A theoretical photocathode emittance model including temperature and field effects

A recently developed model of emittance & brightness of photocathode based on "moments" of the electron emission distribution is extended here to non-zero temperatures and fields. Temperature impacts scattering and affects quantum efficiency. Fields affect emission probability and are important in the presence of low-work function coatings characteristic of cesiated dispenser photocathodes under development. Extensions of theoretical models are given, followed by analysis of their comparison with numerical simulations of the intrinsic emittance and brightness of a photocathode. The methodology is designed to facilitate development of photoemission models into comprehensive particle-in-cell (PIC) to address variation in surface coverage and topology.