INITIAL EMITTANCE AND TEMPORAL RESPONSE MEASUREMENT FOR GaAs BASED PHOTOCATHODES

For future light source based on Energy Recovery Linac (ERL) is planned in KEK. For the ERL, an ultra low emittance, fast temporal response and high current electron source is needed. To achieve these requirements, a high voltage DC gun with a Negative Electron Affinity photo-cathode is under development. In this development, it is important to investigate the performance of photocathodes. We have constructed an ERL gun test stand to measure emittance and temporal profile. We use a solenoid scan technique for emittance measurements and a deflecting cavity technique for temporal profile measurements. In this presentation, we report KEK ERL gun test stand and beam test results. INTRODUCTION NEA GaAs photocathode with DC gun is one of candidate for an electron source of the ERL based next generation light source. In KEK, for the purpose of development for ERL based light source the Compact ERL is constructing [1]. The achievable emittance and duration of pulse of the electron beam from a DC photoemission gun are limited by the initial emittance that depends on Mean Transverse Energy (MTE) of electrons and temporal response of photo cathodes, respectively. To clarify these performances of the GaAs photocathode, we prepared the cathodes with different thicknesses, and measured the emittance and the time response. In this paper, we reported the results of the experiments.