Open Access Version

Abstract:
Depending on the experiment, the focus of the users of synchrotron light sources is on different parameters. Some experiments require high flux X-rays while the pulse length is of no concern. On the other hand a large and growing fraction of BESSY’s user community focuses on functional materials where dynamics on the picosecond and sub picosecond range are essential. To fulfill both requirements BESSY plans a major upgrade to provide high-flux and picosecond-pulse beams simultaneously [1,2]. The unique feature of the BESSY Variable pulse-length Storage Ring (BESSY VSR) will be the simultaneous operation of long (15 ps rms) and short (1.7 ps rms) pulses. This approach is complementary to the concept of Diffraction Limited Storage Rings (DLSR). DLSRs reduce the emittance by two orders of magnitude, but require to lengthen the bunches up to the 100 ps range to reach acceptable life times. The impact this project has on the overall radiation safety at BESSY is discussed. The major aspect is that the number of electrons injected into the storage ring per year will not be increased, thus keeping the annual radiation level through the shielding walls the same. We present the way this number will be controlled by our top-up interlock. The inclusion of super conducting cavities in the storage ring will require additional safety measures, because of possible field emissions whose radiation level we calculated with FLUKA [3,4]. Finally, we present FLUKA calculations for the shielding design of a new facility to test the super conducting cavities of the VSR modules.