Closing in on the design of the BESSY-FEL

The SASE-FEL at LEUTL (APS) (1), the demonstration of SASE laser saturation at wavelengths below 100 nm at TTF (DESY) (2) and the operation of the HGHG-FEL at BNL (3) has stimulated proposals on future 4 th generation light source user facilities in the VUV to soft X-ray spectral range and hard X-rays worldwide, refs. (4-10). The BESSY Soft X-Ray FEL is planned to be built next to the 3 rd generation BESSY II light source, covering the spectral range 62 nm to 1.24 nm. A superconducting 2.25 GeV linac will supply three independent FEL-lines with a highly flexible electron-bunch pattern; the use of APPLE II type undulators will deliver variable photon-beam polarization. These SASE-FELs will permit unprecedented spectral-, spatial- and temporal resolution for user experiments. A Status of the design work is presented in the paper.