A liquid helium transfer line system for superconducting RF cavity

A liquid helium transfer line system was designed and constructed for a prototype 3-cell superconducting cavity (SCC) which was installed in the TRISTAN Accumulator Ring (AR) for electron beam acceleration test. The liquid helium transfer system, about 20 m long, consisting of three helium lines (supply, return and bypass) and two liquid nitrogen lines (supply and return), connects the helium refrigerator or liquid helium dewar at ground level and the SCC cryostat in the underground AR tunnel through a narrow service channel. The operational modes (cooldown, liquefier and refrigerator cooling mode) can be selected by valves in the transfer line system. The system worked very well and the SCC was cooled and tested successfully