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 ∼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.