High-definition velocity-space tomography of fast-ion dynamics

Mirko Salewski, B. Geiger, A.S. Jacobsen, Per Christian Hansen, W.W. Heidbrink, Søren Bang Korsholm, Frank Leipold, Jens Madsen, Dmitry Moseev, Stefan Kragh Nielsen, M. Nocente, T. Odstrčil, Jesper Rasmussen, L. Stagner, Morten Stejner Pedersen, M. Weiland

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Abstract

Velocity-space tomography of the fast-ion distribution function in a fusion plasma is usually a photon-starved tomography method due to limited optical access and signal-to-noise ratio of fast-ion Dα (FIDA) spectroscopy as well as the strive for high-resolution images. In high-definition tomography, prior information makes up for this lack of data. We restrict the target velocity space through the measured absence of FIDA light, impose phase-space densities to be non-negative, and encode the known geometry of neutral beam injection (NBI) sources. We further use a numerical simulation as prior information to reconstruct where in velocity space the measurements and the simulation disagree. This alternative approach is demonstrated for four-view as well as for two-view FIDA measurements. The high-definition tomography tools allow us to study fast ions in sawtoothing plasmas and the formation of NBI peaks at full, half and one-third energy by time-resolved tomographic movies.
Original languageEnglish
Article number106024
JournalNuclear Fusion
Volume56
Issue number10
Number of pages15
ISSN0029-5515
DOIs
Publication statusPublished - 2016

Keywords

  • Fast ions
  • Tomography
  • Tokamaks
  • Sawteeth
  • Neutral beam injection
  • Fast-ion D-alpha spectroscopy

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