Collective Thomson scattering measurements of fast-ion transport due to sawtooth crashes in ASDEX Upgrade

Jesper Rasmussen, Stefan Kragh Nielsen, Morten Stejner Pedersen, J. Galdon-Quiroga, M. Garcia-Munoz, B. Geiger, Asger Schou Jacobsen, F. Jaulmes, Søren Bang Korsholm, N. Lazanyi, Frank Leipold, F. Ryter, Mirko Salewski, M. Schubert, J. Stober, D. Wagner

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Abstract

Sawtooth instabilities can modify heating and current-drive profiles and potentially increase fast-ion losses. Understanding how sawteeth redistribute fast ions as a function of sawtooth parameters and of fast-ion energy and pitch is hence a subject of particular interest for future fusion devices. Here we present the first collective Thomson scattering (CTS) measurements of sawtooth-induced redistribution of fast ions at ASDEX Upgrade. These also represent the first localized fast-ion measurements on the high-field side of this device. The results indicate fast-ion losses in the phase-space measurement volume of about 50% across sawtooth crashes, in good agreement with values predicted with the Kadomtsev sawtooth model implemented in TRANSP and with the sawtooth model in the EBdyna_go code. In contrast to the case of sawteeth, we observe no fast-ion redistribution in the presence of fishbone modes. We highlight how CTS measurements can discriminate between different sawtooth models, in particular when aided by multi-diagnostic velocity-space tomography, and briefly discuss our results in light of existing measurements from other fast-ion diagnostics.
Original languageEnglish
JournalNuclear Fusion
Volume56
Issue number11
Pages (from-to)112014
Number of pages9
ISSN0029-5515
DOIs
Publication statusPublished - 2016

Keywords

  • Fast ions in tokamaks
  • Collective Thomson scattering
  • Fast-ion velocity distribution function
  • Sawtooth instabilities

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