THE UNDULATOR BEAMLINE AT THE SRS DARESBURY

The design and performance of the undulator beamline 5U.1 at the SRS used for soft x-ray spectroscopy is reported and compared with the theoretical expectation of the intensity, resolution, and polarization. The beamline consists of a ten-period permanent magnet variable gap undulator followed by an entrance slitless plane grating monochromator. The energy region covered is from 0.1 to 1 keV. The design is similar to the SX700 but uses a spherical instead of an ellipsoidal focusing mirror. To eliminate the large horizontal beam width at the exit slit the beamline has been modified to include a post-focusing mirror. The spherical focusing mirror has been changed to one with a larger radius resulting in a decreased demagnification, thereby essentially eliminating primary coma. The monochromator contains an ion-etched and lamellar profile 1200-lines/mm plane grating of Pt-coated CVD SiC on a graphite substrate. The high flux of the undulator makes the beam line suitable for SEXAFS studies and for work involving soft x-ray fluorescence detection. The combination of high flux and high resolution is especially advantageous for atomic and molecular spectroscopy and to resolve the quasiatomic structures which are observed in localized 3d transition metal compounds.