Experimental investigation of the radial structure of energetic particle driven modes

L. Horváth, G. Papp, Ph Lauber, G. Por, A. Gude, V. Igochine, B. Geiger, M. Maraschek, L. Guimarais, V. Nikolaeva, G. I. Pokol

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16 Citations (Scopus)

Abstract

Alfvén eigenmodes (AEs) and energetic particle modes (EPMs) are often excited by energetic particles (EPs) in tokamak plasmas. One of the main open questions concerning EP driven instabilities is the non-linear evolution of the mode structure. The aim of the present paper is to investigate the properties of beta-induced AEs (BAEs) and EP driven geodesic acoustic modes (EGAMs) observed in the ramp-up phase of off-axis NBI heated ASDEX Upgrade (AUG) discharges. This paper focuses on the changes in the mode structure of BAEs/EGAMs during the non-linear chirping phase. Our investigation has shown that in the case of the observed down-chirping BAEs the changes in the radial structure are smaller than the uncertainty of our measurement. This behaviour is most probably the consequence of the fact that BAEs are normal modes, thus their radial structure strongly depends on the background plasma parameters rather than on the EP distribution. In the case of rapidly upward chirping EGAMs the analysis consistently shows shrinkage of the mode structure. The proposed explanation is that the resonance in the velocity space moves towards more passing particles which have narrower orbit widths.

Original languageEnglish
Article number112003
JournalNuclear Fusion
Volume56
Issue number11
DOIs
Publication statusPublished - Jul 22 2016

Keywords

  • Alfven eigenmodes
  • energetic ions
  • time-frequency analysis
  • tokamak
  • wave-particle interaction

ASJC Scopus subject areas

  • Nuclear and High Energy Physics
  • Condensed Matter Physics

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    Horváth, L., Papp, G., Lauber, P., Por, G., Gude, A., Igochine, V., Geiger, B., Maraschek, M., Guimarais, L., Nikolaeva, V., & Pokol, G. I. (2016). Experimental investigation of the radial structure of energetic particle driven modes. Nuclear Fusion, 56(11), [112003]. https://doi.org/10.1088/0029-5515/56/11/112003