摘要:

Rigorously sufficient and approximately necessary conditions for the absence of the beam‐Weibel instability are derived. These conditions include previously known stability criteria and resolve the seeming contradiction that these modes can be stabilized by beam temperature when the plasma is cold, but they cannot be stabilized by beam temperature when the plasma has infinitesimally small temperature.

ISSN:0031-9171    

DOI:10.1063/1.863262

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A linear, fully relativistic and electromagnetic analysis of waves perturbing the Brillouin flow state on planar, magnetically insulated gaps is presented. Three independent classes of waves are treated individually; transverse‐magnetic waves propagating normal to the insulating magnetic field, transverse‐electric waves propagating in the same direction, and a set of waves propagating along the magnetic field. Dispersion relations governing discrete modes of oscillation for each class are found and solved for some cases of interest. Only the transverse‐magnetic waves are found to be unstable due to the existence of a Doppler‐shifted plasma reasonance layer at frequencies above the plasma frequency. The scaling of the growth rate for this instability with respect to parameters characterizing the equilibrium state is examined. In addition to these discrete modes, spectral continua associated with localized resonance phenomena in the electron sheath bounding the cathode are described and explained.

ISSN:0031-9171    

DOI:10.1063/1.863263

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The nonlinear evolution of the lower‐hybrid‐drift instability is considered in the guiding‐centers‐on‐axis model. Extremely rapid radial quasi‐linear diffusion of electrons leads to the buildup of a radial electric field Er. Saturation occurs when the Er×B electron drift velocity equals the local ion rotational velocity. Due to the rapid linear growth rate, the unmagnetized ions are unable to shield out Er, which becomes significant long before density profile flattening occurs.

ISSN:0031-9171    

DOI:10.1063/1.863264

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A self‐consistent theory of phase‐space granulations, called ’’clumps’’, has been derived. These fluctuations are produced when regions of different phase‐space density are mixed by the fluctuating electric fields. The source term and turbulent scattering operator for these fluctuations are obtained through a renormalization of the one‐ and two‐point equations for a Vlasov plasma. The proper treatment of the singular behavior exhibited by the two‐point equation, coupled with the self‐consistent approach leads to a number of significant changes compared with previous formulations. The case of electrostatic turbulence is considered throughout this paper. The method of solution is based on the concept of two disparate time scales which allow the treatment of the equal time two‐point equation as an initial condition for its two‐time counterpart. The picture of a ’’test’’ clump emerges quite naturally within such a framework. The source term for the clump correlation function is identified and certain intrinsic properties determined. Physical interpretations of the coefficients in the renormalization are given and their role in energy and momentum conservation demonstrated. The theory is reminiscent of Fokker–Planck analysis with which numerous parallels are drawn.

ISSN:0031-9171    

DOI:10.1063/1.863265

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The diffusion coefficientD⊥for a collisionless hydrogen plasma was measured in the levitated octupole when a weak toroidal field was added. A twenty‐fold decrease in the anomalous diffusion was observed withBt/Bp≳0.1. This reduced level of diffusion was still two orders of magnitude larger than the classical value and the residual level of convective cell activity was responsible for the enhanced transport. Locally trapped particles in the poloidal field mirrors allow the convective cell activity (f<600 Hz) to persist even when the toroidal field was added. The principal effect of the added toroidal field was observed to be a localization of the convective cells in the region where particles are trapped and a shift in thek⊥spectrum to shorter wavelengths.

ISSN:0031-9171    

DOI:10.1063/1.863266

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Anomalous transport in a reversed field theta pinch is examined. The principal effects are anomalous resistivity and rotation generation. Similarity solutions for the resistive decay are found which agree qualitatively with experiment. Also, it is shown that the spin up and anomalous resistivity may be the effect of a single underlying cause, a current‐driven microinstability.

ISSN:0031-9171    

DOI:10.1063/1.863267

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Induced electron currents are studied in systems which are field‐reversed due to ion currents, with no toroidal magnetic field. In such systems, electron flow is induced in the region of closed field lines, with a large velocity shear that can drive a Kelvin–Helmholtz type instability. Analysis of the nonlinear evolution suggests that the instability leads to a rapid dissipation of electron currents. Rough estimates show that the instability is likely to be of importance in field‐reversed ion ring and mirror experiments.

ISSN:0031-9171    

DOI:10.1063/1.863268

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

It is shown that a bifurcation of the equilibrium solutions for straight elliptical plasma columns with a diffuse current profile exists for a suitable choice of the currents in the external conductors.

ISSN:0031-9171    

DOI:10.1063/1.863269

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The acceleration of ions by two isothermal species of electrons, thermal and suprathermal, in a laser‐fusion plasma is investigated. The disassembly of an initially stationary plasma slab, including charge separation effects, is described. Before the rarefaction wave has penetrated appreciably into the slab, an interior Debye sheath which separates the suprathermal and thermal electrons, as well as an exterior sheath at the ion‐vacuum interface is found. As the rarefaction approaches the center of the slab, the dynamics is modified due to the conservation of species number and total energy. The energetics of the long‐time evolution is described by a quasi‐neutral similarity solution appropriate to finite two‐electron species systems.

ISSN:0031-9171    

DOI:10.1063/1.863270

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A model for ion emission from (CH)nand (CH2)nlaser‐produced plasmas containing both hot and cold electron populations is presented. Computed Faraday cup current traces illustrate the point that separate C6+and H+ion current peaks cannot be resolved, showing that care should be excercised when interpreting the total ion current observed experimentally. The slow C6+ions are found to carry most of the ion momentum. A small number of fast C6+and H+ions containing a substantial fraction of the total ion energy are produced. Fast ions, corresponding to those observed experimentally, can thus be generated without the need to invoke inhibition of heat flux into the target, as has been suggested.

ISSN:0031-9171    

DOI:10.1063/1.863271

出版商:AIP    

年代:1981

数据来源: AIP