Scattering of Electromagnetic Waves by Drift Vortex in Plasma

In a quasi-two-dimensional model, the scattering of incident ordinary electromag- netic waves by a dipole-electrostatic drift vortex is studied with first-order Born approximation. The distribution of the scattering cross-section and total cross-section are evaluated analytically in different approximate conditions, and the physical interpretations are discussed. When the wavelength of incident wave is much longer than the vortex radius （kia〈〈1）, it is found that the angle at which the scattering cross-section reaches its maxim depends significantly on the approximation of the parameters of the vortex used. It is also found that the total scattering cross-section has an affinitive relation with the parameters of the plasma, while it is irrelevant to the frequency of the incident wave in a wide range of parameters of the vortex. In a totally different range of parameters when incident wave is in the radar-frequency range （then kia 〈〈 1, the wavelength of incident wave is much shorter than the vortex radius）, the numerical procedure is conducted with computer in order to obtain the distribution and the total expression of the scattering crosssection. Then it is found that the total scattering cross-section in the low frequency range is much larger than that in high frequency range, so the scattering is more effective in the low frequency range than in high frequency range.

A Particle-in-Cell Simulation of Double Layers and Ion-Acoustic Waves

Double layers and ion-acoustic waves are investigated by using a one-dimensional electrostatic particle-in-cell simulation code. Our results show that double layers can be formed even when the drift velocity between electrons and ions is less than the electron thermal velocity. Electron and ion density depressions were clearly seen. Electrons gradually developed a distribu- tion comprising both background and beam components. In fact, as the initial electron-ion drift velocity was less than the electron thermal velocity, intense ion-acoustic waves could be found only at the places where the electron beam was located, suggesting that they are excited by the self-consistently developed electron beam. Besides the Langmuir waves and ion-acoustic waves, the beam mode excited by electron beams produced in our simulation has been clearly found.

A Fokker-Planck Code for Laser-Produced Plasmas

A Fokker-Planck code is developed based upon Epperlein＇s scheme to investigate laser-produced plasmas in relevance to inertial confinement fusion. The equations are integrated implicitly by time-splitting method. Three test problems are simulated to show the versatility of the code. The results are in good agreement with the existing simulations.

Electrodynamic Coupling in the Solar Wind-Magnetosphere-Ionosphere System

This paper presents a brief summary of our recent work based on global MHD simulations of the Solar wind-Magnetosphere-Ionosphere (SMI) system with emphasis on the electrodynamic coupling in the system.The main conclusions obtained are summarized as follows.(1) As a main dynamo of the SMI system,the bow shock contributes to both region 1 Field-Aligned Current (FAC) and cross-tail current.Under strong interplanetary driving conditions and moderate Alfv'en Mach numbers,the bow shock's contribution may exceed more than fifty percent of the total of either region 1 or cross-tail currents.(2) In terms of more than 100 simulation runs with due southward Interplanetary Magnetic Field (IMF),we have found a combined parameter f=E sw P sw M A -1/2 (E sw,P sw,and M A are the solar wind electric field,ram pressure,and Alfv'en Mach number,respectively):both the ionospheric transpolar potential and the magnetopause reconnection voltage vary linearly with f for small f,but saturate for large f.(3) The reconnection voltage is approximately fitted by sin 3/2 (θ IMF /2),where θ IMF is the IMF clock angle.The ionospheric transpolar potential,the voltage along the polar cap boundary,and the electric fields along the merging line however defined they may be,respond differently to θ IMF,so it is not justified to take them as substitutes for the reconnection voltage.