Breakdown of alumina rf windows

The breakdown of alumina rf windows being used in high-power rf systems of accelerators has been investigated. The puncture and the thermal fracture often taking place in s-band pulsed rf systems and in UHF cw rf systems, respectively, are found to be induced by alumina surface heating due to an electron multipactor bombardment accompanied by a luminescence of alumina. It is ascertained that TiN coatings on the alumina window suppress the multipactor, and that the window duration for breakdown is dependent on the microstruture of the alumina ceramic.