A cryogenically cooled channel-cut crystal monochromator using a helium refrigerator and heat exchanger

Silicon crystals at room temperature employed as x-ray monochromators on synchrotron radiation beamlines, when subjected to high-power-density loading, suffer thermal distortions which compromise their x-ray diffraction efficiency and result in a reduction of the inherent brilliance of the synchrotron beam. At cryogenic temperatures however (below 150 K), silicon crystals suffer little or no thermal distortions under high-power-density loading. The design and implementation of a channel-cut silicon crystal monochromator which is cooled to as low as 50 K, using a commercial helium refrigerator and circulation system and a custom-designed heat exchanger for the monochromator crystal, are described. Test results have been obtained on the National Synchrotron Light Source X13B in-vacuum undulator beamline as well as the higher power X25 wiggler beamline. (C) 2002 American Institute of Physics.