摘要:

Bissell and Johnson [Phys. Fluids30, 779 (1987)] have calculated the electrostatic potential variation in the sheath and presheath regions of a collisionless plasma in which the source of ions is assumed to be Maxwellian. To do this, they imposed the generalized Bohm criterion as a boundary condition. In this paper the plasma equation is solved numerically without imposing the Bohm criterion as a boundary condition. The results compare well with their results. In addition, the ion distribution function throughout the plasma region is calculated. Because of this particular source model, the ion distribution at the center of the plasma has a spiked non‐Maxwellian shape.

ISSN:0031-9171    

DOI:10.1063/1.866881

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A Vlasov code developed by Denavit [Phys. Fluids28, 2773 (1985)] was modified and used to study long‐time behavior of the single‐mode bump‐on‐tail instability. Large oscillations, which interrupted his original runs at &ohgr;0T≊1300 shortly after reaching the O’Neil trapping level (OTL), were identified and controlled by heating the cold background electrons. A run to &ohgr;0T=30 000 showed growth well beyond the OTL and eventually saturated at about the level predicted by Simon and Rosenbluth (SR) [Phys. Fluids19, 1567 (1976)], before oscillations set in. A run with warmer background electrons was again interrupted by oscillations. A weakly unstable case was followed to &ohgr;0T=60 000; it also showed growth well beyond the OTL but saturated at an amplitude that was significantly below that predicted by SR. In all cases, the velocity distribution developed strong ripples nearv=0. These are shown to be caused by a numerical grid effect, and they may be responsible for the eventual development of the large oscillations and for the low level of saturation in the weakly unstable case.

ISSN:0031-9171    

DOI:10.1063/1.867008

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Quasilinear diffusion due to the presence of electromagnetic waves in a magnetized relativistic plasma is studied. It is shown that the diffusion equation contains a term (&OHgr;/&ggr;) ∂&Jgr;⟨ f 0⟩, thus taking into account finite gyroradii effects. Furthermore, it is shown that the diffusion coefficient is a tensor that has an antisymmetric part if the wave has a transverse component. Consequently, the quasilinear diffusion process due to transverse waves is described by an equation that contains a drag term.

ISSN:0031-9171    

DOI:10.1063/1.866882

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The optical spectrum of scattered laser radiation from laser‐produced plasmas has been measured between half and twice the incident laser frequency &ohgr;0. Three spectral bands have been found, two of which straddle the 3&ohgr;0/2 spectrum. The third band is located near &ohgr;0/2. These observations can be successfully interpreted in terms of a model in which there is enhanced Thomson scattering into the ‘‘electron line.’’ This enhancement is due to fast electrons creating a local bump‐on‐tail instability [Phys. Rev. Lett.53, 1912 (1984)]. An alternative interpretation in terms of the conventional stimulated Raman scattering and associated anti‐Stokes radiation is inconsistent with our observations.

ISSN:0031-9171    

DOI:10.1063/1.866883

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

New self‐similar solutions describe the subsonic compression of a plasma with an entrained axial magnetic field by a thin cylindrical liner. Effects of Ohmic dissipation, thermal conductivity, and plasma turbulence are included. The self‐similar solutions, obtained in an explicit analytic form, demonstrate that magnetic flux can be compressed by an externally driven annular plasma shell with small losses.

ISSN:0031-9171    

DOI:10.1063/1.866884

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Supersonic cumulative compressions of axial magnetic fields in cylindrically symmetric plasmas are studied. New self‐similar solutions of the ideal magnetohydrodynamic (MHD) equations are presented. The solutions describe cumulative compressions of radially imploding plasma with entrained magnetic fields, subsequent reflections of MHD shock waves from the axis, compressions of hollow plasma liners, and implosions of fast magnetosonic waves.

ISSN:0031-9171    

DOI:10.1063/1.866885

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A fully relativistic local dispersion relation for whistler waves has been solved at closely spaced points along the magnetic field lines of a 2:1 magnetic mirror in which a highly anisotropic, spatially inhomogeneous, hot‐electron plasma is confined. The limiting plasma parameters for convective (spatial) growth have been determined numerically and used to identify plasma conditions leading to maximum amplification of input microwave signals introduced in the form of whistler waves. The maximum gain has been evaluated numerically for a range of values of the hot‐electron plasma within which all major stability criteria are satisfied. Very high gains (∼40 dB) are indicated over the entire range of beta investigated.

ISSN:0031-9171    

DOI:10.1063/1.866886

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A kinetic theory of nonlinear coupling of ion‐Bernstein waves with the kinetic Alfve´n wave in a plasma is developed using a guiding center formalism. The nonlinearity arises through the motion of ions. The coupling coefficient is simplified at the limit where the Alfve´n wave’s wavelength is larger than an ion Larmor radius, whereas the ion‐Bernstein waves may have arbitrary wavelengths. At power levels employed on large devices in the slow wave ion‐cyclotron heating scheme, the excitation of magnetic fluctuations appears a genuine possibility.

ISSN:0031-9171    

DOI:10.1063/1.866887

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Coupled wave equations and the corresponding wave‐energy‐flow conservation law describing the fast magnetosonic and ion‐Bernstein waves are derived for minority heating in the ion‐cyclotron range of frequencies. This fourth‐order full‐wave system is subsequently reduced in order through representation by means of two, completely decoupled, second‐order systems. One is a second‐order equation for the fast wave in which the Bernstein mode is treated as a driven response. The second is coupled‐mode equations for amplitudes varying slowly under the influence of coupling, inhomogeneity, and dissipation. The coupled‐mode equations are approximately solved for both high‐field and low‐field incidence to give the transmission and mode‐conversion coefficients in closed form for arbitrary wavenumbers parallel to the magnetic field. Good agreement with fourth‐order calculations is obtained.

ISSN:0031-9171    

DOI:10.1063/1.866888

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Linear tearing instability is studied in the banana collisionality regime in tokamak geometry. Neoclassical effects produce significant modifications of Ohm’s law and the vorticity equation, so that the growth rate of tearing modes driven by &Dgr;’is dramatically reduced compared to the usual resistive magnetohydrodynamic values. Consequences of this result, regarding the presence of pressure‐gradient‐driven neoclassical resistive interchange instabilities and the evolution of magnetic islands in the Rutherford regime, are discussed.

ISSN:0031-9171    

DOI:10.1063/1.866889

出版商:AIP    

年代:1988

数据来源: AIP