Harmonic correction rings for the PEP-II IR quadrupole magnets

Two harmonic corrector ring magnet designs have been developed to correct field error harmonics generated by quadrupole magnets in the interaction region of PEP-II. They consist of circular arrays of cylindrical permanent magnet pairs which can be both arbitrarily oriented and counter-rotated for strength. This arrangement allows the correctors to be tuned to generate a correction field with arbitrarily selected combinations of harmonics. These correctors are designed such that they can be pre-fabricated and then tuned after the quadrupole magnets have been built and their residual harmonic error content ascertained. The correctors can thus be used to cancel any residual combination of error harmonics in the completed quadrupoles