Proposed model of thermionically assisted breakdown and implementation on electrostatic thrusters

Abstract

A model for thermionically assisted breakdown is proposed which predicts the voltage reduction experienced in low voltage discharges. This reduction in breakdown voltage has been beneficial to numerous engineering applications of arcs and is explored herein specifically for electrostatic thrusters. Full advantage in employing thermionically assisted breakdown is attained by establishing a continuum of electron emission across the primary discharge gap. These electrons must be independent of the discharge itself, being established prior to ignition. The electron emission is therefore achieved by auxiliary emitters across the gap. Electrons amass in a space charge in the vicinity of the assisting device. The particular processes which induce charge multiplication are proposed to be multistep ionization and neutralization of the space charge by ions. Breakdown criteria and a means of estimating the reduction is breakdown voltage requirement are derived. One proposal for the thermionically assisting emission device is the coiled-coil filament, and a scheme for installing such filaments in ionization chambers for electrostatic thrusters is described. Thermionically assisted breakdown implementation should also pertain to arc applications for various primary electrode geometries as well as certain gases.