Ryan Sweeney is a 🏷️#physicist and Manager of Disruption Physics at 📝Commonwealth Fusion Systems, where he leads the disruption strategy for both 📝SPARC and 📝ARC. He is lead author of "MHD stability and disruptions in the SPARC tokamak" (2020) and "ARC disruption physics and strategy" (2026), the two papers that state publicly how each machine is designed to fail safely.

A 📝disruption is the sudden, total loss of plasma confinement — megamps of 📝plasma current extinguished in milliseconds, dumping magnetic and thermal energy into the vessel and potentially generating 📝runaway electrons. His 2020 paper fixes the engineering envelope that follows from this: SPARC's 📝vacuum vessel is designed to withstand predicted unmitigated axisymmetric 📝halo current forces of up to 50 meganewtons, and similarly large loads from 📝eddy currents forced to flow poloidally in the vessel — a modeled worst-case load for a machine that has never disrupted, not a measured one. Sweeney completed his doctorate at Columbia University on locked-mode disruptions at 📝DIII-D, spent two years as a postdoctoral researcher at the 📝ITER Organization on disruption mitigation physics, and then worked at the 📝MIT Plasma Science and Fusion Center on 📝JET and on 📝magnetohydrodynamics for SPARC. His 2026 finding is a scaling result rather than a measurement, and it is the one a reader should carry: "On the whole, disruptions do not get more severe as we step up from SPARC to ARC." ARC's design anticipates roughly one disruption per day.