Development of Short-Period ${\rm Nb}_{3}{\rm Sn}$ Superconducting Undulators for the APS

Superconducting undulators (SCUs) with a period of 14.5 mm are under development for the Advanced Photon Source (APS) using Nb₃Sn superconductors. The initial goal is to install a SCU with a 19- to 29-keV tuning range for the first harmonic photon energy. The design of the SCU assembly includes the interface with the beam chamber as an integral part of the assembly. A four-period Nb₃Sn half SCU was fabricated and tested. After a number of quenches, the SCU was charged to an engineering current density of 1.92 kA/mm ² in the coil pack. This corresponds to a peak field of 1.08 T on the beam axis with a pole gap of 8.5 mm. The achieved current density was approximately 90% of the engineering critical current density for the design calculations. With an operating current density of 1.6 kA/mm ² , the SCU will operate at a peak field of 0.95 T with some degree of stability.