High-Intensity and High-Brightness Source of Moderated Positrons Using a Brilliant gamma Beam

Presently large efforts are conducted towards the development of highly brilliant gamma 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 (superconducting) Energy Recovery Linac (ERL). Particularly ERL's provide an extremely brilliant electron beam, thus enabling to generate highest-quality gamma beams. A 2.5 MeV gamma beam with an envisaged intensity of 10^15 s^-1, as ultimately envisaged for an ERL-based gamma-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 micron thick, 10 mm long) would lead to the emission of 2 x 10^13 (fast) positrons per second, which is four orders of magnitude higher compared to strong radioactive ^22Na 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 x 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.Comment: 9 pages, 3 figure

Spin-polarized low-energy positron beams and their applications

The production and use of low-energy (100 eV to 5 keV) high-intensity, spin-polarized positron beams is reviewed. Methods for obtaining beams with high polarization are discussed. Applications include studies of the moderation process, surface and bulk magnetism, optically active molecules, and the production of polarized anti-protons.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47033/1/339_2004_Article_BF00635183.pd