  In Free Electron Lasers (FEL), a transverse centroid misalignment of
longitudinal slices in an electron bunch reduces the effective overlap between
radiation field and electron bunch and therefore the FEL performance. The
dominant sources of slice misalignments for FELs are the incoherent and
coherent synchrotron radiation within bunch compressors as well as transverse
wake fields in the accelerating cavities. This is of particular importance for
over-compression which is required for one of the key operation modes for the
SwissFEL planned at the Paul Scherrer Institute.
  The centroid shift is corrected using corrector magnets in dispersive
sections, e.g. the bunch compressors. First and second order corrections are
achieved by pairs of sextupole and quadrupole magnets in the horizontal plane
while skew quadrupoles correct to first order in the vertical plane.
Simulations and measurements at the SwissFEL Injector Test Facility are done to
investigate the proposed correction scheme for SwissFEL. This paper presents
the methods and results obtained.
