Effect of gas heating on the spatial structure of a traveling wave sustained Ar discharge

In this work we report a theoretical and experimental study of the influenc e of gas heating on the spatial structure of a microwave Ar discharge susta ined by a traveling surface wave. The theoretical analysis is based on a di scharge model which couples in a self-consistent way electron and heavy par ticle kinetics, discharge electrodynamics, and gas thermal balance. The set of coupled equations used includes the electron Boltzmann equation, the ra te balance equations for the most important excited species and charged par ticles, the gas thermal balance equation, and the equations describing wave propagation and power dissipation. The principal collisional and radiative processes which determine the populations in the Ar(3p(5)4s) and Ar(3p(5)4 p) levels are accounted for. The field strength necessary for steady-state discharge operation is obtained from the balance between total rates of ion ization (including direct and step-wise ionization and energy pooling react ions) and of electron loss due to the diffusion to the wall and bulk recomb ination. The gas thermal balance equation is solved using the experimentall y obtained wall temperature as a boundary value. The model determines the a xial discharge structure, i.e., the axial variation of the main discharge q uantities. An experimental validation of the model predictions is achieved using probe techniques, emission spectroscopy, and radiophysics methods. In particular, spatially resolved measurements of the electron energy distrib ution function, gas temperature, wave electric field components, and wave a ttenuation have been carried out. As a result of the nonuniform wave power absorption along the wave path the gas temperature varies along the column. This variation induces axial changes in the neutral density and the reduce d electric field which strongly affects the particle kinetics and the disch arge electrodynamics, as demonstrated here. (C) 2001 American Institute of Physics.