First measurements of velocity-space resolved intra-ELM fast-ion losses on the TCV tokamak

Edge Localised Modes (ELM) induced fast-ion losses have been characterised in the energy, E, and pitch, λ= v∥/v, space using a unique Fast Ion Loss Detector (FILD) on the Tokamak à Configuration Variable (TCV). The FILD is equipped with a 128 Avalanche Photo Diodes (APDs) camera measuring scintillator emission with a 1MHz bandwidth. The well-defined view lines of the APDs allow for obtaining velocity space information from the emission pattern with unrepresented temporal resolution. Making use of the enhanced FILD capabilities, ELM-induced fast-ion losses were investigated in the ITER Baseline Scenario, mimicking its shape and normalised plasma parameters. Significant fast-ion losses were observed, notably before and during the ELM crashes induced by the presence of a 2/1 MHD instability localised at the plasma’s normalised radius, p = 0.7. The fast-ion interaction with the plasma instabilities is concluded to be unconnected to the presence of the ELMs. During the ELM crashes, there is an observed spread in both the fast-ion pitch and energy that reaches higher values (~75 keV) than expected from the pre-ELM fast-ion population, generated by Neutral Beam Injection at ~27 keV. This implies a fast-ion acceleration during the ELM’s crash. Full orbit neoclassical simulations are used to calculate the neoclassical fast-ion velocity space lost to the FILD and to quantify the neoclassical fast-ion losses.