High field strength wedged-pole hybrid undulator

Abstract

The wedged-pole concept is introduced as a means for enhancing the field strength and field quality of the rare-earth permanent magnet hybrid undulator. The wedged-pole configuration results in higher on-axis field strength since it causes the magnet surface which faces the gap to be driven to the full magnet coercivity, Hc. Pole tip saturation is avoided by angular wedging of the poles and magnets to provide larger pole tip area without sacrificing magnet volume. The advantages of the wedged-pole concept are investigated for an example case with a gap to wavelength ratio of 0.22 and SmCo5 magnets. It is found that the field strength in the fundamental can be improved by as much as 15%. Alternatively, the field quality can be enhanced by operation of the poles far from saturation without loss of field strength. An additional benefit is reduction of the harmonic content in the field distribution.