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TY - CONF AU - Qian, M.F. AU - Dejus, R.J. AU - Piao, Y. AU - Vasserman, I. AU - Xu, J.Z. ED - Liu, Lin ED - Byrd, John M. ED - Neuenschwander, Regis T. ED - Picoreti, Renan ED - Schaa, Volker R. W. TI - A New Method of Undulator Phase Tuning with Mechanical Shimming J2 - Proc. of IPAC2021, Campinas, SP, Brazil, 24-28 May 2021 CY - Campinas, SP, Brazil T2 - International Particle Accelerator Conference T3 - 12 LA - english AB - We developed a new method for tuning the undulator phase errors by shimming the undulator gap profile mechanically. First, the phase errors of a device are calculated based on the initial field measurement; then the desired field strength modulation along the device length is derived from the phase errors; and finally, the gap profile is mechanically shimmed to produce the desire field strength modulation. The method has been successfully applied to the tuning of many new and reused APS Upgrade (APS-U) hybrid permanent magnet undulators. The method is especially effective for tuning the legacy undulators with large phase errors. For instance, an old 33-mm-period undulator with a 23 degree initial rms phase error largely due to radiation damage has been tuned to better than 3 degrees. PB - JACoW Publishing CP - Geneva, Switzerland SP - 2912 EP - 2914 KW - undulator KW - MMI KW - radiation KW - operation KW - permanent-magnet DA - 2021/08 PY - 2021 SN - 2673-5490 SN - 978-3-95450-214-1 DO - doi:10.18429/JACoW-IPAC2021-WEPAB129 UR - https://jacow.org/ipac2021/papers/wepab129.pdf ER -