The Cryogenic Cooling Program at the Advanced Photon Source

This paper describes the experimental and analytical program in cryogenic cooling of high-heatload optics at the Advanced Photon Source. A prototype liquid nitrogen pumping system has been procured. This pump provides a variable flow rate of 1 to 10 gpm of pressurized liquid nitrogen and is sized to handle up to 5 kW of optic heat load. Also, a high-vacuum, doublecrystal monochromator testing tank has been fabricated. This system will be used to test cryogenic crystals at existing synchrotron sources. A finite element analysis has been performed for a cryogenically cooled Si crystal in the inclined geometry for undulator A at 100 mA. The inclination angle was 80°. It was set to diffract from the <111> planes at the first harmonic energy of 4.2 keV. The maximum slope error in the diffraction plane was calculated to be about 1 μrad with a peak temperature of 94 K. An analysis has also been performed for a cryogenically cooled "thin" crystal oriented in the Bragg geometry, which accepts 87% of the first harmonic photons at 3.866 keV. The total absorbed power was 131 W at 100 mA current, and the peak temperature was 124 K.