The ARC Physics Basis is the Journal of Plasma Physics special collection published on 4 June 2026 — five papers, 58 co-authors and 226 pages — setting out the physics case for 📝ARC, the power plant 📝Commonwealth Fusion Systems intends to build in Chesterfield County, Virginia in the early 2030s. It is the same move the company made for 📝SPARC in 2020, one machine further along: publish the design case, in a journal, before construction. This pillar follows the collection's own logic — first what the machine is, then whether it makes the power, then whether it survives making it, and last what any of that has actually demonstrated.
The design point
📝Overview of the Physics Basis for the ARC Fusion Power Plant, led by 📝Jon Hillesheim with nineteen co-authors, fixes the numbers the other four papers work against. ARC V3A runs at 11.4 📝tesla on axis with 12.0 megaamps of 📝plasma current, at 4.62 meters major radius, projecting roughly 1.13 gigawatts of fusion power and at least 400 megawatts of net electricity — the output committed under the 📝power purchase agreement with 📝Dominion Energy. Where SPARC runs in seconds, ARC is designed for fifteen-minute pulses separated by one-minute pauses, which is the difference between an experiment and a generator. A sixth article in the collection, 📝Alex Creely's single-authored "The high-field tokamak physics basis for the ARC fusion power plant," frames the set and is not counted among the announced five.
Making the power
📝Nathan Howard leads the performance and transport paper, and its structure is the reason to trust it. A zero-dimensional operating point was scoped at 1.13 gigawatts, then tested against three independent integrated codes — TRANSP, ASTRA and TORAX — which returned 900 to 1300 megawatts. A published range, rather than a single number, is what an honest prediction looks like. "This integrated modeling indicates that ARC is capable of producing approximately 1 gigawatt of fusion power," Howard has said, and the hedge in that sentence is doing real work.
Surviving the power
Eight times SPARC's fusion power has to go somewhere. 📝Thomas Eich leads the exhaust paper, which dissipates most of the power crossing the last closed flux surface by radiation, seeding roughly 0.9 percent argon in the 📝divertor to reach 📝divertor detachment, using up-down-symmetric divertors with secondary 📝X-points in long, tightly baffled outer legs — and integrating that cold edge with a hot core and enough helium pumping to keep ash out. That geometry is older than this collection: 📝The ARC Divertor Papers, led by 📝Adam Kuang in 2018 and by M. R. K. Wigram in 2019, are where ARC's long-legged X-point target divertor was worked out, in the gap between the 2015 conceptual design and this physics basis. Reading them first makes the exhaust paper legible as the outcome of an eight-year argument rather than a fresh choice.
📝Ryan Sweeney leads the 📝disruption paper, whose central finding is a scaling: every ARC disruption load lands within a factor of two of SPARC's. The design target is one mitigated disruption per day with restart in tens of seconds, backed by 📝massive gas injection and a proposed 📝runaway electrons mitigation coil. The coil itself has its own literature — 📝The Runaway Mitigation Coil Papers, four modeling studies between 2021 and 2024 developing the passive design for SPARC, none of them yet checked against a real disruption on any machine.
📝Nils Leuthold leads the 📝magnetohydrodynamics paper from Columbia, finding the baseline scenario deeply stable to kinks, linearly stable to 📝tearing modes, and controllable against 📝vertical displacement events without dedicated in-vessel coils.
Modeled, not measured
Every number above is an output of simulation. ARC does not exist; SPARC, the machine whose results would calibrate these models, has not yet run. What makes the collection useful anyway is the dependency Sweeney names explicitly — because ARC's loads sit within a factor of two of SPARC's, SPARC becomes the instrument that tests this physics basis rather than merely preceding it. The right way to read these five papers is as a set of falsifiable commitments awaiting their experiment.
One strand of the ARC record is not simulation, and it sits just outside this collection. 📝ARC Engineering Beyond the Physics Basis covers two 2026 papers on the machine's material limits: subsurface gas accumulation in a divertor held in prolonged detachment, and low-cycle fatigue testing of 316 stainless steel and IN718 at 4 kelvin and 77 kelvin. The fatigue data are laboratory measurements. They are the point where the physics basis hands its loads to an engineering literature that can answer with results rather than projections.
We published ARC's physics before breaking ground, and we did it knowing SPARC will check every line of it. That sequence is deliberate.