Runaway electron expulsion during tokamak instabilities

Introduction Runaway Electron (RE) beams with multi-MeV energies can develop within a tokamak plasma during instabilities. REs represent a major concern in tokamaks because when lost to the first wall they can cause significant local energy deposition, melting and damage to plasma-facing components. Key to the successful operation of tokamaks, and in particular of ITER and future energy-generation reactors of the DEMO type, is the understanding of the dynamics of REs to enable efficient control techniques to mitigate their impact on machine operation. Experimentally, REs can be detected using synchrotron radiation detectors, neutron and hard x-ray detectors, soft/hard x-ray detectors to monitor, for example, bremsstrahlung radiation caused by the interaction of REs escaping to the chamber wall or limiter during the development of instabilities, and recently also with Cherenkov detectors. Results are presented from the correlation of the Cherenkov signal with hard x-ray (hxr) counts and with amplitude and phase of magnetic perturbations.