The ARC divertor papers are the 2018 heat-exhaust design study and the 2019 divertor performance assessment that together gave 📝ARC its long-legged, tightly 📝baffled X-point target 📝divertor — the geometry the 2026 exhaust design still uses.
"Conceptual design study for heat exhaust management in the ARC fusion pilot plant", by 📝Adam Kuang and fifteen co-authors in Fusion Engineering and Design, extends 📝The 2015 ARC Design Paper to the question that paper deferred: where does 525 megawatts of fusion power go. The answer reconfigures the superconducting 📝poloidal field coil set — which in ARC sits inside the 📝toroidal field coils — to produce double-null equilibria with long divertor legs running past a secondary 📝X-point, and widens the 📝vacuum vessel to accommodate them without shrinking the plasma. The 📝FLiBe 📝blanket doubles as low-pressure coolant for the divertor; MCNP 📝Monte Carlo neutronics returns a 📝tritium breeding ratio of about 1.08; a 📝tungsten swirl-tube channel is shown capable of exhausting up to 12 megawatts per square meter of surface heat flux.
"Performance assessment of long-legged tightly-baffled divertor geometries in the ARC reactor concept", led by M. R. K. Wigram in Nuclear Fusion in 2019, tests that geometry with the UEDGE edge code. Against a projected heat-flux width of 0.4 millimeters and 93 megawatts of exhaust, a Super-X configuration with 0.5 percent neon reaches passively stable 📝divertor detachment across 80 to 108 megawatts; the X-point target configuration cuts strike-point temperature by roughly a factor of ten below that; and raising 📝separatrix density by half yields fully detached solutions with no 📝impurity seeding at all — which the authors record as a first for reactor-scale edge modeling at that heat-flux width.
The concept is not CFS's invention. 📝Brian LaBombard set out the X-point target divertor in the 2015 ADX proposal and is a co-author, not lead, of the 2018 paper. What these two papers did was carry it into a power plant design, where 📝Thomas Eich's 2026 exhaust paper still finds it — long, tightly baffled outer legs with secondary X-points, now with argon seeding. Every figure in all three is simulation. No long-legged divertor has been operated at reactor conditions, and the 📝flux expansion and 📝strike-point sweep arguments that make the case remain untested at this scale.
ARC's exhaust design has a paper trail. We argued the long-legged divertor in 2018 and simulated it in 2019, years before the 2026 physics basis committed to it — and we inherited the concept from Brian LaBombard's ADX work rather than inventing it.