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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. [ABSTRACT FROM PUBLISHER]

The feasibility of a compact 4.4 T in-vacuum cryogenic Pr2Fe14B-based wavelength shifter was studied at the Taiwan Photon Source. The overall dimensions of the magnet array are height 205 mm, length 240 mm, and width 160 mm; the magnet array operates at magnet gap 5 mm. The roll-off of the central field on the transverse axis was designed to be less than 0.1% between ±20 mm. The magnitudes of the integral multipole field error and the transverse tune shift as a function of transverse position were optimized to be less than 200 G cm and 4 × 10-3 between ±15 mm. A reverse field occurred so that the Pr-Fe-B bulk became partially demagnetized near 295 K, but it was improved upon chamfering the iron poles near the regions of that reverse field to avoid demagnetization of the Pr-Fe-B bulk. [ABSTRACT FROM PUBLISHER]