High-heat-load studies of cryogenically internally cooled silicon double crystal monochromator above and away from cooling channels

High-heat-load studies on Si double crystal monochromator that is internally cooled with liquid nitrogen flow were performed as APS-Upgrade planned to increase ring current to 150 mA. The monochromator consists of two separated Si crystals with diffraction surfaces oriented along (111), diffracting vertically to produce a fixed 35 mm beam offset. Rocking curves were measured for the beam footprint on the first crystal lying both above and away from cooling channels. The beam was produced by two collinear APS undulators type A, each 2.4 m long with 3.3 cm period. Most of the data were obtained for a monochromator set to Bragg diffract at 8 keV for the Si (111) reflection. Through the use of aluminium filters between two sequential ion chambers, we also measured the Si (333) reflection diffracting at 24 keV. We measured the FWHM of rocking curves with either one or both undulators tuned so that the energy of the 1st harmonic matched the Si (111) Bragg energy. Our results show sensitivity to the distance between the beam footprint above and away from cooling channels under high power conditions.