6-m TGM implementation at the Wisconsin Synchrotron Radiation Center (SRC)

Abstract

We recently commissioned the SRC/Vanderbilt University 6‐m toroidal grating monochromator beamline. The problems with mirror heating, signal normalization, monochromator control, and scattered light reduction have led to several innovations on this line, making for a better user interface and adding to the stability and reliability of the final image. We discuss these innovations, and how they affect the user. They include a built‐in laser alignment system, a sapphire windowed gate valve, entrance mirror temperature stabilization, computer automation and control, a beam‐chopper, and the capability of real‐time monitoring of the photon flux during the experiment. We have used noble gas resonance lines to carefully characterize the wavelength resolution of the beamline as a function of energy over a range of beamline parameters. The results demonstrate that by limiting the horizontal width of the image at the slits, and by masking outer portions of the gratings, the flux/bandwidth ratio can be improved at the points where the exit slit location does not coincide with the Rowland circle. These same resonance lines, in conjunction with accurate measurements of the grating rotation angle as a function of scan‐drive displacement, are used to correct for imperfections in the surface of the drive‐flat and thus obtain a precise and accurate determination of wavelength versus scan‐drive displacement.