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

Abstract

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. 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→2, 5→3, 6→2, 7→2 and 9→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→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→2 and 4→3 profiles improves the fit quality significantly, highlighting the importance of complementary spectroscopic measurements for divertor plasma emission studies.

Determination of divertor stray light in high-resolution main chamber Hα spectroscopy in JET-ILW

“…Note, that RIG and ROG are used in the fitting algorithm only to calculate the values of Zeeman splitting for HFS and LFS SOLL spectra and are not used to recover the respective fractions. At 8.75 s, the recovered DSL fraction in the signal appears to be 20% and increases to almost 40% at 13.4 s. Note, that the error of recovering the effective temperatures is not estimated: in our opinion, in such a complicated inverse problem with so many free parameters this error may be substantially higher than that estimated in [17] where the synthetic (not real experimental) data for divertor were analysed in the framework of similar inverse problem but with only 9 free parameters, cf. figures 12 and 13 in [17].…”

Spectroscopic investigations of divertor detachment in TCV

“…There has been considerable work utilizing spectroscopic measurements for understanding detachment, where the characteristics of the recombining region are extracted from the Balmer series emission [3,4,5,6,7]. Typically a high density recombination front forms at the target and moves rapidly towards the x-point as the core plasma density is increased.…”

Effect of reflections on 2D tomographic reconstructions of filtered cameras and on interpreting spectroscopic measurements in the JET ITER-like wall divertor

“…[1][2][3] Moreover, spectroscopic measurements of the divertor emission allow inference of electron density (ne) and temperature (Te) in the divertor. [4][5][6] In JET, in addition to bolometric measurements of total radiation, 7 divertor emission is observed with vertical spectroscopic lines-ofsight, [8][9][10] as well as with a visible-range spectroscopic divertor camera system (KL11). 11 The divertor camera setup consists of four cameras equipped with a selection of changeable narrow bandpass filters with bandwidths of 1-3 nm for visible-range emission of hydrogen isotopes and various impurity species, viewing the divertor tangentially, as shown in Fig.…”