摘要:

A diffusion equation is derived which describes the evolution of a magnetic field in a plasma of arbitrary &bgr; and resistivity. The equation is valid for a one‐dimensional slab geometry, assumes the plasma remains in quasi‐equilibrium throughout its evolution (i.e., pressure balance), and does not include thermal transport. Scaling laws governing the rate of change of the magnetic energy, particle drift energy, and magnetic flux are calculated. It is found that the magnetic free energy can be substantially larger than the particle drift energy and can be an important energy reservoir in driving plasma instabilities (e.g., the lower‐hybrid‐drift instability). In addition, the effect of a spatially varying resistivity on the evolution of a reversed‐field plasma is studied. The resistivity model used is based upon the anomalous transport properties associated with the nonlocal mode structure of the lower‐hybrid‐drift instability. The relevance of this research to laboratory plasmas (e.g., theta pinches, reversed‐field theta pinches) and space plasmas (e.g., the earth’s magnetotail) is discussed.

ISSN:0031-9171    

DOI:10.1063/1.863249

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The neoclassical rate of diffusion is calculated in such a way that the result is applicable to both helically symmetric and toroidally symmetric plasmas.

ISSN:0031-9171    

DOI:10.1063/1.863250

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Convective cell formation and spectral cascade processes due to gravitational drift Alfve´n waves are studied using a new type of model equation. Conservation relations are derived and explosive instability is found for systems near marginal finite &bgr; stability. This instability also remains when the effects of poor as well as favorable curvature regions are included, i.e., for ballooning modes. The anomalous diffusion due to convective cells and quasi‐linear effects are compared.

ISSN:0031-9171    

DOI:10.1063/1.863251

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The thermalization of particle kinetic motion by binary collisions is considered for a plasma withkT∼(10–100)mc2, wheremis the electron mass. At this temperature, the principal mechanism for relaxation of electron motion is via radiationless electron‐electron collisions (Mo&slash;ller scattering). Ions are nonrelativistic, but are energetic enough so that their Coulomb scattering can be treated in the Born approximation. Relaxation times are computed and Boltzmann‐equation Fokker–Planck operators are derived for the various binary‐collision processes. The expression for the rate of kinetic energy exchange between electron and ion gases is derived for the case where the gases are at different temperatures.

ISSN:0031-9171    

DOI:10.1063/1.863226

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The formal theory of the interaction of mildly relativistic electrons with a cyclotron resonant applied electromagnetic field described by geometric optics is developed. The electron distribution function is written as the sum of a quasi‐static partf0and a high frequency partf1. A quasi‐linear theory is employed to describe these. The resulting transport equationf0is written to lowest significant order jointly in the reciprocal of the gyration frequency and the bounce frequency. It includes a relativistic collision term and a drag term associated with synchrotron emission. The linearized equations forf1are solved, and an expression for the high‐frequency current is derived.

ISSN:0031-9171    

DOI:10.1063/1.863227

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The propagation of lower‐hybrid waves in the presence of ponderomotive density fluctuations is considered. The problem is treated in two dimensions, and in order to be able to correctly impose the boundary conditions, the waves are allowed to evolve in time. The fields are described byiv&tgr;−F v&xgr; d&zgr;+v&zgr;&zgr;+‖v‖2v=@qL0, wherevis proportional to the electric field, &tgr; to time, and &zgr; and &xgr; measure distances across and along the lower‐hybrid ray. The behavior of the waves is investigated numerically. If the amplitude of the waves is large enough, the spectrum of the waves broadens and their parallel wavelength becomes shorter. The assumptions made in the formulation preclude the application of these results to the lower‐hybrid heating experiment on Alcator‐A. Nevertheless, there are indications that the physics embodied in this problem are responsible for some of the results of that experiment.

ISSN:0031-9171    

DOI:10.1063/1.863229

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Detailed measurements of heated electron distributions generated in a short density scale length 10.6 &mgr;m laser plasma interaction in the intensity regime 1012≲I(W cm−2)≲1014are reported. Maximum electron energies up to 600 keV observed in this study appear to be inconsistent with characteristic maximum energies of electrons generated by resonant absorption in the warm plasma wave breaking limit. Furthermore, heated electron distributions from foils of thickness much less than the hot electron mean‐free‐path as well as from differentZtargets suggest that reheating of very energetic electrons by multipassing through the resonant region does not occur; rather the highest‐energy electrons are preferentially accelerated in the backward direction with very large single pass energies. Plasma instabilities at the quarter critical as well as those at the critical are thought to be responsible for the generation of the high‐energy electron component. Finally, these studies show that the electron emission spectra are sensitive to the electrical properties of the target support structure.

ISSN:0031-9171    

DOI:10.1063/1.863230

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Numerical studies of radiation at 2&ohgr;pfrom a Langmuir envelope collapsing adiabatically in three dimensions show that the emissivity is higher than expected. A volume emissivity obtained from an approximate density of collapsing packets leads to favorable comparisons with measurements of type‐III solar radio bursts.

ISSN:0031-9171    

DOI:10.1063/1.863231

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The interplay between the Cerenkov and anomalous Doppler interactions in the relaxation of a warm electron beam is investigated by numerical means. The most important feature in the interplay is found to be a nonelastic isotropization. A simple semianalytical model which allows one to estimate various quantities relevant to the relaxation process is also presented.

ISSN:0031-9171    

DOI:10.1063/1.863232

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Equilibrium values of diode current are calculated for cylindrical, magnetically insulated vacuum ion diodes as functions of applied voltage, magnetic flux, and aspect ratio. The analysis is based upon the assumption of a slowly (adiabatically) applied voltage so that electrons are confined to a sheath near the cathode where they undergo E×B drifts in the electric field (E) and the magnetic field (B) in the anode–cathode gap. One‐dimensional cases in which the applied magnetic field is either axial or azimuthal are treated. A previous analysis, conducted under the assumption of cycloidal electron orbits, found that equilibrium solutions often do not exist. It is found that this difficulty is absent when E×B drift orbits are assumed.

ISSN:0031-9171    

DOI:10.1063/1.863233

出版商:AIP    

年代:1981

数据来源: AIP