VESPERS: A Beamline for Combined XRF and XRD Measurements

VESPERS (VEry Sensitive Elemental and Structural Probe Employing Radiation from a Synchrotron) is a bending magnet beamline that is just beginning construction at the Canadian Light Source. The beamline has several novel design elements that are intended to increase its operating flexibility and availability to users. First, there is a requirement to deliver a microscopic beam with a variable bandwidth, thus enabling the generation of Laue diffraction patterns and high yield X-ray fluorescence spectra from the same region preferably simultaneously. Thus, the bandpass of the VESPERS monochromator can be readily changed to focus radiation into the same 2-4 micron diameter area that is either polychromatic or having a bandwidth of 10%, 1.6% or 0.01%. This allows the user to change the diffraction pattern to suit the complexity of the crystal and the spectral signal to noise ratio to suit the detection sensitivity required. Second, the beamline is designed to have two branches capable of operating simultaneously and virtually independently using the same primary optics. These design features are accomplished using four separate beams originating at four pinholes at the entry to the Primary Optical Enclosure. The compound focus design uses spherical mirrors to focus both polychromatic and pre-monochromatic beams onto the intermediate slits. A pair of bendable K-B mirrors in the experimental hutch is used to demagnify the beam further down to micron size. The photon energy of this beamline is 6-30 keV.