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  • Experimental distinction of the molecularly induced Balmer emission contribution and its application for inferring molecular divertor density with 2D filtered camera measurements during detachment in JET L-mode plasmas
    Karhunen, J. ...
    A previously presented model for generating 2D estimates of the divertor plasma conditions at JET from deuterium Balmer line intensity ratios, obtained from tomographic reconstructions of divertor ... camera images, was amended to consider also the Balmer emission arising from molecular processes. Utilizing the AMJUEL and H2VIBR atomic and molecular databases of EIRENE enabled also inference of the molecular divertor density from the distinguished molecularly induced emission. Analysis of a JET L-mode density scan suggests the molecularly induced emission accounting for up to 60–70 and 10–20 of the Balmer D_\alpha and D_\gamma intensities, respectively, at the onset of detachment, while electron-ion recombination becomes increasingly dominant with deepening detachment. Similar observations were made by post-processing EDGE2D-EIRENE simulations, which indicated significant roles of molecular D_2^+ ions and vibrational excitation of the D2 molecules as precursors for the molecularly induced emission. The experimentally inferred molecular density at the outer strike point was found to increase monotonously with decreasing strike point temperature, reaching approximately 30–50 of the local electron density at n_{\mathrm{mol},\mathrm{osp}} = 1–2 \times 10^{20} m−3 at T_\mathrm{e,osp} \approx 0.7 eV. A further steep increase by a factor of 3–5 was observed with decrease of T_\mathrm{e,osp} to 0.5 eV. The observations are in qualitative and reasonable quantitative agreement with EDGE2D-EIRENE predictions of n_{\mathrm{mol},\mathrm{osp}} within the uncertainties of the experimental data.
    Source: Plasma physics and controlled fusion. - ISSN 0741-3335 (Vol. 64, No. 7, 2022, 15 str.)
    Type of material - article, component part
    Publish date - 2022
    Language - english
    COBISS.SI-ID - 135096579
    DOI