Impact of nitrogen molecular breakup on divertor conditions in JET L-mode plasmas using SOLPS-ITER

Journal Article · Sat Apr 12 00:00:00 EDT 2025 · Nuclear Materials and Energy

DOI:https://doi.org/10.1016/j.nme.2025.101929· OSTI ID:2586838

Mäenpää, R. ^[1]; Kumpulainen, H. ^[1]; Groth, M. ^[1]; Horsten, N. ^[2]; Reiter, D. ^[3]; Romazanov, J. ^[4]; Lomanowski, B. ^[5]; Brezinsek, S. ^[4]; Karhunen, J. ^[6]; Lawson, K. D. ^[7]; Meigs, A. G. ^[7]; Menmuir, S. ^[7]; Shaw, A. ^[7]

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1. Aalto Univ. (Finland)
2. Katholieke Univ. Leuven (Belgium)
3. Heinrich-Heine-Univ. (Germany)
4. Forschungszentrum Juelich (Germany)
5. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
6. VTT Technical Research Centre of Finland, Espoo (Finland)
7. UK Atomic Energy Authority (UKAEA), Culham (United Kingdom)

SOLPS-ITER simulations of nitrogen-seeded, low-confinement mode plasmas in the Joint European Torus (JET) predict that the electron temperature in the low-field side (LFS) divertor leg is reduced locally by up to an order of magnitude when nitrogen is assumed to recycle as molecules (N₂) instead of atoms using a fixed nitrogen injection rate. The LFS divertor temperature reduction under the assumption of molecular recycling occurs due to a three-step mechanism: (1) the plasma penetration of nitrogen atoms is increased due to the strong triple bond of the N₂ molecule and the kinetic energy release in the dissociation event, both mechanisms contributing equally, (2) the abundance of (particularly multiply-charged) nitrogen ions in the divertor is increased and (3) the electron temperature is reduced due to the increase in radiation (by up to a factor of 4) from nitrogen ions. Setting the volume-integrated nitrogen radiated power to a constant value (0.6 MW) instead of the nitrogen injection rate, SOLPS-ITER predicts under the molecular nitrogen recycling assumption that the peak line-integrated N II, N III and N IV intensities in the LFS divertor are approximately within 15%, 35% and 5%, respectively, of the reference atomic nitrogen recycling case. The predicted peak N II, N III and N IV intensities under either assumption are within 30%, 65% and 5%, respectively, of measurements using the vertically viewing mirror-link divertor spectrometer (Meigs et al., 2010) in nitrogen-seeded JET L-mode plasmas (Lomanowski et al., 2019). ERO2.0 simulations using a constant nitrogen seeding rate on static background plasma solutions from EDGE2D-EIRENE (previously presented in Mäenpää et al., (2022), revised here to include fast reflections) predict that N II to N IV line emission is increased by 20% to 30% when nitrogen is assumed to recycle as molecules, demonstrating the importance of considering the effect of molecular dissociation reactions on the divertor plasma in a self-consistent manner.

• 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: 2586838
• Journal Information: Nuclear Materials and Energy, Journal Name: Nuclear Materials and Energy Vol. 43; ISSN 2352-1791
• Publisher: Elsevier BV
• Country of Publication: United States
• Language: English

Related Subjects

Divertor
JET
L-mode
Molecule
Nitrogen
Recycling
SOLPS-ITER