Helically wound coils for high field magnets

The winding current density of a superconducting coil is one of the key parameters to realize high field magnet systems with smaller sized superconducting coil. Force-balanced coil (FBC) which is a helically wound toroidal coil can control the distribution of working stresses and minimize the structure requirements by selecting an optimal number of poloidal turns. The winding current density of a superconducting coil is estimated from the relationship between ampere-meters of conductor and structure requirements based on the virial theorem. In this case, the FBC can obtain the stored energy for the same winding current density 20 times larger than that in the toroidal field coils case and about 120 times larger than that in the solenoid case. By applying the FBC concept, superconducting magnets will be realized in smaller size.