Characterization of microwave plasma for electromagnetic modeling in processing applications

Computer modeling is a powerful tool for the design of systems and processes of microwave power engineering; however, its application to devices containing plasma is still limited. Electromagnetic properties of plasma are difficult to measure, and their dependence on operational parameters of the device are system dependent. In this paper, we describe a simple model in which microwave plasma is represented by electric conductivity, frequency of electron-neutral collisions, and plasma frequency. These characteristics are compatible with input media parameters of the finite-difference time-domain (FDTD) technique. To overcome the uncertainty for input generation, we use a series of assumptions to link the input parameters to electron density, average electron velocity, electron collision cross-section, gas temperature, electron temperature, and further, to microwave power and pressure. We discuss the steps to approximate the input parameters based on available data or informed calculations. We demonstrate this approach for an FDTD model of a cylindrical cavity containing plasma in a coaxial quartz vessel and validate the model against analytical results. Simulated patterns of the electric field and frequency responses of the reflection coefficient show that the proposed approach may be practical for determining the operational bounds of applicators with plasma and assisting in their CAD.