Toroidal Field Model Coil (TFMC) is the full-scale high-temperature superconducting magnet built by the 📝MIT Plasma Science and Fusion Center and 📝Commonwealth Fusion Systems that reached a field of 20 tesla on September 5, 2021 — demonstrating the magnet technology on which 📝SPARC is built.
The name states its role precisely: a model — full scale in cross-section and field, built and tested before committing to a production line — of the 📝toroidal field coil design for SPARC. The distinction against its near-neighbors matters: the TFMC is not one of SPARC's eighteen magnets but their proving article, and unlike the 📝VIPER cable, which is a conductor, the TFMC is a complete magnet. It was wound from roughly 267 kilometers of 📝REBCO tape in a 📝no-insulation coil design, stood about three meters tall, and operated at around 20 kelvin.
The 20-tesla result showed that 📝High-Temperature Superconducting (HTS) Magnets could produce fusion-plant-grade fields in a compact device — performance that would otherwise require a machine roughly forty times larger in volume using earlier superconductors. Detailed test results, including a deliberately induced 📝quench, were published in 2024, concluding the magnets are ready for fusion machines. The program record is 📝The SPARC Toroidal Field Model Coil Program (Paper), which reports 20.1 tesla peak field on conductor at 40.5 kiloamps; 📝The TFMC Engineering Papers cover the design, fabrication, 📝cryogenics, current leads, test facility and quench detection beneath it.
The TFMC was the promise we made and kept: when it hit 20 tesla we retired the biggest technical risk between us and net fusion energy, and turned magnet science into a manufacturing problem we are now solving at scale for SPARC.