Pulsed laser surface processing of alumina for high voltage power applications
Berkow, Joshua A.
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As government and industry push for megawatt and gigawatt microwave pulsed power sources, modern vacuum tube technology must keep up. Insulating structures inside the vacuum tubes are key to the generation of these power levels. Surface flashover of the dielectrics, the limiting factor for high power applications, is theorized to be a function of trapped charge at the surface of the dielectric. Laser annealing via excimer laser is a process that shows promise in increasing the surface flashover voltage of dielectrics by removing surface defects. Through partial discharge and surface flashover testing of alumina ceramic dielectrics, the laser annealing process may be shown to be either valid or invalid as a means to control surface flashover. If proven valid, this could result in a new generation of high power vacuum tubes with breakdown strengths an order of magnitude greater than the current designs. The current set of experiments does not yield a definitive answer. The effect of conditioning and the initial uncontrolled screening tests have not been determined. Laser annealing does appear to reduce some of the "random" nature of surface flashover. A correlation between initial microdischarges and surface flashover is proposed. As this is a new and untested area of research, these results yield a greater understanding of the process by which surface flashover occurs.