Keynote talk — Cryogenic cooling techniques and coolers for HTS power applications

All the HTS applications require cryogenic cooling. The operating temperatures from 4 K to 77 K depend on the maximum magnetic field within the HTS component and HTS material property. The operating temperature of HTS insert coils for > 20 T NMR magnets is 4.2 K or lower, which are cooled with liquid helium (LHe). 3T RnBCO MRI magnets, BSCCO motors or generators may operate at 27.1 K cooled with liquid Neon (LNe). MgB₂ SMES (superconducting magnetic energy storage) magnets with the maximum field <; 3 T can be cooled with 20.3 K liquid hydrogen (LH₂). The HTS coils for transformers and saturate-iron type FCL (fault current limiters) operate at 65 to 77 K cooled with liquid nitrogen (LN₂), and the maximum field in the coils is around 1 T. HTS cables and resistive type FCL operate at low field, and cooled with 65-77K LN₂.