High power RF conditioning of 2856 MHz, 40 keV prototype buncher cavity system

An on axis biperiodic buncher cavity system at 2856 MHz with three bunching cells plus one power feed cell has been designed and fabricated for 40 keV pulsed electron beam injection from a thermionic gun. The vacuum and high power RF conditioning prior to the beam injection is presented in this paper. Initially the cavity system along with the in-flange fast current transformer and the beam diagnostics chamber has been baked at 60-65 °C for 22 hours under a vacuum ≤ 6 x 10^-6 mbar. The final ultimate vacuum was 2.3 x 10^-6 mbar and it took 195 seconds to reach to 1 x 10^-5 mbar with the gate valve closed. After this the high power RF conditioning was done from 0.3 MW to 1.2 MW input RF power with 4μsec. pulse at 1 Hz PRF. At this point the ultimate vacuum reached to 2.3 x 10^-6 mbar and reached to 1 x 10^-5 mbar in 195 seconds after closing the gate valve. Finally the system was conditioned with 1MW, 4μsec. RF pulses at 20 Hz PRF. (author)