Experimental characterization of the active and passive fast-ion H-alpha emission in W7-X using FIDASIM

Peter Zs Poloskei*, B. Geiger, A. Jansen van Vuuren, S. Äkäslompolo, O. Ford, A. Spanier, T. W.C. Neelis, P. McNeely, D. Hartmann, W7-X Team

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

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This paper presents the first results from the analysis of Balmer-alpha spectra at Wendelstein 7-X which contain the broad charge exchange emission from fast-ions. The measured spectra are compared to synthetic spectra predicted by the FIDASIM code, which has been supplied with the 3D magnetic fields from VMEC, 5D fast-ion distribution functions from ASCOT, and a realistic Neutral Beam Injection geometry including beam particle blocking elements. Detailed modeling of the beam emission shows excellent agreement between measured beam emission spectra and predictions. In contrast, modeling of beam halo radiation and Fast-Ion H-Alpha signals (FIDA) is more challenging due to strong passive contributions. While about 50% of the halo radiation can be attributed to passive signals from edge neutrals, the FIDA emission—in particular for an edge-localized line of sights—is dominated by passive emission. This is in part explained by high neutral densities in the plasma edge and in part by edge-born fast-ion populations as demonstrated by detailed modeling of the edge fast-ion distribution.

Original languageEnglish
Article number026008
JournalNuclear Fusion
Issue number2
Early online date22 Dec 2023
Publication statusPublished - Feb 2024
MoE publication typeA1 Journal article-refereed


  • fast-particle diagnostic
  • forward modelling
  • plasma physics
  • stellarator


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