Bahrdt, J.; Frentrup, W.; Gaupp, A.; Scheer, M.; Schneider, I.; Wüstefeld, G.: Shimming of the Dynamic Field Integrals of the BESSY II U125 Hybrid Undulator. In: Proceedings of IPAC2011, 4 - 9 September 2011, San Sebastián, Spain. , 2011. - ISBN 978-92-9083-366-6, p. 3248-3250

Within a continuous program the BESSY II undulators are prepared for Topping-Up operation. The U125 planar hybrid undulator has a period length of 125 mm and a pole width of only 60 mm. The horizontal defocusing of the 1.7 GeV e-beam may result in a significant reduction of the horizontal dynamic aperture, reducing the injection efficiency when injecting into the closed gap. The dynamic field integrals are derived from a 2D-Fourier decomposition of the 3D-field. An analytic description of the dynamic field integrals based on the Fourier coefficients is presented. Magic fingers have been installed in order to minimize the dynamic field integrals and to enlarge the good field region of the device.