Addressing the impact of Lyman opacity in inference of divertor plasma conditions with 2D spectroscopic camera analysis of Balmer emission during detachment in JET L-mode plasmas

Journal Article · Tue Jan 28 00:00:00 EST 2025 · Nuclear Materials and Energy

DOI:https://doi.org/10.1016/j.nme.2025.101880· OSTI ID:2586833

Karhunen, Juuso ^[1]; Lomanowski, Bart ^[2]; Lawson, K ^[3]; Meigs, A. G. ^[4]; Aleiferis, S ^[3]; Carvalho, P ^[5]; Shaw, A ^[3]; Solokha, V ^[1]; Groth, Mathias ^[1]; Holm, Andreas ^[6]

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1. Aalto Univ. (Finland)
2. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
3. Culham Science Centre, Abingdon (United Kingdom). Culham Centre for Fusion Energy (CCFE)
4. UK Atomic Energy Authority (UKAEA), Culham (United Kingdom)
5. Univ. of Lisbon (Portugal)
6. Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)

The impact of re-absorption of the deuterium Lyman series emission was addressed in inferring divertor plasma conditions from Balmer series emission with 2D spectroscopic camera analysis during detachment in JET L-mode plasmas. The previously presented methodology was amended by modifying the standard photon emission coefficients and ionization and recombination rate coefficients of the ADAS database to consider the re-population of excited states due to Lyman opacity. This resulted in the estimate for the atomic density near the outer strike point to decrease by up to 75% at the onset of detachment at strike point temperatures of T_e,osp ≈ 1.0–3.0 eV with respect to the strongly overestimated previously obtained values, whereas the estimated electron temperature and density were unaffected by the opacity correction within the scatter of the data and only a moderate reduction by up to 20% was observed in the estimate for the molecularly induced fraction of the Balmer emission. No noticeable change was seen in the ionization rate, calculated from the estimated outer strike point conditions, due to the decrease in the atomic density estimate compensating for the increased values of the opacity-corrected ADAS rate coefficients for ionization. In detached conditions at T_e,osp ≈ 0.5–1.0 eV, 25%–35% lower recombination rates were provided by the opacity-corrected model. The observed effects on the experimental analysis were supported by a corresponding synthetic analysis based on EDGE2D-EIRENE simulations.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Contributing Organization: EUROfusion Tokamak Exploitation Team; JET Contributors
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 2586833
• Journal Information: Nuclear Materials and Energy, Journal Name: Nuclear Materials and Energy Vol. 42; ISSN 2352-1791
• Publisher: Elsevier BV
• Country of Publication: United States
• Language: English

Related Subjects

Balmer emission
Divertor detachment
Fusion
Lyman opacity