TEST OF A HIGH-HEAT-LOAD DOUBLE-CRYSTAL DIAMOND MONOCHROMATOR AT THE ADVANCED PHOTON SOURCE

We have tested the first diamond double-crystal monochromator at the A dvanced Photon Source (APS), The monochromator consisted of two synthe tic type Ib (1 1 1) diamond plates in symmetric Bragg geometry. The si ngle-crystal plates were 6 mm x 5 mm x 0.25 mm and 6 mm x 5 mm x 0.37 mm and showed a combination of mosaic spread/strain of the order of 2- 4 arcsec over a central 1.4 mm-wide strip. The monochromator first cry stal was indirectly cooled by edge contact with a water-cooled copper holder. We studied the performance of the monochromator under the high -power X-ray beam delivered by the APS undulator A. By changing the un dulator gap, we varied the power incident on the first crystal and fou nd no indication of thermal distortions or strains even at the highest incident Power (200 W) and power density (108 W/mm(2) in normal incid ence). The calculated maximum power and power density absorbed by the first crystal were 14.5 W and 2.4 W/mm(2), respectively. We also compa red the maximum intensity delivered by this monochromator and by a sil icon (1 1 1) cryogenically cooled monochromator. For energies in the r ange 6-10 keV, the flux through the diamond monochromator was about a factor of two less than through the silicon monochromator, in good agr eement with calculations. We conclude that water-cooled diamond monoch romators can handle the high-power beams from the undulator beamlines at the APS. As single-crystal diamond plates of larger size and better quality become available, the use of diamond monochromators will beco me a very attractive option.