Abstract
Radio-frequency (rf) photoinjectors are commonly used to generate intense bright electron beams for a wide range of applications, most notably as drivers for X-ray Free-Electron Lasers. The photocathode, mounted inside an rf gun and illuminated by a suitable laser, thereby plays a crucial role as the source of the electrons. The intrinsic emittance and the quantum efficiency of the electron source are determined by the properties of the photocathode's surface material. We present measurements of the intrinsic emittance and the quantum efficiency performed with copper and cesium telluride cathodes in the same rf photoinjector, thus comparing, for the first time, the performance of metal and semiconductor cathodes under the same conditions. Our results are consistent with theoretical expectations and show that the difference in intrinsic emittance for the two types of material is not significant in view of accelerator applications. We conclude that cesium telluride photocathodes provide a much higher quantum efficiency at essentially negligible degradation in beam emittance.
Highlights
Radio-frequency photoinjectors [1] are the most effective way to generate intense bright electron beams
We present measurements of the intrinsic emittance and the quantum efficiency performed with copper and cesium telluride cathodes in the same rf photoinjector, comparing, for the first time, the performance of metal and semiconductor cathodes under the same conditions
By far the strongest interest in rf photoinjectors arises from their use as drivers for high-brightness electron injectors for future linear colliders or X-ray Free-Electron Laser (FEL) facilities, where, in addition to high brightness, a well-defined pulse structure is required
Summary
Radio-frequency (rf) photoinjectors [1] are the most effective way to generate intense bright electron beams. Electrons are produced via the photoelectric effect by a suitable laser impinging on a photocathode mounted inside an rf gun. The rf field of the gun is synchronized to accelerate the electrons to an energy of up to several MeV. By far the strongest interest in rf photoinjectors arises from their use as drivers for high-brightness electron injectors for future linear colliders or X-ray Free-Electron Laser (FEL) facilities, where, in addition to high brightness, a well-defined pulse structure is required. Most of the present and planned X-ray FELs employ laser-driven rf photoinjectors as electron beam sources, including SwissFEL under construction at the Paul Scherrer Institute [6]
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