An elliptical wiggler beamline for the ALS

A beamline for circularly polarized radiation produced by an elliptical wiggler has been designed at the ALS covering the broad energy range from 50 eV to 2000 eV. The rigorous theory of grating diffraction efficiency has been used to maximize transmitted flux. The nature of the elliptical wiggler insertion device creates a challenging optical problem due to the large source size in the vertical and horizontal directions. The requirement of high resolving power combined with the broad tuning range and high heat loads complicate the design. These problems have been solved by using cooled optics and a variable‐included angle monochromator of the ‘‘constant length’’ type with high demagnification onto its entrance slit.