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arXiv · 2511.02035

Experimental verification of space-charge saturation scaling laws in high-gradient photocathode RF guns

Paul Denham·David Garcia·Atharva Kulkarni·Brian Schaap·Ziteng Liu·Pietro Musumeci·Daniele Filippetto
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Abstract

We investigate the limits of photoemission yield in a high-gradient S-band radiofrequency photoinjector in the space-charge-dominated regime. Using an RF phase-scan technique, where the emitted charge is measured as a function of the RF-field phase in the gun, we directly monitor photoemission over a range of launch fields and laser parameters, enabling quantitative characterization of space-charge saturation. Measurements, supported by simulations and analytic modeling, confirm the characteristic charge-field scaling laws for pancake beams and provide the first experimental verification of cigar-regime scaling in an RF photogun. These results establish a predictive framework for identifying the onset of space-charge saturation and guide the optimization of photoinjectors for ultrafast electron diffraction, microscopy, and high-brightness light sources operating at ultra-high gradients.

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Paul Denham, David Garcia, Atharva Kulkarni, Brian Schaap, Ziteng Liu, Pietro Musumeci, Daniele Filippetto. 2025-11-03. Experimental verification of space-charge saturation scaling laws in high-gradient photocathode RF guns. https://arxiv.org/abs/2511.02035

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