High-Current Busbars for a Prototype Homopolar-Toroidal Magnet System for Fusion Ignition

The Ignition Technology Demonstration (ITD) is a full torus, scaled prototype of the 20 T toroidal field (TF) coil of the proposed fusion ignition experiment IGNITEX. The 0.06 scale in linear dimension is based on the linear relation between the peak current of an existing power supply (9 MA) and the current required to produce a 20 T field in the fullscale machine (150 MA). Presented here are the design and performance of a busbar and switch which have successfully transferred a total current of 6.75 MA to the ITD during a 15 T experiment. Design considerations included thermal and electromechanical stresses, material properties in liquid nitrogen, electrical resistance and inductance, and physical integration with the existing power supply. The ITD is driven by a 60 MJ, 9 MA power supply consisting of six 1.5 MA homopolar generators (HPGs) located in the Center for Electromechanics at The University of Texas at Austin (CEM-UT).