|Title||Coulomb collisional processes in space plasmas; relaxation of suprathermal particle distributions|
|Publication Type||Journal Article|
|Year of Publication||2004|
|Journal||Planetary and Space Science|
|Type of Article||Article|
|Keywords||ELECTRON VELOCITY DISTRIBUTION, equations, GAS, H+, KINETIC-MODEL, NUMERICAL-METHODS, POLAR WIND, relaxation, SOLAR-WIND, TEMPERATURE, TRANSITION|
Nonequilibrium distributions of space plasmas are often characterized by extended high-energy tails. This paper provides a detailed analysis of the relaxation of such isotropic nonequilibrium plasmas. We consider an energetic charged species dilutely dispersed in a fully ionized plasma, which acts as a heat bath at equilibrium. The minor constituent is referred to as a "test particle" and collisions between test particles are not included. We study the approach to equilibrium with a finite difference method of solution of the Fokker-Planck equation appropriate for collisions between charged particles. The solution of the Fokker-Planck equation is also presented formally as an expansion in the eigenfunctions of the Fokker-Planck operator. The main objective of the paper is the calculation of the energy-dependent relaxation times of the distribution function. A strong energy dependence for these relaxation times is anticipated since, for Coulomb collisions, the Rutherford cross-section varies with relative speed g as g(-4). Analogous results for neutral species are presented for comparison in the following paper. (C) 2004 Elsevier Ltd. All rights reserved.
|URL||<Go to ISI>://000224217300004|