A study of the influence of plasma–molecule interactions on particle balance during detachment

TCV Team, MST1 team

Research output: Contribution to journalArticlepeer-review


In this work we provide experimental insights into the impact of plasma–molecule interactions on the target ion flux decrease during divertor detachment achieved through a core density ramp in the TCV tokamak. Our improved analysis of the hydrogen Balmer series shows that plasma–molecule processes are strongly contributing to the Balmer series intensities and substantially alter the divertor detachment particle balance. We find that Molecular Activated Recombination (MAR) ion sinks from H2+ (and possibly H) are a factor ∼5 larger than Electron–Ion Recombination (EIR) and are a significant contributor to the observed reduction in the outer divertor ion target flux. Molecular Activated Ionisation (MAI) appears to be substantial during the detachment onset, but further research is required into its magnitude given its uncertainty. Plasma–molecule interactions enhance the Balmer line series emission strongly near the target as detachment proceeds. This indicates enhancements of the Lyman series, potentially affecting power balance in the divertor. As those enhancements vary spatially in the divertor and are different for different transitions, they are expected to result in a separation of the Lyβ and Lyα emission regions. This may have implications for the treatment and diagnosis of divertor opacity. The demonstrated enhancement of the Balmer series through plasma–molecule processes potentially poses a challenge to using the Balmer series for understanding and diagnosing detachment based only on atom–plasma processes.

Original languageEnglish
Article number100922
Number of pages8
JournalNuclear Materials and Energy
Early online date16 Feb 2021
Publication statusPublished - 1 Mar 2021

Bibliographical note

Funding Information:
This work has received support from EPSRC Grant EP/T012250/1 and has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014–2018 and 2019–2020 under grant agreement No 633053 . This work as supported in part by the Swiss National Science Foundation . The views and opinions expressed herein do not necessarily reflect those of the European Commission.

Crown Copyright © 2021 Published by Elsevier Ltd.


  • Detachment
  • Molecules
  • Particle balance
  • Plasma
  • Plasma spectroscopy
  • Tokamak divertor

Cite this