Development of a compact 18-T MF-(NbTi)/sub 3/Sn coil

The magnetic flux density of 18.4 T at 4.2 K was obtained by a 32-mm-bore superconducting coil wound with two grades of tube-processed multifilamentary (NbTi)/sub 3/Sn superconductors in a background field of 13.2 T. The average current density values of this coil were 70 A/mm/sup 2/ in the 18.4 T region and 107 A/mm/sup 2/ in the region less than 16.7 T. The energy stored in the 18-T coil system including background field coils was only 1.48 MJ at 18.4 T. The charging time of this system from 0 T to 18 T is only 12 min. This success encourages the development of high-performance superconductors for the high-field large coils of future thermonuclear fusion machines.