Modeling of microwave discharges in the presence of plasma resonances

Modeling of surface-wave discharges with cylindrical symmetry

This paper presents the modeling of microwave (2.45GHz) discharges with cylindrical symmetry, produced in the absence of an external magnetic field by TM00 surface waves (SW) within either cylindrical or coaxial structures. A stationary, one-dimensional (radial) moment model (including the continuity and the momentum-transfer equations for electrons and positive ions, and the electron mean energy transport equations) is solved self-consistently coupled to Poisson's equation for the space-charge electrostatic field and the appropriated Maxwell's equations for the SW electromagnetic field. The model is solved for argon discharges over a broad range of operating conditions: Average electron densities from 10;{11}to3x10;{12}cm;{-3} and gas pressures from 10;{-2}to5Torr . Results are compared to those of a simplified classical model that disregards charge separation near discharge boundaries, ignoring also the development of electron-plasma resonances caused by the severe electron density gradients within space-charge sheath regions. Simulations show that the presence of a sheath-resonance region has a strong influence on the values of the SW attenuation constant, particularly at low pressures and high electron densities, affecting also the local budget of the discharge power deposition (hence discharge maintenance).

Self-consistent system of equations for a kinetic description of the low-pressure discharges accounting for the nonlocal and collisionless electron dynamics

In low-pressure discharges, where the electron mean free path is larger or comparable with the discharge length, the electron dynamics is essentially nonlocal. Moreover, the electron energy distribution function (EEDF) deviates considerably from a Maxwellian. Therefore, an accurate kinetic description of the low-pressure discharges requires knowledge of the nonlocal conductivity operator and calculation of the non-Maxwellian EEDF. The previous treatments made use of simplifying assumptions: a uniform density profile and a Maxwellian EEDF. In the present study, a self-consistent system of equations for the kinetic description of nonlocal, nonuniform, nearly collisionless plasmas of low-pressure discharges is derived. It consists of the nonlocal conductivity operator and the averaged kinetic equation for calculation of the non-Maxwellian EEDF. The importance of accounting for the nonuniform plasma density profile on both the current density profile and the EEDF is demonstrated.

Parameters and equilibrium profiles for large-area surface-wave sustained plasmas

The equilibrium profiles of the plasma parameters of large-area rf discharges in a finite-length metal-shielded dielectric cylinder are computed using a two-dimensional fluid code. The rf power is coupled to the plasma through edge-localized surface waves traveling in the azimuthal direction along the plasma edge. It is shown that self-consistent accounting for axial plasma diffusion and radial nonuniformity of the electron temperature can explain the frequently reported deviations of experimentally measured radial density profiles from that of the conventional linear diffusion models. The simulation results are in a good agreement with existing experimental data obtained from surface-wave sustained large-diameter plasmas.