Characterization Of A Novel Elliptically Polarized Wiggler

We report on the initial characterization of an elliptically polarized wiggler built by a collaboration between the Advanced Photon Source, the Budker Institute of Nuclear Physics, and the National Synchrotron Light Source. The wiggler has recently been installed in the X13 straight section of the NSLS X-Ray ring. The device consists of a vertical permanent-magnet wiggler and a horizontal electromagnet wiggler. The electromagnets allow the wiggler to produce on-axis circularly polarized soft x-rays with the capability of AC modulation of the polarization. The maximum switching frequency that can be reached is 100 Hz.The degree of circular polarization of the radiation from the wiggler was characterized by making magnetic circular dichroism measurements using the X13A soft x-ray beamline. For a horizontal deflection parameter, K-x, of 1.6, the dichroism effects at the Fe L(2,3) edges indicate a degree of circular polarization of approximately 75% using an aperture with a vertical acceptance of 87 mu rad. Because both the left- and right-circularly polarized photons traverse identical paths through the beamline optical system, significantly smaller intensity fluctuations associated with switching of the polarization were observed than are typically possible at bending magnet beamlines. This, together with the relatively fast modulation rate, means that it will now be feasible to perform a variety of experiments that have not been possible using bending magnet sources.