Precision septum-like dipole magnet for the HERA luminosity upgrade

Within the framework of the HERA luminosity upgrade project Scanditronix Magnet AB has designed in collaboration with AMACC AB, IBA S.A. and DESY a septum-like dipole for the compensation of orbit differences between e⁺-p and e~-p collisions at HERA. The magnet yoke is 640 mm long, 415 mm wide and 550 mm high. The total magnet length is 930 mm. The pole distance is 70 mm, the "good field" region is ± 20 mm centered around the nominal proton orbit. To meet the high field quality requirements for the whole range of field excitation between 0.1 T and 1.1 T VACOFLUX shims have been added to the pole edges to reduce saturation effects. The air gap is extended from the pole region by 235 mm to allow incoming synchrotron radiation light to pass through the magnet without being scattered. The separation between proton and electron beam at the magnet position at 18.88 m away from the interaction point is 121 mm. Carefully chosen thickness of the return yoke, a 13 mm thick shielding plate between proton and electron beam and 40 mm thick mirror plates on the front faces of the magnet reduce the field outside the magnet well below the tolerable value of 0,5_*10^-3 T_*m integrated along the e-orbit.