Effect of high ν/γ electron beams for collective ion acceleration

Abstract

Experimental observations of collective‐effect acceleration with electron beams of various ν/γ (ν is the Budker parameter and γ is the usual relativistic factor) values injected into neutral low‐pressure gases show, for beams with ν/γ near unity, that the peak accelerated ion energy exceeds the energy usually obtained from the deep stationary potential‐well stage. It is suggested that high ν/γ electron beams, with a large transverse kinetic‐energy content, undergo a longer transition period from the stationary to the moving phase and translate with a lower velocity than that expected solely on the basis of space‐charge neutralization processes. Ion trapping during and following the transition stage results in final ion energies much greater than 3E_e, where E_e is the electron beam kinetic energy.