Tomography of the positive-pitch fast-ion velocity distribution in DIII-D plasmas with Alfvén eigenmodes and neoclassical tearing modes

B. Madsen*, M. Salewski, W.W. Heidbrink, L. Stagner, M. Podestà, D. Lin, A.V. Garcia, Per Christian Hansen, J. Huang

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Understanding the effect of Alfvén eigenmodes (AEs) and neoclassical tearing modes (NTMs) on fast ions is highly important for fusion reactors due to potentially strong resonant interactions between the fast ions and the modes. Here, we use the four-view fast-ion D-alpha (FIDA) diagnostic installed in the DIII-D tokamak to reconstruct the fast-ion velocity distribution at two radial positions during two sequential discharges with strong and weak mode activity, respectively. The velocity-space coverage of the diagnostics, however, only allows reliable reconstructions of fast ions with positive pitches. Therefore, we suggest new tomographic inversion methods relying on prior information outside the well-diagnosed region. We find that within the population of fast ions with positive pitches, ions, at all energies, are transported away from the measurement volumes. Comparisons between the reconstructions and kick model simulations, where the mode activity is considered, reveal that low-frequency modes such as the NTMs and low-frequency AEs contribute significantly to the positive-pitch fast-ion transport in the central measurement volume, whereas TAEs and EAEs become important farther out and are responsible for decreased fast-ion confinement.
Original languageEnglish
Article number066024
JournalNuclear Fusion
Volume60
Issue number6
Number of pages17
ISSN0029-5515
DOIs
Publication statusPublished - 2020

Keywords

  • Velocity-space tomography
  • Fast-ion D-alpha spectroscopy
  • Fast ions
  • Alfvén eigenmodes
  • Neoclassical tearing modes
  • Kick model
  • DIII-D tokamak

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