Design of the flange-sealed beam window for EBTP in S 3 FEL

Abstract Beam windows (BWs) serve as the interface between ultra-high vacuum of beamline and low vacuum of beam dump in the Electron Beam Test Platform (EBTP) of the Shenzhen Superconducting Soft X-Ray Free Electron Laser (S 3 FEL), to isolate and protect ultra-high and particle-free (PF) vacuum environments. Different from previous brazed BWs and flange-sealed BWs used in some facilities, a novel flange-sealed BWs with water cooling has been proposed, utilizing a beryllium sheet as the window and flange fastened to achieve vacuum sealing, with the improvements in sealing, high-temperature resistance and cooling performance and advantage of structure simplicity, low cost, easy maintenance and ease of processing without brazing of window to flange or tube. To meet demands of mechanical stability of BW in two operating modes, which might load differential pressure of about 1 atm and energy deposition of electron beam on window film, structural and thermal analysis have been performed to verify the thickness and structure of the window. Besides, the helium detection has been implemented to measure the vacuum leakage of BW, with the results of leakage less than 1 × 10 -10 Pa·m 3 /s at two diffrent seal plane and water cooling channels. To evaluate the robustness of BWs during operation, safety analysis has been conducted with non-ideal situations, including beam shrinkage and lower convective heat transfer coefficient. The results indicate that with shrinkage ratio less than 30%, and the cooling water flow rate higher than 0.8 m/s, BWs could operate safely. This study demonstrates the viability of the flange-sealed BW with water cooling, and provides both theoretical and experimental foundations for their future application.