The sealed, evacuated chamber that contains the fusion plasma and provides the ultra-high vacuum environment required for magnetic confinement — the structural backbone of a tokamak or stellarator.
The vacuum vessel is the primary containment boundary of a magnetic fusion device. It maintains an ultra-high vacuum (typically 10−6 to 10−8 Pa) so that plasma can exist without being quenched by background gas. It also provides structural support for internal components, acts as a secondary confinement barrier for tritium, and supports the first wall, blanket modules, and divertor.[1]
The vacuum vessel must: (1) maintain ultra-high vacuum with leak rates below 10−9 Pa·m³/s; (2) withstand electromagnetic forces during plasma disruptions (hundreds of MN); (3) provide neutron shielding; (4) include hundreds of ports for heating systems, diagnostics, pumping, and remote handling; and (5) be baked to 200°C to desorb water and impurities.[2]
Vacuum vessels for large tokamaks are among the most complex welded structures in engineering. ITER’s vessel requires over 200 km of welding, with strict tolerances and inspection requirements.[3]