Evaluation of RF Micro-Discharge Regimes in the Performance of Evanescent-Mode Cavity Resonators

A number of different RF discharge mechanisms may be important in gas breakdown including ionization, secondary electron emission, and field emission.\footnote{A. Semnani et al. Appl. Phys. Lett., \textbf{102}, 174102 (2013)} However, the impact of each of these mechanisms is a strong function of frequency.\footnote{C. E. Muehe, DTIC Document, (1965)} Consequently, estimating power handling in microwave devices needs to carefully consider the operating frequency. In this paper, we study the frequency-dependent impact of these mechanisms in two evanescent-mode cavity resonators\footnote{K. Chen et al. International Microw. Symp., (2013)} operating at 1 GHz and 50 GHz. The key characteristic of these resonators, unlike typical cavities, is that the resonant electric field is primarily concentrated in a relatively small volume. The smallest dimension of this volume is referred to as critical gap and typically is in the order of a few $\mu$m. The two resonators in this study have the same critical gap size of $19~\mu $m which results in the same gas critical frequency of 6.3 GHz in atmospheric pressure. Plasma simulation results as well as the electromagnetic simulations considering plasma are presented and compared for both cases which operate in different discharge mechanisms.