Beam dynamics in a spectrometer for the polarized positron production experiment

The proposed experiment E-166 at SLAC is designed to demonstrate the possibility of producing longitudinally polarized positrons from circularly polarized photons to be used in future linear collider. The experimental setup utilizes a low emittance 50 GeV electron beam passing through a helical undulator in the final focus test beam line of the SLAC accelerator. Circularly polarized photons generated by the electron beam in the undulator hit a target and produce electron-positron pairs. The purpose of the post-target spectrometer is to select the positron beam and to deliver it to a polarimeter while keeping the positron beam polarization as high as possible. This article analyzes positron transmission and polarization in the E-166 spectrometer experiment. The positron transmission has a maximum value of 7% for a positron beam energy of 5.5 MeV, while positron polarization is approximately 60%