Effect of Magnetic Circuit Imperfections on the Field Performance of In-Vacuum Undulators for the Taiwan Photon Source

In-vacuum undulators are the most important devices for a third-generation light source such as the Taiwan Photon Source. Magnetic arrays of these undulators are designed to minimize the transverse field roll-off which can decrease the dynamic aperture, the lifetime of the electron beam, and the efficiency of injection. Manufacturing errors in the magnet block and pole dimensions, errors of deformation and assembly, and imperfections of design make the transverse magnetic-field roll-off worse and the peak field strength less than designed. These imperfections and errors are inevitable but can be decreased during fabrication. Simulations and experiments have been performed to assess their influences on field performance and to generate schemes for improvement. The experimental setups, simulation models, and results are described in detail in this letter.