Effect of hydrogen loop fluctuation on cold neutron performance with hybrid control system in JSNS

Supercritical hydrogen is selected as a moderator material in Japan Spallation Neutron Source Facility (JSNS). Total nuclear heating in the moderator is estimated to be 3.75 kW at 1 MW proton beam power, which provides a hydrogen cryogenic system as a heat load. The heat load changes significantly due to pulse proton beam operation. A control system to mitigate such heat load changes is required for the hydrogen cryogenic system in order to maintain stable operation and steady cold neutron generation. A hybrid control system, which consists of a heater and an accumulator, is developed and installed in the system. In order to build the optimal control method, the behaviors of hydrogen loop are analyzed with an original computer code. The analysis suggests that a stability of hydrogen system and a cold neutron beam performance by the hybrid fluctuation control system are compatible.