  An effective disruption mitigation system in a tokamak reactor should limit
the exposure of the wall to localized heat losses and to the impact of high
current runaway electron beams, and avoid excessive forces on the structure. We
evaluate with respect to these aspects a two-stage deuterium-neon shattered
pellet injection in an ITER-like plasma, using simulations with the DREAM
framework [M. Hoppe et al (2021) Comp. Phys. Commun. 268, 108098]. To minimize
the obtained runaway currents an optimal range of injected deuterium quantities
is found. This range is sensitive to the opacity of the plasma to Lyman
radiation, which affects the ionization degree of deuterium, and thus avalanche
runaway generation. The two-stage injection scheme, where dilution cooling is
produced by deuterium before a radiative thermal quench caused by neon, reduces
both the hot-tail seed and the localized transported heat load on the wall.
However, during nuclear operation, additional runaway seed sources from the
activated wall and tritium make it difficult to reach tolerably low runaway
currents.
