Monte Carlo simulation of the CHESS C1 beamline

Using the C1 beam line Si(111) monochromator, the narrowest rocking curves we could obtain were of order 150 μr fwhm. This width was understood as coming from dispersion, due to the large energy width of the monochromated beam. The advantages of this setup were that the beam intensity was higher than we needed and the beam size filled the 15mm x 15mm beam line aperture. With such a large beam it was possible to expose the entire diamond in a single scan.

As a means to narrow the energy distribution of the beam, a second monochromator was installed between the C1 monochromator and the diamond. It was a symmetric channel-cut silicon (220) cyrstal. We rotated the crystal about the (220) axis by a few degrees to get rid of the (224) and higher reflections.