Laser surface melting of stainless steel anodes for reduced hydrogen outgassing

High Pulsed Power Electromagnetic (HPEM) devices are used in numerous applications including vacuum electronics, particle accelerators, and microwave generators. Stable, long term HPEM device operation is presently constrained by pulse shortening due to plasma formation in the anode-cathode gap region. Plasma is formed through collisions between secondary electrons and gas molecules, both of which are produced by high energy electron impact at the anode; hydrogen is the most abundant species desorbed from metal surfaces by high energy electron impact. The purpose of the work described here was to determine the feasibility of using anodes of 304 stainless steel (SS), processed by laser surface melting (LSM), to reduce hydrogen outgassing. The LSM technique entails irradiating a sample with the output of a high energy, continuous laser beam, thereby causing melting, flow and re-solidification of the material as the laser beam is scanned across the anode surface. When compared to more conventional processing techniques, such as electropolishing, LSM processing introduces significantly fewer contaminants (especially hydrogen) into the anode surface and has the potential to reduce outgassing by decreasing the number of grain boundaries through which hydrogen can diffuse.