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 $\mathrm{D_2}$ 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: it names recent work and was partly written without a live literature search; it awaits a check by an editor.
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.
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