In late September, CFS completed a month-long test campaign on its first production D-shaped toroidal field coils. These are the same magnets that will encircle the SPARC tokamak now under construction in Devens, Massachusetts. The coils are built with high-temperature superconducting (HTS) tape made from rare-earth barium copper oxide (REBCO), enabling much higher magnetic fields than conventional superconductors.
A DOE review board of magnet specialists from U.S. national laboratories reviewed the test data and confirmed the coils met design specifications. The validation triggered an $8 million payment under DOE’s Milestone-Based Fusion Development Program, the largest first-phase award among the eight companies participating in the initiative. U.S. Energy Secretary Chris Wright personally visited CFS’ headquarters to mark the occasion, touring the SPARC assembly hall where these HTS magnets are being installed.
High-Field Magnets Pass the Test
CFS’ approach builds on MIT research demonstrating that compact, high-field tokamaks could achieve fusion conditions at smaller scale and cost than conventional designs. In 2021, CFS set a world record with a 20-tesla prototype magnet, proving the viability of REBCO conductors for fusion applications. The newly validated coils translate that early success into full-scale production hardware.
The same magnet design will be used in ARC, the first commercial fusion power plant that CFS plans to construct following SPARC. This transition from prototype to serial manufacturing marks a key inflection in fusion hardware maturity, with HTS magnets moving from experimental components to engineered products.
The large-bore, full-scale HTS magnet prototype tested by Commonwealth Fusion Systems in 2021.
Why DOE Validation Matters
Technical Credibility
Third-party validation by DOE experts boosts confidence in CFS’ engineering claims. The magnets performed to specification under external review, a level of independent verification that remains uncommon in the private fusion sector.
Risk Reduction
Magnet performance has been a central technical risk in the CFS/MIT strategy. Demonstrating that full-scale HTS coils function as designed removes a major uncertainty for both SPARC and ARC. Remaining challenges, including plasma sustainment, thermal loading, and materials resilience, persist, but the magnet system is now de-risked.
Federal Alignment
While $8 million is modest relative to CFS’ nearly $3 billion in private funding, the DOE milestone carries symbolic weight. It reflects growing convergence between government fusion programs and privately led technology pathways.
Market Signaling
DOE’s endorsement, combined with Energy Secretary Chris Wright’s site visit, signals institutional acceptance of fusion as an emerging industrial sector. Utilities and strategic partners are responding: Dominion Energy has agreed to collaborate on hosting the first ARC plant, while early investors Eni and Google have extended commitments through long-term power purchase agreements for ARC’s planned 400 MW output in the 2030s.
Closing Thoughts
CFS reports that roughly 65% of SPARC is complete, with commissioning targeted within two years. The validated TF coils will soon be installed, forming the magnetic cage that confines plasma exceeding 100 million °C. If SPARC achieves scientific breakeven (Q > 1), it will validate the high-field compact tokamak approach as a credible route to grid-scale fusion power.