Kasa, M. Doose, C.L. Fuerst, J.D. Gluskin, E. Ivanyushenkov, Y. JACoW Geneva, Switzerland 978-3-95450-180-9 10.18429/JACoW-NAPAC2016-TUB4CO04 English 477-479 TUB4CO04 ion undulator photon quadrupole octupole Contribution to a conference proceedings 2017 2017-01 http://dx.doi.org/10.18429/JACoW-NAPAC2016-TUB4CO04 https://jacow.org/napac2016/papers/tub4co04.pdf One of the primary goals of the superconducting undulator (SCU) program at the Advanced Photon Source (APS) is to achieve a high quality undulator magnetic field without the need for magnetic shimming to tune the device. Over the course of two years, two SCUs were designed, manufactured, assembled, and tested at the APS. Both SCUs were one meter in length with a period of 1.8 cm. After magnetic measurements of the first undulator were completed, several design changes were made in order to improve the quality of the undulator magnetic field. The design modifications were implemented during construction and assembly of the second SCU. The details of the design modifications along with a comparison of the magnetic measurement results will be described.