摘要:

A simple model of the distribution function has been obtained by examining the Willis–Hamel–Lin solution of the BGK equation. This model is an extension of the ellipsoidal model to a large translational nonequilibrium. Once the perpendicular temperatureTpand the number densitynin the ellipsoidal model are replaced by &sgr;TpandC00n, respectively, the model immediately results. Two parameters &sgr; andC00are given as functions ofTp/Trfor various values of an exponent of a power law viscosity‐temperature relationship. The model has been shown to be a valid approximation except for the tail of the distribution function.

ISSN:0031-9171    

DOI:10.1063/1.862439

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

It is shown that one‐dimensional motion of collisionless particles with a step distribution function can be exactly described by gasdynamics.

ISSN:0031-9171    

DOI:10.1063/1.862444

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The problem of nonlinear self‐focusing of Gaussian laser beams is reformulated in terms of a variational principle. By means of approximating Gaussian functions, expressions are obtained for the equilibrium radii and nonlinear frequency shifts of stationary self‐trapped laser beams. The nonsteady propagation is given an illuminating form in terms of a potential function description. The analysis confirms the recent results obtained by moment theory as opposed to those based on paraxial ray approximations.

ISSN:0031-9171    

DOI:10.1063/1.862445

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The dispersion of ion‐acoustic plasma waves is investigated using pulsed CO2laser scattering and homodyne detection techniques. Broadening of the scattered spectrum due to spatial wave damping is demonstrated.

ISSN:0031-9171    

DOI:10.1063/1.862447

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The well‐known drift cyclotron loss cone mode is shown to couple nonlinearly to a low frequency stable Rayleigh–Taylor mode through the process of nonlinear Landau damping. When the drift cyclotron loss cone mode is linearly marginally stable, this coupling leads to an explosive instability, the time scale for which is in some agreement with experimental time scales.

ISSN:0031-9171    

DOI:10.1063/1.862448

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The analysis of cold plasma stabilization of the drift‐cyclotron‐loss‐cone mode in mirror machines is extended to conditions in which the cold plasma is confined by a weak local minimum in the ambipolar potential. These conditions allow stabilization with less electron energy drain than simple axial flow of cold plasma. Scaling laws are derived for the required cold plasma flux, the resulting fluctuation induced ion diffusion, the steady state electron temperature, and the trapped‐ion lifetime.

ISSN:0031-9171    

DOI:10.1063/1.862449

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Emissive Langmuir probes are used to map the plasma potential in the neighborhood of a picket fence cusped magnetic field. Positive potential ’’islands’’ are found in front of the picket fence conductors showing ion confinement by electrostatic self‐plugging of the cusp leaks. This mechanism results in channels whose widths are the order of the hybrid cusp leak widths recently reported.

ISSN:0031-9171    

DOI:10.1063/1.862450

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Early investigations of resistive instability assumed that the plasma was at rest. However, recent work showed that the influence of the natural diffusion velocity (v∼&eegr;/a) on resistive tearing modes was important even in the limit &eegr;→0. Here, the effect of a more general velocity, of the same order as the natural resistive diffusion velocity, but otherwise arbitary, is investigated. It is found that as &eegr;→0 the effect on the stability threshold is finite and independent of the velocity except for its sign. Hence, the threshold is discontinuous atv=0. There is an additional effect of velocity on modes of finite growth rate which may be stabilizing or destabilizing according to the sign and magnitude of the velocity. The present calculations of these effects agree well with numerical simulations of tearing modes.

ISSN:0031-9171    

DOI:10.1063/1.862451

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The evolution of the explosive instability in a beam‐plasma system has been studied using two different computer models; a particle‐in‐cell simulation as well as a fluid model. The initial development of the instability agrees well with the solution of the usual mode coupling equations. The results indicate that the instability in this system saturates because of trapping of electrons by more than one wave leading to a nonlinear frequency shift and a damping of the initially undamped waves.

ISSN:0031-9171    

DOI:10.1063/1.862440

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Three‐wave backscattering instabilities are investigated in a plasma slab with stationary density fluctuations. The noise is of sufficient amplitude to induce random variation in the phase of the coupled waves. The analysis is formulated in terms of the Nyquist theorem. The ensemble average number and distribution of the zeroes of the exact dispersion relation are obtained from the solution of a Fokker–Planck/Boltzmann equation for the probability density of the phase angle of the dispersion relation. Threshold lengths and growth rates obtained are less optimistic for stability than those found in previous random phase investigations. The stabilizing influence of inhomogeneity is weaker in turbulent plasmas than in nonturbulent ones. The analytic results are confirmed in detail by direct numerical simulation of the fundamental equations.

ISSN:0031-9171    

DOI:10.1063/1.862441

出版商:AIP    

年代:1979

数据来源: AIP