Low-voltage, high-current-density electron beam sources

Abstract

We are beginning to study plasma filled diode operation at low voltages to produce electron beams for materials applications. This paper presents our first work in this area. Appropriate electron-beam sources require a low-voltage cathode, plasma to neutralize the beam space charge, and a means of guiding the beam to the target. Candidate cathodes include surface flashover sources, highly-enhanced structures like graphite fibers, and hollow cathodes. Plasma can be produced by a variety of surface-discharge sources, or by ionization of a gas ambient, either by the electron beam precursor or an auxiliary Penning discharge. The beam can be guided either magnetically or electrostatically by a dielectric channel. Two existing, relevant sources are the channel spark, developed at the Karlsruhe Research Center (FZK) (hollow cathode/beam-ionization in gas/dielectric guide) and the plasma filled diode source developed at the Tomsk Institute of High Current Electronics (graphite cathode/Penning discharge in gas/magnetic guide). We began using the FZK channel spark source. After examining different variations, we replaced the hollow cathode with a surface-flashover cathode of rigid coax. This source was used in preliminary thin-film ablative deposition experiments. We next studied at a plasma-filled diode configured like a 'traditional' plasma opening switch. We are focusing on sources where the plasma is produced by breakdown of the ambient gas.