔVT is dominated by OH- adsorption, which is followed by electron trapping in the interface and/or gate insulator. This instability is compensated by interface trap extraction; PBS instability is slightly more complicated than NBS instability. Furthermore, our model is verified using device simulation, which gives insights on how much each mechanism contributes to BS instability. Our result is potentially useful for the design of highly stable CNT-based flexible circuits in the Internet of Things wearable healthcare era.

Streaming gravity mode instability

International Nuclear Information System (INIS)

Wang Shui.

1989-05-01

In this paper, we study the stability of a current sheet with a sheared flow in a gravitational field which is perpendicular to the magnetic field and plasma flow. This mixing mode caused by a combined role of the sheared flow and gravity is named the streaming gravity mode instability. The conditions of this mode instability are discussed for an ideal four-layer model in the incompressible limit. (author). 5 refs

Knockdown of αII spectrin in normal human cells by siRNA leads to chromosomal instability and decreased DNA interstrand cross-link repair

OpenAIRE

McMahon, Laura W.; Zhang, Pan; Sridharan, Deepa M.; Lefferts, Joel A.; Lambert, Muriel W.

2009-01-01

Nonerythroid α-spectrin (αIISp) is a structural protein involved in repair of DNA interstrand cross-links and is deficient in cells from patients with Fanconi anemia (FA), which are defective in ability to repair cross-links. In order to further demonstrate the importance of the role that αIISp plays in normal human cells and in the repair defect in FA, αIISp was knocked down in normal cells using siRNA. Depletion of αIISp in normal cells by siRNA resulted in chromosomal instability and cellu...

A nonlinear scenario for development of vortex layer instability in gravity field

International Nuclear Information System (INIS)

Goncharov, V. P.

2007-01-01

A Hamiltonian version of contour dynamics is formulated for models of constant-vorticity plane flows with interfaces. The proposed approach is used as a framework for a nonlinear scenario for instability development. Localized vortex blobs are analyzed as structural elements of a strongly perturbed wall layer of a vorticity-carrying fluid with free boundary in gravity field. Gravity and vorticity effects on the geometry and velocity of vortex structures are examined. It is shown that compactly supported nonlinear solutions (compactons) are candidates for the role of particle-like vortex structures in models of flow breakdown. An analysis of the instability mechanism demonstrates the possibility of a self-similar collapse. It is found that the vortex shape stabilizes at the final stage of the collapse, while the vortex sheet strength on its boundary increases as (t 0 - t) -1 , where t 0 is the collapse time

Generation of mesoscale F layer structure and electric fields by the combined Perkins and Es layer instabilities, in simulations

Directory of Open Access Journals (Sweden)

R. B. Cosgrove

2007-07-01

Full Text Available The generic equilibrium configuration of the nighttime midlatitude ionosphere consists of an F layer held up against gravity by winds and/or electric fields, and a sporadic E (Es layer located by a sheared wind field, which experiences the same electric fields as the F layer. This configuration is subject to two large-scale (e.g. >10 km "layer instabilities": one of the F layer known as the Perkins instability, and another of the Es layer which has been called the Es layer instability. Electric fields on scales larger than (about 10 km map very efficiently between the Es and F layers, and the two instabilities have a similar geometry, allowing them to interact with one another. As shown through a linear growth rate analysis, the two most important parameters governing the interaction are the relative horizontal velocity between the Es and F layers, and the integrated conductivity ratio ΣH/ΣPF, where ΣH and ΣPF are the field line integrated Hall conductivity of the Es layer, and the field line integrated Pedersen conductivity of the F layer, respectively. For both large and small relative velocities the growth rate was found to be more than double that of the Perkins instability alone, when ΣHΣPF=1.8. However, the characteristic eigenmode varies considerably with relative velocity, and different nonlinear behavior is expected in these two cases. As a follow up to the linear growth rate analysis, we explore in this article the nonlinear evolution of the unstable coupled system subject to a 200 km wavelength initial perturbation of the F layer, using a two-dimensional numerical solution of the two-fluid equations, as a function of relative horizontal velocity and ΣHΣPF. We find that when ΣHΣPF⪝0.5 the Perkins instability is able to control the dynamics and modulate the F layer altitude in 2 to 3 h time. However, the electric fields remain small until the altitude modulation is extremely large, and even then they are not large enough to

Normal equivariant forms of vector fields

International Nuclear Information System (INIS)

Sanchez Bringas, F.

1992-07-01

We prove a theorem of linearization of type Siegel and a theorem of normal forms of type Poincare-Dulac for germs of holomorphic vector fields in the origin of C 2 , Γ -equivariants, where Γ is a finite subgroup of GL (2,C). (author). 5 refs

MHD instabilities in astrophysical plasmas: very different from MHD instabilities in tokamaks!

Science.gov (United States)

Goedbloed, J. P.

2018-01-01

The extensive studies of MHD instabilities in thermonuclear magnetic confinement experiments, in particular of the tokamak as the most promising candidate for a future energy producing machine, have led to an ‘intuitive’ description based on the energy principle that is very misleading for most astrophysical plasmas. The ‘intuitive’ picture almost directly singles out the dominant stabilizing field line bending energy of the Alfvén waves and, consequently, concentrates on expansion schemes that minimize that contribution. This happens when the wave vector {{k}}0 of the perturbations, on average, is perpendicular to the magnetic field {B}. Hence, all macroscopic instabilities of tokamaks (kinks, interchanges, ballooning modes, ELMs, neoclassical tearing modes, etc) are characterized by satisfying the condition {{k}}0 \\perp {B}, or nearly so. In contrast, some of the major macroscopic instabilities of astrophysical plasmas (the Parker instability and the magneto-rotational instability) occur when precisely the opposite condition is satisfied: {{k}}0 \\parallel {B}. How do those instabilities escape from the dominance of the stabilizing Alfvén wave? The answer to that question involves, foremost, the recognition that MHD spectral theory of waves and instabilities of laboratory plasmas could be developed to such great depth since those plasmas are assumed to be in static equilibrium. This assumption is invalid for astrophysical plasmas where rotational and gravitational accelerations produce equilibria that are at best stationary, and the associated spectral theory is widely, and incorrectly, believed to be non-self adjoint. These complications are addressed, and cured, in the theory of the Spectral Web, recently developed by the author. Using this method, an extensive survey of instabilities of astrophysical plasmas demonstrates how the Alfvén wave is pushed into insignificance under these conditions to give rise to a host of instabilities that do not

Super-Gaussian transport theory and the field-generating thermal instability in laser–plasmas

International Nuclear Information System (INIS)

Bissell, J J; Ridgers, C P; Kingham, R J

2013-01-01

Inverse bremsstrahlung (IB) heating is known to distort the electron distribution function in laser–plasmas from a Gaussian towards a super-Gaussian, thereby modifying the equations of classical transport theory (Ridgers et al 2008 Phys. Plasmas 15 092311). Here we explore these modified equations, demonstrating that super-Gaussian effects both suppress traditional transport processes, while simultaneously introducing new effects, such as isothermal (anomalous Nernst) magnetic field advection up gradients in the electron number density n e , which we associate with a novel heat-flow q n ∝∇n e . Suppression of classical phenomena is shown to be most pronounced in the limit of low Hall-parameter χ, in which case the Nernst effect is reduced by a factor of five, the ∇T e × ∇n e field generation mechanism by ∼30% (where T e is the electron temperature), and the diffusive and Righi–Leduc heat-flows by ∼80 and ∼90% respectively. The new isothermal field advection phenomenon and associated density-gradient driven heat-flux q n are checked against kinetic simulation using the Vlasov–Fokker–Planck code impact, and interpreted in relation to the underlying super-Gaussian distribution through simplified kinetic analysis. Given such strong inhibition of transport at low χ, we consider the impact of IB on the seeding and evolution of magnetic fields (in otherwise un-magnetized conditions) by examining the well-known field-generating thermal instability in the light of super-Gaussian transport theory (Tidman and Shanny 1974 Phys. Fluids 12 1207). Estimates based on conditions in an inertial confinement fusion (ICF) hohlraum suggest that super-Gaussian effects can reduce the growth-rate of the instability by ≳80%. This result may be important for ICF experiments, since by increasing the strength of IB heating it would appear possible to inhibit the spontaneous generation of large magnetic fields. (paper)

Super-Gaussian transport theory and the field-generating thermal instability in laser-plasmas

Science.gov (United States)

Bissell, J. J.; Ridgers, C. P.; Kingham, R. J.

2013-02-01

Inverse bremsstrahlung (IB) heating is known to distort the electron distribution function in laser-plasmas from a Gaussian towards a super-Gaussian, thereby modifying the equations of classical transport theory (Ridgers et al 2008 Phys. Plasmas 15 092311). Here we explore these modified equations, demonstrating that super-Gaussian effects both suppress traditional transport processes, while simultaneously introducing new effects, such as isothermal (anomalous Nernst) magnetic field advection up gradients in the electron number density ne, which we associate with a novel heat-flow qn∝∇ne. Suppression of classical phenomena is shown to be most pronounced in the limit of low Hall-parameter χ, in which case the Nernst effect is reduced by a factor of five, the ∇Te × ∇ne field generation mechanism by ˜30% (where Te is the electron temperature), and the diffusive and Righi-Leduc heat-flows by ˜80 and ˜90% respectively. The new isothermal field advection phenomenon and associated density-gradient driven heat-flux qn are checked against kinetic simulation using the Vlasov-Fokker-Planck code impact, and interpreted in relation to the underlying super-Gaussian distribution through simplified kinetic analysis. Given such strong inhibition of transport at low χ, we consider the impact of IB on the seeding and evolution of magnetic fields (in otherwise un-magnetized conditions) by examining the well-known field-generating thermal instability in the light of super-Gaussian transport theory (Tidman and Shanny 1974 Phys. Fluids 12 1207). Estimates based on conditions in an inertial confinement fusion (ICF) hohlraum suggest that super-Gaussian effects can reduce the growth-rate of the instability by ≳80%. This result may be important for ICF experiments, since by increasing the strength of IB heating it would appear possible to inhibit the spontaneous generation of large magnetic fields.

Analysis of rainfall-induced slope instability using a field of local factor of safety

Science.gov (United States)

Lu, Ning; Şener-Kaya, Başak; Wayllace, Alexandra; Godt, Jonathan W.

2012-01-01

Slope-stability analyses are mostly conducted by identifying or assuming a potential failure surface and assessing the factor of safety (FS) of that surface. This approach of assigning a single FS to a potentially unstable slope provides little insight on where the failure initiates or the ultimate geometry and location of a landslide rupture surface. We describe a method to quantify a scalar field of FS based on the concept of the Coulomb stress and the shift in the state of stress toward failure that results from rainfall infiltration. The FS at each point within a hillslope is called the local factor of safety (LFS) and is defined as the ratio of the Coulomb stress at the current state of stress to the Coulomb stress of the potential failure state under the Mohr-Coulomb criterion. Comparative assessment with limit-equilibrium and hybrid finite element limit-equilibrium methods show that the proposed LFS is consistent with these approaches and yields additional insight into the geometry and location of the potential failure surface and how instability may initiate and evolve with changes in pore water conditions. Quantitative assessments applying the new LFS field method to slopes under infiltration conditions demonstrate that the LFS has the potential to overcome several major limitations in the classical FS methodologies such as the shape of the failure surface and the inherent underestimation of slope instability. Comparison with infinite-slope methods, including a recent extension to variably saturated conditions, shows further enhancement in assessing shallow landslide occurrence using the LFS methodology. Although we use only a linear elastic solution for the state of stress with no post-failure analysis that require more sophisticated elastoplastic or other theories, the LFS provides a new means to quantify the potential instability zones in hillslopes under variably saturated conditions using stress-field based methods.

Low-field Instabilities in Nb$_{3}$Sn Multifilamentary Wires the Possible Role of Unreacted Nb

CERN Document Server

Devred, A; Celentano, G; Fabbricatore, P; Ferdeghini, C; Greco, M; Gambardella, U

2007-01-01

We report an experimental study aiming to demonstrate the not negligible role of unreacted Nb on the magnetic instabilities in superconducting Nb$_{3}$Sn multifilamentary wires, observable through partial flux jumps at magnetic field values below 0.5 T. The analysed wires were recently developed for use as dipoles required in future high-energy proton accelerators and are based on powder-in-tube technology. We studied both unreacted (only involving Nb filaments) and reacted wires, finding flux jump instabilities in both cases when performing magnetic measurements. The results can be interpreted on the basis of the critical state model and are coherent with the intrinsic stability criterion.

A simplified numerical analysis of helical instabilities of arcs in axial magnetic field

International Nuclear Information System (INIS)

Gong Ye; Lu Wenyan; Liu Jinyuan; Zheng Shu; Gong Jiquan

2002-01-01

The energy equations were simplified by the correct electrostatic ordering under electrostatic approximation. The effects of the external axial magnetic field, the current profiles and arc currents on the helical instabilities of arcs were studied by using numerical method. In the presence of the external magnetic field, numerical results show that when the current profile of an arc column is the uniform distribution, the short wavelength perturbation can be stabilized by positive direction magnetic field, whereas the long wavelength perturbation can be stabilized by reverse magnetic field. When the current profile of an arc column has a parabolic distribution, in the short wavelength perturbation case, the effect of positive direction magnetic field on the arc stability is very small. However, its stabilizing effect is enhanced for the long wavelength perturbation. The intermediate and long wavelength perturbations can also be stabilized by reverse magnetic field

Resistive wall instabilities and tearing mode dynamics in the EXTRAP T2R thin shell reversed-field pinch

Science.gov (United States)

Malmberg, J.-A.; Brunsell, P. R.

2002-01-01

Observations of resistive wall instabilities and tearing mode dynamics in the EXTRAP T2R thin shell (τw=6 ms) reversed field pinch are described. A nonresonant mode (m=1,n=-10) with the same handedness as the internal field grows nearly exponentially with an average growth time of about 2.6 ms (less than 1/2 of the shell time) consistent with linear stability theory. The externally nonresonant unstable modes (m=1,n>0), predicted by linear stability theory, are observed to have only low amplitudes (in the normal low-Θ operation mode of the device). The radial field of the dominant internally resonant tearing modes (m=1,n=-15 to n=-12) remain low due to spontaneous fast mode rotation, corresponding to angular phase velocities up to 280 krad/s. Phase aligned mode structures are observed to rotate toroidally with an average angular velocity of 40 krad/s, in the opposite direction of the plasma current. Toward the end of the discharge, the radial field of the internally resonant modes grows as the modes slow down and become wall-locked, in agreement with nonlinear computations. Fast rotation of the internally resonant modes has been observed only recently and is attributed to a change of the front-end system (vacuum vessel, shell, and TF coil) of the device.

Genomic instability and radiation

Energy Technology Data Exchange (ETDEWEB)

Little, John B [Harvard School of Public Health, Boston, MA 02115 (United States)

2003-06-01

Genomic instability is a hallmark of cancer cells, and is thought to be involved in the process of carcinogenesis. Indeed, a number of rare genetic disorders associated with a predisposition to cancer are characterised by genomic instability occurring in somatic cells. Of particular interest is the observation that transmissible instability can be induced in somatic cells from normal individuals by exposure to ionising radiation, leading to a persistent enhancement in the rate at which mutations and chromosomal aberrations arise in the progeny of the irradiated cells after many generations of replication. If such induced instability is involved in radiation carcinogenesis, it would imply that the initial carcinogenic event may not be a rare mutation occurring in a specific gene or set of genes. Rather, radiation may induce a process of instability in many cells in a population, enhancing the rate at which the multiple gene mutations necessary for the development of cancer may arise in a given cell lineage. Furthermore, radiation could act at any stage in the development of cancer by facilitating the accumulation of the remaining genetic events required to produce a fully malignant tumour. The experimental evidence for such induced instability is reviewed. (review)

Genomic instability and radiation

International Nuclear Information System (INIS)

Little, John B

2003-01-01

Genomic instability is a hallmark of cancer cells, and is thought to be involved in the process of carcinogenesis. Indeed, a number of rare genetic disorders associated with a predisposition to cancer are characterised by genomic instability occurring in somatic cells. Of particular interest is the observation that transmissible instability can be induced in somatic cells from normal individuals by exposure to ionising radiation, leading to a persistent enhancement in the rate at which mutations and chromosomal aberrations arise in the progeny of the irradiated cells after many generations of replication. If such induced instability is involved in radiation carcinogenesis, it would imply that the initial carcinogenic event may not be a rare mutation occurring in a specific gene or set of genes. Rather, radiation may induce a process of instability in many cells in a population, enhancing the rate at which the multiple gene mutations necessary for the development of cancer may arise in a given cell lineage. Furthermore, radiation could act at any stage in the development of cancer by facilitating the accumulation of the remaining genetic events required to produce a fully malignant tumour. The experimental evidence for such induced instability is reviewed. (review)

The effect of spin induced magnetization on Jeans instability of viscous and resistive quantum plasma

International Nuclear Information System (INIS)

Sharma, Prerana; Chhajlani, R. K.

2014-01-01

The effect of spin induced magnetization and electrical resistivity incorporating the viscosity of the medium is examined on the Jeans instability of quantum magnetoplasma. Formulation of the system is done by using the quantum magnetohydrodynamic model. The analysis of the problem is carried out by normal mode analysis theory. The general dispersion relation is derived from set of perturbed equations to analyse the growth rate and condition of self-gravitational Jeans instability. To discuss the influence of resistivity, magnetization, and viscosity parameters on Jeans instability, the general dispersion relation is reduced for both transverse and longitudinal mode of propagations. In the case of transverse propagation, the gravitating mode is found to be affected by the viscosity, magnetization, resistivity, and magnetic field strength whereas Jeans criterion of instability is modified by the magnetization and quantum parameter. In the longitudinal mode of propagation, the gravitating mode is found to be modified due to the viscosity and quantum correction in which the Jeans condition of instability is influenced only by quantum parameter. The other non-gravitating Alfven mode in this direction is affected by finite electrical resistivity, spin induced magnetization, and viscosity. The numerical study for the growth rate of Jeans instability is carried out for both in the transverse and longitudinal direction of propagation to the magnetic field. The effect of various parameters on the growth rate of Jeans instability in quantum plasma is analysed

Kelvin-Helmholtz instability in solar spicules

Directory of Open Access Journals (Sweden)

H Ebadi

2016-12-01

Full Text Available Magneto hydrodynamic waves, propagating along spicules, may become unstable and the expected instability is of Kelvin-Helmholtz type. Such instability can trigger the onset of wave turbulence leading to an effective plasma heating and particle acceleration. In present study, two-dimensional magneto hydrodynamic simulations performed on a Cartesian grid is presented in spicules with different densities, moving at various speeds depending on their environment. Simulations being applied in this study show the onset of Kelvin-Helmholtz type instability and transition to turbulent flow in spicules. Development of Kelvin-Helmholtz instability leads to momentum and energy transport, dissipation, and mixing of fluids. When magnetic fields are involved, field amplification is also possible to take place

Gravitational instability of thermally anisotropic plasma

International Nuclear Information System (INIS)

Singh, B.; Kalra, G.L.

1986-01-01

The equations of Chew, Goldberger, and Low (1956) modified to include the heat flux vector and self-gravitation are used to study the gravitational instability of unbounded plasma placed in a uniform static magnetic field. The linear stability analysis shows that some of the additional terms which arise as a result of higher moments are of the same order of magnitude as the terms in the original Chew, Goldberger, and Low theory. The influence of these terms on the gravitational instability has been specially examined. It is found that the gravitational instability sets in at a comparatively shorter wavelength and the growth rate is enhanced owing to the inclusion of these terms in the case where the propagation vector is along the magnetic field. The condition for instability is, however, unaltered when the direction of propagation is transverse to the direction of magnetic field. 19 references

Plasma wave instability and amplification of terahertz radiation in field-effect-transistor arrays

International Nuclear Information System (INIS)

Popov, V V; Tsymbalov, G M; Shur, M S

2008-01-01

We show that the strong amplification of terahertz radiation takes place in an array of field-effect transistors at small DC drain currents due to hydrodynamic plasmon instability of the collective plasmon mode. Planar designs compatible with standard integrated circuit fabrication processes and strong coupling of terahertz radiation to plasmon modes in FET arrays make such arrays very attractive for potential applications in solid-state terahertz amplifiers and emitters

Normal-Mode Splitting in a Weakly Coupled Optomechanical System

Science.gov (United States)

Rossi, Massimiliano; Kralj, Nenad; Zippilli, Stefano; Natali, Riccardo; Borrielli, Antonio; Pandraud, Gregory; Serra, Enrico; Di Giuseppe, Giovanni; Vitali, David

2018-02-01

Normal-mode splitting is the most evident signature of strong coupling between two interacting subsystems. It occurs when two subsystems exchange energy between themselves faster than they dissipate it to the environment. Here we experimentally show that a weakly coupled optomechanical system at room temperature can manifest normal-mode splitting when the pump field fluctuations are antisquashed by a phase-sensitive feedback loop operating close to its instability threshold. Under these conditions the optical cavity exhibits an effectively reduced decay rate, so that the system is effectively promoted to the strong coupling regime.

Normal velocity freeze-out of the Richtmyer-Meshkov instability when a rarefaction is reflected

Science.gov (United States)

Wouchuk, J. G.; Sano, T.

2015-02-01

The Richtmyer-Meshkov instability (RMI) develops when a shock front hits a rippled contact surface separating two different fluids. After the incident shock refraction, a transmitted shock is always formed and another shock or a rarefaction is reflected back. The pressure-entropy-vorticity fields generated by the rippled wave fronts are responsible for the generation of hydrodynamic perturbations in both fluids. In linear theory, the contact surface ripple reaches an asymptotic normal velocity which is dependent on the incident shock Mach number, fluids density ratio, and compressibilities. It was speculated in the past about the possibility of getting a zero value for the asymptotic normal velocity, a phenomenon that was called "freeze-out" [G. Fraley, Phys. Fluids 29, 376 (1986), 10.1063/1.865722; K. Mikaelian, Phys. Fluids 6, 356 (1994), 10.1063/1.868091, A. L. Velikovich et al., Phys. Plasmas 8, 592 (2001), 10.1063/1.1335829]. In a previous paper, freeze-out was studied for the case when a shock is reflected at the contact surface [J. G. Wouchuk and K. Nishihara, Phys. Rev. E 70, 026305 (2004), 10.1103/PhysRevE.70.026305]. In this work the freeze-out of the RMI is studied for the case in which a rarefaction is reflected back. Two different regimes are found: nearly equal preshock densities at the interface at any shock intensity, and very large density difference for strong shocks. The contour curves that relate shock Mach number and preshock density ratio are obtained in both regimes for fluids with equal and different compressibilities. An analysis of the temporal evolution of different cases of freeze-out is shown. It is seen that the freeze-out is the result of the interaction between the unstable interface and the rippled wave fronts. As a general and qualitative criterion to look for freeze-out situations, it is seen that a necessary condition for freeze-out is the same orientation for the tangential velocities generated at each side of the contact

Star formation through thermal instability of radiative plasma with finite electron inertia and finite Larmor radius corrections

Energy Technology Data Exchange (ETDEWEB)

Kaothekar, Sachin, E-mail: sackaothekar@gmail.com [Department of Physics, Mahakal Institute of Technology, Ujjain-456664, Madhya Pradesh (India)

2016-08-15

I have studied the effects of finite electron inertia, finite ion Larmor radius (FLR) corrections, and radiative heat-loss function on the thermal instability of an infinite homogeneous, viscous plasma incorporating the effect of thermal conductivity for star formation in interstellar medium (ISM). A general dispersion relation is derived using the normal mode analysis method with the help of relevant linearized perturbation equations of the problem. The wave propagation is discussed for longitudinal and transverse directions to the external magnetic field and the conditions of modified thermal instabilities and stabilities are discussed in different cases. We find that the thermal instability criterion is get modified into radiative instability criterion by inclusion of radiative heat-loss functions with thermal conductivity. The viscosity of medium removes the effect of FLR corrections from the condition of radiative instability. Numerical calculation shows stabilizing effect of heat-loss function, viscosity and FLR corrections, and destabilizing effect of finite electron inertia on the thermal instability. Results carried out in this paper shows that stars are formed in interstellar medium mainly due to thermal instability.

Star formation through thermal instability of radiative plasma with finite electron inertia and finite Larmor radius corrections

Directory of Open Access Journals (Sweden)

Sachin Kaothekar

2016-08-01

Full Text Available I have studied the effects of finite electron inertia, finite ion Larmor radius (FLR corrections, and radiative heat-loss function on the thermal instability of an infinite homogeneous, viscous plasma incorporating the effect of thermal conductivity for star formation in interstellar medium (ISM. A general dispersion relation is derived using the normal mode analysis method with the help of relevant linearized perturbation equations of the problem. The wave propagation is discussed for longitudinal and transverse directions to the external magnetic field and the conditions of modified thermal instabilities and stabilities are discussed in different cases. We find that the thermal instability criterion is get modified into radiative instability criterion by inclusion of radiative heat-loss functions with thermal conductivity. The viscosity of medium removes the effect of FLR corrections from the condition of radiative instability. Numerical calculation shows stabilizing effect of heat-loss function, viscosity and FLR corrections, and destabilizing effect of finite electron inertia on the thermal instability. Results carried out in this paper shows that stars are formed in interstellar medium mainly due to thermal instability.

Suppression of the Richtmyer-Meshkov Instability in the Presence of a Magnetic Field

International Nuclear Information System (INIS)

Ravi Samtaney

2003-01-01

We present numerical evidence from two dimensional simulations that the growth of the Richtmyer-Meshkov instability is suppressed in the presence of a magnetic field. A bifurcation occurs during the refraction of the incident shock on the density interface which transports baroclinically generated vorticity away from the interface to a pair of slow or intermediate magnetosonic shocks. Consequently, the density interface is devoid of vorticity and its growth and associated mixing is completely suppressed

WELLBORE INSTABILITY: CAUSES AND CONSEQUENCES

Directory of Open Access Journals (Sweden)

Borivoje Pašić

2007-12-01

Full Text Available Wellbore instability is one of the main problems that engineers meet during drilling. The causes of wellbore instability are often classified into either mechanical (for example, failure of the rock around the hole because of high stresses, low rock strength, or inappropriate drilling practice or chemical effects which arise from damaging interaction between the rock, generally shale, and the drilling fluid. Often, field instances of instability are a result of a combination of both chemical and mechanical. This problem might cause serious complication in well and in some case can lead to expensive operational problems. The increasing demand for wellbore stability analyses during the planning stage of a field arise from economic considerations and the increasing use of deviated, extended reach and horizontal wells. This paper presents causes, indicators and diagnosing of wellbore instability as well as the wellbore stresses model.

Gravitational instability in isotropic MHD plasma waves

Science.gov (United States)

Cherkos, Alemayehu Mengesha

2018-04-01

The effect of compressive viscosity, thermal conductivity and radiative heat-loss functions on the gravitational instability of infinitely extended homogeneous MHD plasma has been investigated. By taking in account these parameters we developed the six-order dispersion relation for magnetohydrodynamic (MHD) waves propagating in a homogeneous and isotropic plasma. The general dispersion relation has been developed from set of linearized basic equations and solved analytically to analyse the conditions of instability and instability of self-gravitating plasma embedded in a constant magnetic field. Our result shows that the presence of viscosity and thermal conductivity in a strong magnetic field substantially modifies the fundamental Jeans criterion of gravitational instability.

ROLE OF MAGNETIC FIELD STRENGTH AND NUMERICAL RESOLUTION IN SIMULATIONS OF THE HEAT-FLUX-DRIVEN BUOYANCY INSTABILITY

International Nuclear Information System (INIS)

Avara, Mark J.; Reynolds, Christopher S.; Bogdanović, Tamara

2013-01-01

The role played by magnetic fields in the intracluster medium (ICM) of galaxy clusters is complex. The weakly collisional nature of the ICM leads to thermal conduction that is channeled along field lines. This anisotropic heat conduction profoundly changes the instabilities of the ICM atmosphere, with convective stabilities being driven by temperature gradients of either sign. Here, we employ the Athena magnetohydrodynamic code to investigate the local non-linear behavior of the heat-flux-driven buoyancy instability (HBI) relevant in the cores of cooling-core clusters where the temperature increases with radius. We study a grid of two-dimensional simulations that span a large range of initial magnetic field strengths and numerical resolutions. For very weak initial fields, we recover the previously known result that the HBI wraps the field in the horizontal direction, thereby shutting off the heat flux. However, we find that simulations that begin with intermediate initial field strengths have a qualitatively different behavior, forming HBI-stable filaments that resist field-line wrapping and enable sustained vertical conductive heat flux at a level of 10%-25% of the Spitzer value. While astrophysical conclusions regarding the role of conduction in cooling cores require detailed global models, our local study proves that systems dominated by the HBI do not necessarily quench the conductive heat flux

Adolescent patellar instability: current concepts review.

Science.gov (United States)

Clark, D; Metcalfe, A; Wogan, C; Mandalia, V; Eldridge, J

2017-02-01

Patellar instability most frequently presents during adolescence. Congenital and infantile dislocation of the patella is a distinct entity from adolescent instability and measurable abnormalities may be present at birth. In the normal patellofemoral joint an increase in quadriceps angle and patellar height are matched by an increase in trochlear depth as the joint matures. Adolescent instability may herald a lifelong condition leading to chronic disability and arthritis. Restoring normal anatomy by trochleoplasty, tibial tubercle transfer or medial patellofemoral ligament (MPFL) reconstruction in the young adult prevents further instability. Although these techniques are proven in the young adult, they may cause growth arrest and deformity where the physis is open. A vigorous non-operative strategy may permit delay of surgery until growth is complete. Where non-operative treatment has failed a modified MPFL reconstruction may be performed to maintain stability until physeal closure permits anatomical reconstruction. If significant growth remains an extraosseous reconstruction of the MPFL may impart the lowest risk to the physis. If minor growth remains image intensifier guided placement of femoral intraosseous fixation may impart a small, but acceptable, risk to the physis. This paper presents and discusses the literature relating to adolescent instability and provides a framework for management of these patients. Cite this article: Bone Joint J 2017;99-B:159-70. ©2017 The British Editorial Society of Bone & Joint Surgery.

Hydrodynamic instability of compressible fluid in porous medium

International Nuclear Information System (INIS)

Argal, Shraddha; Tiwari, Anita; Sharma, P K; Prajapati, R P

2014-01-01

The hydrodynamic Rayleigh -Taylor instability of two superposed compressible fluids in porous medium has been studied. The dispersion relation is derived for such a medium by using normal mode analysis. The RT instability is discussed for various simplified configuration. The effect of porosity and dynamic viscosity has been analyzed and it is observed that porosity and dynamic viscosity have stabilizing effect on the Rayleigh- Taylor instability of compressible fluids.

Dynamical instabilities in magnetohydrodynamic wind-cloud interactions

Science.gov (United States)

Banda-Barragan, Wladimir Eduardo; Parkin, Elliot Ross; Crocker, Roland M.; Federrath, Christoph; Bicknell, Geoffrey Vincent

2015-08-01

We report the results from a comprehensive numerical study that investigates the role of dynamical instabilities in magnetohydrodynamic interactions between winds and spherical clouds in the interstellar medium. The growth of Kelvin-Helmholtz (KH) and Rayleigh-Taylor (RT) instabilities at interfaces between wind and cloud material is responsible for the disruption of clouds and the formation of filamentary tails. We show how different strengths and orientations of the initial magnetic field affect the development of unstable modes and the ultimate morphology of these filaments. In the weak field limit, for example, KH instabilities developing at the flanks of clouds are dominant, whilst they are suppressed when stronger fields are considered. On the other hand, perturbations that originate RT instabilities at the leading edge of clouds are enhanced when fields are locally stronger. The orientation of the field lines also plays an important role in the structure of filaments. Magnetic ropes are key features of systems in which fields are aligned with the wind velocity, whilst current sheets are favoured when the initial field is preferentially transverse to the wind velocity. We compare our findings with analytical predictions obtained from the linear theory of hydromagnetic stability and provide a classification of filamentary tails based on their morphology.

FAST MAGNETIC RECONNECTION IN THE SOLAR CHROMOSPHERE MEDIATED BY THE PLASMOID INSTABILITY

International Nuclear Information System (INIS)

Ni, Lei; Kliem, Bernhard; Lin, Jun; Wu, Ning

2015-01-01

Magnetic reconnection in the partially ionized solar chromosphere is studied in 2.5 dimensional magnetohydrodynamic simulations including radiative cooling and ambipolar diffusion. A Harris current sheet with and without a guide field is considered. Characteristic values of the parameters in the middle chromosphere imply a high magnetic Reynolds number of ∼10 6 -10 7 in the present simulations. Fast magnetic reconnection then develops as a consequence of the plasmoid instability without the need to invoke anomalous resistivity enhancements. Multiple levels of the instability are followed as it cascades to smaller scales, which approach the ion inertial length. The reconnection rate, normalized to the asymptotic values of magnetic field and Alfvén velocity in the inflow region, reaches values in the range ∼0.01-0.03 throughout the cascading plasmoid formation and for zero as well as for strong guide field. The outflow velocity reaches ≈40 km s –1 . Slow-mode shocks extend from the X-points, heating the plasmoids up to ∼8 × 10 4 K. In the case of zero guide field, the inclusion of both ambipolar diffusion and radiative cooling causes a rapid thinning of the current sheet (down to ∼30 m) and early formation of secondary islands. Both of these processes have very little effect on the plasmoid instability for a strong guide field. The reconnection rates, temperature enhancements, and upward outflow velocities from the vertical current sheet correspond well to their characteristic values in chromospheric jets

FAST MAGNETIC RECONNECTION IN THE SOLAR CHROMOSPHERE MEDIATED BY THE PLASMOID INSTABILITY

Energy Technology Data Exchange (ETDEWEB)

Ni, Lei; Kliem, Bernhard; Lin, Jun [Yunnan Observatories, Chinese Academy of Sciences, Kunming 650011 (China); Wu, Ning, E-mail: leini@ynao.ac.cn [School of Tourism and Geography, Yunnan Normal University, Kunming 650031 (China)

2015-01-20

Magnetic reconnection in the partially ionized solar chromosphere is studied in 2.5 dimensional magnetohydrodynamic simulations including radiative cooling and ambipolar diffusion. A Harris current sheet with and without a guide field is considered. Characteristic values of the parameters in the middle chromosphere imply a high magnetic Reynolds number of ∼10{sup 6}-10{sup 7} in the present simulations. Fast magnetic reconnection then develops as a consequence of the plasmoid instability without the need to invoke anomalous resistivity enhancements. Multiple levels of the instability are followed as it cascades to smaller scales, which approach the ion inertial length. The reconnection rate, normalized to the asymptotic values of magnetic field and Alfvén velocity in the inflow region, reaches values in the range ∼0.01-0.03 throughout the cascading plasmoid formation and for zero as well as for strong guide field. The outflow velocity reaches ≈40 km s{sup –1}. Slow-mode shocks extend from the X-points, heating the plasmoids up to ∼8 × 10{sup 4} K. In the case of zero guide field, the inclusion of both ambipolar diffusion and radiative cooling causes a rapid thinning of the current sheet (down to ∼30 m) and early formation of secondary islands. Both of these processes have very little effect on the plasmoid instability for a strong guide field. The reconnection rates, temperature enhancements, and upward outflow velocities from the vertical current sheet correspond well to their characteristic values in chromospheric jets.

Modulational instability for an induced field in the far-wake region of a space vehicle

International Nuclear Information System (INIS)

Liao Jingjing; Deng Qian; Qu Wen

2012-01-01

The behavior of the induced field and the generation of density cavitons in the far-wake region (|k 0 | → 0) of a space vehicle can be described by a set of nonlinear coupling equations. Modulational instability of the induced field is investigated on the basis of the nonlinear equations. The results show that the induced field is modulationally unstable and will collapse into spatial localized structures; meanwhile, density cavitons will be generated. The characteristic scale and the maximum growth rate of the induced field depend not only on the angle between the amplitude of pump waves E 0 and the perturbation wave vector k, but also on the energy density of pump waves |E 0 | 2 . (paper)

Structure of magnetic field disturbances under development of disruptive instability in the ''Tokamak-6''

International Nuclear Information System (INIS)

Merezhkin, V.G.

1978-01-01

The structure and dynamics of disturbances of a poloidal field during the development of the breakaway instability in the Tokamak-6 are investigated. The behaviour of the symmetric and dipole field component, and the peculiarities of the structure of screw disturbances in a minor and major breakaways are analyzed. It was established that the structure of screw disturbances in minor breakaways is unchangeable and that the rearrangement in major breakaways is of a discrete nature. The relationship between the symmetric and screw components of disturbances of the poloidal field at the forward front of the disturbance increase was revealed. Data on the increments, scales and structure of screw disturbances, the ratios between the symmetric and screw components of field disturbances, and also on the magnitude of energy losses in typical breakaways are given

Spatiotemporal character of the Bobylev-Pikin flexoelectric instability in a twisted nematic bent-core liquid crystal exposed to very low frequency fields.

Science.gov (United States)

Krishnamurthy, K S

2014-05-01

The Bobylev-Pikin striped-pattern state induced by a homogeneous electric field is a volume flexoelectric instability, originating in the midregion of a planarly aligned nematic liquid crystal layer. We find that the instability acquires a spatiotemporal character upon excitation by a low frequency (0.5 Hz) square wave field. This is demonstrated using a bent-core liquid crystal, initially in the 90°-twisted planar configuration. The flexoelectric modulation appears close to the cathode at each polarity reversal and, at low voltage amplitudes, decays completely as the field becomes steady. Correspondingly, at successive polarity changes, the stripe direction switches between the alignment directions at the two substrates. For large voltages, the stripes formed nearly along the alignment direction at the cathode gradually reorient toward the midplane director. These observations are generally attributed to inhomogeneous and time-dependent field conditions that come to exist after each polarity reversal. Polarity dependence of the instability is attributed to the formation of intrinsic double layers that bring about an asymmetry in surface fields. Momentary field elevation near the cathode following a voltage sign reversal and concomitant gradient flexoelectric polarization are considered the key factors in accounting for the surfacelike modulation observed at low voltages.

Amplification due to two-stream instability of self-electric and magnetic fields of an ion beam propagating in background plasma

Science.gov (United States)

Tokluoglu, Erinc K.; Kaganovich, Igor D.; Carlsson, Johan A.; Hara, Kentaro; Startsev, Edward A.

2018-05-01

Propagation of charged particle beams in background plasma as a method of space charge neutralization has been shown to achieve a high degree of charge and current neutralization and therefore enables nearly ballistic propagation and focusing of charged particle beams. Correspondingly, the use of plasmas for propagation of charged particle beams has important applications for transport and focusing of intense particle beams in inertial fusion and high energy density laboratory plasma physics. However, the streaming of beam ions through a background plasma can lead to the development of two-stream instability between the beam ions and the plasma electrons. The beam electric and magnetic fields enhanced by the two-stream instability can lead to defocusing of the ion beam. Using particle-in-cell simulations, we study the scaling of the instability-driven self-electromagnetic fields and consequent defocusing forces with the background plasma density and beam ion mass. We identify plasma parameters where the defocusing forces can be reduced.

Instabilities in mimetic matter perturbations

Energy Technology Data Exchange (ETDEWEB)

Firouzjahi, Hassan; Gorji, Mohammad Ali [School of Astronomy, Institute for Research in Fundamental Sciences (IPM), P.O. Box 19395-5531, Tehran (Iran, Islamic Republic of); Mansoori, Seyed Ali Hosseini, E-mail: firouz@ipm.ir, E-mail: gorji@ipm.ir, E-mail: shosseini@shahroodut.ac.ir, E-mail: shossein@ipm.ir [Physics Department, Shahrood University of Technology, P.O. Box 3619995161 Shahrood (Iran, Islamic Republic of)

2017-07-01

We study cosmological perturbations in mimetic matter scenario with a general higher derivative function. We calculate the quadratic action and show that both the kinetic term and the gradient term have the wrong sings. We perform the analysis in both comoving and Newtonian gauges and confirm that the Hamiltonians and the associated instabilities are consistent with each other in both gauges. The existence of instabilities is independent of the specific form of higher derivative function which generates gradients for mimetic field perturbations. It is verified that the ghost instability in mimetic perturbations is not associated with the higher derivative instabilities such as the Ostrogradsky ghost.

Effect of hall currents on thermal instability of dusty couple stress fluid

Directory of Open Access Journals (Sweden)

Aggarwal Amrish Kumar

2016-09-01

Full Text Available In this paper, effect of Hall currents on the thermal instability of couple-stress fluid permeated with dust particles has been considered. Following the linearized stability theory and normal mode analysis, the dispersion relation is obtained. For the case of stationary convection, dust particles and Hall currents are found to have destabilizing effect while couple stresses have stabilizing effect on the system. Magnetic field induced by Hall currents has stabilizing/destabilizing effect under certain conditions. It is found that due to the presence of Hall currents (hence magnetic field, oscillatory modes are produced which were non-existent in their absence.

