Magnetic Field Design of a Superconducting Wiggler in the SAGA-LS Storage Ring

A magnetic field design for a superconducting (SC) wiggler system, which has been installed in the Saga light source storage ring, was described. The wiggler is a three-pole type, consisting of a 4.0-T SC center magnet and two normal-conducting side magnets; thus, each pole forms a magnet. Since the wiggler consists of isolated magnets, reduction of the first field integral of the center SC magnet was important from the viewpoint of suppression of the orbit displacement. For this purpose, the center SC magnet was designed to have a separated iron core with field clamps and no transverse return yoke. This concept made magnetic field negative regions near the center peak magnetic field on the electron beam orbit to reduce the first field integral and beam meandering. Heat generations due to eddy currents and the magnetic field due to supporting structures were calculated to have ignorable effects. The appropriateness of the design has been confirmed through daily stable operation at the light source.