Electron random walk and collisional crossover in a gas in presence of electromagnetic waves and magnetostatic fields

Abstract

This paper deals with random walk of electrons and collisional crossover in a gas evolving toward a plasma, in presence of electromagnetic (EM) waves and magnetostatic (B) fields, a fundamental subject of importance in areas requiring generation and confinement of wave assisted plasmas. In presence of EM waves and B fields, the number of collisions N suffered by an electron with neutral gas atoms while diffusing out of the volume during the walk is significantly modified when compared to the conventional field free square law diffusion; N=1.5(Λ/λ)2, where Λ is the characteristic diffusion length and λ is the mean free path. There is a distinct crossover and a time scale associated with the transition from the elastic to inelastic collisions dominated regime, which can accurately predict the breakdown time (τc) and the threshold electric field (EBD) for plasma initiation. The essential features of cyclotron resonance manifested as a sharp drop in τc, lowering of EBD and enhanced electron energy gain is well reproduced in the constrained random walk.