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

Abstract Edge Localised Modes (ELMs) induced fast-ion losses have been characterised in the energy, E , and pitch, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>λ</mml:mi> <mml:mo>=</mml:mo> <mml:msub> <mml:mi>v</mml:mi> <mml:mo>∥</mml:mo> </mml:msub> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mi>v</mml:mi> </mml:mrow> </mml:math> , space using a unique Fast Ion Loss Detector (FILD) on the tokamak à configuration variable. The FILD is equipped with a 128 Avalanche Photo Diodes (APDs) camera measuring scintillator emission with a 1 MHz bandwidth. The well-defined view lines of the APDs allow for obtaining velocity space information from the emission pattern with unprecedented 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, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>ρ</mml:mi> <mml:mo>∼</mml:mo> <mml:mn>0.7</mml:mn> </mml:mrow> </mml:math> . The fast-ion interaction with the plasma instability 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 (∼ 70 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.