Difference between revisions of "Monte Carlo simulation of the CHESS C1 beamline"
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| − | 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 | + | 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 12mm 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. The narrowest rocking curve width we saw with the second monochromator in place was about 20 μr fwhm, still larger than the intrinsic Darwin width of diamond (220) of 7 μr at 15 keV, but much better than before. However the vertical beam dimension was now reduced from | + | 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. The narrowest rocking curve width we saw with the second monochromator in place was about 20 μr fwhm, still larger than the intrinsic Darwin width of diamond (220) of 7 μr at 15 keV, but much better than before. However the vertical beam dimension was now reduced from 12 mm down to about 3 mm. |
A Monte Carlo program has been written to simulate the behaviour of the C1 beam line for diamond rocking curve measurements. The Monte Carlo will be used to | A Monte Carlo program has been written to simulate the behaviour of the C1 beam line for diamond rocking curve measurements. The Monte Carlo will be used to | ||
| − | * reproduce the observed | + | * reproduce the observed rocking curve widths, |
| + | * explain why the second monochromator reduced the beam size, | ||
| + | * test ideas for a new monochromator that can combine high. | ||
| + | definition with a large beam spot size and good intensity. | ||
| + | The Monte Carlo program was used to simulate the C1 beam line under the following conditions. | ||
| + | # vertical source size 2 mm rms, | ||
| + | # flat source spectrum over the range 14.89 - 15.11 keV, | ||
| + | # distance from source to first monochromator 20 m, | ||
| + | # first monochromator is Si(111) with b=4, | ||
| + | # second monochromator (when present) is Si(220) with b=1, | ||
| + | # diamond scanned ±500 μr around the (220) peak at 15 keV. | ||
Revision as of 11:34, 10 March 2007
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 12mm 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. The narrowest rocking curve width we saw with the second monochromator in place was about 20 μr fwhm, still larger than the intrinsic Darwin width of diamond (220) of 7 μr at 15 keV, but much better than before. However the vertical beam dimension was now reduced from 12 mm down to about 3 mm.
A Monte Carlo program has been written to simulate the behaviour of the C1 beam line for diamond rocking curve measurements. The Monte Carlo will be used to
- reproduce the observed rocking curve widths,
- explain why the second monochromator reduced the beam size,
- test ideas for a new monochromator that can combine high.
definition with a large beam spot size and good intensity. The Monte Carlo program was used to simulate the C1 beam line under the following conditions.
- vertical source size 2 mm rms,
- flat source spectrum over the range 14.89 - 15.11 keV,
- distance from source to first monochromator 20 m,
- first monochromator is Si(111) with b=4,
- second monochromator (when present) is Si(220) with b=1,
- diamond scanned ±500 μr around the (220) peak at 15 keV.
