Aspects of radiation safety for a topping-up operation of BESSY

The synchrotron light source BESSY consists of a 50 MeV microtron, a full energy synchrotron and a 1.9 GeV storage ring and is in operation since 1998. Increased requirements lead to the plan, to offer topping-up operation to the users. Topping-up means injection with open beamshutters. Based on a successful model for the estimation of the electron losses, we investigated the effect of topping-up injections in the experimental hall with FLUKA simulations. The BESSY experimental hall is divided in a free part and 16 small parts close to the front ends, that are not accessible to the users. The FLUKA simulations result, that if the electron losses during injection are limited to 10%, the annual dose in the accessible part of the experimental hall is below 1 mSv/a. Topping-Up means injection with closed undulator gaps too. Here we used FLUKA to calculate the energy dose in the Fe–Nd–B material of the BESSY undulators from the electron losses in the undulator vacuum chamber. These simulations also show, that it is necessary to limit the electron losses in the storage ring to 10% to avoid an unacceptable demagnetization within few years of operation.