Building the Runway: A New Superconducting Magnet Test Facility Made for the SPARC Toroidal Field Model Coil

Abstract

A new superconducting magnet test facility was created at the MIT Plasma Science and Fusion Center (PSFC) for the SPARC Toroidal Field Model Coil (TFMC) program. The facility was designed and constructed in parallel with the TFMC between 2019 and 2021, with capabilities and design approaches tailored to the needs of this project and its timeline. The major components of the facility include a new cryostat (outer dimensions, 5.3 m×3.7 m×1.5 m) with open bore; a novel cooling system circulating supercritical helium in a closed-loop to provide ∼600 W cooling power at ∼20 bar-a, ∼20 K; a 50 kA, ±10 V power supply with supporting nitrogen-cooled HTS binary current leads operating at record currents, as well as VIPER-cable HTS cold bus; and a new instrumentation and PLCbased control system handling ∼650 input and output signals distributed between the facility and the test article. Substantial legacy infrastructure inherited from the PSFC's Alcator C-Mod tokamak program, including liquid nitrogen facilities and 10 MW of AC power, was instrumental in the rapid deployment of these new systems. Immediately after initial commissioning, the facility was used successfully to test the SPARC TFMC, operating the magnet in a campaign achieving 20 T on the coil, as well as a second campaign performing quench testing. The facility has since undergone several upgrades and has been used in campaigns of other test articles, and it is expected that the facility will remain a resource for the community for the foreseeable future to develop fusion magnets and related technology.