Optical techniques for electron-beam characterizations on the APS SASE FELproject

At the Advanced Photon Source (APS) the injector linac's DC thermionic gun is being supplemented by a low-emittance RF thermionic gun that will suppor t the SASE FEL project. To address the anticipated smaller beam sizes, the standard Chromox beam-profiling screens are being complemented by optical t ransition radiation (OTR) and Ce-doped YAG single-crystal converters. Direc t comparisons of the effective conversion efficiency, spatial resolution, a nd time response of the three converter screen types have been performed us ing the DC thermionic gun's beam accelerated to 400-650 MeV. An apparent bl urring 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 performe d with a streak camera. Initial beam images of the RF-thermionic gun beam h ave also been obtained. (C) 1999 Published by Elsevier Science B.V. All rig hts reserved.