Stability and instability of hydromagnetic Taylor-Couette flows

Science.gov (United States)

Rüdiger, Günther; Gellert, Marcus; Hollerbach, Rainer; Schultz, Manfred; Stefani, Frank

2018-04-01

Decades ago S. Lundquist, S. Chandrasekhar, P. H. Roberts and R. J. Tayler first posed questions about the stability of Taylor-Couette flows of conducting material under the influence of large-scale magnetic fields. These and many new questions can now be answered numerically where the nonlinear simulations even provide the instability-induced values of several transport coefficients. The cylindrical containers are axially unbounded and penetrated by magnetic background fields with axial and/or azimuthal components. The influence of the magnetic Prandtl number Pm on the onset of the instabilities is shown to be substantial. The potential flow subject to axial fields becomes unstable against axisymmetric perturbations for a certain supercritical value of the averaged Reynolds number Rm bar =√{ Re ṡ Rm } (with Re the Reynolds number of rotation, Rm its magnetic Reynolds number). Rotation profiles as flat as the quasi-Keplerian rotation law scale similarly but only for Pm ≫ 1 while for Pm ≪ 1 the instability instead sets in for supercritical Rm at an optimal value of the magnetic field. Among the considered instabilities of azimuthal fields, those of the Chandrasekhar-type, where the background field and the background flow have identical radial profiles, are particularly interesting. They are unstable against nonaxisymmetric perturbations if at least one of the diffusivities is non-zero. For Pm ≪ 1 the onset of the instability scales with Re while it scales with Rm bar for Pm ≫ 1. Even superrotation can be destabilized by azimuthal and current-free magnetic fields; this recently discovered nonaxisymmetric instability is of a double-diffusive character, thus excluding Pm = 1. It scales with Re for Pm → 0 and with Rm for Pm → ∞. The presented results allow the construction of several new experiments with liquid metals as the conducting fluid. Some of them are described here and their results will be discussed together with relevant diversifications of

On the instability of wave-fields with JONSWAP spectra to inhomogeneous disturbances, and the consequent long-time evolution

Science.gov (United States)

Ribal, A.; Stiassnie, M.; Babanin, A.; Young, I.

2012-04-01

The instability of two-dimensional wave-fields and its subsequent evolution in time are studied by means of the Alber equation for narrow-banded random surface-waves in deep water subject to inhomogeneous disturbances. A linear partial differential equation (PDE) is obtained after applying an inhomogeneous disturbance to the Alber's equation and based on the solution of this PDE, the instability of the ocean wave surface is studied for a JONSWAP spectrum, which is a realistic ocean spectrum with variable directional spreading and steepness. The steepness of the JONSWAP spectrum depends on γ and α which are the peak-enhancement factor and energy scale of the spectrum respectively and it is found that instability depends on the directional spreading, α and γ. Specifically, if the instability stops due to the directional spreading, increase of the steepness by increasing α or γ can reactivate it. This result is in qualitative agreement with the recent large-scale experiment and new theoretical results. In the instability area of α-γ plane, a long-time evolution has been simulated by integrating Alber's equation numerically and recurrent evolution is obtained which is the stochastic counterpart of the Fermi-Pasta-Ulam recurrence obtained for the cubic Schrödinger equation.

Instabilities constraint and relativistic mean field parametrization

International Nuclear Information System (INIS)

Sulaksono, A.; Kasmudin; Buervenich, T.J.; Reinhard, P.-G.; Maruhn, J.A.

2011-01-01

Two parameter sets (Set 1 and Set 2) of the standard relativistic mean field (RMF) model plus additional vector isoscalar nonlinear term, which are constrained by a set of criteria 20 determined by symmetric nuclear matter stabilities at high densities due to longitudinal and transversal particle–hole excitation modes are investigated. In the latter parameter set, δ meson and isoscalar as well as isovector tensor contributions are included. The effects in selected finite nuclei and nuclear matter properties predicted by both parameter sets are systematically studied and compared with the ones predicted by well-known RMF parameter sets. The vector isoscalar nonlinear term addition and instability constraints have reasonably good effects in the high-density properties of the isoscalar sector of nuclear matter and certain finite nuclei properties. However, even though the δ meson and isovector tensor are included, the incompatibility with the constraints from some experimental data in certain nuclear properties at saturation point and the excessive stiffness of the isovector nuclear matter equation of state at high densities as well as the incorrect isotonic trend in binding the energies of finite nuclei are still encountered. It is shown that the problem may be remedied if we introduce additional nonlinear terms not only in the isovector but also in the isoscalar vectors. (author)

Plasma physics and instabilities

International Nuclear Information System (INIS)

Lashmore-Davies, C.N.

1981-01-01

These lectures procide an introduction to the theory of plasmas and their instabilities. Starting from the Bogoliubov, Born, Green, Kirkwood, and Yvon (BBGKY) hierarchy of kinetic equations, the additional concept of self-consistent fields leads to the fundamental Vlasov equation and hence to the warm two-fluid model and the one-fluid MHD, or cold, model. The properties of small-amplitude waves in magnetized (and unmagnetized) plasmas, and the instabilities to which they give rise, are described in some detail, and a complete chapter is devoted to Landau damping. The linear theory of plasma instabilities is illustrated by the current-driven electrostatic kind, with descriptions of the Penrose criterion and the energy principle of ideal MHD. There is a brief account of the application of feedback control. The non-linear theory is represented by three examples: quasi-linear velocity-space instabilities, three-wave instabilities, and the stability of an arbitrarily largeamplitude wave in a plasma. (orig.)

Dynamical Instability and Soliton Concept

International Nuclear Information System (INIS)

Kartavenko, V.G.

1994-01-01

The problem of dynamical instability and clustering (stable fragments formation) in a breakup of excited nuclear systems are considered from the points of view of the soliton concept. It is noted that the volume (spinodal) instability can be associated with nonlinear terms, and the surface (Rayleigh-Taylor type) instability, with the dispersion terms in the evolution equations. The spinodal instability and the Rayleigh-Taylor instability may compensate each other and lead to stable quasi-soliton type objects. The simple analytical model is presented to illustrate this physical picture. The time evolution of an initially compressed cold nuclear system is analysed in the framework of the inverse mean-field method. It is demonstrated that the nonlinearity and dispersion terms of the evolution equations can lead to clusterization in the final channel. 8 p

Influence of a magnetic field on the Taylor instability in magnetic fluids

International Nuclear Information System (INIS)

Vislovich, A.N.

1986-01-01

The influence of a magnetic field on the stability of Couette flow between rotating cylinders is investigated in the narrow gap approximation. The governing mechanism of the instability is the classical Taylor mechanism. It was shown that rotation of the outer cylinder in the same direction as the inner does not result in a qualitative change in the structure of the theshold perturbations. When the cylinders rotate in different directions in an ordinary fluid, the Taylor vortices develop in the domain of the gap between the inner cylinder and the fluid layer for which v 0 = 0

Metamorphosis of helical magnetorotational instability in the presence of axial electric current.

Science.gov (United States)

Priede, Jānis

2015-03-01

This paper presents numerical linear stability analysis of a cylindrical Taylor-Couette flow of liquid metal carrying axial electric current in a generally helical external magnetic field. Axially symmetric disturbances are considered in the inductionless approximation corresponding to zero magnetic Prandtl number. Axial symmetry allows us to reveal an entirely new electromagnetic instability. First, we show that the electric current passing through the liquid can extend the range of helical magnetorotational instability (HMRI) indefinitely by transforming it into a purely electromagnetic instability. Two different electromagnetic instability mechanisms are identified. The first is an internal pinch-type instability, which is due to the interaction of the electric current with its own magnetic field. Axisymmetric mode of this instability requires a free-space component of the azimuthal magnetic field. When the azimuthal component of the magnetic field is purely rotational and the axial component is nonzero, a new kind of electromagnetic instability emerges. The latter, driven by the interaction of electric current with a weak collinear magnetic field in a quiescent fluid, gives rise to a steady meridional circulation coupled with azimuthal rotation.

A general approach to optomechanical parametric instabilities

International Nuclear Information System (INIS)

Evans, M.; Barsotti, L.; Fritschel, P.

2010-01-01

We present a simple feedback description of parametric instabilities which can be applied to a variety of optical systems. Parametric instabilities are of particular interest to the field of gravitational-wave interferometry where high mechanical quality factors and a large amount of stored optical power have the potential for instability. In our use of Advanced LIGO as an example application, we find that parametric instabilities, if left unaddressed, present a potential threat to the stability of high-power operation.

An experimental investigation of flow instability between two heated parallel channels with supercritical water

Energy Technology Data Exchange (ETDEWEB)

Xi, Xi; Xiao, Zejun, E-mail: fabulous_2012@sina.com; Yan, Xiao; Li, Yongliang; Huang, Yanping

2014-10-15

Highlights: • Flow instability experiment between two heated channels with supercritical water is carried out. • Two kinds of out of phase flow instability are found and instability boundaries under different working conditions are obtained. • Dynamics characteristics of flow instability are analyzed. - Abstract: Super critical water reactor (SCWR) is the generation IV nuclear reactor in the world. Under normal operation, water enters SCWR from cold leg with a temperature of 280 °C and then leaves the core with a temperature of 500 °C. Due to the sharp change of temperature, there is a huge density change in the core, which could result in potential flow instability and the safety of reactor would be threatened consequently. So it is necessary to carry out relevant investigation in this field. An experimental investigation which concerns with out of phase flow instability between two heated parallel channels with supercritical water has been carried out in this paper. Due to two INCONEL 625 pipes with a thickness of 6.5 mm are adopted, more experimental results are attained. To find out the influence of axial power shape on the onset of flow instability, each heated channel is divided into two sections and the heating power of each section can be controlled separately. Finally the instability boundaries are obtained under different inlet temperatures, axial power shapes, total inlet mass flow rates and system pressures. The dynamics characteristics of out of phase oscillation are also analyzed.

Self-Induced Faraday Instability Laser

Science.gov (United States)

Perego, A. M.; Smirnov, S. V.; Staliunas, K.; Churkin, D. V.; Wabnitz, S.

2018-05-01

We predict the onset of self-induced parametric or Faraday instabilities in a laser, spontaneously caused by the presence of pump depletion, which leads to a periodic gain landscape for light propagating in the cavity. As a result of the instability, continuous wave oscillation becomes unstable even in the normal dispersion regime of the cavity, and a periodic train of pulses with ultrahigh repetition rate is generated. Application to the case of Raman fiber lasers is described, in good quantitative agreement between our conceptual analysis and numerical modeling.

Measurements of the momentum and current transport from tearing instability in the Madison Symmetric Torus reversed-field pinch

International Nuclear Information System (INIS)

Kuritsyn, A.; Fiksel, G.; Almagri, A. F.; Miller, M. C.; Mirnov, V. V.; Prager, S. C.; Sarff, J. S.; Brower, D. L.; Ding, W. X.

2009-01-01

In this paper measurements of momentum and current transport caused by current driven tearing instability are reported. The measurements are done in the Madison Symmetric Torus reversed-field pinch [R. N. Dexter, D. W. Kerst, T. W. Lovell, S. C. Prager, and J. C. Sprott, Fusion Technol. 19, 131 (1991)] in a regime with repetitive bursts of tearing instability causing magnetic field reconnection. It is established that the plasma parallel momentum profile flattens during these reconnection events: The flow decreases in the core and increases at the edge. The momentum relaxation phenomenon is similar in nature to the well established relaxation of the parallel electrical current and could be a general feature of self-organized systems. The measured fluctuation-induced Maxwell and Reynolds stresses, which govern the dynamics of plasma flow, are large and almost balance each other such that their difference is approximately equal to the rate of change of plasma momentum. The Hall dynamo, which is directly related to the Maxwell stress, drives the parallel current profile relaxation at resonant surfaces at the reconnection events. These results qualitatively agree with analytical calculations and numerical simulations. It is plausible that current-driven instabilities can be responsible for momentum transport in other laboratory and astrophysical plasmas.

Spin peierls instability against S-like anisotropic superconductivity in framework of the mean field RVB-Hubbard model

International Nuclear Information System (INIS)

Wrobel, P.; Jacak, L.

1988-01-01

It is shown theoretically that the superconducting transition in the framework of RVB mean field treatment in nearly half-filled band Hubbard model is substantially influenced by spin density wave instability. The reasonable SDW and SC ordering phase diagram for doped La 2 CuO 4 compounds is found

Magnetization, Low Field Instability and Quench of RHQT Nb(3)Al Strands

Energy Technology Data Exchange (ETDEWEB)

Yamada, R.; Wake, M.; Kikuchi, A.; Velev, V.; /Fermilab

2009-01-01

Since 2005, we made and tested three RHQT Nb{sub 3}Al strands, one with Nb matrix and two with Ta matrix, which are fully stabilized with Cu electroplating. We observed anomalously large magnetization curves extending beyond 1 to 1.5 Tesla with the F1 Nb matrix strand at 4.2 K, when we measured its magnetization with a balanced coil magnetometer. This problem was eliminated with the Ta matrix strands operating at 4.2 K. But with these strands a similar but smaller anomalous magnetization was observed at 1.9 K. We studied these phenomena with FEM. With the F1 Nb matrix strand, it is explained that at low external field, inter-filamentary coupling currents in the outer layers of sub-elements create a shielding effect. It reduces the inside field, keeps the inside Nb matrix superconductive, and stands against a higher outside field beyond the Hc of Nb. At an even higher external field, the superconductivity of the whole Nb matrix collapses and releases a large amount of energy, which may cause a big quench. Depending on the size of the energy in the strand or the cable, a magnet could quench, causing the low field instability. Some attempt to analyze the anomaly with FEM is presented.

Reflex muscle contraction in anterior shoulder instability.

Science.gov (United States)

Wallace, D A; Beard, D J; Gill, R H; Eng, B; Carr, A J

1997-01-01

Reduced proprioception may contribute to recurrent anterior shoulder instability. Twelve patients with unilateral shoulder instability were investigated for evidence of deficient proprioception with an activated pneumatic cylinder and surface electromyography electrodes; the contralateral normal shoulder was used as a control. The latency between onset of movement and the detection of muscle contraction was used as an index of proprioception. No significant difference in muscle contraction latency was detected between the stable and unstable shoulders, suggesting that there was no significant defect in muscular reflex activity. This study does not support the use proprioception-enhancing physiotherapy in the treatment of posttraumatic anterior shoulder instability.

Electromagnetic theory of the radiative Pierce instability

International Nuclear Information System (INIS)

Klochkov, D.N.; Rukhadze, A.A.

1997-01-01

A study is made of the radiative Pierce instability of a relativistic electron beam propagating in a waveguide in the presence of an infinitely strong magnetic field. The perturbation theory is used to find the growth rates and conditions of instability over a broad range of the beam current. It is shown that, under the Pierce boundary conditions, the instability is Raman in nature, and there is no current threshold for the instability. This allows the instability saturation level to be accurately determined from the condition for the violation of the Cherenkov resonance and the radiation efficiency to be estimated

Mirror Instability in the Turbulent Solar Wind

Energy Technology Data Exchange (ETDEWEB)

Hellinger, Petr [Astronomical Institute, CAS, Bocni II/1401,CZ-14100 Prague (Czech Republic); Landi, Simone; Verdini, Andrea; Franci, Luca [Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze Largo E. Fermi 2, I-50125 Firenze (Italy); Matteini, Lorenzo, E-mail: petr.hellinger@asu.cas.cz [Department of Physics, Imperial College London, London SW7 2AZ (United Kingdom)

2017-04-01

The relationship between a decaying strong turbulence and the mirror instability in a slowly expanding plasma is investigated using two-dimensional hybrid expanding box simulations. We impose an initial ambient magnetic field perpendicular to the simulation box, and we start with a spectrum of large-scale, linearly polarized, random-phase Alfvénic fluctuations that have energy equipartition between kinetic and magnetic fluctuations and a vanishing correlation between the two fields. A turbulent cascade rapidly develops, magnetic field fluctuations exhibit a Kolmogorov-like power-law spectrum at large scales and a steeper spectrum at sub-ion scales. The imposed expansion (taking a strictly transverse ambient magnetic field) leads to the generation of an important perpendicular proton temperature anisotropy that eventually drives the mirror instability. This instability generates large-amplitude, nonpropagating, compressible, pressure-balanced magnetic structures in a form of magnetic enhancements/humps that reduce the perpendicular temperature anisotropy.

Spectrum of ballooning instabilities in a stellarator

Energy Technology Data Exchange (ETDEWEB)

Cooper, W A [Ecole Polytechnique Federale, Lausanne (Switzerland). Centre de Recherche en Physique des Plasma (CRPP); Singleton, D B [Australian National Univ., ANU Supercomputing Facility, Canberra (Australia); Dewar, R L [Australian National Univ., Canberra, ACT (Australia). Research School of Physical Sciences

1995-08-01

The recent revival of interest in the application of the `ballooning formalism` to low-frequency plasma instabilities has prompted a comparison of the Wentzel-Brillouin-Kramers (WKB) ballooning approximation with an (in principle) exact normal mode calculation for a three-dimensional plasma equilibrium. Semiclassical quantization, using the ideal magnetohydrodynamic (MHD) ballooning eigenvalue to provide a local dispersion relation, is applied to a ten-field period stellarator test case. Excellent qualitative agreement, and good quantitative agreement is found with predictions from the TERPSICHORE code for toroidal mode numbers from 1 to 14 and radial mode numbers from 0 to 2. The continuum bands predicted from three-dimensional WKB theory are too narrow to resolve. (author) 3 figs., 24 refs.

Spectrum of ballooning instabilities in a stellarator

International Nuclear Information System (INIS)

Cooper, W.A.; Singleton, D.B.; Dewar, R.L.

1995-08-01

The recent revival of interest in the application of the 'ballooning formalism' to low-frequency plasma instabilities has prompted a comparison of the Wentzel-Brillouin-Kramers (WKB) ballooning approximation with an (in principle) exact normal mode calculation for a three-dimensional plasma equilibrium. Semiclassical quantization, using the ideal magnetohydrodynamic (MHD) ballooning eigenvalue to provide a local dispersion relation, is applied to a ten-field period stellarator test case. Excellent qualitative agreement, and good quantitative agreement is found with predictions from the TERPSICHORE code for toroidal mode numbers from 1 to 14 and radial mode numbers from 0 to 2. The continuum bands predicted from three-dimensional WKB theory are too narrow to resolve. (author) 3 figs., 24 refs

Effect of Surface Tension Anisotropy and Welding Parameters on Initial Instability Dynamics During Solidification: A Phase-Field Study

Science.gov (United States)

Yu, Fengyi; Wei, Yanhong

2018-05-01

The effects of surface tension anisotropy and welding parameters on initial instability dynamics during gas tungsten arc welding of an Al-alloy are investigated by a quantitative phase-field model. The results show that the surface tension anisotropy and welding parameters affect the initial instability dynamics in different ways during welding. The surface tension anisotropy does not influence the solute diffusion process but does affect the stability of the solid/liquid interface during solidification. The welding parameters affect the initial instability dynamics by varying the growth rate and thermal gradient. The incubation time decreases, and the initial wavelength remains stable as the welding speed increases. When welding power increases, the incubation time increases and the initial wavelength slightly increases. Experiments were performed for the same set of welding parameters used in modeling, and the results of the experiments and simulations were in good agreement.

Role of parametric decay instabilities in generating ionospheric irregularities

International Nuclear Information System (INIS)

Kuo, S.P.; Cheo, B.R.; Lee, M.C.

1983-01-01

We show that purely growing instabilities driven by the saturation spectrum of parametric decay instabilities can produce a broad spectrum of ionospheric irregularities. The threshold field Vertical BarE/sub th/Vertical Bar of the instabilities decreases with the scale lengths lambda of the ionospheric irregularities as Vertical BarE/sub th/Vertical Barproportionallambda -2 in the small-scale range ( -2 with scale lengths larger than a few kilometers. The excitation of kilometer-scale irregularities is strictly restricted by the instabilities themselves and by the spatial inhomogeneity of the medium. These results are drawn from the analyses of four-wave interaction. Ion-neutral collisions impose no net effect on the instabilities when the excited ionospheric irregularities have a field-aligned nature

Instability of the Shukla mode in a dusty plasma containing equilibrium density and magnetic field inhomogeneities

International Nuclear Information System (INIS)

Shukla, P.K.; Bharuthram, R.; Schlickeiser, R.

2004-01-01

It is shown that the dispersive Shukla mode [P.K. Shukla, Phys. Lett. A 316, 238 (2003)] can become unstable in the presence of equilibrium density and magnetic field inhomogeneities in a dusty plasma. A new dispersion relation for our nonuniform dusty magnetoplasma is derived and analyzed to show the modification of the Shukla mode frequency and its amplification due to combined action of the plasma density and magnetic field gradients. The present instability may account for the origin of low-frequency electromagnetic turbulence in molecular clouds and in cometary plasmas

Relativistic Buneman instability in the laser breakout afterburner

International Nuclear Information System (INIS)

Albright, B. J.; Yin, L.; Bowers, Kevin J.; Hegelich, B. M.; Flippo, K. A.; Kwan, T. J. T.; Fernandez, J. C.

2007-01-01

A new laser-driven ion acceleration mechanism has been identified in particle-in-cell simulations of high-contrast-ratio ultraintense lasers with very thin (10 s of nm) solid targets [Yin et al., Laser and Particle Beams 24, 291 (2006); Yin et al., Phys. Plasmas 13, 072701 (2007)]. After a brief period of target normal sheath acceleration (TNSA), 'enhanced' TNSA follows. In this stage, the laser rapidly heats all the electrons in the target as the target thickness becomes comparable to the skin depth and enhanced acceleration of the ions results. Then, concomitant with the laser penetrating the target, a large accelerating longitudinal electric field is generated that co-moves with the ions. This last phase has been termed the laser 'breakout afterburner' (BOA). Earlier work suggested that the BOA was associated with the Buneman instability that efficiently converts energy from the drift of the electrons into the ions. In this Brief Communication, this conjecture is found to be consistent with particle-in-cell simulation data and the analytic dispersion relation for the relativistic Buneman instability

Numerical studies of the Kelvin-Hemholtz instability in a coronal jet

Science.gov (United States)

Zhao, Tian-Le; Ni, Lei; Lin, Jun; Ziegler, Udo

2018-04-01

Kelvin-Hemholtz (K-H) instability in a coronal EUV jet is studied via 2.5D MHD numerical simulations. The jet results from magnetic reconnection due to the interaction of the newly emerging magnetic field and the pre-existing magnetic field in the corona. Our results show that the Alfvén Mach number along the jet is about 5–14 just before the instability occurs, and it is even higher than 14 at some local areas. During the K-H instability process, several vortex-like plasma blobs with high temperature and high density appear along the jet, and magnetic fields have also been rolled up and the magnetic configuration including anti-parallel magnetic fields forms, which leads to magnetic reconnection at many X-points and current sheet fragments inside the vortex-like blob. After magnetic islands appear inside the main current sheet, the total kinetic energy of the reconnection outflows decreases, and cannot support the formation of the vortex-like blob along the jet any longer, then the K-H instability eventually disappears. We also present the results about how the guide field and flux emerging speed affect the K-H instability. We find that a strong guide field inhibits shock formation in the reconnecting upward outflow regions but helps secondary magnetic islands appear earlier in the main current sheet, and then apparently suppresses the K-H instability. As the speed of the emerging magnetic field decreases, the K-H instability appears later, the highest temperature inside the vortex blob gets lower and the vortex structure gets smaller.

Effects of stochastic field lines on the pressure driven MHD instabilities in the Large Helical Device

Science.gov (United States)

Ohdachi, Satoshi; Watanabe, Kiyomasa; Sakakibara, Satoru; Suzuki, Yasuhiro; Tsuchiya, Hayato; Ming, Tingfeng; Du, Xiaodi; LHD Expriment Group Team

2014-10-01

In the Large Helical Device (LHD), the plasma is surrounded by the so-called magnetic stochastic region, where the Kolmogorov length of the magnetic field lines is very short, from several tens of meters and to thousands meters. Finite pressure gradient are formed in this region and MHD instabilities localized in this region is observed since the edge region of the LHD is always unstable against the pressure driven mode. Therefore, the saturation level of the instabilities is the key issue in order to evaluate the risk of this kind of MHD instabilities. The saturation level depends on the pressure gradient and on the magnetic Reynolds number; there results are similar to the MHD mode in the closed magnetic surface region. The saturation level in the stochastic region is affected also by the stocasticity itself. Parameter dependence of the saturation level of the MHD activities in the region is discussed in detail. It is supported by NIFS budget code ULPP021, 028 and is also partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research 26249144, by the JSPS-NRF-NSFC A3 Foresight Program NSFC: No. 11261140328.

Absolute and convective instabilities of a film flow down a vertical fiber subjected to a radial electric field

Science.gov (United States)

Liu, Rong; Chen, Xue; Ding, Zijing

2018-01-01

We consider the motion of a gravity-driven flow down a vertical fiber subjected to a radial electric field. This flow exhibits rich dynamics including the formation of droplets, or beads, driven by a Rayleigh-Plateau mechanism modified by the presence of gravity as well as the Maxwell stress at the interface. A spatiotemporal stability analysis is performed to investigate the effect of electric field on the absolute-convective instability (AI-CI) characteristics. We performed a numerical simulation on the nonlinear evolution of the film to examine the transition from CI to AI regime. The numerical results are in excellent agreement with the spatiotemporal stability analysis. The blowup behavior of nonlinear simulation predicts the formation of touchdown singularity of the interface due to the effect of electric field. We try to connect the blowup behavior with the AI-CI characteristics. It is found that the singularities mainly occur in the AI regime. The results indicate that the film may have a tendency to form very sharp tips due to the enhancement of the absolute instability induced by the electric field. We perform a theoretical analysis to study the behaviors of the singularities. The results show that there exists a self-similarity between the temporal and spatial distances from the singularities.

A recursive field-normalized bibliometric performance indicator: an application to the field of library and information science.

Science.gov (United States)

Waltman, Ludo; Yan, Erjia; van Eck, Nees Jan

2011-10-01

Two commonly used ideas in the development of citation-based research performance indicators are the idea of normalizing citation counts based on a field classification scheme and the idea of recursive citation weighing (like in PageRank-inspired indicators). We combine these two ideas in a single indicator, referred to as the recursive mean normalized citation score indicator, and we study the validity of this indicator. Our empirical analysis shows that the proposed indicator is highly sensitive to the field classification scheme that is used. The indicator also has a strong tendency to reinforce biases caused by the classification scheme. Based on these observations, we advise against the use of indicators in which the idea of normalization based on a field classification scheme and the idea of recursive citation weighing are combined.

Electromagnetic theory of the radiative Pierce instability

International Nuclear Information System (INIS)

Klochkov, D.N.; Rukhadze, A.A.

1997-01-01

The radiative Pierce instability of a relativistic electron beam in a waveguide stabilized by an infinite strong magnetic field is considered. the increment and conditions for instability development in a wide interval of the beam currents are determined on the basis of the perturbation theory. It is shown that the instability has always the Raman character and is threshold less in current for the Pierce boundary conditions. It permits sufficiently strictly to define the instability saturation level from breaking the resonance condition and to estimate the radiation efficiency

White-light parametric instabilities in plasmas.

Science.gov (United States)

Santos, J E; Silva, L O; Bingham, R

2007-06-08

Parametric instabilities driven by partially coherent radiation in plasmas are described by a generalized statistical Wigner-Moyal set of equations, formally equivalent to the full wave equation, coupled to the plasma fluid equations. A generalized dispersion relation for stimulated Raman scattering driven by a partially coherent pump field is derived, revealing a growth rate dependence, with the coherence width sigma of the radiation field, scaling with 1/sigma for backscattering (three-wave process), and with 1/sigma1/2 for direct forward scattering (four-wave process). Our results demonstrate the possibility to control the growth rates of these instabilities by properly using broadband pump radiation fields.

Mode-locking via dissipative Faraday instability.

Science.gov (United States)

Tarasov, Nikita; Perego, Auro M; Churkin, Dmitry V; Staliunas, Kestutis; Turitsyn, Sergei K

2016-08-09

Emergence of coherent structures and patterns at the nonlinear stage of modulation instability of a uniform state is an inherent feature of many biological, physical and engineering systems. There are several well-studied classical modulation instabilities, such as Benjamin-Feir, Turing and Faraday instability, which play a critical role in the self-organization of energy and matter in non-equilibrium physical, chemical and biological systems. Here we experimentally demonstrate the dissipative Faraday instability induced by spatially periodic zig-zag modulation of a dissipative parameter of the system-spectrally dependent losses-achieving generation of temporal patterns and high-harmonic mode-locking in a fibre laser. We demonstrate features of this instability that distinguish it from both the Benjamin-Feir and the purely dispersive Faraday instability. Our results open the possibilities for new designs of mode-locked lasers and can be extended to other fields of physics and engineering.

Beta-limiting MHD Instabilities in Improved-performance NSTX Spherical Torus Plasmas

International Nuclear Information System (INIS)

J.E. Menard; M.G. Bell; R.E. Bell; E.D. Fredrickson D.A. Gates: S.M. Kaye; B.P. LeBlanc; R. Maingi; D. Mueller; S.A. Sabbagh; D. Stutman; C.E. Bush; D.W. Johnson; R. Kaita; H.W. Kugel; R.J. Maqueda; F. Paoletti; S.F Paul; M. Ono; Y.-K.M. Peng; C.H. Skinner; E.J. Synakowski; the NSTX Research Team

2003-01-01

Global magnetohydrodynamic stability limits in the National Spherical Torus Experiment (NSTX) have increased significantly recently due to a combination of device and operational improvements. First, more routine H-mode operation with broadened pressure profiles allows access to higher normalized beta and lower internal inductance. Second, the correction of a poloidal field coil induced error-field has largely eliminated locked tearing modes during normal operation and increased the maximum achievable beta. As a result of these improvements, peak beta values have reached (not simultaneously) β t = 35%, β N = 6.4, N > = 4.5, β N /l i = 10, and β P = 1.4. High β P operation with reduced tearing activity has allowed a doubling of discharge pulse-length to just over 1 second with sustained periods of β N ∼ 6 above the ideal no-wall limit and near the with-wall limit. Details of the β limit scalings and β-limiting instabilities in various operating regimes are described

Mixed-Mode Oscillations in Complex-Plasma Instabilities

International Nuclear Information System (INIS)

Mikikian, Maxime; Cavarroc, Marjorie; Coueedel, Lenaiec; Tessier, Yves; Boufendi, Laiefa

2008-01-01

Instabilities in dusty plasmas are frequent phenomena. We show that some instabilities can be described by mixed-mode oscillations often encountered in chemical systems or neuronal dynamics and studied through dynamical system theories. The time evolution of these instabilities is studied through the change in the associated waveform. Frequency and interspike interval are analyzed and compared to results obtained in other scientific fields concerned by mixed-mode oscillations

Physical understanding of the instability spectrum and the feedback control of resistive wall modes in reversed field pinch

International Nuclear Information System (INIS)

Wang, Z.R.; Guo, S.C.

2011-01-01

The cylindrical MHD model integrated with a feedback system is applied to the study of resistive wall mode (RWM) in reversed field pinch (RFP) plasmas. The model takes into account the compressibility, longitudinal flow, viscosity and resistive wall with a finite thickness. The study, via both analytical and numerical analyses, provides a physical understanding on the following subjects: firstly, on the nature of the instability spectrum of the RWM observed in RFP plasmas; specifically, the growth rates of the two groups of the RWMs (internally non-resonant and externally non-resonant) have opposite dependence on the variation of the field reversal. Secondly, on the response of the unstable plasmas to the feedback control in RFPs, the mode behaviour in plasmas under the feedback is clarified and discussed in detail. Finally, the linear solutions of time evolution of RWM instability in various feedback scenarios are given. The effects of the wall proximity, the sensor location and the system response time are discussed, respectively.

Ballooning-mirror instability and internally driven Pc 4--5 wave events

International Nuclear Information System (INIS)

Cheng, C.Z.; Qian, Q.; Takahashi, K.; Lui, A.T.Y.

1994-03-01

A kinetic-MHD field-aligned eigenmode stability analysis of low frequency ballooning-mirror instabilities has been performed for anisotropic pressure plasma sin the magnetosphere. The ballooning mode is mainly a transverse wave driven unstable by pressure gradient in the bad curvature region. The mirror mode with a dominant compressional magnetic field perturbation is excited when the product of plasma beta and pressure anisotropy (P perpendicular /P parallel > 1) is large. From the AMPTE/CCE particle and magnetic field data observed during Pc 4--5 wave events the authors compute the ballooning-mirror instability parameters and perform a correlation study with the theoretical instability threshold. They find that compressional Pc 5 waves approximately satisfy the ballooning-mirror instability condition, and transverse Pc 4--5 waves are probably related to resonant ballooning instabilities with small pressure anisotropy

Combined tangential-normal vector elements for computing electric and magnetic fields

International Nuclear Information System (INIS)

Sachdev, S.; Cendes, Z.J.

1993-01-01

A direct method for computing electric and magnetic fields in two dimensions is developed. This method determines both the fields and fluxes directly from Maxwell's curl and divergence equations without introducing potential functions. This allows both the curl and the divergence of the field to be set independently in all elements. The technique is based on a new type of vector finite element that simultaneously interpolates to the tangential component of the electric or the magnetic field and the normal component of the electric or magnetic flux. Continuity conditions are imposed across element edges simply by setting like variables to be the same across element edges. This guarantees the continuity of the field and flux at the mid-point of each edge and that for all edges the average value of the tangential component of the field and of the normal component of the flux is identical

Linear instability and nonlinear motion of rotating plasma

International Nuclear Information System (INIS)

Liu, J.

1985-01-01

Two coupled nonlinear equations describing the flute dynamics of the magnetically confined low-β collisionless rotating plasma are derived. The linear instability and nonlinear dynamics of the rotating column are analyzed theoretically. In the linear stability analysis, a new sufficient condition of stability is obtained. From the exact solution of eigenvalue equation for Gaussian density profile and uniform rotation of the plasma, the stability of the system strongly depends on the direction of plasma rotation, FLR effect and the location of the conducting wall. An analytic expression showing the finite wall effect on different normal modes is obtained and it explains the different behavior of (1,0) normal mode from other modes. The sheared rotation driven instability is investigated by using three model equilibrium profiles, and the analytic expressions of eigenvalues which includes the wall effect are obtained. The analogy between shear rotation driven instability and the instability driven by sheared plane parallel flow in the inviscid fluid is analyzed. Applying the linear analysis to the central cell of tandem mirror system, the trapped particle instability with only passing electronics is analyzed. For uniform rotation and Gaussian density profile, an analytic expression that determines the stability boundary is found. The nonlinear analysis shows that the nonlinear equations have a solitary vortex solution which is very similar to the vortex solution of nonlinear Rossby wave equation

Foldover, quasi-periodicity, spin-wave instabilities in ultra-thin films subject to RF fields

Energy Technology Data Exchange (ETDEWEB)

D' Aquino, M. [Department of Electrical Engineering, University of Napoli ' Federico II' , Naples I-80125 (Italy)]. E-mail: mdaquino@unina.it; Bertotti, G. [Istituto Nazionale di Ricerca Metrologica (INRIM), I-10135 Turin (Italy); Serpico, C. [Department of Electrical Engineering, University of Napoli ' Federico II' , Naples I-80125 (Italy); Mayergoyz, I.D. [ECE Department and UMIACS, University of Maryland, College Park, MD 20742 (United States); Bonin, R. [Istituto Nazionale di Ricerca Metrologica (INRIM), I-10135 Turin (Italy); Guida, G. [Department of Electrical Engineering, University of Napoli ' Federico II' , Naples I-80125 (Italy)

2007-09-15

We study magnetization dynamics in a uniaxial ultra-thin ferromagnetic disk subject to spatially uniform microwave external fields. The rotational invariance of the system is such that the only admissible spatially uniform steady states are periodic (P-modes) and quasi-periodic (Q-modes) modes. The stability of P-modes versus spatially uniform and nonuniform perturbations is studied by using spin-wave analysis and the instability diagram for all possible P-modes is computed. The predictions of the spin-wave analysis are compared with micromagnetic simulations.

Electron beam instabilities in gyrotron beam tunnels

International Nuclear Information System (INIS)

Pedrozzi, M.; Alberti, S.; Hogge, J.P.; Tran, M.Q.; Tran, T.M.

1997-10-01

Electron beam instabilities occurring in a gyrotron electron beam can induce an energy spread which might significantly deteriorate the gyrotron efficiency. Three types of instabilities are considered to explain the important discrepancy found between the theoretical and experimental efficiency in the case of quasi-optical gyrotrons (QOG): the electron cyclotron maser instability, the Bernstein instability and the Langmuir instability. The low magnetic field gradient in drift tubes of QOG makes that the electron cyclotron maser instability can develop in the drift tube at very low electron beam currents. Experimental measurements show that with a proper choice of absorbing structures in the beam tunnel, this instability can be suppressed. At high beam currents, the electrostatic Bernstein instability can induce a significant energy spread at the entrance of the interaction region. The induced energy spread scales approximately linearly with the electron beam density and for QOG one observes that the beam density is significantly higher than the beam density of an equivalent cylindrical cavity gyrotron. (author) figs., tabs., refs

BUOYANCY INSTABILITIES IN A WEAKLY COLLISIONAL INTRACLUSTER MEDIUM

Energy Technology Data Exchange (ETDEWEB)

Kunz, Matthew W.; Stone, James M. [Department of Astrophysical Sciences, Princeton University, Peyton Hall, 4 Ivy Lane, Princeton, NJ 08544 (United States); Bogdanovic, Tamara; Reynolds, Christopher S., E-mail: kunz@astro.princeton.edu, E-mail: jstone@astro.princeton.edu, E-mail: tamarab@astro.umd.edu, E-mail: chris@astro.umd.edu [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)

2012-08-01

The intracluster medium (ICM) of galaxy clusters is a weakly collisional plasma in which the transport of heat and momentum occurs primarily along magnetic-field lines. Anisotropic heat conduction allows convective instabilities to be driven by temperature gradients of either sign: the magnetothermal instability (MTI) in the outskirts of clusters and the heat-flux buoyancy-driven instability (HBI) in their cooling cores. We employ the Athena magnetohydrodynamic code to investigate the nonlinear evolution of these instabilities, self-consistently including the effects of anisotropic viscosity (i.e., Braginskii pressure anisotropy), anisotropic conduction, and radiative cooling. We find that, in all but the innermost regions of cool-core clusters, anisotropic viscosity significantly impairs the ability of the HBI to reorient magnetic-field lines orthogonal to the temperature gradient. Thus, while radio-mode feedback appears necessary in the central few Multiplication-Sign 10 kpc, heat conduction may be capable of offsetting radiative losses throughout most of a cool core over a significant fraction of the Hubble time. Magnetically aligned cold filaments are then able to form by local thermal instability. Viscous dissipation during cold filament formation produces accompanying hot filaments, which can be searched for in deep Chandra observations of cool-core clusters. In the case of MTI, anisotropic viscosity leads to a nonlinear state with a folded magnetic field structure in which field-line curvature and field strength are anti-correlated. These results demonstrate that, if the HBI and MTI are relevant for shaping the properties of the ICM, one must self-consistently include anisotropic viscosity in order to obtain even qualitatively correct results.

Field-induced magnetic instability and quantum criticality in the antiferromagnet CeCu2Ge2.

Science.gov (United States)

Liu, Yi; Xie, Donghua; Wang, Xiaoying; Zhu, Kangwei; Yang, Ruilong

2016-01-13

The magnetic quantum criticality in strongly correlated electron systems has been considered to be closely related with the occurrence of unconventional superconductivity. Control parameters such as magnetic field, pressure or chemical doping are frequently used to externally tune the quantum phase transition for a deeper understanding. Here we report the research of a field-induced quantum phase transition using conventional bulk physical property measurements in the archetypal antiferromagnet CeCu2Ge2, which becomes superconductive under a pressure of about 10 GPa with Tc ~ 0.64 K. We offer strong evidence that short-range dynamic correlations start appearing above a magnetic field of about 5 T. Our demonstrations of the magnetic instability and the field-induced quantum phase transition are crucial for the quantum criticality, which may open a new route in experimental investigations of the quantum phase transition in heavy-fermion systems.

Single bunch instabilities in an SSC

International Nuclear Information System (INIS)

Ruth, R.D.

1984-01-01

In this note coherent instability thresholds are estimated for the SSC and discuss some of the subsequent design restrictions. The various instabilities are set out in a block diagram with the essential features of each. The assumption is made that long wavelength coupled bunch effects can be cured effectively by a feedback system (both longitudinal and transverse) and that the impedance of the feedback system is such as to cancel that of the environment (at low frequency). Alternatively, the long wake field is assumed to be exactly canceled, on the average, by a feedback wake field. This leaves only single bunch effects. Thresholds for fast-blowup are discussed both in the longitudinal and transverse and the transverse mode coupling instability more familiar in electron/positron storage rings is covered. The impedances considered are a broadband impedance and the resistive wall impedance

Ionospheric modification and parametric instabilities

International Nuclear Information System (INIS)

Fejer, J.A.

