Baseline design of the hall D polarized photon beam

As part of the Jefferson Lab 12 GeV upgrade a new photon beam facility based on coherent bremsstrahlung will be built. The 12 GeV electron beam will pass through a 20 micron thick single crystal diamond generating photons via both incoherent and coherent bremsstrahlung. A 1.5 T 6.3 m long normal conducting dipole magnet will momentum analyze the electrons which emitted the photons. Two detector packages consisting of a scintillator PMT hodoscope and a scintillating fiber array with SiPM readout are used to detect these electrons. The photon beam generated in the crystal is a combination of photons generated by both the coherent and incoherent bremsstrahlung process, however the coherent bremsstrahlung photons have a different angular momentum relation than the incoherent bremsstrahlung photons. By collimating the photon beam after a 76 m drift distance the incoherent component can be suppressed relative to the coherent resulting in a high quality polarized beam.