A thermal deformation optimization method for cryogenically cooled silicon crystal monochromators under high heat load

• Published in: Journal of synchrotron radiation Vol. 31; no. 2; pp. 260 - 267
• Main Authors: Liu, Jiayin, Ji, Zhan, Fan, Yichen, Yan, Xinxin, Wang, Miaomiao, Qin, Hongliang
• Format: Journal Article
• Language: English
• Published: 5 Abbey Square, Chester, Cheshire CH1 2HU, England International Union of Crystallography 01.03.2024; John Wiley & Sons, Inc
• Subjects: Cooling; cryo-cooled scheme; Crystal surfaces; Deformation; Distortion; Emittance; Footprints; Light sources; Maximum power density; monochromator; Monochromators; Optimization; Photons; Radiation; Radiation sources; Research Papers; Silicon; silicon crystal; Synchrotron radiation; Temperature distribution; thermal deformation; monochromator; cryo-cooled scheme; thermal deformation; silicon crystal
• ISSN: 1600-5775; 0909-0495; 1600-5775
• DOI: 10.1107/S1600577523010664

A method to optimize the thermal deformation of an indirectly cryo‐cooled silicon crystal monochromator exposed to intense X‐rays at a low‐emittance diffraction‐limited synchrotron radiation source is presented. The thermal‐induced slope error of the monochromator crystal has been studied as a function of heat transfer efficiency, crystal temperature distribution and beam footprint size. A partial cooling method is proposed, which flattens the crystal surface profile within the beam footprint by modifying the cooling contact area to optimize the crystal peak temperature. The optimal temperature varies with different photon energies, which is investigated, and a proper cooling strategy is obtained to fulfil the thermal distortion requirements over the entire photon energy range. At an absorbed power up to 300 W with a maximum power density of 44.8 W mm−2 normal incidence beam from an in‐vacuum undulator, the crystal thermal distortion does not exceed 0.3 µrad at 8.33 keV. This method will provide references for the monochromator design on diffraction‐limited synchrotron radiation or free‐electron laser light sources. A partial cooling method is proposed for minimizing thermal deformation of the monochromator crystal at low‐emittance diffraction‐limited synchrotron radiation beamlines. The influence of the heat transfer efficiency, crystal temperature distribution and beam size on crystal surface was investigated, and a set of thermal deformation optimization techniques for high‐heat‐load monochromators was developed.