Parametric instabilities in magnetized bi-ion and dusty plasmas

The excitation of low frequency modes of oscillations in a magnetized bi-ion or dusty plasma with parametric pumping of the magnetic field is analysed. The equation of motion governing the perturbed plasma is derived and parametrically excited transverse modes propagating along the magnetic field are found. With multiple ion species or charged dust present, a number of different circularly polarized modes can be excited. The stability of these modes is investigated as a function of the plasma parameters. The modulational instabilities of large amplitude normal modes, modified by the extra ion species or dust and propagating along the magnetic field, are also investigated Article presented at the International Conference on the Frontiers of Plasma Physics and Technology, 9–14 December 2002, Bangalore, India.     

Parametric decay instabilities of lower hybrid wave into electromagnetic wave

The parametric decay instabilities of lower hybrid wave into electromagnetic modes are investigated in homogenous magnetized plasma. The resonant decay instabilities and the oscillating two stream instabilities are studied numerically in detail.     

Parametric excitation of magnetic electron drift vortex modes by Langmuir waves

A new multi-dimensional parametric interaction coupling Langmuir waves with magnetic electron drift vortex modes is presented. A general dispersion relation for the parametric instabilities is derived, and the growth rates of the decay and modulational instabilities are obtained. The present instabilities can be the source of large-scale magnetic fields near the critical surface of a laser-produced plasma.     

Wave Instabilities of a Collisionless Plasma in Fluid Approximation

Wave properties and instabilities in a magnetized, anisotropic, collisionless, rarefied hot plasma in fluid approx‐imation are studied, using the 16‐moments set of the transport equations obtained from the Vlasov equations. These equations differ from the CGL‐MHD fluid model (single fluid equations by Chew, Goldberger, and Low [5,9]) by including two anisotropic heat flux evolution equations, where the fluxes invalidate the double polytropic CGL laws. We derived the general dispersion relation for linear compressible wave modes. Besides the classic incompressible fire hose modes there appear four types of compressible wave modes: two fast and slow mirror modes – strongly modified compared to the CGL model – and two thermal modes. In the presence of initial heat fluxes along the magnetic field the wave properties become different for the waves running forward and backward with respect to the magnetic field. The well known discrepancies between the results of the CGL‐MHD fluid model and the kinetic theory are now removed: i) The mirror slow mode instability criterion is now the same as that in the kinetic theory. ii) Similarly, in kinetic studies there appear two kinds of fire hose instabilities ‐ incompressible and compressible ones. These two instabilities can arise for the same plasma parameters, and the instability of the new compressible oblique fire hose modes can become dominant. The compressible fire hose instability is the result of the resonance coupling of three retrograde modes ‐ two thermal modes and a fast mirror mode. The results can be applied to the theory of solar and stellar coronal and wind models (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Instabilities Driven by an Intense Beam in a Plasma-Filled Dielectric-Lined Waveguide Immersed in a Finite Axial Magnetic Field

A linear analysis is described on stabilities driven by an intense relativistic electron beam in an infinitely long, plasma-filled, and dielectric-lined circular waveguide immersed in a finite strength axial magnetic field. A dispersion equation is derived from the cold fluid theory and solved numerically. Beam-plasma instabilities due to interaction between beam modes and the Trivelpiece-Gould modes appear as well as the Cherenkov and the cyclotron Cherenkov instabilities. Parametric researches are carried out varying magnetic field strength, plasma density, and dielectric constant. Effects of a finite magnetic field and plasma filling are discussed in connection with the possibilities of using this system as a microwave radiation source.     

Relativistic Linear Theory in the Absence of External Fields

The dielectric tensor for a multi-component, homogeneous, field-free relativistic plasma is derived in manifestly covariant form. From the dielectric tensor, linear dispersion relations are obtained explicitly when each component of the plasma is isotropic in its rest frame. If the components are relativistic Maxwellians, these dispersion relations are expressible in terms of the relativistic plasma dispersion function. Special attention is given to the Weible and two-stream instabilities and to the normal modes of a quiescent, hot electron gas. For the last case the dispersion relations are solved numerically and compared against computer simulation data. An appendix applies the formalism to cold plasmas.     

