CFS science on other people's machines is the group of ten peer-reviewed papers, published between 2023 and 2026, in which Commonwealth Fusion Systems–affiliated authors report measurements taken on tokamaks the company neither owns nor operates.
Those machines are 📝JET, 📝MAST Upgrade, 📝ASDEX Upgrade, 📝TCV, 📝DIII-D and 📝Alcator C-Mod, and the cluster does two jobs at once. It is the empirical evidence that CFS scientists publish in the open literature about hardware other institutions built and run, not only about 📝SPARC. It is also the clearest case in this library of the third kind of number — measured elsewhere, applied here. Every figure below names the machine it was taken on, because a JET measurement is not a SPARC result, and reading it as one misleads exactly as badly as reading a projection as an achievement.
Two of the papers are diagnostics fielded on MAST Upgrade, both in Review of Scientific Instruments 94 (2023) and both co-authored by 📝Matt Reinke from 📝Oak Ridge National Laboratory and CFS. Fabio Federici of the 📝York Plasma Institute led the prototype infrared video 📝bolometer paper (10.1063/5.0128768), the first IRVB deployed on a 📝spherical tokamak and the first anywhere designed to view the lower 📝X-point; on MAST-U with conventional 📝divertor geometry and only intrinsic impurities, 📝divertor detachment progressed as it does on large-aspect-ratio tokamaks, the radiation peak moving along the 📝separatrix from the targets toward the X-point. Jack Lovell of ORNL and the 📝UK Atomic Energy Authority led the companion overview of the MAST-U resistive bolometer system (10.1063/5.0128750).
Three more are boundary turbulence, and their machines are C-Mod, TCV and a six-device set. 📝Adam Kuang is the CFS co-author on two: gas-puff-imaging measurements of 📝filament (blob) velocity in the Alcator C-Mod 📝scrape-off layer, led by O. E. Garcia of UiT The Arctic University of Norway, where blob size and radial velocity both rise with core density and cross from sheath-connected to resistive scaling as the empirical density limit is approached (10.1088/1361-6587/ae6bbb); and a 📝Langmuir probe comparison of intermittent far-SOL fluctuations across six tokamaks — Alcator C-Mod, DIII-D, TCV, 📝KSTAR, MAST and MAST-U (10.1088/1361-6587/ae7157). 📝Thomas Body is the CFS co-author on the TCV-X21 validation paper led by Y. Wang of the 📝Swiss Plasma Center, which found filament velocities in GBS simulations agreeing with TCV measurements while the simulated filament sizes ran large (10.1088/1361-6587/ae6d71).
Two are 📝disruption physics, both with 📝Ryan Sweeney as the CFS author, and both carry numbers that belong to JET and DIII-D. B. Stein-Lubrano of the 📝MIT Plasma Science and Fusion Center led the JET study of thermal energy mitigation (10.1063/5.0261146): argon–📝deuterium 📝massive gas injection on JET radiates typically more than three times as much near the injector as toroidally distant from it, and once that plume peaking is accounted for, the radiated thermal energy fraction in two neon–deuterium shattered-pellet cases rises from no-plume estimates of 0.31 and 0.66 to lower bounds of 0.84 and 0.92. E. M. Hollmann led the DIII-D and JET study of 📝runaway electrons plateau partial recombination (10.1088/1741-4326/acb4aa), in which massive H2 or D2 injection drops thermal electron density roughly a hundredfold, over about 5 ms on DIII-D and about 15 ms on JET; the extrapolation to 📝ITER and SPARC in that paper is a 1D-model projection, and it predicts recombination will be difficult in SPARC because of its high runaway current density.
Two are codes and controllers validated against machines that exist. A. Redl of the 📝Max Planck Institute for Plasma Physics led the experimental validation of HEAT on ASDEX Upgrade (Fusion Science and Technology 81, 623–641, 2025; 10.1080/15361055.2025.2478720), with 📝Tom Looby — the author of the HEAT code itself — third and 📝Thomas Eich fourth. Allen M. Wang of MIT PSFC led a neural state-space model of TCV rampdowns, with Mark Boyer of CFS among the authors, trained on 311 TCV pulses of which only five sat in the reactor-relevant high-performance regime, then used with reinforcement learning to design trajectories that avoid instability limits; a predict-first TCV experiment raised 📝plasma current 20% above baseline. It circulated as a preprint in March 2025 (10.21203/rs.3.rs-6050911/v1) and was published in Nature Communications 16, 8877, in October 2025 (10.1038/s41467-025-63917-x).
The tenth is core physics on JET and the most conspicuous of the set. Physical Review Letters 134, 095103 (2025), led by J. Ruiz Ruiz of the University of Oxford with 📝Jon Hillesheim as the CFS co-author among fifteen authors, reports the first experimental detection of a zero-frequency fluctuation pumped by an 📝Alfvén eigenmode in a magnetically confined 📝plasma, correlated in JET with higher deep-core 📝ion temperature and improved confinement (10.1103/physrevlett.134.095103). The paper is Oxford's; the CFS stake in it is one author.
Our people fielded bolometers on MAST Upgrade, analyzed argon injection in JET disruptions, and validated HEAT against ASDEX Upgrade infrared data years before SPARC makes its first plasma. Those results belong to those machines and those teams — what we take from them is calibration for a machine that has not yet run.