Design and test of high power X-band dry load for SXFEL and SHINE

BackgroundThe Shanghai soft X-ray Free Electron Laser (SXFEL) and the Shanghai High repetition rate XFEL and Extreme light facility (SHINE) are equipped with various high-power microwave components, including traveling wave accelerating tubes, deflection cavities, pulse compressors, etc.PurposeThis study aims to develop two high-power stainless steel absorbing loads, so as to meet the testing and operational requirements of these components at high power levels.MethodsFirstly, an initial load model was designed through simulation methods, and the microwave parameters were optimized. Then, the convection heat transfer coefficient in the waterway was calculated using theoretical calculations. Based on this information, thermal analysis was conducted on the mechanical model of the load to determine its temperature distribution under working conditions. Finally, the loads were manufactured and their RF parameters were measured using a vector network analyzer both in the clamping state and after welding.ResultsThe two X-band loads feature a waveguide structure with periodic grooves, and are operated at 11.424 GHz and 11.988 GHz respectively. The simulation results show that the bandwidth of two loads below -20 dB near the center frequency reaches over 100 MHz. The experimental test results are in good agreement with the simulation calculation results, meeting the design requirements.ConclusionsThe developed high power X-band dry loads described in this study satisfy operating requirements for SXFEL and SHINE.