Electron and positron swarms: Collision and transport data and kinetic phenomena

Abstract

A broad review of electron swarm studies completed recently is presented with a common thread of both being motivated by major applications which use swarm physics as part of their phenomenological foundation and also with a strong presence of nonconservative (electron number changing) collisions. The review is mainly based on the activities of Gaseous Electronics Laboratory Belgrade and it cannot cover all recent and ongoing activities in swarm physics but it attempts to cover the majority of topics covered by swarm physicists in general. Thus we start with recent determinations of the cross sections from the transport data and calculations of the transport data from the cross sections from other sources in gases such as NO, N2O and mixtures of Ar and N2. We proceed to show how the presence of radicals affects the transport coefficients in CF4, a gas with great potential for applications. The basic features of the transport are discussed for dc and rf electric and magnetic fields. In those two chapters we mainly focus on kinetic phenomena such as negative absolute mobility, non-conservative effects in particle transport and how angle between magnetic and electric field affects the transport coefficients. We also discuss application of semi empirical formulas. Finally we analyze positron transport and its difference from the transport of electrons. The Positronium formation cross section is significantly larger than that for analogous electron non-conservative processes (i.e. electron attachment). Thus transport of positrons gives a much stronger nonconservative effects including a new effect of the negative differential conductivity (NDC) in the bulk (WB - velocity of the center of the swarm that is relevant for the real space diffusion equation) drift velocity while the conditions required for NDC do not exist for the flux drift velocity (w F - mean velocity of particles in the swarm that is relevant for the calculations of flux when using continuity relation).