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Inferring divertor plasma properties from hydrogen Balmer and Paschen series spectroscopy in JET-ILW.

Lomanowski, B.A. and Meigs, A.G. and Sharples, R.M. and Stamp, M. and Guillemaut, C. and Contributors, J. (2015) 'Inferring divertor plasma properties from hydrogen Balmer and Paschen series spectroscopy in JET-ILW.', Nuclear fusion., 55 (12). p. 123028.


A parametrised spectral line profile model is formulated to investigate the diagnostic scope for recovering plasma parameters from hydrogenic Balmer and Paschen series spectroscopy in the context of JET-ILW divertor plasmas. The separate treatment of Zeeman and Stark contributions in the line model is tested against the PPP-B code which accounts for their combined influence on the spectral line shape. The proposed simplified model does not fully reproduce the Stark–Zeeman features for the α and β transitions, but good agreement is observed in the line width and wing profiles, especially for n  >  5. The line model has been applied to infer radial density profiles in the JET-ILW divertor with generally good agreement between the D $5\to 2$ , $5\to 3$ , $6\to 2$ , $7\to 2$ and $9\to 2$ lines for high recycling and detached conditions. In an L-mode detached plasma pulse the Langmuir probe measurements typically underestimated the density by a factor 2–3 and overestimated the electron temperature by a factor of 5–10 compared to spectroscopically derived values. The line model is further used to generate synthetic high-resolution spectra for low-n transitions to assess the potential for parameter recovery using a multi-parametric fitting technique. In cases with 4 parameter fits with a single Maxwellian neutral temperature component the D $4\to 3$ line yields the best results with parameter estimates within 10% of the input values. For cases with 9 parameter fits inclusive of a multi-component neutral velocity distribution function the quality of the fits is degraded. Simultaneous fitting of the D $3\to 2$ and $4\to 3$ profiles improves the fit quality significantly, highlighting the importance of complementary spectroscopic measurements for divertor plasma emission studies.

Item Type:Article
Full text:(AM) Accepted Manuscript
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Publisher statement:This is an author-created, un-copyedited version of an article published in Nuclear Fusion. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at
Date accepted:21 October 2015
Date deposited:10 February 2016
Date of first online publication:December 2015
Date first made open access:19 November 2016

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