Commonwealth Fusion Systems broke ground on SPARC in Devens, Massachusetts — the first privately funded experiment designed to achieve a burning plasma and net energy from fusion.
In 2024, Commonwealth Fusion Systems (CFS) began construction of SPARC at its campus in Devens, Massachusetts, marking the most ambitious milestone yet for the private fusion industry. SPARC is designed to be the first privately funded fusion device to achieve a burning plasma — a state in which the energy from fusion-produced alpha particles dominates the plasma heating, sustaining the fusion reaction with minimal external input. If successful, it would produce a fusion gain (Q) greater than 2 and potentially approaching 10, generating roughly 140 MW of fusion power.[1]
SPARC's enabling technology is high-temperature superconducting (HTS) magnets made from rare-earth barium copper oxide (REBCO) tape. In September 2021, CFS demonstrated a 20-tesla large-bore HTS magnet — the strongest fusion-relevant magnet ever built — validating the core technology that makes SPARC possible. Higher magnetic field strength allows a smaller, more economical tokamak to achieve the same plasma performance as a much larger device with conventional superconductors.[2]
CFS was spun out of MIT's Plasma Science and Fusion Center (PSFC) in 2018, building on decades of tokamak research at MIT's Alcator series of devices. The SPARC design was developed in collaboration with MIT researchers and published in a series of peer-reviewed papers in the Journal of Plasma Physics in 2020, establishing its physics basis in the open scientific literature. CFS subsequently raised over $2 billion in private funding, making it the most well-capitalized private fusion company in the world.[3]
SPARC's primary mission is to demonstrate net energy from fusion — a Q significantly greater than 1 — in a compact, high-field tokamak. Beyond the headline number, it must validate several critical physics and engineering elements:
Burning plasma regime: In a Q ≥ 2 plasma, alpha particle heating exceeds external heating, creating a qualitatively new regime of plasma behavior. How the plasma responds to dominant alpha heating — including the stability of internal transport barriers, the behavior of energetic particle modes, and the dynamics of the helium ash — will inform the design of every subsequent fusion power plant.
HTS magnets at scale: While the 2021 magnet test validated a single coil, SPARC requires an integrated toroidal field coil system operating reliably in a fusion nuclear environment. Demonstrating this engineering integration is arguably as important as the plasma physics result.
Compact tokamak economics: By achieving high performance in a small device, SPARC aims to prove the economic thesis that HTS magnets can shrink the path to commercial fusion, reducing construction timelines and capital costs compared to conventional approaches.
SPARC is explicitly a science experiment, not a power plant. It has no tritium breeding blanket, no electricity generation capability, and a limited number of planned D-T pulses. Its success would pave the way for ARC, CFS's planned first-of-a-kind fusion pilot plant, which would incorporate breeding, power conversion, and continuous operation. The company has stated a goal of delivering ARC in the early 2030s, though the timeline depends on SPARC's results and on the regulatory framework for fusion that is still being developed.