Automated operation modes for the ESS cryogenic moderator system

Abstract At the European Spallation Source (ESS), a Cryogenic Moderator System (CMS) circulates a subcooled liquid hydrogen (17.5 K and 1.0 MPa) to cool two hydrogen moderators, with nuclear heating estimated to be 6.7 kW (to be increased to four in the future). The CMS is cooled by a helium refrigerator system with a cooling power of 30.3 kW at 15 K, which is called the Target Moderator Cryoplant (TMCP). The CMS combined with the TMCP is designed to operate automatically, with an automated operation control system being developed, featuring seven operational modes: cooldown, steady-state, energy-save, beam injection, warm-up, quick warm-up and ortho-to-parahydrogen measurement modes. Installation of the CMS was completed in February 2024. Subsequently, preliminary CMS commissioning, excluding the moderators, is currently underway using nitrogen and helium to study the operational parameters. This paper presents a detailed description of the control logic for each operational mode.