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

MST1 team, TCV team, Kevin Verhaegh, Bruce Lipschultz, James Harrison, Basil Duval, Chris Bowman, Alexandre Fil, Daljeet Singh Gahle, David Moulton, Omkar Myatra, Artur Perek, Christian Theiler, Mirko Wensing

Research output: Contribution to journalArticlepeer-review

17 Citations (Scopus)
3 Downloads (Pure)


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 - 31 Mar 2021


  • detachment
  • molecules
  • particle balance
  • plasma
  • plasma spectroscopy
  • tokamak divertor


Dive into the research topics of 'A study of the influence of plasma–molecule interactions on particle balance during detachment'. Together they form a unique fingerprint.

Cite this