RF-windows used at the KEKB linac

Abstract In the KEKB linac (8 GeV electrons and 3.5 GeV positrons), 58 pulsed klystrons (2856 MHz, 40 MW, 4 μs, 50 pps) are used for electron/positron acceleration. Alumina pill-box windows are installed in the klystrons and waveguides in order to isolate the vacuum from the atmosphere and to pass rf power. Breakdown of alumina ceramics is one of the most serious problems concerning stable operation. A temperature rise (ΔT) on a pill-box housing during rf operation is good for breakdown diagnostics and this has been measured periodically. The measured values are summarized statistically and broken windows are also analyzed.