Undulator A characteristics and specifications

The Advanced Photon Source (APS) Undulator A is a planar device optimized for the hard x-ray region. In the mature phase of operation, it satisfies the requirement of providing high brilliance x-rays continuously over the tuning range from 4.2 key to above 30 key, using the first and the third harmonic radiation from the undulator. This is achieved through the choice of the 3.3-cm long period, the hybrid undulator design, and the stringent requirements on the magnetic field quality. The undulator is 2.4 m long (including the end sections) with 72 periods. The magnetic structure consists of Nd-Fe-B magnets with vanadium permendur poles. The field errors are specified in this paper to ensure that the third harmonic radiation from the actual device will achieve at least 70% of its theoretical brilliance. The first harmonic is less sensitive to field errors and thus should attain brilliance even closer to the theoretical value. The predicted magnetic fields at various gap values based on a detail design of the magnetic structure of Undulator A are listed in this paper.