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A cooled double crystal monochromator system is used on many high heat load X-ray synchrotron radiation beamlines in order to select, by diffraction, a narrow spectrum of the beam. The wavelength of the diffracted beam is tuned by changing the angle of incidence, per the Bragg equation. Thermal deformation of the first crystal monochromatorand the potential loss of beam brillianceis often a main concern. However, if downstream beam focusing is planned, the lensing effect of the monochromator must be considered even if thermal deformations are small enough to have any imperceptible impact on intensity. In this paper we report on recent experiments at an Advanced Photon Source (APS) beamline that uses focuses compound diffractive lenses downstream of an X-ray monochromator system. Increasing the X-ray beam power by increasing the storage ring current from 100 mA to 130 mA resulted in the doubling of the focal distance, to some location outside the experimental hutch. We show quantitatively that this is be due to the well-known lensing effect of a distorted monochromator that results in the creation of a virtual source, at some distance downstream of the actual source. An analysis of the defocusing and options to mitigate are provided.

An engineering research program has been conducted at the Advanced Photon Source (APS) in order to determine the thermomechanical conditions that lead to crack formation in GlidCop 1 , a material commonly used to fabricate X-ray absorbers at X-ray synchrotron facilities. This dispersion-strengthened copper alloy is a proprietary material and detailed technical data of interest to the synchrotron community is limited. The results from the research program have allowed new design criteria to be established for GlidCop 1 X-ray absorbers based upon the thermomechanically induced fatigue behavior of the material. X-ray power from APS insertion devices was used to expose 30 GlidCop 1 samples to 10000 thermal loading cycles each under various beam power conditions, and all of the samples were metallurgically examined for crack presence/geometry. In addition, an independent testing facility was hired to measure temperature-dependent mechanical data and uniaxial mechanical fatigue data for numerous GlidCop 1 samples. Data from these studies support finite element analysis (FEA) simulation and parametric models, allowing the development of a thermal fatigue model and the establishment of new design criteria so that the thermomechanically induced fatigue life of X-ray absorbers may be predicted. It is also demonstrated how the thermal fatigue model can be used as a tool to geometrically optimize X-ray absorber designs.

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