A model of electron acceleration in a current sheet of flares is studied by the analytical approximation solution and the test particle simulation. The electron can be trapped in a potential of propagating electrostatic wave. The trapped electron moving with the phase velocity v p of wave may be effectively accelerated by ev p/c × B z force along the outflow direction in the current sheet, if a criterion condition K > 0 for electron surfing acceleration is satisfied. The electron will be accelerated continuously until the electron de-trap from the wave potential at the turning point S.
WANG DeYu1 & LU QuanMing2 1 Purple Mountain Observatory, Nanjing 210008, China
A model of collisional RF sheath with negative ions is discussed in this paper. The influences of collision and negative ions on the parameters of the sheath are studied through numerical simulation. It is found that when the collision coefficient increases and the RF power is fixed, the electrode potential and sheath electric field potential increase, the electrode current and thickness of the sheath decrease. When the negative ion content changes, the same phenomenon Occurs,
In this paper, a new method to derive the Fokker-Planck coefficients defined by a non-Maxwellian velocity distribution function for the field particles is presented. The three- fold integral and the new Debye cutoff parameter, which were introduced by CHANG and LI, are applied. Therefore, divergence difficulties and the customary replacement of relative velocity g by thermal velocity vth are naturally avoided. The probability function P（v, Av） for non- Maxwellian scattering is derived by the method of choosing velocity transfer Av, which is a true measure of collision intensity, as an independent variable. The method enables the difference between small-angle scattering and small-momentum-transfer collisions of the inverse-square force to be well clarified. With the help of the probability function, the Fokker-Planck coefficients are obtained by a normal original Fokker-Planck approach. The friction and diffusion coefficients of the Fokker-Planck equation are modified for non-Maxwellian scattering and are used to investigate the relaxation processes for the weakly coupled plasma. The profiles of the relaxation rates show that the slowing down and deflection processes are weakened in the conditions of non-Maxwellian scattering.
This article presents a study we have made of one class of coherent structures of the tripolar vortex. Considering the sheared flow and sheared magnetic field which are common in the thermonuclear plasma and space plasma, we have simulated the dynamics of the tripolar vortex. The results show that the tripolar vortex is largely stable in most cases, but a strongly sheared magnetic field will make the structure less stable, and lead it to decays into single vortices with the large space scale. These results are consistent with findings from former research about the dipolar vortex.
Lower-hybrid drift instability （LHDI） in a Harris current sheet including a uniform background distribution is investigated in linear local kinetic theory. It is found that the introduction of a uniform background distribution reduces the growth rate and real frequency of LHDI at all wavelengths. Some physical explanations about the effects of the background distribution are provided.
In this paper, a solution to the Fokker-Planck equation is presented, which is extended to the field particles＇ high-energy-tail non-Maxwellian velocity distribution function in transport theory. Based on the correct physical concept of collision intensity, introduced by CHANG and LI, the electrical conductivities for like-particles collisions are obtained in different conditions. The modified Fokker-Planck coefficients for non-Maxwellian scattering are applied in the study. It is found that the parallel part of the collision operator plays an important role. The non-Maxwellian scattering will stimulate the transport processes in various degrees with mutative deviation parameters.
