Locked mode disruptions in DIII-D and application to ITER

Disruptions are rapid loss of plasma confinement in tokamaks, which could damage large tokamaks like ITER. Recent work identified the thermal quench in JET locked mode disruptions with a resistive wall tearing mode. New research finds a similar instability in a DIII-D locked mode shot. The instability is studied with simulations, theory, and comparison to experimental data. Linear theory is extended to include resistive wall modes with a rational surface in the plasma. Linear simulations show the mode is stable for an ideal wall, and unstable with a resistive wall. Nonlinear simulations show that the mode grows to large amplitude, causing a thermal quench. The mode onset occurs when the radius of the q =2 rational surface is sufficiently close to the plasma edge. These results are important for ITER, greatly mitigating the effects of disruptions