MIT’s compact high-field tokamak that held the world record for plasma pressure and pioneered the high-field approach to fusion — the direct scientific predecessor to SPARC.
Alcator C-Mod was a compact, high-field divertor tokamak operated by MIT’s Plasma Science and Fusion Center (PSFC) in Cambridge, Massachusetts. It achieved first plasma in May 1993 and its final shot on 30 September 2016, completing approximately 33,000 plasma shots over 23 years. It was the largest university-operated fusion experiment and the only diverted tokamak operating at or above ITER’s magnetic field strength.[1]
On its final day of operation (30 September 2016), C-Mod set a world record: 2.05 atmospheres volume-averaged plasma pressure, surpassing its own 2005 record of 1.77 atm. This remains the world record for plasma pressure in a magnetic confinement fusion device.[2]
I-mode: A novel confinement regime discovered at C-Mod featuring an edge energy transport barrier without an accompanying particle transport barrier — achieving H-mode-level energy confinement while avoiding core impurity accumulation.[3]
All-molybdenum walls: C-Mod was the only diverted tokamak to use exclusively high-Z refractory metal plasma-facing components, providing data directly relevant to ITER’s tungsten divertor design.
“Alcator” stands for ALto CAmpo TORo (Italian: “High Field Torus”), coined by Bruno Coppi. The series: Alcator A (1973–1979), Alcator C (1978–1987, first to exceed the Lawson density-time product), and C-Mod (1993–2016).[4]
C-Mod is the direct scientific predecessor to SPARC and ARC. The “high-field path” it pioneered — now enabled by HTS magnets rather than copper — is the foundation of Commonwealth Fusion Systems’ commercial fusion strategy.