Study of operational modes of cool-down and warm-up processes for the ESS large-scale 20 K helium refrigeration system

In the beginning, the European Spallation Source (ESS) will install two hydrogen moderators where the nuclear heating is estimated to be 6.7 kW at 5 MW proton beam power. The ESS cryogenic moderator system (CMS) has the function to circulate a subcooled liquid hydrogen through the moderatos. It is cooled through a heat exchanger by a large-scale 20 K helium refrigeration system with a cooling capacity of 30.3 kW at 15K, which is called Target Moderator Cryoplant (TMCP). The commissioning of the TMCP cold box and the two compressor skids was completed in 2019. Cryogenic transfer lines with a length of 300 m (CTL) and a valve box located next to the CMS cold box were installed during the summer of 2022. In this paper, the TMCP cool-down and warm-up processes have been studied and the operational parameters have been optimized based on the result of the CMS cool-down simulation.