Combining theory and experiment to model electron emission from polycrystalline tungsten cathode surfaces

In this work, we have constructed a simplified statistical model of electron emission for polycrystalline W cathode surfaces. Construction of this emission model requires knowledge of which surfaces are present, the area fractions of each surface, and the work function values of each surface. To create our model, we have drawn upon previous work which used Density Functional Theory (DFT) to explore the effect of O, Ba and Ba-O adsorbates on the work function and stability of W surfaces, and have combined these DFT data with experimentally-derived surface grain orientations from polycrystalline W cathodes obtained using electron backscatter diffraction (EBSD). Using our model, we have constructed semiempirical cathode Miram curves and practical work function distribution (PWFD) curves based on DFT data, EBSD data of real cathode surfaces, and well-known empirical emission equations.