Studies of Electrode-Plasma Effects on Breakdown at RF Frequencies

The goals and objectives of this project focus on simulations and basic research for understanding fundamental details of processes at the cathode such as electron emission, outgassing, and breakdown under RF conditions for vacuum electronics and high power applications. Details relating the role of both photoemission and photoionization are included in the breakdown physics, with the former process shown to be dominant at atmospheric pressure. Other aspects such as space-charge, proximity- and density-dependent dynamic screening, out-gassing and plasma formation are probed based on many-body charge transport coupled with the Fast Multipole Method, as they all directly affect the efficiency and reliability of high power microwave (HPM) systems. Comprehensive electron emission included evaluations of material properties (e.g., workfunction), and internal potentials that were folded into the Schrodinger Wave Equation for transmission probability analysis. In addition, surface changes (e.g., oxide over-layer, adsorbates) that alter material work function, thus adversely impacting electron emission, are also studied based on Density Functional Theory. Additionally, the effort this year included simulations to study carbon fibers, which were shown to significantly reduce outgassing. Also, geometric variations in emitter structures from an atomistic standpoint, not just macroscopic field enhancements, were considered through numerical analysis. Finally, an important question that was addressed based on fundamental physics and materials science, was the role of adsorbates on the Secondary Electron Yield (SEY).