Tapering the Field Amplitude of a Uniform Gap Permanent Magnet Undulator

• Published in: Japanese Journal of Applied Physics 1998-06, Vol.37 (6R), p.3563
• Main Authors: Bhalchandra Gore, Bhalchandra Gore, Vivek Asgekar, Vivek Asgekar
• Format: Article
• Language: English
• ISSN: 0021-4922; 1347-4065
• DOI: 10.1143/JJAP.37.3563

A method to taper the field amplitude in permanent magnet undulators without changing the undulator gap is presented. It is based on the deviations in the field patterns of the magnet blocks produced by the incorrect orientation of the magnetization vector. The appropriate arrangement of the magnet blocks in the undulator is determined by solving a set of linear equations obtained using the field values which characterize the tapered field profile. The versatility of the method is demonstrated by simulating different profile shapes using the same set of magnet blocks. It is shown that undulator field profiles of required shape and size can be obtained by using magnet blocks of proper specifications. The results of the simulations carried out to study the effects of the taper size, profile shape and the undulator gap on the widths of the distributions of the block magnetization components are presented. As a practical realization of the method a fifteen period long undulator with linearly decreasing field amplitude is assembled. The results of the magnetic field measurements of this undulator are also presented.