AVS 53rd International Symposium
    Plasma Science and Technology Wednesday Sessions
       Session PS2-WeA

Paper PS2-WeA6
Experimental and Theoretical Studies of Atmospheric Pressure Direct Current Microplasma Argon Discharges

Wednesday, November 15, 2006, 3:40 pm, Room 2011

Session: Atmospheric and Microplasmas
Presenter: Q. Wang, University of Houston
Authors: Q. Wang, University of Houston
I. Koleva, Sofia University, Bulgaria
D.J. Economou, University of Houston
V.M. Donnelly, University of Houston
N. Sadeghi, University Joseph Fourier-Grenoble & CNRS, France
Correspondent: Click to Email
A combination of plasma diagnostics and modeling were performed on a slot-type DC microplasma discharge in argon at atmospheric pressures. The gas temperature was measured by N@sub 2@ emission spectroscopy (C -> B transition) by adding small quantities of nitrogen (<200 ppm) into the Ar gas feed. It was found that the rotational population distribution of the N@sub 2@ C-state is not in Boltzmann equilibrium. This is because energy transfer between Ar metastables and N@sub 2@ molecules and electron impact excitation of N@sub 2@ result in two different rotational state distributions (two rotational temperatures) in the N@sub 2@ (C v=0,1,2) state. At the same time, the rotational-to-translational (R-T) energy transfer is not fast enough to equilibrate the rotational distribution with the gas temperature. A two-temperature model was applied to simulate the N@sub 2@ C -> B rotational spectra, and the gas temperature was determined from the lower of the two temperature values. At 760 Torr and 18 kW/cm@super 3@ power density, the gas temperature was between 500 K and 1100 K, depending on position between the electrodes. Electron densities were determined from the spectral line broadening of H-@beta@ emission. The electron density in the bulk plasma was the 10@super 14@ cm@super -3@ range. A model of a DC argon microplasma discharge was in agreement with experimental data. Spatially resolved gas temperature measurements as a function of gas flow through the microplasma also agreed with the model. The gas temperature decreased with increasing gas flow due to convective removal of heat. The gas temperature peaked off axis near the cathode as ions accelerated in the cathode sheath and deposited part of their energy in frequent collisions with the neutral gas.