2008 Volume 5 Issue 3 Pages 237-245
The SPring-8 compact SASE source (SCSS) test accelerator for XFEL/SPring-8 was constructed in 2005 to perform proof-of-principle experiments for stable SASE FEL operation. The first lasing at 49 nm, though not reached saturation, was observed with the 250-MeV electron beam in June 2006. Towards the saturation, we started stabilizing the RF system for the injector section, which dramatically facilitated the lasing condition. The stable operation enables us to tune each of the machine parameter, for instance transversal beam focusing and a beam trajectory in the two undulators, much more precisely by using the lasing response. The second undulator, which did not sufficiently contribute to the first lasing because of large multipole field errors, was replaced by new one. These improvements led us to the successful observation of continuous SASE saturation at the wavelength ranging from ～50 to 60 nm in September 2007. A pulse-energy of 30 μJ is routinely obtained at 60 nm. The stable and intense EUV SASE FEL has been offered for user experiments since October 2007. Analysis of the obtained SASE saturation data with a 3D-FEL simulation code, SIMPLEX, suggests that the electron beam emittance of 0.6 πmm·mrad is unffected by the bunch compression process with over three hundred compression factor. This result proves the validity of our bunch compression scheme that starts from velocity bunching of uniform and long cylindrical electron beam instead of initially short and intense electron beam from a RF photo-cathode.
