A sudden, catastrophic loss of plasma confinement in a tokamak that can unleash destructive electromagnetic forces, thermal loads, and runaway electron beams on the vessel structure.
A disruption is the rapid, uncontrolled termination of the plasma current in a tokamak. It typically unfolds in three phases: a precursor phase in which MHD instabilities grow and confinement degrades; a thermal quench lasting 0.1–3 ms during which 80–100% of the stored thermal energy is dumped onto the first wall and divertor; and a current quench lasting 5–100 ms in which the plasma current decays to zero, inducing large eddy currents and mechanical forces in the vacuum vessel and in-vessel components.1
Disruptions can be triggered by a range of operational faults. The most common causes are: exceeding the Greenwald density limit, which leads to radiative collapse and locked modes; approaching the ideal MHD stability boundary at high normalized pressure (βN); vertical displacement events (VDEs) caused by loss of vertical position control; and impurity influxes from wall interactions that cool the edge and trigger tearing modes. In each case, growing magnetic islands eventually overlap, stochasticizing the core magnetic field and destroying confinement within microseconds.3
The three principal hazards of a disruption are: (1) thermal loads from the thermal quench, which can melt or erode plasma-facing surfaces; (2) electromagnetic forces from the current quench, including halo currents that flow through the vessel wall and produce asymmetric toroidal forces; and (3) runaway electrons—a relativistic beam generated when the toroidal electric field during the current quench exceeds the critical Dreicer field, accelerating seed electrons to tens of MeV. A single runaway beam impact can punch through centimeters of stainless steel.2
Disruption management follows a hierarchy: avoidance through real-time stability control and operational-boundary enforcement; prediction using machine-learning classifiers trained on multi-machine databases; and mitigation via massive material injection (shattered pellet injection or massive gas injection) to radiate stored energy isotropically and suppress runaway electron formation by raising the post-thermal-quench density above the runaway avalanche threshold. ITER’s disruption mitigation system will use multiple shattered-pellet injectors as a primary safeguard.4