Characterization of Cs-Sb cathodes for high charge RF photoinjectors
摘要
Future accelerators such as CLIC (Compact LInear Collider), require high brightness electron beams that could be produced with a photoinjector (laser-driven electron source). Cs2Te photocathodes in combination with ultra-violet (UV) laser beams are currently used in many photoinjector facilities, but requirements to the electron sources for future accelerators like CLIC are more demanding. The main challenge for the CLIC drive beam photoinjector is to achieve high bunch charges (8.4 nC), high bunch repetition rates (500 MHz) within long trains (140 s) and with suciently long cathode lifetimes. In particular the laser pulse energy in UV, for such long pulse trains, is currently limited due to a degradation of the beam quality during the 4th harmonic frequency conversion process. Using the 2nd harmonic (green laser beam), provided it is matched with a low photoemission threshold photocathode material, would overcome this limitation. Cesium antimonide (Cs3Sb), being a photoemissive material in the visible range, could be a good candidate for this purpose. The main goal of this PhD thesis is to provide a comprehensive experimental investigation of the use of this delicate material for photoinjector applications. The experimental activities, devoted to asses the feasibility of producing high quality Cs3Sb cathodes, include production by thin lm deposition and characterization of the photoemissive properties in a DC gun beam line. The performance of Cs-Sb photocathodes was tested in a high charge RF photoinjector setup allowing to measure their main features. X-ray photoelectron spectroscopy analyses were used to correlate the measured photoemissive properties with the cathode composition as well as to investigate the cathode deterioration observed during operation. A close comparison with the Cs2Te cathodes performance is also discussed. This study represents a step forward in the development of photocathodes for applications in high charge RF photoinjectors, providing a