Study of Cs-Te photocathode for rf electron gun

At Waseda University, we have been studying high quality electron beam with an rf electron gun. In recent accelerator study and application researches, high quality electron beam are strongly required. Photocathode is a key component to generate higher quality electron beam, thus we started to develop a Cs-Te photocathode as an electron source since 2007. Cs-Te photocathode shows high quantum efficiency (Q.E.) (∼10 %) and has long life time (∼several months). From 2013, we built a photocathode evaporation chamber and started photocathode study. In this study, our purpose is to clarify their property and to establish an ideal evaporation recipe. We succeeded in producing high quality Cs-Te photocathode, and electron beam generated by our Cs-Te photocathode shows high charge (4.6 nC/bunch) and high Q.E. (1.74 %) in our rf electron gun. Furthermore, we found a Q.E recovery after Cs deposition process and it causes higher Q.E. than usual due to, we believe, Cs deposition quantity or Cs deposition speed. Thus we are now surveying the optimum Cs evaporation parameters. In this conference, we will report a detail of our photocathode development system, the latest progress of optimization study of Cs-Te photocathode and future plans.