Collisional Relaxation of Electron Tail Distribution

Abstract

Relaxation due to the Coulomb collisions of the electron velocity distribution function with a high energy tail is investigated in detail. In the course of the relaxation, a `saddle' point can be created in velocity space owing to v -3 dependence of the deflection rate and a positive slope or a `dip' appears in the tail direction. The time evolution of the electron tail is studied analytically. A comparison is made with numerical results by using a Fokker-Planck code. Also discussed is the kinetic instability concerned with the positive slope during the relaxation.