Commonwealth Fusion Systems Powers Up Full Magnet Array for SPARC Reactor
Commonwealth Fusion Systems (CFS) has successfully energized the complete toroidal field magnet system at its commercial fusion campus in Devens, Massachusetts, achieving a sustained magnetic field strength of 20 tesla across the full tokamak architecture. This event marks the conclusion of the assembly phase for the SPARC demonstration machine, which is designed to be the first fusion device in history to produce more energy than it consumes.
The test, conducted late Sunday, involved ramping up current through all 18 High-Temperature Superconducting (HTS) coils simultaneously, verifying the structural and electromagnetic integrity of the confinement cage. Engineers monitored the system as the field strength surpassed the threshold required to confine superheated hydrogen plasma, holding the load steady for four hours to stress-test the cooling loops.
The breakthrough relies on the proprietary “VIPER” cable technology developed by CFS in collaboration with MIT’s Plasma Science and Fusion Center. Unlike traditional fusion experiments like ITER in France, which use low-temperature superconductors requiring massive physical footprints to achieve necessary field strengths, the SPARC magnets utilize Rare Earth Barium Copper Oxide (REBCO) tape. This material allows the magnets to operate at slightly higher temperatures—around 20 Kelvin rather than near absolute zero—while generating significantly stronger magnetic fields in a much smaller volume. The successful integration of these 18 coils proves that HTS technology can be manufactured at an industrial scale and assembled into the precise geometry required for a functioning tokamak.
Chief Science Officer Brandon Sorbom confirmed that the magnetic pressure exerted on the coils during the test exceeded 100 atmospheres, a force equivalent to the pressure found at the bottom of the Mariana Trench. The magnets successfully contained these forces without deformation, validating the novel exo-skeletal structural support designed to hold the tokamak together. This structural resilience is critical because the SPARC reactor aims to heat hydrogen isotopes to over 100 million degrees Celsius, a temperature where the fuel turns into plasma and fuses to release helium and high-energy neutrons. Without a flawless magnetic bottle, the plasma would touch the vessel walls and instantly cool, halting the reaction.
With the magnet systems validated, the facility is now moving toward the “First Plasma” milestone, currently scheduled for early 2026. The operational plan calls for a stepwise increase in input power, culminating in a Deuterium-Tritium fuel campaign aimed at achieving a Q-factor greater than one. A Q-factor greater than one implies that the fusion reaction generates more thermal power than is pumped in to sustain it, a feat that has eluded scientists for seven decades. The data gathered from this magnet test suggests that the confinement margins are sufficient to hit a Q-factor of 2 or higher, providing a buffer that boosts confidence in the reactor’s net-energy performance.
The ramifications of this success extend to the future commercialization of fusion power through the planned ARC (Affordable, Robust, Compact) power plant. The data from Devens indicates that the cost per watt of HTS magnet production has fallen by approximately 30 percent over the last two years due to improved manufacturing yields. If SPARC succeeds in generating net energy next year, CFS intends to break ground on the ARC pilot plant by 2028, targeting grid connectivity in the early 2030s. This timeline places the company aggressively ahead of state-sponsored fusion programs, positioning the private sector as the primary driver for deploying zero-carbon, baseload fusion energy.
