摘要:

The ambipolar radial electric field in a nonaxisymmetric plasma can be described by a nonlinear diffusion equation. This equation is shown to possess solitary wave solutions. A model nonlinear diffusion equation with a cubic nonlinearity is studied. An explicit analytic step‐like form for the solitary wave is found. It is shown that the solitary wave solutions are linearly stable against all but translational perturbations. Collisions of these solitary waves are studied and three possible final states are found: two diverging solitary waves, two stationary solitary waves, or two converging solitary waves leading to annihilation.

ISSN:0031-9171    

DOI:10.1063/1.865954

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

An analytical theory of current‐driven, ion‐cyclotron turbulence that treats incoherent phase‐space density granulations (clumps) is presented. In contrast to previous investigations it focuses on the physically relevant regime of weak collective dissipation, where waves and clumps coexist. The threshold current for nonlinear instability is calculated and is found to deviate from the linear threshold by up to 7%. A necessary condition for the existence of stationary wave‐clump turbulence is derived and shown to be analogous to the test‐particle model, fluctuation–dissipation theorem result. The structure of three‐dimensional magnetized clumps is characterized. It is proposed that nonlinear instability is saturated by collective dissipation due to ion‐wave scattering. For this wave‐clump turbulence regime, it is found that the fluctuation level (e&Jgr;/Te)rms≤0.1, and that the modification of anomalous resistivity to levels predicted by conventional nonlinear wave theories is moderate. In marked contrast to the quasilinear prediction, it is also shown that ion heating significantly exceeds electron heating, and that a drag force on electrons sustains a steady current and is set up to counteract the accelerating electric field along field lines.

ISSN:0031-9171    

DOI:10.1063/1.865955

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The electron surface mode dispersion relation, including Landau damping, is obtained for a vacuum–plasma interface. Unlike previous work, the interface is permitted to have a finite width and no wall boundary conditions are assumed. When the density gradient scale lengthLnis large compared with a Debye lengthk−1Dand small compared with a surface mode wavelength 2&pgr;k−1, then the mode frequency is &ohgr;=(&ohgr;p/21/2) (1+kLn/6), and the Landau damping rate is &ggr; =−[6/(2&pgr;)1/2]&ohgr;p/(kDLn). These expressions are much different than the comparable expressions for a wall‐confined plasma.

ISSN:0031-9171    

DOI:10.1063/1.865957

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

When particle orbits are trapped very near a cyclotron harmonic resonance, the quasilinear concept of weakly perturbed, uncorrelated passages through resonance breaks down, and nonlinear effects become important. In numerical as well as analytic studies, it is demonstrated that relativistic detuning of the resonance can be important for electrons even at low initial energies (∼20 eV) and that coupling to perturbed parallel motion can lead to strong interactions for values of the turning point where the wave frequency differs from a harmonic multiple of the bounce‐averaged gyrofrequency by an integral multiple of the bounce frequency. The resultant motion is described by large periodic energy excursions for which small‐angle Coulomb collisions or other randomization processes are required to realize net heating. Analytic formulas are derived describing the energy excursion behavior and heating in a mildly relativistic limit. Also, a Monte Carlo numerical model of the collisional effects on the orbits has been employed to study electron heating at the second‐harmonic cyclotron resonance and to test the analytic results. In certain regimes of collisionality, a strong enhancement over quasilinear heating has been found.

