Abstract
Impurities (H2, D2, Ne or Ar) injected into steady (non-disrupting) discharges with massive gas injection (MGI) are shown to mix into the plasma core dominantly via magnetohydrodynamic activity during the plasma thermal quench (TQ). Mixing efficiencies of injected impurities into the plasma core are measured to be of order 0.05-0.4. 0D modeling of the experiments is found to reproduce observed TQ and current quench durations reasonably well (typically within plus/minus 25% or so), although shutdown onset times are underestimated (by around 2x). Preliminary 0D modeling of ITER based on DIII-D mixing efficiencies suggests that MGI will work well in ITER with regard to disruption heat load and vessel force mitigation, but may not collisionally suppress runaway electrons.