A decade-long effort at the Advanced Photon Source (APS) of Argonne National Laboratory (ANL) on development of superconducting undulators culminated in December 2012 with the installation of the first superconducting undulator "SCU0" into Sector 6 of the APS storage ring. The device was commissioned in January 2013 and has been in user operation since. This paper presents the magnetic and cryogenic design of the SCU0 together with the results of stand-alone cold tests. The initial commissioning and characterization of SCU0 as well as its operating experience in the APS storage ring are described.

Development of superconducting undulators continues at the Advanced Photon Source (APS). Two years after successful installation and commissioning of the first relatively short superconducting undulator "SCU0" in Sector 6 of the APS storage ring, the second 1.1-m-long superconducting undulator "SCU1" was installed in Sector 1 of the APS. The device has been in user operation since its commissioning in May 2015. This paper describes the magnetic and cryogenic design of the SCU1 together with the results of stand-alone cold tests. The SCU1's magnetic and cryogenic performance as well as its operating experience in the APS storage ring are also presented.

The helical undulator for the proposed International Linear Collider (ILC) positron source requires highpermeability steel poles and superconducting coils to meet the ILC parameters. A short-model undulator with a period of 14 mm was designed, fabricated including highpermeability steel poles, and tested in LHe. The ends of the model were designed to wind the Nb 3 Sn double helix without any conductor joints. After a few quenches in the first excitation test, the current density in the coil reached 1.28 kA/mm 2 , which was approximately 90% of the estimated short-sample critical current density. The periodic on-axis fields were mapped at two azimuth angles. Excluding the end fields, the standard deviation of the field amplitudes and higher harmonic coefficients for the periodic field were less than 7 × 10 -3 and 5 × 10 -3 , respectively.

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