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.

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Heat loading tests were conducted with up to 360 W ofundulator radiation incident on liquidgallium-cooled silicon monochromators. Rocking curve measurements and temperature profiles (infrared camera) were obtained as a function of beam current. With large heat loads, the width of the rocking curves were observed to broaden and the gain in output flux per rnA of beam current was significantly less at high beam currents than during low-current operation. The best performance was obtained using a slotted crystal with cooling channels located 0.76 mm below the surface. This crystal showed strong heating effects only above 40 rnA and continued to produce an increase in output flux with beam current at the highest current tested of76 rnA.

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