A review of magnetic field measurements of full scale conduction cooled superconducting undulator coils

Abstract

Synchrotron light sources employ undulators to produce brilliant photon beams. Most synchrotrons and all free electron lasers use undulators made by permanent magnets. Superconducting undulators can produce, for the same geometry, a higher peak magnetic field on axis with respect to permanent magnet ones, and have the additional advantage of being radiation hard. Recently superconducting undulators have been successfully applied in the Karlsruhe Institute of Technology synchrotron and in the Advanced Photon Source at the Argonne National Laboratory. While precise measurement techniques to characterize the magnetic field for permanent magnet undulators are well established, new developments have been necessary in the past few years to magnetically characterize superconducting undulators. After an introduction on undulators and the measurements needed to be performed before operating such devices with electron beams, this paper reviews magnetic field measurements of full scale conduction cooled superconducting undulator coils. Current and future methods used for the characterization of the magnetic field, after installation of such coils in the final cryostat, are also discussed.

Review and prospects of world-wide superconducting undulator development for synchrotrons and FELs

“…It should be pointed that the moving/stretched wire method is so far the standard technique for measuring the field integrals in SCUs. The largest uncertainty comes from the mismatch between the magnetic plane and the wire moving plane [163]. Schematic of (a) moving wire system, (b) pulsed wire system, and (c) rotating coil system.…”

“…Schematic of (a) moving wire system, (b) pulsed wire system, and (c) rotating coil system. Reproduced from [163]. © IOP Publishing Ltd. All rights reserved.…”

“…This requires carefully tuning local magnetic fields and correcting the field integrals along the undulator axis based on advanced magnetic field measurement systems. In the following, we briefly summarize available magnetic field measurement techniques for SCUs, more details can be find in the review paper from Casalbuoni [163].…”

A GdBCO bulk staggered array undulator

“…In the last decade superconducting undulators based on NbTi have been developed both in Europe [15] and in the US [16]. For period lengths above 15 mm, they are more effective in generating large magnetic field than CPMU [17].…”

Magnetic Tb75Fe25 Nanoglass for Cryogenic Permanent Magnet Undulator

“…Moreover, the amorphous alloy of TbFe can be used as a cryogenically cooled permanent magnet undulator (CPMU) in modern synchrotron radiation facilities across the world. In the present time, rare earth-based CPMUs such as Nd 2 Fe 14 B and Pr 2 Fe 14 B are extensively used. − …”