摘要:

Plasma heating by lower‐hybrid waves has been studied using a two‐and‐one‐half‐dimensional electrostatic code with more realistic plasma and source models than previously used. Mode couplings between wavenumber modes of opposite sign occur when two propagation cones meet. The resulting smallerk∥and/or higher &ohgr; modes propagate in the interior. These modes appear to be plausible mechanisms for tail heating of electrons and ions.

ISSN:0031-9171    

DOI:10.1063/1.863353

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The existence of nonlinear periodic Langmuir waves that are time dependent in any frame of reference is demonstrated, the phase and amplitude modulations being induced by the oscillating motion of trapped particles. Large amplitude modulations can be found even for weak trapped particles densities. Sideband instabilities are strongly modified by the oscillating motion when the energy dependence of the bounce frequency is taken into account.

ISSN:0031-9171    

DOI:10.1063/1.863354

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The nonlinear dynamics of the bump‐on‐tail instability is considered. The eigenmodes have discretekbecause of finite periodic boundary conditions. Increasing a critical parameter (the number density) above its neutral stable value by a small fractional amount &Dgr;2, one mode becomes unstable. The nonlinear dynamics of the unstable mode is determined by means of the multiple time scale method. Usually, limit cycle behavior is found. A short comparison with quasi‐linear theory is given, and the results are compared with experiment.

ISSN:0031-9171    

DOI:10.1063/1.863355

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The magnetohydrodynamic stability of axisymmetric field reversed equilibria (compact tori) without a toroidal magnetic field is studied. It is shown that axis encircling ions do not interact with modes having a short wavelength in the toroidal (symmetry) direction. A large toroidal aspect ratio equilibrium with nearly circular flux surfaces is found to be stable to ballooning modes if the axis encircling ions carry more than half the current. In the opposite limit, e.g., elliptical flux surfaces with aspect ratio as large as 5, ninety percent of the current must be carried by axis‐encircling ions. In a thermal plasma (a reversed field theta pinch, for example) only a fraction of the outer flux surfaces are unstable if &rgr;i/L, the ratio of ion gyroradius to scale length, is greater than 0.3, and if the flux surfaces are not too elongated.

ISSN:0031-9171    

DOI:10.1063/1.863356

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Particle transport rates for a trace impurity are calculated for a Pfirsch–Schlu¨ter regime plasma consisting of a main ion and all the charge states of a background impurity. The main ion is taken to be much lighter than all impurities, but masses and charges are otherwise arbitrary. Qualitative trends of the transport rates with variations in the trace impurity mass and background impurity concentrations are discussed.

ISSN:0031-9171    

DOI:10.1063/1.863357

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A variational formulation of transport for a closed field line, large aspect ratio bumpy torus in the low collision frequency limit is presented. The relatively large radial excursions made by those particles with canceling magnetic and electric poloidal drifts requires generalization of previous neoclassical techniques. General expressions for the transport coefficients of both charge species are given. Explicit numerical coefficients are evaluated under certain simplifying assumptions for both the banana and nonbanana species.

ISSN:0031-9171    

DOI:10.1063/1.863358

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The rate at which current penetrates to the interior of a plasma during the current rise phase of a discharge is found to be greatly enhanced by anomalous viscosity due to electromagnetic turbulence.

ISSN:0031-9171    

DOI:10.1063/1.863359

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The absorption and scattering of laser light in laser fusion targets is very dependent on the exact form of the laser induced density profiles. The possible profiles that can exist are examined using a simple isothermal model. It is shown that four different structures are possible. The flow speed profiles and the speed of the critical surface are determined for each of these structures. It is shown that two of these structures are locally overdense and can exist in an underdense plasma, and thus may have a large effect on the amount of light reaching the critical surface.

ISSN:0031-9171    

DOI:10.1063/1.863360

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The intensity of the electromagnetic radiation produced by a free electron laser can be substantially increased by applying a dc electric field at the time of saturation. By using a proper dc electric field strength, a substantial number of trapped electrons can become clamped in the decelerating phase and continuously transfer the dc electric field energy into the locked high frequency radiation. A modulational instability is observed when the radiation intensity exceeds some threshold, and ultimately terminates the conversion process.

ISSN:0031-9171    

DOI:10.1063/1.863361

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The importance of radial losses in collisional multiple mirror confinement is investigated for arbitrary values of &bgr;. Classical radial diffusion and complete fluid stability are assumed. Analytical and numerical solutions of the coupled axial and radial diffusion problem are found. The results can be characterized in terms of a single parameter &agr;∼(&tgr;z/&tgr;x)1/2where &tgr;zand &tgr;xare average values of the axial and radial confinement times. Radial losses are unimportant for &agr;≲0.5 and improvement in overall confinement can be achieved by increasing &bgr; for these small values of &agr;. When applied to existing reactor designs, the theory shows that radial losses are significant for one‐component reactors but can be made negligible for two‐component (wetwood burner) reactors.

ISSN:0031-9171    

DOI:10.1063/1.863362

出版商:AIP    

年代:1981

数据来源: AIP