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TY - UNPB AU - Smedley, J. ED - Meseck, Atoosa ED - McAteer, Meghan ED - Schaa, Volker R.W. ED - V\xF6lker, Jens TI - Using a Protective Layer for Alkali Cathodes J2 - Proc. of ERL2019, Berlin, Germany, 15-20 September 2019 CY - Berlin, Germany T2 - ICFA Advanced Beam Dynamics Workshop on Energy Recovery Linacs T3 - 63 LA - english AB - The photocathode community has been dramatically improving semiconductor cathode performance in recent years, especially in terms of demonstrated mean transverse energy and surface roughness. While the demonstrated QE has also modestly increased, comparatively little effort has been devoted to the parameter most critical to ERL performance - cathode lifetime, especially under high average current operating conditions. This presentation will focus on one approach to improving lifetime - creating a mono-atomic layer of a material with hexagonal pores over the cathode surface. Ideally these pores are too small for Cs to escape the surface, mitigating the effects of both local heating due to the drive laser and ion bombardment induced sputter loss. Further, the coating will limit the diffusion of oxidizers onto the surface, providing some resistance to chemical contamination. The theory of electron transport through the monolayers will be discussed, as well as theory and experimental results for two hexagonal monolayers, graphene and hexagonal BN. The growth of alkali antimonides on both of these materials has been demonstrated, with some loss of QE performance. PB - JACoW Publishing CP - Geneva, Switzerland ER -