Development of a new active-type gradient corrector for an AVF cyclotron

A new type of a gradient corrector with active coils has been developed for beam focusing and bending in the extraction region of the RCNP AVF cyclotron. The gradient corrector is of quadrupole type consisting of a pair of a C-type iron yoke separated each other. A sixteen-turn hollow conductor was coiled around each side yoke, and the two iron dipoles generate a linear field gradient independently. A field gradient up to 9 T/m are available under excitation of a cyclotron main coil for focusing a heavy ion beam with magnetic rigidity up to 1.6 T-m. The position of the gradient corrector is variable within +/-20 mm from a beam extraction axis. Production of the designed field gradient was verified by a field measurement using a Hall-element under excitation of the main coil. We have succeeded in focusing an extracted beam at an object point of the MEBT optics by a combination of the gradient corrector and a quadrupole triplet. Correction of an extracted beam orbit was also demonstrated by optimizing the coil current and position of the gradient corrector.