The Advanced Light Source (ALS) at the Lawrence Berkeley Laboratory requires insertion devices with fields sufficiently accurate to take advantage of the small omittance of the ALS electron beam. To maintain the spectral performance of the synchrotron radiation and to limit steering effects on the electron beam these errors must be smaller than 0.25%. This paper develops a procedure for calculating the steering error due to misalignment of the easy axis of the permanent magnet material. The procedure is based on a three dimensional theory of the design of hybrid insertion devices developed by one of us. The acceptable tolerance for easy axis misalignment is found for a 5 cm period undulator proposed for the ALS.

The U5.0 undulator, currently under design, is the first in a series of insertion devices planned for the Advanced Light Source at LBL U5.0 parameters include a 5 cm period, 5 m length with a 0.837 T maximum field at a 14 mm gap. A hybrid configuration utilizing Nd-Fe-B permanent magnet material and Vanadium Permendur poles is used for the magnetic structure. Construction is modular with many pole assemblies attached to a pole mount, which in turn is fastened onto one of the backing beams. Vertical field integral correction at the ends is with permanent magnet rotators. The support structure features a 4-post configuration, a rigid base with 3 kinematic floor supports and 2 rigid 5 m long backing beams that fit within the 2.4 m high accelerator enclosure. The drive system is computer controlled utilizing a stepper motor and shaft encoder coupled to a roller-screw/nut and chain drive train. Vacuum chamber design is a rigid configuration with a 10 mm vertical by 218 mm horizontal aperture of 55 m length. Chamber fabrication features a two-piece welded chamber of 5083 H321 aluminum. Pumping is with ion and titanium sublimation pumps. 'This work supported by the

An integrated system to produce and utilize variable-polarization radiation from a crossed undulator source on the Aladdin storage ring is being designed in a multilaboratory collaboration. Brief discussions of the motivation and options available precede a description of the source. Comments on ongoing work are also presented.

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