Active Species in Plasmas Produced by Microwave Cavities
DOI:
https://doi.org/10.9734/bpi/mono/978-93-91595-70-8/CH8Keywords:
Microwave plasmas sources, low pressure, atmospheric gas pressure, Ar metastable atoms densities, N2 vibrational temperatures, LTE plasmasAbstract
The microwave plasmas have been studied from low to atmospheric gas pressure in rare gases (mainly Ar) and gas mixtures containing N2. At low gas pressure, it is found the surface wave plasmas, produced by patented launchers Surfatron and Surfaguide, which were developped by Michel Moisan in the Plasmas Lab. of the Montreal Univ. since 1975 [1]. At high gas pressure from a few Torr up to the atmospheric gas pressure, the SW plasmas Surfatron at low power and Surfaguide at high power are still operating. It is also given the results obtained by a resonant cavity in N2-xO2 with x=0-20%.
It is presently reported the detection of plasma active species obtained by optical spectroscopy.
The main used frequency was 2450 MHz .The plasma power could vary from a few Watts (surfatron) up to a few 103 Watts (Surfaguide, resonant cavity). The plasma can be produced in a static gas flow, mainly at low gas pressure and up to several liters par minute (slpm) at high gas pressures.
The optical spectroscopy was setup first to obtain the spatial distribution of radiative species, mainly in Ar gas at low gas pressure in the perspective to characterize the SW plasmas. Then the radial distribution of Ar metastable density was obtained by resonant optical absorption.
At medium (a few Torr) up to the atmospheric gas pressure, flowing HF plasmas (resonant cavity) and SW plasmas were produced in gas mixtures with N2 to produce N-atoms and other active species such as N2 metastable molecules and N2+ ions which are studied inside the plasma and in afterglow conditions. It is dicussed the kinetics reactions relating the N2( X,v) , N2(A,v’) , N2(B,v’), N2(C,v’), N2+ (X,v’) and N2+ (B,v’) interfering in the radiative emissions of N2 (B,v’) , N2 (C,v’) and N2+ (B,v’) states.
At atmospheric gas pressure, the plasmas are mainly in Ar dominant gas, more easy to ionize. In these conditions, the plasmas are characterized by the electron density and the gas temperature which will be reported for specific microwave plasmas sources. Depending on plasmas parameters as powers, flow rates and exit tube diameters, the plasmas were more and less near the Local Thermodynamic Equilibrium (LTE) as demonstrated in Montreal Univ., Lisbon IST and Cordoba Univ.
