Fabrication and Measurement of Cesiated Metal Photocathodes

Abstract

A requirement for accelerator applications such as free electron lasers is a high current, high quality electron beam. This is achieved using a photoinjector, where a drive laser modulates the electron emission of a cathode in an electric field. Current photocathodes are plagued with limited efficiency and short lifetime, due to contamination or evaporation of a photosensitive surface layer. An ideal photocathode would have high efficiency in the visible range, long lifetime, and prompt emission. Cathodes with high efficiency typically have limited lifetime, and vice versa. A potential solution is the dispenser cathode, where limited lifetime is overcome by periodic in situ regeneration that restores the photosensitive surface. This project prepares for fabrication of dispenser cathodes by studying properties of cesiated tungsten. A test facility was constructed and used to fabricate and test cesiated tungsten cathodes, whose behavior closely agreed with recently developed photoemission theory at the Naval Research Laboratory.