Study of Interaction between Fast Ions and MHD Instabilities by Fusion Product Measurements in Joint European Torus

Abstract

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 β N . 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 100 keV beam ions. The origin and amplitude of these non-resonant losses are investigated.

Fast-ion energy resolution by one-step reaction gamma-ray spectrometry

“…In GRS the γ-rays emitted by fusion plasmas are spectrally analyzed [14,15]. Today the highest γ-ray fluxes from fusion plasmas are achieved at JET where GRS is routinely used [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]. The high nuclear reaction rates in the upcoming DT campaign at JET [1,33] and later in burning plasmas at ITER and DEMO will further enhance the γ-ray emission [14,15,34,35].…”

“…Each peak can be related to a nuclear reaction by the γ-ray energy. GRS measurements at moderate spectral resolution have been made at Doublet-III [36], TFTR [37], JET [16][17][18][19][20][21][22][23][24] and JT-60U [38,39]. New detectors [27,40] allow GRS measurements at very high spectral resolution sufficient to resolve the spectral shapes of the individual peaks as demonstrated at JET [25][26][27][28][29][30][31] and ASDEX Upgrade [41].…”

Velocity-space observation regions of high-resolution two-step reaction gamma-ray spectroscopy

“…Gamma-ray spectroscopy (GRS) is an essential diagnostic to study fast ions in fusion plasmas [1,2]. Early GRS measurements in tokamaks have been made at Doublet-III [3], TFTR [4], JET [5][6][7][8][9][10][11][12][13] and JT-60U [14,15]. More recently, high-resolution GRS measurements have been made at JET [16][17][18][19][20][21] and ASDEX Upgrade [22] thanks to the development of new detectors [18,23].…”

“…More recently, high-resolution GRS measurements have been made at JET [16][17][18][19][20][21] and ASDEX Upgrade [22] thanks to the development of new detectors [18,23]. GRS is particularly well-suited for large, hot devices such as JET [5][6][7][8][9][10][11][12][13][16][17][18][19][20][21], ITER [24] or DEMO [25] since high temperatures enhance fusion reaction rates and hence γ-ray fluxes [1,2].…”

“…Many nuclear reactions in hot fusion plasmas lead to γ-ray emission [1,2]. At JET, several species including alpha particles, helium-3, deuterium or hydrogen have been measured using GRS [5][6][7][8][9][10][11][12][13][16][17][18][19][20][21]. These fast ions are generated in fusion reactions, by ion cyclotron resonance heating (ICRH) or by neutral beam injection (NBI) [7].…”