摘要:

Solutions for double layers (DL), propagating obliquely to the magnetic field with a speed near the slow ion‐acoustic velocity are presented. Using fluid equations for the ions and an arbitrary equation of state for the electrons, it is shown that in such a system, DL solutions exist for the two‐electron Boltzmann model. No DL exists when the electrons are isothermal, and when the free and reflected electrons are described by Maxwell distributions.

ISSN:0031-9171    

DOI:10.1063/1.865924

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The inside of a time‐stationary strong electrostatic potential structure is characterized by the absence of thermal plasma and by the presence of electron and ion beams, the beam energies being related to the local plasma potential. The operation of collecting and emitting Langmuir probes and double probes within such potential structures is analyzed. It is demonstrated that a floating double probe will not measure the electric field of a strong potential structure without substantial reinterpretation of the potential between the probes. A prescription for the reinterpretation is given. Some probe–surface effects are considered, as are the effects of strong magnetic fields.

ISSN:0031-9171    

DOI:10.1063/1.865925

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The symmetry property of the magnetohydrodynamic (MHD) wave propagation operator is utilized to express the toroidal eigenmodes as a superposition of the mutually orthogonal cylindrical modes. Because of the degeneracy among cylindrical modes with the same frequency but resonant surfaces of different helicity, the toroidal perturbation produces a zeroth‐order mixing of the above modes. The toroidal eigenmodes of frequency &ohgr;20have multiple resonant surfaces, with each surface shifted relative to its cylindrical position and carrying a multispectral content. Thus a single helicity toroidal antenna of frequency &ohgr;0couples strongly to all different helicity resonant surfaces with matching local Alfve´n frequency. Zeroth‐order coupling between modes in the continuum and global Alfve´n modes also results from toroidicity and degeneracy. The perturbation technique used in this study is the MHD counterpart of the quantum‐mechanical methods and is applicable through the entire range of the MHD spectrum.

ISSN:0031-9171    

DOI:10.1063/1.865926

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The equations governing the diffusion and transport of a fully collisional plasma across a strong magnetic field in a bounded domain are analyzed. Following a relatively short relaxation time, the diffusion exhibits universal properties independent of the choice of initial data. Mathematically this appears as a time asymptotic solution which is space‐time separable. The temporal decay rate is a nonlinear eigenvalue which is found via the solution of a related eigenvalue problem. This determines the spatial distribution of both the particle density and the pressure. Some of the transport effects caused by Bremsstrahlung radiation, particle, and heat injection are considered, and the conditions under which the system evolves into an equilibrium are examined.

ISSN:0031-9171    

DOI:10.1063/1.865927

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Entropy increase and comparison principles are found for the Fokker–Planck equation for the radiation field in a homogeneous plasma with constant electron temperature. When emission– absorption is neglected, this is used to find equilibrium distributions that have the form of a Planck distribution plus a &dgr; function at zero photon energy. For distributions below the Planck and with emission–absorption included, a rate of entropy increase is obtained. Numerical results confirm these conclusions.

ISSN:0031-9171    

DOI:10.1063/1.865928

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A quasilinear method is developed for determining saturated tearing mode magnetic island widths in axisymmetric toroidal plasmas with arbitrary cross‐sectional shape, aspect ratio, or plasma pressure (beta). The method is applied to compute magnetic island widths in force‐free toroidal plasmas with aspect ratio as low as 2.0 and elongation between 1.0 and 2.0. It is found that current suppression within the magnetic island strongly increases the saturated width while current peaking reduces width. The effects of current profile, geometry, and harmonic mixing are also studied.

ISSN:0031-9171    

DOI:10.1063/1.865929

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The theory of resistive instabilities (tearing and interchange) has been reworked including the full collisional viscous tensor and thermal conductivity in cylindrical geometry. The existence of stationary states made possible by the presence of viscous effects is established. These states are important as they form the basis for calculating anomalous heat transport in weakly nonlinear regimes.

ISSN:0031-9171    

DOI:10.1063/1.865930

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

An exact solution for the magnetohydrodynamic equations for a time‐dependent, two‐dimensional flow of an incompressible plasma of finite conductivity in a hyperbolic magnetic field is given. This solution admits a nonzero initial current density, and predicts a sequence of events associated with the evolution of a current sheet in a plasma subjected to an initial hyperbolic magnetic field configuration. This is confirmed by laboratory experiments. Next, the calculation is extended to include the density variations in the plasma. The corresponding solution predicts that the current sheet at the neutral point evolves more rapidly when the plasma density builds up locally around the magnetic neutral point.

ISSN:0031-9171    

DOI:10.1063/1.865931

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A magnetosonic shock wave propagating obliquely to a magnetic field is studied by theory and simulation, with particular attention to the resonant ion acceleration (thevp×Bacceleration) by the shock. Theoretical analysis based on a two‐fluid model shows that, in the laminar shock, the electric field strength in the direction normal to the wave is about (mi/me)1/2times larger for the quasiperpendicular shock than that for the quasiparallel shock, which is a reflection of the fact that the width of the quasiperpendicular shock is much smaller than that of the quasiparallel shock. Time evolution of a totally self‐consistent magnetosonic shock wave is studied by using a 2 1/2 ‐dimensional fully relativistic, fully electromagnetic particle simulation with full ion and electron dynamics. Even the low Mach number shock wave can significantly accelerate some ions by thevp×Bacceleration. The resonant ion acceleration occurs more strongly in the quasiperpendicular shock, because the magnitude of this acceleration is proportional to the electric field strength.

ISSN:0031-9171    

DOI:10.1063/1.865932

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

In the reversed field pinch (RFP), magnetic field perturbations having zero poloidal mode number and any toroidal mode number are resonant at the field reversal surface. Such perturbations are a particular threat to the RFP because of their weak radial dependence at low toroidal mode number, and because the toroidal field ripple is essentially of this type. The widths of the resulting islands are calculated in this paper. The self‐consistent plasma response is included through the assumption that the plasma relaxes to a Taylor force‐free state. The connection with linear tearing mode theory is established for those limits where arbitrarily large islands result from infinitesimal perturbations. Toroidal effects are considered, and application of the theory to RFP experiments is discussed.

ISSN:0031-9171    

DOI:10.1063/1.865933

出版商:AIP    

年代:1986

数据来源: AIP