Development of a new waveguide valve using RF choke flange for PLS linac

Waveguide valves capable of handling a peak power of 80 MW are required at the time of klystron replacement in PLS Linac. We designed a U-shaped waveguide valve and made two prototypes. However, they have some problems caused by RF power leak from the waveguide to the vacuum enclosure. This caused an increase of vacuum pressure and arcing in the vacuum chamber at the power level of 60 MW. A new choke flange has been designed with MAFIA code to solve problems caused by the RF power leak. A model choke flange has been fabricated and tested with a Network Analyzer and a 600 W solid state amplifier. It was observed that the RF leak at the choke flange can be reduced more than 20 dB in comparison with no choke case. High power RF test for the new waveguide valve with RF choke flange was performed in S-band resonant ring. The RF transmission through the valve was achieved up to 125 MW peak power level at the pulse width of 4 μs and the repetition rate of 30 Hz