R&D activity on high QE alkali photocathodes for RF guns

R&D on high quantum efficiency (QE) alkali photocathode is in progress at Milano in the context of the ARES-TTF (Tesla Test Facility) program. High QE multialkali antimonide and cesium telluride cathodes have been produced in an advanced preparation system. Photoemitter preparation procedures have been set-up, in collaboration with the SESAMO lab. of the University of Modena, using Auger electron spectroscopy (AES): the AES technique was used, in conjunction with sputter erosion, to obtain the in-depth profile of the photoemissive film. In this way, photocathode preparation parameters (substratum cleaning procedure and temperature, alkali metal deposition rate, etc.) have been optimised. The spectral response of the photocathodes and the QE spatial distribution over the cathode surface has been measured using different light sources (254 nm<?<670 nm) and an optical scanning system. The photocathode poisoning effect and the changes in the photoemissive response due to the reaction with different gases have been investigated exposing the photoemitters, in a controlled way, to methane, carbon monoxide, carbon dioxide and oxygen. The good results so far obtained brought in Milano the responsibility of the production of cesium telluride photocathodes for the TTF Injector II. A preparation system for this application will be operative at Argonne within the end of 1995.