Design of the superconducting 45 degree dipole for the CEBAF high resolution spectrometer

The 460-ton dipole for the Hall A 4-GeV/c High Resolution Spectrometer has a bend angle of 45 degrees , with an 8.4-m radius of curvature and an effective length of 6.6 m. It has a useful width of 100 cm and a 25-cm gap at the central radius of curvature. The dipole provides focusing in the dispersive plane by means of rotated (by 30 degrees ) entrance and exit pole faces as well as a field index of -1.25. The end contour geometries have been designed to eliminate higher-order aberrations. The maximum central field is 1.6 T at 4 GeV/c. A field quality of 2*10/sup -4/ (maximum deviation from the design value) is required over an excitation range from 0.16 T to 1.6 T. The 1.8-kA conductor is a 36-wire flattened cable. It has been designed to have limited cryostability at 4.5 K and 1.3 atm. Each coil is wound as one double pancake against the outer wall of the helium vessel in order to react the in-plane (hoop) loads. The bath-cooled, planar coil features negative curvature on its inner radius and at the exit. The coil produces 400 KAT at full excitation. The stored energy of this magnet is 3.5 MJ.