Performance limits of indirectly cryogenically cooled silicon monochromators--experimental results at the APS.

The results of high-heat-load tests of indirectly cryogenically cooled silicon monochromators are presented. The measurements show that, provided that the total power absorbed by the crystal is less than approximately 150 W, indirect cryogenically cooled silicon monochromators will perform well, with thermal-induced slope errors of less than 2 arcsec. At the Advanced Photon Source, this corresponds to the undulator closed-gap (11 mm) condition at 100 mA with white-beam slit sizes slightly larger than the full width at half-maximum of the radiation central cones. The dependence of the slope errors on the thermomechanical properties of silicon are discussed and clearly demonstrated.