SPURIOUS VERTICAL DISPERSION CORRECTION FOR PETRA III

The spurious vertical dispersion, arising due to the misalignment and rotational errors of the magnets in the storage rings dedicated for synchrotron radiation sources are highly undesirable in the low emittance machines, as this contributes to the vertical beam size of the photon beam. This is a matter of concern in PETRA III, a 6GeV positron storage ring with a horizontal beam emittance of 1nm.rad and 1 % emittance coupling. In this paper the local and/or global vertical dispersion correction in the ring after getting a corrected orbit with combined horizontal dispersion correction of the perturbed lattice are discussed. The global vertical dispersion is corrected using the vertical corrector magnets used for orbit correction and 12 skew quadrupole magnets are used at three locations viz. two damping wiggler sections and the new octant with DBA cells, with a pair of skew quadrupoles on either side to correct locally without disturbing the dispersion out side. A SVD method can also be used considering the BPMs (Beam Position Monitors) on either side of insertion devices using skew quadrupoles to minimize the vertical dispersion in those locations so that the vertical emittance can be maintained at a desired value