scholarly journals Resonant Weibel instability in counterstreaming plasmas with temperature anisotropies

2009 ◽  
Vol 76 (1) ◽  
pp. 49-56 ◽  
Author(s):  
M. LAZAR ◽  
M. E. DIECKMANN ◽  
S. POEDTS
Keyword(s):  
Plasma Temperature ◽  
Thermal Velocity ◽  
Temperature Anisotropy ◽  
Large Wave ◽  
Thermal Emissions ◽  
Weibel Instability ◽  
Wave Numbers ◽  
Transverse Temperature ◽  
New Feature ◽  
The Stability

AbstractThe Weibel instability, driven by a plasma temperature anisotropy, is non-resonant with plasma particles: it is purely growing in time, and does not oscillate. The effect of a counterstreaming plasma is examined. In a counterstreaming plasma with an excess of transverse temperature, the Weibel instability arises along the streaming direction. Here it is proved that for large wave-numbers the instability becomes resonant with a finite real (oscillation) frequency, ωr ≠ 0. When the plasma flows faster, with a bulk velocity larger than the parallel thermal velocity, the instability becomes dominantly resonant. This new feature of the Weibel instability can be relevant for astrophysical sources of non-thermal emissions and the stability of counterflowing plasma experiments.

scholarly journals Causality and stability conditions of a conformal charged fluid

2020 ◽  
Vol 2020 (8) ◽  
Author(s):  
Farid Taghinavaz
Keyword(s):  
Chemical Potential ◽  
Second Law Of Thermodynamics ◽  
Dense Medium ◽  
Wave Number ◽  
Second Law ◽  
Stability Conditions ◽  
Charged Fluid ◽  
Large Wave ◽  
The Stability ◽  
Large Wave Number

Abstract In this paper, I study the conditions imposed on a normal charged fluid so that the causality and stability criteria hold for this fluid. I adopt the newly developed General Frame (GF) notion in the relativistic hydrodynamics framework which states that hydrodynamic frames have to be fixed after applying the stability and causality conditions. To do this, I take a charged conformal matter in the flat and 3 + 1 dimension to analyze better these conditions. The causality condition is applied by looking to the asymptotic velocity of sound hydro modes at the large wave number limit and stability conditions are imposed by looking to the imaginary parts of hydro modes as well as the Routh-Hurwitz criteria. By fixing some of the transports, the suitable spaces for other ones are derived. I observe that in a dense medium having a finite U(1) charge with chemical potential μ0, negative values for transports appear and the second law of thermodynamics has not ruled out the existence of such values. Sign of scalar transports are not limited by any constraints and just a combination of vector transports is limited by the second law of thermodynamic. Also numerically it is proved that the most favorable region for transports $$ {\tilde{\upgamma}}_{1,2}, $$ γ ˜ 1 , 2 , coefficients of the dissipative terms of the current, is of negative values.

PARABOLIC LIMIT AND STABILITY OF THE VLASOV–FOKKER–PLANCK SYSTEM

2000 ◽  
Vol 10 (07) ◽  
pp. 1027-1045 ◽  
Author(s):  
F. POUPAUD ◽  
J. SOLER
Keyword(s):  
Free Path ◽  
Space Dimension ◽  
Mass Density ◽  
Mean Free Path ◽  
Convergence Result ◽  
Limit Equation ◽  
Thermal Velocity ◽  
The Stability ◽  
Parabolic Limit ◽  
Fokker Planck

In this paper the stability of the Vlasov–Poisson–Fokker–Planck with respect to the variation of its constant parameters, the scaled thermal velocity and the scaled thermal mean free path, is analyzed. For the case in which the scaled thermal velocity is the inverse of the scaled thermal mean free path and the latter tends to zero, a parabolic limit equation is obtained for the mass density. Depending on the space dimension and on the hypothesis for the initial data, the convergence result in L1 is weak and global in time or strong and local in time.

STUDIES OF THE ENERGY SPECTRUM AND THE WAVE FUNCTION FOR LOW ENERGY EXCITED STATES IN LIQUID HELIUM II

2007 ◽  
Vol 21 (21) ◽  
pp. 1383-1390
Author(s):  
DE-HUA LIN ◽  
PING ZOU ◽  
ZHONG-WEI ZHANG ◽  
HONG-LEI WANG ◽  
JUN PAN ◽  
...  
Keyword(s):  
Experimental Data ◽  
Wave Function ◽  
Energy Spectrum ◽  
Liquid Helium ◽  
Excited States ◽  
Low Energy ◽  
Large Wave ◽  
Helium Ii ◽  
Wave Numbers ◽  
Specific Temperature

