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 set-up 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 whilst keeping the positron beam polarization as high as possible. This paper 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%