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

R. Mäenpää; H. Kumpulainen; M. Groth; N. Horsten; D. Reiter; J. Romazanov; B. Lomanowski; S. Brezinsek; J. Karhunen; K. D. Lawson; A. G. Meigs; S. Menmuir; A. Shaw

doi:10.1016/j.nme.2025.101929

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

R. Mäenpää^*, H. Kumpulainen, M. Groth, N. Horsten, D. Reiter, J. Romazanov, B. Lomanowski, S. Brezinsek, J. Karhunen, K. D. Lawson, A. G. Meigs, S. Menmuir, A. Shaw

^*Corresponding author for this work

BA4511 Fusion energy

Research output: Contribution to journal › Article › Scientific › peer-review

Abstract

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.

Original language	English
Article number	101929
Journal	Nuclear Materials and Energy
Volume	43
DOIs	https://doi.org/10.1016/j.nme.2025.101929
Publication status	Published - Jun 2025
MoE publication type	A1 Journal article-refereed

Funding

This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No 101052200 — EUROfusion). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them. This work made use of the Triton cluster, part of the Science-IT project at Aalto University. N. Horsten is a postdoctoral fellow of the Research Foundation Flanders (FWO) under grant number 12AES24N. We gratefully acknowledge the invaluable code support provided by Dr. Xavier Bonnin and Dr. David Coster.

Keywords

Divertor
JET
L-mode
Molecule
Nitrogen
Recycling
SOLPS-ITER

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

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Mäenpää, R., Kumpulainen, H., Groth, M., Horsten, N., Reiter, D., Romazanov, J., Lomanowski, B., Brezinsek, S., Karhunen, J., Lawson, K. D., Meigs, A. G., Menmuir, S., & Shaw, A. (2025). Impact of nitrogen molecular breakup on divertor conditions in JET L-mode plasmas using SOLPS-ITER. Nuclear Materials and Energy, 43, Article 101929. https://doi.org/10.1016/j.nme.2025.101929

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

abstract = "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 M{\"a}enp{\"a}{\"a} 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.",

keywords = "Divertor, JET, L-mode, Molecule, Nitrogen, Recycling, SOLPS-ITER",

author = "R. M{\"a}enp{\"a}{\"a} and H. Kumpulainen and M. Groth and N. Horsten and D. Reiter and J. Romazanov and B. Lomanowski and S. Brezinsek and J. Karhunen and Lawson, {K. D.} and Meigs, {A. G.} and S. Menmuir and A. Shaw",

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doi = "10.1016/j.nme.2025.101929",

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T1 - Impact of nitrogen molecular breakup on divertor conditions in JET L-mode plasmas using SOLPS-ITER

AU - Mäenpää, R.

AU - Kumpulainen, H.

AU - Groth, M.

AU - Horsten, N.

AU - Reiter, D.

AU - Romazanov, J.

AU - Lomanowski, B.

AU - Brezinsek, S.

AU - Karhunen, J.

AU - Lawson, K. D.

AU - Meigs, A. G.

AU - Menmuir, S.

AU - Shaw, A.

PY - 2025/6

Y1 - 2025/6

N2 - 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.

AB - 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.

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KW - JET

KW - L-mode

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KW - Nitrogen

KW - Recycling

KW - SOLPS-ITER

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

Abstract

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Keywords

UN SDGs

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