Commonwealth Fusion Systems Delivers its First Fusion Magnet — A Stronger, Smaller Design

Commonwealth Fusion Systems, an MIT spin-out fusion energy company, led by Bob Mumgaard, Dan Brunner, Brandon Sorbom, and Zach Hartwig, has completed and delivered its first cutting-edge, superstrong magnet — a culmination of years of work to develop and manufacture the foundational technology to bring fusion energy to the grid.  

A 24-ton steel-clad toroidal field magnet was transported to the SPARC facility in Devens, Massachusetts, marking the first of 18 magnets needed for the fusion machine. The milestone marks CFS’s transition from prototypes to full-scale production, supported by a dedicated manufacturing facility designed to produce magnets in volume. This production capability underpins plans to scale from SPARC to the ARC fusion power plant program, beginning in Virginia and expanding to a wider fleet of plants.

SPARC and ARC are tokamak fusion machines that use powerful magnets to confine a superheated plasma, which must reach roughly 100 million degrees Celsius for fusion to occur and release usable energy. Their design relies on high-temperature superconductors (HTS), a breakthrough material that carries large electrical currents with zero loss and can endure the extreme magnetic fields required inside a tokamak.

HTS makes it possible to build smaller, stronger magnets, enabling more compact and affordable tokamaks. SPARC and ARC use HTS-based TF, PF, and CS magnets, with TF magnets built using NINT “pancake” construction. “NINT lets us build stronger, smaller magnets faster,” Sorbom said.

The NINT approach works because SPARC’s TF magnets operate with steady current. In pulsed systems, superconducting cables must be insulated so that current follows a fixed path. But with steady current, insulation isn’t needed; the current automatically stays in the superconducting tape, avoiding the higher-resistance metal around it, like choosing fast snow over concrete. The “NT” also means the tape isn’t twisted, since steady current eliminates the need for the helical twist used in pulsed magnets.

Developing NINT magnets wasn’t easy. The work began at MIT and advanced through the TFMC prototype test in 2021. Saehan Lenzen, Director of NINT Magnet Production, has witnessed the company evolve over four years. What started as a scrappy design-heavy effort has become a refined production operation, with smooth workflows from HTS tape insertion to final testing and welding. With 17 magnets still to deliver, the team is applying all the lessons learned to ensure quality and consistency.