Advanced photocathode simulation and theory

A low work function dispenser type photocathode that is self-annealing or repairing would have a substantial impact on Free Electron Lasers (FELs). On such a cathode, the emitting surface is constantly renewed by replenishment of low-work-function material. A photo-dispenser cathode should operate at a relatively low temperature compared to a conventional dispenser cathode and is anticipated to be robust and long-lived. Coatings cause a reduction in the transport barrier experienced by the electrons through a complex modification of the potential at the surface, e.g., a reduction in work function due to dipole effects. In this work, we describe our theoretical program to address such effects, as part of a program concurrent with experimental efforts to develop dispenser cathodes for use in high power RF photoinjectors. In particular, we discuss the development of a generalised Transmission Coefficient approach, its application to photoemission from metals, and progress towards developing a methodology for the determination of the general emission barrier profile.