1979-01-01

Thresholds and linear growth rates for stimulated Brillouin and Raman scattering and for the parametric decay instability are derived by using arguments of energy transfer. For this purpose an expression for the ponderomotive force is derived. Conditions under which the partial pressure force due to differential dissipation exceeds the ponderomotive force are also discussed. Stimulated Brillouin and Raman scattering are weakly excited by existing incoherent backscatter radars. The parametric decay instability is strongly excited in ionospheric heating experiments. Saturation theories of the parametric decay instability are therefore described. After a brief discussion of the purely growing instability the effect of using several pumps is discussed as well as the effects of inhomogenicity. Turning to detailed theories of ionospheric heating, artificial spread F is discussed in terms of a purely growing instability where the nonlinearity is due to dissipation. Field-aligned short-scale striations are explained in terms of dissipation of the parametrically excited Langmuir waves (plasma oscillations): they might be further amplified by an explosive instability (except the magnetic equator). Broadband absorption is probably responsible for the 'overshoot' effect: the initially observed level of parametrically excited Langmuir waves is much higher than the steady state level

Profile relaxation and tilt instability in a field-reversed configuration

International Nuclear Information System (INIS)

Ohtani, H.; Horiuchi, R.; Sato, T.

2003-01-01

The profile relaxation from a magnetic hydrodynamic (MHD) profile to a kinetic equilibrium in field-reversed configurations (FRCs) is investigated by two-dimensional electromagnetic particle simulation. The radial oscillation takes place in order to relax an excess energy in the MHD profile, and the system spontaneously relaxes toward a kinetic equilibrium. In this kinetic equilibrium, the hollow electron current profile is realized as a result of the combined effects of the single particle orbits and the ion finite Larmor radius, and the ion current profile becomes peaked due to the effect of the ion meandering motion. Three-dimensional full electromagnetic particle simulation is also performed to study the stability of these kinetic equilibrium against the tilt mode. The growth rate of the tilt instability is reduced by the kinetic effects. It is found that the stabilization effect of tilt mode becomes much distinct when the current density changes from the peaked profile to the hollow one. (author)

Profile relaxation and tilt instability in a field-reversed configuration

International Nuclear Information System (INIS)

Ohtani, H.; Horiuchi, R.; Sato, T.

2002-10-01

The profile relaxation from a magnetohydrodynamic (MHD) profile to a kinetic equilibrium in field-reversed configurations (FRCs) is investigated by two-dimensional electromagnetic particle simulation. The radial oscillation takes place in order to relax an excess energy in the MHD profile, and the system spontaneously relaxes toward a kinetic equilibrium. In this kinetic equilibrium, the hollow electron current profile is realized as a result of the combined effects of the single particle orbits and the ion finite Larmor radius, and the ion current profile becomes peaked due to the effect of the ion meandering motion. Three-dimensional full electromagnetic particle simulation is also performed to study the stability of these kinetic equilibrium against the tilt mode. The growth rate of the tilt instability is reduced by the kinetic effects. It is found that the stabilization effect of tilt mode becomes much distinct when the current density changes from the peaked profile to the hollow one. (author)

Profile relaxation and tilt instability in a field-reversed configuration

International Nuclear Information System (INIS)

Ohtani, H.; Horiuchi, R.; Sato, T.

2002-01-01

The profile relaxation from a magnetichydrodynamic (MHD) profile to a kinetic equilibrium in field-reversed configurations (FRCs) in investigated by two-dimensional electromagnetic particle simulation. The radial oscillation takes place in order to relax an excess energy in the MHD profile, and the system spontaneously relaxes toward a kinetic equilibrium. In this kinetic equilibrium, the hollow electron current profile is realized as a result of the combined effects of the single particle orbits and the ion finite Larmor radius, and the ion current profile becomes peaked due to the effect of the ion meandering motion. Three-dimensional full electromagnetic particle simulations is also performed to study the stability of these kinetic equilibrium against the tilt mode. The growth rate of the tilt instability is reduced by the kinetic is effects. It is found that the stabilization effect of tilt mode becomes much distinct when the current density changes from the peaked profile to the hollow one. (author)

Plasma-column instabilities in a reversed-field pinch without a shell

Energy Technology Data Exchange (ETDEWEB)

Schmid, P.G.

1988-01-01

Plasma column instabilities in a Reversed Field Pinch (RFP) without a shell were investigated in the Colorado Reversatron RFP. The Reversatron RFP (aspect ration R/a = 50 cm/8cm) is a toroidal plasma containment device consisting of a vacuum chamber, a thick conducting shell, modular shells, magnetic field producing coils and diagnostics to characterize the plasma. RFP discharges were set up in the Reversatron in three different experimental configurations: with a thick conducting shell, with a modular shell and with no shell. In two of the configurations, a shell enclosed the plasma column to provide some plasma stability. A vertical magnetic field provided equilibrium in experiments without a shell. Data from discharges without a shell indicated that the plasma duration was greatly reduced and the plasma resistance increased compared to the discharges with a thick shell. Plasma position probes indicated large plasma centriod displacements corresponding to a n = 1 and a n = 3 kink coincident with the peak of the plasma current and the start of a discharge termination phase. The modular shell lengthened the discharge duration and lowered the plasma resistance to values intermediate between the plasma with a thick shell and the plasma with no shell. The modular shell suppressed the large plasma column displacements observed in the RFP plasma without a shell.

Plasma-column instabilities in a reversed-field pinch without a shell

International Nuclear Information System (INIS)

Schmid, P.G.

1988-01-01

Plasma column instabilities in a Reversed Field Pinch (RFP) without a shell were investigated in the Colorado Reversatron RFP. The Reversatron RFP (aspect ration R/a = 50 cm/8cm) is a toroidal plasma containment device consisting of a vacuum chamber, a thick conducting shell, modular shells, magnetic field producing coils and diagnostics to characterize the plasma. RFP discharges were set up in the Reversatron in three different experimental configurations: with a thick conducting shell, with a modular shell and with no shell. In two of the configurations, a shell enclosed the plasma column to provide some plasma stability. A vertical magnetic field provided equilibrium in experiments without a shell. Data from discharges without a shell indicated that the plasma duration was greatly reduced and the plasma resistance increased compared to the discharges with a thick shell. Plasma position probes indicated large plasma centriod displacements corresponding to a n = 1 and a n = 3 kink coincident with the peak of the plasma current and the start of a discharge termination phase. The modular shell lengthened the discharge duration and lowered the plasma resistance to values intermediate between the plasma with a thick shell and the plasma with no shell. The modular shell suppressed the large plasma column displacements observed in the RFP plasma without a shell

Instabilities and nonequilibrium structures

International Nuclear Information System (INIS)

Tirapegui, E.; Villarroel, D.

1987-01-01

Physical systems can be studied both near to and far from equilibrium where instabilities appear. The behaviour in these two regions is reviewed in this book, from both the theoretical and application points of view. The influence of noise in these situations is an essential feature which cannot be ignored. It is therefore discussed using phenomenological and theoretical approaches for the numerous problems which still remain in the field. This volume should appeal to mathematicians and physicists interested in the areas of instability, bifurcation theory, dynamical systems, pattern formation, nonequilibrium structures and statistical mechanics. (Auth.)

Potential Role of Meiosis Proteins in Melanoma Chromosomal Instability

International Nuclear Information System (INIS)

Lindsey, S. F.; Byrnes, D. M.; Eller, M. S.; Rosa, A. M.; Dabas, N.; Escandon, J.; Grichnik, J. M.; Grichnik, J. M.; Grichnik, J. M.; Grichnik, J. M.

2013-01-01

Melanomas demonstrate chromosomal instability (CIN). In fact, CIN can be used to differentiate melanoma from benign nevi. The exact molecular mechanisms that drive CIN in melanoma have yet to be fully elucidated. Cancer/testis antigens are a unique group of germ cell proteins that are found to be primarily expressed in melanoma as compared to benign nevi. The abnormal expression of these germ cell proteins, normally expected only in the testis and ovaries, in somatic cells may lead to interference with normal cellular pathways. Germ cell proteins that may be particularly critical in CIN are meiosis proteins. Here, we review pathways unique to meiosis with a focus on how the aberrant expression of meiosis proteins in normal mitotic cells "meiomitosis"could impact chromosomal instability in melanoma and other cancers.

Inhomogeneity driven by Higgs instability in a gapless superconductor

International Nuclear Information System (INIS)

Giannakis, Ioannis; Hou Defu; Huang Mei; Ren Haicang

2007-01-01

The fluctuations of the Higgs and pseudo Nambu-Goldstone fields in the 2-flavor color superconductivity (2SC) phase with mismatched pairing are described in the nonlinear realization framework of the gauged Nambu-Jona-Lasinio model. In the gapless 2SC phase, not only Nambu-Goldstone currents can be spontaneously generated, but also the Higgs field exhibits instablity. The Nambu-Goldstone currents generation indicates the formation of the single plane wave Larkin-Ovchinnikov-Fulde-Ferrel state and breaks rotation symmetry, while the Higgs instability favors spatial inhomogeneity and breaks translation invariance. In this paper, we focus on the Higgs instability which has not drawn much attention yet. The Higgs instability cannot be removed without a long range force, thus it persists in the gapless superfluidity and induces phase separation. In the case of gapless 2-flavor color superconductivity state, the Higgs instability can only be partially removed by the electric Coulomb energy. However, it is not excluded that the Higgs instability might be completely removed in the charge neutral gapless color-flavor locked phase by the color Coulomb energy

Corona-induced electrohydrodynamic instabilities in low conducting liquids

Energy Technology Data Exchange (ETDEWEB)

Vega, F.; Perez, A.T. [Depto. Electronica y Electromagnetismo, Facultad de Fisica, Universidad de Sevilla, Avda. Reina Mercedes, s/n. 41012, Sevilla (Spain)

2003-06-01

The rose-window electrohydrodynamic (EHD) instability has been observed when a perpendicular field with an additional unipolar ion injection is applied onto a low conducting liquid surface. This instability has a characteristic pattern with cells five to 10 times greater than those observed in volume instabilities caused by unipolar injection. We have used corona discharge from a metallic point to perform some measurements of the rose-window instability in low conducting liquids. The results are compared to the linear theoretical criterion for an ohmic liquid. They confirmed that the minimum voltage for this instability is much lower than that for the interfacial instability in high conducting liquids. This was predicted theoretically in the dependence of the critical voltage as a function of the non-dimensional conductivity. It is shown that in a non-ohmic liquid the rose window appears as a secondary instability after the volume instability. (orig.)

Theoretical and numerical study of Rayleigh-Taylor instabilities in magnetized plasmas

International Nuclear Information System (INIS)

Andrei, A. Ivanov

2001-06-01

In this thesis we're studying both the general case of the 'classic' Rayleigh-Taylor instability (in incompressible fluids) and more specific cases of the instabilities of Rayleigh-Taylor type in magnetized plasmas, in the liners or wire array implosions etc. We have studied the influence of the Hall diffusion of magnetic field on the growth rate of the instability. We have obtained in this work a self-similar solution for the widening of the initial profile of the magnetic field and for the wave of the penetration of magnetic field. After that the subsequent evolution of the magnetic field in plasma opening switches (POS) has been examined. We have shown the possibility of the existence of a strong rarefaction wave for collisional and non-collisional cases. This wave can explain the phenomenon of the opening of POS. The effect of the suppression of Rayleigh-Taylor instability by forced oscillations of the boundary between two fluids permits us to propose some ideas for the experiments of inertial fusion. We have considered the general case of the instability, in other words - two incompressible viscous superposed fluids in a gravitational field. We have obtained an exact analytical expression for the growth rate and then we have analyzed the influence of the parameters of external 'pumping' on the instability. These results can be applied to a wide range of systems, starting from classic hydrodynamics and up to astrophysical plasmas. The scheme of wire arrays has become recently a very popular method to obtain a high power X-radiation or for a high quality implosion in Z-pinches. The experimental studies have demonstrated that the results of implosion are much better for the case of multiple thin wires situated cylindrically than in a usual liner scheme. We have examined the problem modeling the stabilization of Rayleigh-Taylor instability for a wire array system. The reason for instability suppression is the regular spatial modulation of the surface plasma

The retest distribution of the visual field summary index mean deviation is close to normal.

Science.gov (United States)

Anderson, Andrew J; Cheng, Allan C Y; Lau, Samantha; Le-Pham, Anne; Liu, Victor; Rahman, Farahnaz

2016-09-01

When modelling optimum strategies for how best to determine visual field progression in glaucoma, it is commonly assumed that the summary index mean deviation (MD) is normally distributed on repeated testing. Here we tested whether this assumption is correct. We obtained 42 reliable 24-2 Humphrey Field Analyzer SITA standard visual fields from one eye of each of five healthy young observers, with the first two fields excluded from analysis. Previous work has shown that although MD variability is higher in glaucoma, the shape of the MD distribution is similar to that found in normal visual fields. A Shapiro-Wilks test determined any deviation from normality. Kurtosis values for the distributions were also calculated. Data from each observer passed the Shapiro-Wilks normality test. Bootstrapped 95% confidence intervals for kurtosis encompassed the value for a normal distribution in four of five observers. When examined with quantile-quantile plots, distributions were close to normal and showed no consistent deviations across observers. The retest distribution of MD is not significantly different from normal in healthy observers, and so is likely also normally distributed - or nearly so - in those with glaucoma. Our results increase our confidence in the results of influential modelling studies where a normal distribution for MD was assumed. © 2016 The Authors Ophthalmic & Physiological Optics © 2016 The College of Optometrists.

Normalized Noise Power Spectrum of Full Field Digital Mammography System

International Nuclear Information System (INIS)

Isa, Norriza Mohd; Wan Hassan, Wan Muhamad Saridan

2010-01-01

A method to measure noise power spectrum of a full field digital mammography system is presented. The effect of X-ray radiation dose, size and configuration of region of interest on normalized noise power spectrum (NNPS) was investigated. Flat field images were acquired using RQA-M2 beam quality technique (Mo/Mo anode-filter, 28 kV, 2 mm Al) with different clinical radiation doses. The images were cropped at about 4 cm from the edge of the breast wall and then divided into different size of non-overlapping or overlapping segments. NNPS was determined through detrending, 2-D fast Fourier transformation and normalization. Our measurement shows that high radiation dose gave lower NNPS at a specific beam quality.

Cell Survival and DNA Damage in Normal Prostate Cells Irradiated Out-of-Field.

LENUS (Irish Health Repository)

Shields, L

2014-10-31

Interest in out-of-field radiation dose has been increasing with the introduction of new techniques, such as volumetric modulated arc therapy (VMAT). These new techniques offer superior conformity of high-dose regions to the target compared to conventional techniques, however more normal tissue is exposed to low-dose radiation with VMAT. There is a potential increase in radiobiological effectiveness associated with lower energy photons delivered during VMAT as normal cells are exposed to a temporal change in incident photon energy spectrum. During VMAT deliveries, normal cells can be exposed to the primary radiation beam, as well as to transmission and scatter radiation. The impact of low-dose radiation, radiation-induced bystander effect and change in energy spectrum on normal cells are not well understood. The current study examined cell survival and DNA damage in normal prostate cells after exposure to out-of-field radiation both with and without the transfer of bystander factors. The effect of a change in energy spectrum out-of-field compared to in-field was also investigated. Prostate cancer (LNCaP) and normal prostate (PNT1A) cells were placed in-field and out-of-field, respectively, with the PNT1A cells being located 1 cm from the field edge when in-field cells were being irradiated with 2 Gy. Clonogenic and γ-H2AX assays were performed postirradiation to examine cell survival and DNA damage. The assays were repeated when bystander factors from the LNCaP cells were transferred to the PNT1A cells and also when the PNT1A cells were irradiated in-field to a different energy spectrum. An average out-of-field dose of 10.8 ± 4.2 cGy produced a significant reduction in colony volume and increase in the number of γ-H2AX foci\\/cell in the PNT1A cells compared to the sham-irradiated control cells. An adaptive response was observed in the PNT1A cells having first received a low out-of-field dose and then the bystander factors. The PNT1A cells showed a significant

Small amplitude waves and linear firehose and mirror instabilities in rotating polytropic quantum plasma

Science.gov (United States)

Bhakta, S.; Prajapati, R. P.; Dolai, B.

2017-08-01

The small amplitude quantum magnetohydrodynamic (QMHD) waves and linear firehose and mirror instabilities in uniformly rotating dense quantum plasma have been investigated using generalized polytropic pressure laws. The QMHD model and Chew-Goldberger-Low (CGL) set of equations are used to formulate the basic equations of the problem. The general dispersion relation is derived using normal mode analysis which is discussed in parallel, transverse, and oblique wave propagations. The fast, slow, and intermediate QMHD wave modes and linear firehose and mirror instabilities are analyzed for isotropic MHD and CGL quantum fluid plasmas. The firehose instability remains unaffected while the mirror instability is modified by polytropic exponents and quantum diffraction parameter. The graphical illustrations show that quantum corrections have a stabilizing influence on the mirror instability. The presence of uniform rotation stabilizes while quantum corrections destabilize the growth rate of the system. It is also observed that the growth rate stabilizes much faster in parallel wave propagation in comparison to the transverse mode of propagation. The quantum corrections and polytropic exponents also modify the pseudo-MHD and reverse-MHD modes in dense quantum plasma. The phase speed (Friedrichs) diagrams of slow, fast, and intermediate wave modes are illustrated for isotropic MHD and double adiabatic MHD or CGL quantum plasmas, where the significant role of magnetic field and quantum diffraction parameters on the phase speed is observed.

Light-induced ion-acoustic instability of rarefied plasma

International Nuclear Information System (INIS)

Krasnov, I.V.; Sizykh, D.V.

1987-01-01

A new method of ion-acoustic instability excitation under the effect of coherent light, resonance to ion quantum transitions on collisionless plasma, is suggested. The light-induced ion-acoustic instability (LIIAI) considered is based on the induced progressive nonequilibrium resonance particles in the field of travelling electromagnetic wave. Principal possibility to use LIIAI in high-resolution spectroscopy and in applied problems of plasma physics, related to its instability, is pointed out

Fluctuations and instabilities of a holographic metal

Science.gov (United States)

Jokela, Niko; Järvinen, Matti; Lippert, Matthew

2013-02-01

We analyze the quasinormal modes of the D2-D8' model of 2+1-dimensional, strongly-coupled, charged fermions in a background magnetic field and at non-zero density. The model is known to include a quantum Hall phase with integer filling fraction. As expected, we find a hydrodynamical diffusion mode at small momentum and the nonzero-temperature holographic zero sound, which becomes massive above a critical magnetic field. We confirm the previously-known thermodynamic instability. In addition, we discover an instability at low temperature, large mass, and in a charge density and magnetic field range near the quantum Hall phase to an inhomogeneous striped phase.

Edge instabilities of topological superconductors

Energy Technology Data Exchange (ETDEWEB)

Hofmann, Johannes S. [Institut fuer Theoretische Physik und Astrophysik, Universitaet Wuerzburg (Germany); Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany); Assaad, Fakher F. [Institut fuer Theoretische Physik und Astrophysik, Universitaet Wuerzburg (Germany); Schnyder, Andreas P. [Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany)

2016-07-01

Nodal topological superconductors display zero-energy Majorana flat bands at generic edges. The flatness of these edge bands, which is protected by time-reversal and translation symmetry, gives rise to an extensive ground state degeneracy and a diverging density of states. Therefore, even arbitrarily weak interactions lead to an instability of the flat-band edge states towards time-reversal and translation-symmetry broken phases, which lift the ground-state degeneracy. Here, we employ Monte Carlo simulations combined with mean-field considerations to examine the instabilities of the flat-band edge states of d{sub xy}-wave superconductors. We find that attractive interactions induce a complex s-wave pairing instability together with a density wave instability. Repulsive interactions, on the other hand, lead to ferromagnetism mixed with spin-triplet pairing at the edge. We discuss the implications of our findings for experiments on cuprate high-temperature superconductors.

MHD instability studies in ISX-B

International Nuclear Information System (INIS)

Pare, V.K.; Dunlap, J.L.; Navarro, A.P.; Burris, R.D.

1979-01-01

MHD instabilities in Ohmically and beam heated ISX-B plasmas have been studied using collimated x-ray and Mirnov loop diagnostics. The diagnostic systems will be described and the instability signals will be illustrated for a variety of discharges. The latter will include those observed in connection with low and high β operation, density clamping, pellet injection, and deliberate introduction of toroidal field ripple

Genome instabilities arising from ribonucleotides in DNA.

Science.gov (United States)

Klein, Hannah L

2017-08-01

Genomic DNA is transiently contaminated with ribonucleotide residues during the process of DNA replication through misincorporation by the replicative DNA polymerases α, δ and ε, and by the normal replication process on the lagging strand, which uses RNA primers. These ribonucleotides are efficiently removed during replication by RNase H enzymes and the lagging strand synthesis machinery. However, when ribonucleotides remain in DNA they can distort the DNA helix, affect machineries for DNA replication, transcription and repair, and can stimulate genomic instabilities which are manifest as increased mutation, recombination and chromosome alterations. The genomic instabilities associated with embedded ribonucleotides are considered here, along with a discussion of the origin of the lesions that stimulate particular classes of instabilities. Copyright © 2017 Elsevier B.V. All rights reserved.

POD analysis of the instability mode of a low-speed streak in a laminar boundary layer

Science.gov (United States)

Deng, Si-Chao; Pan, Chong; Wang, Jin-Jun; Rinoshika, Akira

2017-12-01

The instability of one single low-speed streak in a zero-pressure-gradient laminar boundary layer is investigated experimentally via both hydrogen bubble visualization and planar particle image velocimetry (PIV) measurement. A single low-speed streak is generated and destabilized by the wake of an interference wire positioned normal to the wall and in the upstream. The downstream development of the streak includes secondary instability and self-reproduction process, which leads to the generation of two additional streaks appearing on either side of the primary one. A proper orthogonal decomposition (POD) analysis of PIV measured velocity field is used to identify the components of the streak instability in the POD mode space: for a sinuous/varicose type of POD mode, its basis functions present anti-symmetric/symmetric distributions about the streak centerline in the streamwise component, and the symmetry condition reverses in the spanwise component. It is further shown that sinuous mode dominates the turbulent kinematic energy (TKE) through the whole streak evolution process, the TKE content first increases along the streamwise direction to a saturation value and then decays slowly. In contrast, varicose mode exhibits a sustained growth of the TKE content, suggesting an increasing competition of varicose instability against sinuous instability.

Asymptotic behavior of the mixed mass in Rayleigh–Taylor and Richtmyer–Meshkov instability induced flows

Energy Technology Data Exchange (ETDEWEB)

Zhou, Ye; Cabot, William H. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Thornber, Ben [The University of Sydney, School of Aerospace, Mechanical and Mechatronic Engineering, New South Wales 2006, Sydney (Australia)

2016-05-15

Rayleigh–Taylor instability (RTI) and Richtmyer–Meshkov instability (RMI) are serious practical issues in inertial confinement fusion research, and also have relevance to many cases of astrophysical fluid dynamics. So far, much of the attention has been paid to the late-time scaling of the mixed width, which is used as a surrogate to how well the fluids have been mixed. Yet, the actual amount of mixed mass could be viewed as a more direct indicator on the evolution of the mixing layers due to hydrodynamic instabilities. Despite its importance, there is no systematic study as yet on the scaling of the mixed mass for either the RTI or the RMI induced flow. In this article, the normalized mixed mass (Ψ) is introduced for measuring the efficiency of the mixed mass. Six large numerical simulation databases have been employed: the RTI cases with heavy-to-light fluid density ratios of 1.5, 3, and 9; the single shock RMI cases with density ratios of 3 and 20; and a reshock RMI case with density ratio of 3. Using simulated flow fields, the normalized mixed mass Ψ is shown to be more sensitive in discriminating the variation with Atwood number for the RTI flows. Moreover, Ψ is demonstrated to provide more consistent results for both the RTI and RMI flows when compared with the traditional mixedness parameters, Ξ and Θ.

Theoretical and numerical studies of Rayleigh-Taylor instabilities in magnetized plasmas

International Nuclear Information System (INIS)

Ivanov, A.A.

2001-06-01

The instabilities of Rayleigh-Taylor type are considered in the thesis. The topic of the thesis was inspired by recent advances in the physics of plasma compression, especially with the aid of systems like Z-pinch. Rayleigh-Taylor instability (RTI) plays an important role in the evolution of magnetized plasmas in these experiments, as well as in stellar plasmas and classic fluids. For the phenomena concerning the nuclear fusion the RTI is very often the factor limiting the possibility of compression. In the current work we try to examine in detail the characteristic features of the instabilities of this type in order to eliminate their detrimental influence. In this thesis we are studying both the general case of the 'classic' Rayleigh-Taylor instability (in incompressible fluids) and more specific cases of the instabilities of Rayleigh-Taylor type in magnetized plasmas, in the liners or wire array implosions etc. We have studied the influence of the Hall diffusion of magnetic field on the growth rate of the instability. We have obtained in this work a self-similar solution for the widening of the initial profile of the magnetic field and for the wave of the penetration of magnetic field. After that the subsequent evolution of the magnetic field in plasma opening switches (POS) has been examined. We have shown the possibility of the existence of a strong rarefaction wave for collisional and non-collisional cases. This wave can explain the phenomenon of the opening of POS. The effect of the suppression of Rayleigh-Taylor instability by forced oscillations of the boundary between two fluids permits us to propose some ideas for the experiments of inertial fusion. We have considered the general case of the instability, in other words, two incompressible viscous superposed fluids in a gravitational field. We have obtained an exact analytical expression for the growth rate and then we have analyzed the influence of the parameters of external 'pumping' on the instability

Fingerprints of dynamical instabilities

International Nuclear Information System (INIS)

Chomaz, Ph.; Colonna, M.; Guarnera, A.

1993-01-01

It is explained why any reduced descriptions, such as mean field approximation, are stochastic in nature. It is shown that the introduction of this stochastic dynamics leads to a predictive theory in a statistical sens whatever the individual trajectories are characterized by the occurrence of bifurcations, instabilities or phase transitions. Concerning nuclear matter, the spinodal instability is discussed. In such a critical situation, the possibility to replace the stochastic part of the collision integral in the Boltzmann-Langevin model by the numerical noise associated with the finite number of test particles in ordinary BUU treatment is studied. It is shown that the fingerprints of these instabilities are kept during the evolution because of the relatively long recombination time compared with the typical time scales imposed by the Coulomb repulsion and the possible collective expansion. (author) 5 refs., 12 figs

Centrifugally Driven Rayleigh-Taylor Instability

Science.gov (United States)

Scase, Matthew; Hill, Richard

2017-11-01

The instability that develops at the interface between two fluids of differing density due to the rapid rotation of the system may be considered as a limit of high-rotation rate Rayleigh-Taylor instability. Previously the authors have considered the effect of rotation on a gravitationally dominated Rayleigh-Taylor instability and have shown that some growth modes of instability may be suppressed completely by the stabilizing effect of rotation (Phys. Rev. Fluids 2:024801, Sci. Rep. 5:11706). Here we consider the case of very high rotation rates and a negligible gravitational field. The initial condition is of a dense inner cylinder of fluid surrounded by a lighter layer of fluid. As the system is rotated about the generating axis of the cylinder, the dense inner fluid moves away from the axis and the familiar bubbles and spikes of Rayleigh-Taylor instability develop at the interface. The system may be thought of as a ``fluid-fluid centrifuge''. By developing a model based on an Orr-Sommerfeld equation, we consider the effects of viscosity, surface tension and interface diffusion on the growth rate and modes of instability. We show that under particular circumstances some modes may be stabilized. School of Mathematical Sciences.

Normalized noise power spectrum of full field digital mammography system

International Nuclear Information System (INIS)

Norriza Mohd Isa; Wan Muhamad Saridan Wan Hassan

2009-01-01

A method to measure noise power spectrum of a full field digital mammography system is presented. The effect of X-ray radiation dose, size and configuration of region of interest on normalized noise power spectrum (NNPS) was investigated. Flat field images were acquired using RQA-M2 beam quality technique (Mo/Mo anode-filter, 28 kV, 2 mm Al) with different clinical radiation doses. The images were cropped at about 4 cm from the edge of the breast wall and then divided into different size of non-overlapping or overlapping segments. NNPS was determined through detrending, 2-D fast Fourier transformation and normalization. Our measurement shows that high radiation dose gave lower NNPS at a specific beam quality. (Author)

Unparticle-Higgs field mixing: Mikheyev-Smirnov-Wolfenstein resonances, seesaw mechanism, and spinodal instabilities

International Nuclear Information System (INIS)

Boyanovsky, D.; Holman, R.; Hutasoit, Jimmy A.

2009-01-01

Motivated by slow-roll inflationary cosmology we study a scalar unparticle weakly coupled to a Higgs field in the broken symmetry phase. The mixing between the unparticle and the Higgs field results in a seesaw type matrix and the mixing angles feature a Mikheyev-Smirnov-Wolfenstein (MSW) effect as a consequence of the unparticle field being noncanonical. We find two (MSW) resonances for small and large spacelike momenta. The unparticlelike mode features a nearly flat potential with spinodal instabilities and a large expectation value. An effective potential for the unparticlelike field is generated from the Higgs potential, but with couplings suppressed by a large power of the small seesaw ratio. The dispersion relation for the Higgs-like mode features an imaginary part even at ''tree level'' as a consequence of the fact that the unparticle field describes a multiparticle continuum. Mixed unparticle-Higgs propagators reveal the possibility of oscillations, albeit with short coherence lengths. The results are generalized to the case in which the unparticle features a mass gap, in which case a low energy MSW resonance may occur for lightlike momenta depending on the scales. Unparticle-Higgs mixing leads to an effective unparticle potential of the new-inflation form. Slow-roll variables are suppressed by seesaw ratios and the anomalous dimensions and favor a red spectrum of scalar perturbations consistent with cosmic microwave background data.

Unparticle-Higgs field mixing: Mikheyev-Smirnov-Wolfenstein resonances, seesaw mechanism, and spinodal instabilities

Science.gov (United States)

Boyanovsky, D.; Holman, R.; Hutasoit, Jimmy A.

2009-04-01

Motivated by slow-roll inflationary cosmology we study a scalar unparticle weakly coupled to a Higgs field in the broken symmetry phase. The mixing between the unparticle and the Higgs field results in a seesaw type matrix and the mixing angles feature a Mikheyev-Smirnov-Wolfenstein (MSW) effect as a consequence of the unparticle field being noncanonical. We find two (MSW) resonances for small and large spacelike momenta. The unparticlelike mode features a nearly flat potential with spinodal instabilities and a large expectation value. An effective potential for the unparticlelike field is generated from the Higgs potential, but with couplings suppressed by a large power of the small seesaw ratio. The dispersion relation for the Higgs-like mode features an imaginary part even at “tree level” as a consequence of the fact that the unparticle field describes a multiparticle continuum. Mixed unparticle-Higgs propagators reveal the possibility of oscillations, albeit with short coherence lengths. The results are generalized to the case in which the unparticle features a mass gap, in which case a low energy MSW resonance may occur for lightlike momenta depending on the scales. Unparticle-Higgs mixing leads to an effective unparticle potential of the new-inflation form. Slow-roll variables are suppressed by seesaw ratios and the anomalous dimensions and favor a red spectrum of scalar perturbations consistent with cosmic microwave background data.

Azimuthal magnetorotational instability with super-rotation

Science.gov (United States)

Rüdiger, G.; Schultz, M.; Gellert, M.; Stefani, F.

2018-02-01

It is demonstrated that the azimuthal magnetorotational instability (AMRI) also works with radially increasing rotation rates contrary to the standard magnetorotational instability for axial fields which requires negative shear. The stability against non-axisymmetric perturbations of a conducting Taylor-Couette flow with positive shear under the influence of a toroidal magnetic field is considered if the background field between the cylinders is current free. For small magnetic Prandtl number the curves of neutral stability converge in the (Hartmann number,Reynolds number) plane approximating the stability curve obtained in the inductionless limit . The numerical solutions for indicate the existence of a lower limit of the shear rate. For large the curves scale with the magnetic Reynolds number of the outer cylinder but the flow is always stable for magnetic Prandtl number unity as is typical for double-diffusive instabilities. We are particularly interested to know the minimum Hartmann number for neutral stability. For models with resting or almost resting inner cylinder and with perfectly conducting cylinder material the minimum Hartmann number occurs for a radius ratio of \\text{in}=0.9$ . The corresponding critical Reynolds numbers are smaller than 4$ .

Aerodynamic instability: A case history

Science.gov (United States)

Eisenmann, R. C.

1985-01-01

The identification, diagnosis, and final correction of complex machinery malfunctions typically require the correlation of many parameters such as mechanical construction, process influence, maintenance history, and vibration response characteristics. The progression is reviewed of field testing, diagnosis, and final correction of a specific machinery instability problem. The case history presented addresses a unique low frequency instability problem on a high pressure barrel compressor. The malfunction was eventually diagnosed as a fluidic mechanism that manifested as an aerodynamic disturbance to the rotor assembly.

Instabilities of higher dimensional compactifications

International Nuclear Information System (INIS)

Accetta, F.S.

1987-02-01

Various schemes for cosmological compactification of higher dimensional theories are considered. Possible instabilities which drive the ground state with static internal space to de Sitter-like expansion of all dimensions are discussed. These instabilities are due to semiclassical barrier penetration and classical thermal fluctuations. For the case of the ten dimensional Chapline-Manton action, it is possible to avoid such difficulties by balancing one-loop Casimir corrections against monopole contributions from the field strength H/sub MNP/ and fermionic condensates. 10 refs

Can Chronic Ankle Instability be Prevented? Rethinking Management of Lateral Ankle Sprains.

Science.gov (United States)

Denegar, Craig R.; Miller, Sayers J., III

2002-01-01

Investigates whether chronic ankle instability can be prevented, discussing: the relationship between mechanical and functional instability; normal ankle mechanics, sequelae to lateral ankle sprains, and abnormal ankle mechanics; and tissue healing, joint dysfunction, and acute lateral ankle sprain management. The paper describes a treatment model…

Wakefields and Instabilities in Linear Accelerators

CERN Document Server

Ferrario, M.; Palumbo, L.

2014-12-19

When a charged particle travels across the vacuum chamber of an accelerator, it induces electromagnetic fields, which are left mainly behind the generating particle. These electromagnetic fields act back on the beam and influence its motion. Such an interaction of the beam with its surro undings results in beam energy losses, alters the shape of the bunches, and shifts the betatron and synchrotron frequencies. At high beam current the fields can even lead to instabilities, thus limiting the performance of the accelerator in terms of beam quality and current intensity. We discuss in this lecture the general features of the electromagnetic fields, introducing the concepts of wakefields and giving a few simple examples in cylindrical geometry. We then show the effect of the wakefields on the dynamics of a beam in a linac, dealing in particular with the beam breakup instability and how to cure it.

Stripes instability of an oscillating non-Brownian iso-dense suspension of spheres

Science.gov (United States)

Roht, Y. L.; Ippolito, I.; Hulin, J. P.; Salin, D.; Gauthier, G.

2018-03-01

We analyze experimentally the behavior of a non-Brownian, iso-dense suspension of spheres submitted to periodic square wave oscillations of the flow in a Hele-Shaw cell of gap H. We do observe an instability of the initially homogeneous concentration in the form of concentration variation stripes transverse to the flow. The wavelength of these regular spatial structures scales roughly as the gap of the cell and is independent of the particle concentration and of the period of oscillation. This instability requires large enough particle volume fractions φ≥ 0.25 and a gap large enough compared to the sphere diameter (H/d ≥ 8) . Mapping the domain of the existence of this instability in the space of the control parameters shows that it occurs only in a limited range of amplitudes of the fluid displacement. The analysis of the concentration distribution across the gap supports a scenario of particle migration towards the wall followed by an instability due to a particle concentration gradient with a larger concentration at the walls. In order to account for the main features of this stripes instability, we use the theory of longitudinal instability due to normal stresses difference and recent observations of a dependence of the first normal stresses difference on the particle concentration.

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

Premixed Flames Under Microgravity and Normal Gravity Conditions

Science.gov (United States)

Krikunova, Anastasia I.; Son, Eduard E.

2018-03-01

Premixed conical CH4-air flames were studied experimentally and numerically under normal straight, reversed gravity conditions and microgravity. Low-gravity experiments were performed in Drop tower. Classical Bunsen-type burner was used to find out features of gravity influence on the combustion processes. Mixture equivalence ratio was varied from 0.8 to 1.3. Wide range of flow velocity allows to study both laminar and weakly turbulized flames. High-speed flame chemoluminescence video-recording was used as diagnostic. The investigations were performed at atmospheric pressure. As results normalized flame height, laminar flame speed were measured, also features of flame instabilities were shown. Low- and high-frequency flame-instabilities (oscillations) have a various nature as velocity fluctuations, preferential diffusion instability, hydrodynamic and Rayleigh-Taylor ones etc., that was explored and demonstrated.

Microbunching instability in a chicane: Two-dimensional mean field treatment

Directory of Open Access Journals (Sweden)

Gabriele Bassi

2009-08-01

Full Text Available We study the microbunching instability in a bunch compressor by a parallel code with some improved numerical algorithms. The two-dimensional charge/current distribution is represented by a Fourier series, with coefficients determined through Monte Carlo sampling over an ensemble of tracked points. This gives a globally smooth distribution with low noise. The field equations are solved accurately in the lab frame using retarded potentials and a novel choice of integration variables that eliminates singularities. We apply the scheme with parameters for the first bunch compressor system of FERMI@Elettra, with emphasis on the amplification of a perturbation at a particular wavelength and the associated longitudinal bunch spectrum. Gain curves are in rough agreement with those of the linearized Vlasov system at intermediate wavelengths, but show some deviation at the smallest wavelengths treated and show the breakdown of a coasting beam assumption at long wavelengths. The linearized Vlasov system is discussed in some detail. A new 2D integral equation is derived which reduces to a well-known 1D integral equation in the coasting beam case.

Papaloizou-Pringle instability suppression by the magnetorotational instability in relativistic accretion discs

Science.gov (United States)

Bugli, M.; Guilet, J.; Müller, E.; Del Zanna, L.; Bucciantini, N.; Montero, P. J.

2018-03-01

Geometrically thick tori with constant specific angular momentum have been widely used in the last decades to construct numerical models of accretion flows on to black holes. Such discs are prone to a global non-axisymmetric hydrodynamic instability, known as Papaloizou-Pringle instability (PPI), which can redistribute angular momentum and also lead to an emission of gravitational waves. It is, however, not clear yet how the development of the PPI is affected by the presence of a magnetic field and by the concurrent development of the magnetorotational instability (MRI). We present a numerical analysis using three-dimensional GRMHD simulations of the interplay between the PPI and the MRI considering, for the first time, an analytical magnetized equilibrium solution as initial condition. In the purely hydrodynamic case, the PPI selects as expected the large-scale m = 1 azimuthal mode as the fastest growing and non-linearly dominant mode. However, when the torus is threaded by a weak toroidal magnetic field, the development of the MRI leads to the suppression of large-scale modes and redistributes power across smaller scales. If the system starts with a significantly excited m = 1 mode, the PPI can be dominant in a transient phase, before being ultimately quenched by the MRI. Such dynamics may well be important in compact star mergers and tidal disruption events.

Hypercapnic normalization of BOLD fMRI: comparison across field strengths and pulse sequences

DEFF Research Database (Denmark)

Cohen, Eric R.; Rostrup, Egill; Sidaros, Karam

2004-01-01

to be more accurately localized and quantified based on changes in venous blood oxygenation alone. The normalized BOLD signal induced by the motor task was consistent across different magnetic fields and pulse sequences, and corresponded well with cerebral blood flow measurements. Our data suggest...... size, as well as experimental, such as pulse sequence and static magnetic field strength (B(0)). Thus, it is difficult to compare task-induced fMRI signals across subjects, field strengths, and pulse sequences. This problem can be overcome by normalizing the neural activity-induced BOLD fMRI response...... for global stimulation, subjects breathed a 5% CO(2) gas mixture. Under all conditions, voxels containing primarily large veins and those containing primarily active tissue (i.e., capillaries and small veins) showed distinguishable behavior after hypercapnic normalization. This allowed functional activity...

Bosonic instability of charged black holes

International Nuclear Information System (INIS)

Gaina, A.B.; Ternov, I.M.

1986-01-01

The processes of spontaneous and induced production and accumulation of charged bosons on quasibound superradiant levels in the field of Kerr-Newman black hole is analysed. It is shown that bosonic instability may be caused exclusively by the rotation of the black hole. Particulary, the Reissner-Nordstrom configuration is stable. In the case of rotating and charged black hole the bosonic instability may cause an increase of charge of the black hole

Topological instability of a semi-bounded magnetic fluid drop under influence of magnetic and ultrasound fields

Energy Technology Data Exchange (ETDEWEB)

Bashtovoi, V., E-mail: bashv@rambler.ru [Belarussian National Technical University, 65 Nezavisimosti Ave., Minsk 220013 (Belarus); Reks, A. [Belarussian National Technical University, 65 Nezavisimosti Ave., Minsk 220013 (Belarus); Baev, A. [Institute of Applied Physics of NAS of Belarus, 16 Akademicheskaya str., Minsk 220072 (Belarus); Mansoor, Al-Jhaish Taha Malik [Belarussian National Technical University, 65 Nezavisimosti Ave., Minsk 220013 (Belarus)

2017-06-01

Theoretical and experimental results on deformation and disintegration on parts (topological instability) of semi-bounded magnetic fluid drop placed on horizontal plate in the presence of gravity and vertical external uniform magnetic field, and the influence of acoustic wave on these processes, as well as an experimental results of acoustic fountain on free surface of magnetic fluid are presented. The role of individual mechanisms leading to disintegration is analyzed, and analytical relationships and experimental dependences for critical parameters are established.

