Conceptualization of a Cryogenic 250-A Power Supply for High-Temperature-Superconducting (HTS) Magnets of Future Particle Accelerators

Future particle accelerators for high-energy physics experiments such as the Future Circular Collider (FCC) at CERN employ high-temperature-superconducting (HTS) magnets to guide and focus the particle beams. However, the high-current/large-cross-section copper conductors used to connect the HTS magnet coils to the power supply conventionally located outside of the cryostat create a thermal leakage path, which ultimately results in high energy consumption of the cryocoolers. The heat leak-in could be reduced by power delivery through the cryostat’s heat shield at higher voltage levels and hence with lower currents. However, then a power electronic conversion to the low voltage and high current needed by the HTS magnets must be provided inside of the cryostat. Given the increased complexity, such a concept is only sensible if the resulting total heat load, i.e., the sum of the converter losses and the (then lower) leak-in losses, is so low that a clear improvement of the overall energy efficiency results. In this paper, we therefore conceptualize a cryogenic power supply for a 250-A HTS magnet, which operates at 60 K. Considering the strict EMI limits applicable in the CERN environment, a co-design method for the current leads and a full-bridge multiphase buck dc-dc converter is introduced and used to explore the design trade-offs. The results indicate that a reduction of the total heat load by about a factor of three to four compared to the state of the art seems feasible, i.e., from about 21 W to about 5 W.