Microwave Argon Plasma Torch

A theoretical and experimental investigation of a microwave (2.45 GHz) Argon plasma torch driven by a surface wave is presented. The theoretical model couples in a self-consistent way the wave electrodynamics and the electron and heavy particle kinetics. The set of coupled equations includes: Maxwell's equations, the electron Boltzmann equation, including electron-electron collisions, and the particle balance equations for electrons, excited atoms (4s, 4p, 3d, 5s, 5p, 4d, 6s), and atomic (Ar$^{+})$ and molecular ions (Ar$_{2}^{+})$. The input parameters of the model are: gas pressure (760 Torr), plasma radius ($R$ = 0.75 cm), dielectric permittivity ($\varepsilon _{d}$ = 4.0) and tube thickness (d = 0.15 cm) as well as the measured axial profile of the gas temperature (3500 K - 1500 K). The latter was determined from measurements of the rotational temperature of the OH molecular band in the range 306 - 315 nm. Phase and amplitude sensitive recording provides the data for the axial wavenumber and wave attenuation coefficient. The wavenumber decreases along the generated plasma torch. The electron density (N$_{e})$ axial profile as determined from measurements of H$_{\beta }$ Stark broadening is in agreement with the theoretical one.