Electron beam bunch length characterizations using incoherent and coherenttransition radiation on the APS SASE FEL project

The Advanced Photon Source (APS) injector linac has been reconfigured with a low-emittance RF thermionic gull and a photocathode (PC) RF gun to suppor t self-amplified spontaneous emission (SASE) free-electron laser (FEL) expe riments. One of the most critical parameters for optimizing SASE performanc e (gain length) is the electron beam peak current, which requires a charge measurement and a bunch length measurement capability. We report here initi al measurements of the latter using both incoherent optical transition radi ation (OTR) and coherent transition radiation (CTR). A visible light Hamama tsu C5680 synchroscan streak camera was used to measure the thermionic RF g un beam's bunch length (sigma similar to 2-3 ps) via OTR generated by the b eam at 220 MeV and 200 mA macropulse average current. In addition, a CTR mo nitor (Michelson Interferometer) based on a Golay cell as the far-infrared (FIR) detector has been installed at the 40-MeV station in the beamline. In itial observations of CTR signal strength variation with gull cc-magnet cur rent and interferograms have been obtained. Progress in characterizing the beam at these locations and a comparison to other bunch length determinatio ns will be presented. (C) 2000 Published by Elsevier Science B.V. All right s reserved.