Hydrogen Outgassing and Secondary Electron Reduction From Laser-Processed Stainless Steel Anodes*

Dept of Physics and Astronomy, Ohio University Athens, OH USA One of the problems associated with long term operation of high pulsed power, vacuum electronic devices is pulse shortening, which is caused by hydrogen outgassing and by secondary electron emission from the anode. We recently showed the feasibility of Laser Surface Melting (LSM) of stainless steel (SS) anodes to reduce hydrogen outgassing from SS samples subjected to 50 keV electron bombardment. The results showed a reduction in outgassing from LSM-treated SS. This was attributed to a reduction in the number of grain boundaries, which serve as trapping sites for hydrogen. We have since measured the hydrogen depth profiles of treated and untreated samples by Elastic Recoil Detection in order to more completely understand the mechanism for reduced outgassing. The results indicate a significant reduction in residual hydrogen within the melt depth $( \sim 15 \mu \mathrm {m})$ of LSM-treated samples due to the small solubility of hydrogen in molten steel. We describe here a more complete model of the mechanism for reduced hydrogen outgassing that includes both a reduction in the number of trapping sites as well a reduction in the residual hydrogen concentration within the melt depth of LSMtreated samples. We conclude by describing the use of vacuum arc re-melted steel as an anode material and describe the effect of laser patterning of such samples to reduce secondary electron yield.