Design of a prototype 20 Tesla, single turn, toroidal field coil for the Fusion Ignition Experiment (IGNITEX)

The electromagnetic design of the Fusion Ignition Experiment (IGNITEX) combines unconventional pulsed-power and magnet technologies. The experiment should produce an ignited plasma in a relatively simple and low-cost way. The proposed IGNITEX toroidal field (TF) coil is a 20-T, single-turn, toroidal magnet powered by homopolar generators (HPGs). In order to demonstrate the magnet technologies, a 0.06-scale prototype toroidal field coil is being built to be powered by an existing 60-MJ, 9-MA, HPG power supply as part of the Ignition Technology Demonstration (ITD) program. The design of ITD and its relevance to the full-scale IGNITEX TF coil are described. Selection criteria for the high-strength conductor alloy are discussed. Elimination of turn-to-turn electrical insulation in the single-turn design permits better use of the available inner leg area for stress and thermal management. It is therefore possible for the magnet assembly to have physical properties very close to that of the conductor alloy. Fabrication and assembly procedures are discussed. The design of the preload structure, the cryostat, and the busbar system are described