Impact of Resonant Magnetic Perturbations on the Toroidal Location of the Runaway Electron Final Loss Strike Point

It is demonstrated that the peak toroidal impact phase of the post-disruption runaway electrons (REs) can be varied shot to shot by means of applied static nonaxisymmetric (3D) magnetic fields, or resonant magnetic perturbations (RMPs). In the experiments, high-current (500 kA), purged RE plateaus (i.e., low impurity postdisruption plasmas with current carried completely by REs) were terminated on the DIII-D tokamak center post. The global toroidal impact peak of the REs appears to be dominantly set by the toroidal phase of a wall-locked tearing mode, typically (m/n)=(2/1), but sometimes (m/n)=(3/2). In the absence of external RMP, the locked mode reliably locks close to a preferred toroidal phase ϕ≃75° probably set by intrinsic error fields. With applied RMP, the locked mode and RE impact phase is pushed to a new location. When the tearing mode is (m/n)=(2/1), the phase is well controlled and tracks the applied RMP phase, but in the case of an (m/n)=(3/2) tearing mode, the new phase location is not well controlled. These results could have an application in international thermonuclear experimental reactor and other fusion power plant-sized tokamaks as a method for spreading disruption first wall damage from REs.