Design and Research of Ultra-High Vacuum Chain Clamp Flange for Hefei Advanced Light Facility

Hefei advanced light facility(HALF) using multi-bend achromat(MBA) lattice is planned to be built as a diffraction-limited storage ring(DLSR) in low energy region. Compared with the third-generation light source, the MBA lattice has a more compact layout, so the distance between focusing magnets decreases greatly.Such compactness dissatisfies the installation of the commonly used ConFlat(CF) flange. The ultra-high vacuum(UHV) chain clamp flange only needs a ring of soft chain clamp to fasten two flanges, whose axial dimension, much lower than that of CF flange, is determined by the width of the chain clamp. In addition, the flange mounting is along the radial direction, which requires less installation space. Therefore, the chain clamp flange can meet the demands of the HALF vacuum system. Although the chain clamp flange has been applied in some large facilities around the world, its key techniques are monopolized by foreign vendors, and domestic-related studies are scarce. In order to solve these difficulties, a set of chain clamp flanges with the knife-edge sealing structure were designed. The minimal sealing torque was tested, and the flange was repeatedly mounted and unmounted eight times to evaluate working life. The experiments of bakeout cycles and putting flanges into liquid nitrogen were also carried out. The results indicate that the leak rate of the designed flange can reach the standard of the UHV flange, and the flange has good tolerance for temperature changing. The sealing force and stress distribution of the OFC gaskets have been calculated by force analysis and the finite element method. In future work, the chain clamp flange will be expanded to all sorts of diameters, forming a standardized vacuum component.