Phase-Shimming of the BESSY II in-Vacuum APPLE II Undulator IVUE32 with Transverse Slides

The phase shimming of an in-vacuum APPLE II undulator requests a precise slit adjustment between neighbouring magnet rows besides the conventional gap tuning such as in an in-vacuum undulator. In an out-of-vacuum APPLE II, the slit between the magnet rows is precisely defined via a stiff needle bearing, which is located closely to the critical volume. In the APPLE II design, the slit adjustment must be done from outside of the vacuum chamber far away from the electron beam. In this article, we discuss the tolerances of systematic phase errors of various types and their relaxation with emittance and energy spread. We developed specific transverse slides for the slit adjustment to achieve full flexibility in phase tuning. We discuss their capability in slit adjustment precision in the readily assembled and evacuated system. The discussions are based on spectral and FEM-simulations.