Structure design and implementation of a water cooling sub-20 nm multilayer Kirkpatrick-Baez mirror system in the Structural Dynamics beamline ID23 at HEPS

The first water-cooling nano multilayer Kirkpatrick-Baez mirror system in the Structural Dynamics beamline (ID23) at High Energy Photon Source (HEPS) has been implemented. An Invar gantry is engineered to achieve a balance between light weight and stability. The cooling system, including eutectic gallium-indium (eGaIn), copper braids and a cooling water circuit with a multi-bend copper pipe in a compact space, decouples movement and mitigates vibration. The mirror cooling holders introduce less than 0.5 nm RMS height error and 0.1 µrad RMS slope error in the mirror surface shapes. A series of stability tests is applied to verify the mechanism structure. In a 1 h test assessment using a water-cooling flow of 4.5 L min^-1, the system demonstrated a positional stability of 5.96 nm and an angular stability of 86.76 nrad from 1 Hz to 500 Hz. The focal spot size of 13.39 nm × 15.15 nm (H × V) at a photon energy of 21.8 keV demonstrates the system's performance.