ITER VDE modeling for disruption mitigation design

ITER has a vacuum vessel (VV) of a wall time $sim 500$~ms, while the

desired current quench time $ au_{CQ}$ is around 100~ms, so there is

little room for active feedback control from coils outside the VV, in

contrast to current tokamaks. The first wall and blanket modules are

constructed and arranged on ITER to impede net toroidal current, so

they would not obstruct the poloidal magnetic flux from penetrating

through. A current-carrying plasma column can thus scrape off against

the first wall while the effect of a good flux conserver is felt at a

standoff distance away. This two-layer setup also channels the halo

current in ways that are different from current tokamak experiments.

The consequence is that both the VDE dynamics and its mitigation would

require special consideration to simulate on current tokamak

experiments, the subtlety of which can be clarified by modeling. Here

we report a comprehensive suite of simulation codes that track both

the axisymmetric and 3D VDE dynamics, and the physics findings on how

a VDE can be effectively mitigated on ITER. $^*$Work supported under

TDS SciDAC project.