Influence of electron-neutral elastic collisions on the instability of an ion-contaminated cylindrical electron cloud: 2D3V PIC-with-MCC simulations

Abstract

This paper is a simulation based investigation of the effect of elastic collisions and effectively elastic-like excitation collisions between electrons and background neutrals on the dynamics of a cylindrically trapped electron cloud that also has an ion contaminant mixed in it. Effects of the collisions on the instability are evident from alteration in the growth rate and energetics of the ion resonance instability caused by the presence of background neutrals as compared to a vacuum background. Further in order to understand if the non-ionizing collisions can independently be a cause of destabilization of an electron cloud, a second set of numerical experiments were performed with pure electron plasmas making non-ionizing collisions with different densities of background neutrals. These experiments reveal that the nature of potential energy extraction from the electron cloud by the non-ionizing collisions is not similar to the potential energy extraction of other destabilizing processes \textit{e.g.} a resistive wall instability. This difference in the energy extraction process renders these non-ionizing collisions incapable of independently triggering an instability of the cloud.