MeV-range fast ion losses induced by fishbones on JET

C. Perez Von Thun, A. Perona, T. Johnson, S. E. Sharapov, M. Reich, V. G. Kiptily, M. Cecconello, Antti Salmi, V. Ya Goloborod'ko, S. D. Pinches, M. García-Muñoz, D. Darrow, M. Brix, I. Voitsekhovitch

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13 Citations (Scopus)

Abstract

Energy and pitch angle resolved measurements of highly energetic (megaelectronvolt (MeV) range) suprathermal ions ejected from the plasma through interaction with fishbone oscillations are presented. The measurements are obtained with a 2D scintillator probe diagnostic installed on JET, which is designed to detect lost ions only above a certain energy threshold (E min,D ∼ 200 keV). In the case reported here the lost ions are identifiedasfast protons which had been accelerated to high energies by ICRF minority heating. The energy of the lost protons (∼0.5-4 MeV) is approximately one order of magnitude higher than the energy of the injected beam ions (maximum 130 keV) driving the fishbone. Losses arrivingat the probe are enhanced by about a factor 10-20 with respect to MHD-quiescent levels, and are found to increase quadratically with the fishbone amplitude. Using a number of simplifying assumptions, numerical simulations have been performed which combine the HAGIS, MISHKA and SELFO codes (where the distribution function predicted by SELFO has been validated against neutral particle analyser measurements). The losses are found to originate from orbit stochastic diffusion of trapped protons near the plasma boundary or from counter-passing protons deep in the plasma core, which transit under the influence of the fishbone into an unconfined trapped orbit. The simulations show further that the losses are of non-resonant type. The simulated energy and pitch angle distribution of the losses, the temporal behaviour of the losses during a fishbone cycle and the scaling of the losses with the fishbone amplitude are compared with experiment. The simulation results are mostly in broad agreement with experiment, but some of the predictions could not be reconciled with experiment using this model.

Original languageEnglish
Article number084009
JournalNuclear Fusion
Volume50
Issue number8
DOIs
Publication statusPublished - 1 Aug 2010
MoE publication typeA1 Journal article-refereed

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