Ionization wave propagation in a He plasma jet in a controlled gas environment

Characterizing ionization wave propagation in low temperature plasma jets is critical to predicting production of reactive species and plasma–surface interactions for biomedical applications and surface functionalization. In this paper, results from optical emission and laser induced fluorescence me...

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Bibliographic Details
Published in:Journal of applied physics 2020-08, Vol.128 (8)
Main Authors: Lietz, Amanda M., Barnat, Edward V., Foster, John E., Kushner, Mark J.
Format: Article
Language:English
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
Biomedical materials
Charge coupled devices
electron density
Electron density measurement
electron impact ionization
Emission
Helium
Ionization potentials
Ionization waves
ions and properties
Laser induced fluorescence
Low temperature
Mathematical models
numerical methods
photoelectron emission
Photoelectrons
Photoionization
Plasma
plasma confinement
Plasma jets
Plasma material interactions
Propagation
Wave propagation
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Summary:Characterizing ionization wave propagation in low temperature plasma jets is critical to predicting production of reactive species and plasma–surface interactions for biomedical applications and surface functionalization. In this paper, results from optical emission and laser induced fluorescence measurements of the ionization wave in a He plasma jet operating in a controlled gas environment are discussed and used for comparison with numerical modeling. The ionization wave was observed using ICCD (Intensified Charge Coupled Device) imaging and characterized by time and spatially resolved electron density measurements using laser-collision-induced fluorescence. The plasma jet was initially characterized using pure He (nominally at 200 Torr), while varying pressure and voltage. When operating in pure He, the ionization wave broadly expands exiting the plasma tube. Increasing the operating pressure reduces the speed and isotropic expansion of the ionization wave. The jet operated with a humid He shroud was also studied. The humid He shroud results in the electron density increasing and having an annular profile due to the lower ionization potential of H2O compared to He and localized photoionization in the mixing region. Numerical modeling highlighted the importance of resonance radiation emitted by excited states of He, photoelectron emission from the quartz tube, and the kinetic behavior of the electrons produced by photoionization ahead of the ionization front.
ISSN:0021-8979
1089-7550
DOI:10.1063/5.0020264