Photo-electron Beam Longitudinal Phase Space Tomography Studies at the Atf

The longitudinal phase space distribution of electron beam plays critical role in ultra-short electron bunch production, coherent radiation, free electron laser (FEL) and many other applications. Photocathode RF gun is capable of controlling not only the transverse emittance of electron beam, but also longitudinal emittance. The longitudinal phase space distribution of photoelectron beam was investigated at the Brookhaven Accelerating Test Facility (BNL-ATF) using tomography technique [1]. The longitudinal phase space distribution is reconstructed by measuring the energy spectrums of the beam for different RF phases. We will first briefly describe the principle of tomography technique and the ATF experiment set-up. The longitudinal emittance as function of RF gun phase was measured first time. The longitudinal emittance growth caused by the space charge effect was observed.