ISSN:0031-9171    

DOI:10.1063/1.865985

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

By using the propagator expansion method applied to an electon–ion plasma near thermal equilibrium, a closed‐form solution is found for the high‐frequency, collisional dielectric function in the electrostatic approximation to the first order in the plasma parameter when the Balescu–Lenard collision operator [Phys. Fluids3, 52 (1960); Ann. Phys. (N.Y.)3, 390 (1960)] is used to describe electron–electron and electron–ion collisions. The Balescu–Lenard dielectric function is shown to be an entire function of the complex frequency variable &ohgr;. Since an exact solution for the collisional propagator for the Balescu–Lenard problem is probably impossible, these results illustrate the usefulness of the propagator expansion method as a way of obtaining the dielectric function for collisional plasmas. A comparison is made between the Balescu–Lenard result for the plasma conductivity as the wave vectork → 0 and the Guernsey result, obtained by Oberman, Ron, and Dawson [Phys. Fluids5, 1514 (1962)]. By solving the Balescu–Lenard dispersion relation in the long wavelength approximation, a formula is obtained for the total damping rate for Langmuir waves &Ggr;k, which is the sum of the collisionless (Landau) part &ggr;Lkand the collisional part &ggr;&ngr;k. A numerical solution of the Balescu–Lenard dispersion relation has also been performed, and the analytical and numerical results for the damping rates are compared at long wavelengths. Comparisons of the Balescu–Lenard damping rate to the quantum mechanical result obtained by Dubois, Gilinsky, and Kivelson [Phys. Rev. Lett.8, 419 (1962)] and to other results are also made.

ISSN:0031-9171    

DOI:10.1063/1.865986

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The oscillatory pattern of the electrostatic potential radiated in a hot magnetoplasma at frequencies &ohgr;<min (&ohgr;p, &ohgr;c) is examined in terms of the intrinsic diffraction phenomenon: &ohgr;pand &ohgr;care, respectively, the electron plasma and cyclotron frequencies. It is shown that the potential maxima are located on equally spaced cones parallel to the resonance cone. The spacing of these cones, measured along the ambient magnetic field, is simply related tok∥I, the parallel component of the largest unattenuated wave vector. The consistency of these features with experimental observations is shown. A method of measurement of the electron temperature is derived.

ISSN:0031-9171    

DOI:10.1063/1.865988

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Using the KBM perturbation technique, the stability of oblique modulation of ion‐acoustic waves in a two‐ion plasma is studied. It is found that the presence of a small amount of lighter ion impurities significantly changes the instability domain in the &ohgr;‐&fgr; plane. The effect of the concentration and mass of impurity ions on the modulational instability is discussed in detail. The threshold amplitude for instability and nonlinear frequency shift of the wave are also calculated. The predictions of the theory are found to be in good agreement with the experimental observations.

ISSN:0031-9171    

DOI:10.1063/1.865989

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Drift vortices in plasmas described by the Petviashvili equation in the case of strong temperature inhomogeneities or by the Hasegawa–Mima equation in the case of density gradients are investigated. Both equations allow for two‐dimensional vortex solutions. The models are reviewed and the forms of the vortices are discussed. In the temperature‐gradient case, the stationary solutions are only known numerically, whereas in the density gradient case analytical expressions exist. The latter are called modons; here the ground states are investigated. The result of a stability calculation is that both types of two‐dimensional solutions, for the Petviashvili equation as well as the Hasegawa–Mima equation, are stable. The methods used to prove this result are either direct (constructing Liapunov functionals) or indirect, and then based on variational principles.

ISSN:0031-9171    

DOI:10.1063/1.865990

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The general set of low‐frequency nonlinear fluid equations describing microturbulence in an inhomogeneous warm plasma with a strong magnetic field is shown to possess two‐dimensional solitary vortex solutions.

ISSN:0031-9171    

DOI:10.1063/1.866019

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Using Braginskii’s two fluid equations, the stability of resistive ballooning modes is examined in the presence of parallel thermal conduction, anomalous electron viscosity, and radial thermal conductivity. A generalized set of coupled second‐order differential equations in &fgr; and &psgr; is derived in ballooning space and is solved to obtain analytical solutions in two interesting frequency regimes,SCs/qR ≪ ‖&ohgr;‖ ≪ Cs/  qRand ‖&ohgr;‖ ≫ Cs/qR. It is shown that the anomalous thermal transport term excites the newm=1 resistive ballooning mode (‖&ohgr;‖ ≫ Cs/qR) with a large growth rate. The excitation of them=2 type (or &Dgr;’driven) mode, on the other hand, is found to be strongly influenced by both anomalous electron viscosity and radial thermal conduction. Finally, the additional effect of parallel electron thermal conduction is shown to give new resistive ballooning modes with significantly large growth rates varying as fractional powers of anomalous electron viscosity and classical thermal conductivity.

ISSN:0031-9171    

DOI:10.1063/1.865969

出版商:AIP    

年代:1986

数据来源: AIP