Runaway electron losses enhanced by resonant magnetic perturbations

Paper i proceeding, 2011

Disruptions in large tokamaks can lead to the generation of a relativistic runaway electron beam that may cause serious damage to the first wall. To suppress the runaway beam the application of resonant magnetic perturbations (RMP) has been suggested. In this work we investigate the effect of resonant magnetic perturbations on the confinement of runaway electrons by simulating their drift orbits in magnetostatic perturbed fields and calculating the transport and orbit losses for various initial energies and different magnetic perturbation configurations. In the simulations we use model configurations with existing (TEXTOR) and planned (ITER) RMP systems, and solve the relativistic, gyro-averaged drift equations for the runaway electrons including the electric field, radiation losses and collisions. The results indicate that runaway electrons are well confined in the core of the device, but the onset time of runaway losses closer to the edge is dependent on the magnetic perturbation level, which can thereby affect the maximum runaway current. Runaway electrons are rapidly lost from regions where the normalised perturbation amplitude \delta B/B is larger than 0.1% in a properly chosen perturbation geometry. This applies to the region outside the radius corresponding to the normalised flux \psi = 0.5 in ITER, when the ELM mitigation coils are used at maximum current in their most favourable configuration.