Mitigation of rotational instability of high-beta field-reversed configuration by double-sided magnetized plasmoid injection

Energy Technology Data Exchange (ETDEWEB)

Itagaki, H.; Inomoto, M. [Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan); Asai, T.; Takahashi, Ts. [College of Science and Technology, Nihon University, 1-8-14 Kanda Surugadai, Chiyoda-ku, Tokyo 101-8308 (Japan)

2014-03-15

Active control of destructive rotational instability in a high-beta field-reversed configuration (FRC) plasma was demonstrated by using double-sided plasmoid injection technique. The elliptical deformation of the FRC's cross section was mitigated as a result of substantial suppression of spontaneous spin-up by the plasmoid injection. It was found that the injected plasmoid provided better stability against the rotational mode, suggesting that the compensation of the FRC's decaying magnetic flux might help to suppress its spin-up.

Normal forms of invariant vector fields under a finite group action

International Nuclear Information System (INIS)

Sanchez Bringas, F.

1992-07-01

Let Γ be a finite subgroup of GL(n,C). This subgroup acts on the space of germs of holomorphic vector fields vanishing at the origin in C n . We prove a theorem of invariant conjugation to a normal form and linearization for the subspace of invariant elements and we give a description of these normal forms in dimension n=2. (author)

Computer simulations of electromagnetic cool ion beam instabilities. [in near earth space

Science.gov (United States)

Gary, S. P.; Madland, C. D.; Schriver, D.; Winske, D.

1986-01-01

Electromagnetic ion beam instabilities driven by cool ion beams at propagation parallel or antiparallel to a uniform magnetic field are studied using computer simulations. The elements of linear theory applicable to electromagnetic ion beam instabilities and the simulations derived from a one-dimensional hybrid computer code are described. The quasi-linear regime of the right-hand resonant ion beam instability, and the gyrophase bunching of the nonlinear regime of the right-hand resonant and nonresonant instabilities are examined. It is detected that in the quasi-linear regime the instability saturation is due to a reduction in the beam core relative drift speed and an increase in the perpendicular-to-parallel beam temperature; in the nonlinear regime the instabilities saturate when half the initial beam drift kinetic energy density is converted to fluctuating magnetic field energy density.

Rayleigh-Taylor instability of cylindrical jets with radial motion

International Nuclear Information System (INIS)

Chen, X.M.; Schrock, V.E.; Peterson, P.F.

1997-01-01

Rayleigh-Taylor instability of an interface between fluids with different densities subjected to acceleration normal to itself has interested researchers for almost a century. The classic analyses of a flat interface by Rayleigh and Taylor have shown that this type of instability depends on the direction of acceleration and the density differences of the two fluids. Plesset later analyzed the stability of a spherically symmetric flows (and a spherical interface) and concluded that the instability also depends on the velocity of the interface as well as the direction and magnitude of radial acceleration. The instability induced by radial motion in cylindrical systems seems to have been neglected by previous researchers. This paper analyzes the Rayleigh-Taylor type of instability for a cylindrical surface with radial motions. The results of the analysis show that, like the spherical case, the radial velocity also plays an important role. As an application, the example of a liquid jet surface in an Inertial Confinement Fusion (ICF) reactor design is analyzed. (orig.)

One-dimensional modulation instability in biased two-photon photorefractive-photovoltaic crystals

International Nuclear Information System (INIS)

Zhan Kaiyun; Hou Chunfeng; Li Xin

2010-01-01

The one-dimensional modulation instability of broad optical beams in biased two-photon photorefractive-photovoltaic crystals is investigated under steady-state conditions. Our analysis indicates that the modulation instability growth rate depends on the external bias field, the bulk photovoltaic effect and the ratio of the intensity of the incident beam to that of the dark irradiance. Moreover, our results show that this modulation instability growth rate is the same as that in two-photon photorefractive-photovoltaic crystals under open circuit conditions in the absence of an external bias field, and the modulation instability growth rate in two-photon biased photorefractive-nonphotovoltaic crystals can be predicted when the bulk photovoltaic effect is neglected.

Liquid conductor model of instabilities in a pinched discharge

Energy Technology Data Exchange (ETDEWEB)

Dattnery, A; Lehnert, B [Dept. of Electronics, Royal Institute of Technology, Stockholm (Sweden); Lundquist, S [Swedish State Power Board (Sweden)

1958-07-01

The pinched gas discharge experiments seem to have been handicapped by the great speed with which the instability develops as well as by the light coming from impurities instead of the main body of pinched gas. In the present work a liquid conductor is used in order to study the structure of the instabilities. The study of a pinch was made with and without the axial magnetic field. In cases with a magnetic field, the currents and fields were chosen so as to give a longitudinal magnetic field equal to or three times the azimuthal field at the boundary of the mercury stream. The study of the results shows that in the case without an external magnetic field there is a similarity between the behavior of the pinch in a stream of mercury and in an ionized gas column. The stabilizing action of the surface tension is small and the instabilities develop easily. The case with an external magnetic field is more complicated. The magnetic lines of force are not frozen into the medium; they can 'escape' from the medium. In this case the magnetic field has no stabilizing effect. The influence of conducting walls around the mercury column will be studied in forthcoming experiments.

Simple lecture demonstrations of instability and self-organization

International Nuclear Information System (INIS)

Mayer, V V; Varaksina, E I; Saranin, V A

2014-01-01

A dielectric liquid layer with an electric field created inside it is proposed as a means for demonstrating the phenomenon of self-organization. The field is produced by the distributed charge transferred by a corona discharge from the tip to the liquid surface. The theory of the phenomenon is presented. An analogy with the Rayleigh – Taylor instability is drawn and a comparison with the Benard instability is given. The practicality of the method for both natural sciences and the humanities is discussed. (methodological notes)

Two-dimensional electrodynamic structure of the normal glow discharge in an axial magnetic field

Energy Technology Data Exchange (ETDEWEB)

Surzhikov, S. T., E-mail: surg@ipmnet.ru [Russian Academy of Sciences, Institute for Problems in Mechanics (Russian Federation)

2017-03-15

Results are presented from numerical simulations of an axisymmetric normal glow discharge in molecular hydrogen and molecular nitrogen in an axial magnetic field. The charged particle densities and averaged azimuthal rotation velocities of electrons and ions are studied as functions of the gas pressure in the range of 1–5 Torr, electric field strength in the range of 100–600 V/cm, and magnetic field in the range of 0.01–0.3 T. It is found that the axial magnetic field does not disturb the normal current density law.

Gauge-Independent Scales Related to the Standard Model Vacuum Instability

CERN Document Server

Espinosa, Jose R.; Konstandin, Thomas; Riotto, Antonio

2017-01-01

The measured (central) values of the Higgs and top quark masses indicate that the Standard Model (SM) effective potential develops an instability at high field values. The scale of this instability, determined as the Higgs field value at which the potential drops below the electroweak minimum, is about $10^{11}$ GeV. However, such a scale is unphysical as it is not gauge-invariant and suffers from a gauge-fixing uncertainty of up to two orders of magnitude. Subjecting our system, the SM, to several probes of the instability (adding higher order operators to the potential; letting the vacuum decay through critical bubbles; heating up the system to very high temperature; inflating it) and asking in each case physical questions, we are able to provide several gauge-invariant scales related with the Higgs potential instability.

A biological-based model that links genomic instability, bystander effects, and adaptive response

International Nuclear Information System (INIS)

Scott, B.R.

2004-01-01

This paper links genomic instability, bystander effects, and adaptive response in mammalian cell communities via a novel biological-based, dose-response model called NEOTRANS 3 . The model is an extension of the NEOTRANS 2 model that addressed stochastic effects (genomic instability, mutations, and neoplastic transformation) associated with brief exposure to low radiation doses. With both models, ionizing radiation produces DNA damage in cells that can be associated with varying degrees of genomic instability. Cells with persistent problematic instability (PPI) are mutants that arise via misrepair of DNA damage. Progeny of PPI cells also have PPI and can undergo spontaneous neoplastic transformation. Unlike NEOTRANS 2 , with NEOTRANS 3 newly induced mutant PPI cells and their neoplastically transformed progeny can be suppressed via our previously introduced protective apoptosis-mediated (PAM) process, which can be activated by low linear energy transfer (LET) radiation. However, with NEOTRANS 3 (which like NEOTRANS 2 involves cross-talk between nongenomically compromised [e.g., nontransformed, nonmutants] and genomically compromised [e.g., mutants, transformants, etc.] cells), it is assumed that PAM is only activated over a relatively narrow, dose-rate-dependent interval (D PAM ,D off ); where D PAM is a small stochastic activation threshold, and D off is the stochastic dose above which PAM does not occur. PAM cooperates with activated normal DNA repair and with activated normal apoptosis in guarding against genomic instability. Normal repair involves both error-free repair and misrepair components. Normal apoptosis and the error-free component of normal repair protect mammals by preventing the occurrence of mutant cells. PAM selectively removes mutant cells arising via the misrepair component of normal repair, selectively removes existing neoplastically transformed cells, and probably selectively removes other genomically compromised cells when it is activated

Instabilities excited by head-on collisions of two relativistic electron beams

Energy Technology Data Exchange (ETDEWEB)

Kou Shu-Ying

1982-02-01

In this paper, we studied the instabilities excited by head-on collision of two relativistic electron beams in transporting, taking account of the magnetic field B/sub 0/ and the thermal pressure delp of the beams. The conditions under which the instabilities occur and the growth rate of instabilities are obtained. The results show that these instabilities can be excited or inhibited by controlling the velocity of the beams.

Transverse instability excited by rf deflecting modes for PEP

International Nuclear Information System (INIS)

Chao, A.W.; Yao, C.Y.

1979-11-01

We have looked at the possible transverse instability effects which are caused by the deflecting modes of the rf cavities in PEP. The results are obtained by applying the expression of the instability damping rate. We have assumed that there equal bunches equally spaced in PEP. We have worked out the equivalent for a single bunch beam. The effect of chromaticity ξ is included as a frequency shift in the bunch mode spectra. We rewrite this result in terms of the transverse wake field instead of the impedance. We include an application of the Sacherer formalism to the case of resistive wall. The resulting expression of the damping rate contains two terms. The first term corresponds to the effect of the short wake fields; it agrees with the result of the head-tail instability as derived by Sands. A numerical estimate of this resistive-wall head tail case for PEP is given. It re-confirms that the resistive wall instability is not a serious problem for PEP. The second term gives the effect of long wake fields and it agrees with the result of Courant and Sessler. 10 refs., 2 figs

Anomalous plasma transport due to electron temperature gradient instability

International Nuclear Information System (INIS)

Tokuda, Sinji; Ito, Hiroshi; Kamimura, Tetsuo.

1979-01-01

The collisionless drift wave instability driven by an electron temperature inhomogeneity (electron temperature gradient instability) and the enhanced transport processes associated with it are studied using a two-and-a-half dimensional particle simulation code. The simulation results show that quasilinear diffusion in phase space is an important mechanism for the saturation of the electron temperature gradient instability. Also, the instability yields particle fluxes toward the hot plasma regions. The heat conductivity of the electron temperature perpendicular to the magnetic field, T sub(e'), is not reduced by magnetic shear but remains high, whereas the heat conductivity of the parallel temperature, T sub(e''), is effectively reduced, and the instability stabilized. (author)

Temperature-gradient instability induced by conducting end walls

International Nuclear Information System (INIS)

Berk, H.L.; Ryutov, D.D.; Tsidulko, Yu.A.

1990-04-01

A new rapidly growing electron temperature gradient instability is found for a plasma in contact with a conducting wall. The linear instability analysis is presented and speculations are given for its nonlinear consequences. This instability illustrates that conducting walls can produce effects that are detrimental to plasma confinement. This mode should be of importance in open-ended systems including astrophysical plasmas, mirror machines and at the edge of tokamaks where field lines are open and are connected to limiters or divertors. 16 refs., 2 figs

Model of E-Cloud Instability in the Fermilab Recycler

Energy Technology Data Exchange (ETDEWEB)

Balbekov, V. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)

2015-06-24

Simple model of electron cloud is developed in the paper to explain e-cloud instability of bunched proton beam in the Fermilab Recycler. The cloud is presented as an immobile snake in strong vertical magnetic field. The instability is treated as an amplification of the bunch injection errors from the batch head to its tail. Nonlinearity of the e-cloud field is taken into account. Results of calculations are compared with experimental data demonstrating good correlation.

Parametric instabilities excited by localized pumps near the lower-hybrid frequency

International Nuclear Information System (INIS)

Kuo, Y.Y.; Chen, L.

1976-04-01

Parametric instabilities excited in non-uniform plasmas by spatially localized pump fields oscillating near the local lower-hybrid frequency are analytically investigated. Corresponding threshold conditions, temporal growth rates, and spatial amplification factors are obtained for the oscillating-two-stream instability and the decay instabilities due to nonlinear electron and ion Landau dampings

Resistive instabilities of current sheets in the solar wind

Energy Technology Data Exchange (ETDEWEB)

Dobrowolny, M [CNR, Laboratorio per il Plasma nello Spazio, Frascati, Italy; Trussoni, E [CNR, Laboratorio di Cosmo-Geofisica, Turin, Italy

1979-03-01

Resistive magnetohydrodynamic instabilities are investigated numerically for non-antisymmetric magnetic field profiles similar to those indicated in spacecraft data on solar wind discontinuities. The eigenvalue problem derived for the growth rate of possible instabilities from dimensionless equations for velocity and magnetic field perturbations is solved starting from the outer regions where the plasma is frozen to the magnetic field. For an antisymmetric magnetic profile, calculations show only tearing modes to be present, with instabilities occurring only at long wavelengths, while for a non-antisymmetric magnetic profile resembling the observed solar wind, calculations indicate the presence of rippling modes driven by resistivity gradients, in addition to the tearing modes. Calculations of the scale lengths of variation of the reversing component based on a scaling law relating the maximum growth rate to the magnetic Reynolds number are found to agree with observed solar current sheet scale lengths.

Linear simulations of the cylindrical Richtmyer-Meshkov instability in magnetohydrodynamics

KAUST Repository

Bakhsh, Abeer

2016-03-09

Numerical simulations and analysis indicate that the Richtmyer-Meshkov instability(RMI) is suppressed in ideal magnetohydrodynamics(MHD) in Cartesian slab geometry. Motivated by the presence of hydrodynamic instabilities in inertial confinement fusion and suppression by means of a magnetic field, we investigate the RMI via linear MHD simulations in cylindrical geometry. The physical setup is that of a Chisnell-type converging shock interacting with a density interface with either axial or azimuthal (2D) perturbations. The linear stability is examined in the context of an initial value problem (with a time-varying base state) wherein the linearized ideal MHD equations are solved with an upwind numerical method. Linear simulations in the absence of a magnetic field indicate that RMI growth rate during the early time period is similar to that observed in Cartesian geometry. However, this RMI phase is short-lived and followed by a Rayleigh-Taylor instability phase with an accompanied exponential increase in the perturbation amplitude. We examine several strengths of the magnetic field (characterized by β=2p/B^2_r) and observe a significant suppression of the instability for β ≤ 4. The suppression of the instability is attributed to the transport of vorticity away from the interface by Alfvén fronts.

Faraday instability on patterned surfaces

Science.gov (United States)

Feng, Jie; Rubinstein, Gregory; Jacobi, Ian; Stone, Howard

2013-11-01

We show how micro-scale surface patterning can be used to control the onset of the Faraday instability in thin liquid films. It is well known that when a liquid film on a planar substrate is subject to sufficient vibrational accelerations, the free surface destabilizes, exhibiting a family of non-linear standing waves. This instability remains a canonical problem in the study of spontaneous pattern formation, but also has practical uses. For example, the surface waves induced by the Faraday instability have been studied as a means of enhanced damping for mechanical vibrations (Genevaux et al. 2009). Also the streaming within the unstable layer has been used as a method for distributing heterogeneous cell cultures on growth medium (Takagi et al. 2002). In each of these applications, the roughness of the substrate significantly affects the unstable flow field. We consider the effect of patterned substrates on the onset and behavior of the Faraday instability over a range of pattern geometries and feature heights where the liquid layer is thicker than the pattern height. Also, we describe a physical model for the influence of patterned roughness on the destabilization of a liquid layer in order to improve the design of practical systems which exploit the Faraday instability.

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

Richtmyer–Meshkov instability of a thermal interface in a two-fluid plasma

KAUST Repository

Bond, D.

2017-11-03

We computationally investigate the Richtmyer–Meshkov instability of a density interface with a single-mode perturbation in a two-fluid, ion–electron plasma with no initial magnetic field. Self-generated magnetic fields arise subsequently. We study the case where the density jump across the initial interface is due to a thermal discontinuity, and select plasma parameters for which two-fluid plasma effects are expected to be significant in order to elucidate how they alter the instability. The instability is driven via a Riemann problem generated precursor electron shock that impacts the density interface ahead of the ion shock. The resultant charge separation and motion generates electromagnetic fields that cause the electron shock to degenerate and periodically accelerate the electron and ion interfaces, driving Rayleigh–Taylor instability. This generates small-scale structures and substantially increases interfacial growth over the hydrodynamic case.

Modeling of flow-dominated MHD instabilities at WiPPAL using NIMROD

Science.gov (United States)

Flanagan, K.; McCollam, K. J.; Milhone, J.; Mirnov, V. V.; Nornberg, M. D.; Peterson, E. E.; Siller, R.; Forest, C. B.

2017-10-01

Using the NIMROD (non-ideal MHD with rotation - open discussion) code developed at UW-Madison, we model two different flow scenarios to study the onset of MHD instabilities in flow-dominated plasmas in the Big Red Ball (BRB) and the Plasma Couette Experiment (PCX). Both flows rely on volumetric current drive, where a large current is drawn through the plasma across a weak magnetic field, injecting J × B torque across the whole volume. The first scenario uses a vertical applied magnetic field and a mostly radial injected current to create Couette-like flows which may excite the magnetorotational instability (MRI). In the other scenario, a quadrupolar field is applied to create counter-rotating von Karman-like flow that demonstrates a dynamo-like instability. For both scenarios, the differences between Hall and MHD Ohm's laws are explored. The implementation of BRB geometry in NIMROD, details of the observed flows, and instability results are shown. This work was funded by DoE and NSF.

Gauge-independent scales related to the Standard Model vacuum instability

International Nuclear Information System (INIS)

Espinosa, J.R.; Garny, M.; Konstandin, T.; Riotto, A.

2016-08-01

The measured (central) values of the Higgs and top quark masses indicate that the Standard Model (SM) effective potential develops an instability at high field values. The scale of this instability, determined as the Higgs field value at which the potential drops below the electroweak minimum, is about 10"1"1 GeV. However, such a scale is unphysical as it is not gauge invariant and suffers from a gauge-fixing uncertainty of up to two orders of magnitude. Subjecting our system, the SM, to several probes of the instability (adding higher order operators to the potential; letting the vacuum decay through critical bubbles; heating up the system to very high temperature; inflating it) and asking in each case physical questions, we are able to provide several gauge-invariant scales related with the Higgs potential instability.

Longwave instabilities and patterns in fluids

CERN Document Server

Shklyaev, Sergey

2017-01-01

This book summarizes the main advances in the field of nonlinear evolution and pattern formation caused by longwave instabilities in fluids. It will allow readers to master the multiscale asymptotic methods and become familiar with applications of these methods in a variety of physical problems.  Longwave instabilities are inherent to a variety of systems in fluid dynamics, geophysics, electrodynamics, biophysics, and many others. The techniques of the derivation of longwave amplitude equations, as well as the analysis of numerous nonlinear equations, are discussed throughout. This book will be of value to researchers and graduate students in applied mathematics, physics, and engineering, in particular within the fields of fluid mechanics, heat and mass transfer theory, and nonlinear dynamics. .

Normalized noise power spectrum of full field digital mammography detector system

International Nuclear Information System (INIS)

Norriza Mohd Isa; Wan Muhamad Saridan Wan Hassan

2009-01-01

Full text: A method to measure noise power spectrum of a full field digital mammography system is presented. The effect of X-ray radiation dose, size and configuration of region of interest on normalized noise power spectrum (NNPS) was investigated. Flat field images were acquired using RQA-M2 beam quality technique (Mo/Mo anode-filter, 28 kV, 2 mm Al) with different clinical radiation doses. The images were cropped at about 4 cm from the edge of the breast wall and then divided into different size of non-overlapping or overlapping segments. NNPS was determined through de trending, 2-D fast Fourier transformation and normalization. Our measurement shows that high radiation dose gave lower NNPS at a specific beam quality. (author)

Topographic-driven instabilities in terrestrial bodies

Science.gov (United States)

Vantieghem, S.; Cebron, D.; Herreman, W.; Lacaze, L.

2013-12-01

Models of internal planetary fluid layers (core flows, subsurface oceans) commonly assume that these fluid envelopes have a spherical shape. This approximation however entails a serious restriction from the fluid dynamics point of view. Indeed, in the presence of mechanical forcings (precession, libration, nutation or tides) due to gravitational interaction with orbiting partners, boundary topography (e.g. of the core-mantle boundary) may excite flow instabilities and space-filling turbulence. These phenomena may affect heat transport and dissipation at the main order. Here, we focus on instabilities driven by longitudinal libration. Using a suite of theoretical tools and numerical simulations, we are able to discern a parameter range for which instability may be excited. We thereby consider deformations of different azimuthal order. This study gives the first numerical evidence of the tripolar instability. Furthermore, we explore the non-linear regime and investigate the amplitude as well as the dissipation of the saturated instability. Indeed, these two quantities control the torques on the solid layers and the thermal transport. Furthermore, based on this results, we address the issue of magnetic field generation associated with these flows (by induction or by dynamo process). This instability mechanism applies to both synchronized as non-synchronized bodies. As such, our results show that a tripolar instability might be present in various terrestrial bodies (Early Moon, Gallilean moons, asteroids, etc.), where it could participate in dynamo action. Simulation of a libration-driven tripolar instability in a deformed spherical fluid layer: snapshot of the velocity magnitude, where a complex 3D flow pattern is established.

The coalescence instability in solar flares

Science.gov (United States)

Tajima, T.; Brunel, F.; Sakai, J.-I.; Vlahos, L.; Kundu, M. R.

1985-01-01

The nonlinear coalescence instability of current carrying solar loops can explain many of the characteristics of the solar flares such as their impulsive nature, heating and high energy particle acceleration, amplitude oscillations of electromagnetic and emission as well as the characteristics of two-dimensional microwave images obtained during a flare. The plasma compressibility leads to the explosive phase of loop coalescence and its overshoot results in amplitude oscillations in temperatures by adiabatic compression and decompression. It is noted that the presence of strong electric fields and super-Alfvenic flows during the course of the instability play an important role in the production of nonthermal particles. A qualitative explanation on the physical processes taking place during the nonlinear stages of the instability is given.

Flutter instability of cantilevered carbon nanotubes caused by magnetic fluid flow subjected to a longitudinal magnetic field

Science.gov (United States)

Sadeghi-Goughari, Moslem; Jeon, Soo; Kwon, Hyock-Ju

2018-04-01

CNT (Carbon nanotube)-based fluidic systems hold a great potential for emerging medical applications such as drug delivery for cancer therapy. CNTs can be used to deliver anticancer drugs into a target site under a magnetic field guidance. One of the critical issues in designing such systems is how to avoid the vibration induced by the fluid flow, which is undesirable and may even promote the structural instability. The main objective of the present research is to develop a fluid structure interaction (FSI) model to investigate the flutter instability of a cantilevered CNT induced by a magnetic fluid flow under a longitudinal magnetic field. The CNT is assumed to be embedded in a viscoelastic matrix to consider the effect of biological medium around it. To obtain a dynamical model for the system, the Navier-Stokes theory of magnetic-fluid flow is coupled to the Euler-Bernoulli beam model for CNT. The small size effects of the magnetic fluid and CNT are considered through the small scale parameters including Knudsen number (Kn) and the nonlocal parameter. Then, the extended Galerkin's method is applied to solve the FSI governing equations, and to derive the stability diagrams of the system. Results show how the magnetic properties of the fluid flow have an effect on improving the stability of the cantilevered CNT by increasing the flutter velocity.

Resonant Drag Instabilities in protoplanetary disks: the streaming instability and new, faster-growing instabilities

Science.gov (United States)

Squire, Jonathan; Hopkins, Philip F.

2018-04-01

We identify and study a number of new, rapidly growing instabilities of dust grains in protoplanetary disks, which may be important for planetesimal formation. The study is based on the recognition that dust-gas mixtures are generically unstable to a Resonant Drag Instability (RDI), whenever the gas, absent dust, supports undamped linear modes. We show that the "streaming instability" is an RDI associated with epicyclic oscillations; this provides simple interpretations for its mechanisms and accurate analytic expressions for its growth rates and fastest-growing wavelengths. We extend this analysis to more general dust streaming motions and other waves, including buoyancy and magnetohydrodynamic oscillations, finding various new instabilities. Most importantly, we identify the disk "settling instability," which occurs as dust settles vertically into the midplane of a rotating disk. For small grains, this instability grows many orders of magnitude faster than the standard streaming instability, with a growth rate that is independent of grain size. Growth timescales for realistic dust-to-gas ratios are comparable to the disk orbital period, and the characteristic wavelengths are more than an order of magnitude larger than the streaming instability (allowing the instability to concentrate larger masses). This suggests that in the process of settling, dust will band into rings then filaments or clumps, potentially seeding dust traps, high-metallicity regions that in turn seed the streaming instability, or even overdensities that coagulate or directly collapse to planetesimals.

Current filamentation caused by the electrochemical instability in a fully ionized plasma

International Nuclear Information System (INIS)

Haines, M.G.; Marsh, F.

1983-01-01

This chapter is primarily concerned with the non-linear development of electrothermal instabilities in a fully ionized plasma discharge in which the current is predominantly carried parallel to an applied magnetic field, as in the Tokamak configuration. Discusses instabilities with wave-number K perpendicular to magnetic field B and current J; the non-linear steady state; amplitude of the filaments; and runaway electrons and ion acoustic instabilities. Concludes that the steady non-linear amplitude of the fully developed instability shows a spiky filamentary structure with the possibility of the generation of runaway electrons and ion acoustic turbulence in the current maxima. Finds that the addition of bremsstrahlung radiation loss enhances the instability, reducing the critical ratio of T /SUB e/ to T /SUB i/ for its onset, and yielding a maximum ion temperature attainable by Joule heating and equipartition

Rayleigh-Taylor instability of cylindrical jets with radial motion

Energy Technology Data Exchange (ETDEWEB)

Chen, Xiang M. [GE Nuclear, Wilmington, NC (United States); Schrock, V.E.; Peterson, P.F. [Univ. of California, Berkeley, CA (United States)

1995-09-01

Rayleigh-Taylor instability of an interface between fluids with different densities subjected to accelleration normal to itself has interested researchers for almost a century. The classic analyses of a flat interface by Rayleigh and Taylor have shown that this type of instability depends on the direction of acceleration and the density differences of the two fluids. Plesset later analyzed the stability of a spherically symmetric flows (and a spherical interface) and concluded that the instability also depends on the velocity of the interface as well as the direction and magnitude of radial acceleration. The instability induced by radial motion in cylindrical systems seems to have been neglected by previous researchers. This paper analyzes the Rayleigh-Taylor type of the spherical case, the radial velocity also plays an important role. As an application, the example of a liquid jet surface in an Inertial Confinement Fusion (ICF) reactor design is analyzed.

Gravitomagnetic Instabilities in Anisotropically Expanding Fluids

Science.gov (United States)

Kleidis, Kostas; Kuiroukidis, Apostolos; Papadopoulos, Demetrios B.; Vlahos, Loukas

Gravitational instabilities in a magnetized Friedman-Robertson-Walker (FRW) universe, in which the magnetic field was assumed to be too weak to destroy the isotropy of the model, are known and have been studied in the past. Accordingly, it became evident that the external magnetic field disfavors the perturbations' growth, suppressing the corresponding rate by an amount proportional to its strength. However, the spatial isotropy of the FRW universe is not compatible with the presence of large-scale magnetic fields. Therefore, in this paper we use the general-relativistic version of the (linearized) perturbed magnetohydrodynamic equations with and without resistivity, to discuss a generalized Jeans criterion and the potential formation of density condensations within a class of homogeneous and anisotropically expanding, self-gravitating, magnetized fluids in curved space-time. We find that, for a wide variety of anisotropic cosmological models, gravitomagnetic instabilities can lead to subhorizontal, magnetized condensations. In the nonresistive case, the power spectrum of the unstable cosmological perturbations suggests that most of the power is concentrated on large scales (small k), very close to the horizon. On the other hand, in a resistive medium, the critical wave-numbers so obtained, exhibit a delicate dependence on resistivity, resulting in the reduction of the corresponding Jeans lengths to smaller scales (well bellow the horizon) than the nonresistive ones, while increasing the range of cosmological models which admit such an instability.

Local study of helical magnetorotational instability in viscous Keplerian disks

Science.gov (United States)

MahdaviGharavi, M.; Hajisharifi, K.; Mehidan, H.

2018-03-01

In this paper, regarding the recent detection of significant azimuthal magnetic field in some accretion disks such as protostellar (Donati et al. in Nature 438:466, 2005), the multi-fluid model has been employed to analysis the stability of Keplerian rotational viscous dusty plasma system in a current-free helical magnetic field structure. Using the fluid-Maxwell equations, the general dispersion relation of the excited modes in the system has been obtained by applying the local approximation method in the linear perturbation theory. The typical numerical analysis of the obtained dispersion relation in the high-frequency regime shows that the presence of azimuthal magnetic field component in Keplerian flow has a considerable role in the stability conditions of the system. It also shows that the magnetic field helicity has a stabilization role against the magnetorotational instability (MRI) in the system due to contraction of the unstable wavelength region and decreasing the maximum growth rate of the instability. In this sense, the stabilization role of the viscosity term is more considerable for HMRI (instability in the presence of azimuthal magnetic field component) than the corresponding MRI (instability in the absence of azimuthal magnetic field component). Moreover, considering the discovered azimuthal magnetic field in these systems, the MRI can be arisen in the over-all range of dust grains construction values in contract with traditional MRI. This investigation can greatly contribute to better understanding the physics of some astrophysical phenomena, such as the main source of turbulence and angular momentum transport in protostellar and the other sufficiently ionized astrophysical disks, where the azimuthal magnetic field component in these systems can play a significant role.

Non-uniform current distribution in a force-cooled superconductor under changing magnetic field

International Nuclear Information System (INIS)

Koizumi, Norikiyo

2000-02-01

Strands in a large current force-cooled superconductor, referred to a CICC (cable-in-conduit conductor) hereafter, are coated with formvar (insulated layer) or chrome plating (high resistive layer) to reduce coupling current loss due to magnetic field variation. The author first carried out an experiment of the large superconducting coil consisting of such CICCs for demonstration of their applicability to a large superconducting coil. These CICCs exhibited instability, i.e. the normal zone propagation with thermal runaway (quench), at 1/20 and 1/5 of the expected conductor critical currents, respectively. The author constructed the database of this instability and studies its reason through experimental and theoretical investigations and then finds such instability is caused as a result of non-uniform current distribution in the conductor. Joule heating loss at electrical connections at the ends of the conductor should be small. Therefore, the strands in the CICC are electrically connected from each other with low resistance there. Circulation current is induced in the loop composed of the strands electrically connected at the ends of the conductor if its leakage magnetic flux is not completely vanished. The non-uniform current distribution is caused as a result of superimposition of the circulation and transport currents. The strand carrying large current becomes the normal state when it reaches or approaches to its critical current. Thus, the strands are twisted in order to vanish the leakage magnetic flux. The instability due to the current imbalance was not observed in the middle-scale coil (an element coil, such as a single double-pancake, of a large superconducting coil) consisting of the conductor in which the formvar-coated strands were twisted as above-mentioned. Consequently, it was believed that the leakage magnetic flux could be vanished by the normal twisting. However, the magnetic field increases in a large coil as a result of piling element coils

Study of current instabilities in high resistivity gallium arsenide

International Nuclear Information System (INIS)

Barraud, A.

1968-01-01

We have shown the existence and made a study of the current oscillations produced in high-resistivity gallium arsenide by a strong electric field. The oscillations are associated with the slow travelling of a region of high electrical field across the whole sample. An experimental study of the properties of these instabilities has made it possible for us to distinguish this phenomenon from the Gunn effect, from acoustic-electric effects and from contact effects. In order to account for this type of instability, a differential trapping mechanism involving repulsive impurities is proposed; this mechanism can reduce the concentration of charge carriers in the conduction band at strong electrical fields and can lead to the production of a high-field domain. By developing this model qualitatively we have been able to account for all the properties of high-resistance gallium arsenide crystals subjected to a strong electrical field: increase of the Hall constant, existence of a voltage threshold for these oscillations, production of domains of high field, low rate of propagation of these domains, and finally the possibility of inverting the direction of the propagation of the domain without destroying the latter. A quantitative development of the model makes it possible to calculate the various characteristic parameters of these instabilities. Comparison with experiment shows that there is a good agreement, the small deviations coming especially from the lack of knowledge concerning transport properties in gallium arsenide subjected to high fields. From a study of this model, it appears that the instability phenomenon can occur over a wide range of repulsive centre concentrations, and also for a large range of resistivities. This is the reason why it appears systematically in gallium arsenide of medium and high resistivity. (authors) [fr

Kinematics of Nonlinearly Interacting MHD Instabilities in a Plasma

International Nuclear Information System (INIS)

Hansen, Alexander K.

2000-01-01

Plasmas play host to a wide variety of instabilities. For example, tearing instabilities use finite plasma resistivity to exploit the free energy provided by plasma currents parallel to the magnetic field to alter the magnetic topology of the plasma through a process known as reconnection. These instabilities frequently make themselves known in magnetic confinement experiments such as tokamaks and reversed field pinches (RFPs). In RFP plasmas, in fact, several tearing instabilities (modes) are simultaneously active, and are of large amplitude. Theory predicts that in addition to interacting linearly with magnetic perturbations from outside the plasma, such as field errors or as resistive wall, the modes in the RFP can interact nonlinearly with each other through a three-wave interaction. In the current work investigations of both the linear (external) and nonlinear contributions to the kinematics of the tearing modes in the Madison Symmetric Torus (MST) RFP are reported Theory predicts that tearing modes will respond only to magnetic perturbations that are spatially resonant with them, and was supported by experimental work done on tokamak devices. The results in this work verified that the theory is still applicable to the RFP, in spite of its more complicated magnetic mode structure, involving perturbations of a single poloidal mode number

Higher-order modulation instability in nonlinear fiber optics.

Science.gov (United States)

Erkintalo, Miro; Hammani, Kamal; Kibler, Bertrand; Finot, Christophe; Akhmediev, Nail; Dudley, John M; Genty, Goëry

2011-12-16

We report theoretical, numerical, and experimental studies of higher-order modulation instability in the focusing nonlinear Schrödinger equation. This higher-order instability arises from the nonlinear superposition of elementary instabilities, associated with initial single breather evolution followed by a regime of complex, yet deterministic, pulse splitting. We analytically describe the process using the Darboux transformation and compare with experiments in optical fiber. We show how a suitably low frequency modulation on a continuous wave field induces higher-order modulation instability splitting with the pulse characteristics at different phases of evolution related by a simple scaling relationship. We anticipate that similar processes are likely to be observed in many other systems including plasmas, Bose-Einstein condensates, and deep water waves. © 2011 American Physical Society

Performance through Deformation and Instability

Science.gov (United States)

Bertoldi, Katia

2015-03-01

Materials capable of undergoing large deformations like elastomers and gels are ubiquitous in daily life and nature. An exciting field of engineering is emerging that uses these compliant materials to design active devices, such as actuators, adaptive optical systems and self-regulating fluidics. Compliant structures may significantly change their architecture in response to diverse stimuli. When excessive deformation is applied, they may eventually become unstable. Traditionally, mechanical instabilities have been viewed as an inconvenience, with research focusing on how to avoid them. Here, I will demonstrate that these instabilities can be exploited to design materials with novel, switchable functionalities. The abrupt changes introduced into the architecture of soft materials by instabilities will be used to change their shape in a sudden, but controlled manner. Possible and exciting applications include materials with unusual properties such negative Poisson's ratio, phononic crystals with tunable low-frequency acoustic band gaps and reversible encapsulation systems.

The effect of tangled magnetic fields on instabilities in tokamak plasmas

International Nuclear Information System (INIS)

Thornton, A J; Kirk, A; Harrison, J R; Chapman, I T; Cahyna, P; Nardon, E

2014-01-01

The high pressure gradients in the edge of a tokamak plasma can lead to the formation of explosive plasma instabilities known as edge localised modes (ELMs). The control of ELMs is an important requirement for the next generation of fusion devices such as ITER. Experiments performed on the Mega Amp Spherical Tokamak (MAST) at Culham have shown that the application of non-axisymetric resonant magnetic perturbations (RMPs) can be used to mitigate ELMs. During the application of the RMPs, clear structures are observed in visible- light imaging of the X-point region. These lobes, or tangles, have been observed for the first time and their appearance is correlated with the mitigation of ELMs. Tangle formation is seen to be associated with the RMPs penetrating the plasma and may be important in explaining why the ELM frequency increases during ELM mitigation. Whilst the number and location of the tangles can be explained by vacuum magnetic field modelling, obtaining the correct radial extent of the tangles requires the plasma response to be taken into account

Nonlinear Effects at the Fermilab Recycler e-Cloud Instability

Energy Technology Data Exchange (ETDEWEB)

Balbekov, V. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)

2016-06-10

Theoretical analysis of e-cloud instability in the Fermilab Recycler is represented in the paper. The e-cloud in strong magnetic field is treated as a set of immovable snakes each being initiated by some proton bunch. It is shown that the instability arises because of injection errors of the bunches which increase in time and from bunch to bunch along the batch being amplified by the e-cloud electric field. The particular attention is given to nonlinear additions to the cloud field. It is shown that the nonlinearity is the main factor which restricts growth of the bunch amplitude. Possible role of the field free parts of the Recycler id discussed as well. Results of calculations are compared with experimental data demonstrating good correlation.

Local instabilities in magnetized rotational flows: A short-wavelength approach

OpenAIRE

Kirillov, Oleg N.; Stefani, Frank; Fukumoto, Yasuhide

2014-01-01

We perform a local stability analysis of rotational flows in the presence of a constant vertical magnetic field and an azimuthal magnetic field with a general radial dependence. Employing the short-wavelength approximation we develop a unified framework for the investigation of the standard, the helical, and the azimuthal version of the magnetorotational instability, as well as of current-driven kink-type instabilities. Considering the viscous and resistive setup, our main focus is on the cas...

Snake instability of dark solitons across the BEC-BCS crossover: An effective-field-theory perspective

Science.gov (United States)

Lombardi, G.; Van Alphen, W.; Klimin, S. N.; Tempere, J.

2017-09-01

In the present article the snake instability mechanism for dark solitons in superfluid Fermi gases is studied in the context of a recently developed effective field theory [S. N. Klimin et al., Eur. Phys. J. B 88, 122 (2015), 10.1140/epjb/e2015-60213-4]. This theoretical treatment has proven to be suitable to study stable dark solitons in quasi-one-dimensional setups across the BEC-BCS crossover. In this paper the nodal plane of the stable soliton solution is perturbed by adding a transverse modulation. The numerical solution of the system of coupled nonlinear differential equations describing the amplitude of the perturbation leads to an estimate of the growth rate and characteristic length scale of the instability, which are calculated for a wide range of interaction regimes and compared to other theoretical predictions. The behavior of the maximum transverse size that the atomic cloud can have in order to preserve the stability is described across the BEC-BCS crossover. The analysis of the effects of spin imbalance on this critical length reveals a stabilization of the soliton with increasing imbalance and therefore provides the experimental community with a method to achieve the realization of stable solitons in real three-dimensional configurations, without reducing the system dimensionality.

Two-stream instability in pulsar magnetospheres

International Nuclear Information System (INIS)

Usov, V.V.

1987-01-01

If the electron-positron plasma flow from the pulsar environment is stationary, the two-stream instability does not have enough time to develop in the pulsar magnetosphere. In that case the outflowing electron-positron plasma gathers into separate clouds. The clouds move along magnetic field lines and disperse as they go farther from the pulsar. At a distance of about 10 to the 8th cm from the pulsar surface, the high-energy particles of a given cloud catch up with the low-energy particles that belong to the cloud going ahead of it. In this region of a pulsar magnetosphere, the energy distribution of plasma particles is two-humped, and a two-stream instability may develop. The growth rate of the instability is quite sufficient for its development. 17 references

Molecular Mechanisms of Radiation-Induced Genomic Instability in Human Cells

Energy Technology Data Exchange (ETDEWEB)

Howard L. Liber; Jeffrey L. Schwartz

2005-10-31

There are many different model systems that have been used to study chromosome instability. What is clear from all these studies is that conclusions concerning chromosome instability depend greatly on the model system and instability endpoint that is studied. The model system for our studies was the human B-lymphoblastoid cell line TK6. TK6 was isolated from a spontaneously immortalized lymphoblast culture. Thus there was no outside genetic manipulation used to immortalize them. TK6 is a relatively stable p53-normal immortal cell line (37). It shows low gene and chromosome mutation frequencies (19;28;31). Our general approach to studying instability in TK6 cells has been to isolate individual clones and analyze gene and chromosome mutation frequencies in each. This approach maximizes the possibility of detecting low frequency events that might be selected against in mass cultures.

