Zhang, Y.S. Liang, H. Lu, Y.S. Shen, D.S. Zhang, L. JACoW Publishing Geneva, Switzerland 2673-5520 978-3-95450-250-9 10.18429/JACoW-MEDSI2023-TUPYP018 English 55-57 vacuum cavity photon cryogenics ISOL Contribution to a conference proceedings 2024 2024-07 https://doi.org/10.18429/JACoW-MEDSI2023-TUPYP018 https://jacow.org/medsi2023/papers/tupyp018.pdf Horizontal diffracting double crystal monochromator(HDCM) are usually used in a 4th generation light source beamline due to the larger source size in the horizontal direction. This paper introduces the mechanical design and optimization of a HDCM for Low-dimension Structure Probe Beamline of HEPS. In order to achieve the high stability requirement of 50nrad RMS, the structural design is optimized and modal improved through FEA. In order to meet the requirement of a total crystal slope error below 0.3¿rad, FEA optimizations of the clamping for first and second crystal are carried out. The vacuum chamber is optimized to become more compact, improving the maintainability. Fabrication of the HDCM is under way. The results show that the design is capable of guarantee the required surface slope error, stability, and adjustment requirements.