摘要:

The methods of numerical solution of the electron fluid dynamical equations that govern wave breakdown, and were described in a previous paper, are applied here to the various situations under which these waves have been observed. Samples of the detailed structures of the waves are presented. Solutions have been investigated for both negatively and positively driven waves, into both ionized and nonionized media, and for waves followed by a large current as in a lightning return stroke.

ISSN:0031-9171    

DOI:10.1063/1.865233

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The electron‐cyclotron maser instability is studied for energetic electrons with a loss‐cone distribution. The instability can occur at all angles of propagation for a wide range of parameters. The growth rate is significantly reduced by the presence of a population of cold electrons, and the instability can be supressed if the density of the cold electrons is sufficiently large and the temperature of the energetic electrons is not too high.

ISSN:0031-9171    

DOI:10.1063/1.865234

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Several experiments have evidenced oscillatory patterns of the electrostatic potential radiated by a small antenna in a hot magnetoplasma. Several previous interpretations based on analytical calculations and numerical computations are discussed; they are found not to be exhaustive or completely satisfactory. A new mechanism responsible for these structures is proposed. It consists of a filtering by the plasma of the wave vectors of the radiated waves. This mechanism is caused by the existence of a restricted range of undamped wave vectors surrounded by highly damped ones. This phenomenon, presently named ‘‘intrinsic diffraction,’’ is used to interpret both the spatial oscillations of the potential around the resonance cone when &ohgr;<min(&ohgr;p, &ohgr;c) and around the direction perpendicular to the magnetostatic field whenn&ohgr;c<&ohgr;<(n+1)&ohgr;c; &ohgr;, &ohgr;p, &ohgr;care, respectively, the wave, the plasma, and the electron‐cyclotron frequencies, andnis any positive integer. The results of both analytical calculations and numerical computations are found to be in good agreement within the two frequency ranges. The location and the amplitude of the oscillatory structure are simply related to the width of the domain of unattenuated wave vectors. New diagnosis methods for the plasma temperature are suggested from this model. Additional directivity and curvature effects related to the topology of the wavenumber surfaces are discussed. The generalization of the use of the intrinsic diffraction picture is proposed.

ISSN:0031-9171    

DOI:10.1063/1.865235

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The nonlinear saturation of the single‐mode, bump‐on‐tail instability is studied by numerical solutions of the Vlasov equation. Modes close to marginal stability are found to saturate with a field amplitudeE∝&Dgr;2, where the small parameter &Dgr;=2(&ohgr;−&ohgr;’)/&ohgr;’defines the difference between the mode frequency &ohgr; and the frequency &ohgr;’of the marginally stable mode. This scaling agrees with O’Neil’s theory [Phys. Fluids14, 1204 (1971)] of the two‐stream instability, anddoesnotconfirmthe time asymptotic analysis of Simon and Rosenbluth [Phys. Fluids19, 1567 (1976)], which predicts larger amplitudes withE∝&Dgr;1/2.

ISSN:0031-9171    

DOI:10.1063/1.865236

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The linear and quasilinear theories of the ion mixing mode are discussed in the electrostatic limit. The source of free energy for the instability is the ion temperature gradient. The parameter relevant to this calculation is &eegr;i=(d ln Ti/dr)/(d ln n/dr). Generally, this mode has a phase velocity comparable to the ion thermal velocity and there exist values of &eegr;ithat yield maximum growth. By using a time‐asymptotic formalism, we are able to discuss the quasilinear saturation of this mode. Short wavelength modes saturate at small amplitudes, ‖e&fgr;1/Ti‖2≤(&eegr;i−&eegr;c)/&eegr;c, where &eegr;cis the value of &eegr;iat marginal stability, and the saturated state is stable against further perturbations. Long wavelength modes also saturate, though the saturation is of the ‘‘hard’’ type: the saturated state itself is unstable. When saturation occurs, it is caused by reduced inverse ion Landau damping brought about both by the nonlinear frequency shift and by quasilinear modifications to the ion distribution function.

ISSN:0031-9171    

DOI:10.1063/1.865237

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A set of reduced magnetohydrodynamic equations for mean and fluctuating fields is derived and applied to the dynamo effect in reversed field pinch (RFP) and tokamak plasmas. There are two dynamo effects, the first arising from mean field equilibrium, and the second from the fluctuations. The dynamo effect does not drive a net current in steady state. The quasilinear dynamo caused both by growing and stationary tearing modes is calculated and found to be consistent with field reversal in RFP’s. Numerical solutions of the equations are presented, which are in qualitative agreement with experiment and other computations.

ISSN:0031-9171    

DOI:10.1063/1.865238

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Two‐fluid theory is used to calculate the nonlinear effect of a finite‐amplitude ion‐cyclotron wave on the simple interchange stability of a magnetically confined plasma. The ion‐cyclotron wave nonlinearly modifies interchange stability through ponderomotive effects and coupling to sidebands of the ion‐cyclotron wave. Nonlinear stability criteria for flute modes are derived. The nonuniformity and polarization of the ion‐cyclotron wave significantly influence the results. A theoretical explanation for recent experimental observations in axisymmetric mirror and tandem mirror plasmas of reduced levels of magnetohydrodynamic activity in the presence of ion‐cyclotron resonant heating remains elusive.

ISSN:0031-9171    

DOI:10.1063/1.865239

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The full viscosity tensor for an axisymmetric toroidal plasma in the collisional regime (with strong rotation) is calculated, including gyroviscosity andO(&egr;) poloidal variations over the flux surface. It is shown that the resulting viscous force is of sufficient magnitude to account for the radial transfer of toroidal momentum that must be inferred in order to explain the rotation measurements in tokamak experiments. The consequences of a viscous force of this form and magnitude on particle transport and on the evolution of toroidal and poloidal rotation velocities are discussed.

ISSN:0031-9171    

DOI:10.1063/1.865240

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The wave equations for the second harmonic ion‐cyclotron heating as derived from the Maxwell equations, rather than the model fourth‐order equation, are solved analytically. With a better treatment of the wave field near the second harmonic resonance layer, the WKBJ solution can be improved to give results valid over a larger range of tunneling parameters than those derived in a previous work on a similar subject [J. Plasma Phys.27, 327 (1982)]. Dissipation is also discussed and connection with the Budden model is shown.

ISSN:0031-9171    

DOI:10.1063/1.865241

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Level curves for the resistive compressible ballooning growth rates and the ideal ballooning stability boundaries with incompressibility and perpendicular compressibility are determined in the parameter space of shear‐versus‐pressure gradient for realistic tokamak equilibria. The trajectories of these level curves differ from the ideal incompressible stability boundary in this space.

ISSN:0031-9171    

DOI:10.1063/1.865242

出版商:AIP    

年代:1985

数据来源: AIP