Halbach undulators using right triangular magnets

Abstract

Undulators and wigglers based on Halbach arrays have been in widespread use since their description in the 1980s, due to the high fields they generate from permanent magnets. The most common implementation of a pure permanent magnet Halbach undulator consists of four magnetic segment widths per undulator period. In typical undulators with periods of order ∼cm it is straightforward to use sufficiently small magnetic segments to achieve the desired undulator period. However, in the context of new microundulators with periods of order ∼mm or shorter, there is a lower bound on the feature sizes achievable by existing fabrication techniques. This motivates the use of modified Halbach arrays comprised of right triangle magnet segments with only two magnet segment widths per undulator period. These configurations are demonstrated to have superior field strengths to up-down arrays with no increase to the undulator period. Additional considerations arising from the broken symmetries in such configurations, such as the presence of previously forbidden harmonic components, are also considered. Such right triangle Halbach arrays may be fabricated using MEMS techniques for use in the next generation of compact light sources.