This note describes the optics design of a single dipole tagging spectrometer for GlueX. Firstly, TRANSPORT calculations were carried out to optimize the dipole magnet pole shape and orientation and to find the focal surface positions. Then a finite element model of the magnet was designed, and its magnetic field map was calculated using TOSCA. Based on the calculated magnetic field, electron beam trajectories were calculated and the tagger optics was calculated by raytracing. The tagger optics properties calculated by raytracing agree well with the results calculated by TRANSPORT at the parallel to point and the point to point foci. However, due to the different ray bundles defined in the TRANSPORT and raytracing calculations, large differences were found in the beam spot sizes calculated by these two methods in horizontal and vertical directions at positions other than the two focusing positions. The “phase space” concept used to describe the beam in TRANSPORT is no longer valid for the energy degraded electron beams in the raytracing calculation. Therefore the optical properties at positions other than the normal foci can only be calculated correctly by raytracing. The effects of the non abrupt terminated field boundary on the tagger properties were also discussed.
