Commonwealth Fusion begins SPARC commissioning before 2027 Q>1 campaign

Commonwealth Fusion Systems has begun commissioning SPARC and plans to turn the tokamak on in 2027 to start a campaign aimed at producing more fusion power than it consumes, AIP Science Light reported. No magnetic confinement device has yet reached that threshold. How SPARC's output is measured will decide whether the result counts as proof or as another contested claim.

Three independent measurements

SPARC's team has planned three separate measurements of fusion power, according to a paper by Prasoon Raj and colleagues in Review of Scientific Instruments that AIP Science Light summarized. The first counts the global flux of neutrons leaving the plasma, which requires careful calibration of detectors inside the vessel. The second reads the neutron spectrum and maps where the neutrons come from to produce a fusion rate. The third calculates the same rate from profiles of plasma temperature, density and fuel. Each method relies on different physics, so one broken instrument cannot carry the result alone.

Raj said the Q>1 result "will set a major scientific milestone and guide decisions across a multi-billion-dollar industry worldwide." "When all three agree, no single hidden error can explain the result," he said.

Assembly at 75 per cent

Assembly has advanced far enough for that campaign to look real. At a campus in Devens, Massachusetts, SPARC uses 18 D-shaped magnets wound from high-temperature superconducting tape. Fortune reported in January 2026 that CFS had just installed the first of the 18. In May 2026, crews lowered the second 48-ton half of the vacuum vessel into Tokamak Hall and joined the chamber, Autonocion reported. That work took the machine to roughly 75 per cent complete, according to CFS co-founder and chief science officer Brandon Sorbom. TechCrunch had reported in October 2025 that the device was about two-thirds complete.

Once the chamber is sealed, technicians will line the inside with tungsten panels because the plasma they face runs hotter than 100 million degrees Celsius, several times the core of the Sun. Autonocion reported that the tape order for the full machine runs toward 10 million meters. A CFS prototype coil reached 20 tesla in 2021, a record for a magnet of that size, the report said.

Stronger fields let CFS shrink the tokamak rather than build a machine the size of ITER. SPARC is designed to produce up to 140 MW of fusion power in bursts of about 10 seconds, Autonocion reported. That is a pulse, not a power station.

What the result would mean

If SPARC reaches Q>1, CFS plans to build ARC, its first commercial plant, a 400 MW facility outside Richmond, Virginia, in the early 2030s. ARC would cost more than $2.5 billion and sit at the James River Industrial Center in Chesterfield County on land leased from Dominion Energy, Yahoo Finance reported. Google has committed to buy 200 MW from ARC, half its output, TechCrunch reported. That contract gives the Q>1 result a customer.

What happens next

CFS plans to turn SPARC on in 2027 to begin the Q>1 campaign. ITER, the international tokamak in southern France, will not run on its deuterium-tritium fuel until 2039, Autonocion reported, more than a decade after SPARC's planned campaign.