Design, fabrication and test of the react and wind, Nb3Sn, LDX floating coil

The Levitated Dipole Experiment (LDX) is an innovative approach to explore the magnetic confinement of fusion plasma. A superconducting solenoid (floating coil) is magnetically levitated for up to 8 hours in the center of a 5-meter diameter vacuum vessel. The floating coil maximum field is 5.3 T, and a react-and-wind Nb₃Sn conductor was selected to enable continued field production as the coil warms from 5 K during the experiment up to a final temperature of about 10 K. The coil is wound using an 18-strand Rutherford cable soldered into a half-hard copper channel, and is self protected during quench. The coil is insulated during winding and then vacuum impregnated with epoxy. The impregnated coil is tested with 2 kA operating current at 4.2 K, and then a single, low resistance joint is formed at the outer diameter of the coil before the coil is enclosed in its toroidal helium vessel. This paper presents details of the coil design and manufacturing procedures, with special attention to the techniques used to protect the coil from excessive strain damage throughout the manufacturing process