Interpretation of Lyman opacity measurements in JET with the ITER-like wall using a particle balance approach

Lomanowski, Bartosz A.; Groth, M.; Coffey, Ivor; Karhunen, Juuso; Maggi, Costanza; Meigs, Andrew; Menmuir, Sheena; O mullane, Martin

doi:10.1088/1361-6587/ab7432

Interpretation of Lyman opacity measurements in JET with the ITER-like wall using a particle balance approach

Journal Article · Mon Apr 27 00:00:00 EDT 2020 · Plasma Physics and Controlled Fusion

DOI:https://doi.org/10.1088/1361-6587/ab7432· OSTI ID:1649521

^[1]; Groth, M. ^[2]; Coffey, Ivor ^[3]; Karhunen, Juuso ^[2]; ^[3]; Meigs, Andrew ^[3]; Menmuir, Sheena ^[3]; ^[4]

Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Aalto Univ., Otaniemi (Finland)
Culham Science Centre, Abingdon (United Kingdom). Culham Centre for Fusion Energy (CCFE), EURATOM/UKAEA Fusion Association
Univ. of Strathclyde, Glasgow (United Kingdom)

Recent measurements of the Ly_β/D_α ratio in the JET ITER-like wall (ILW) divertor show comparatively more pronounced Ly_β reabsorption relative to previous results in JET with the carbon wall (JET-C). At the outer horizontal target ion current rollover point a Ly_β reabsorption rate of 60% is measured, increasing to 80% in more pronounced detachment, implying a Ly_α reabsorption rate of 90%–98%. The radially resolved Ly_β/D_α measurements are used to constrain Lyman opacity corrections to atomic rate coefficients using the population escape factor technique in order to capture the local changes to the excited state population structure in the high Lyman opacity regions at and outboard of the outer strike point. To check the self-consistency of the Lyman opacity measurements, a detailed spectroscopic interpretation of the outer divertor particle balance is presented, in which the impact of opacity corrections to the Ly_α inverse photon efficiency coefficients is assessed. A five-fold deficit in the estimated D⁺ source rate obtained with optically thin plasma assumptions is reconciled once the opacity corrections are factored into the Ly_α photon rate to ionization rate conversion. The experiment results are reproduced in EDGE2D-EIRENE density scan simulations in which an imposed ad hoc Lyman reabsorption rate is recovered spectroscopically using synthetic measurements, and a similar shortfall in the D⁺ source rate estimates is reconciled using Lyman opacity corrected atomic data. The model limitations prevent a more detailed self-consistent analysis of the Lyman opacity impact on divertor parameters and detachment evolution, and hence motivate renewed efforts to re-establish routine exploitation of the photon transport modelling capabilities in the EIRENE code package. Lyman opacity corrections to atomic data coefficients are necessary for spectroscopic interpretation of the JET-ILW divertor plasma, with significant influence on the divertor plasma also a likely consequence of the presence of strong Ly_α reabsorption. Finally, a scan of auxiliary heating powers spanning L-mode and H-mode conditions reveals a strong correlation of the measured Ly_β opacity with the outer target temperature, suggesting new possibilities for using Lyman opacity measurements in establishing detachment scalings.

View Accepted Manuscript (DOE)

Research Organization:: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Fusion Energy Sciences (FES)

Grant/Contract Number:: AC05-00OR22725

OSTI ID:: 1649521

Alternate ID(s):: OSTI ID: 23028764

Journal Information:: Plasma Physics and Controlled Fusion, Journal Name: Plasma Physics and Controlled Fusion Journal Issue: 6 Vol. 62; ISSN 0741-3335

Publisher:: IOP ScienceCopyright Statement

Country of Publication:: United States

Language:: English

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