Temperature, Silicon Crystal Monochromators at the Chess F-2 Wiggler Station

Introduction This Light Source Note summarizes the results of the single crystal monochromator high-heat-load tests performed at the CHESS F-2 wiggler station. The results from two different cooling geometries will be presented: (1) the "pin-post" crystal and (2) the "criss-cross" crystal. The data presented were taken in August 1993 (water-cooled pin-post) and in April 1995 (water-and gallium-cooled pin-post crystal and gallium-cooled criss-cross crystal). The motivation for trying these cooling (or heat exchanger) geometries is to improve the heat transfer efficiency over that of the conventional slotted crystals. Calculations suggest that the pin-post or the micro channel design can significantly improve the thermal performance of the crystal [1]. The pin-post crystal used here was fabricated by Rocketdyne Albuquerque Operations (RAO, formerly Rockwell Power Systems). From the performance of the conventional slotted crystals, it was thought that increased turbulence in the flow pattern may also enhance the heat transfer. The criss-cross crystal was a simple attempt to achieve the increased flow turbulence. The criss-cross crystal was partly fabricated in-house (cutting, etching and polishing) and bonded by RAO. Finally, a performance comparison among all the different room temperature silicon monochromators that have been tested by the APS will be presented. The data will include measurements with the slotted crystal and the core-drilled crystals. Altogether, the data presented here were taken at the CHESS F-2 wiggler station between 1991 and 1995. Figure 1 shows the first APS prototype pin-post crystal fabricated by Rocketdyne Albuquerque Operations. The face plate of the crystal is Si(111). After the final assembly, the "hot-wall" thickness of the face-plate was ground down to 1 mm. In-house double-crystal rocking curve measurements show that, over an area of 10x4 mm 2, the fabrication-induced strains were about 1.5 arc seconds. At that time (-1993), our in-house topography station was not ready, and thus no topographs of the crystal were taken. The first synchrotron test of this crystal took place at the F2 wiggler station at CHESS in August 1993. The experimental setup is shown in figure 2. Note that since the x-ray beam from the wiggler is actually shared between the F1 and F2 stations, only half the wiggler beam (horizontally) is available in F2. Thus, the horizontal power profile of the beam in F2 is half a parabola, with the hottest part of the beam being the north side. With all the slits wide open, the total size of the beam into …