Gas evolution in epoxy under irradiation and maximum allowable beam loss in the proposed 800 MeV proton synchrotron

In the 800 MeV proton synchrotron under study as an intense pulsed source of neutrons, it is proposed to make the vacuum chambers an integral part of the magnets, both dipole and quadrupole. The design of a magnet will consist of magnet yoke laminations and coils enclosed in a stainless steel vacuum-tight shell. The magnet will be impregnated with epoxy under vacuum, leaving a clear path through the poles for the beam. There will be a considerable quantity of epoxy within the stainless steel shell. This epoxy will suffer radiation damage, mainly from beam loss to the walls, and gaseous products, predominantly hydrogen, will be evolved in the breakdown of the epoxy. This note is intended to show very crudely the limits of the radiation and beam loss from a purely vacuum standpoint with certain simplifying assumptions. The mechanical and electrical properties of the epoxy during irradiation will not be considered. The gas evolved from the epoxy will be related to the beam loss, the pumping speed and the vacuum pressure required. (author)