Design, Fabrication, and Assembly of the SPARC Toroidal Field Model Coil
R. Vieira, David Arsenault, Raheem Barnett, L. Bartoszek, W. Beck, Sarah Chamberlain, JL Cheng, Eric Dombrowski, J. Doody, Darby Dunn, J. Estrada, Vincent Fry, Sarah Garberg, T. Golfinopoulos, A. S. Greenberg, S. R. HELLER, A. Hubbard, Daniel Korsun, Sergey Kuznetsov, B. LaBombard, Chris Lammi, Rick Leccacorvi, Matthew Levine, David Chavarria Mendoza, K. Metcalfe, Philip C. Michael, Theodore Mouratidis, R. Mumgaard, JP Muncks, Richard A. Murray, Daniel A. Nash, A. Pfeiffer, Samuel Pierson, Alexi Radovinsky, Ron Rosati, Michael W. Rowell, Erica Salazar, Shane Schweiger, S. Shiraiwa, Brandon Sorbom, Peter W. Stahle, Ken Stevens, Deepthi Tammana, Thomas Toland, Matthew T. Vernacchia, E. Voirin, A. J. Warner, Amy Watterson, D.G. Whyte, S. Wilcox, Lihua Zhou, A. Zhukovsky, Zachary Hartwig
Abstract
The SPARC Toroidal Field Model Coil (TFMC) is the first large-scale (∼3 m), high-field (∼20 T) superconducting fusion magnet based on Rare Earth Yttrium Barium Copper Oxide (REBCO). Its objective was to retire risk for the toroidal field magnet in the SPARC tokamak, a burning plasma class magnetic confinement fusion energy device. Weighing 10,058 kg and utilizing 270 km of REBCO, the TFMC is a non-insulated, stack-in-plate style superconducting magnet. It has three main components: (1) the winding pack; (2) the structural case; and (3) the case extensions, or plena. The winding pack is composed of sixteen single pancakes with two termination plates top and bottom. The pancakes are Nitronic 40 radial plates machined with spiral channels on one side for the REBCO tape stack and single-pass channels on the opposite side for supercritical helium coolant. After assembly, each pancake undergoes a vacuum-pressure impregnation solder process to provide good mechanical protection of the REBCO tape stack and efficient thermal and electrical connectivity within each pancake. The pancakes are bolted along the inner and outer perimeter to provide mechanical and thermal connectivity while inter-pancake joints provide low resistance current transfer between pancakes. The top and bottom termination plates facilitate electrical connection to a superconducting feeder system. Embedded throughout the winding pack are 211 voltage taps, 34 temperature sensors, 34 helium flow monitors, 4 Hall probes, and 4 resistive surface heaters. The winding pack is contained within a structural case, a “trough and lid” style design composed of two Nitronic 50 forgings machined to shape and bolted together. The case reacts the large electromechanical stresses approaching 1 GPa during operation and serves as a pressure vessel that enables 20 bar supercritical helium flow that cools the winding pack and case. Two case extensions or “plena” are attached to the case with unique high-pressure feedthroughs to provide winding pack access for current, cooling, and instrumentation, completing the magnet assembly.