1 The SPARC Toroidal Field Model Coil Program Zachary S. Hartwig, Rui F. Vieira, Darby Dunn, Theodore Golfinopoulos, Brian LaBombard, Christopher Lammi, Phil Michael, Susan Agabian, David Arsenault, Raheem Barnett, Mike Barry, Larry Bartoszek, William K. Beck, David Bellofatto, Daniel Brunner, William Burke, Jason Burrows, William Byford, Charles Cauley, Sarah Chamberlain, David Chavarria, JL Cheng, James Chicarello, Van Diep, Eric Dombrowski, Jeffrey Doody, Raouf Doos, Brian Eberlin, Jose Estrada, Vincent Fry, Matthew Fulton, Sarah Garberg, Robert Granetz, Aliya Greenberg, Martin Greenwald, Samuel Heller, Amanda Hubbard, Ernest Ihloff, James Irby, Mark Iverson, Peter Jardin, Daniel Korsun, Sergey Kuznetsov, Stephen Lane-Walsh, Richard Landry, Richard Lations, Rick Leccacorvi, Matthew Levine, George Mackay, Kristen Metcalfe, Kevin Moazeni, John Mota, Theodore Mouratidis, Robert Mumgaard, JP Muncks, Richard Murray, Daniel Nash, Ben Nottingham, Colin O’Shea, Andrew Pfeiffer, Samuel Pierson, Clayton Purdy, Alexi Radovinsky, Dhananjay K. Ravikumar, Veronica Reyes, Nicolo Riva, Ron Rosati, Michael Rowell, Erica E. Salazar, Fernando Santoro, Akhdiyor Sattarov, Wayne Saunders, Patrick Schweiger, Shane Schweiger, Maise Shepard, Syun’ichi Shiraiwa, Maria Silveira, FT Snowman, Brandon Sorbom, Peter Stahle, Ken Stevens, Joshua Stillerman, Deepthi Tammana, Thomas Toland, David Tracey, Ronnie Turcotte, Kiran Uppalapati, Matthew Vernacchia, Christopher Vidal, Erik Voirin, Alex Warner, Amy Watterson, Dennis G. Whyte, Sidney Wilcox, Michael Wolf, Bruce Wood, Lihua Zhou, Alex Zhukovsky. Abstract— The SPARC Toroidal Field Model Coil (TFMC) Program was a three-year effort between 2018 and 2021 that developed novel Rare Earth Yttrium Barium Copper Oxide (REBCO) superconductor technologies and then successfully utilized these technologies to design, build, and test a first-in-class, high-field (~20 T), representative-scale (~3 m) superconducting toroidal field coil. With the principal objective of demonstrating mature, large-scale, REBCO magnets, the project was executed jointly by the MIT Plasma Science and Fusion Center (PSFC) and Commonwealth Fusion Systems (CFS) as a technology enabler of the high-field pathway to fusion energy and, in particular, as a risk retirement program for the TF magnet in the SPARC net-energy fusion tokamak. Weighing 10,058 kg (22,174 lb) and utilizing 270 km (168 mi) of REBCO, the TFMC is a no-insulation magnet comprising a winding pack This paper was submitted to arXiv on August 18 2023. The SPARC TFMC Program was a joint effort between the MIT Plasma Science and Fusion Center (PSFC) and Commonwealth Fusion Systems (CFS). The work was funded by CFS, and the parties have pursued patent protection relating to inventions. CFS has exclusive commercial rights to the technology for energy generation. Corresponding author: Zachary S. Hartwig <hartwig@psfc.mit.edu> Author affiliations based on associated institution at the time of contribution. Zachary S. Hartwig, Rui F. Vieira, Theodore Golfinopolous, Brian LaBombard, Phil Michael, Susan Agabian, David Arsenault, William K. Beck, David Bellofatto, William Burke, Jason Burrows, William Byford, Charles Cauley, James Chicarello, Jeffrey Doody, Vincent Fry, Matthew Fulton, Robert Granetz, Martin Greenwald, Amanda Hubbard, Ernest Ihloff, James Irby, Mark Iverson, Daniel Korsun, , Stephen Lane-Walsh, Richard Landry, Richard Lations, Rick Leccacorvi, George Mackay, Kevin Moazeni, John Mota, Theodore Mouratidis, Richard Murray, Andrew Pfeiffer, Samuel Pierson, Alexi Radovinsky, DJ Ravikumar, Nicolo Riva, Ron Rosati, Michael Rowell, Erica E. Salazar, Fernando Santoro, Wayne Saunders, Shane Schweiger, Syun’ichi Shiraiwa, Maria Silveira, FT Snowman, Peter Stahle, Joshua Stillerman, Thomas Toland, David Tracey, Christopher Vidal, Amy Watterson, Dennis G. Whyte, Bruce Wood, Lihua Zhou, and Alex Zhukovsky are with the MIT Plasma Science and Fusion Center, Cambridge MA 02139 USA. of sixteen REBCO stack-in-plate style pancakes and twoij termination plates inside a Nitronic-50 structural case, which also serves as a pressure vessel for the cryogenic coolant flowing through channels in the winding pack. To execute the TFMC tests, a new magnet test facility was built and commissioned at the MIT PSFC. A centerpiece of the test facility is a pair of 50 kA LN2-cooled REBCO binary current leads and VIPER REBCO cable feeder system. A novel liquid-free cryocooler-based cryogenic system provided 20 K supercritical helium. The magnet is integrated with the feeder and helium circulation system inside a large 20 m 3 vacuum cryostat, which contains internal LN2 radiation shields and access for facility and magnet instrumentation. The TFMC achieved its programmatic goal of experimentally demonstrating a large-scale high-field Darby Dunn, Christopher Lammi, Raheem Barnett, Michael Barry, Daniel Brunner, Sarah Chamberlain, David Chavarria, JL Cheng, Van Diep, Eric Dombrowski, Raouf Doos, Brian Eberlin, Sarah Garberg, Aliya Greenberg, Samuel Heller, Peter Jardin, Sergey Kuznetsov, Chris Lammi, Matthew Levine, Kristen Metcalfe, Robert Mumgaard, JP Muncks, Daniel Nash, Ben Nottingham, Colin O’Shea, Clayton Purdy, Veronica Reyes, Akhdiyor Sattarov, Patrick Schweiger, Maise Shepard, Brandon Sorbom, Ken Stevens, Deepthi Tammana, Ronnie Turcotte, Kiran Uppalapati, Matthew Vernacchia, Alex Warner, and Sidney Wilcox are with Commonwealth Fusion Systems, Devens MA 01434 USA. Larry Bartoszek is with Bartoszek Engineering, Aurora IL 60506 USA. Erik Voirin is with eViorin Engineering Consulting, Batavia IL 60510 USA. Michael Wolf is with Karlsruhe Institute of Technology, 76131 Karlsruhe Germany.