Study of Interaction Between Fast Ions and MHD Instabilities by Fusion Product Measurements in Joint European Torus
Fast ion redistribution and losses caused by plasma disruptions, Toroidal Alfvén Eigenmodes (TAE) and fishbones are measured with a suite of improved gamma-ray diagnostics, Neutral Particle Analyser (NPA), neutron spectrometry, Faraday Cups and a Scintillator Probe (SP). Fast ion populations in the MeV energy range were generated in fusion reactions and were also produced by 3rd harmonic Ion Cyclotron Resonance Heating (ICRH). Significant fast ion losses preceding plasma disruptions were often detected by SP in discharges with high bN. These losses were caused by the m = 2/n = 1 kink mode and typically occurred at the time of thermal quench, before the current quench. Core-localised TAE modes inside the q = 1 radius causing redistribution of the fast ions in the resonance energy range were directly measured for the first time with the gamma-ray camera, confirming that the TAE instability expels fast ions from inside the q = 1 radius and triggers the monster sawtooth crashes. Energy and pitch angle resolved SP measurements of lost fusion products in the MeV energy range were found to correlate with low-frequency fishbone oscillations driven by 100keV beam ions. The origin and amplitude of these nonresonant losses are investigated.