Liquid gallium cooling of silicon crystals in high intensity photon beams (invited)

Abstract

Further tests on liquidnitrogencooled, thin siliconcrystal monochromators using a focused wiggler synchrotron beam Rev.Performance of a liquidnitrogencooled, thin silicon crystal monochromator on a highpower, focused wiggler synchrotron beam Rev. Sci. Instrum. 66, 3494 (1995); 10.1063/1.1145460 Recent experiments with liquid gallium cooling of crystal diffraction opticsa) Rev. Sci.The high-brilliance, insertion-device-based photon beams of the next generation of synchrotron sources (Argonne's APS and Grenoble's ESRF) will deliver large thermal loads (1-10 kW) to the first optical elements. Considering the problems that present synchrotron users are experiencing with beams from recently installed insertion devices, new and improved methods of cooling these first optical elements, particularly when they are diffraction crystals, are clearly needed. A series of finite element calculations were performed to test the efficiency of new cooling geometries and various cooling fluids. The best results were obtained with liquid Ga metal flowing in channels just below the surface of the crystal. Ga was selected because of its good thermal conductivity and thermal capacity, low melting point, high boiling point, low kinetic viscosity, and very low vapor pressure. Its very low vapor pressure, even at elevated temperatures, makes it especially attractive in UHV conditions. A series of experiments were conducted at CHESS in February of 1988 that compared liquid gaHium-cooled silicon diffraction crystals with watercooled crystals. A six-pole wiggler beam was used to perform these tests on three different Si crystals, two with new cooling geometries and the one presently in use. A special high-pressure electromagnetic induction pump, recently developed at Argonne, was used to circulate the liquid gallium through the silicon crystals. In all experiments, the specially cooled crystal was used as the first crystal in a two crystal monochromator. An infrared camera was used to monitor the thermal profiles and correlated them with rocking curve measurements. A second set of cooling experiments were conducted in June of 1988 that used the intense, highly collimated beam from the newly installed ANL/CHESS undulator. Tests were performed on two new Ga-cooled Si crystals and compared with the standard water-cooled Si crystal. One of the crystals had cooling channels at two levels in the crystal that allowed one to actively control the shape of the crystal surface. The second one had rectangular cooling channels located just beneath the diffraction surface. Both crystals showed major improvements over the water-cooled crystal.

Heat transfer studies for a crystal in a synchrotron radiation beamline

“…In this section, we first obtain temperature distribution in the crystal using rigorous FE analysis. It is seen that there is a large discrepancy between the values of maximum temperature rise in the crystal calculated analytically using existing formulae and the FEM results (Smither et al 1989). We, considering some realistic assumptions, have modified analytical formulae.…”

“…There are variations to these cooling schemes. For ultra high heat loads (radiation from insertion devices) cooling is direct and the coolant is liquid gallium (Smither et al 1989). In addition, some improvised methods like use of thin crystals (Freund et al 1992), Si crystals at cryogenic temperatures , Kuzay 1992, Wang et al 1995, jet cooling (Berman & Hart 1992) etc.…”

“…In spite of numerous FE calculations, very little guideline exists for performance prediction of a new monochromator on a new synchrotron source. Analytical formulae (Smither et al 1989), based on simple physical arguments, have limited applicability in predicting the performance of crystals.…”

<title>Adaptive optics for high-power beamlines using diamond crystal monochromators</title>

“…3 shows the schematic design of a water-jet cooled crystal monochromator. A diamond crystal (1), its diameter between 6 to 10 mm and thickness between 0.1 to 1 mm, is brazed to a copper frame (2). The diamond crystal is cooled by a water jet (3) which is placed co-a_dally within a connecting bar (4) holding the copper frame.…”

<title>Liquid-metal cooling of synchrotron optics</title>

“…The hydraulic diameter d is a parameter that takes into account the size and shape of the cooling channels and is just the diameter of a circular cooling channel. In the case of a rectangular cooling channel, d is approximated by equation (6) …”