High-heat-load synchrotron tests of room-temperature, silicon crystal monochromators at the CHESS F-2 wiggler station

Abstract

Int roduc t ioq 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 (waterand 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 microchannel design can significantly improve the thermal performance of the crystal Ill. The pinpost 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. Here, the assumption is that the MTDWat, = 3 MTDgallim. This assumption comes from past empirical observations. Theoretical calculations [2,3] suggest that, depending on the actual geometry, MTDWabr = 1.5-2.5 MTDgallium. Thus, for example, in figure 26, the MTD for the liquid-galliumcooled slotted crystal ranges from 4-7 O C. We assume then, that if water were used as a coolant instead, the MTD ranges would be from 12-21" C, as shown in figure 27.

A thermal deformation optimization method for cryogenically cooled silicon crystal monochromators under high heat load

“…For hard X-ray monochromators, the crystal thermal deformation would not only broaden the rocking curve, resulting in flux loss and worse energy resolution, but also deform the wavefront, which has a negative impact on beam angular divergence and coherence preservation. In order to remove the high heat loads efficiently and improve optical performance, several liquid nitrogen (LN2) cooled silicon crystal monochromators have been applied successfully at high heat loads since the early 1990s (Lee et al, 1995;Mochizuki et al, 1995;Shastri et al, 2002;Wang et al, 2010;Stimson et al, 2019), owing to the combined advantages of high thermal conductivity and low thermal expansion coefficient at cryogenic temperatures for silicon crystal (Zhang, 1993;Lee et al, 2000Lee et al, , 2001. Subsequently, extensive research has been conducted successively on high-heat-load monochromator cooling techniques (Cao et al, 2011;Khorunzhii et al, 2003).…”

<title>Progress in silicon-to-silicon direct bonding and its application to synchrotron x-ray optics</title>

“…Figure 1 shows a typical arrangement for such a setup. A cooling fluid (we have investigated the use of both water [2] and liquid gallium [3]) flows in from the bottom, over the fins of the heat exchanger, and out through the exit port. The optimal thickness, length, and spacing of the fins that make up the heat exchanger, and hot face thickness (fin-to-diffraction-surface distance) depend strongly on the properties and flow velocity of the coolant used.…”