Monte Carlo calculations of the bremsstrahlung radiation environment expected in the future Particle beam fusion accelerator facility PBFA II

The Sandia National Laboratories Particle Beam Fusion Accelerator PBFA II is expected to produce significant amounts of prompt penetrating radiation from bremsstrahlung. In the present study the radiation environment for two voltages, 30 and 5 MV, has been calculated using a threedimensional electron-photon transport code. Because of the facility design changes required with the high-voltage lithium ion option, most calculations were done at 30 MV. The dose to personnel, about 1 mrad for the 30-MV option, is acceptable. Reliable operation of electronic components, however, requires significant changes to systems in various stages of completion. Shielding and relocation options that minimize interference with the completion schedule of the accelerator and with its operation and maintenance have been investigated. We find that an array of control devices located in the east alcove of the basement should be moved to the main control/monitor screen room in the low bay A thicker top cover on the vacuum chamber and a higher water level in the pulse-forming section allow electronics in the screen room to cope with the hard 30-MV spectrum. A two-stage shield has been designed to protect the KrF laser and its associated electronics, which cannot be removed from the basement. The two-stage shield consists of a thick steel bottom cover on the vacuum chamber and a thick shield wall on the north alcove of the basement