Rotating magnetic shallow water waves and instabilities in a sphere

Science.gov (United States)

Márquez-Artavia, X.; Jones, C. A.; Tobias, S. M.

2017-07-01

Waves in a thin layer on a rotating sphere are studied. The effect of a toroidal magnetic field is considered, using the shallow water ideal MHD equations. The work is motivated by suggestions that there is a stably stratified layer below the Earth's core mantle boundary, and the existence of stable layers in stellar tachoclines. With an azimuthal background field known as the Malkus field, ?, ? being the co-latitude, a non-diffusive instability is found with azimuthal wavenumber ?. A necessary condition for instability is that the Alfvén speed exceeds ? where ? is the rotation rate and ? the sphere radius. Magneto-inertial gravity waves propagating westward and eastward occur, and become equatorially trapped when the field is strong. Magneto-Kelvin waves propagate eastward at low field strength, but a new westward propagating Kelvin wave is found when the field is strong. Fast magnetic Rossby waves travel westward, whilst the slow magnetic Rossby waves generally travel eastward, except for some ? modes at large field strength. An exceptional very slow westward ? magnetic Rossby wave mode occurs at all field strengths. The current-driven instability occurs for ? when the slow and fast magnetic Rossby waves interact. With strong field the magnetic Rossby waves become trapped at the pole. An asymptotic analysis giving the wave speed and wave form in terms of elementary functions is possible both in polar trapped and equatorially trapped cases.

Hydrodynamic instabilities in inertial confinement fusion

International Nuclear Information System (INIS)

Hoffman, N.M.

1995-01-01

The focus of these (two) lectures is on buoyancy-driven instabilities of the Rayleigh-Taylor type, which are commonly regarded as the most important kind of hydrodynamic instability in inertial-confinement-fusion implosions. The paper is intended to be pedagogical rather than research-oriented, and so is by no means a comprehensive review of work in this field. Rather, it is hoped that the student will find here a foundation on which to build an understanding of current research, and the experienced researcher will find a compilation of useful results. (author)

Jeans instability in a quantum dusty magnetoplasma

International Nuclear Information System (INIS)

Salimullah, M.; Jamil, M.; Shah, H. A.; Murtaza, G.

2009-01-01

Jeans instability in a homogeneous cold quantum dusty plasma in the presence of the ambient magnetic field and the quantum effect arising through the Bohm potential has been examined using the quantum magnetohydrodynamic model. It is found that the Jeans instability is significantly reduced by the presence of the dust-lower-hybrid wave and the ion quantum effect. The minimum wavenumber for Jeans stability depends clearly on ion quantum effect and the dust-lower-hybrid frequency also.

Review of Coupled Bunch Instabilities in the LHC

CERN Document Server

Angal-Kalinin, Deepa

2002-01-01

In order to reach the required luminosity, the LHC will have a large number of high intensity bunches. Coupled bunch instabilities can therefore be excited by the higher order modes (HOMs)of the RF cavities, by parasitic cavities and by the transverse resistive wall effect. This report summarises the growth times of the coupled bunch instabilities taking into account the HOMs (damped or undamped)relevant for the 200 MHz normal conducting cavities, the 400 MHz superconducting cavities, as well as other parasitic cavities. It is shown that, with the damped HOMs of the RF cavities, the coupled bunch instabilities remain within control for the LHC operation.As far as the transverse resistive wall effect at injection disconcerned,it is demonstrated that the corresponding growth times can be safely compensated by the proposed transverse feedback system [1].

Collisionless shock experiments with lasers and observation of Weibel instabilities

Energy Technology Data Exchange (ETDEWEB)

Park, H.-S., E-mail: park1@llnl.gov; Huntington, C. M.; Fiuza, F.; Levy, M. C.; Pollock, B. B.; Remington, B. A.; Ross, J. S.; Ryutov, D. D.; Turnbull, D. P.; Weber, S. V. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Drake, R. P.; Kuranz, C. C. [University of Michigan, Ann Arbor, Michigan 48109 (United States); Froula, D. H.; Rosenberg, M. [Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14636 (United States); Gregori, G.; Meinecke, J. [University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Koenig, M. [LULI, Ecole Polytechnique, Palaiseau (France); Kugland, N. L. [Lam Research Corporation, Fremont, California 94538 (United States); Lamb, D. Q.; Tzeferacos, P. [University of Chicago, Chicago, California 94538 (United States); and others

2015-05-15

Astrophysical collisionless shocks are common in the universe, occurring in supernova remnants, gamma ray bursts, and protostellar jets. They appear in colliding plasma flows when the mean free path for ion-ion collisions is much larger than the system size. It is believed that such shocks could be mediated via the electromagnetic Weibel instability in astrophysical environments without pre-existing magnetic fields. Here, we present laboratory experiments using high-power lasers and investigate the dynamics of high-Mach-number collisionless shock formation in two interpenetrating plasma streams. Our recent proton-probe experiments on Omega show the characteristic filamentary structures of the Weibel instability that are electromagnetic in nature with an inferred magnetization level as high as ∼1% [C. M. Huntington et al., “Observation of magnetic field generation via the weibel instability in interpenetrating plasma flows,” Nat. Phys. 11, 173–176 (2015)]. These results imply that electromagnetic instabilities are significant in the interaction of astrophysical conditions.

Investigation of universal plasma instabilities. Final report

International Nuclear Information System (INIS)

Lashinsky, H.

1977-01-01

This project was undertaken in order to carry out a comprehensive experimental investigation of universal plasma instabilities under a variety of conditions and a wide range of experimental parameters to scale the results appropriately to make comparisons with plasmas of thermonuclear interest. Of particular importance are the roles played by collisions and resonance particles (Landau damping and excitation) and the various stages in the development of the instabilities i.e., the linear onset of the instability, the quasilinear stage, and the transition to turbulence. General nonlinear effects such as mode locking and mode competition, and the relation of these phenomena to plasma turbulence, are also of great interest and were studied experimentally. The ultimate aim was to measure certain plasma transport coefficients in the plasma under stable and turbulent conditions with the particular view of evaluating the effect of the universal plasma instabilities of plasma confinement in a magnetic field

Beta-limiting MHD instabilities in improved performance NSTX spherical torus plasmas

International Nuclear Information System (INIS)

Menard, J.E.; Bell, M.G.; Bell, R.E.

2003-01-01

Global magnetohydrodynamic stability limits in the National Spherical Torus Experiment (NSTX) have increased significantly recently due to a combination of device and operational improvements. First, more routine H-mode operation with broadened pressure profiles allows access to higher normalized beta and lower internal inductance. Second, the correction of a poloidal field coil induced error-field has largely eliminated locked tearing modes during nor- mal operation and increased the maximum achievable beta. As a result of these improvements, peak beta values have reached (not simultaneously) β t = 35%, β N 6.5, N > = 4.5, β / l i =10, and β= 1.4. High β P operation with reduced tearing activity has allowed a doubling of discharge pulse-length to just over 1 second with sustained periods of β N ∼ 6. Details of the β limit scalings and β-limiting instabilities in various operating regimes are described. (author)

Use of an electric field in an electrostatic liquid film radiator.

Science.gov (United States)

Bankoff, S G; Griffing, E M; Schluter, R A

2002-10-01

Experimental and numerical work was performed to further the understanding of an electrostatic liquid film radiator (ELFR) that was originally proposed by Kim et al.(1) The ELFR design utilizes an electric field that exerts a normal force on the interface of a flowing film. The field lowers the pressure under the film in a space radiator and, thereby, prevents leakage through a puncture in the radiator wall. The flowing film is subject to the Taylor cone instability, whereby a cone of fluid forms underneath an electrode and sharpens until a jet of fluid is pulled toward the electrode and disintegrates into droplets. The critical potential for the instability is shown to be as much as an order of magnitude higher than that used in previous designs.(2) Furthermore, leak stoppage experiments indicate that the critical field is adequate to stop leaks in a working radiator.

Plasma instabilities and turbulence in non-Abelian gauge theories

Energy Technology Data Exchange (ETDEWEB)

Scheffler, Sebastian Herwig Juergen

2010-02-17

Several aspects of the thermalisation process in non-Abelian gauge theories are investigated. Both numerical simulations in the classical statistical approximation and analytical computations in the framework of the two-particle-irreducible effective action are carried out and their results are compared to each other. The physical quantities of central importance are the correlation functions of the gauge field in Coulomb and temporal axial gauge as well as the gauge invariant energy-momentum tensor. Following a general introduction, the theoretical framework of the ensuing investigations is outlined. In doing so, the range of validity of the employed approximation schemes is discussed as well. The first main part of the thesis is concerned with the early stage of the thermalisation process where particular emphasis is on the role of plasma instabilities. These investigations are relevant to the phenomenological understanding of present heavy ion collision experiments. First, an ensemble of initial conditions motivated by the ''colour glass condensate'' is developed which captures characteristic properties of the plasma created in heavy ion collisions. Here, the strong anisotropy and the large occupation numbers of low-momentum degrees of freedom are to be highlighted. Numerical calculations demonstrate the occurrence of two kinds of instabilities. Primary instabilities result from the specific initial conditions. Secondary instabilities are caused by nonlinear fluctuation effects of the preceding primary instabilities. The time scale associated with the instabilities is of order 1 fm/c. It is shown that the plasma instabilities isotropize the initially strongly anisotropic ensemble in the domain of low momenta (instabilities in an idealised setup is investigated. In the second part, the

Plasma instabilities and turbulence in non-Abelian gauge theories

International Nuclear Information System (INIS)

Scheffler, Sebastian Herwig Juergen

2010-01-01

Several aspects of the thermalisation process in non-Abelian gauge theories are investigated. Both numerical simulations in the classical statistical approximation and analytical computations in the framework of the two-particle-irreducible effective action are carried out and their results are compared to each other. The physical quantities of central importance are the correlation functions of the gauge field in Coulomb and temporal axial gauge as well as the gauge invariant energy-momentum tensor. Following a general introduction, the theoretical framework of the ensuing investigations is outlined. In doing so, the range of validity of the employed approximation schemes is discussed as well. The first main part of the thesis is concerned with the early stage of the thermalisation process where particular emphasis is on the role of plasma instabilities. These investigations are relevant to the phenomenological understanding of present heavy ion collision experiments. First, an ensemble of initial conditions motivated by the ''colour glass condensate'' is developed which captures characteristic properties of the plasma created in heavy ion collisions. Here, the strong anisotropy and the large occupation numbers of low-momentum degrees of freedom are to be highlighted. Numerical calculations demonstrate the occurrence of two kinds of instabilities. Primary instabilities result from the specific initial conditions. Secondary instabilities are caused by nonlinear fluctuation effects of the preceding primary instabilities. The time scale associated with the instabilities is of order 1 fm/c. It is shown that the plasma instabilities isotropize the initially strongly anisotropic ensemble in the domain of low momenta (< or similar 1 GeV). Essential results can be translated from the gauge group SU(2) to SU(3) by a simple rescaling procedure. Finally, the role of Nielsen-Olesen instabilities in an idealised setup is investigated. In the second part, the quasi

Quantum effects on the Rayleigh-Taylor instability in a horizontal inhomogeneous rotating plasma

International Nuclear Information System (INIS)

Hoshoudy, G. A.

2009-01-01

The Rayleigh-Taylor instability is studied analytically in inhomogeneous plasma rotating uniformly in an external transverse magnetic field. The influence of the quantum mechanism is considered. For a stratified layer the linear growth rate is obtained. Some special cases that isolate the effect of various parameters on the growth rate of the Rayleigh-Taylor instability are discussed. It is shown that for some cases, the presence of the external transverse magnetic field beside the quantum effect will bring about more stability on the Rayleigh-Taylor instability.

Testing the gravitational instability hypothesis?

Science.gov (United States)

Babul, Arif; Weinberg, David H.; Dekel, Avishai; Ostriker, Jeremiah P.

1994-01-01

We challenge a widely accepted assumption of observational cosmology: that successful reconstruction of observed galaxy density fields from measured galaxy velocity fields (or vice versa), using the methods of gravitational instability theory, implies that the observed large-scale structures and large-scale flows were produced by the action of gravity. This assumption is false, in that there exist nongravitational theories that pass the reconstruction tests and gravitational theories with certain forms of biased galaxy formation that fail them. Gravitational instability theory predicts specific correlations between large-scale velocity and mass density fields, but the same correlations arise in any model where (a) structures in the galaxy distribution grow from homogeneous initial conditions in a way that satisfies the continuity equation, and (b) the present-day velocity field is irrotational and proportional to the time-averaged velocity field. We demonstrate these assertions using analytical arguments and N-body simulations. If large-scale structure is formed by gravitational instability, then the ratio of the galaxy density contrast to the divergence of the velocity field yields an estimate of the density parameter Omega (or, more generally, an estimate of beta identically equal to Omega(exp 0.6)/b, where b is an assumed constant of proportionality between galaxy and mass density fluctuations. In nongravitational scenarios, the values of Omega or beta estimated in this way may fail to represent the true cosmological values. However, even if nongravitational forces initiate and shape the growth of structure, gravitationally induced accelerations can dominate the velocity field at late times, long after the action of any nongravitational impulses. The estimated beta approaches the true value in such cases, and in our numerical simulations the estimated beta values are reasonably accurate for both gravitational and nongravitational models. Reconstruction tests

Unified formulation for inhomogeneity-driven instabilities in the lower-hybrid range

International Nuclear Information System (INIS)

Silveira, O.J.G.; Ziebell, L.F.; Gaelzer, R.; Yoon, Peter H.

2002-01-01

A local dispersion relation that describes inhomogeneity-driven instabilities in the lower-hybrid range is derived following a procedure that correctly describes energy exchange between waves and particles in inhomogeneous media, correcting some inherent ambiguities associated with the standard formalism found in the literature. Numerical solutions of this improved dispersion relation show that it constitutes a unified formulation for the instabilities in the lower-hybrid range, describing the so-called modified two-stream instability, excited by the ion cross-field drift, including the ion Weibel instability, and also describing the lower-hybrid drift instability, which is due to inhomogeneity effects on the electron population

The Onset of Magnetic Reconnection: Tearing Instability in Current Sheets with a Guide Field

Science.gov (United States)

Daldorff, L. K. S.; Klimchuk, J. A.; Knizhnik, K. J.

2016-12-01

Magnetic reconnection is fundamental to many solar phenomena, ranging from coronal heating, to jets, to flares and CMEs. A poorly understood yet crucial aspect of reconnection is that it does not occur until magnetic stresses have built to sufficiently high levels for significant energy release. If reconnection were to happen too soon, coronal heating would be weak and flares would be small. As part of our program to study the onset conditions for magnetic reconnection, we have investigated the instability of current sheets to tearing. Surprisingly little work has been done on this problem for sheets that include a guide field, i.e., for which the field rotates by less than 180 degrees. This is the most common situation on the Sun. We present numerical 3D resistive MHD simulations of several sheets and show how the behaviour depends on the shear angle (rotation). We compare our results to the predictions of linear theory and discuss the nonlinear evolution in terms of plasmoid formation and the interaction of different oblique tearing modes. The relevance to the Sun is explained.

Lower hybrid parametric instabilities nonuniform pump waves and tokamak applications

International Nuclear Information System (INIS)

Berger, R.L.; Chen, L.; Kaw, P.K.; Perkins, F.W.

1976-11-01

Electrostatic lower hybrid ''pump'' waves often launched into tokamak plasmas by structures (e.g., waveguides) whose dimensions are considerably smaller than characteristic plasma sizes. Such waves propagate in well-defined resonance cones and give rise to parametric instabilities driven by electron E x B velocities. The finite size of the resonance cone region determines the threshold for both convective quasimode decay instabilities and absolute instabilities. The excitation of absolute instabilities depends on whether a travelling or standing wave pump model is used; travelling wave pumps require the daughter waves to have a definite frequency shift. Altogether, parametric instabilities driven by E x B velocities occur for threshold fields significantly below the threshold for filamentation instabilities driven by pondermotive forces. Applications to tokamak heating show that nonlinear effects set in when a certain power-per-wave-launching port is exceeded

Wetting front instability in an initially wet unsaturated fracture

International Nuclear Information System (INIS)

Nicholl, M.J.; Glass, R.J.; Nguyen, H.A.

1992-01-01

Experimental results exploring gravity-driven wetting front instability in a pre-wetted, rough-walled analog fracture are presented. Initial conditions considered include a uniform moisture field wetted to field capacity of the analog fracture and the structured moisture field created by unstable infiltration into an initially dry fracture. As in previous studies performed under dry initial conditions, instability was found to result both at the cessation of stable infiltration and at flux lower than the fracture capacity under gravitational driving force. Individual fingers were faster, narrower, longer, and more numerous than observed under dry initial conditions. Wetting fronts were found to follow existing wetted structure, providing a mechanism for rapid recharge and transport

Wetting front instability in an initially wet unsaturated fracture

International Nuclear Information System (INIS)

Nicholl, M.J.; Glass, R.J.; Nguyen, H.A.

1993-01-01

Experimental results exploring gravity-driven wetting from instability in a pre-wetted, rough-walled analog fractures such as those at Yucca Mountain are presented. Initial conditions considered include a uniform moisture field wetted to field capacity of the analog fracture and the structured moisture field created by unstable infiltration into an initially dry fracture. As in previous studies performed under dry initial conditions, instability was found to result both at the cessation of stable infiltration and at flux lower than the fracture capacity under gravitational driving force. Individual fingers were faster, narrower, longer, and more numerous than observed under dry initial conditions. Wetting fronts were found to follow existing wetted structure, providing a mechanism for rapid recharge and transport

Coherent betatron instability in the Tevatron

International Nuclear Information System (INIS)

Bogacz, S.A.; Harrison, M.; Ng, K.Y.

1988-01-01

The coherent betatron instability was first observed during the recent 1987-88 Tevatron fixed target run. In this operating mode 1000 consecutive bunches are loaded into the machine at 150 GeV with a bunch spacing of 18.8 /times/ 10 -9 sec (53 MHz). The normalized transverse emittance is typically 15 π /times/ 10 -6 m rad in each plane with a longitudinal emittance of about 1.5 eV-sec. The beam is accelerated to 800 GeV in 13 sec. and then it is resonantly extracted during a 23 sec flat top. As the run progressed the bunch intensities were increased until at about 1.4 /times/ 10 10 ppb (protons per bunch) we experienced the onset of a coherent horizontal oscillation taking place in the later stages of the acceleration cycle (>600 GeV). This rapidly developing coherent instability results in a significant emittance growth, which limits machine performance and in a catastrophic scenario it even prevents extraction of the beam. In this paper we will present a simple analytic description of the observed instability. We will show that a combination of a resistive wall coupled bunch effect and a single bunch slow head-tail instability is consistent with the above observations. Finally, a systematic numerical analysis of our model (growth-time vs chromaticity plots) points to the existence of the ≥1 slow head-tail modes as a plausible mechanism for the observed coherent instability. This last claim, as mentioned before, does not have conclusive experimental evidence, although it is based on a very good agreement between the measured values of the instability growth-time and the ones calculated on the basis of our model. 4 refs., 3 figs

Transient growth of a Vlasov plasma in a weakly inhomogeneous magnetic field

KAUST Repository

Ratushnaya, Valeria

2016-12-17

We investigate the stability properties of a collisionless Vlasov plasma in a weakly inhomogeneous magnetic field using non-modal stability analysis. This is an important topic in a physics of tokamak plasma rich in various types of instabilities. We consider a thin tokamak plasma in a Maxwellian equilibrium, subjected to a small arbitrary perturbation. Within the framework of kinetic theory, we demonstrate the emergence of short time scale algebraic instabilities evolving in a stable magnetized plasma. We show that the linearized governing operator (Vlasov operator) is non-normal leading to the transient growth of the perturbations on the time scale of several plasma periods that is subsequently followed by Landau damping. We calculate the first-order distribution function and the electric field and study the dependence of the transient growth characteristics on the magnetic field strength and perturbation parameters of the system. We compare our results with uniformly magnetized plasma and field-free Vlasov plasma.

Transient growth of a Vlasov plasma in a weakly inhomogeneous magnetic field

KAUST Repository

Ratushnaya, Valeria; Samtaney, Ravi

2016-01-01

We investigate the stability properties of a collisionless Vlasov plasma in a weakly inhomogeneous magnetic field using non-modal stability analysis. This is an important topic in a physics of tokamak plasma rich in various types of instabilities. We consider a thin tokamak plasma in a Maxwellian equilibrium, subjected to a small arbitrary perturbation. Within the framework of kinetic theory, we demonstrate the emergence of short time scale algebraic instabilities evolving in a stable magnetized plasma. We show that the linearized governing operator (Vlasov operator) is non-normal leading to the transient growth of the perturbations on the time scale of several plasma periods that is subsequently followed by Landau damping. We calculate the first-order distribution function and the electric field and study the dependence of the transient growth characteristics on the magnetic field strength and perturbation parameters of the system. We compare our results with uniformly magnetized plasma and field-free Vlasov plasma.

Dissipative drift instability in dusty plasma

Directory of Open Access Journals (Sweden)

Nilakshi Das

2012-03-01

Full Text Available An investigation has been done on the very low-frequency electrostatic drift waves in a collisional dusty plasma. The dust density gradient is taken perpendicular to the magnetic field B0⃗, which causes the drift wave. In this case, low-frequency drift instabilities can be driven by E1⃗×B0⃗ and diamagnetic drifts, where E1⃗ is the perturbed electric field. Dust charge fluctuation is also taken into consideration for our study. The dust- neutral and ion-neutral collision terms have been included in equations of motion. It is seen that the low-frequency drift instability gets damped in such a system. Both dust charging and collision of plasma particles with the neutrals may be responsible for the damping of the wave. Both analytical and numerical techniques have been used while developing the theory.

Off-equatorial current-driven instabilities ahead of approaching dipolarization fronts

Science.gov (United States)

Zhang, Xu; Angelopoulos, V.; Pritchett, P. L.; Liu, Jiang

2017-05-01

Recent kinetic simulations have revealed that electromagnetic instabilities near the ion gyrofrequency and slightly away from the equatorial plane can be driven by a current parallel to the magnetic field prior to the arrival of dipolarization fronts. Such instabilities are important because of their potential contribution to global electromagnetic energy conversion near dipolarization fronts. Of the several instabilities that may be consistent with such waves, the most notable are the current-driven electromagnetic ion cyclotron instability and the current-driven kink-like instability. To confirm the existence and characteristics of these instabilities, we used observations by two Time History of Events and Macroscale Interactions during Substorms satellites, one near the neutral sheet observing dipolarization fronts and the other at the boundary layer observing precursor waves and currents. We found that such instabilities with monochromatic signatures are rare, but one of the few cases was selected for further study. Two different instabilities, one at about 0.3 Hz and the other at a much lower frequency, 0.02 Hz, were seen in the data from the off-equatorial spacecraft. A parallel current attributed to an electron beam coexisted with the waves. Our instability analysis attributes the higher-frequency instability to a current-driven ion cyclotron instability and the lower frequency instability to a kink-like instability. The current-driven kink-like instability we observed is consistent with the instabilities observed in the simulation. We suggest that the currents needed to excite these low-frequency instabilities are so intense that the associated electron beams are easily thermalized and hence difficult to observe.

Anisotropic electron distribution functions and the transition between the Weibel and the whistler instabilities

International Nuclear Information System (INIS)

Pegoraro, F.; Palodhi, L.; Califano, F.

2013-01-01

Electron distribution functions that are anisotropic in phase space are a common feature of collisionless plasmas both in space and in the laboratory and the investigation of the processes through which these distributions relax is of primary interest. In fact, the free energy that is made available by the unbalance of the particle “temperatures” in the different directions can be transferred, depending on the plasma conditions, to quasistatic magnetic fields, to electromagnetic or electrostatic coherent structures or to particle acceleration. The anisotropy of the electron distribution function in an unmagnetized plasma can give rise to the onset of the well known Weibel instability which generates a quasistatic magnetic field. If a magnetic field is already present in the plasma, the Weibel instability driven by the anisotropy of the electron energy distribution turns into the so called whistler instability, in which case circularly polarized whistler waves are generated by the relaxation of the electron distribution function. Whistler waves are actually ubiquitous in plasmas and their generation has been extensively studied in recent years in the laboratory. Whistler instabilities have been reported in space where bursts of whistler mode magnetic noise are found to be present in the magnetosphere, close to the magnetopause and are also a likely source of several different magnetospheric fluctuations including plasmaspheric hiss and magnetospheric chorus. In this presentation the transition between non resonant (Weibel-type) and resonant (whistler) instabilities is investigated numerically in plasma configurations with an ambient magnetic field of increasing amplitudes. The Vlasov-Maxwell system is solved in a configuration where the fields have three components but depend only on one coordinate and on time. The nonlinear evolution of these instabilities is shown to lead to the excitation of electromagnetic and electrostatic modes at the first few harmonics

Electroacoustic control of Rijke tube instability

Science.gov (United States)

Zhang, Yumin; Huang, Lixi

2017-11-01

Unsteady heat release coupled with pressure fluctuation triggers the thermoacoustic instability which may damage a combustion chamber severely. This study demonstrates an electroacoustic control approach of suppressing the thermoacoustic instability in a Rijke tube by altering the wall boundary condition. An electrically shunted loudspeaker driver device is connected as a side-branch to the main tube via a small aperture. Tests in an impedance tube show that this device has sound absorption coefficient up to 40% under normal incidence from 100 Hz to 400 Hz, namely over two octaves. Experimental result demonstrates that such a broadband acoustic performance can effectively eliminate the Rijke-tube instability from 94 Hz to 378 Hz (when the tube length varies from 1.8 m to 0.9 m, the first mode frequency for the former is 94 Hz and the second mode frequency for the latter is 378 Hz). Theoretical investigation reveals that the devices act as a damper draining out sound energy through a tiny hole to eliminate the instability. Finally, it is also estimated based on the experimental data that small amount of sound energy is actually absorbed when the system undergoes a transition from the unstable to stable state if the contrpaol is activated. When the system is actually stabilized, no sound is radiated so no sound energy needs to be absorbed by the control device.

Instability of equatorial protons in Jupiter's mid-magnetosphere

International Nuclear Information System (INIS)

Northrop, T.G.; Schardt, A.W.

1980-01-01

Two different models for the distribution function are fit to the Jovian protons seen by Pioneer 10 inbound. The models reproduce the observed energy and angular distributions. These models are then used to assess the collisionless mirror instability. Because of the pancake proton angular distributions in the equatorial ring current region, the ring current particle population appears to be mirror unstable at times, with instability growth rates of approx.10 min. Such a time is consistent with observed proton flux autocorrelation times. An instability such as this (there are other candidates) may be responsible for the previously established proton flux flowing parallel to the magnetic field away from the equatorial region

Patellofemoral instability in children: T2 relaxation times of the patellar cartilage in patients with and without patellofemoral instability and correlation with morphological grading of cartilage damage.

Science.gov (United States)

Kang, Chang Ho; Kim, Hee Kyung; Shiraj, Sahar; Anton, Christopher; Kim, Dong Hoon; Horn, Paul S

2016-07-01

Patellofemoral instability is one of the most common causes of cartilage damage in teenagers. To quantitatively evaluate the patellar cartilage in patients with patellofemoral instability using T2 relaxation time maps (T2 maps), compare the values to those in patients without patellofemoral instability and correlate them with morphological grades in patients with patellofemoral instability. Fifty-three patients with patellofemoral instability (mean age: 15.9 ± 2.4 years) and 53 age- and gender-matched patients without patellofemoral instability were included. Knee MR with axial T2 map was performed. Mean T2 relaxation times were obtained at the medial, central and lateral zones of the patellar cartilage and compared between the two groups. In the patellofemoral instability group, morphological grading of the patellar cartilage (0-4) was performed and correlated with T2 relaxation times. Mean T2 relaxation times were significantly longer in the group with patellofemoral instability as compared to those of the control group across the patellar cartilage (Student's t-test, Ppatellofemoral instability, patellar cartilage damage occurs across the entire cartilage with the highest T2 values at the apex. T2 relaxation times directly reflect the severity in low-grade cartilage damage, which implies an important role for T2 maps in differentiating between normal and low-grade cartilage damage.

Nonlinear stage of a Z-pinch instability

International Nuclear Information System (INIS)

Garanin, S.F.; Chernyshev, Y.D.

1987-01-01

The nonlinear evolution of the sausage instability is analyzed for a Z-pinch with a fully developed skin effect in the current. Two-dimensional numerical calculations carried out on the sausage instability show that its occurrence leads to a stage describable by a self-similar solution when the length of the neck is fixed and the plasma compression is isentropic. At a perturbation wavelength small in comparison with the pinch radius, this stage is preceded by a stage which reduces to a nonlinear Rayleigh--Taylor instability. The dynamics of the motion of magnetic field ''bubbles'' and of plasma ''jets'' is analyzed in this case. The plasma jets emerging from the pinch do not block the pinch from the current source

Anisotropic gravitational instability

International Nuclear Information System (INIS)

Polyachenko, V.L.; Fridman, A.M.

1988-01-01

Exact solutions of stability problems are obtained for two anisotropic gravitational systems of different geometries - a layer of finite thickness at rest and a rotating cylinder of finite radius. It is shown that the anisotropic gravitational instability which develops in both cases is of Jeans type. However, in contrast to the classical aperiodic Jeans instability, this instability is oscillatory. The physics of the anisotropic gravitational instability is investigated. It is shown that in a gravitating layer this instability is due, in particular, to excitation of previously unknown interchange-Jeans modes. In the cylinder, the oscillatory Jeans instability is associated with excitation of a rotational branch, this also being responsible for the beam gravitational instability. This is the reason why this instability and the anisotropic gravitational instability have so much in common

The effect of magnetic field on instabilities of heat transfer from an obstacle in a channel

International Nuclear Information System (INIS)

Rashidi, S.; Esfahani, J.A.

2015-01-01

This paper presents forced convective heat transfer in a channel with a built-in square obstacle. The governing equations with the boundary conditions are solved using a finite volume method. The computations were done for a fixed blockage ratio (S=1/8) at Pr=0.71, and Reynolds (Re) and Stuart (N) numbers ranging from 1 to 250 and 0 to 10, respectively. The results are presented to show the effect of the channel walls and streamwise magnetic field at different Reynolds numbers on forced convection heat transfer from a square cylinder. A correlation is obtained for Nusselt number, in which the effect of a magnetic field is taken into account. The obtained results revealed that the existence of channel walls decreases the effects of magnetic field on Nusselt number. It also showed that by increasing Stuart number the thickness of thermal boundary layer increases and the convective heat transfer decreases. - Highlights: • The magnetic field is used to control the instabilities of heat transfer. • The thickness of thermal boundary layer increases by increasing Stuart number. • Unsteadiness in temperature field increases with increase in Reynolds number. • Time-averaged Nusselt number decreases with increase in Stuart number. • The Lorentz forces are much denser near the surface of the obstacle

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

3D Relativistic Magnetohydrodynamic Simulations of Current-Driven Instability. 1; Instability of a Static Column

Science.gov (United States)

Mizuno, Yosuke; Lyubarsky, Yuri; ishikawa, Ken-Ichi; Hardee, Philip E.

2010-01-01

We have investigated the development of current-driven (CD) kink instability through three-dimensional relativistic MHD simulations. A static force-free equilibrium helical magnetic configuration is considered in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. We found that the initial configuration is strongly distorted but not disrupted by the kink instability. The instability develops as predicted by linear theory. In the non-linear regime the kink amplitude continues to increase up to the terminal simulation time, albeit at different rates, for all but one simulation. The growth rate and nonlinear evolution of the CD kink instability depends moderately on the density profile and strongly on the magnetic pitch profile. The growth rate of the kink mode is reduced in the linear regime by an increase in the magnetic pitch with radius and the non-linear regime is reached at a later time than for constant helical pitch. On the other hand, the growth rate of the kink mode is increased in the linear regime by a decrease in the magnetic pitch with radius and reaches the non-linear regime sooner than the case with constant magnetic pitch. Kink amplitude growth in the non-linear regime for decreasing magnetic pitch leads to a slender helically twisted column wrapped by magnetic field. On the other hand, kink amplitude growth in the non-linear regime nearly ceases for increasing magnetic pitch.

THREE-DIMENSIONAL RELATIVISTIC MAGNETOHYDRODYNAMIC SIMULATIONS OF CURRENT-DRIVEN INSTABILITY. I. INSTABILITY OF A STATIC COLUMN

International Nuclear Information System (INIS)

Mizuno, Yosuke; Nishikawa, Ken-Ichi; Lyubarsky, Yuri; Hardee, Philip E.

2009-01-01

We have investigated the development of current-driven (CD) kink instability through three-dimensional relativistic magnetohydrodynamic simulations. A static force-free equilibrium helical magnetic configuration is considered in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. We found that the initial configuration is strongly distorted but not disrupted by the kink instability. The instability develops as predicted by linear theory. In the nonlinear regime, the kink amplitude continues to increase up to the terminal simulation time, albeit at different rates, for all but one simulation. The growth rate and nonlinear evolution of the CD kink instability depend moderately on the density profile and strongly on the magnetic pitch profile. The growth rate of the kink mode is reduced in the linear regime by an increase in the magnetic pitch with radius and reaches the nonlinear regime at a later time than the case with constant helical pitch. On the other hand, the growth rate of the kink mode is increased in the linear regime by a decrease in the magnetic pitch with radius and reaches the nonlinear regime sooner than the case with constant magnetic pitch. Kink amplitude growth in the nonlinear regime for decreasing magnetic pitch leads to a slender helically twisted column wrapped by magnetic field. On the other hand, kink amplitude growth in the nonlinear regime nearly ceases for increasing magnetic pitch.

The longitudinal wall impedance instability in a heavy-ion fusion driver

International Nuclear Information System (INIS)

Callahan, D.A.; Langdon, A.B.; Friedman, A.; Haber, I.

1997-01-01

For more than ten years [J. Bisognano, I. Haber, L. Smith, IEEE Trans. Nucl. Sci. NS-30, 2501 (1983)], the longitudinal wall impedance instability was thought to be a serious threat to the success of heavy-ion driven inertial confinement fusion. This instability is a open-quotes resistive wallclose quotes instability, driven by the impedance of the induction modules used to accelerate the beam. Early estimates of the instability growth rate predicted tens of e-folds due to the instability which would modulate the current and increase the longitudinal momentum spread and prevent focusing the ion beam on the small spot needed at the target. We have simulated this instability using an r-z particle-in-cell code which includes a model for the module impedance. These simulations, using driver parameters, show that growth due to the instability is smaller than in previous calculations. We have seen that growth is mainly limited to one head to tail transit by a space-charge wave. In addition, the capacitive component of the module impedance, which was neglected in the early work of Lee [E. P. Lee, Proc. Linear Accelerator Conference, (UCRL-86452), Santa Fe, NM, 1981] significantly reduces the growth rate. We have also included in the simulation intermittently applied axial confining fields which are thought to be the major source of perturbations to seed the longitudinal instability. Simulations show the beam can adjust to a systematic error in the longitudinal confining fields while a random error excites the most unstable wavelength of the instability. These simulations show that the longitudinal instability must be taken into account in a driver design, but it is not the major factor it was once thought to be. copyright 1997 American Institute of Physics

Hessian matrix approach for determining error field sensitivity to coil deviations

Science.gov (United States)

Zhu, Caoxiang; Hudson, Stuart R.; Lazerson, Samuel A.; Song, Yuntao; Wan, Yuanxi

2018-05-01

The presence of error fields has been shown to degrade plasma confinement and drive instabilities. Error fields can arise from many sources, but are predominantly attributed to deviations in the coil geometry. In this paper, we introduce a Hessian matrix approach for determining error field sensitivity to coil deviations. A primary cost function used for designing stellarator coils, the surface integral of normalized normal field errors, was adopted to evaluate the deviation of the generated magnetic field from the desired magnetic field. The FOCUS code (Zhu et al 2018 Nucl. Fusion 58 016008) is utilized to provide fast and accurate calculations of the Hessian. The sensitivities of error fields to coil displacements are then determined by the eigenvalues of the Hessian matrix. A proof-of-principle example is given on a CNT-like configuration. We anticipate that this new method could provide information to avoid dominant coil misalignments and simplify coil designs for stellarators.

The thermo magnetic instability in hot viscose plasmas

Science.gov (United States)

Haghani, A.; Khosravi, A.; Khesali, A.

2017-10-01

Magnetic Rotational Instability (MRI) can not performed well in accretion disks with strong magnetic field. Studies have indicated a new type of instability called thermomagnetic instability (TMI) in systems where Nernst coefficient and gradient temperature were considered. Nernst coefficient would appear if Boltzman equation could be expanded through ω_{Be} (cyclotron frequency). However, the growth rate of this instability was two magnitude orders below MRI growth (Ωk), which could not act the same as MRI. Therefor, a higher growth rate of unstable modes was needed. In this paper, rotating viscid hot plasma with strong magnetic filed was studied. Firstly, a constant alpha viscosity was studied and then a temperature sensitive viscosity. The results showed that the temperature sensitive viscosity would be able to increase the growth rate of TMI modes significantly, hence capable of acting similar to MRI.

Efficiency Versus Instability in Plasma Accelerators

Energy Technology Data Exchange (ETDEWEB)

Lebedev, Valeri [Fermilab; Burov, Alexey [Fermilab; Nagaitsev, Sergei [Fermilab

2017-01-05

Plasma wake-field acceleration in a strongly nonlinear (a.k.a. the blowout) regime is one of the main candidates for future high-energy colliders. For this case, we derive a universal efficiency-instability relation, between the power efficiency and the key instability parameter of the witness bunch. We also show that in order to stabilize the witness bunch in a regime with high power efficiency, the bunch needs to have high energy spread, which is not presently compatible with collider-quality beam properties. It is unclear how such limitations could be overcome for high-luminosity linear colliders.

Magnetohydrodynamic instability in annular linear induction pump

International Nuclear Information System (INIS)

Araseki, Hideo; Kirillov, Igor R.; Preslitsky, Gennady V.; Ogorodnikov, Anatoly P.

2006-01-01

In the previous work, the authors showed some detailed aspects of the magnetohydrodynamic instability arising in an annular linear induction pump: the instability is accompanied with a low frequency pressure pulsation in the range of 0-10 Hz when the magnetic Reynolds number is larger than unity; the low frequency pressure pulsation is produced by the sodium vortices that come from some azimuthal non-uniformity of the applied magnetic field or of the sodium inlet velocity. In the present work, an experiment and a numerical analysis are carried out to verify the pump winding phase shift that is expected as an effective way to suppress the instability. The experimental data shows that the phase shift suppresses the instability unless the slip value is so high, but brings about a decrease of the developed pressure. The numerical results indicate that the phase shift causes a local decrease of the electromagnetic force, which results in the suppression of the instability and the decrease of the developed pressure. In addition, it is exhibited that the intensity of the double-supply-frequency pressure pulsation is in nearly the same level in the case with and without the phase shift

Jeans instability of rotating magnetized quantum plasma: Influence of radiation

Energy Technology Data Exchange (ETDEWEB)

Joshi, H., E-mail: hjoshi8525@yahoo.com [Department of Physics, Mewar University, Chittorgarh (Raj.) India (India); Pensia, R. K. [Department of Physics, Govt. Girls College, Neemuch (M.P.) India (India)

2015-07-31

The effect of radiative heat-loss function and rotation on the Jeans instability of quantum plasma is investigated. The basic set of equations for this problem is constructed by considering quantum magnetohydrodynamic (QMHD) model. Using normal mode analysis, the general dispersion relation is obtained. This dispersion relation is studied in both, longitudinal and transverse direction of propagations. In both case of longitudinal and transverse direction of propagation, the Jeans instability criterion is modified due to presence of radiative heat-loss function and quantum correction.

Oblique Alfvén instabilities driven by compensated currents

Energy Technology Data Exchange (ETDEWEB)

Malovichko, P. [Main Astronomical Observatory, NASU, Kyiv (Ukraine); Voitenko, Y.; De Keyser, J., E-mail: voitenko@oma.be [Solar-Terrestrial Centre of Excellence, Space Physics Division, Belgian Institute for Space Aeronomy, Ringlaan-3-Avenue Circulaire, B-1180 Brussels (Belgium)

2014-01-10

Compensated-current systems created by energetic ion beams are widespread in space and astrophysical plasmas. The well-known examples are foreshock regions in the solar wind and around supernova remnants. We found a new oblique Alfvénic instability driven by compensated currents flowing along the background magnetic field. Because of the vastly different electron and ion gyroradii, oblique Alfvénic perturbations react differently on the currents carried by the hot ion beams and the return electron currents. Ultimately, this difference leads to a non-resonant aperiodic instability at perpendicular wavelengths close to the beam ion gyroradius. The instability growth rate increases with increasing beam current and temperature. In the solar wind upstream of Earth's bow shock, the instability growth time can drop below 10 proton cyclotron periods. Our results suggest that this instability can contribute to the turbulence and ion acceleration in space and astrophysical foreshocks.

Oblique Alfvén instabilities driven by compensated currents

International Nuclear Information System (INIS)

Malovichko, P.; Voitenko, Y.; De Keyser, J.

