Status of BESSY II, a high brilliance synchrotron light source in the VUV to XUV range

The approval of the BESSY II project marked the start of the construction of the first third generation synchrotron light source in Germany. BESSY II, designed for low emittance (ε=6·10^-9 radm) and the incorporation of a large number of insertion devices (IDs) is expected to deliver VUV to XUV radiation with a brilliance in excess of 10¹⁸photons/(sec·mm²·mrad² ·0.1% bandwidth), the photon energies ranging from 10 to 2000 eV from undulators and wigglers. Photon spectra with a critical energy of 11.5 keV will be generated in the 6 T field of a superconducting wavelength shifter (WLS) which is planned to be installed in one of the 14 straight sections available for insertion devices. The decision to build BESSY II at a new site at Berlin Adlershof gave the challenge for a complete redesign of the storage ring without the severe boundaries compared to earlier proposals, with respect to requirements and practicabilities of constructing an accelerator complex mid in the center of West-Berlin