The effect of magnetic perturbations on runaway dynamics

Disruptions in large tokamaks can lead to the generation of a relativistic runaway (RE) electron beam that may cause serious damage to the first wall. To suppress the RE beamthe application of resonant magnetic perturbations (RMP) has been suggested. We investigate the effect of resonant magnetic perturbations by simulating the RE drift orbits inmagnetostatic perturbed fields and calculating the transport and orbit losses for various particle energies and different magnetic perturbation configurations. In the simulations we use model configurations with the planned ITER RMP system and solve the relativistic, gyro-averaged drift equations for the runaway electrons including radiation losses and collisions. The results indicate that runaway electrons are rapidly lost from regions where thenormalised perturbation amplitude δB/B is larger than ∼0.1% in a properly chosen perturbation geometry. This corresponds to the outer half of the confinement volume in ITER. We show that despite the chaotic magnetic topology the ensemble behaviour can only be approximated by a diffusion process