2014-01-01

Compensated-current systems created by energetic ion beams are widespread in space and astrophysical plasmas. The well-known examples are foreshock regions in the solar wind and around supernova remnants. We found a new oblique Alfvénic instability driven by compensated currents flowing along the background magnetic field. Because of the vastly different electron and ion gyroradii, oblique Alfvénic perturbations react differently on the currents carried by the hot ion beams and the return electron currents. Ultimately, this difference leads to a non-resonant aperiodic instability at perpendicular wavelengths close to the beam ion gyroradius. The instability growth rate increases with increasing beam current and temperature. In the solar wind upstream of Earth's bow shock, the instability growth time can drop below 10 proton cyclotron periods. Our results suggest that this instability can contribute to the turbulence and ion acceleration in space and astrophysical foreshocks.

A free boundary approach to the Rosensweig instability of ferrofluids

Science.gov (United States)

Parini, Enea; Stylianou, Athanasios

2018-04-01

We establish the existence of saddle points for a free boundary problem describing the two-dimensional free surface of a ferrofluid undergoing normal field instability. The starting point is the ferrohydrostatic equations for the magnetic potentials in the ferrofluid and air, and the function describing their interface. These constitute the strong form for the Euler-Lagrange equations of a convex-concave functional, which we extend to include interfaces that are not necessarily graphs of functions. Saddle points are then found by iterating the direct method of the calculus of variations and applying classical results of convex analysis. For the existence part, we assume a general nonlinear magnetization law; for a linear law, we also show, via convex duality, that the saddle point is a constrained minimizer of the relevant energy functional.

The superradiant instability regime of the spinning Kerr black hole

Science.gov (United States)

Hod, Shahar

2016-07-01

Spinning Kerr black holes are known to be superradiantly unstable to massive scalar perturbations. We here prove that the instability regime of the composed Kerr-black-hole-massive-scalar-field system is bounded from above by the dimensionless inequality Mμ r+ is the dimensionless ratio between the horizon radii of the black hole. It is further shown that this analytically derived upper bound on the superradiant instability regime of the spinning Kerr black hole agrees with recent numerical computations of the instability resonance spectrum.

Peierls instability and optical properties of bilayer polyacene

Energy Technology Data Exchange (ETDEWEB)

Zhang, Longlong, E-mail: zhanglonglong@tyut.edu.cn [The College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024 (China); Xie, Shijie [School of Physics, Shandong University, Jinan 250100 (China)

2017-05-03

Highlights: • The Peierls instability of bilayer polyacene is discussed. • The external electric field effect on bilayer polyacene is discussed. • The pressure effect on bilayer polyacene is discussed. • The optical properties of bilayer polyacene are discussed. - Abstract: We reveal that bilayer polyacene can be the gapped state due to the intralayer Peierls instability. There are six topologically inequivalent Peierls-distorted structures and they are degenerate in energy. The external electric field can tune the Peierls gap and induce the semiconductor-to-metallic phase transitions. The optical conductivity spectra are calculated in an attempt to categorize the Peierls-distorted structures. The strength of the interlayer coupling essentially affects the electronic properties and the optical selection rules.

D branes in background fluxes and Nielsen-Olesen instabilities

International Nuclear Information System (INIS)

Russo, Jorge G.

2016-01-01

In quantum field theory, charged particles with spin ≥1 may become tachyonic in the present of magnetic fluxes above some critical field, signaling an instability of the vacuum. The phenomenon is generic, in particular, similar instabilities are known to exist in open and closed string theory, where a spinning string state can become tachyonic above a critical field. In compactifications involving RR fluxes F_p_+_2, the quantum states which could become tachyonic by the same Nielsen-Olesen mechanism are Dp branes. By constructing an appropriate background with RR magnetic flux that takes into account back-reaction, we identify the possible tachyonic Dp brane states and compute the formula for the energy spectrum in a sector. More generally, we argue that in any background RR magnetic flux, there are high spin Dp quantum states which become very light at critical fields.

D branes in background fluxes and Nielsen-Olesen instabilities

Energy Technology Data Exchange (ETDEWEB)

Russo, Jorge G. [Institució Catalana de Recerca i Estudis Avançats (ICREA),Pg. Lluis Companys, 23, 08010 Barcelona (Spain); Department de Fisica Cuantica i Astrofisica and Institut de Ciències del Cosmos,Universitat de Barcelona, Martí Franquès, 1, 08028 Barcelona (Spain)

2016-06-06

In quantum field theory, charged particles with spin ≥1 may become tachyonic in the present of magnetic fluxes above some critical field, signaling an instability of the vacuum. The phenomenon is generic, in particular, similar instabilities are known to exist in open and closed string theory, where a spinning string state can become tachyonic above a critical field. In compactifications involving RR fluxes F{sub p+2}, the quantum states which could become tachyonic by the same Nielsen-Olesen mechanism are Dp branes. By constructing an appropriate background with RR magnetic flux that takes into account back-reaction, we identify the possible tachyonic Dp brane states and compute the formula for the energy spectrum in a sector. More generally, we argue that in any background RR magnetic flux, there are high spin Dp quantum states which become very light at critical fields.

Instability and electrical response of small laminar coflow diffusion flames under AC electric fields: Toroidal vortex formation and oscillating and spinning flames

KAUST Repository

Xiong, Yuan; Chung, Suk-Ho; Cha, Min

2016-01-01

Dynamical and electrical responses of a small coflow diffusion flame were investigated by applying a high-voltage alternating current (AC), to a fuel jet nozzle. High-speed imaging and electrical diagnostics were adopted to capture flame dynamics and electrical signals, such as voltage (V ), frequency (f ) and current (I ). In the V -f domain of 0-5kV and 0-5kHz, AC-driven instabilities, resulting in various flame modes such as an oscillation, pinch-off and spinning of flames were identified. Characteristic frequency of each mode was determined and a visualization of near-nozzle flow structures suggested a close causality of initial counter-rotating vortices (inner and outer toroidal vortices - ITV and OTV), to the other observed flame. An axisymmetric ITV shedding was identified within oscillating and pinch-off modes, while asymmetric ITV shedding was identified with the spinning mode. Integrated electric power over several AC periods correlated well with variation in the flame surface area for these instabilities, demonstrating that measured electric power is a potential indicator of combustion instabilities in electric-field-assisted combustion.

Instability and electrical response of small laminar coflow diffusion flames under AC electric fields: Toroidal vortex formation and oscillating and spinning flames

KAUST Repository

Xiong, Yuan

2016-06-24

Dynamical and electrical responses of a small coflow diffusion flame were investigated by applying a high-voltage alternating current (AC), to a fuel jet nozzle. High-speed imaging and electrical diagnostics were adopted to capture flame dynamics and electrical signals, such as voltage (V ), frequency (f ) and current (I ). In the V -f domain of 0-5kV and 0-5kHz, AC-driven instabilities, resulting in various flame modes such as an oscillation, pinch-off and spinning of flames were identified. Characteristic frequency of each mode was determined and a visualization of near-nozzle flow structures suggested a close causality of initial counter-rotating vortices (inner and outer toroidal vortices - ITV and OTV), to the other observed flame. An axisymmetric ITV shedding was identified within oscillating and pinch-off modes, while asymmetric ITV shedding was identified with the spinning mode. Integrated electric power over several AC periods correlated well with variation in the flame surface area for these instabilities, demonstrating that measured electric power is a potential indicator of combustion instabilities in electric-field-assisted combustion.

Long-wavelength negative mass instabilities in high current betatrons

International Nuclear Information System (INIS)

Godfrey, B.B.; Hughes, T.P.

1985-01-01

Growth rates of negative mass instabilities in conventional and modified betatrons are calculated by analytic methods and by performing three-dimensional particle simulations. In contrast to earlier work, toroidal corrections to the field equations are included in the analytic model. As a result, good agreement with numerical simulations is obtained. The simulations show that the nonlinear development of the instabilities can seriously disrupt the beam

Arthrography of the traumatized wrist: correlation with radiography and the carpal instability series

Energy Technology Data Exchange (ETDEWEB)

Levinsohn, E.M.; Palmer, A.K.

1983-03-01

Arthrography with fluoroscopic monitoring was used to assess the soft tissues of the wrist in 100 patients who had chronic traumatic pain but did not have rheumatoid arthritis. Findings were correlated with plain radiographs and the carpal instability series. Arthrograms were normal in 26% of cases and demonstrated perforation of the triangular fibrocartilage in 26%, radiocarpal-midcarpal communication in 30%, capsular lesions in 31%, lymphatic opacification in 12%, and tendon sheath filling in 10%. Communication between the radiocarpal and pisiform-troiquetral compartments, a normal finding, was seen in 69%. There was a significant association between perforation of the triangular fibrocartilage and both ulna-plus variance and carpal instability.

MHD Kelvin-Helmholtz instability in non-hydrostatic equilibrium

International Nuclear Information System (INIS)

Laghouati, Y; Bouabdallah, A; Zizi, M; Alemany, A

2007-01-01

The present work deals with the linear stability of a magnetohydrodynamic shear flow so that a stratified inviscid fluid rotating about a vertical axis when a uniform magnetic field is applied in the direction of the streaming or zonal flow. In geophysical flow, the stability of the flow is determined by taking into account the nonhydrostatic condition depending on Richardson number R i and the deviation δ from hydrostatic equilibrium. According to Stone (Stone P H 1971 J. Fluid. Mech. 45 659), it is shown that such deviation δ decreases the growth rates of three kinds of instability which can appear as geostrophic (G), symmetric (S) and Kelvin-Helmholtz (K-H) instabilities. To be specific, the evolution of the flow is therefore considered in the light of the influence of magnetic field, particularly, on K-H instability. The results of this study are presented by the linear stability of a magnetohydrodynamic, with horizontal free-shear flow of stratified fluid, subject to rotation about the vertical axis and uniform magnetic field in the zonal direction. Results are discussed and compared to previous works as Chandrasekhar (Chandrasekhar S 1961 Hydrodynamic and hydromagnetic stability (Oxford: Clarendon Press) chapter 11 pp 481-513) and Stone

Radar observations of density gradients, electric fields, and plasma irregularities near polar cap patches in the context of the gradient-drift instability

Science.gov (United States)

Lamarche, Leslie J.; Makarevich, Roman A.

2017-03-01

We present observations of plasma density gradients, electric fields, and small-scale plasma irregularities near a polar cap patch made by the Super Dual Auroral Radar Network radar at Rankin Inlet (RKN) and the northern face of Resolute Bay Incoherent Scatter Radar (RISR-N). RKN echo power and occurrence are analyzed in the context of gradient-drift instability (GDI) theory, with a particular focus on the previously uninvestigated 2-D dependencies on wave propagation, electric field, and gradient vectors, with the latter two quantities evaluated directly from RISR-N measurements. It is shown that higher gradient and electric field components along the wave vector generally lead to the higher observed echo occurrence, which is consistent with the expected higher GDI growth rate, but the relationship with echo power is far less straightforward. The RKN echo power increases monotonically as the predicted linear growth rate approaches zero from negative values but does not continue this trend into positive growth rate values, in contrast with GDI predictions. The observed greater consistency of echo occurrence with GDI predictions suggests that GDI operating in the linear regime can control basic plasma structuring, but measured echo strength may be affected by other processes and factors, such as multistep or nonlinear processes or a shear-driven instability.

Absolute parametric instability in a nonuniform plane plasma

Indian Academy of Sciences (India)

The paper reports an analysis of the effect of spatial plasma nonuniformity on absolute parametric instability (API) of electrostatic waves in magnetized plane waveguides subjected to an intense high-frequency (HF) electric field using the separation method. In this case the effect of strong static magnetic field is considered.

Jeans Instability of the Self Gravitating Viscoelastic Ferromagnetic ...

Indian Academy of Sciences (India)

67

neutron stars, white dwarf stars and supernovae. The instability problems in astrophysical domain are generally investigated by considering the uniform character of magnetic field and rotation. Larson (2003) in the study related to the star formation revealed that this idealization of uniform character of magnetic field and ...

A theory of two-stream instability in two hollow relativistic electron beams

International Nuclear Information System (INIS)

Uhm, H.S.

1993-01-01

Stability properties of two-stream instability of two hollow electron beams are investigated. The equilibrium configuration consists of two intense relativistic hollow electron beams propagating through a grounded conducting cylinder. Analysis of the longitudinal two-stream instability is carried out within the framework of the linearized Vlasov--Maxwell equations for the equilibrium distribution function, in which beam electrons have a Lorentzian distribution in the axial momentum. Dispersion relation of the longitudinal two-stream instability is derived. Stability criteria from this dispersion relation indicate that the normalized velocity difference Δβ between the beams should be within a certain range of value to be unstable. Growth rate of the instability is a substantial fraction of the real frequency, thereby indicating that the longitudinal two-stream instability is an effective means of beam current modulation. Transverse instability of hollow electron beams is also investigated. Dispersion relation of the coupled transverse oscillation of the beams is derived and numerical investigation of this dispersion relation is carried out. Growth rate of the kink instability is a substantial fraction of the diocotron frequency, which may pose a serious threat to the two-stream klystron

Instability limits for spontaneous double layer formation

International Nuclear Information System (INIS)

Carr, J. Jr.; Galante, M. E.; McCarren, D.; Scime, E. E.; Sears, S.; VanDervort, R. W.; Magee, R. M.; Reynolds, E.

2013-01-01

We present time-resolved measurements that demonstrate that large amplitude electrostatic instabilities appear in pulsed, expanding helicon plasmas at the same time as particularly strong double layers appear in the expansion region. A significant cross-correlation between the electrostatic fluctuations and fluctuations in the number of ions accelerated by the double layer electric field is observed. No correlation is observed between the electrostatic fluctuations and ions that have not passed through the double layer. These measurements confirm that the simultaneous appearance of the electrostatic fluctuations and the double layer is not simple coincidence. In fact, the accelerated ion population is responsible for the growth of the instability. The double layer strength, and therefore, the velocity of the accelerated ions, is limited by the appearance of the electrostatic instability

Beyond the veil: Inner horizon instability and holography

International Nuclear Information System (INIS)

Balasubramanian, Vijay; Levi, Thomas S.

2004-01-01

We show that scalar perturbations of the eternal, rotating Banados-Teitelboim-Zanelli (BTZ) black hole should lead to an instability of the inner (Cauchy) horizon, preserving strong cosmic censorship. Because of backscattering from the geometry, plane-wave modes have a divergent stress tensor at the event horizon, but suitable wave packets avoid this difficulty, and are dominated at late times by quasinormal behavior. The wave packets have cuts in the complexified coordinate plane that are controlled by requirements of continuity, single-valuedness, and positive energy. Due to a focusing effect, regular wave packets nevertheless have a divergent stress energy at the inner horizon, signaling an instability. We propose that this instability, which is localized behind the event horizon, is detected holographically as a breakdown in the semiclassical computation of dual conformal field theory (CFT) expectation values in which the analytic behavior of wave packets in the complexified coordinate plane plays an integral role. In the dual field theory, this is interpreted as an encoding of physics behind the horizon in the entanglement between otherwise independent CFTs

Stress views in the radiography of scapholunate instability

International Nuclear Information System (INIS)

Ozcelik, Abdurrahman; Guenal, Izge; Koese, Nusret

2005-01-01

Aim: On the suspected carpal instabilities stress views are recommended but not often used. The present study evaluates the reliability of the dorsal and volar stress radiographs on patients with posttraumatic wrist pain. Patients and methods: Stress radiographs of the wrists were examined in 22 patients with chronic wrist pain and the results were compared with scaphoid shift test and standard and positional views. The stress examination consists of applying to the wrist dorsal and volar stresses on the hand. Results: Static scapholunate instability was diagnosed in 4 patients in whom 3 of them had positive scaphoid shift test sign as well. There were, however, 18 patients with dynamic scapholunate instability in whom the standard films were normal but dorsal stress radiography showed gap greater than 3 mm between the scaphoid and lunate. Conclusion: Stress tests may provide considerable information in the evaluation of a patient who has a painful wrist in whom routine and special views do not demonstrate scapholunate dissociation

Adiabatic instability in coupled dark energy/dark matter models

International Nuclear Information System (INIS)

Bean, Rachel; Flanagan, Eanna E.; Trodden, Mark

2008-01-01

We consider theories in which there exists a nontrivial coupling between the dark matter sector and the sector responsible for the acceleration of the Universe. Such theories can possess an adiabatic regime in which the quintessence field always sits at the minimum of its effective potential, which is set by the local dark matter density. We show that if the coupling strength is much larger than gravitational, then the adiabatic regime is always subject to an instability. The instability, which can also be thought of as a type of Jeans instability, is characterized by a negative sound speed squared of an effective coupled dark matter/dark energy fluid, and results in the exponential growth of small scale modes. We discuss the role of the instability in specific coupled cold dark matter and mass varying neutrino models of dark energy and clarify for these theories the regimes in which the instability can be evaded due to nonadiabaticity or weak coupling.

Experimental study on low pressure flow instability

International Nuclear Information System (INIS)

Jiang Shengyao; Wu Xinxin; Wu Shaorong; Bo Jinhai; Zhang Youjie

1997-05-01

The experiment was performed on the test loop (HRTL-5), which simulates the geometry and system design of the 5 MW reactor. The flow behavior for a wide range of inlet subcooling, in which the flow undergoes from single phase to two phase, is described in a natural circulation system at low pressure (p = 0.1, 0.24 MPa). Several kinds of flow instability, e.g. subcooled boiling instability, subcooled boiling induced flashing instability, pure flashing instability as well as flashing coupled density wave instability and high frequency flow oscillation, are investigated. The mechanism of flashing and flashing concerned flow instability, which has never been studied well in this field, is especially interpreted. The experimental results show that, firstly, for a low pressure natural circulation system the two phase flow is unstable in most of inlet subcooling conditions, the two phase stable flow can only be reached at very low inlet subcooling; secondly, at high inlet subcooling the flow instability is dominated by subcooled boiling in the heated section, and at middle inlet subcooling is dominated by void flashing in the adiabatic long riser; thirdly, in two phase stable flow region the condition for boiling out of the core, namely, single phase flow in the heated section, two phase flow in the riser due to vapor flashing, can be realized. The experimental results are very important for the design and accident analysis of the vessel and swimming pool type natural circulation nuclear heating reactor. (7 refs., 10 figs., 1 tab.)

Electric Field and Plasma Density Observations of Irregularities and Plasma Instabilities in the Low Latitude Ionosphere Gathered by the C/NOFS Satellite

Science.gov (United States)

Pfaff, Robert F.; Freudenreich, H.; Rowland, D.; Klenzing, J.; Liebrecht, C.

2012-01-01

The Vector Electric Field Investigation (VEFI) on the C/NOFS equatorial satellite provides a unique data set which includes detailed measurements of irregularities associated with the equatorial ionosphere and in particular with spread-F depletions. We present vector AC electric field observations gathered on C/NOFS that address a variety of key questions regarding how plasma irregularities, from meter to kilometer scales, are created and evolve. The talk focuses on occasions where the ionosphere F-peak has been elevated above the C/NOFS satellite perigee of 400 km as solar activity has increased. In particular, during the equinox periods of 2011, the satellite consistently journeyed below the F-peak whenever the orbit was in the region of the South Atlantic anomaly after sunset. During these passes, data from the electric field and plasma density probes on the satellite have revealed two types of instabilities which had not previously been observed in the C/NOFS data set: The first is evidence for 400-500km-scale bottomside "undulations" that appear in the density and electric field data. In one case, these large scale waves are associated with a strong shear in the zonal E x B flow, as evidenced by variations in the meridional (outward) electric fields observed above and below the F-peak. These undulations are devoid of smaller scale structures in the early evening, yet appear at later local times along the same orbit associated with fully-developed spread-F with smaller scale structures. This suggests that they may be precursor waves for spread-F, driven by a collisional shear instability, following ideas advanced previously by researchers using data from the Jicamarca radar. A second result is the appearance of km-scale irregularities that are a common feature in the electric field and plasma density data that also appear when the satellite is near or below the F-peak at night. The vector electric field instrument on C/NOFS clearly shows that the electric field

Absolute parametric instability in a nonuniform plane plasma ...

Indian Academy of Sciences (India)

Abstract. The paper reports an analysis of the effect of spatial plasma nonuniformity on absolute parametric instability (API) of electrostatic waves in magnetized plane waveguides subjected to an intense high-frequency (HF) electric field using the separation method. In this case the effect of strong static magnetic field is ...

Increased particle confinement with the use of external dc bias field in the CTX spheromak

International Nuclear Information System (INIS)

Barnes, C.W.; Hoida, H.W.; Henins, I.; Fernandez, J.C.; Jarboe, T.R.; Marklin, G.J.

1985-01-01

Spheromaks are formed in a mesh flux conserver in the presence of an external dc bias field. The spheromaks remain stable to tilt instabilities with ratios of bias-to-spheromak flux of up to 47 +- 7%. Normally applied bias flux puts the spheromak separatrix inside the metal mesh and improves the particle confinement

Model for the saturation of the hydromagnetic Rayleigh--Taylor instability

International Nuclear Information System (INIS)

Roderick, N.F.; Hussey, T.W.

1984-01-01

The saturation of the hydromagnetic Rayleigh--Taylor instability is caused by the reduction of driving current in the bubble region between the spikes formed as the instability develops. For short wavelengths linear magnetic field diffusion provides the necessary smoothing of the magnetic field to reduce the driving force. For wavelengths longer than the magnetic field diffusion length, the current is shorted through material which expands into the bubble region. This initially low density accumulates in the bubble and eventually provides a source of sufficiently high conductivity plasma which reduces the magnetic field penetration to the front of the bubble. Simple analytic models have been developed to verify and and quantify these predictions. These models have been compared with two-dimensional magnetohydrodynamic calculations for imploding plasma shells and give good agreement with these more detailed simulations

Effect of FLR correction on Rayleigh -Taylor instability of quantum and stratified plasma

International Nuclear Information System (INIS)

Sharma, P.K.; Tiwari, Anita; Argal, Shraddha; Chhajlani, R.K.

2013-01-01

The Rayleigh Taylor instability of stratified incompressible fluids is studied in presence of FLR Correction and quantum effects in bounded medium. The Quantum magneto hydrodynamic equations of the problem are solved by using normal mode analysis method. A dispersion relation is carried out for the case where plasma is bounded by two rigid planes z = 0 and z = h. The dispersion relation is obtained in dimensionless form to discuss the growth rate of Rayleigh Taylor instability in presence of FLR Correction and quantum effects. The stabilizing or destabilizing behavior of quantum effect and FLR correction on the Rayleigh Taylor instability is analyzed. (author)

Jeans instability of magnetized quantum plasma: Effect of viscosity, rotation and finite Larmor radius corrections

International Nuclear Information System (INIS)

Jain, Shweta; Sharma, Prerana; Chhajlani, R. K.

2015-01-01

The Jeans instability of self-gravitating quantum plasma is examined considering the effects of viscosity, finite Larmor radius (FLR) corrections and rotation. The analysis is done by normal mode analysis theory with the help of relevant linearized perturbation equations of the problem. The general dispersion relation is obtained using the quantum magneto hydrodynamic model. The modified condition of Jeans instability is obtained and the numerical calculations have been performed to show the effects of various parameters on the growth rate of Jeans instability

Kinetic instability of electrostatic ion cyclotron waves in inter-penetrating plasmas

Science.gov (United States)

Bashir, M. F.; Ilie, R.; Murtaza, G.

2018-05-01

The Electrostatic Ion Cyclotron (EIC) instability that includes the effect of wave-particle interaction is studied owing to the free energy source through the flowing velocity of the inter-penetrating plasmas. It is shown that the origin of this current-less instability is different from the classical current driven EIC instability. The threshold conditions applicable to a wide range of plasma parameters and the estimate of the growth rate are determined as a function of the normalized flowing velocity ( u0/vt f e ), the temperature ( Tf/Ts ) and the density ratios ( nf 0/ns 0 ) of flowing component to static one. The EIC instability is driven by either flowing electrons or flowing ions, depending upon the different Doppler shifted frequency domains. It is found that the growth rate for electron-driven instability is higher than the ion-driven one. However, in both cases, the denser (hotter) is the flowing plasma, the lesser (greater) is the growth rate. The possible applications related to the terrestrial solar plasma environment are also discussed.

Hybrid simulations of radial transport driven by the Rayleigh-Taylor instability

Science.gov (United States)

Delamere, P. A.; Stauffer, B. H.; Ma, X.

2017-12-01

Plasma transport in the rapidly rotating giant magnetospheres is thought to involve a centrifugally-driven flux tube interchange instability, similar to the Rayleigh-Taylor (RT) instability. In three dimensions, the convective flow patterns associated with the RT instability can produce strong guide field reconnection, allowing plasma mass to move radially outward while conserving magnetic flux (Ma et al., 2016). We present a set of hybrid (kinetic ion / fluid electron) plasma simulations of the RT instability using high plasma beta conditions appropriate for Jupiter's inner and middle magnetosphere. A density gradient, combined with a centrifugal force, provide appropriate RT onset conditions. Pressure balance is achieved by initializing two ion populations: one with fixed temperature, but varying density, and the other with fixed density, but a temperature gradient that offsets the density gradient from the first population and the centrifugal force (effective gravity). We first analyze two-dimensional results for the plane perpendicular to the magnetic field by comparing growth rates as a function of wave vector following Huba et al. (1998). Prescribed perpendicular wave modes are seeded with an initial velocity perturbation. We then extend the model to three dimensions, introducing a stabilizing parallel wave vector. Boundary conditions in the parallel direction prohibit motion of the magnetic field line footprints to model the eigenmodes of the magnetodisc's resonant cavity. We again compare growth rates based on perpendicular wave number, but also on the parallel extent of the resonant cavity, which fixes the size of the largest parallel wavelength. Finally, we search for evidence of strong guide field magnetic reconnection within the domain by identifying areas with large parallel electric fields or changes in magnetic field topology.

Normal ground state of dense relativistic matter in a magnetic field

International Nuclear Information System (INIS)

Gorbar, E. V.; Miransky, V. A.; Shovkovy, I. A.

2011-01-01

The properties of the ground state of relativistic matter in a magnetic field are examined within the framework of a Nambu-Jona-Lasinio model. The main emphasis of this study is the normal ground state, which is realized at sufficiently high temperatures and/or sufficiently large chemical potentials. In contrast to the vacuum state, which is characterized by the magnetic catalysis of chiral symmetry breaking, the normal state is accompanied by the dynamical generation of the chiral shift parameter Δ. In the chiral limit, the value of Δ determines a relative shift of the longitudinal momenta (along the direction of the magnetic field) in the dispersion relations of opposite chirality fermions. We argue that the chirality remains a good approximate quantum number even for massive fermions in the vicinity of the Fermi surface and, therefore, the chiral shift is expected to play an important role in many types of cold dense relativistic matter, relevant for applications in compact stars. The qualitative implications of the revealed structure of the normal ground state on the physics of protoneutron stars are discussed. A noticeable feature of the Δ parameter is that it is insensitive to temperature when T 0 , where μ 0 is the chemical potential, and increases with temperature for T>μ 0 . The latter implies that the chiral shift parameter is also generated in the regime relevant for heavy ion collisions.

Suppression of electromechanical instability in fiber-reinforced dielectric elastomers

Directory of Open Access Journals (Sweden)

Rui Xiao

2016-03-01

Full Text Available The electromechanical instability of dielectric elastomers has been a major challenge for the application of this class of active materials. In this work, we demonstrate that dielectric elastomers filled with soft fiber can suppress the electromechanical instability and achieve large deformation. Specifically, we developed a constitutive model to describe the dielectric and mechanical behaviors of fiber-reinforced elastomers. The model was applied to study the influence of stiffness, nonlinearity properties and the distribution of fiber on the instability of dielectric membrane under an electric field. The results show that there exists an optimal fiber distribution condition to achieve the maximum deformation before failure.

Nonlinear development of the sausage instability in dense Z-pinches

International Nuclear Information System (INIS)

Colombant, D.; Mosher, D.

1989-01-01

In this paper, a 2d envelope model is described for the nonlinear development of the sausage instability in dense Z-pinches. Numerical solutions for various cases of interest are provided which lay the foundation for a quantitative model of nonthermal neutron emission in dense Z-pinches by determining the induced electric fields associated with the development of the instability

Fire Hose Instability in the Multiple Magnetic Reconnection

Science.gov (United States)

Alexandrova, A.; Retino, A.; Divin, A. V.; Le Contel, O.; Matteini, L.; Breuillard, H.; Deca, J.; Catapano, F.; Cozzani, G.; Nakamura, R.; Panov, E. V.; Voros, Z.

2017-12-01

We present observations of multiple reconnection in the Earth's magnetotail. In particular, we observe an ion temperature anisotropy characterized by large temperature along the magnetic field, between the two active X-lines. The anisotropy is associated with right-hand polarized waves at frequencies lower than the ion cyclotron frequency and propagating obliquely to the background magnetic field. We show that the observed anisotropy and the wave properties are consistent with linear kinetic theory of fire hose instability. The observations are in agreement with the particle-in-cell simulations of multiple reconnection. The results suggest that the fire hose instability can develop during multiple reconnection as a consequence of the ion parallel anisotropy that is produced by counter-streaming ions trapped between the X-lines.

Hydromagnetic thermosolutal instability of compressible walters' (model B' rotating fluid permeated with suspended particles in porous medium

Directory of Open Access Journals (Sweden)

G Rana

2016-09-01

Full Text Available The thermosolutal instability of compressible Walters' (model B' elastico-viscous rotating fluid permeated with suspended particles (fine dust in the presence of vertical magnetic field in porous medium is considered. By applying normal mode analysis method, the dispersion relation has been derived and solved analytically. It is observed that the rotation, magnetic field, suspended particles and viscoelasticity introduce oscillatory modes. For stationary convection the Walters' (model B' fluid behaves like an ordinary Newtonian fluid and it is observed that the rotation and stable solute gradient has stabilizing effects and suspended particles are found to have destabilizing effect on the system, whereas the medium permeability has stabilizing or destabilizing effect on the system under certain conditions. The magnetic field has destabilizing effect in the absence of rotation, whereas in the presence of rotation, magnetic field has stabilizing or destabilizing effect under certain conditions.

A new normalization method based on electrical field lines for electrical capacitance tomography

International Nuclear Information System (INIS)

Zhang, L F; Wang, H X

2009-01-01

Electrical capacitance tomography (ECT) is considered to be one of the most promising process tomography techniques. The image reconstruction for ECT is an inverse problem to find the spatially distributed permittivities in a pipe. Usually, the capacitance measurements obtained from the ECT system are normalized at the high and low permittivity for image reconstruction. The parallel normalization model is commonly used during the normalization process, which assumes the distribution of materials in parallel. Thus, the normalized capacitance is a linear function of measured capacitance. A recently used model is a series normalization model which results in the normalized capacitance as a nonlinear function of measured capacitance. The newest presented model is based on electrical field centre lines (EFCL), and is a mixture of two normalization models. The multi-threshold method of this model is presented in this paper. The sensitivity matrices based on different normalization models were obtained, and image reconstruction was carried out accordingly. Simulation results indicate that reconstructed images with higher quality can be obtained based on the presented model

Parametric instabilities in an electron beam plasma system

International Nuclear Information System (INIS)

Nakach, R.; Cuperman, S.; Gell, Y.; Levush, B.

1981-01-01

The excitation of low frequency parametric instabilities by a finite wave length pump in a system consisting of a warm electron plasma traversed by a warm electron beam is investigated in a fluid dissipationless model. The dispersion relation for the three-dimensional problem in a magnetized plasma with arbitrary directions for the waves is derived, and the one-dimensional case is analyzed numerically. For the one-dimensional back-scattering decay process, it is found that when the plasma-electron Debye length (lambda sub(D)sup(p)) is larger than the beam-electron Debye length (lambda sub(D)sup(b)), two low frequency electrostatic instability branches with different growth rates may simultaneously exist. When lambda sub(D)sup(p) approximately lambda sub(D)sup(b), the large growth rate instability found in the analysis depends strongly on the amplitude of the pump field. In the case (lambda sub(D)sup(p) < lambda sub(D)sup(b)) only one low frequency instability branch is generally excited

Electron surfing acceleration by the electron two-stream instability in a weak magnetic field

International Nuclear Information System (INIS)

Dieckmann, M E; Shukla, P K

2006-01-01

The thermalization of relativistically flowing colliding plasmas is not well understood. The transition layer, in which both plasmas interact and thermalize, is wide and highly structured and the instabilities in this layer may yield non-thermal particle distributions and shock-less energy dissipation. The objective in this work is to explore the ability of an electron two-stream instability for thermalizing a plasma beam that moves at the mildly relativistic speed 0.3c through weakly magnetized plasma and to identify the resulting particle distributions. It is demonstrated here with particle-in-cell simulations that the electron two-stream instability leads to waves that propagate within a wide angular range relative to the flow velocity. The waves are thus not planar, as required for efficient electron surfing acceleration (ESA). The short lifetime of the waves implies, however, only weak modifications of the ESA by the oblique modes, since the waves are sufficiently homogeneous. The ion (proton) beams are not modulated, which would be required to extract some of their energy. The instability can thus heat the electrons significantly, but it fails to accelerate them to relativistic energies and it cannot form a shock layer by thermalizing the protons, at least not for the system and the resolved timescales considered here

Electron surfing acceleration by the electron two-stream instability in a weak magnetic field

Energy Technology Data Exchange (ETDEWEB)

Dieckmann, M E; Shukla, P K [Institut fuer Theoretische Physik IV, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)

2006-10-15

The thermalization of relativistically flowing colliding plasmas is not well understood. The transition layer, in which both plasmas interact and thermalize, is wide and highly structured and the instabilities in this layer may yield non-thermal particle distributions and shock-less energy dissipation. The objective in this work is to explore the ability of an electron two-stream instability for thermalizing a plasma beam that moves at the mildly relativistic speed 0.3c through weakly magnetized plasma and to identify the resulting particle distributions. It is demonstrated here with particle-in-cell simulations that the electron two-stream instability leads to waves that propagate within a wide angular range relative to the flow velocity. The waves are thus not planar, as required for efficient electron surfing acceleration (ESA). The short lifetime of the waves implies, however, only weak modifications of the ESA by the oblique modes, since the waves are sufficiently homogeneous. The ion (proton) beams are not modulated, which would be required to extract some of their energy. The instability can thus heat the electrons significantly, but it fails to accelerate them to relativistic energies and it cannot form a shock layer by thermalizing the protons, at least not for the system and the resolved timescales considered here.

Studies of thermal-hydrodynamic flow instability, (3)

International Nuclear Information System (INIS)

Suzuoki, Akira

1978-01-01

In the flow system in which large density change occurs midway, sometimes steady flow cannot be maintained according to the conditions, and pulsating flow or the scamper of flow occurs. This phenomenon is called flow instability, and is noticed as one of the causes to obstruct the normal operation in boilers, BWRs and the steam generators for FBRs with parallel evaporating tube system. In the pulsating instability, there are density wave oscillation and pressure wave oscillation. The author has studied the density wave oscillation occurring in the steam generators for FBRs and in this paper, the role played by two-phase flow regarding the occurrence of flow instability, and the effect of the existence of interphase slip on the role played by two-phase flow are reported. The theoretical analysis and the results of the analysis taking a steam generator heated with sodium as the example are described. Regarding flow stability, two-phase flow part generates the variation of weight velocity with different phase in steam single phase part, accepting enthalpy variation in water single phase part. In this action, the effect of interphase slip was observed, and the variation of reverse phase is apt to occur in slip flow as compared with homogeneous flow. Accordingly, flow instability is apt to occur in slip flow. (Kako, I.)

Buneman instability and Pierce instability in a collisionless bounded plasma

International Nuclear Information System (INIS)

Iizuka, Satoru; Saeki, Koichi; Sato, Noriyoshi; Hatta, Yoshisuke

1983-01-01

A systematic experiment is performed on the Buneman instability and the Pierce instability in a bounded plasma consisting of beam electrons and stationary ions. Current fluctuations are confirmed to be induced by the Buneman instability. On the other hand, the Pierce instability gives rise to a current limitation. The phenomena are well explained by Mikhailovskii's theory taking account of ion motion in a bounded plasma. (author)

Plasma sheet instability related to the westward traveling surge

International Nuclear Information System (INIS)

Roux, A.; Perraut, S.; Robert, P.; Morane, A.; Pedersen, A.; Korth, A.; Kremser, G.; Aparicio, B.; Rodgers, D.; Pellinen, R.

1991-01-01

The detailed analysis of an isolated dispersionless substorm is performed on the basis of field and particle data collected in situ by the geostationary satellite GEOS 2 and of data from ground-based instruments installed close to the GEOS 2 magnetic footprint. These data give evidence for (1) quasi-periodic variations of the magnetic field configuration, which is alternatively taillike and dipolelike, (2) in-phase oscillations of the flux of energetic electrons, which is high when the configuration is dipolelike and vice versa, (3) a gradient in the flux of energetic ions, which is, on the average, earthward but undergoes large fluctuations around this average direction, and (4) large transient fluctuations of the quasi-dc electric field, which reverses its direction from eastward to westward. It is shown that these results are consistent with the development of an instability which leads to a westward propagating wave. The source of the instability is the differential drift of energetic electrons and ions in a highly stressed magnetic field configuration (in a high β plasma). Evidence is given for a system of localized field-aligned currents flowing alternately earthward and equatorward at the leading and trailing edges of the westward propagating wave. This current system resulting from the temporal development of the instability produces the so-called Pi 2 pulsations, at the ionospheric level. The closure of this current system in the equatorial region leads to a current antiparallel to the tail current, and therefore to its reduction or cancellation. This reduction/cancellation of the tail current restores the dipole magnetic field (dipolarization) and generates a large westward directed induced electric field (injection)

Dorsal surgical stabilisation using tension bands for treatment of traumatic atlanto-occipital instability in a cat.

Science.gov (United States)

Vedrine, B; Maurin, M P

2017-12-01

An atlanto-occipital instability secondary to a dog bite was diagnosed in a 4-year-old Persian cat. Dorsal stabilisation of the instability was made with two OrthoFiber prostheses (Securos), which were used as tension bands between the nuchal crests of the occipital bone and the spinous process of the axis. Total recovery was achieved 4 days after surgery. Normal alignment of the atlanto-occipital joint was observed on survey radiographs taken 6 weeks post-surgery. Although the right loop had failed, the alignment was still normal and no neurological after-effects could be identified. Dorsal divergent tension bands between the nuchal crests of the occipital bone and the spinous process of the axis can be used to stabilise traumatic atlanto-occipital instability. © 2017 Australian Veterinary Association.

On the instability of a spatially confined electron beam in a magnetized plasma

International Nuclear Information System (INIS)

Strangeway, R.J.

1980-01-01

The instability of a field-aligned electron beam of finite width streaming through a uniform magnetized plasma is investigated. The nature of the normal modes, and the wave field variation within the beam region are studied. It is found that an electrostatic approximation is useful in describing the general form of the dispersion relation, specifically showing how the beam width controls the range of allowed solutions. The electrostatic approximation is shown to be good for most of the range of frequencies considered. When the electron gyrofrequency is greater than the electron plasma frequency, the theory predicts that the cold plasma upper-hybrid resonance (Z mode) is stable to negative Landau damping. A criterion for applying this result to beam-plasma systems other than the ones investigated here is developed, and it is found that the effect should be more readily observable in laboratory experiments than in space plasmas. (author)

Impedance and instability threshold estimates in the main injector I

International Nuclear Information System (INIS)

Martens, M.A.; Ng, K.Y.

1994-03-01

One of the important considerations in the design of the Main Injector is the beam coupling impedances in the vacuum chamber and the stability of the beam. Along with the higher intensities comes the possibility of instabilities which lead to growth in beam emittances and/or the loss of beam. This paper makes estimations of the various impedances and instability thresholds based on impedance estimations and measurements. Notably missing from this paper is any analysis of transition crossing and its potential limitations on beam intensity and beam emittance. Future work should consider this issue. The body of the work contains detailed analysis of the various impedance estimations and instability threshold calculations. The calculations are based on the Main Injector beam intensity of 6 x 10 10 protons per bunch, 95% normalized transverse emittances of 20π mm-mrad, and 95% normalized longitudinal emittance of 0.1 eV-s at 8.9 GeV injection energy and 0.25 eV-s at 150 GeV flattop energy. The conclusions section summarizes the results in the paper and is meant to be readable by itself without referring to the rest of the paper. Also in the conclusion section are recommendations for future investigations

Parametric decay instabilities in ECR heated plasmas

International Nuclear Information System (INIS)

Porkolab, M.

