An Analysis of a Potential Compact Positron Beam Source

For positron studies in plasma wakefield accelerators such as AWAKE, the development of new, cheaper, and compact positron beam sources is necessary. Using the GBAR experiment's positron trap as an example source, this paper explores converting that trapped positron plasma into a usable beam. Bunching is initially accomplished by an electrostatic buncher and the beam is accelerated to 148 keV by pulsed electrostatic accelerators. This is necessary for injection into the $\beta$-matched rf cavities operating at 600 MHz, which bring the positron beam to a transverse emittance of 1.3 $\pi$ mrad mm, a longitudinal emittance of 93.3 $\pi$ keV mm, $\sigma_z$ of 1.85 mm and an energy of 22 MeV. The beamline used here is far simpler and less expensive than those at many facilities, such as SLAC, allowing for a cheap source of positron beams, potentially opening up positron beam studies to many facilities that could not previously afford such a source.