Elliptical multipole wiggler facility at the Advanced Photon Source

The use of circularly polarized radiation is advantageous for the study of magnetic materials using x-ray scattering techniques. The APS is an ideal source of x-ray radiation for such studies. We present a description of the elliptical multipole wiggler (EMW) [S. Yamamoto, H. Kawata, H. Kitamura, and M. Ando, Phys. Rev. Lett. 62, 2672 (1989)] to be constructed at the APS. This device has been chosen for reasons of tunability and special polarization properties. This insertion device is capable of producing circularly polarized x rays on axis. The EMW period will be λ_u=16 cm, the number of full strength poles in the hybrid structure is 31, and the device length is 2.8 m. The hybrid magnetic structure produces a peak vertical magnetic field with K_y=14 and the electromagnet provides horizontal magnetic field with K _x=1-2. The frequency of the horizontal field change is up to 10 Hz. The beamline will consist of three stations operating in tandem with only one station receiving x rays at any one time. The three stations have three distinct functions, namely Compton scattering, magnetic scattering, and surface scattering. Special considerations will be made to insure the proper control of the polarization when using circular polarized light. The design of the elliptical multipole wiggler beam line will follow an approach very close to that developed by Kawata et al. [Rev. Sci. Instrum. 60, 1885 (1989)]. Our objective is to obtain a high photon flux with energies above 40 keV and well characterized polarization.