1982-01-01

The possibility of parametric excitation of electron Bernstein waves and low frequency ion oscillations during ECR heating at omega/sub o/ approx. = l omega/sub ce/, l = 1,2 is examined. In particular, the thresholds for such instabilities are calculated. It is found that Bernstein waves and lower hybrid quasi-modes have relatively low homogeneous where T/sub e/ approx. = T/sub i/. Thus, these processes may lead to nonlinear absorption and/or scattering of the incident pump wave. The resulting Bernstein waves may lead to either more effective heating (especially during the start-up phase) or to loss of microwave energy if the decay waves propagate out of the system before their energy is absorbed by particles. While at omega/sub o/ = omega/sub UH/ the threshold is reduced due to the WKB enhancement of the pump wave, (and this instability may be important in tokamaks) in EBT's and tandem mirrors the instability at omega /sub o/ greater than or equal to 2 omega/sub ce/ may be important. The instability may persist even if omega > 2 omega/sub ce/ and this may be the case during finite beta depression of the magnetic field in which case the decay waves may be trapped in the local magnetic well so that convective losses are minimized. The excited fluctuations may lead to additional scattering of the ring electrons and the incident microwave fields. Application of these calculations to ECR heating of tokamaks, tandem mirrors, and EBT's will be examined

Competing processes of whistler and electrostatic instabilities in the magnetosphere

International Nuclear Information System (INIS)

Omura, Y.; Matsumoto, H.

1987-01-01

Competing processes of whistler mode and electrostatic mode instabilities induced by an electron beam are studied by a linear growth rate analysis and by an electromagnetic particle simulation. In addition to a background cold plasma we assumed an electron beam drifting along a static magnetic field. We studied excitation of whistler and electrostatic mode waves in the direction of the static magnetic field. We first calculated linear growth rates for the whistler mode and electrostatic mode instabilities, assuming various possible parameters in the equatorial magnetosphere. We found that the growth rate for the electrostatic instability is always larger than that of the whistler mode instability. A short simulation run with a monoenergetic electron beam demonstrates that a monoenergetic beam can hardly give energy to whistler mode waves as a result of competition with faster growing electrostatic waves, because the beam electrons are trapped and diffused by the electrostatic waves, and hence the growth rates for whistler mode waves become very small. A long simulation run starting with a warm electron beam demonstrates that whistler mode waves are excited in spite of the small growth rates and the coexisting quasi-linear electrostatic diffusion process

Width of electromagnetic wave instability spectrum in tungsten plate

International Nuclear Information System (INIS)

Rinkevich, A.B.

1995-01-01

Based on the study of high-frequency signal modulation and spectrum analysis of the envelope a measurement of spectrum width for electromagnetic wave instability was carried out under conditions of current pulse action on tungsten plate in magnetic field. The existence of amplitude-frequency wave modulation was revealed. The width of current disturbance spectrum in a specimen was evaluated. Current disturbances are shown to cause the instability of electromagnetic wave. 11 refs.; 6 figs

Direct measurement of the image displacement instability in a linear induction accelerator

Science.gov (United States)

Burris-Mog, T. J.; Ekdahl, C. A.; Moir, D. C.

2017-06-01

The image displacement instability (IDI) has been measured on the 20 MeV Axis I of the dual axis radiographic hydrodynamic test facility and compared to theory. A 0.23 kA electron beam was accelerated across 64 gaps in a low solenoid focusing field, and the position of the beam centroid was measured to 34.3 meters downstream from the cathode. One beam dynamics code was used to model the IDI from first principles, while another code characterized the effects of the resistive wall instability and the beam break-up (BBU) instability. Although the BBU instability was not found to influence the IDI, it appears that the IDI influences the BBU. Because the BBU theory does not fully account for the dependence on beam position for coupling to cavity transverse magnetic modes, the effect of the IDI is missing from the BBU theory. This becomes of particular concern to users of linear induction accelerators operating in or near low magnetic guide fields tunes.

Suppression of the Transit -Time Instability in Large-Area Electron Beam Diodes

Science.gov (United States)

Myers, Matthew C.; Friedman, Moshe; Swanekamp, Stephen B.; Chan, Lop-Yung; Ludeking, Larry; Sethian, John D.

2002-12-01

Experiment, theory, and simulation have shown that large-area electron-beam diodes are susceptible to the transit-time instability. The instability modulates the electron beam spatially and temporally, producing a wide spread in electron energy and momentum distributions. The result is gross inefficiency in beam generation and propagation. Simulations indicate that a periodic, slotted cathode structure that is loaded with resistive elements may be used to eliminate the instability. Such a cathode has been fielded on one of the two opposing 60 cm × 200 cm diodes on the NIKE KrF laser at the Naval Research Laboratory. These diodes typically deliver 600 kV, 500 kA, 250 ns electron beams to the laser cell in an external magnetic field of 0.2 T. We conclude that the slotted cathode suppressed the transit-time instability such that the RF power was reduced by a factor of 9 and that electron transmission efficiency into the laser gas was improved by more than 50%.

Suppression of the transit-time instability in large-area electron beam diodes

International Nuclear Information System (INIS)

Myers, Matthew C.; Friedman, Moshe; Sethian, John D.; Swanekamp, Stephen B.; Chan, L.-Y.; Ludeking, Larry

2002-01-01

Experiment, theory, and simulation have shown that large-area electron-beam diodes are susceptible to the transit-time instability. The instability modulates the electron beam spatially and temporally, producing a wide spread in electron energy and momentum distributions. The result is gross inefficiency in beam generation and propagation. Simulations indicate that a periodic, slotted cathode structure that is loaded with resistive elements may be used to eliminate the instability. Such a cathode has been fielded on one of the two opposing 60 cm x 200 cm diodes on the NIKE KrF laser at the Naval Research Laboratory. These diodes typically deliver 600 kV, 500 kA, 250 ns electron beams to the laser cell in an external magnetic field of 0.2 T. We conclude that the slotted cathode suppressed the transit-time instability such that the RF power was reduced by a factor of 9 and that electron transmission efficiency into the laser gas was improved by more than 50%

Macro-environment of breast carcinoma: frequent genetic alterations in the normal appearing skins of patients with breast cancer.

Science.gov (United States)

Moinfar, Farid; Beham, Alfred; Friedrich, Gerhard; Deutsch, Alexander; Hrzenjak, Andelko; Luschin, Gero; Tavassoli, Fattaneh A

2008-05-01

Genetic abnormalities in microenvironmental tissues with subsequent alterations of reciprocal interactions between epithelial and mesenchymal cells play a key role in the breast carcinogenesis. Although a few reports have demonstrated abnormal fibroblastic functions in normal-appearing fibroblasts taken from the skins of breast cancer patients, the genetic basis of this phenomenon and its implication for carcinogenesis are unexplored. We analyzed 12 mastectomy specimens showing invasive ductal carcinomas. In each case, morphologically normal epidermis and dermis, carcinoma, normal stroma close to carcinoma, and stroma at a distant from carcinoma were microdissected. Metastatic-free lymphatic tissues from lymph nodes served as a control. Using PCR, DNA extracts were examined with 11 microsatellite markers known for a high frequency of allelic imbalances in breast cancer. Losses of heterozygosity and/or microsatellite instability were detected in 83% of the skin samples occurring either concurrently with or independently from the cancerous tissues. In 80% of these cases at least one microsatellite marker displayed loss of heterozygosity or microsatellite instability in the skin, which was absent in carcinoma. A total of 41% of samples showed alterations of certain loci observed exclusively in the carcinoma but not in the skin compartments. Our study suggests that breast cancer is not just a localized genetic disorder, but rather part of a larger field of genetic alterations/instabilities affecting multiple cell populations in the organ with various cellular elements, ultimately contributing to the manifestation of the more 'localized' carcinoma. These data indicate that more global assessment of tumor micro- and macro-environment is crucial for our understanding of breast carcinogenesis.

Parametric instabilities of rotor-support systems with application to industrial ventilators

Science.gov (United States)

Parszewski, Z.; Krodkiemski, T.; Marynowski, K.

1980-01-01

Rotor support systems interaction with parametric excitation is considered for both unequal principal shaft stiffness (generators) and offset disc rotors (ventilators). Instability regions and types of instability are computed in the first case, and parametric resonances in the second case. Computed and experimental results are compared for laboratory machine models. A field case study of parametric vibrations in industrial ventilators is reported. Computed parametric resonances are confirmed in field measurements, and some industrial failures are explained. Also the dynamic influence and gyroscopic effect of supporting structures are shown and computed.

Polarization modulational instability in a birefringent optical fiber ...

Indian Academy of Sciences (India)

We obtain conditions for the occurrence of polarization modulational instability in the anomalous and normal dispersion regimes for the coupled nonlinear Schrödinger equation modelling fourth order dispersion effects when the linearly polarized pump is oriented at arbitrary angles with respect to the slow and fast axes of ...

Evidence-based rehabilitation of athletes with glenohumeral instability.

Science.gov (United States)

Cools, Ann M; Borms, Dorien; Castelein, Birgit; Vanderstukken, Fran; Johansson, Fredrik R

2016-02-01

To give an overview of current knowledge and guidelines with respect to evidence-based rehabilitation of athletes with glenohumeral instability. This narrative review combines scientific evidence with clinical guidelines based on the current literature to highlight the different components of the rehabilitation of glenohumeral instability. Depending on the specific characteristics of the instability pattern, the severity, recurrence, and direction, the therapeutic approach may be adapted to the needs and demands of the athlete. In general, attention should go to (1) restoration of rotator cuff strength and inter-muscular balance, focusing on the eccentric capacity of the external rotators, (2) normalization of rotational range of motion with special attention to the internal rotation ROM, (3) optimization of the flexibility and muscle performance of the scapular muscles, and (4) gradually increasing the functional sport-specific load on the shoulder girdle. The functional kinetic chain should be implemented throughout all stages of the rehabilitation program. Return to play should be based on subjective assessment as well as objective measurements of ROM, strength, and function. This paper summarizes evidence-based guidelines for treatment of glenohumeral instability. These guidelines may assist the clinician in the prevention and rehabilitation of the overhead athlete. Expert opinion, Level V.

Hose-Modulation Instability of Laser Pulses in Plasmas

International Nuclear Information System (INIS)

Sprangle, P.; Krall, J.; Esarey, E.

1994-01-01

A laser pulse propagating in a uniform plasma or a preformed plasma density channel is found to undergo a combination of hose and modulation instabilities, provided the pulse centroid has an initial tilt. Coupled equations for the laser centroid and envelope are derived and solved for a finite-length laser pulse. Significant coupling between the centroid and the envelope, harmonic generation in the envelope, and strong modification of the wake field can occur. Methods to reduce the growth rate of the laser hose instability are demonstrated

Two-dimensional Nonlinear Simulations of Temperature-anisotropy Instabilities with a Proton-alpha Drift

Science.gov (United States)

Markovskii, S. A.; Chandran, Benjamin D. G.; Vasquez, Bernard J.

2018-04-01

We present two-dimensional hybrid simulations of proton-cyclotron and mirror instabilities in a proton-alpha plasma with particle-in-cell ions and a neutralizing electron fluid. The instabilities are driven by the protons with temperature perpendicular to the background magnetic field larger than the parallel temperature. The alpha particles with initially isotropic temperature have a nonzero drift speed with respect to the protons. The minor ions are known to influence the relative effect of the proton-cyclotron and mirror instabilities. In this paper, we show that the mirror mode can dominate the power spectrum at the nonlinear stage even if its linear growth rate is significantly lower than that of the proton-cyclotron mode. The proton-cyclotron instability combined with the alpha-proton drift is a possible cause of the nonzero magnetic helicity observed in the solar wind for fluctuations propagating nearly parallel to the magnetic field. Our simulations generally confirm this concept but reveal a complex helicity spectrum that is not anticipated from the linear theory of the instability.

Global sawtooth instability measured by magnetic coils in the JET tokamak

International Nuclear Information System (INIS)

Duperrex, P.A.; Pochelon, A.; Edwards, A.; Snipes, J.

1992-05-01

This paper describes measurements of the sawtooth instability in JET, in which the instability wave function is shown to extend to the edge where it is measured using magnetic coils. The numerous magnetic probes in JET allow the time evolution of the (n=0,1,2,3) toroidal Fourier components to be analysed. The n=1 magnetic component is similar to the m=1 soft X-ray centroid motion. This fact indicates the potential of edge signals in retrieving the poloidal mode spectrum of the q=m/n=1 surface. The spectrum evolution of the instability is compared for normal sawteeth (NST) and quasi-stabilised 'monster' sawteeth (MST). The spectrum is slowly decreasing with n for NST and all the components belong to one ballooning-like deformation, whereas MST show a large n=1 kink-like motion with small and independent accompanying higher n modes. Important equilibrium changes occur already during the growth of the instability and the growth rate is much faster than exponential. Both these facts imply a non-linear nature of the instability growth. Parametric dependence of growthrates, amplitudes, toroidal spectrum shape, etc., are studied to characterize the NST and MST instabilities. (author) 20 figs., 2 tabs., 46 refs

Electron Debye scale Kelvin-Helmholtz instability: Electrostatic particle-in-cell simulations

International Nuclear Information System (INIS)

Lee, Sang-Yun; Lee, Ensang; Kim, Khan-Hyuk; Lee, Dong-Hun; Seon, Jongho; Jin, Ho

2015-01-01

In this paper, we investigated the electron Debye scale Kelvin-Helmholtz (KH) instability using two-dimensional electrostatic particle-in-cell simulations. We introduced a velocity shear layer with a thickness comparable to the electron Debye length and examined the generation of the KH instability. The KH instability occurs in a similar manner as observed in the KH instabilities in fluid or ion scales producing surface waves and rolled-up vortices. The strength and growth rate of the electron Debye scale KH instability is affected by the structure of the velocity shear layer. The strength depends on the magnitude of the velocity and the growth rate on the velocity gradient of the shear layer. However, the development of the electron Debye scale KH instability is mainly determined by the electric field generated by charge separation. Significant mixing of electrons occurs across the shear layer, and a fraction of electrons can penetrate deeply into the opposite side fairly far from the vortices across the shear layer

Nonlinear development of the two-plasmon decay instability in three dimensions

Energy Technology Data Exchange (ETDEWEB)

Vu, H. X. [University of California, San Diego, La Jolla, California 92093 (United States); DuBois, D. F.; Russell, D. A. [Lodestar Research Corporation, Boulder, Colorado 80301 (United States); Myatt, J. F.; Zhang, J. [Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623 (United States); Department of Mechanical Engineering, University of Rochester, Rochester, New York 14627 (United States)

2014-04-15

Most recent experiments on the excitation of the two plasmon-decay (TPD) instability involve a three-dimensional (3D) array of overlapping laser beams. Our recent two dimensional (2D) simulations suggested that Langmuir cavitation and collapse are important nonlinear saturation mechanisms for TPD. There are important quantitative differences in the Langmuir collapse process in 2D and 3D. To address these and other issues, we have developed a 3D Zakharov code. It has been applied to study the evolution of TPD from absolute instabilities (arising from 3D laser geometries) to the nonlinear state (J. Zhang et al., Phys. Rev. Lett. (submitted)). The present paper concentrates on the nonlinear saturated state excited by the collective action of two crossed laser beams with arbitrary polarizations. Remarkable agreement between 3D and 2D simulations is found for several averaged physical quantities when the beams are polarized in their common plane. As in the previous 2D simulations, we find: (a) the collective, initially convectively unstable triad modes dominate after a sub-picosecond burst, (b) Langmuir cavitation and collapse are important nonlinearities, and (c) that the statistics of intense cavitons are characteristic of a Gaussian random process. The 3D steady-state saturated Langmuir energy level is about 30% higher than in 2D. The auto-correlation functions of the Langmuir envelope field and of the low-frequency electron density field yield the spatial shape of the strongest collapsing cavitons which are 3D ellipsoids whose orientation depends on the laser polarizations. This tilting of the caviton's strongest electric field direction away from the normal to the target surface is a major new 3D result. This tilting may deflect the hot electron flux and thereby mitigate target preheat.

Analysis of the high frequency longitudinal instability of bunched beams using a computer model

International Nuclear Information System (INIS)

Messerschmid, E.; Month, M.

1976-01-01

The effects of high frequency longitudinal forces on bunched beams are investigated using a computer model. These forces are thought to arise from the transfer of energy between the beam and various structures in the vacuum chamber, this coupling being characterized by a longitudinal impedance function. The simulation is performed with a passive cavity-like element. It is found that the instability can be generated if three conditions are fulfilled: (1) the impedance must be sufficiently large, (2) the induced field must have a fast wake, and (3) the frequency of the induced field must be high enough. In particular, it is shown that the coasting beam threshold criterion for the longitudinal impedance accurately describes the onset of instability, if local values along the bunch of energy spread and current are used. It is also found that the very fast initial growth rate is in good agreement with linear theory and that the coasting beam overshoot expression may be used as a rough guide of the limiting growth for unstable bunches. Concerning the wake field, it is shown how the instability tends to disappear as the fields persist longer. It is furthermore demonstrated that as the wavelength of the unstable mode is increased, initially unstable conditions begin to weaken and vanish. This, it should be emphasized, is primarily a result of the strong correlation between the unstable mode frequency and the time rate of attenuation of the induced fields. ISR parameters are used throughout and a correspondence between the microwave instability observed in the ISR bunches and the simulated instability is suggested. (Auth.)

Study of the internal structure, instabilities, and magnetic fields in the dense Z-pinch

Energy Technology Data Exchange (ETDEWEB)

Ivanov, Vladimir V. [Univ. of Nevada, Reno, NV (United States)

2016-08-17

Z-pinches are sources of hot dense plasma which generates powerful x-ray bursts and can been applied to various areas of high-energy-density physics (HEDP). The 26-MA Z machine is at the forefront of many of these applications, but important aspects of HEDP have been studied on generators at the 1 MA current level. Recent development of laser diagnostics and upgrade of the Leopard laser at Nevada Terawatt Facility (NTF) give new opportunities for the dense Z-pinch study. The goal of this project is the investigation of the internal structure of the stagnated Z pinch including sub-mm and micron-scale instabilities, plasma dynamics, magnetic fields, and hot spots formation and initiation. New plasma diagnostics will be developed for this project. A 3D structure and instabilities of the pinch will be compared with 3D MHD and spectroscopic modeling and theoretical analysis. The structure and dynamics of stagnated Z pinches has been studied with x-ray self-radiation diagnostics which derive a temperature map of the pinch with a spatial resolution of 70-150 µm. The regular laser diagnostics at 532 nm does not penetrate in the dense pinch due to strong absorption and refraction in trailing plasma. Recent experiments at NTF showed that shadowgraphy at the UV wavelength of 266 nm unfolds a fine structure of the stagnated Z-pinch with unprecedented detail. We propose to develop laser UV diagnostics for Z pinches with a spatial resolution <5 μm to study the small-scale plasma structures, implement two-frame shadowgraphy/interferometry, and develop methods for investigation of strong magnetic fields. New diagnostics will help to understand better basic physical processes in Z pinches. A 3D internal structure of the pinch and characteristic instabilities will be studied in wire arrays with different configurations and compared with 3D MHD simulations and analytical models. Mechanisms of “enhanced heating” of Z-pinch plasma will be studied. Fast dynamics of stagnated

Kinetic instabilities in relativistic plasmas: the Harris instability revisited

International Nuclear Information System (INIS)

Tautz, R.C.

2008-01-01

Plasma instabilities that generate aperiodic fluctuations are of outstanding importance in the astrophysical context. Two prominent examples are the electromagnetic Weibel instability and the electrostatic Harris instability, which operate in initially non-magnetized and magnetized plasmas, respectively. In this talk, the original formulation of the Harris instability will be reviewed and generalizations will be presented such as the inclusion of (1) relativistic effects, (2) ion effects, and (3) mode coupling. It will be shown that, with these modifications, a powerful method has been developed for the determination of both the existence and the growth rate of low-frequency instabilities. Applications can be found in astrophysical jets, where the rest frame can be used and so no parallel motion is present. At the end of the talk, how the particle composition of gamma-ray burst jets can be predicted using the Harris technique. (author)

Carpal instability

International Nuclear Information System (INIS)

Schmitt, R.; Froehner, S.; Coblenz, G.; Christopoulos, G.

2006-01-01

This review addresses the pathoanatomical basics as well as the clinical and radiological presentation of instability patterns of the wrist. Carpal instability mostly follows an injury; however, other diseases, like CPPD arthropathy, can be associated. Instability occurs either if the carpus is unable to sustain physiologic loads (''dyskinetics'') or suffers from abnormal motion of its bones during movement (''dyskinematics''). In the classification of carpal instability, dissociative subcategories (located within proximal carpal row) are differentiated from non-dissociative subcategories (present between the carpal rows) and combined patterns. It is essential to note that the unstable wrist initially does not cause relevant signs in standard radiograms, therefore being ''occult'' for the radiologic assessment. This paper emphasizes the high utility of kinematographic studies, contrast-enhanced magnetic resonance imaging (MRI) and MR arthrography for detecting these predynamic and dynamic instability stages. Later in the natural history of carpal instability, static malalignment of the wrist and osteoarthritis will develop, both being associated with significant morbidity and disability. To prevent individual and socio-economic implications, the handsurgeon or orthopedist, as well as the radiologist, is challenged for early and precise diagnosis. (orig.)

Onset of superradiant instabilities in the composed Kerr-black-hole–mirror bomb

Directory of Open Access Journals (Sweden)

Shahar Hod

2014-09-01

Full Text Available It was first pointed out by Press and Teukolsky that a system composed of a spinning Kerr black hole surrounded by a reflecting mirror may develop instabilities. The physical mechanism responsible for the development of these exponentially growing instabilities is the superradiant amplification of bosonic fields confined between the black hole and the mirror. A remarkable feature of this composed black-hole–mirror-field system is the existence of a critical mirror radius, rmstat, which supports stationary (marginally-stable field configurations. This critical (‘stationary’ mirror radius marks the boundary between stable and unstable black-hole–mirror-field configurations: composed systems whose confining mirror is situated in the region rmrmstat are unstable (that is, there are confined field modes which grow exponentially over time. In the present paper we explore this critical (marginally-stable boundary between stable and explosive black-hole–mirror-field configurations. It is shown that the innermost (smallest radius of the confining mirror which allows the extraction of rotational energy from a spinning Kerr black hole approaches the black-hole horizon radius in the extremal limit of rapidly-rotating black holes. We find, in particular, that this critical mirror radius (which marks the onset of superradiant instabilities in the composed system scales linearly with the black-hole temperature.

Variable field-to-normal angles in the shock foreshock boundary observed by ISEE 1 and 2

International Nuclear Information System (INIS)

Greenstadt, E.W.; Mellot, M.M.

1985-01-01

Saturated ULF waves in the foreshock, with amplitudes comparable to the magnitude of the average field, are convected by the solar wind to the quasi-parallel shock where the average field-normal angle is less than, or about, 45 0 . Several examples from ISEE 1 and 2 magnetometer data show waves that defined local, instantaneous field-normal angles very different periodically from the average. Local geometric conditions at the nominally quasi-parallel shock varied from nearly parallel to nearly perpendicular, at the periods of typical upstream waves. Clear magnetic shock transitions occurred under temporarily quasi-perpendicular geometry

Chromosomal duplication strains of Aspergillus nidulans and their instability

International Nuclear Information System (INIS)

Azevedo, J.L. de; Almeida Okino, L.M. de

1981-01-01

Strains of Aspergillus nidulans with chromosomal duplication were obtained after gamma irradiation followed by crossing of the translocated strains with normal strains. From 20 analysed colonies, 12 have shown translocations induced by irradiation. Segregants from four of these translocation strains crossed to normal strains have shown to be unstable although presenting normal morphology. Two segregants were genetically analysed. The first one has shown a duplication of part of linkage groups VIII and the second one presented a duplication of a segment of linkage group V. These new duplication strains in A. nidulans open new perspectives of a more detailed study of the instability phenomenon in this fungus. (Author) [pt

Delayed chromosomal instability caused by large deletion

International Nuclear Information System (INIS)

Ojima, M.; Suzuki, K.; Kodama, S.; Watanabe, M.

2003-01-01

Full text: There is accumulating evidence that genomic instability, manifested by the expression of delayed phenotypes, is induced by X-irradiation but not by ultraviolet (UV) light. It is well known that ionizing radiation, such as X-rays, induces DNA double strand breaks, but UV-light mainly causes base damage like pyrimidine dimers and (6-4) photoproducts. Although the mechanism of radiation-induced genomic instability has not been thoroughly explained, it is suggested that DNA double strand breaks contribute the induction of genomic instability. We examined here whether X-ray induced gene deletion at the hprt locus induces delayed instability in chromosome X. SV40-immortalized normal human fibroblasts, GM638, were irradiated with X-rays (3, 6 Gy), and the hprt mutants were isolated in the presence of 6-thioguanine (6-TG). A 2-fold and a 60-fold increase in mutation frequency were found by 3 Gy and 6 Gy irradiation, respectively. The molecular structure of the hprt mutations was determined by multiplex polymerase chain reaction of nine exons. Approximately 60% of 3 Gy mutants lost a part or the entire hprt gene, and the other mutants showed point mutations like spontaneous mutants. All 6 Gy mutants show total gene deletion. The chromosomes of the hprt mutants were analyzed by Whole Human Chromosome X Paint FISH or Xq telomere FISH. None of the point or partial gene deletion mutants showed aberrations of X-chromosome, however total gene deletion mutants induced translocations and dicentrics involving chromosome X. These results suggest that large deletion caused by DNA double strand breaks destabilizes chromosome structure, which may be involved in an induction of radiation-induced genomic instability

Thermodynamic instabilities in hot and dense nuclear matter

Directory of Open Access Journals (Sweden)

Lavagno A.

2016-01-01

Full Text Available We study the presence of thermodynamic instabilities in a hot and dense nuclear medium where a nuclear phase transition can take place. Similarly to the low density nuclear liquid-gas phase transition, we show that such a phase transition is characterized by pure hadronic matter with both mechanical instability (fluctuations on the baryon density that by chemical-diffusive instability (fluctuations on the strangeness concentration. The analysis is performed by requiring the global conservation of baryon number and zero net strangeness in the framework of an effective relativistic mean field theory with the inclusion of the Δ(1232-isobars, hyperons and the lightest pseudoscalar and vector meson degrees of freedom. It turns out that in this situation hadronic phases with different values of strangeness content may coexist, altering significantly meson-antimeson ratios.

Rayleigh Taylor instability of two superposed compressible fluids in un-magnetized plasma

International Nuclear Information System (INIS)

Sharma, P K; Tiwari, A; Argal, S; Chhajlani, R K

2014-01-01

The linear Rayleigh Taylor instability of two superposed compressible Newtonian fluids is discussed with the effect of surface tension which can play important roles in space plasma. As in both the superposed Newtonian fluids, the system is stable for potentially stable case and unstable for potentially unstable case in the present problem also. The equations of the problem are solved by normal mode method and a dispersion relation is obtained for such a system. The behaviour of growth rate is examined in the presence of surface tension and it is found that the surface tension has stabilizing influence on the Rayleigh Taylor instability of two superposed compressible fluids. Numerical analysis is performed to show the effect of sound velocity and surface tension on the growth rate of Rayleigh Taylor instability. It is found that both parameters have stabilizing influence on the growth rate of Rayleigh Taylor instability.

Cluster observations of reconnection due to the Kelvin-Helmholtz instability at the dawnside magnetospheric flank

Directory of Open Access Journals (Sweden)

K. Nykyri

2006-10-01

Full Text Available On 3 July 2001, the four Cluster satellites traversed along the dawnside magnetospheric flank and observed large variations in all plasma parameters. The estimated magnetopause boundary normals were oscillating in the z-direction and the normal component of the magnetic field showed systematic  2–3 min bipolar variations for 1 h when the IMF had a small positive b_z-component and a Parker-spiral orientation in the x,y-plane. Brief  33 s intervals with excellent deHoffman Teller frames were observed satisfying the Walén relation. Detailed comparisons with 2-D MHD simulations indicate that Cluster encountered rotational discontinuities generated by Kelvin-Helmholtz instability. We estimate a wave length of  6 R_E and a wave vector with a significant z-component.

Nonlinear evolution of the lower-hybrid drift instability

International Nuclear Information System (INIS)

Brackbill, J.U.; Forslund, D.W.; Quest, K.B.; Winske, D.

1984-01-01

The results of simulations of the lower-hybrid drift instability in a neutral sheet configuration are described. The simulations use an implicit formulation to relax the usual time step limitations and thus extend previous explicit calculations to weaker gradients, larger mass ratios, and long times compared with the linear growth time. The numerical results give the scaling of the saturation level, heating rates, resistivity, and cross-field diffusion and a demonstration by comparison with a fluid electron model that dissipation in the lower-hybrid drift instability is caused by electron kinetic effects

Instabilities and nonstatistical behavior in globally coupled systems

International Nuclear Information System (INIS)

Perez, G.; Cerdeira, H.A.

1992-01-01

The mean field in a globally coupled system of chaotic logistic maps does not obey the standard rules of statistics, even for systems of very large sizes. This indicates the existence of intrinsic instabilities in its evolution. Here these instabilities are related to the very nonsmooth behavior of mean values in a single logistic map, as a function of its parameter. Problems of this kind do not affect a similar system of coupled tent maps, where good statistical behavior has been found. We also explore the transition between these two regimes

Instability timescale for the inclination instability in the solar system

Science.gov (United States)

Zderic, Alexander; Madigan, Ann-Marie; Fleisig, Jacob

2018-04-01

The gravitational influence of small bodies is often neglected in the study of solar system dynamics. However, this is not always an appropriate assumption. For example, mutual secular torques between low mass particles on eccentric orbits can result in a self-gravity instability (`inclination instability'; Madigan & McCourt 2016). During the instability, inclinations increase exponentially, eccentricities decrease (detachment), and orbits cluster in argument of perihelion. In the solar system, the orbits of the most distant objects show all three of these characteristics (high inclination: Volk & Malhotra (2017), detachment: Delsanti & Jewitt (2006), and argument of perihelion clustering: Trujillo & Sheppard (2014)). The inclination instability is a natural explanation for these phenomena.Unfortunately, full N-body simulations of the solar system are unfeasible (N ≈ O(1012)), and the behavior of the instability depends on N, prohibiting the direct application of lower N simulations. Here we present the instability timescale's functional dependence on N, allowing us to extrapolate our simulation results to that appropriate for the solar system. We show that ~5 MEarth of small icy bodies in the Sedna region is sufficient for the inclination instability to occur in the outer solar system.

Electric-field induced surface instabilities of soft dielectrics and their effects on optical transmittance and scattering

Science.gov (United States)

Shian, Samuel; Kjeer, Peter; Clarke, David R.

2018-03-01

When a voltage is applied to a percolative, mechanically compliant mat of carbon nanotubes (CNTs) on a smooth elastomer bilayer attached to an ITO coated glass substrate, the in-line optical transmittance decreases with increasing voltage. Two regimes of behavior have been identified based on optical scattering, bright field optical microscopy, and confocal optical microscopy. In the low field regime, the electric field produces a spatially inhomogeneous surface deformation of the elastomer that causes local variations in optical refraction and modulates the light transmittance. The spatial variation is associated with the distribution of the CNTs over the surface. At higher fields, above a threshold voltage, an array of pits in the surface form by a nucleation and growth mechanism and these also scatter light. The formation of pits, and creases, in the thickness of the elastomer, is due to a previously identified electro-mechanical surface instability. When the applied voltage is decreased from its maximum, the transmittance returns to its original value although there is a transmittance hysteresis and a complicated time response. When the applied voltage exceeds the threshold voltage, there can be remnant optical contrast associated with creasing of the elastomer and the recovery time appears to be dependent on local jamming of CNTs in areas where the pits formed. A potential application of this work as an electrically tunable privacy window or camouflaging devices is demonstrated.

KELVIN-HELMHOLTZ INSTABILITY OF A CORONAL STREAMER

Energy Technology Data Exchange (ETDEWEB)

Feng, L.; Gan, W. Q. [Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, 210008 Nanjing (China); Inhester, B., E-mail: lfeng@pmo.ac.cn [Max-Planck-Institut fuer Sonnensystemforschung, Max-Planck-Str.2, D-37191 Katlenburg-Lindau (Germany)

2013-09-10

Shear-flow-driven instability can play an important role in energy transfer processes in coronal plasma. We present for the first time the observation of a kink-like oscillation of a streamer that is probably caused by the streaming kink-mode Kelvin-Helmholtz instability (KHI). The wave-like behavior of the streamer was observed by the Large Angle and Spectrometric Coronagraph Experiment C2 and C3 on board the SOlar and Heliospheric Observatory. The observed wave had a period of about 70-80 minutes, and its wavelength increased from 2 R{sub Sun} to 3 R{sub Sun} in about 1.5 hr. The phase speeds of its crests and troughs decreased from 406 {+-} 20 to 356 {+-} 31 km s{sup -1} during the event. Within the same heliocentric range, the wave amplitude also appeared to increase with time. We attribute the phenomena to the MHD KHI, which occurs at a neutral sheet in a fluid wake. The free energy driving the instability is supplied by the sheared flow and sheared magnetic field across the streamer plane. The plasma properties of the local environment of the streamer were estimated from the phase speed and instability threshold criteria.

Effect of the thermal spread in a beam on the radiative Pierce instability

International Nuclear Information System (INIS)

Klochkov, D.N.; Pekar, M.Yu.; Rukhadze, A.A.

1999-01-01

The linear dynamics of the radiative Pierce instability in a single plane in the case of the relativistic electron beam with T temperature stabilized through a strong magnetic field, is considered. It is shown that the instability increment decreases with the thermal spread growth [ru

Three-dimensional instability analysis of boundary layers perturbed by streamwise vortices

Science.gov (United States)

Martín, Juan A.; Paredes, Pedro

2017-12-01

A parametric study is presented for the incompressible, zero-pressure-gradient flat-plate boundary layer perturbed by streamwise vortices. The vortices are placed near the leading edge and model the vortices induced by miniature vortex generators (MVGs), which consist in a spanwise-periodic array of small winglet pairs. The introduction of MVGs has been experimentally proved to be a successful passive flow control strategy for delaying laminar-turbulent transition caused by Tollmien-Schlichting (TS) waves. The counter-rotating vortex pairs induce non-modal, transient growth that leads to a streaky boundary layer flow. The initial intensity of the vortices and their wall-normal distances to the plate wall are varied with the aim of finding the most effective location for streak generation and the effect on the instability characteristics of the perturbed flow. The study includes the solution of the three-dimensional, stationary, streaky boundary layer flows by using the boundary region equations, and the three-dimensional instability analysis of the resulting basic flows by using the plane-marching parabolized stability equations. Depending on the initial circulation and positioning of the vortices, planar TS waves are stabilized by the presence of the streaks, resulting in a reduction in the region of instability and shrink of the neutral stability curve. For a fixed maximum streak amplitude below the threshold for secondary instability (SI), the most effective wall-normal distance for the formation of the streaks is found to also offer the most stabilization of TS waves. By setting a maximum streak amplitude above the threshold for SI, sinuous shear layer modes become unstable, as well as another instability mode that is amplified in a narrow region near the vortex inlet position.

Effect of dust on tilted electrostatic resistive instability in a Hall thruster

Science.gov (United States)

Tyagi, Jasvendra; Singh, Sukhmander; Malik, Hitendra K.

2018-03-01

Effect of negatively charged dust on resistive instability corresponding to the electrostatic wave is investigated in a Hall thruster plasma when this purely azimuthal wave is tilted and strong axial component of wave vector is developed. Analytical calculations are done to obtain the relevant dispersion equation, which is solved numerically to investigate the growth rate of the instability. The magnitude of the growth rate in the plasma having dust particles is found to be much smaller than the case of pure plasma. However, the instability grows faster for the increasing dust density and the higher charge on the dust particles. The higher magnetic field is also found to support the instability.

Scaling of plasma turbulence resulting from parametric instabilities

International Nuclear Information System (INIS)

Ott, E.

1976-01-01

Dimensional analysis is used to obtain results on the turbulent state resulting from parametric instabilities of an initially cold plasma. The results include the possibility of an applied magnetic field, multiple ion species, and arbitrary dimensionality

Instabilities in electromagnetic quasilevitation.

Science.gov (United States)

Spragg, Kirk; Letout, Sebastien; Ernst, R; Sneyd, Alfred; Fautrelle, Yves

2014-05-01

We investigate free-surface instabilities occurring in various industrial processes involving liquid metal. Of particular interest is the behavior of the free surface of a pool of liquid metal when it is submitted to an alternating magnetic field. Experimentally, we study the effect of a vertical alternating medium-frequency magnetic field on an initially circular pool. We observe various types of behavior according to magnetic field amplitude, e.g., axisymmetric deformations, azimuthal mode structures, slow radial oscillation of the pool perimeter, and random rotation of the pool around its center. Drop rotation could be attributed to nonsymmetric shape deformations. The effect of oxidation leads to drastic changes in pool behavior. The experimental results are then compared to a linear stability analysis of the free surface of a circular liquid drop.

Patellofemoral instability in children: T2 relaxation times of the patellar cartilage in patients with and without patellofemoral instability and correlation with morphological grading of cartilage damage

International Nuclear Information System (INIS)

Kang, Chang Ho; Kim, Hee Kyung; Shiraj, Sahar; Anton, Christopher; Kim, Dong Hoon; Horn, Paul S.

2016-01-01

Patellofemoral instability is one of the most common causes of cartilage damage in teenagers. To quantitatively evaluate the patellar cartilage in patients with patellofemoral instability using T2 relaxation time maps (T2 maps), compare the values to those in patients without patellofemoral instability and correlate them with morphological grades in patients with patellofemoral instability. Fifty-three patients with patellofemoral instability (mean age: 15.9 ± 2.4 years) and 53 age- and gender-matched patients without patellofemoral instability were included. Knee MR with axial T2 map was performed. Mean T2 relaxation times were obtained at the medial, central and lateral zones of the patellar cartilage and compared between the two groups. In the patellofemoral instability group, morphological grading of the patellar cartilage (0-4) was performed and correlated with T2 relaxation times. Mean T2 relaxation times were significantly longer in the group with patellofemoral instability as compared to those of the control group across the patellar cartilage (Student's t-test, P<0.05) with the longest time at the central area. Positive correlation was seen between mean T2 relaxation time and morphological grading (Pearson correlation coefficiency, P<0.001). T2 increased with severity of morphological grading from 0 to 3 (mixed model, P<0.001), but no statistical difference was seen between grades 3 and 4. In patellofemoral instability, patellar cartilage damage occurs across the entire cartilage with the highest T2 values at the apex. T2 relaxation times directly reflect the severity in low-grade cartilage damage, which implies an important role for T2 maps in differentiating between normal and low-grade cartilage damage. (orig.)

Normal Threshold Size of Stimuli in Children Using a Game-Based Visual Field Test.

Science.gov (United States)

Wang, Yanfang; Ali, Zaria; Subramani, Siddharth; Biswas, Susmito; Fenerty, Cecilia; Henson, David B; Aslam, Tariq

2017-06-01

The aim of this study was to demonstrate and explore the ability of novel game-based perimetry to establish normal visual field thresholds in children. One hundred and eighteen children (aged 8.0 ± 2.8 years old) with no history of visual field loss or significant medical history were recruited. Each child had one eye tested using a game-based visual field test 'Caspar's Castle' at four retinal locations 12.7° (N = 118) from fixation. Thresholds were established repeatedly using up/down staircase algorithms with stimuli of varying diameter (luminance 20 cd/m 2 , duration 200 ms, background luminance 10 cd/m 2 ). Relationships between threshold and age were determined along with measures of intra- and intersubject variability. The Game-based visual field test was able to establish threshold estimates in the full range of children tested. Threshold size reduced with increasing age in children. Intrasubject variability and intersubject variability were inversely related to age in children. Normal visual field thresholds were established for specific locations in children using a novel game-based visual field test. These could be used as a foundation for developing a game-based perimetry screening test for children.

Convective instability of RCP modes for a magnetized chiral plasma

International Nuclear Information System (INIS)

Torres-Silva, Hector; Sakanaka, P.H.; Reggiani, N.

1998-01-01

Using the Maxwell's equations and the proposed constitutive relations for a chiral plasma medium, the dispersion relations for right circularly polarized waves, (RCP), depending on the characteristics of the distribution, a new mode conversion and instabilities are found due to the chiral effect. From the dispersion relations and considering that the chirowave magnetic field may be important when the condition of velocity isotropy is dropped, we find that growing modes (instabilities) can occur at resonance and for frequencies below the electron gyrofrequency. We study, in this paper, the convective instability of RCP waves in a two-component bi-Lorentzian chiroplasma which can model the solar wind particle distributions. (author)

Electromagnetic ion beam instability upstream of the earth's bow shock

International Nuclear Information System (INIS)

Gary, S.P.; Gosling, J.T.; Forslund, D.W.

1981-01-01

The linear theory of the electromagnetic ion beam instability for arbitrary angles of propagation has been studied. The parameters considered in the theory are typical of the solar wind upstream of the earth's bow shock when a 'reflected' proton beam is present. Maximum growth occurs for propagation parallel to the ambient field B, but this instability also displays significant growth at wave-vectors oblique to B, Oblique, unstable modes seem to be the likely source of the compressive magnetic fluctuations recently observed in conjunction with 'diffuse' ion population. An energetic ion beam does not directly give rise to linear growth of either ion acoustic or whistler mode instabilities

Possible parametric instabilities of beat waves in a transversely magnetized plasma

International Nuclear Information System (INIS)

Salimullah, M.

1988-05-01

The effect of an external magnetic field on the various possible parametric instabilities of the longitudinal beat wave at the difference frequency of two incident laser beams in a hot plasma has been thoeretically investigated. The kinetic equation is employed to obtain the nonlinear response of the magnetized electrons due to the nonlinear coupling of the beat wave with the low-frequency electrostatic plasma modes. It is noted that the growth rates of the three-wave and the four-wave parametric instabilities can be influenced by the external transverse magnetic field. (author). 20 refs, 3 figs

Anisotropic instability in a laser heated plasma

International Nuclear Information System (INIS)

Sangam, A.; Morreeuw, J.-P.; Tikhonchuk, V. T.