On the theory of instabilities arising at quark-gluon plasma formation

Collisions of two degenerate quark Fermi liquids are studied. It is shown that there arise instabilities, which manifest themselves in propagation of growing oscillations corresponding to the modes existing in a Fermi liquid at rest. Quark jets are likely to appear in the directions of the growing oscillations propagation.

The instabilities studied in this work are similar to the beam instability in ordinary electron plasma.     

Backscattering and Absorptive Parametric Instabilities Involving the Lower Hybrid Mode in a Magnetized Plasma

The theories of two decay-type parametric instabilities involving the lower hybrid mode in a magnetized plasma are presented. In the first of these, a pump wave of ordinary polarization causes the growth of a backward propagating transverse wave and a longitudinal lower hybrid wave, all with wave vectors perpendicular to the external magnetic field. The second instability concerns the parametric excitation of the upper hybrid and the lower hybrid modes.     

Scenario of instabilities driven equilibration of the quark-gluon plasma

Due to anisotropic momentum distribution the parton system produced at the early stage of relativistic heavy-ion collisions is unstable with respect to the magnetic plasma modes. The instabilities isotropize the system and thus speed up the process of its equilibration. The scenario of instabilities-driven isotropization is reviewed.     

Dynamic model for plasma opening switches

A dynamic model for plasma opening switches is proposed. The basis of the model is the appearance and development of force instabilities (pinch and sausage) in a spatially nonuniform plasma accelerated by a magnetic field as a driver piston. The proposed model does not require the invocation of subtle effects in the pinch collapse phase and makes it possible, without going beyond the framework of magnetohydrodynamics, to explain the principal operating features of plasma opening switches and to obtain quantitative estimates consistent with experiment. Zh. Tekh. Fiz. 69, 25–29 (May 1999)     

Symmetry systematics of pressure—induced phase transitions

Abstract

Most pressure induced phase transitions are diffusionless. Because of this, there exists a one-to-one correspondence between the positions of atoms in the parent and the product phases, which, therefore, show interesting symmetry relationships. In this paper, we have used these for discussing a symmetry classification of pressure induced phase transitions into four categories: iso-symmetric, group-subgroup, intersection group, and order-disorder transitions. Various examples illustrating this classification scheme are discussed. The importance of this classification is in understanding the mechanism of pressure indbced phase transitions, where both theoretical calculations and experimental measurements are employed to analyse related phenomena like softening of phonon modes, elastic instabilities, diffraction patterns, and orientation relations.     

Field-reversed configurations in an unmagnetized plasma

An oscillating magnetic field is applied with a loop antenna to an unmagnetized plasma. At small amplitudes the field is evanescent. At large amplitudes the field magnetizes the electrons, which allows deeper field penetration in the whistler modes. Field-reversed configurations are formed at each half cycle. Electrons are energized. Transient whistler instabilities produce high-frequency oscillations in the magnetized plasma volume.     

Whistler instability in an electron-magnetohydrodynamic spheromak

A three-dimensional magnetic vortex, propagating in the whistler mode, has been produced in a laboratory plasma. Its magnetic energy is converted into electron kinetic energy. Non-Maxwellian electron distributions are formed which give rise to kinetic whistler instabilities. The propagating vortex radiates whistler modes along the ambient magnetic field. A new instability mechanism is proposed.     

Chaotic regime of Alfvén Eigenmode wave-particle interaction

The chaotic regime in Alfvén eigenmode wave-particle interaction is identified for the first time in the tokamak plasma of the Joint European Torus. The Alfvén modes are driven by energetic hydrogen minority ions produced by ion cyclotron resonance heating. The experimental signatures of the chaotic regime include spectral broadening, phase flips, and nonperiodic amplitude variations. These phenomena are found to be consistent with a general nonlinear theory of kinetic instabilities near stability threshold developed by Berk, Breizman, and Pekker.     

