Magnetic Measurement System for the NSLS Superconducting Undulator Vertical Test Facility

One of the challenges of small-gap superconducting undulators is measurement of magnetic fields within the cold bore to characterize the device performance and to determine magnetic field errors for correction or shimming, as is done for room-temperature undulators. Both detailed field maps and integrated field measurements are required. This paper describes a 6-element, cryogenic Hall probe field mapper for the NSLS superconducting undulator Vertical Test Facility (VTF) [1]. The probe is designed to work in an aperture only 3 mm high. A pulsed-wire insert is also being developed, for visualization of the trajectory, for locating steering errors and for determining integrated multi-pole errors. The pulsed-wire insert is interchangeable with the Hall probe mapper. The VTF and the magnetic measurement systems can accommodate undulators up to 0.4 m in length.