Issue 76

Beam Dynamics Newsletter

5.9 The Characterization of Metal Photo-cathode for High Brightness Electron Beam Photo-injectors

CANDIDATE: Jessica Scifo, La Sapienza, Rome
SUPERVISOR: Prof. Massimo Ferrario
GRADUATION: September 2018

A high peak current and low emittance electron beam is required by several applications in the accelerator physics field, e.g., Free Electron Laser (FEL) radiation sources, Plasma Wake Field Acceleration (PWFA) experiments, generation of THz radiation and Inverse Compton Scattering sources. The performance of the photo-cathode is essential to increase the brightness of the electron beam, and so it is therefore of primary importance to analyze and optimize the quantum efficiency (QE) of the photo-cathode and the intrinsic emittance of the emitted electrons. For this reason, in several facilities, many experimental and computational studies are in progress to produce more efficient photo-cathodes. This approach looks at the photo-cathode like a “variable” and sensitive object in terms of surface modifications and contaminants due to laser radiation, RF fields breakdown and vacuum variation of its environment. A R&D activity on photo-cathodes is under development also at the SPARC_LAB test facility in order to fully know and characterize each stage of the photo-cathode “life” and improve their performances in terms of quantum efficiency and electron beam intrinsic emittance. In the present work, two distinct aspects of emittance study are presented: the theoretical study of solenoid optics and the surface preparation and analysis. Since the Cu QE is rather low (\( \ge 105 \)) and since several applications demand high QE electron sources, there is a growing interest in the international community to investigate the behavior of novel photo-cathode materials. In this regards I have performed also preliminary characterization measurements on a Yttrium thin film grown by pulsed laser ablation technique on Cu photo-cathode.