Design of a helical staggered undulator

A helical staggered undulator with a short period was designed to generate elliptically polarized photons. To enhance the helical field, cryogenic permanent-magnet blocks were added between the poles in hybrid-type staggered arrays, and a further exotic holmium pole was used in an analysis of the pure-type staggered arrays. A greater helical field strength was achieved with an optimal solenoid field. A helical staggered magnet with rotation of the poles was investigated; the stronger horizontal and vertical fields generated elliptically polarized photons over a much wider range. The spectral performance with elliptical polarization is presented. The field homogeneity and the distribution of the integral field on the transverse axis were calculated. The field performance of a helical staggered structure was examined with a three-period mock-up.