First commissioning of the ESS cryogenic moderator system using nitrogen and helium

Abstract A cryogenic moderator system (CMS) has been designed to supply subcooled liquid hydrogen at 17 K, with a parahydrogen fraction exceeding 99.5%, to each moderator, maintaining an average temperature rise within 3 K. The heat load is effectively removed by a large-scale 20 K helium refrigeration plant, which is called the Target Moderator Cryoplant (TMCP), with a cooling capacity of 30.3 kW at 15 K. TMCP commissioning was carried out independently until December 2022. Operational procedures were thoroughly studied to establish an automatic TMCP-CMS control system. Installation of the CMS was completed in January, 2024. Commissioning of the CMS-TMCP was conducted without connecting the moderators, utilizing nitrogen and helium before hydrogen operation. This paper will describe the first cooldown operation and performance evaluation test results.