Application of parallel heat exchangers in helium refrigerators for mitigating effects of pulsed load from fusion devices

Tokamaks and Stellarators generate heat loads that are pulsating in nature. The helium refrigerators employed for cooling these fusion devices are, however, designed for a steady heat load. Unless they are appropriately adapted and controlled, process parameters under pulsed load may vary to such an extent which may lead of plant instability. In this paper, performance of a J–T stage as a part of modified Claude cycle based helium refrigerator has been analyzed subjecting it to a pulsed heat load for understanding of the behavior of the components. Pulsed heat load results in the fluctuation of mass flow rate in the return stream that needs to be mitigated. The analyses focus both on the equipment and their interactions in the cycle and a concept of parallel heat exchangers has been applied. There is a steady decrease in liquid level in Dewar when the plant is designed with a capacity equal to the time-averaged heat load. Introduction of parallel heat exchanger mitigates mass flow rate fluctuation by 15% with only one additional heat exchanger at the last stage. There is promise for a higher mitigation effect when more heat exchangers are used in parallel in more number of stages. The study may be extended to entire helium plant used in fusion devices.

Research highlights
► Simulation revealed adverse effects of heat load from fusion device on helium plant.
► Flow fluctuation leads to ineffective heat transfer and decreases plant capacity.
► Use of parallel heat exchangers reduced the flow fluctuation by 15%.
► This also compensated the reduction in refrigerator capacity.
► This may ensure the continuous cooling requirement of fusion devices.