Improvement of an S-band RF gun with a Cs2Te photocathode for the KEK-ATF

A laser-driven RF gun with a Cs2Te photocathode, a device modeled after the BNL-IV RF gun, has been in development at KEK since 2002. This gun has been operated as an electron source for the Accelerator Test Facility (ATF) and generates a beam with an operational intensity of up to 3.2 nC per bunch. Based on successful results at the ATF, this gun has been applied several times for new research at universities. From 2002 onwards, successive improvements have been incorporated into newer models of the RF gun. Most recently, in 2008, a new gun incorporating all of the earlier modifications was produced for the ATF. Tests have confirmed a significant improvement of the Q-value of the latest model. A typical transverse emittance of 1.3 π mm mrad has been obtained under the following conditions: solenoid field of 0.18 T, beam intensity of 1.6 nC per bunch, and RF power of 9 MW. This RF gun equipped with the Cs2Te photocathode is being used for the advanced research programs at the ATF. A survey of its performance has recently been completed.