DEVELOPMENT OF BETTER QUANTUM EFFICIENCY AND LONG LIFETIME IRIDIUM CERIUM PHOTOCATHODE FOR HIGH CHARGE ELECTRON RF GUN

We have been developing a new photocathode material as an electron source for the SuperKEKB electron linac. This injector is required to obtain a low emittance and high charge electron beams in order to achieve the highest luminosity all over the world. The required properties of a new photocathode are reasonably high quantum efficiency (QE > 10 -4 ) and high laser durability to achieve a longterm (> 1 year) accelerator operation. We succeeded in developing an iridium cerium (Ir5Ce) photocathode which has a reasonably high QE (~ 9.1×10 -4