High-heat-load studies of silicon and diamond monochromators using the APS/CHESS prototype undulator Page: 3 of 45
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High-Heat-Load Studies of Silicon and Diamond Monochromators
Using the APS/CHESS Prototype Undulator
D.M. Mills, W.-K. Lee, R.K. Smither and P. B. Fernandez
Advanced Photon Source
Argonne National Laboratory
9700 S. Cass Avenue
Argonne, IL 60439
The results of the latest high-heat-load studies made on the APS/CHESS prototype undulator are
summarized. Four different crystals were tested: two slotted, symmetrically cut silicon crystals and a core-
drilled, asymmetrically cut silicon crystal (which were gallium cooled), and a diamond crystal that was jet cooled
using water. The purpose of the silicon crystal tests was to reevaluate the surface power loading at which
appreciable degradation of the diffraction efficiency was observed. The diamond tests, allotted only a brief period
of time during the testing period, were our first attempt at using diamonds for high-heat-flux x-ray
monochromators and were performed primarily to gain first-hand experience with diamond monochromators.
Measurements with the silicon crystal at 5 keV reconfirmed our previous measurements of performance
degradation at around 4-6 watts/mm2 using liquid gallium with slotted coolant channels. A value of only 2
watts/mm2 was observed to cause a degradation of the diffraction performance at 15 keV with the same crystals
due to the increased sensitivity to strain because of the reduced Darwin widths. The performance of the
asymmetric crystal, with its core-drilled coolant channels, was not found to be as good as that of the slotted
crystals. This was probably due to poorer heat transfer properties of the core-drilled geometry in combination
with the narrowing of the rocking curves because of the asymmetric cut. Fabrication issues for construction of the
gallium-cooled crystals is also discussed.
Although the diamonds were only successfully tested at low total power (17 watts total incident power, 25
w/mm2 incident power density), the results were very encouraging and motivated us to accelerate our program on
the use of diamonds for high-heat-load monochromators.
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Mills, D.M.; Lee, W.K.; Smither, R.K. & Fernandez, P.B. High-heat-load studies of silicon and diamond monochromators using the APS/CHESS prototype undulator, report, September 16, 1994; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc791889/m1/3/: accessed March 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.