Electron density and recombination rate measurements in CO-seeded optically pumped plasmas
Electron production rate and electron density in cold optically pumped CO{endash}Ar and CO{endash}N{sub 2} plasmas in the presence of small amounts of O{sub 2} and NO have been measured using a Thomson discharge probe and microwave attenuation. Nonequilibrium ionization in the plasmas is produced by an associative ionization mechanism in collisions of highly vibrationally excited CO molecules. It is shown that adding small amounts of O{sub 2} or NO (50{endash}100 mTorr) to the baseline gas mixtures at P=100torr results in an increase of the electron density by up to a factor of 20{endash}40 (from n{sub e}{lt}10{sup 10}cm{sup {minus}3} to n{sub e}=(1.5{endash}3.0){times}10{sup 11}cm{sup {minus}3}). This occurs while the electron production rate either decreases (as in the presence of O{sub 2}) or remains nearly constant within a factor of 2 (as in the presence of NO). It is also shown that the electron{endash}ion recombination rates inferred from these measurements decrease by two to three orders of magnitude compared to their baseline values (with no additives in the cell), down to {beta}{congruent}1.5{times}10{sup {minus}8}cm{sup 3}/s with 50{endash}100 mTorr of oxygen or nitric oxide added to the baseline CO{endash}Ar mixture, and {beta}{congruent}(2to3){times}10{sup {minus}7}cm{sup 3}/s with 75{endash}100 mTorr of O{sub 2} or NO added to the baseline CO{endash}N{sub 2} mixture. The overall electron{endash}ion removal rates in the presence of equal amounts of O{sub 2} or NO additives turn out to be very close, which shows that the effect of electron attachment to oxygen at these conditions is negligible. These results suggest a novel method of electron density control in cold laser-sustained steady-state plasmas and open a possibility of sustaining stable high-pressure nonequilibrium plasmas at high electron densities and low plasma power budget. {copyright} 2001 American Institute of Physics.
- Sponsoring Organization:
- (US)
- OSTI ID:
- 40203696
- Journal Information:
- Journal of Applied Physics, Vol. 89, Issue 11; Other Information: DOI: 10.1063/1.1359754; Othernumber: JAPIAU000089000011005903000001; 072109JAP; PBD: 1 Jun 2001; ISSN 0021-8979
- Publisher:
- The American Physical Society
- Country of Publication:
- United States
- Language:
- English
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