A superconducting dipole concept for the CEBAF high resolution spectrometers

CEBAF (Continuous Electron Beam Accelerator Facility) requires a pair of high-resolution spectrometers (HRS) for performance of electron/hadron coincidence experiments at up to 4 GeV/c. Momentum analysis for each arm is provided by a 45° vertical bending dipole having a useful field volume 6.0 m long × 30-40 cm wide (pole gap) × 80 cm high. A resistive 30-cm-gap dipole has been selected for the reference 4-GeV/c HRS, utilizing a qQQDQQ magnet configuration. However, recent studies aimed at equipment cost reduction indicate that a 40-cm-gap superconducting dipole based on less stringent field uniformity requirements may be attractive, either with the reference HRS or with a revised design, using fewer magnet elements. The concept described is an H-frame superconducting magnet, with contoured poles and resistive interpole field shaping coils, to achieve a field quality of 1 G/cm across the aperture at all useful excitation levels. This approach yields minimal pole width and requires only conventional fabrication tolerances