摘要:

Both one‐ and two‐dimensional particle simulation models have been used to study the nonlinear behavior of the electrostatic hydrogen cyclotron instabilities driven by the electron current along the magnetic field. It is found that the instability saturates as a result of electron velocity space diffusion along the magnetic field. The cyclotron waves remain highly coherent in the nonlinear stage. When the electron drift speed is comparable to the thermal speed, substantial ion heating as well as particle cross‐field diffusion comparable to Bohm diffusion has been observed. Comparisons of the simulation results with the theoretical predictions and the observations in both laboratory and space plasmas are discussed.

ISSN:0031-9171    

DOI:10.1063/1.863484

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Computer simulation is used to investigate current‐driven microinstabilities in a simple reversed field (neutral sheet) configuration. A long wavelength, predominantly electromagnetic, instability develops at the reversal point as a consequence of the lower hybrid drift instability, which is excited away from the reversal point where the density gradients are steep. The resulting anomalous resistivity is much smaller at the null point.

ISSN:0031-9171    

DOI:10.1063/1.863485

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Ion pressure gradient‐driven drift modes are analyzed for their parametric dependence on the shear, the toroidal aspect ratio, and the pressure gradient using the ballooning toroidal mode theory. An approximate formula for the anomalous ion thermal conductivity is derived for the turbulent regime.

ISSN:0031-9171    

DOI:10.1063/1.863486

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The stability of multipoles having a purely poloidal field to ballooning modes of high toroidal mode number is studied. First, a perturbation theory based on largemis discussed, and it is found that the first‐order correction to the &bgr; limit is of order 1/m. Next, the equations for a linear quadrupole and octopole are solved and the results are compared with recent multipole experiments.

ISSN:0031-9171    

DOI:10.1063/1.863487

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A formulation of the stability behavior of a finite‐length pinch is presented. A general initial perturbation is expressed as a uniformly convergent sum over a complete discretekset. A variational calculation is then performed, based on the energy principle, in which the end‐boundary conditions appear as constraints. The requisite Lagrange multipliers mutually couple the elemental periodic excitations. The resulting extended form of &dgr;Wstill admits a proper second‐variation treatment so that the minimization and stability considerations of Newcomb remain applicable. Comparison theorems are discussed as is the relevance of this end‐effect model to the stability of solar coronal loops.

ISSN:0031-9171    

DOI:10.1063/1.863488

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Cyclotron resonance absorption in a plasma with arbitrary stratification of the magnetic field is considered. Using the absorption coefficient derived for perpendicular stratification, simple analytic estimates of the absorption can be made for artrary stratification.

ISSN:0031-9171    

DOI:10.1063/1.863489

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

In a collisionless cold plasma, the limit has been obtained of a resonance electric field peak at oblique incidence of ap‐polarized electromagnetic wave upon an inhomogeneous plasma as a result of the nonlinear relativistic treatment of plasma waves.

ISSN:0031-9171    

DOI:10.1063/1.863498

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Consideration of the effect of a uniform pump field on the particle orbits in a Vlasov plasma leads to a modified diffusion coefficient. When the particles oscillate in the pump field, the turbulent wave phase velocity seen by the particles is Doppler shifted by multiples of &ohgr;0/k(&ohgr;0is the pump frequency). Hence, strong interactions between the particles and various components of the turbulent field will take place. It is shown that when the pump field is sufficiently strong:E0⩾(4&pgr;n0Te)1/2, bulk heating can dominate over tail heating and excitation of electrons to energy levels higher than the normal suprathermal values is possible. This field strength is within the range of laser fusion.

ISSN:0031-9171    

DOI:10.1063/1.863499

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A common simplifying assumption made in the consideration of radio‐frequency heating of tokamaks near the lower hybrid frequency is that the wavelength imposed by the coupling device parallel to the magnetic field is not modified by gradients along the field. In the present calculation, the parallel wavelength is allowed to vary, and important effects are found on wave penetration and damping if the toroidal aspect ratio (Rmajor/rminor) is less than approximately five. The calculation shows that heating at the center of a small aspect ratio torus is inhibited by a decrease ink∥if waves are launched at the outside, and that it may be possible to change the plasma current via electron Landau damping with a coupler of symmetric power spectrum by placing the coupler at the top (or bottom) of the torus.

ISSN:0031-9171    

DOI:10.1063/1.863500

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The dynamics of electrons in a low‐frequency wave propagating perpendicular to a uniform magnetic field are studied and the implications of these results for transport and heating by the lower hybrid drift instability are explored. Below a thresholde&fgr;/Ti≊ 0.25–1.0, all electron energy exchange with the wave is reversible and no plasma transport is possible. Above this threshold, trapping of electrons by the wave potentials takes place and causes irreversible electron heating and diffusion. These results imply that anomolous transport in inhomogeneous plasma with weak drifts (diamagnetic velocity less than the ion thermal velocity) may be substantially less than previously predicted.

ISSN:0031-9171    

DOI:10.1063/1.863501

出版商:AIP    

年代:1981

数据来源: AIP