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 strai ght section of the NSLS X-Ray ring. The device consists of a vertical permanent-magnet wiggler and a horizontal electromagnet wiggler. The e lectromagnets allow the wiggler to produce on-axis circularly polarize d soft x-rays with the capability of AC modulation of the polarization . The maximum switching frequency that can be reached is 100 Hz.The de gree of circular polarization of the radiation from the wiggler was ch aracterized by making magnetic circular dichroism measurements using t he 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 deg ree of circular polarization of approximately 75% using an aperture wi th a vertical acceptance of 87 mu rad. Because both the left- and righ t-circularly polarized photons traverse identical paths through the be amline optical system, significantly smaller intensity fluctuations as sociated with switching of the polarization were observed than are typ ically possible at bending magnet beamlines. This, together with the r elatively fast modulation rate, means that it will now be feasible to perform a variety of experiments that have not been possible using ben ding magnet sources.