Commonwealth Fusion Systems formally began stacking toroidal-field coils for its SPARC tokamak this week, marking the start of integrated magnet assembly at the company's 47-acre Devens campus. The 18 TF coils, each weighing roughly 75 tonnes, will be lowered into position over a six-month sequence using a custom gantry built by Mammoet.

Each coil is wound from REBCO high-temperature superconducting tape co-developed with Faraday Factory Japan and Fujikura. CFS achieved a 20-tesla sustained field on a full-scale prototype coil last week — the program's strongest endurance benchmark to date.

Each coil is wound from REBCO high-temperature superconducting tape co-developed with Faraday Factory Japan and Fujikura.

First plasma remains scheduled for late 2027. Net energy gain, defined by CFS as Q > 10 on a deuterium-tritium pulse, is targeted for 2028. The company has raised more than $3 billion to date, the largest cumulative private investment in any fusion developer.