Superconducting toroidal field coil system for STARFIRE

The 12 element toroidal field coil array has a characteristic envelope radius of about 14 meters, within which is contained 50 GJ of stored magnetic energy. The basic design is based upon employment of 4 K helium bath cooled Nb3Sn superconductor for the high field region, NbTi being utilized from 9 tesla down. The option of employing NbTi alloy throughout, bath cooled at 3.5 K saturation temperature, is also presented. A 24 kA, three level, unsoldered Rutherford cable design has been selected for the conductor: four field graded regions are employed to minimize coil thickness. Minimum copper current densities are set by stability considerations in the high field region and by coil production considerations at low field. All significant conductor hoop and bearing loads are borne by a stainless steel frame structure which surrounds, and is interwound with, the conductor. The coils are pancake wound within an austenitic stainless steel helium vessel. Partial height flanking layers are employed to maximize space utilization in the critical centerpost region