Helical wiggler design with an array of uniform, small, permanent magnets

Abstract

An ideal helical wiggler field can be generated inside a cylindrical waveguide by an array of permanent magnets properly distributed and oriented within a cylindrical shell surrounding the waveguide. An approach to the design of the array of magnets and means for assessing the quality of the resultant wiggler field are discussed. The design is optimized in the sense of maximized coupling from the magnets to the field region, subject to practical constraints of uniformity of strength of each magnet in the array. For any array of magnets, the quality of the generated field is expressed in terms of the relative levels of undesired harmonics of the pure wiggler. A “bandolier” design is suggested and evaluated quantitatively, demonstrating that useful wigglers can be generated with a reasonable number of small, uniform permanent magnets.