End-field design and tuning methods for insertion devices

Abstract

The magnetic field distribution, gap-dependent steering, and integrated magnetic multipole moments of insertion devices installed in synchrotron radiation sources have stringent requirements for yielding high brightness without adversely perturbing the electron orbit. Correct termination of the ends of the device yields a large number of full-field poles and helps achieve gap-independent steering. End-field tuning methods used for the Advanced Photon Source insertion devices are reviewed. Techniques include magnet strength reduction, reduced height poles, magnetic shims, and pole shaping. Measurements show that two-imensional finite element analysis is a useful tool for predicting general field shape and trajectories. However, experimental entrance steering of different devices with identical end configurations shows variance, necessitating empirical fine tuning of each device.