Abstract
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.
Highlights
High Power Source (HPS) devices are used in numerous applications including vacuum electronics [1,2,3], particle acceleration [4,5], and microwave generation [2,6]
In order to form samples for depth characterization and outgassing evaluation, the stainless steel (SS) samples were processed by raster scanning the laser beam across the surface in a uniform pattern
These features represent areas of the SS surface morphology that were incompletely melted by laser surface melting (LSM) and most likely result from the specific choice of scan parameters for the results shown here
Summary
High Power Source (HPS) devices are used in numerous applications including vacuum electronics [1,2,3], particle acceleration [4,5], and microwave generation [2,6]. Electropolishing has been the method of choice [8,11,15] since it both reduces the surface roughness of anode materials and creates an oxide layer that further reduces hydrogen outgassing. The LSM processing technique entails irradiating a sample with the output of a high energy continuous laser beam, thereby causing melting, flow and resolidification of the material as the laser beam is scanned across the sample surface. This process has the potential of reducing outgassing by forming a more crystalline layer (with fewer grain boundaries), thereby reducing the number of potential sites that can trap hydrogen in the metal [16]. We show here that LSM processing of 304SS does lead to reduced H2 outgassing during electron bombardment
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