Scaling of benign runaway beam termination to ITER
In plain words
Experiments found that puffing light gas into an existing runaway beam can make it end harmlessly, spreading its energy over a large wall area. Whether this works at ITER's much larger beam energy is unknown.
Precise statement
In JET, DIII-D and TCV, low-$Z$ (D2) injection into a runaway plateau purges high-$Z$ impurities, lowers resistivity and triggers a large MHD instability that deposits the beam energy over a wide wetted area with little avalanche regeneration. Determine whether this benign termination survives at ITER beam current and energy, where regeneration and the instability's wetted area differ. An answer is yes or no for the ITER reference runaway plateau, with the predicted peak wall energy deposition.
What would settle it
3D MHD-kinetic simulations validated on JET and DIII-D benign terminations, applied to ITER parameters.
Status in the literature
Unverified note
Benign termination was demonstrated on JET, DIII-D and TCV in 2021-2024; a 2024 model found an upper neutral-pressure limit for it (arXiv:2412.14721).