摘要:

A class of microinstabilities which is likely to exist in plasmas confined in magnetic mirror geometries is examined. These waves propagate across the magnetic field in a homogeneous plasma at multiples of the ion cyclotron frequency. The instabilities are found when all electromagnetic terms are included in the theory. They exist even when&bgr;≪1(perpendicular ion beta) since there are still parametric regions where electromagnetic contributions are larger than the electrostatic terms. Growth rates for a value of&bgr;of 0.01 are of the order of several percent of the ion cyclotron frequency even for loss‐cone distributions that are reasonably well randomized.

ISSN:0031-9171    

DOI:10.1063/1.1693623

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The change of energy and phase of a particle gyrating in a homogeneous magnetic field and a perpendicularly propagating electrostatic wave is calculated analytically for resonant and nonresonant frequencies in the regime where the wavelength2&pgr;k⊥−1is of the order of the gyroradiusa. This new result provides a quantitative basis for a simple wave‐particle interaction model and resolves certain discrepancies between previously obtained results and numerical calculations of the ranges ofk⊥afor which instability is possible. The long‐time behavior of the particle motion is discussed using a stroboscopic orbit theory. Significant modifications of the particle orbits by a single wave, which necessitate the use of a “strong turbulence” theory, are shown to occur ife&dgr;&psgr;/KT⊥∼(2&pgr;)1/2(K⊥a)−1/2(&ohgr;−l&OHgr;) /&ohgr;, wheree&dgr;&psgr;/KT⊥is the ratio of wave potential energy to perpendicular particle kinetic energy andlis the harmonic number.

ISSN:0031-9171    

DOI:10.1063/1.1693624

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The phenomenon of nonlinear Landau damping is investigated for damping on an adiabatic species. It is shown that the cancellation which leads to the(&kgr;&lgr;D)4dependence for damping on a hydrodynamic species no longer occurs; rather, the four‐wave resonance term (driven spectra term) of the governing matrix element dominates the resonant three‐wave term (induced spectra term), leading to the conjecture that, for a plasma with an adiabatic constituent, nonlinear Landau damping on that constituent may well dominate the nonlinear mode coupling processes. A detailed investigation of such damping is conducted for the case of two equidense zero temperature ion beams streaming through a hot, adiabatic electron plasma. A nonlinear Landau damping instability on the electrons is found which cannot be limited in the usual quasilinear sense. The instability serves to heat the electrons driving the system to a linear ion‐ion streaming instability.

ISSN:0031-9171    

DOI:10.1063/1.1693625

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The effect of an explosive instability on the plasma distribution functions is calculated for a specific initial distribution. It is found that this change in the plasma distribution (a) limits the possible level of field energy and (b) greatly increases the time required for the field to approach this limit compared with the explosion time calculated by ignoring the change in the distribution.

ISSN:0031-9171    

DOI:10.1063/1.1693626

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

For configurations relevant to transverse electromagnetic instabilities, two independent energy constants are derived within the framework of the fully nonlinear Vlasov‐Maxwell equations. It is assumed that the spatial variation in equilibrium and perturbed quantities is perpendicular to a uniform external magnetic fieldB0. The caseB0 = 0is not excluded, and the spatial variations may be one‐or two‐dimensional. The energy constants, which are applicable in both the stable and unstable regimes, exhibit precisely how the energy is partitioned between the fields and the individual components of plasma kinetic energy perpendicular and parallel to the propagation direction. The corresponding constants at the quasilinear level of description are also examined.

ISSN:0031-9171    

DOI:10.1063/1.1693627

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A new surface wave instability is derived for a magnetically confined pure electron gas column with density34<2&ohgr;p02/&OHgr;02<1. The equilibrium configuration consists of two superimposed electron beams aligned parallel to the confining magnetic fieldB0, and rotating with different azimuthal velocities about the axis of symmetry. The instability, which is of the two‐stream form, results from the interaction of surface waves on each of the two superimposed beams.

ISSN:0031-9171    

DOI:10.1063/1.1693628

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A current flowing across a uniform magnetic field is considered. Turbulently induced anomalous electron collisions allow electrons to diffuse across the magnetic field. The anomalous electron collisions can destabilize a negative energy ion wave and thus cause substantial ion heating. This process may be of interest in collisionless shocks and turbulent heating experiments.

ISSN:0031-9171    

DOI:10.1063/1.1693629

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Coupled kinetic equations for the density of plasmasNk&agr;(t)and spatially averaged distribution functionfj(v, t)are presented in the electrostatic approximation for a weakly turbulent, unmagnetized plasma. Discrete particle collisions are neglected, and resonant three‐wave processes(&ohgr;k&agr; = &ohgr;k′&bgr;+&ohgr;k″&ggr;, k = k′+k″)are assumed to provide the dominant collective interaction mechanism. By taking appropriate velocity moments of the kinetic equations for the particles, rate equations for the changes in (spatially averaged) mean velocityVj(t)and kinetic energy relative to the meanKj(t)for each plasma component are derived. The resulting rate equations describe the bulk features of the reaction of the particle distributions (i.e., acceleration and heating rates) to resonant three‐wave interactions, and are applicable in both the nonlinearly stable and explosively unstable regimes. As an example corresponding to explosive instability, the self‐consistent evolution of well‐displaced counterstreaming ion beams in a hot electron background is examined. It is found that as the energy in the field fluctuations increases, the ion beams lose kinetic energy of mean motion, and the electrons and ions gain kinetic energy relative to the mean. This produces significant alterations in the background dielectric properties. Within the context of a simple model for the particle distributions, the region ofkspace for which the three‐wave resonance conditions can be satisfied shrinks to zero volume, which quenches the nonlinear instability.

ISSN:0031-9171    

DOI:10.1063/1.1693630

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A method is described for solving the magnetohydrodynamic equations for nonlinear plasma waves and turbulence due to macroinstabilities. It is argued that the dominant nonlinear effect for macroinstabilities is the scattering of fluid elements of charge by plasma waves. The consequent wave‐fluid interaction causes an enhanced diffusion coefficient in the continuity equation and an identical enhanced viscosity coefficient in the momentum equation. This enhanced plasma transport is analogous to the eddy transport and Reynolds stress of neutral turbulence. A nonlinear dispersion relation is obtained from the linear dispersion relation by simply adding the enhanced diffusion term to the frequency. It is shown that linear macroinstabilities are stabilized by the enhanced diffusion, and viscosity, terms. As examples, the enhanced diffusion coefficients, and density and electric field fluctuations are calculated for resistive instabilities.

ISSN:0031-9171    

DOI:10.1063/1.1693631

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Two instability mechanisms which could occur under the conditions found in a perpendicular collisionless shock wave are considered. Both mechanisms are due to the negative energy character of the electron Bernstein waves propagating in the direction of the current flow in the shock. The effect of the voltage jump through the shock, and the density and magnetic field gradients at the shock front are considered. Both instability mechanisms occur only within a definite band ofkvalues. The first mechanism is due to a resonance between the ion acoustic wave and one of the Bernstein harmonics and the second to resonant ions absorbing energy from a negative energy Bernstein mode. The first case requiresTe≫Tiwhereas the second case can occur for arbitrary values of the ratioTi/Te, although the maximum effect occurs when this ratio is of order unity.

ISSN:0031-9171    

DOI:10.1063/1.1693632

出版商:AIP    

年代:1971

数据来源: AIP