Comparative study on cooling schemes for Hefei Advanced Light Facility beamline reflector

BackgroundThe ultra-high-resolution monochromator in Hefei Advanced Light Facility (HALF) impose stringent demands on both the surface error and stability of Plane Mirror (PM).PurposeThis study aims to compare three cooling schemes and evaluate their effects on surface error of PM under high heat loads.MethodFirstly, finite element analysis (FEA) simulations were systematically conducted on a 360-mm-long silicon substrate subjected to maximum absorbed power of 64 W with peak power density of 0.2 W·mm-2. Then, three cooling configurations were analyzed: side cooling using liquid metal (eGaIn) thermal interface, side cooling with indium film interface, and internal cooling with embedded channels. Finally, surface deformation was evaluated by peak-to-valley distortion and root mean square (RMS) residual slope error at cooling water flow rate of 2 L·min-1.ResultsThe FEA results show that the liquid metal (eGaIn) side-cooling method demonstrates optimal performance with total RMS surface error of 190 nrad, satisfying the 200 nrad design threshold without clamping deformation. The indium-based side cooling exhibits comparable thermal efficiency with 190 nrad total error but requires 0.6 MPa clamping pressure, resulting in 51 nrad clamping-induced deformation and higher flow-induced vibration. The internal cooling achieves minimal thermal deformation with 179 nrad total error but experiences significant flow-induced vibration due to proximity of cooling channels to optical surface.ConclusionsThe liquid metal side cooling strategy provides superior preservation of optical surface quality, it effectively balances thermal contact resistance with mitigation of flow-induced vibration through mechanically isolated support structure. Compared to indium film side cooling (contact resistance: 8.3×10-5 m2·K·W-1 at 0.6 MPa) and internal cooling, the liquid metal (eGaIn) side cooling (thermal contact resistance: 1×10-5 m2·K·W-1) approach demonstrates critical advantages in extreme thermal-mechanical operating conditions for fourth-generation synchrotron radiation sources.