Efficient Calculation Method of the Critical Current of Nested High-Field Magnets

A load line method has been used to calculate the critical current of superconducting magnets. However, in high-temperature superconducting tapes that have a rectangular cross section, as the critical currents vary depending on the direction of an external magnetic field, the load line method cannot be used to precisely calculate the critical currents of the HTS magnets because it cannot fully consider the magnetic anisotropy of the HTS tape. In nested HTS magnets that have multiple layers, calculating the critical current considering the magnetic anisotropy is very time consuming. This paper presents an efficient calculation method to calculate the critical current of nested HTS magnets. The secant method and the fixed-point iteration method are used to reduce the calculation time. The critical currents of two nested HTS magnets are calculated: a double magnet consisting of a YBCO inner coil and a BSCCO outer coil and a triple magnet consisting of a YBCO inner coil, a YBCO middle coil, and a BSCCO outer coil. The calculation results demonstrate that it is possible to very effectively calculate the critical current of nested HTS magnets by using a combination of the secant method and the fixed-point iteration method.