First-Principles Model of Miram Curve from Polycrystalline Tungsten Cathodes

Previously, we constructed a first-principles statistical model to predict the non-uniform emission from polycrystalline tungsten cathodes, which incorporated microstructure characterization results, crystallographic-orientation-specific work function values via density functional theory (DFT), and temperature-limited (TL) emission physics. This previous model could only predict the TL region of the Miram curve and not the transition between TL and full-space-charge-limited (FSCL) regions. In this work, we have expanded our model to predict emission along the entire Miram curve, including the transition from TL to FSCL regions, without any empirical assumptions on work function distribution or empirical emission equations. This more advanced model provides a pathway to understanding the complex physics of emission from heterogeneous cathode surfaces, which is a key issue for the commercial production and use of thermionic cathodes in vacuum electronic devices.