Self-Aligned Field Analyzer with Laser Instrumentation

SAFALI is an abbreviation for “Self-Aligned Field Analyzer with Laser Instrumentation”. It is used when measuring the field profile and field integrals of cryogenically cooled permanent magnet undulators (CPMUs) and other in-vacuum undulators. The magnetic structure of those systems is often not accessible for the common Hall probe set-up that runs on a flat granite bench. In particular, the field profile of a CPMU will change with temperature and those undulators have to be measured and tuned under cold conditions which can only be provided while in vacuum. The Hall probe and its guiding system must therefore be situated inside the vacuum chamber. In order to guarantee a reproducible and accurate measurement with respect to the laboratory coordinate system (as it would be provided by the levelled granite bench), an optical laser system is used to determine the position of the Hall probe during its longitudinal movement. A dynamic feedback system will then correct for any divergences and ensures a highly stable and accurate measurement.

A detailed description and display of the set-up can be found in this open access paper by its developers from SPring-8, Japan:
Tanaka T et al., Proceedings of FEL 2007 (Novosibirsk, Russia, 2007), WEPPH052, 468–71

SAFALI set-ups are used at DESY for the mapping of the magnetic profiles of in-vacuum and cryogenically cooled undulators.

Contact: A. Schöps, S. Telawane, P. Vagin, M. Tischer