Effects of water addition on OH radical generation and plasma properties in an atmospheric argon microwave plasma jet

Journal Article · Thu Sep 01 00:00:00 EDT 2011 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.3632970· OSTI ID:22036712

Srivastava, Nimisha; Chuji, Wang ^[1]

---

1. Department of Physics and Astronomy and the Energy Institute, Mississippi State University, Mississippi State, Mississippi 39762 (United States)

Water vapor was added to the feeding gas of a continuous atmospheric argon (Ar) microwave plasma jet to study its influence on plasma shape, plasma gas temperature, and OH radical concentrations. The plasma jet was created by a 2.45 GHz microwave plasma source operating at constant power of 104 W with H{sub 2}O-Ar mixture flow rate of 1.7 standard liter per minute (slm). With an increase in the H{sub 2}O/Ar ratio from 0.0 to 1.9%, the plasma jet column length decreased from 11 mm to 4 mm, and the plasma jet became unstable when the ratio was higher than 1.9%; elevation of plasma gas temperature up to 330 K was observed in the plasma temperature range of 420-910 K. Optical emission spectroscopy showed that the dominant plasma emissions changed from N{sub 2} in the pure Ar plasma jet to OH with the addition of water vapor, and simulations of emission spectra suggested non-Boltzmann distribution of the rotational levels in the OH A-state (v'=0). Spatially resolved absolute OH number densities along the plasma jet axis were measured using UV cavity ringdown spectroscopy of the OH (A-X) (0-0) band in the H{sub 2}O/Ar ratio range of 0.0-1.9%. The highest OH number density is consistently located in the vicinity of the plasma jet tip, regardless of the H{sub 2}O/Ar ratio. OH number density in the post-tip region follows approximately an exponential decay along the jet axis with the fastest decay constant of 3.0 mm in the H{sub 2}O/Ar ratio of 1.5%. Given the low gas temperature of 420-910 K and low electron temperature of 0.5-5 eV along the jet axis, formation of the OH radical is predominantly due to electron impact induced dissociation of H{sub 2}O and dissociative recombination of H{sub 2}O{sup +} resulting from the Penning ionization process.

• OSTI ID: 22036712
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 5 Vol. 110; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ARGON
ELECTRON TEMPERATURE
EMISSION SPECTRA
EMISSION SPECTROSCOPY
GHZ RANGE
HYDROXYL RADICALS
ION TEMPERATURE
IONIZATION
MICROWAVE RADIATION
PLASMA
PLASMA DENSITY
PLASMA DIAGNOSTICS
PLASMA INSTABILITY
PLASMA JETS
PLASMA SIMULATION
SCANNING LIGHT MICROSCOPY
WATER