摘要:

Two cases are investigated. In the first case the electron distribution is assumed to have a loss‐cone feature. It is found that the plasma can amplify electromagnetic waves near the electron cyclotron frequency, as expected. However, the growth rate is significantly larger than that used in an approximate calculation in which a slightly different physical model was considered. The present discussion is restricted to the fast extraordinary‐ mode radiation. One of the important conclusions is that, due to the combined relativistic and loss‐cone effects, the cutoff frequency can be lower than the electron cyclotron frequency, a result in contrast with that obtained with the usual ’’cold plasma’’ approximation. In the second case a drift motion along the ambient magnetic field is studied. It is found that the cyclotron damping can occur under certain conditions.

ISSN:0031-9171    

DOI:10.1063/1.863325

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The problem of the linear conversion of a Langmuir wave to a transverse electromagnetic wave in the presence of a density gradient has been solved numerically with appropriate boundary conditions. A reciprocity principle was found, allowing the deduction of solutions of this problem from those obtained from the transverse‐Langmuir conversion. This model has been applied to study the spectrum emitted from an inhomogeneous plasma, including the effect of the antenna radiation pattern. Experiments have been performed in a large unmagnetized dc discharge plasma (ne∼5×1010cm−3,Te= 1.3 eV, gradient scale lengthL= 100−1000 cm). The shape of the spectrum observed with a horn antenna agrees with the theoretical one, but the deduced level of Langmuir fluctuations is much higher than the thermal level. This enhancement is due to the presence of primary energetic (E= 60 eV) electrons.

ISSN:0031-9171    

DOI:10.1063/1.863326

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Stability properties are investigated for purely growing (Re&ohgr; = 0) tearing modes at marginal stability (Im&ohgr; = 0) for a rotating, nonrelativistic cylindrically symmetric ion layer immersed in an axial magnetic field. The analysis is carried out within the framework of a Vlasov‐fluid model in which the electrons are described as a macroscopic cold fluid, and the layer ions are described by the Vlasov equation. Tearing‐mode stability properties are calculated numerically for azimuthally symmetric perturbations about an ion layer equilibrium with temperature anisotropy. The marginal stability eigenvalue equation is solved numerically for the perturbation amplitude and the normalized axial wavenumbers at marginal stability in terms of temperature anisotropy, layer radius, and magnetic field depression on the axis. It is found that the range of unstable wavenumbers decreases as T‖‖/T⊥is increased, and numerical estimates are made of the anisotropy required for complete stabilization.

ISSN:0031-9171    

DOI:10.1063/1.863336

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A positive ambipolar potential arising from large transport rates of electrons relative to ions in stochastic magnetic fields gives an outward force on the ions. It can reverse the neoclassical inward convection of the impurity ions in tokamaks. This process may by responsible for the observed decays of line emissions from high charge states of silicon in an impurity study experiment in Alcator.

ISSN:0031-9171    

DOI:10.1063/1.863337

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Magnetic field generation in the underdense plasma due to the nonlinear interaction of an electromagnetic wave and a plasma is investigated. It is shown that the collisional absorption of the electromagnetic wave induces a nonlinear anistropy in the electron pressure tensor, which is responsible for a large source of the dc magnetic field. Six different regimes of interest appear, depending on four characteristic parameters related to the collision rate, the thermal effects, hydrodynamic convection, and the duration of the experiment. The theory is supported by a detailed comparison with recent microwave plasma experiments.

ISSN:0031-9171    

DOI:10.1063/1.863338

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The ponderomotive effects and magnetic field generation due to the nonlinear interaction of short‐wavelength ion turbulence with an electromagnetic wave are studied using the Dawson and Oberman model, which exactly describes the electron‐ion interaction in the limit of infinite ion‐to‐electron mass ratio. The differences from the results of the heuristic Landau model are stressed, in particular for nonthermal ion correlations and for an electromagnetic wave frequency slightly exceeding the electron plasma frequency.

ISSN:0031-9171    

DOI:10.1063/1.863339

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Quasi‐linear saturation of the amplitude of coherent backward ionization waves is studied using the slowly varying parameters or Van der Pol’s method. The result is a nonlinear Landau equation which describes the growth and saturation of the wave amplitude. The analytical expression of the most important nonlinear saturation term predicts results in accordance with earlier experimental observations.

ISSN:0031-9171    

DOI:10.1063/1.863340

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Toroidal systems of arbitrary cross section without toroidal magnetic field are analyzed via the double adiabatic fluid equations. Such systems are shown to be unstable if there exists one closed field line on which the average of &kgr;rB2is positive, where &kgr; is the curvature. A similar criterion is derived for linear system and is applied to a noncircularzpinch.

ISSN:0031-9171    

DOI:10.1063/1.863341

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The thermosolutal instability of a plasma in the presence of a transverse magnetic field is studied to include the effects of the finiteness of the ion Larmor radius. The finite Larmor radius and stable solute gradient are found to have stabilizing effects on stationary convection. The case of overstable modes is also considered wherein necessary conditions for the existence of overstability are derived.

ISSN:0031-9171    

DOI:10.1063/1.863342

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The variational structure of the Vlasov–Maxwell integral equations is derived for a plasma equilibrium having two ignorable coordinates. It is shown that the kernel of the Maxwell equations is a self‐adjoint integral operator. This operator may also be represented as a differential equation of arbitrary order. This representation is useful when the differential operator is truncated to finite order, yielding a system of intrinsically self‐adjoint differential equations.

ISSN:0031-9171    

DOI:10.1063/1.863343

出版商:AIP    

年代:1981

数据来源: AIP