SPARC and the high-field path*

The SPARC tokamak and accompanying R&D program is based around the high-field approach to near-term fusion power in a privately funded milestone-based risk-retirement program. Building on Alcator C-Mod results, SPARC is a pre-conceptual design to use high-temperature superconductors (HTS) in a compact (R₀=1.65), high-field (B₀=12 T) pulsed tokamak to demonstrate net-gain from fusion energy for the first time. SPARC builds on the well-established tokamak physics basis for ITER as well as the previous series of high-field copper tokamak designs (Ignitor, CIT, BPX, and FIRE). Whereas the high-field copper designs were seen as technological dead-ends due to the large recirculating power, HTS—with its high critical magnetic field—now provides a technological pathway towards compact, tokamak-based fusion power plants such as that envisioned in the ARC design. The technological, physics, and organizational approach for the high-field path keyed on SPARC and HTS magnets will be discussed and placed in context as part of the wider fusion R&D effort.