Reduction of radial magnetic fields in HTS solenoids with different constraint conditions

The critical current of HTS solenoid is heavily dependent on the value of radial magnetic fields in the coil winding section: the higher radial magnetic field in the winding section, the lower critical current of HTS solenoid is. So, we need to reduce the radial magnetic field components of the solenoid as much as possible to get high performance HTS magnet. In this paper we investigate various HTS coil shapes, obtained from the optimum algorithm, in which the radial magnetic field components are minimized. Three different constraints were used during optimization calculation: (1) fixed magnet volume condition, (2) fixed center magnetic field condition, and (3) maximum magnetic energy storage condition. The calculated results using those three different constraints showed almost similar shapes to one another and turned out to be effective to reduce the radial magnetic fields in the winding section. Finally, it is pointed out that two or three sectioned multi-magnet shape, which can be deduced from the calculated shape, could be more optimal to reduce the radial magnetic field in the coil, and more practical to fabricate.