The Role of Low Intrinsic Emittance in Modern Photoinjector Brightness

Abstract

Reducing the intrinsic emittance of photocathodes is one of the most promising routes to improving the brightness of electron sources. However, when emittance growth occurs during beam transport (for example, due to space-charge), it is possible that this emittance growth overwhelms the contribution of the photocathode and, thus, in this case source emittance improvements are not beneficial. Using multi-objective genetic optimization, we investigate the role intrinsic emittance plays in determining the final emittance of several space-charge dominated photoinjectors, including those for high repetition rate free electron lasers and ultrafast electron diffraction. We introduce a new metric to predict the scale of photocathode emittance improvements that remain beneficial and explain how additional tuning is required to take full advantage of new photocathode technologies. Additionally, we determine the scale of emittance growth due to point-to-point Coulomb interactions with a fast tree-based space-charge solver. Our results show that in the realistic high brightness photoinjector applications under study, the reduction of thermal emittance to values as low as 50 pm/um (1 meV MTE) remains a viable option for the improvement of beam brightness.

arXiv comment12 pages, 7 figures

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Cited by in corpus (7)

• A single-crystal alkali antimonide photocathode: high efficiency in the ultra-thin limit
• A kiloelectron-volt ultrafast electron micro-diffraction apparatus using low emittance semiconductor photocathodes
• Versatile, high brightness, cryogenic photoinjector electron source
• Point-to-Point Coulomb Effects in High Brightness Photoelectron Beamlines for Ultrafast Electron Diffraction
• A Comparison-Relationship-Surrogate Evolutionary Algorithm for Multi-Objective Optimization
• Design, fabrication, and tuning of a THz-driven electron gun
• Emittance Mapping in rf Guns