Speaker
Description
The rotating tungsten target at the European Spallation Source (ESS) is the first of its kind to be cooled by high-temperature gaseous helium. The cooling system, Target Helium Cooling System (THCS), is mainly comprising of the primary cooling loop and the associated pressure control and storage system. The primary cooling circuit incorporates gas circulators, heat exchangers and purification units, while the pressure control system enables helium inventory management and operational flexibility. To ensure adequate cooling of the target wheel under all operating conditions, the THCS is designed to circulate helium at mass flows between 1.8 and 2.7 kg/s, temperatures from 30 to 240 °C and pressures from 7 to 11 bar(a).
The main planned turbo-circulator solution was complemented by the introduction of a screw circulator at a late project stage. The building was adapted for operation with the turbo-circulator only, and heavily impacted several installed systems.
The resulting coexistence of two circulator technologies increased operational reliability but also added complexity in system integration, auxiliary support systems and gas confinement.
Commissioning has shown that the dynamic behaviour of the THCS operating with the screw circulator is sensitive to variations in operating parameters, particularly pressure losses, flow-induced effects and vibration phenomena. As of spring 2026, the system has been successfully commissioned under cold operational conditions, providing valuable insights into performance margins and optimisation needs.
The experience gained at ESS contributes to the understanding of high-temperature helium cooling for future high-power spallation target systems.