Thermal quench in ITER locked mode disturbances

Disruptions in ITER could be much milder in ITER than in JET and

present experiments. They might be called disturbances rather than disruptions.

In JET, it was found that the thermal quench (TQ) in  locked mode disruptions is

caused by resistive wall tearing modes (RWTMs) [Strauss, Phys Plasma 28, 032501 (2021)].

This result was obtained by comparison of theory and M3D simulations with JET data.

The RWTM growth rate is a form of resistive wall mode branching from a tearing mode,

with growth rate proportional to the resistive wall magnetic penetration time to the

-4/9 power. The TQ time  is given by the

smaller of the RWTM growth time or the parallel thermal transport time

in a stochastic magnetic field. The parallel thermal transport is associated with the TQ precursor.

In ITER, the resistive wall penetration time is 50 times  longer than in

present experiments.  The growth time of the RWTM in ITER could be as large as

100 ms [Strauss, Phys. Plasma 28 (2021)].

In ITER, the edge might be significantly

hotter, and the thermal conductivity might be in the collisionless regime.

The thermal loss is determined by the TQ precursor, with a time scale of

10 - 30 ms.

The loss time scales would be sufficiently long that runaway electrons and

divertor melting should be much less of a problem than anticipated.

To turn disruptions to disturbances, two conditions are needed--

a highly conducting wall, and a cool enough edge. These slow the RWTM and parallel

thermal conduction.