Further Studies of Collective Acceleration of Positive Particles Using Intense Electron Beams

Abstract

FURTHER STUDIES OF COLLECTIVE ACCELERATION OF POSITIVE PARTICLES USING INTENSE ELECTRON BEAMS B. Ecker and S. Putnam Physics International Company, San Leandro, CA., 94577 and D. Drickey, Department of Physics, UCLA Protons at 12 MeV and nitrogen nuclei (Nf7) at 29 MeV were produced during propaga- tion of a pulsed 100 kA, 1 MV electron beam (peak values) through initially neutral hydro- gen and nitrogen, respectively. Applied longi- tudinal magnetic fields of 250 gauss or more severely suppressed proton acceleration: 100 gauss had no effect. Protons having at least 3 MeV were observed 11 cm from the plane of injection of the electron beam into the gas- filled acceleration region. At the time of acceleration, the electron beam current front had already propagated substantially beyond the acceleration region. Use of a colder beam than in a previous study1 resulted in increa- sed particle energy and in greater sensitivity of proton energy to hydrogen density. The localized pinch model is strongly supported by some of the data and is compatible with all results. Introduction The first observation of ions accelera- ted by intense electron beams propagating thrcugh initially neutral gas was in 1970 by Graybill and Uglurn.z Since then a number of experimental studies have been reported,lr3'6 gya;;e;;$p;; yF3 Is have been put forth to have been presenied. 133!3 three review papers The present study was a small program that aimed at bringing us closer to a definite conclusion about the na- ture of the acceleration process and its cut- off mechanisms. To this end we have investi- gated mainly the effects of electron beam temperature and of an applied longitudinal magnetic field, and the spatial and temporal relationship between the electron beam and the accelerated ion bunch. As pointed out by Yonas,l5 of the four theoretical models thus