High-intensity and high-brightness source of moderated positrons using a brilliant γ beam

Presently, large efforts are conducted toward the development of highly brilliant γ beams via Compton back scattering of photons from a high-brilliance electron beam, either on the basis of a normal-conducting electron linac or a (super-conducting) Energy Recovery Linac (ERL). Particularly, ERLs provide an extremely brilliant electron beam, thus enabling the generation of highest-quality γ beams. A 2.5 MeV γ beam with an envisaged intensity of 10 15 photons s −1 , as ultimately envisaged for an ERL-based γ -beam facility, narrow band width (10 −3 ), and extremely low emittance (10 −4 mm 2 mrad 2 ) offers the possibility to produce a high-intensity bright polarized positron beam. Pair production in a face-on irradiated W converter foil (200 μm thick, 10 mm long) would lead to the emission of 2×10 13 (fast) positrons per second, which is four orders of magnitude higher compared to strong radioactive 22 Na sources conventionally used in the laboratory. Using a stack of converter foils and subsequent positron moderation, a high-intensity low-energy beam of moderated positrons can be produced. Two different source setups are presented: a high-brightness positron beam with a diameter as low as 0.2 mm, and a high-intensity beam of 3×10 11 moderated positrons per second. Hence, profiting from an improved moderation efficiency, the envisaged positron intensity would exceed that of present high-intensity positron sources by a factor of 100.