Current status of the Modifications of the Former HERA Cryogenic Plant for the XFEL Facility

The Hadron-Electron-Ring-Accelerator (HERA) at the German Electron Synchrotron (DESY) in Hamburg, Germany, was in operation between 1990 and 2007. The required cooling capacity for the superconducting magnets was provided by a cryogenic system consisting of three identical helium refrigeration plants. Due to the implementation of the X-ray free electron laser European XFEL, two of the existing HERA refrigeration plants have been adapted to the new heat load requirements of the XFEL-linac. A 2 K cooling loop of approximately 2.6 kW comprising a string of four cold compressors has been included into the existing refrigerator system. Efficient operation for 17.5 GeV beam load, for future up-grade options, and high turn down ability during partial load operation are key features of this modified cryoplant. A stepwise commissioning concept has been applied in order to compensate any changes in the overall XFEL project schedule. Another challenge was to revamp, install and commission the XFEL cryoplant under continuous operation of the third cryoplant, which is still providing refrigeration power forthe FLASH-linac and other consumers.