Emittance Measurements of the Advanced Photon Source Photocathode Rf Gun*

The Advanced Photon Source (APS) photocathode rf gun is the primary beam source for the APS Low-Energy Undulator Test Line (LEUTL) free-electron laser (FEL) experiment. In the current operating regime of LEUTL, peak current has been the dominant factor in determining FEL performance. As LEUTL’s operational wavelength is reduced, however, the beam emittance will play an increasingly important role. Thus, efforts are underway to more completely characterize, control, and predict photocathode gun performance. This paper reports the results of recent emittance measurements using the APS photocathode gun, and comparison of these measurements with simulation.