Design and Operation of the Dual Return Valves to Stabilize Helium Vessel Pressure of the SRF Module

The Taiwan Photon Source at National Synchrotron Radiation Research Center selects the KEK-B type superconducting radio-frequency (SRF) module to deliver RF energy to the 3-GeV electrons circulated in the storage ring. Each SRF module has its own control valve box to adjust the flow rate of transferring cryogens to SRF module and back to the cryogenic plant. The major dynamic cryogenic load comes from the various quantity of vaporized liquid helium along the transferring path from the liquid helium Dewar to SRF module, whereas the dynamic surface heating by various RF gap voltages is successfully eliminated by a heater compensation unit. To regulate pressure of the liquid helium vessel at high stability, two cryogenic valves of different sizes for the cold return gas are equipped on each control valve box. Both the design and measured performance of the dual return valves are presented herein. Currently the pressure fluctuation can be suppressed to +/- 2 mbar at the nominal operation condition. A venturi-type flow meter on the return line for gaseous helium is used to monitor the static heat load on the liquid helium under various operation conditions. It is aimed to further reduce the pressure fluctuation by optimizing the operating parameters of the controllers for the dual return valves.