2007-01-01

The theory of the Weibel instability induced by the inverse Bremsstrahlung absorption of a laser light in an underdense plasma is revisited. It is shown that previous analyses have strongly overestimated the effect by neglecting the stabilizing term related to the interaction of the generated quasistatic magnetic field with the laser-heated electrons. The revised model leads to a reduction of the growth rate by more than a factor of 10, to strong reduction of the domain of unstable modes and to inversion of the direction of the unstable wave vectors in the long wavelength limit. The consequences of this instability on the laser plasma interaction are also discussed

Ion acoustic instability of HPT particles, FAC density, anomalous ...

Indian Academy of Sciences (India)

R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

electromagnetic field grow at the expense of the electron kinetic energy and as a result, vari- ous instabilities set in. The magnetometer data indicate that these waves are spatially corre- lated with perturbations; we interpret them as field aligned current (FAC) layers directed into and out of the auroral ionosphere. Kinetic the-.

Induction of genetic instability in ρ53 in primary cultures of normal human urothelium exposed low-dose of gamma radiation

International Nuclear Information System (INIS)

Colucci, S.; Mothersill, C.; Seymour, C.; Harney, J.; Gamble, S.; Arrand, J.

1997-01-01

We have previously shown that primary explant cultures of human urothelium exposed to low doses of gamma radiation subsequently exhibit a high level of stable P53 but it was not clear from those studies whether this protein stabilisation occurred through epigenetic events or as a result of mutation. In these experiments, primary urothelium cultures from five different patients were exposed to 0.5 and 5 Gy γ- radiation from a 60 Cobalt source and allowed to grow for 7- 10 division cycles to allow development of any radiation-induced, non lethal changes in the urothelial cells. C-myc, Bcl-2, and stable P53 protein expression was found to be elevated in cultures following both radiation doses. Following 0.5 Gy exposure, the cultures also developed multiple distinct 'foci' of rapidly-dividing cells which strongly over-expressed P53. These grew on a background of morphologically normal cells. When such foci were selectively analysed for their p53 mutation status by PCR-SSCPE, there was evidence that they contained cells which had developed changes to thr p53 gene post-irradiation. These changes appeared to occur more frequently in focal cells than in cells of normal morphological appearance in the same culture. DNA sequence analysis of the p53 gene in 0.5 Gy-induced foci displayed frame shift mutations in some cases. These results may have mechanistic importance given the controversy regarding low-dose radiation effects and p53-related genomic instability. (authors)

Tail anisotropy instability during plasma current rise by lower-hybrid waves in a tokamak

International Nuclear Information System (INIS)

Yamagiwa, Mitsuru.

1986-01-01

Tail anisotropy instability during lower-hybrid current rise is investigated. Tail formation by lower-hybrid waves is studied by using a Fokker-Planck equation combined with the return field and the rf associated terms. Quasi-linear relaxation of the electron tail distribution under the influence of the plasma waves excited due to the instability is examined. It is found that the instability condition is related to the strength of the parallel diffusion by lower-hybrid waves and the ratio of the electron cyclotron frequency to the electron plasma frequency. The time scale between the instability spikes and the suppression of the instability by electron cyclotron heating are also discussed. (author)

Stabilization of Rayleigh-Taylor instability due to the spontaneous magnetic field in laser produced plasma

International Nuclear Information System (INIS)

Ogasawara, Masatada; Takita, Masami.

1981-08-01

Spontaneous magnetic fields due to the temperature gradient nabla T 0 produced by a focussed laser beam on one point of a pellet are taken into account in deriving the dispersion relation of Rayleigh-Taylor instability. Growth rate γ decreases with time. Density fluctuation with wavelength shorter than 1.5(R/L sub(T)) x (n sub(s)/n 0 )sup(1/2) μm is remarkably stabilized, where R, L sub(T), n sub(s) and n 0 are the radius of a pellet, L sub(T)sup(-1) = + nabla T 0 /T 0 + , number densities of solid and the pellet. Validity condition of the theory is γt 0 >> 1 or in another form R >> L, where t 0 is the time of thermal expansion of a pellet and L -1 = + nabla n 0 /n 0 + . (author)

Direct measurement of the image displacement instability in a linear induction accelerator

Directory of Open Access Journals (Sweden)

T. J. Burris-Mog

2017-06-01

Full Text Available The image displacement instability (IDI has been measured on the 20 MeV Axis I of the dual axis radiographic hydrodynamic test facility and compared to theory. A 0.23 kA electron beam was accelerated across 64 gaps in a low solenoid focusing field, and the position of the beam centroid was measured to 34.3 meters downstream from the cathode. One beam dynamics code was used to model the IDI from first principles, while another code characterized the effects of the resistive wall instability and the beam break-up (BBU instability. Although the BBU instability was not found to influence the IDI, it appears that the IDI influences the BBU. Because the BBU theory does not fully account for the dependence on beam position for coupling to cavity transverse magnetic modes, the effect of the IDI is missing from the BBU theory. This becomes of particular concern to users of linear induction accelerators operating in or near low magnetic guide fields tunes.

Dosimetry of normal and wedge fields for a cobalt-60 teletherapy unit

International Nuclear Information System (INIS)

Tripathi, U.B.; Kelkar, N.Y.

1980-01-01

A simple analytical method for computation of dose distributions for normal and wedge fields is described and the use of the method in planning radiation treatment is outlined. Formulas has been given to compute: (1) depth dose along central axis of cobalt-60 beam, (2) dose to off-axis points, and (3) dose distribution for a wedge field. Good agreement has been found between theoretical and experimental values. With the help of these formulae, the dose at any point can be easily and accurately calculated and radiotherapy can be planned for tumours of very odd shape and sizes. The limitation of the method is that the formulae have been derived for 50% field definition. For cobalt-60 machine having any other field definition, appropriate correction factors have to be applied. (M.G.B.)

The coalescence instability in solar flares

International Nuclear Information System (INIS)

Tajima, T.; Brunel, F.; Sakai, J.I.; Vlahos, L.; Kundu, M.R.

1984-01-01

The non-linear coalescence instability of current carrying solar loops can explain many of the characteristics of the solar flares such as their impulsive nature, heating and high energy particle acceleration, amplitude oscillations of electromagnetic emission as well as the characteristics of 2-D microwave images obtained during a flare. The plasma compressibility leads to the explosive phase of loop coalescence and its overshoot results in amplitude oscillations in temperatures by adiabatic compression and decompression. We note that the presence of strong electric fields and super-Alfvenic flows during the course of the instabilty paly an important role in the production of non-thermal particles. A qualitative explanation on the physical processes taking place during the non-linear stages of the instability is given. (author)

PARTICLE-IN-CELL SIMULATIONS OF CONTINUOUSLY DRIVEN MIRROR AND ION CYCLOTRON INSTABILITIES IN HIGH BETA ASTROPHYSICAL AND HELIOSPHERIC PLASMAS

International Nuclear Information System (INIS)

Riquelme, Mario A.; Quataert, Eliot; Verscharen, Daniel

2015-01-01

We use particle-in-cell simulations to study the nonlinear evolution of ion velocity space instabilities in an idealized problem in which a background velocity shear continuously amplifies the magnetic field. We simulate the astrophysically relevant regime where the shear timescale is long compared to the ion cyclotron period, and the plasma beta is β ∼ 1-100. The background field amplification in our calculation is meant to mimic processes such as turbulent fluctuations or MHD-scale instabilities. The field amplification continuously drives a pressure anisotropy with p > p ∥ and the plasma becomes unstable to the mirror and ion cyclotron instabilities. In all cases, the nonlinear state is dominated by the mirror instability, not the ion cyclotron instability, and the plasma pressure anisotropy saturates near the threshold for the linear mirror instability. The magnetic field fluctuations initially undergo exponential growth but saturate in a secular phase in which the fluctuations grow on the same timescale as the background magnetic field (with δB ∼ 0.3 (B) in the secular phase). At early times, the ion magnetic moment is well-conserved but once the fluctuation amplitudes exceed δB ∼ 0.1 (B), the magnetic moment is no longer conserved but instead changes on a timescale comparable to that of the mean magnetic field. We discuss the implications of our results for low-collisionality astrophysical plasmas, including the near-Earth solar wind and low-luminosity accretion disks around black holes

Collisionless Kelvin-Helmholtz instability and vortex-induced reconnection in the external region of the Earth magnetotail

International Nuclear Information System (INIS)

Pegoraro, F; Faganello, M; Califano, F

2008-01-01

In a magnetized plasma streaming with a non uniform velocity, the Kelvin-Helmholtz instability plays a major role in mixing different plasma regions and in stretching the magnetic field lines leading to the formation of layers with a sheared magnetic field where magnetic field line reconnection can take place. A relevant example is provided by the formation of a mixing layer between the Earth's magnetosphere and the solar wind at low latitudes during northward periods. In the considered configuration, in the presence of a magnetic field nearly perpendicular to the plane defined by the velocity field and its inhomogeneity direction, velocity shear drives a Kelvin-Helmholtz instability which advects and distorts the magnetic field configuration. If the Alfven velocity associated to the in-plane magnetic field is sufficiently weak with respect to the variation of the fluid velocity in the plasma, the Kelvin-Helmholtz instability generates fully rolled-up vortices which advect the magnetic field lines into a complex configuration, causing the formation of current layers along the inversion curves of the in-plane magnetic field component. Pairing of the vortices generated by the Kelvin-Helmholtz instability is a well know phenomenon in two-dimensional hydrodynamics. Here we investigate the development of magnetic reconnection during the vortex pairing process and show that completely different magnetic structures are produced depending on how fast the reconnection process develops on the time scale set by the pairing process.

Coherent instabilities of a relativistic bunched beam

International Nuclear Information System (INIS)

Chao, A.W.

1982-06-01

A charge-particle beam contained in an accelerator vacuum chamber interacts electromagnetically with its environment to create a wake field. This field than acts back on the beam, perturbing the particle motion. If the beam intensity is high enough, this beam-environment interaction may lead to an instability and to subsequent beam loss. The beam and its environment form a dynamical system, and it is this system that will be studied. 84 references

Coherent instabilities of a relativistic bunched beam

Energy Technology Data Exchange (ETDEWEB)

Chao, A.W.

1982-06-01

A charge-particle beam contained in an accelerator vacuum chamber interacts electromagnetically with its environment to create a wake field. This field than acts back on the beam, perturbing the particle motion. If the beam intensity is high enough, this beam-environment interaction may lead to an instability and to subsequent beam loss. The beam and its environment form a dynamical system, and it is this system that will be studied. 84 references.

Searching the beginning of BWR power instability events with the Hilbert Huang transform

International Nuclear Information System (INIS)

Blázquez, Juan; Montalvo, Cristina; García-Berrocal, Agustín; Balbás, Miguel

2013-01-01

Highlights: ► The report of the instability is enriched by including its beginning and its end. ► The Hilbert Huang transform (HHT) is used for indentifying both. ► The first Intrinsic Mode Function (IMF) detects both. ► The methodology is applied to neutron detector signals from two plants. ► The Decay Ratio of IMF 1 is calculated. - Abstract: When a BWR instability takes place, the Regulator usually demands a report which must include many aspects such as the initial time of the instability and also the measurements adopted by the operator at that time. This initial time normally is difficult to know from the available data. In this work, a methodology is proposed to determine accurately when the instability began based on the Hilbert–Huang transform. The Empirical Mode Decomposition is applied to neutron detector signals coming from two plants which have recorded them during real instability events. The first intrinsic mode function shows sharply the beginning and the end of the incident. Besides, through the instantaneous amplitude and frequency of the first mode a kind of Decay Ratio can be assigned allowing us to obtain a sharper description of the instability

On MHD waves, fire-hose and mirror instabilities in anisotropic plasmas

Directory of Open Access Journals (Sweden)

L.-N. Hau

2007-09-01

Full Text Available Temperature or pressure anisotropies are characteristic of space plasmas, standard magnetohydrodynamic (MHD model for describing large-scale plasma phenomena however usually assumes isotropic pressure. In this paper we examine the characteristics of MHD waves, fire-hose and mirror instabilities in anisotropic homogeneous magnetized plasmas. The model equations are a set of gyrotropic MHD equations closed by the generalized Chew-Goldberger-Low (CGL laws with two polytropic exponents representing various thermodynamic conditions. Both ions and electrons are allowed to have separate plasma beta, pressure anisotropy and energy equations. The properties of linear MHD waves and instability criteria are examined and numerical examples for the nonlinear evolutions of slow waves, fire-hose and mirror instabilities are shown. One significant result is that slow waves may develop not only mirror instability but also a new type of compressible fire-hose instability. Their corresponding nonlinear structures thus may exhibit anticorrelated density and magnetic field perturbations, a property used for identifying slow and mirror mode structures in the space plasma environment. The conditions for nonlinear saturation of both fire-hose and mirror instabilities are examined.

Particle acceleration by inverse-Weibel instability

International Nuclear Information System (INIS)

Kawata, S.

1996-01-01

A high demagnetization rate delta B/delta t can be obtained through fast decoupling of a magnetic field from an electric circuit which generates the magnetic field. Nowadays fast decoupling is possible by present switching technologies. A high particle-acceleration gradient can be obtained in an inductive acceleration system compared with that in a conventional induction accelerator. Based on this new proposal, inductive ion and electron accelerations were investigated numerically. The mechanism presented can be considered as pseudo-inverse Weibel instability. (author). 3 figs., 7 refs

Particle acceleration by inverse-Weibel instability

Energy Technology Data Exchange (ETDEWEB)

Kawata, S [Nagaoka Univ. of Technology (Japan). Dept. of Electrical Engineering

1997-12-31

A high demagnetization rate delta B/delta t can be obtained through fast decoupling of a magnetic field from an electric circuit which generates the magnetic field. Nowadays fast decoupling is possible by present switching technologies. A high particle-acceleration gradient can be obtained in an inductive acceleration system compared with that in a conventional induction accelerator. Based on this new proposal, inductive ion and electron accelerations were investigated numerically. The mechanism presented can be considered as pseudo-inverse Weibel instability. (author). 3 figs., 7 refs.

SIMULATIONS OF THE KELVIN–HELMHOLTZ INSTABILITY DRIVEN BY CORONAL MASS EJECTIONS IN THE TURBULENT CORONA

Energy Technology Data Exchange (ETDEWEB)

Gómez, Daniel O.; DeLuca, Edward E. [Harvard-Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA 02138 (United States); Mininni, Pablo D. [Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and Instituto de Física de Buenos Aires, Ciudad Universitaria, 1428 Buenos Aires (Argentina)

2016-02-20

Recent high-resolution Atmospheric Imaging Assembly/Solar Dynamics Observatory images show evidence of the development of the Kelvin–Helmholtz (KH) instability, as coronal mass ejections (CMEs) expand in the ambient corona. A large-scale magnetic field mostly tangential to the interface is inferred, both on the CME and on the background sides. However, the magnetic field component along the shear flow is not strong enough to quench the instability. There is also observational evidence that the ambient corona is in a turbulent regime, and therefore the criteria for the development of the instability are a priori expected to differ from the laminar case. To study the evolution of the KH instability with a turbulent background, we perform three-dimensional simulations of the incompressible magnetohydrodynamic equations. The instability is driven by a velocity profile tangential to the CME–corona interface, which we simulate through a hyperbolic tangent profile. The turbulent background is generated by the application of a stationary stirring force. We compute the instability growth rate for different values of the turbulence intensity, and find that the role of turbulence is to attenuate the growth. The fact that KH instability is observed sets an upper limit on the correlation length of the coronal background turbulence.

Effect of gyroviscosity on the small axial wavelength internal kink instability in the Z-pinch

International Nuclear Information System (INIS)

Scheffel, J.; Faghihi, M.

1987-03-01

The effect of ion gyroviscosity on the stability of m=1 small axial wavelength kinks in a z-pinch with purely poloidal magnetic field is investigated by normal mode methods. We use the Incompressible FLR MHD model; a collisionless fluid model introduced to include Finite Larmor Radius effects. For vanishing Larmor radius, a stability criterion which coincides with that of ideal MHD is found; the Kadomtsev criterion 2rdp/dr+m/sp2/B/sp2///my//sb0/> or = 0. This criterion predicts instability unless the current density becomes singular at the centre of the pinch. When the Larmor radius terms of the ion pressure tensor are included, we find that marginally unstable (ideal) modes are stabilized. (authors)

Conditions for l =1 Pomeranchuk instability in a Fermi liquid

Science.gov (United States)

Wu, Yi-Ming; Klein, Avraham; Chubukov, Andrey V.

2018-04-01

We perform a microscopic analysis of how the constraints imposed by conservation laws affect q =0 Pomeranchuk instabilities in a Fermi liquid. The conventional view is that these instabilities are determined by the static interaction between low-energy quasiparticles near the Fermi surface, in the limit of vanishing momentum transfer q . The condition for a Pomeranchuk instability is set by Flc (s )=-1 , where Flc (s ) (a Landau parameter) is a properly normalized partial component of the antisymmetrized static interaction F (k ,k +q ;p ,p -q ) in a charge (c) or spin (s) subchannel with angular momentum l . However, it is known that conservation laws for total spin and charge prevent Pomeranchuk instabilities for l =1 spin- and charge-current order parameters. Our study aims to understand whether this holds only for these special forms of l =1 order parameters or is a more generic result. To this end we perform a diagrammatic analysis of spin and charge susceptibilities for charge and spin density order parameters, as well as perturbative calculations to second order in the Hubbard U . We argue that for l =1 spin-current and charge-current order parameters, certain vertex functions, which are determined by high-energy fermions, vanish at Fl=1 c (s )=-1 , preventing a Pomeranchuk instability from taking place. For an order parameter with a generic l =1 form factor, the vertex function is not expressed in terms of Fl=1 c (s ), and a Pomeranchuk instability may occur when F1c (s )=-1 . We argue that for other values of l , a Pomeranchuk instability may occur at Flc (s )=-1 for an order parameter with any form factor.

Instability waves and transition in adverse-pressure-gradient boundary layers

Science.gov (United States)

Bose, Rikhi; Zaki, Tamer A.; Durbin, Paul A.

2018-05-01

Transition to turbulence in incompressible adverse-pressure-gradient (APG) boundary layers is investigated by direct numerical simulations. Purely two-dimensional instability waves develop on the inflectional base velocity profile. When the boundary layer is perturbed by isotropic turbulence from the free stream, streamwise elongated streaks form and may interact with the instability waves. Subsequent mechanisms that trigger transition depend on the intensity of the free-stream disturbances. All evidence from the present simulations suggest that the growth rate of instability waves is sufficiently high to couple with the streaks. Under very low levels of free-stream turbulence (˜0.1 % ), transition onset is highly sensitive to the inlet disturbance spectrum and is accelerated if the spectrum contains frequency-wave-number combinations that are commensurate with the instability waves. Transition onset and completion in this regime is characterized by formation and breakdown of Λ vortices, but they are more sporadic than in natural transition. Beneath free-stream turbulence with higher intensity (1-2 % ), bypass transition mechanisms are dominant, but instability waves are still the most dominant disturbances in wall-normal and spanwise perturbation spectra. Most of the breakdowns were by disturbances with critical layers close to the wall, corresponding to inner modes. On the other hand, the propensity of an outer mode to occur increases with the free-stream turbulence level. Higher intensity free-stream disturbances induce strong streaks that favorably distort the boundary layer and suppress the growth of instability waves. But the upward displacement of high amplitude streaks brings them to the outer edge of the boundary layer and exposes them to ambient turbulence. Consequently, high-amplitude streaks exhibit an outer-mode secondary instability.

Instabilities responsible for magnetic turbulence in laboratory rotating plasma

International Nuclear Information System (INIS)

Mikhailovskii, A.B.; Lominadze, J.G.; Churikov, A.P.; Erokhin, N.N.; Pustovitov, V.D.; Konovalov, S.V.

2008-01-01

Instabilities responsible for magnetic turbulence in laboratory rotating plasma are investigated. It is shown that the plasma compressibility gives a new driving mechanism in addition to the known Velikhov effect due to the negative rotation frequency gradient. This new mechanism is related to the perpendicular plasma pressure gradient, while the density gradient gives an additional drive depending also on the pressure gradient. It is shown that these new effects can manifest themselves even in the absence of the equilibrium magnetic field, which corresponds to nonmagnetic instabilities

Pinch instabilities in Taylor-Couette flow.

Science.gov (United States)

Shalybkov, Dima

2006-01-01

The linear stability of the dissipative Taylor-Couette flow with an azimuthal magnetic field is considered. Unlike ideal flows, the magnetic field is a fixed function of a radius with two parameters only: a ratio of inner to outer cylinder radii, eta, and a ratio of the magnetic field values on outer and inner cylinders, muB. The magnetic field with 0rotation. The unstable modes are located into some interval of the axial wave numbers for the flow stable without magnetic field. The interval length is zero for a critical Hartmann number and increases with an increasing Hartmann number. The critical Hartmann numbers and length of the unstable axial wave number intervals are the same for every rotation law. There are the critical Hartmann numbers for m=0 sausage and m=1 kink modes only. The sausage mode is the most unstable mode close to Ha=0 point and the kink mode is the most unstable mode close to the critical Hartmann number. The transition from the sausage instability to the kink instability depends on the Prandtl number Pm and this happens close to one-half of the critical Hartmann number for Pm=1 and close to the critical Hartmann number for Pm=10(-5). The critical Hartmann numbers are smaller for kink modes. The flow stability does not depend on magnetic Prandtl numbers for m=0 mode. The same is true for critical Hartmann numbers for both m=0 and m=1 modes. The typical value of the magnetic field destabilizing the liquid metal Taylor-Couette flow is approximately 10(2) G.

Nonlinear instability and chaos in plasma wave-wave interactions

International Nuclear Information System (INIS)

Kueny, C.S.

1993-01-01

Conventional linear stability analysis may fail for fluid systems with an indefinite free energy functional. When such a system is linearly stable, it is said to possess negative energy modes. Instability may then occur either via dissipation of the negative energy modes. Instability may then occur either via dissipation of the negative energy modes. Instability may then occur either via dissipitation of the negative energy modes, or nonlinearly via resonant wave-wave coupling, which leads to explosive growth. In the dissipationaless case, it is conjectured that intrinsic chaotic behavior may allow initially non-resonant systems to reach resonance by diffusion in phase space. This is illustrated for a simple equilibrium involving cold counter-streaming ions. The system is described in the fluid approximation by a Hamilitonian functional and associated noncanonical Poisson bracket. By Fourier decomposition and appropriate coordinate transformations, the Hamilitonian for the perturbed energy is expressed in action-angle form. The normal modes correspond to Doppler-shifted ion-acoustic waves of positive and negative energy. Nonlinear coupling leads to decay instability via two-wave interactions, which occur generically for long enough wavelengths. Three-wave interactions which occur in isolated, but numerous, regions of parameter space can drive either decay instability or explosive instability. When the resonance for explosive growth is detuned, a stable region exists around the equilibrium point in phase space, while explosive growth occurs outside of a separatrix. These interactions may be described exactly if only one resonance is considered, while multiple nonlinear terms make the Hamiltonian nonintegradable. Simple Hamiltonians of two and three degrees of freedom are studied numerically using symplectic integration algorithms, including an explicit algorithm derived using Lie algebraic methods

Compact dispersion relations for parametric instabilities of electromagnetic waves in magnetized plasmas

International Nuclear Information System (INIS)

Cohen, B.I.

1987-01-01

The existence of compact dispersion relations for parametric instabilities of coherent electromagnetic waves in magnetized plasmas is addressed here. In general, comprehensive dispersion relations for parametric instabilities in unmagnetized plasmas become more complicated in the presence of an applied time-independent magnetic field. This is demonstrated with a fluid perturbation theory. A compact dispersion relation for parametric instabilities in unmagnetized plasma is heuristically extended here to the case of a magnetized plasma. This dispersion relation gives the correct results in a variety of circumstances of interest in considering electron cyclotron heating applications

Instabilities and nonstatistical behavior in globally coupled systems

International Nuclear Information System (INIS)

Perez, G.; Cerdeira, H.A.

1992-08-01

The mean field in a globally coupled system of chaotic logistic maps does not obey the standard rules of statistics, even for systems of very large sizes. This indicates the existence of intrinsic instabilities in its evolution. Here these instabilities are related to the very non-smooth behavior of mean values in a single logistic map, as a function of its parameter. Problems of this kind do not affect a similar system of coupled tent maps, where good statistical behavior has been found. We also explore the transition between these two regimes. (author). 15 refs, 9 figs

Chronicle of ion-current instabilities: old and new

International Nuclear Information System (INIS)

Landau, R.W.

1975-07-01

For counter-streaming ion currents along a uniform magnetic field, a purely growing instability exists with a growth rate as high as 16 times the ion gyrofrequency. When the streaming ions are only 1 percent of the stationary ions, the growth rate is still 4 times the gyrofrequency, but the real part is near the lower hybrid frequency. These instabilities are in addition to the Drummond-Rosenbluth ion mode. Finite β effects increase the growth rate and can be important for β greater than 10 -4 . In all this, T/sub parallel,+/ = T/sub parallel,-/ and T/sub perpendicular to/ = 0. (U.S.)

The Hall instability of unsteady inhomogeneous axially symmetric magnetized plasmas

International Nuclear Information System (INIS)

Shtemler, Yuri M.; Mond, Michael; Liverts, Edward

2004-01-01

The Hall instability in cylindrically symmetric resistive magnetized plasmas in vacuum is investigated. The unperturbed self-similar equilibrium solutions for imploding Z-pinches with time-dependent total current I t ∼t S ,S>1/3, are subjected by short-wave sausage perturbations. The instability criterion is derived in slow-time, frozen-radius approximation. In cylindrically symmetric configurations the instability is driven by the magnetic field curvature. The near-axis and near-edge branches of the neutral curve in the plane of the inverse Hall parameter and phase velocity with the frozen radial coordinate as a parameter are separated by the critical point, where the modified gradient from the unperturbed number density changes sign. The critical radius may be treated as a new characteristic size of the Z-pinch that emerges due to the instability: the pinch is envisaged restructured by the short-scale high-frequency Hall instability, in which a central stable core is surrounded by an outer shell. Such a modified equilibrium may explain the observed enhanced stability against magnetohydrodynamic modes

Ponderomotive force effects on temperature-gradient-driven instabilities

International Nuclear Information System (INIS)

Sundaram, A.K.; Hershkowitz, N.

1992-01-01

The modification of temperature-gradient-driven instabilities due to the presence of nonuniform radio-frequency fields near the ion cyclotron frequency is investigated in the linear regime. Employing the fluid theory, it is shown that the induced field line compression caused by ion cyclotron range of frequencies (ICRF) fields makes the net parallel compressibility positive, and thus provides a stabilizing influence on the ion-temperature-gradient-driven mode for an appropriately tailored profile of radio-frequency (rf) pressure. Concomitantly, the radial ponderomotive force generates an additional contribution via coupling between the perturbed fluid motion and the equilibrium ponderomotive force and this effect plays the role of dissipation to enhance or decrease the growth of temperature-gradient-driven modes depending upon the sign of rf pressure gradients. For decreased growth of temperature-gradient-driven instabilities, the plasma density gradients and rf pressure gradients must have opposite signs while enhancement in growth arises when both gradients have the same sign. Finally, the kinetic effects associated with these modes are briefly discussed

A Note on the First Integrals of Vector Fields with Integrating Factors and Normalizers

Directory of Open Access Journals (Sweden)

Jaume Llibre

2012-06-01

Full Text Available We prove a sufficient condition for the existence of explicit first integrals for vector fields which admit an integrating factor. This theorem recovers and extends previous results in the literature on the integrability of vector fields which are volume preserving and possess nontrivial normalizers. Our approach is geometric and coordinate-free and hence it works on any smooth orientable manifold.

Effects of three-mode field interactions in laser instabilities and in beat-frequency spectroscopy

International Nuclear Information System (INIS)

Herdow, S.T.

1982-01-01

Population pulsations are fluctuations in the population difference (of a two level system) due to the presence of two or more coherent waves interfering in the medium. In this work, the author shows that population pulsations generated by three waves, a central wave and two mode-locked sidebands, are responsible for both the multiwavelength and the single-wavelength instabilities of single-mode lasers containing homgeneously-broadened media. The role of the population pulsations in establishing these instabilities, however, diminish as the central mode is detuned away from the atomic resonance frequency. For homogeneously-broadened lasers, the author finds two regions of single-wavelength instability. The first is at line center, for which population pulsations are solely responsible, and the second is off line center where the unsaturated medium provides the required gain and anomalous dispersion. For the case of inhomogeneously-broadened lasers, the author shows that population pulsations significantly increase the instability range over that predicted by Casperson for single-mode bad-cavity lasers. Both the unidirectional ring and the standing-wave cavities are treated. The Fourier expansion technique, used in this work, for treating three-frequency operation in saturation spectroscopy is shown to be equivalent (in appropriate limits) to the linear stability analysis in laser theory and optical bistability. The author also shows, in single-sideband saturation spectroscopy, that for long interaction lengths propagation effects can significantly influence the absorption and dispersion coefficients of the medium. Finally, the author shows that under certain conditions the pronounced splitting effects of the population pulsations develop into regions of intense absorption

An analytic study of the perpendicularly propagating electromagnetic drift instabilities in the Magnetic Reconnection Experiment

International Nuclear Information System (INIS)

Wang Yansong; Kulsrud, Russell; Ji, Hantao

2008-01-01

A local linear theory is proposed for a perpendicularly propagating drift instability driven by relative drifts between electrons and ions. The theory takes into account local cross-field current, pressure gradients, and modest collisions as in the Magnetic Reconnection Experiment [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)]. The unstable waves have very small group velocities in the direction of the pressure gradient, but have a large phase velocity near the relative drift velocity between electrons and ions in the direction of the cross-field current. By taking into account the electron-ion collisions and applying the theory in the Harris sheet, we establish that this instability could be excited near the center of the Harris sheet and have enough e-foldings to grow to large amplitude before it propagates out of the unstable region. Comparing with the other magnetic reconnection related instabilities (lower-hybrid-drift instability, modified two-stream instability, etc.) studied previously, we believe the instability we found is a favorable candidate to produce anomalous resistivity because of its unique wave characteristics, such as electromagnetic component, large phase velocity, and small group velocity in the cross-current-layer direction.

A comparative study of plasma heating by ion acoustic and modified two-stream instabilities at subcritical quasi-perpendicular shocks

International Nuclear Information System (INIS)

Winske, D.; Giacalone, J.; Thomsen, M.F.; Mellott, M.M.

1987-01-01

Plasma heating due to the ion instability and the modified two-stream instability is examined for quasi-perpendicular subcritical shocks. Electron and ion heating is investigated as a function of upstream electron to ion temperature ratio and plasma beta using second-order heating rates. A simple shock model is employed in which the cross-field electron-ion drift speed is adjusted until the total (adiabatic plus anomalous) heating matches that required by the Rankine-Hugoniot relations. Quantities such as the width of the shock and the maximum electric field fluctuations are also calculated, and the results are compared with the ISEE data set of subcritical box shock crossings. The observed width of the shock, the amount of plasma heating, and the low-frequency electric field intensity are in reasonably good agreement with the calculations for the modified two-stream instability. On the other hand, the wave intensities at higher frequency are about 4 orders of magnitude smaller than those predicted for the ion acoustic instability at saturation, consistent with the fact that the measured shock widths imply cross-field drift speeds that are below threshold for this instability. It is therefore concluded that the dissipation at these shocks is most likely due to the lower frequency, modified two-stream instability

An Obliquely Propagating Electromagnetic Drift Instability in the Lower Hybrid Frequency Range

International Nuclear Information System (INIS)

Hantao Ji; Russell Kulsrud; William Fox; Masaaki Yamada

2005-01-01

By employing a local two-fluid theory, we investigate an obliquely propagating electromagnetic instability in the lower hybrid frequency range driven by cross-field current or relative drifts between electrons and ions. The theory self-consistently takes into account local cross-field current and accompanying pressure gradients. It is found that the instability is caused by reactive coupling between the backward propagating whistler (fast) waves in the moving electron frame, and the forward propagating sound (slow) waves in the ion frame when the relative drifts are large. The unstable waves we consider propagate obliquely to the unperturbed magnetic field and have mixed polarization with significant electromagnetic components. A physical picture of the instability emerges in the limit of large wave number characteristic of the local approximation. The primary positive feedback mechanism is based on reinforcement of initial electron density perturbations by compression of electron fluid via induced Lorentz force. The resultant waves are qualitatively consistent with the measured electromagnetic fluctuations in reconnecting current sheet in a laboratory plasma

Pump instability phenomena generated by fluid forces

Science.gov (United States)

Gopalakrishnan, S.

1985-01-01

Rotor dynamic behavior of high energy centrifugal pumps is significantly affected by two types of fluid forces; one due to the hydraulic interaction of the impeller with the surrounding volute or diffuser and the other due to the effect of the wear rings. The available data on these forces is first reviewed. A simple one degree-of-freedom system containing these forces is analytically solved to exhibit the rotor dynamic effects. To illustrate the relative magnitude of these phenomena, an example of a multistage boiler feed pump is worked out. It is shown that the wear ring effects tend to suppress critical speed and postpone instability onset. But the volute-impeller forces tend to lower the critical speed and the instability onset speed. However, for typical boiler feed pumps under normal running clearances, the wear ring effects are much more significant than the destabilizing hydraulic interaction effects.

Mlh1 deficiency in normal mouse colon mucosa associates with chromosomally unstable colon cancer

Science.gov (United States)

Pussila, Marjaana; Törönen, Petri; Einarsdottir, Elisabet; Katayama, Shintaro; Krjutškov, Kaarel; Holm, Liisa; Kere, Juha; Peltomäki, Päivi; Mäkinen, Markus J; Linden, Jere; Nyström, Minna

2018-01-01

Abstract Colorectal cancer (CRC) genome is unstable and different types of instabilities, such as chromosomal instability (CIN) and microsatellite instability (MSI) are thought to reflect distinct cancer initiating mechanisms. Although 85% of sporadic CRC reveal CIN, 15% reveal mismatch repair (MMR) malfunction and MSI, the hallmarks of Lynch syndrome with inherited heterozygous germline mutations in MMR genes. Our study was designed to comprehensively follow genome-wide expression changes and their implications during colon tumorigenesis. We conducted a long-term feeding experiment in the mouse to address expression changes arising in histologically normal colonic mucosa as putative cancer preceding events, and the effect of inherited predisposition (Mlh1+/−) and Western-style diet (WD) on those. During the 21-month experiment, carcinomas developed mainly in WD-fed mice and were evenly distributed between genotypes. Unexpectedly, the heterozygote (B6.129-Mlh1tm1Rak) mice did not show MSI in their CRCs. Instead, both wildtype and heterozygote CRC mice showed a distinct mRNA expression profile and shortage of several chromosomal segregation gene-specific transcripts (Mlh1, Bub1, Mis18a, Tpx2, Rad9a, Pms2, Cenpe, Ncapd3, Odf2 and Dclre1b) in their colon mucosa, as well as an increased mitotic activity and abundant numbers of unbalanced/atypical mitoses in tumours. Our genome-wide expression profiling experiment demonstrates that cancer preceding changes are already seen in histologically normal colon mucosa and that decreased expressions of Mlh1 and other chromosomal segregation genes may form a field-defect in mucosa, which trigger MMR-proficient, chromosomally unstable CRC. PMID:29701748

Arcuate ligament of the wrist: normal MR appearance and its relationship to palmar midcarpal instability: a cadaveric study

International Nuclear Information System (INIS)

Chang, Weiling; Peduto, Anthony J.; Aguiar, Rodrigo O.C.; Trudell, Debra J.; Resnick, Donald L.

2007-01-01

To describe the magnetic resonance (MR) imaging and gross anatomic appearance of the scaphocapitate (SC) ligament and triquetrohamocapitate (THC) ligament, which are the radial and ulnar limbs of the composite arcuate ligament, a critical volar midcarpal stabilizing ligament. T1 spin-echo and 3D gradient-echo MR imaging in the standard, coronal oblique, and axial oblique planes were performed both before and following midcarpal arthrography in seven cadaveric wrists. The seven specimens were then sectioned in selected planes to optimally visualize the SC and THC ligaments. These specimens were analyzed and correlated with their corresponding MR images. The SC and THC ligaments can be visualized in MR images as structures of low signal intensity that form an inverted ''V'' joining the proximal and distal carpal rows. The entire ligamentous complex is best visualized with coronal and axial oblique MR imaging but can also be seen in standard imaging planes. SC and THC ligaments together form the arcuate ligament of the wrist. Their function is crucial to the normal functioning of the wrist. Palmar midcarpal instability (PMCI) is a resulting condition when abnormalities of these ligaments occur. Dedicated MR imaging in the coronal and axial imaging planes can be performed in patients suspected of having PCMI. (orig.)

Arcuate ligament of the wrist: normal MR appearance and its relationship to palmar midcarpal instability: a cadaveric study

Energy Technology Data Exchange (ETDEWEB)

Chang, Weiling [Veterans Administration Medical Center, Department of Radiology, San Diego, CA (United States); Sharp-Grossmont Hospital, Department of Radiology, La Mesa, CA (United States); Peduto, Anthony J. [Veterans Administration Medical Center, Department of Radiology, San Diego, CA (United States); Westmead Hospital and Western Clinical School of Sydney University, Department of Radiology, Sydney (Australia); Aguiar, Rodrigo O.C. [Veterans Administration Medical Center, Department of Radiology, San Diego, CA (United States); Universidade Federal do Rio de Janeiro, Rio de Janerio (Brazil); Trudell, Debra J.; Resnick, Donald L. [Veterans Administration Medical Center, Department of Radiology, San Diego, CA (United States)

2007-07-15

To describe the magnetic resonance (MR) imaging and gross anatomic appearance of the scaphocapitate (SC) ligament and triquetrohamocapitate (THC) ligament, which are the radial and ulnar limbs of the composite arcuate ligament, a critical volar midcarpal stabilizing ligament. T1 spin-echo and 3D gradient-echo MR imaging in the standard, coronal oblique, and axial oblique planes were performed both before and following midcarpal arthrography in seven cadaveric wrists. The seven specimens were then sectioned in selected planes to optimally visualize the SC and THC ligaments. These specimens were analyzed and correlated with their corresponding MR images. The SC and THC ligaments can be visualized in MR images as structures of low signal intensity that form an inverted ''V'' joining the proximal and distal carpal rows. The entire ligamentous complex is best visualized with coronal and axial oblique MR imaging but can also be seen in standard imaging planes. SC and THC ligaments together form the arcuate ligament of the wrist. Their function is crucial to the normal functioning of the wrist. Palmar midcarpal instability (PMCI) is a resulting condition when abnormalities of these ligaments occur. Dedicated MR imaging in the coronal and axial imaging planes can be performed in patients suspected of having PCMI. (orig.)

To the theory of the Pierce instability of neutralized electron flows

International Nuclear Information System (INIS)

Ignatov, A.M.; Rukhadze, A.A.

1984-01-01

The Pierce instability of a nonrelativistic electron beam in an exernal fi inite magnetic field is investigated. Analytical expressions for a critical electron density in limiting cases of strong or weak magnetic field have been fo ound. The critical electron density is shown to increase with a decrease in the magnetic field strength

Pressure-anisotropy-induced nonlinearities in the kinetic magnetorotational instability

Science.gov (United States)

Squire, J.; Quataert, E.; Kunz, M. W.

2017-12-01

In collisionless and weakly collisional plasmas, such as hot accretion flows onto compact objects, the magnetorotational instability (MRI) can differ significantly from the standard (collisional) MRI. In particular, pressure anisotropy with respect to the local magnetic-field direction can both change the linear MRI dispersion relation and cause nonlinear modifications to the mode structure and growth rate, even when the field and flow perturbations are very small. This work studies these pressure-anisotropy-induced nonlinearities in the weakly nonlinear, high-ion-beta regime, before the MRI saturates into strong turbulence. Our goal is to better understand how the saturation of the MRI in a low-collisionality plasma might differ from that in the collisional regime. We focus on two key effects: (i) the direct impact of self-induced pressure-anisotropy nonlinearities on the evolution of an MRI mode, and (ii) the influence of pressure anisotropy on the `parasitic instabilities' that are suspected to cause the mode to break up into turbulence. Our main conclusions are: (i) The mirror instability regulates the pressure anisotropy in such a way that the linear MRI in a collisionless plasma is an approximate nonlinear solution once the mode amplitude becomes larger than the background field (just as in magnetohyrodynamics). This implies that differences between the collisionless and collisional MRI become unimportant at large amplitudes. (ii) The break up of large-amplitude MRI modes into turbulence via parasitic instabilities is similar in collisionless and collisional plasmas. Together, these conclusions suggest that the route to magnetorotational turbulence in a collisionless plasma may well be similar to that in a collisional plasma, as suggested by recent kinetic simulations. As a supplement to these findings, we offer guidance for the design of future kinetic simulations of magnetorotational turbulence.

Instabilities in superconductors and in intense laser produced plasma's