Speaker
Description
High-gradient operation in photocathode RF guns enables brighter beams and is often combined with high--quantum-efficiency semiconductor photocathodes such as Cs$_2$Te. To study photoemission from Cs$_2$Te under these conditions, we develop a Monte Carlo model of carrier transport and emission in a thin-film semiconductor that uses electronic, phonon, dielectric, and optical properties obtained from density-functional-theory calculations, together with a thin-film interference model for the optical excitation. The photoemission model is coupled to photoinjector simulations of the L-band gun at the Argonne Wakefield Accelerator and benchmarked against recent high-gradient measurements of quantum efficiency versus accelerating gradient and RF phase using a 262~nm UV laser. By comparing measurement and simulation, we identify how strong RF fields modify carrier transport and escape probability in Cs$_2$Te and how space charge field affects the emission. We also discuss the implications of these effects for achievable beam brightness in high-gradient guns.
Funding Agency
This work was supported by the Laboratory Directed Research and Development program at LANL; U.S. DOE Office of Science HEP awards DE-SC0021928, DE-SC0024445; and ANL contract DE-AC02-06CH11357
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