AVS 52nd International Symposium
    Plasma Science and Technology Wednesday Sessions
       Session PS-WeA

Paper PS-WeA10
Diagnostics and Simulations of a Helium Micro-Discharge at Atmospheric Pressure

Wednesday, November 2, 2005, 5:00 pm, Room 302

Session: Atmospheric Plasmas and Microdischarges
Presenter: Q. Wang, University of Houston
Authors: Q. Wang, University of Houston
D.J. Economou, University of Houston
V.M. Donnelly, University of Houston
I. Koleva, University of Sofia
Correspondent: Click to Email
Spatially resolved measurements (resolution ~ 6 µm) were taken across an L=200 µm slot-type discharge in an atmospheric pressure direct current helium microplasma. Gas temperature profiles were determined from N@sub 2@ emission rotational spectroscopy. Stark splitting of the hydrogen Balmer-@beta@ line was used to investigate the electric field distribution in the cathode sheath region. Electron densities were evaluated from the analysis of the spectral line broadenings of H-@beta@ emission. The gas temperature was between 350 and 550 K, peaking nearer the cathode and increasing with power. The electron density in the bulk plasma was in the range 4-7 x 10@super 13@ cm@super-3@. The electric field peaked at the cathode (~60 kV cm@super -1@) and decayed to small values over a distance of ~ 50 µm (sheath edge) from the cathode. These experimental data are in generally good agreement with a self-consistent one-dimensional model of the discharge. The influence of gas heating on the discharge properties (such as current-voltage characteristic, cathode and anode sheath profiles), was also investigated. As the discharge current increased, the simulations indicate that the anode sheath turned from a positive ion sheath to an electron sheath, with concomitant changes in the sheath electric field profile and direction. This can be explained, based on the balance of charged particle gain and loss. Gas flow does not have a significant effect on gas temperature because of the high thermal conductivity of helium.