An MIT spinout racing to build the world's first compact, high-field tokamak using high-temperature superconducting magnets. CFS has attracted over $2 billion in funding and is constructing its SPARC demonstration device in Devens, Massachusetts.
Commonwealth Fusion Systems (CFS) was founded in 2018 as a spinout from the MIT Plasma Science and Fusion Center (PSFC). The company was co-founded by Bob Mumgaard, who serves as CEO, along with Dennis Whyte, Martin Greenwald, Dan Brunner, Brandon Sorbom, and Zach Hartwig — researchers who had spent years developing the concept of a compact, high-field tokamak enabled by a new generation of superconducting magnets.1
The founding thesis was straightforward: advances in high-temperature superconducting (HTS) tape, specifically rare-earth barium copper oxide (REBCO), could enable magnetic fields strong enough to confine plasma in a device far smaller than ITER, dramatically reducing cost and construction timelines.
CFS pursues the compact tokamak concept. Unlike conventional tokamaks that rely on low-temperature superconducting magnets limited to roughly 5–6 Tesla, CFS uses REBCO-based HTS magnets capable of producing fields exceeding 20 Tesla. Because fusion power density scales as the fourth power of magnetic field strength, this allows a much smaller device to achieve equivalent performance.2
The company's demonstration device, SPARC, is designed to produce a burning plasma with a fusion gain (Q) greater than 2, meaning it would produce at least twice as much fusion energy as the heating power injected into the plasma. If successful, SPARC would be the first privately built device to achieve net energy from fusion.
CFS has raised more than $2 billion in total funding. Its $1.8 billion Series B round, closed in late 2021, was at the time the largest single fundraise in the private fusion sector. Investors include Breakthrough Energy Ventures (Bill Gates), Tiger Global Management, Google, Temasek, and the Ontario Teachers' Pension Plan, among others.3
CFS is headquartered in Devens, Massachusetts, where it has built a large manufacturing and assembly campus for SPARC construction. The company has been manufacturing HTS magnet coils at scale and assembling the tokamak's major components.
It is important to note that while the 20 Tesla magnet demonstration was independently verified, the projected performance of SPARC itself — including its anticipated Q > 2 — remains a projection based on physics modeling. No plasma has yet been produced in the device. CFS's timeline has experienced some delays relative to initial projections, which is common in large-scale engineering projects of this complexity.4
CFS represents one of the most heavily capitalized and technically credible private fusion ventures. Its strategy of leveraging an established confinement concept (the tokamak) with a step-change improvement in magnet technology has attracted both significant private investment and ongoing collaboration with MIT.5