A novel superconducting octupole magnet for photon scattering experiments

A superconducting octupole magnet capable of producing a variable high magnetic field in three dimensions has been designed and constructed. Eight cone-shape superconducting coils are arranged octahedrally to form four independent dipole pairs, facilitating five 30 deg. conic bore holes and a 210 deg. slit opening for large angle photon-in-photon-out experiments. To achieve high magnetic field and liquid-helium-free operation, holmium pole pieces, HTS (high Tc superconducting) current leads, and a GM-type cryocooler are employed. The maximum magnetic field and the full current excitation time are measured to be 3.65 T and 20 min, respectively. A relay circuit for switching the magnet field along different major directions is also presented