Abstract
We report the experimental generation, acceleration, and characterization of a uniformly filled electron bunch obtained via space-charge-driven expansion (often referred to as ``blow-out regime'') in an L-band (1.3-GHz) radiofrequency photoinjector. The beam is photoemitted from a cesium-telluride semiconductor photocathode using a short ($<200\text{ }\text{ }\mathrm{fs}$) ultraviolet laser pulse. The produced electron bunches are characterized with conventional diagnostics and the signatures of their ellipsoidal character are observed. We especially demonstrate the production of ellipsoidal bunches with charges up to $\ensuremath{\sim}0.5\text{ }\text{ }\mathrm{nC}$ corresponding to a $\ensuremath{\sim}20$-fold increase compared to previous experiments with metallic photocathodes.
Highlights
Three-dimensional uniformly filled ellipsoidal charge distributions produce space-charge fields that have a linear dependence on position within the distribution [1,2]
We especially demonstrate the production of ellipsoidal bunches with charges up to $0:5 nC corresponding to a $20-fold increase compared to previous experiments with metallic photocathodes
We have experimentally demonstrated the production of a uniformly filled ellipsoidal bunch in an L-band rf photoinjector by illuminating a Cs2Te photocathode with an ultrashort UV pulse
Summary
Three-dimensional uniformly filled ellipsoidal charge distributions produce space-charge fields that have a linear dependence on position within the distribution [1,2]. The Serafini-Luiten technique is relatively simple to implement, especially with the availability of a short-pulse laser, but has limitations regarding the achievable minimum transverse emittance [8] This is because for a given accelerating field at the photocathode and desired bunch charge, the blow-out regime requires large transverse laser spots at the photocathode with consequent large thermal transverse normalized emittance. This type of operating regime has generally not been selected for, e.g., FEL applications. The present work supports the use of the blow-out regime in low-frequency electron guns with a limited peak field Such guns are foreseen as sources for high-frequency multiuser FEL facilities [19,20]
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