Design and simulation of the PSI electrostatic positron beam

For the design of the brightness enhancement stages a detailed phase space analysis based on unconventional focusing configurations and on-ray tracing simulations has resulted in a reduction of the field-extracted beam of 10 cm diameter and ET of 20 eV down to a spot size of 8 mm. After a second remoderation stage reducing the beam size by a further factor of 25, a straightforward electrostatic transport of the positrons to the target at ground potential allows the beam to be tuned between a few eV and 60 keV. The main result is summarized in a beam phase-space at the target of less than 300 μm40 mrad for energies above a few 100 eV increasing to 500 μm120 m at a few eV.