In this paper, we study the elementary excitations and energy spectrum proposed by L. D. Landau in liquid helium II. On the basis of the energy spectrum for the phonons and rotons, we put forward a uniform expression of energy spectrum in liquid helium II, which is limited in a specific temperature range. By using the wave function for low energy excited states proposed by R. P. Feynman or the modified one proposed by Feynman and Cohen, it can be found that the estimated energy spectrum is quite different from the experimental data, especially for the region with large wave numbers. By proposing an improved form for the wave function, we re-analyze the energy spectrum in liquid helium II, and our results show a better agreement with the experimental data.

scholarly journals Enstrophy Cascade and Smagorinsky Model of 2D Turbulent Flows

2001 ◽  
Vol 17 (3) ◽  
pp. 121-129
Author(s):  
Mei-Jiau Huang
Keyword(s):  
Reynolds Number ◽  
Large Eddy Simulation ◽  
Turbulent Flows ◽  
Smagorinsky Model ◽  
Large Wave ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Wave Numbers ◽  
Enstrophy Cascade ◽  
Stretching Effect

ABSTRACTDirect numerical simulations of 2D turbulent flows, freely decaying as well as forced, are performed to examine the mechanism of the enstrophy cascade and serve as a template of developing LES models. The stretching effect on the 2D vorticity gradients is emphasized on the analogy of the stretching effect on 3D vorticity. The enstrophy cascade rate, the Reynolds stresses and the associated eddy viscosity for 2D turbulence are correspondingly derived and investigated. Proposed herein is that the enstrophy cascade rate to be modeled in a large-eddy simulation can be and should be calculated using the only available large-eddy information, especially when the Reynolds number is not very large or when the flow is not stationary.The simulation results suggest all Kolmogorov's, Kraichnan's, and Saffman's similarity spectra. The Kolmogorov's spectrum appears in front of forced wave numbers and creates a subrange of a zero enstrophy cascade rate and a constant energy cascade rate. The Saffman's spectrum is the dissipation spectrum at large wave numbers. Kraichnan's spectrum shows up at intermediate wave numbers when the Reynolds number is sufficiently high. When the Smagorinsky model is employed for a large eddy simulation, its inability of capturing the significant reverse cascade phenomenon as observed in the DNS data becomes a fatal defect. Nonetheless, if only the mean cascade rate is concerned, the required Smagorinsky constant is evaluated using the DNS data and compared with the theoretical prediction of the Kraichnan's spectrum.

Wave Propagation and Instability in a Circular Semi-Infinite Liquid Jet Harmonically Forced at the Nozzle

1978 ◽  
Vol 45 (3) ◽  
pp. 469-474 ◽  
Author(s):  
D. B. Bogy
Keyword(s):  
Wave Propagation ◽  
Radiation Condition ◽  
Liquid Jet ◽  
Propagation Characteristics ◽  
Frequency Spectra ◽  
One Dimensional ◽  
Wave Numbers ◽  
Complex Wave ◽  
The Stability ◽  
The Waves

The linearized form of the inviscid, one-dimensional Cosserat jet equations derived by Green [6] are used to study wave propagation in a circular jet with surface tension. The frequency spectra are shown for complex wave numbers for a complete range of Weber numbers. The propagation characteristics of the waves are studied in order to determine which branches of the frequency spectra to use in the semi-infinite jet problem with harmonic forcing at the nozzle. Two of the four branches are eliminated by a radiation condition that energy must be outgoing at infinity; the remaining two branches are used to satisfy the nozzle boundary conditions. The variation of the jet radius along its length is shown graphically for various Weber numbers and forcing frequencies. The stability or instability is explained in terms of the behavior of the two propagating phases.

Uncoupled Wave Systems and Dispersion in an Infinite Solid Cylinder

1989 ◽  
Vol 56 (2) ◽  
pp. 347-355 ◽  
Author(s):  
Yoon Young Kim
Keyword(s):  
Cylindrical Surface ◽  
Wave Motion ◽  
Fourier Number ◽  
Large Wave ◽  
Surface Conditions ◽  
Asymptotic Nature ◽  
Wave Numbers ◽  
Complex Wave ◽  
Insight Into ◽  
Free Cylindrical Surface

In this study, it is shown that there exist uncoupled wave systems for general non-axisymmetric wave propagation in an infinite isotropic cylinder. Two cylindrical surface conditions corresponding to the uncoupled wave systems are discussed. The solutions of the uncoupled wave systems are shown to provide proper bounds of Pochhammer’s equation for a free cylindrical surface. The bounds, which are easy to construct for any Fourier number in the circumferential direction, can be used to trace the branches of Pochhammer’s equation. They also give insight into the modal composition of the branches of Pochhammer’s equation at and between the intersections of the bounds. More refined dispersion relations of Pochhammer’s equation are possible through an asymptotic analysis of the itersections of the branches of Pochhammer’s equation with one family of the bounds. The asymptotic nature of wave motion corresponding to large wave numbers, imaginary or complex, for Pochhammer’s equation is studied. The wave motion is asymptotically equivoluminal for large imaginary wave numbers, and is characterized by coupled dilatation and shear for large complex wave numbers.

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