Optical techniques for electron-beam characterizations on the APS SASE FEL project

At the Advanced Photon Source (APS) the injector linacʹs DC thermionic gun is being supplemented by a low-emittance RF thermionic gun that will support the SASE FEL project. To address the anticipated smaller beam sizes, the standard Chromox beam-profiling screens are being complemented by optical transition radiation (OTR) and Ce-doped YAG single-crystal converters. Direct comparisons of the effective conversion efficiency, spatial resolution, and time response of the three converter screen types have been performed using the DC thermionic gunʹs beam accelerated to 400–650 MeV. An apparent blurring of observed beam size with increasing incident charge areal density in the YAG crystal was observed for the first time. Only the OTR was prompt enough for the few-ps domain micropulse bunch length measurements performed with a streak camera. Initial beam images of the RF-thermionic gun beam have also been obtained.