ARC: A compact, high-field, fusion nuclear science facility and demonstration power plant with demountable magnets is the 2015 conceptual design study, published in Fusion Engineering and Design by 📝Brandon Sorbom and twelve co-authors under 📝Dennis Whyte, that laid out the power plant 📝Commonwealth Fusion Systems was founded three years later to build.
Its argument is a chain, and each link is a number. New 📝REBCO 📝superconductor allowed roughly 23 📝tesla of peak field on the coil; that permitted 9.2 T on axis in a machine of only 3.3 meters major radius; and because 📝fusion power density rises with the fourth power of field, a device that small could still project 200–250 megawatts of electricity at a plasma gain of 📝Q ≈ 13.6. The paper made two further choices that still define the program. Its 📝toroidal field coils carry demountable joints, so the 📝vacuum vessel can be lifted out and replaced rather than sealed for the machine's life — a debt to 📝Leslie Bromberg's 2001 work. And it surrounds the plasma with a liquid 📝FLiBe 📝blanket that moderates neutrons, removes heat at 900 kelvin into a Brayton cycle, and breeds 📝tritium at a ratio of at least 1.1.
It was a conceptual study, not a machine. The ARC now in design has moved well away from these parameters — 11.4 T on axis, 4.62 m major radius, roughly 1.13 gigawatts of fusion power — and it is that later design, not this one, that the 📝ARC physics basis papers of 2026 assess. What survived intact is the thesis: field strength buys compactness, and compactness buys iteration speed.
This paper is our founding document. We started the company because the design worked on paper and the magnets to build it had just become possible.