Radiation safety aspects of the linac coherent light source project at SLAC+

The linac coherent light source (LCLS) is a self-amplified spontaneous emission based free electron laser (FEL) that is being designed and built at the Stanford Linear Accelerator Center (SLAC) by a multi-laboratory collaboration. This facility will provide ultra-short pulses of coherent X-ray radiation with the fundamental harmonic energy tunable over the energy range of 0.82-8.2 keV. One-third of the existing SLAC linac will compress and accelerate the electron beam to energies ranging from 4.5 to 14.35 GeV. The beam will then be transported through a 130-m long undulator, emit FEL and spontaneous radiation. After passing through the undulator, the electron beam is bent to the main electron dump. The LCLS will have two experiment halls as well as X-ray optics and infrastructure necessary to make use of the FEL for research and development in a variety of scientific fields. The facility design will incorporate features that would make it possible to expand in future such that up to six independent undulators can be used. While some of the radiation protection issues for the LCLS are similar to those encountered at both high-energy electron linacs and synchrotron radiation facilities, LCLS poses new challenges as well. Some of these new issues include: the length of the facility and of the undulator, the experimental floor in line with the electron beam and the occupancy near 0∘, and the very high instantaneous intensity of the FEL. The shielding design criteria, methodology, and results from Monte Carlo and analytical calculations are presented.