UC Merced

Traditional plasma systems typically operate at low pressures and centimeter scale reactors. However, during the last decade or so, there is an active interest in the downscaling of devices and plasmas are no exception. Because of the popular pd (pressure times gap size) scaling, such plasmas have to operate at or near atmospheric pressure and are referred to as microplasmas or microdischarges. While downscaling the plasma device, field emission of electrons and their interaction with micro discharge due to high electric fields has shown to affect both pre-and post-breakdown operation of these discharge. In this context, we present computational data for the ionization coefficient (α) at high electric fields. A zero-dimensional Monte Carlo code is used to determine the variation of α as a function of electric field for various gases to use in device-level models. Results are also presented for the dependence of alpha (α) in a spatially varying electric field. While alpha (α) represents the volume process in a discharge, the most important surface process in microdischarge is field emission which is characterized by the field enhancement factor (β). Comparison of experimental data with theoretical data for argon, hydrogen, carbon dioxide and dry air are presented to predict an inverse dependence of βeff on electric field.

Finally, device-level models are also formulated for the post-breakdown operation of field emission assisted microdischarges as motivated by novel cathodes with excellent field emission properties. In this context we present a non-linear sheath model for direct current field emitted assisted microdischarges. The main focus of this work is to develop a self-consistent sheath model that includes the effects of field induced electron emission without assuming a linear electric field. The results obtained from the non-linear sheath model for various parameters including current-voltage characteristics, and current density profiles of ion/electro are validated with PIC/MCC simulation of an argon microdicharge.