Wiggler tune shift compensation on the Daresbury SRS

The higher brilliance lattice of SRS-2 (Synchrotron Radiation Source-2) leads to an increased perturbation arising from the 5 T superconducting wavelength shifter. In order to reduce this problem a new method of vertical tune correction has been introduced that minimizes the residual beta function modulation around the ring. This is achieved by a local correction to the member of the main quadrupole family immediately adjacent to the wiggler magnet. A high current, active shunt system has been developed and is now in routine use. Design and commissioning experience are described. The technique will be essential to the planned addition of a second wiggler in the SRS. The existing shunt design capability of ~100 A will be sufficient to correct for the effect of the proposed 6 T wiggler magnet