Runaway electron current after mitigated disruptions in ITER
In plain words
ITER plans to shoot frozen pellets of deuterium and neon into a disrupting plasma to radiate its energy safely. Whether this also prevents a dangerous runaway electron beam, which grows by an avalanche of knock-on collisions, is uncertain.
Precise statement
In ITER disruptions mitigated by shattered pellet injection (SPI, fragmented D2 and Ne pellets), a small runaway seed from hot-tail generation, tritium beta decay and Compton scattering of gamma rays from the activated wall is amplified by avalanche multiplication. Compute the final runaway current versus injected D and Ne quantities, including losses through stochastic magnetic fields during the thermal quench and runaway-driven kinetic instabilities, and determine whether any injection scheme keeps the runaway current below the wall-tolerable level.
What would settle it
Validated 3D MHD plus kinetic runaway modeling of ITER SPI scenarios, confirmed by ITER commissioning disruptions.
Status in the literature
Unverified note
2026 modeling with improved physics (arXiv:2602.22177) finds most D-T H-mode SPI scenarios exceed tolerable runaway currents but identifies one theoretically viable D-T scheme; no experiment reaches ITER-scale avalanche gain.