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A design study has been performed for a positron beam with an energy of 500MeV to be realized at the applied physics area of the Mainz Microtron MAMI.Positrons will be created after pair conversion of bremsstrahlung, produced bythe 855 MeV electron beam af MAMI in a tungsten converter target. From the twoconceivable geometries (i) pair conversion in the bremsstrahlung convertertarget itself, and (ii) bremsstrahlung pair conversion in a separated leadfoil, the former was considered in detail. Positrons will be energy selectedwithin an outside open electron beam-line bending magnet, and bent back by anadditional sector magnet. Magnetic focusing elements in between are designed toprepare in a well shielded positron target chamber about 6 m away from thetarget a beam with horizontal and vertical emittances of epsilon_v = 0.055 pimm mrad (1 sigma), and epsilon_h = 0.12 pi mm mrad (1 sigma), respectively, fora 10 micro m thick amorphous tungsten target and negligible momentum spread. Atan accepted positron band width of 1 MeV, spots are expected vertically with anangular spread of 0.064 mrad and a size of 5.0 mm (FWHM), and horizontally withan angular spread of 0.64 mrad and a size of 7.7 mm (FWHM). The positron yieldamounts to 13.1 per second, 1 MeV positron energy band width, and 1 nA electronbeam current.

the european physical journal. d, atomic, molecular and optical physics/the european physical journal. d, atomic, molecular, optical and plasma physics

Design study for a 500 MeV positron beam at the Mainz Microtron MAMI