Development of High-Charge, Low-Emittance, DAW Type RF Gun for SuperKEKB

Abstract

We are developing a new RF gun for SuperKEKB. High-charge, low-emittance electron and positron beams are required for SuperKEKB. The required injection electron beam has a charge of 5 nC and an emittance of 20 mm-mrad at an energy of 7.0 GeV. In this linac, a photo cathode S-band RF gun will be used as the electron beam source. An advanced RF gun is required for high-charge, low-emittance beam generation. Thus, we developed a Disk and Washer (DAW) type photo cathode RF gun. LaB₆ and Ir₅Ce were tested as photo cathode materials. Normally, LaB₆ or Ir₅Ce are used as a thermionic cathode, however we evaluated the performance of the materials as a photo cathode. The beam commissioning results showed that Ir₅Ce has high quantum efficiency and long life time. Nd:YAG laser was used for RF gun operation. The SESAM (Semiconductor Saturable Absorber Mirror) mode locked laser was used for oscillator (frequency: 52 MHz). The obtained laser pulse energy was 4 mJ with pulse length of 30 psec at wave length of 266 nm. Finally, we obtained the beam charge of 4.8 nC by using the DAW type RF gun and Ir₅Ce cathode.