Authors
Foisal B T Siddiki, M Krychowiak, O Schmitz, M Vécsei, A Knieps, F Henke, D Gradic, Y Boumendjel, C Killer, A Pandey, W7-X Team
Published in
The Review of scientific instruments. Volume 97. Issue 10. Oct 01, 2026.
Abstract
A new helium beam diagnostic has been implemented at the outboard midplane of the stellarator Wendelstein 7-X (W7-X) to measure edge plasma parameters in the scrape-off layer (SOL). The system provides localized measurements of electron density (ne) and temperature (Te) through spectroscopic observation of atomic helium emission lines combined with a collisional radiative model (CRM) with a radial spatial resolution of 4.5 mm. A gaseous beam of neutral helium atoms is injected radially into the plasma, and the resulting line emission is collected using a Schmidt Czerny Turner spectrometer. In this work, we discuss the successful implementation of the diagnostic, including the optical setup, data acquisition, and the analysis approach to obtain the ne(R, t) and Te(R, t) profiles using an advanced CRM. The diagnostic is benchmarked against a colocated alkali beam diagnostic and compared with other edge diagnostics, including the Multipurpose Manipulator, divertor Langmuir probes, and the divertor helium beam. These comparisons show that the midplane helium beam measurements are consistent with the expected edge plasma parameter range. A magnetic field line mapping methodology has also been established to enable cross-diagnostic comparisons in the three-dimensional island SOL geometry of W7-X. First, measurements from recent experimental campaigns demonstrate that the diagnostic can resolve radial ne and Te profiles in the main SOL region, providing a new capability for characterizing edge transport in W7-X.
PMID:
42862043
Bibliographic data and abstract were imported from PubMed on 12 Oct 2026.
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