Design Considerations for SMES Systems Using and/or High-Temperature Superconductors

MgB₂ and high-temperature superconductors (HTS) are expected to reduce refrigeration energy requirements for superconducting coils. If MgB₂ and HTS carry usable current densities at high magnetic fields, in contrast to NbTi superconductors, superconducting magnetic energy storage (SMES) systems will be realized in smaller coil dimensions and shorter conductor lengths. In this work, the design considerations for the SMES systems using MgB₂ and/or HTS coils have been discussed. The required specifications of MgB₂ and HTS coils with a liquid hydrogen cooling are: (1) the target critical current density of MgB₂ and HTS should be higher than 1000 A/mm² (w/o stabilizer) at 15~20 K and 5~10 T in order to improve small-sized SMES coils, (2) MgB₂ and HTS coils require about 50-kA class superconductors with lengths of 5~10 km from the viewpoint of the coil construction, (3) the coil windings should be optimized in order to prevent a decrease in the operating current density within an allowable stress of MgB₂ and HTS at high magnetic fields, (4) the force-balanced coil (FBC) is an optimal coil configuration that can enhance the operating current density and obtain the stored energy for the same current density about 100 times larger than that in the solenoid case by the effect of the minimization of the working stresses