Breakdown of Alumina RF Windows and its Inhibition

Abstract

Breakdown phenomena in alumina windows for high-power rf use is studied. A multipactor due to high yields of secondary electron emission causes F-center oxygen vacancies of alumina, which induces surface melting. High-purity alumina without micro-porosities or pre-existing F-centers are durable under high-power rf operation. TiN coatings can effecitively suppress the multipactor, when the thickness is optimized so as to reduce secondary electrons and to avoid any excessive heating due to rf loss. The surface discharge observed on the TiN coated surface during higher power operation indicates the electron-trapping in surface defects and the electron avalanche accompanied by luminescence.