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

Lomanowski, B.A.; Meigs, A.G.; Sharples, R.M.; Stamp, M.; Guillemaut, C.; Contributors, J.

Abstract

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.

Citation

Lomanowski, B., Meigs, A., Sharples, R., Stamp, M., Guillemaut, C., & Contributors, J. (2015). Inferring divertor plasma properties from hydrogen Balmer and Paschen series spectroscopy in JET-ILW. Nuclear Fusion, 55(12), Article 123028. https://doi.org/10.1088/0029-5515/55/12/123028

• Journal Article Type: Article
• Acceptance Date: Oct 21, 2015
• Publication Date: Dec 1, 2015
• Deposit Date: Dec 20, 2015
• Publicly Available Date: Nov 19, 2016
• Journal: Nuclear Fusion
• Print ISSN: 0029-5515
• Electronic ISSN: 1741-4326
• Publisher: IOP Publishing
• Peer Reviewed: Peer Reviewed
• Volume: 55
• Issue: 12
• Article Number: 123028
• DOI: https://doi.org/10.1088/0029-5515/55/12/123028
• Public URL: https://durham-repository.worktribe.com/output/1395996
• Related Public URLs: http://adsabs.harvard.edu/abs/2015NucFu..55l3028L