The influence of different quantum yields for photons and secondary emission yields for ions striking a surface is investigated. Using a one-dimensional particle-in-cell simulation, these secondary emission coefficients are varied to observe the impact on discharge current. The discharge is assumed to occur in pure helium gas at a pressure of 75 torr. To handle binary particle interactions, the Direct Simulation Monte Carlo (DSMC) method is utilized. The model includes electron-neutral interactions, neutral-neutral interactions, and photon-neutral interactions. It is observed that the discharge current in the early stages of discharge is heavily dependent upon the quantum yield due to photon impact. In the later stages of discharge, the current depends on both the quantum yield and secondary emission coefficient for ion impact.
In most models of vacuum breakdown, there is some initial emission of electrons from the cathodic surface, usually employing some form of Fowler-Nordheim emission. While this may be correct for 'textbook' surfaces, it is generally unreliable for real surfaces and fitted parameters are often used. For example, the beta employed is generally unphysical based on usual definitions (e.g., it incorporates more, but unexplained, physics than just a geometry-based field concentration effect). In this work, we describe experimental efforts to better characterize which surface structure parameters influence the vacuum field emission current.