Radial Damping by Octupole for ZGS Beam

Landau damping by the octupolar tune spread is used to prevent the radial blowup of the beam during the acceleration cycle. The octupole field is produced by a set of pole face windings in the ring magnets. The strength of the octupole field, which is controlled by the Zero Gradient Synchrotron (ZGS) programmer, is set to give a tune profile of ν_X = 0.83 + 0.008 × a², where a is the radial coordinate of the aperture in unit of cm. The radial damper feedback system, which has been operating for some years, has been replaced by this octupole, and the radial stability is remarkably improved by the new system.