Nuclear fusion: bringing a star down to Earth

Nuclear fusion offers the potential for being a near limitless energy source by fusing together deuterium and tritium nuclei to form helium inside a plasma burning at 100 million K. However, scientific and engineering challenges remain. This paper describes how such a plasma can be confined on Earth, and discusses the similarities and differences with fusion in stars. It focuses on the magnetic confinement technique and, in particular, the method used in a tokamak. The confinement achieved in the equilibrium state is reviewed and it is shown how the confinement can be too good, leading to explosive instabilities at the plasma edge called edge localised modes (ELMs). It is shown how the impact of ELMs can be minimised by the application of magnetic perturbations and discusses the physics behind the penetration of these perturbations into what is ideally a perfect conducting plasma.     

Nonphysical noises and instabilities in plasma simulation due to a spatial grid

A series of plasma numerical simulation has been performed in order to understand the enhancement of nonphysical noises and instabilities due to the use of a spatial grid. Several different superparticle models including the Nearest Grid Point (NGP) model, Cloud-in-Cell (CIC) or Particle-in-Cell (PIC) models, Lewis energy conserving code, and the multipole expansion code have been examined for a Maxwellian plasma and a one beam plasma using a one-dimensional, one-specie (electron) plasma. An instability was observed for all of the models when the Debye length was too small compared with the grid size. When the Debye length is comparable to the grid size, no instabilities were observed. However, the enhancement of noises at high frequencies (ω > 3ω_pe may not always be negligible- even for long wavelength modes for the NGP model. For the NGP and CIC, PIC models, the experimental results are in good agreement with Langdon's theory. It is observed that the dipole expansion model, which is the first-order approximation to the multipole expansion scheme, is similar to CIC, PIC models in many respects and appears to be the same order of approximation.     

Stability-transport modeling of the SINP tokamak discharges

A one-dimensional stability transport code has been developed to simulate the evolution of tokamak plasma discharges. Explicit finite-difference methods have been used to follow the temporal evolution of the electron temperature equation. The poloidal field diffusion equation has been solved at every time step. The effects of MHD instabilities have been incorporated by solving equations for MHD mixing and tearing modes as and when required. The code has been applied to follow the evolution of tokamak plasma discharges obtained in the Saha Institute of Nuclear Physics (SINP) tokamak. From these simulations, we have been able to identify the possible models of thermal conductivity, diffusion and impurity contents in these discharges. Effects of different MHD modes have been estimated. It has been found that in low q ₀ discharge m=1, n=1 and m=2, n=1 modes play major role in discharge evolution. These modes are found to result in the positive jump in the loop voltage which was also observed in the experiments. Hollow current density profile j _φ and negative shear in the q profile have also been found in the rising phase of a discharge.     

Transport equations and QCD collective modes in a self-consistent covariant background gauge

Following an interpretation of high-temperature instabilities of perturbative QCD, a self-consistent covariant background gauge quantization is proposed. Non-perturbative classically gauge invariant gluon, ghost, and quark equations of motion for coupled one- and two-point functions are derived in binary collision approximation (RPA). A stability analysis is described to determine coloured and colourless collective modes. Preliminary results indicate non-perturbative behaviour of the quark-gluon plasma involving self-consistent classical background fields. It leads to mass generation for gluons as well as for collective modes.     

Filamentation and stimulated Brillouin scattering in a turbulent plasma

This paper presents a theory of filamentation and stimulated Brillouin scattering (SBS) of high-frequency electromagnetic radiation in a weakly collisional plasma with ion-acoustic turbulence. When the square of the wavelength of the plasma perturbations is less than the product of the two mean free path lengths of an electron with respect to its collisions with turbulent fluctuations and with electrons, the influence of cold highly collisional electrons on the parametric instabilities becomes apparent. It is shown that the plasma turbulence lowers the filamentation threshold, and the SBS threshold can be either lowered or raised. The dependence of the SBS and filamentation thresholds on the electron mean free path length in the turbulent plasma and on the anisotropy of the plasma turbulence is determined. The corresponding dependence of the spatial scale of the most efficiently growing filaments and their spatial growth rate are found. Zh. éksp. Teor. Fiz. 113, 629–645 (February 1998)