AVS 51st International Symposium
    Plasma Science and Technology Thursday Sessions
       Session PS-ThM

Paper PS-ThM7
Comparison of Atmospheric Pressure Helium Plasmas Operating in the Abnormal Glow and Recovery Modes

Thursday, November 18, 2004, 10:20 am, Room 213A

Session: Atmospheric and Microdischarges
Presenter: X. Yang, University of California, Los Angeles
Authors: R.F. Hicks, University of California, Los Angeles
X. Yang, University of California, Los Angeles
M. Moravej, University of California, Los Angeles
G. Nowling, University of California, Los Angeles
S. Babayan, Surfx Technologies
J. Penelon, Surfx Technologies
Correspondent: Click to Email
The properties of a radio-frequency atmospheric pressure plasma fed with helium and nitrogen were investigated. Two discharge modes were identified with current-voltage measurements and optical emission spectroscopy. After the discharge was struck, the plasma entered an abnormal glow regime with a maximum power density of 4.8 W/cm@super 2@, corresponding to a current density and voltage of 0.73 A/cm@super 2@ and 317 V. Further increasing the power caused the plasma to shift into a new "recovery" mode with a dramatic reduction of current and voltage and a surge in power to 416 W/cm@super 2@. This transition is attributed to sheath breakdown. The spatial emission intensity between the electrodes in the abnormal glow reached a maximum 0.25 mm away from the electrodes. In contrast, the recovery mode exhibited maximum emission intensity at the edge of the electrodes, with an intensity 200 times higher than that of the abnormal glow. The neutral gas temperature measured in the abnormal and recovery modes equaled 75 and 250 °C, respectively. The density of nitrogen atoms produced in the plasma was determined by measuring the temporal decay rate of the first-positive emission of nitrogen molecules, i.e., N@sub 2@(B) @super __@> N@sub 2@(A) + h@nu@. It was found that with 0.4 vol.% N@sub 2@, the abnormal and recovery modes produced 1.0x10@super 16@ and 1.7x10@super 16@ cm@super -3@ N atoms at maximum power densities of 4.8 and 416 W/cm@super 2@, respectively. These results indicate that the abnormal glow is more efficient at dissociating molecules into reactive species. A thorough discussion of the physics and chemistry of the atmospheric pressure plasma will be provided at the meeting.