Operation of 2 K cryogenic system with cold compressors for the SHINE test facility

Abstract

The Shanghai high repetition rate X-ray free electron laser (XFEL) and extreme light facility (SHINE), a quasi-continuous wave hard XFEL facility, is currently under construction. In order to test all the superconducting components, assembled cryomodules and undulators, the SHINE test facility that consists of various test benches has been built. A superfluid cryoplant with 1 kW@2K was installed, commissioned, acceptance tested and turned into operation to support the cryogenic tests. The plant consists not only of a standard compressor system and cold box but also of a process vacuum system for 2 K operation. In the 2 K cryogenic system, three-stage cold compressors are firstly used to compress helium vapor at a mass flow of up to 50 g/s from 28 mbar to about 400 mbar. Afterwards, the sub-atmospheric helium is continually pressurize to the suction pressure of the warm compressors by five parallel process vacuum pumps. During the first eight months of 2 K operations, the tuning of the cold compressor regulation has been implemented to adapt the different static and dynamic heat loads. A helium pressure stability of superconducting cavities better than ±0.15 mbar at 31 mbar was achieved inside the vertical test bench with additional heating power of 160 W. In this paper, the pump down procedure and the operation results of cryogenic system at 2 K will be described.