Effects of humidity on the dynamics and electron recombination of a pin-to-pin discharge in He + H2O at atmospheric pressure

Alexandra Brisset, Benjamin Harris, Aaron Dickenson, Kari Niemi, James Walsh, Erik Wagenaars*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Control of the plasma chemistry is essential for the effectiveness of atmospheric pressure plasmas in many applications. For this, the effects of the humidity of the feed gas on the discharge chemistry need to be considered. Detailed studies are scarce and many of them are dominated by surface interactions, obscuring any volume effects. Here, a negative nanosecond pulsed discharge is generated in a pin-pin 3 mm gap geometry in He + H2O that enables the study of volume kinetics due to minimal surface area. The effect of humidity on the discharge development, electric field and electron density is investigated through experiments and modelling. It is found that the presence of water vapour affects both the electron density at the start of the pulse (remaining from the previous pulse) and the ionisation rates during the ignition phase, leading to a complex dependence of the discharge development speed depending on the water concentration. The electron decay is studied using the 0D global kinetics model GlobalKin. The dominant reactions responsible for the electron decay depending on the concentration of water vapour are determined by comparing experimental and simulated results and these reactions are grouped in simplified kinetic models. It is found that with water concentrations increasing from 0 to 2500 ppm, the complexity of the dominant reactions increases with in particular O2+, H2O3+ and water clusters becoming important for high water concentrations. This work also provides experimental data for validation of kinetic models of plasmas in controlled environments.

Original languageEnglish
Article number045008
Number of pages12
JournalPlasma Sources Science and Technology
Issue number4
Publication statusPublished - 14 Apr 2022

Bibliographical note

Funding Information:
This work was supported by the EP/S026584/1 and EP/S025790/1 research programs. The authors would like to thank Professor Mark Kushner for providing the GlobalKin code used in this work, and for continued useful discussions.

Publisher Copyright:
© 2022 The Author(s). Published by IOP Publishing Ltd.


  • electric field
  • electron recombination
  • nanosecond discharge
  • Stark broadening

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