Advances in the development of a Cherenkov diagnostic system to study runaway electron losses

Uncontrolled rapid loss of runaway current represents one of the most critical issues in tokamak reactors. Significant research efforts are necessary to study and understand efficient ways to control Runaway Electrons (REs) and to implement adequate control schemes to prevent disruptions. In this context, the aim of the study presented here is to identify the potential of a Cherenkov optical diagnostics in detecting runaway electron losses in the presence of magnetic islands, in a scenario that is more controllable than a disruption. The Cherenkov probe was recently installed and tested in FTU in collaboration with the Polish National Centre for Nuclear Research (NCBJ). Data interpretation and correlation with several other diagnostics operating in FTU, brought out the high level of detail provided by the Cerenkov probe in detecting RE losses driven by magnetic islands. The development of the diagnostic system was designed to enable RE energy-discrimination and simultaneous detection at two toroidal/poloidal positions to evaluate the potential of this diagnostic system for implementation in next-generation fusion reactors. The demonstration and testing of the improved diagnostic system is planned for the upcoming FTU experimental campaign.