MHD induced fast-ion losses on ASDEX Upgrade

M. García-Mũoz, H.-U. Fahrbach, S.D. Pinches, V. Bobkov, M. Brüdgam, M. Gobbin, S. Günter, V. Igochine, Ph. Lauber, M.J. Mantsinen, M. Maraschek, L. Marrelli, P. Martin, P. Piovesan, E. Poli, K. Sassenberg, G. Tardini, H. Zohm

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A detailed knowledge of the interplay between MHD instabilities and energetic particles has been gained from direct measurements of fast-ion losses (FILs). Time-resolved energy and pitch angle measurements of FIL caused by neoclassical tearing modes (NTMs) and toroidicity-induced Alfven eigenmodes (TAEs) have been obtained using a scintillator based FIL detector. The study of FIL due to TAEs has revealed the existence of a new core-localized MHD fluctuation, the Sierpes mode. The Sierpes mode is a non-pure Alfvenic fluctuation which appears in the acoustic branch, dominating the transport of fast-ions in ICRF heated discharges. The internal structure of both TAEs and Sierpes mode has been reconstructed by means of highly resolved multichord soft x-ray measurements. A spatial overlapping of their eigenfunctions leads to a FIL coupling, showing the strong influence that a core-localized fast-ion driven MHD instability may have on the fast-ion transport. We have identified the FIL mechanisms due to NTMs as well as due to TAEs. Drift islands formed by fast-ions in particle phase space are responsible for the loss of NBI fast-ions due to NTMs. In ICRF heated plasmas, a resonance condition fulfilled by the characteristic trapped fast-ion orbit frequencies leads to a phase matching between fast-ion orbit and NTM or TAE magnetic fluctuation. The banana tips of a resonant trapped fast-ion bounce radially due to an E × B drift in the TAE case. The NTM radial bounce of the fast-ion banana tips is caused by the radial component of the perturbed magnetic field lines. © 2009 IAEA, Vienna.
Original languageEnglish
Article number085014
Pages (from-to)-
JournalNuclear Fusion
Issue number8
Publication statusPublished - 2009
Externally publishedYes


All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • Nuclear and High Energy Physics

Cite this

García-Mũoz, M., Fahrbach, H-U., Pinches, S. D., Bobkov, V., Brüdgam, M., Gobbin, M., ... Zohm, H. (2009). MHD induced fast-ion losses on ASDEX Upgrade. Nuclear Fusion, 49(8), -. [085014].