Measurement of a 2D fast-ion velocity distribution function by tomographic inversion of fast-ion D-alpha spectra

Mirko Salewski, B. Geiger, Asger Schou Jacobsen, M. García-Muñoz, W.W. Heidbrink, Søren Bang Korsholm, Frank Leipold, Jens Madsen, Dmitry Moseev, Stefan Kragh Nielsen, Jesper Rasmussen, Morten Stejner Pedersen, G. Tardini, M. Weiland

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We present the first measurement of a local fast-ion 2D velocity distribution function f(v‖, v⊥). To this end, we heated a plasma in ASDEX Upgrade by neutral beam injection and measured spectra of fast-ion Dα (FIDA) light from the plasma centre in three views simultaneously. The measured spectra agree very well with synthetic spectra calculated from a TRANSP/NUBEAM simulation. Based on the measured FIDA spectra alone, we infer f(v‖, v⊥) by tomographic inversion. Salient features of our measurement of f(v‖, v⊥) agree reasonably well with the simulation: the measured as well as the simulated f(v‖, v⊥) are lopsided towards negative velocities parallel to the magnetic field, and they have similar shapes. Further, the peaks in the simulation of f(v‖, v⊥) at full and half injection energies of the neutral beam also appear in the measurement at similar velocity-space locations. We expect that we can measure spectra in up to seven views simultaneously in the next ASDEX Upgrade campaign which would further improve measurements of f(v‖, v⊥) by tomographic inversion.
Original languageEnglish
JournalNuclear Fusion
Issue number2
Pages (from-to)023005
Publication statusPublished - 2014


  • Fast-ion velocity distribution function
  • Tomography
  • Inverse problems
  • Fast ions in tokamaks


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