Design and testing of a compact triple differential pumping chamber for gas attenuators

The gas attenuator (GAT) is a crucial device to attenuate the intensity of the free-electron laser for Shenzhen Superconducting Soft X-ray Free-electron Laser (S³FEL). In most current GATs, high-pumping-speed mechanical pumps have been employed as the first stage of the differential pumping system (DPS) to achieve the working pressure transition. Thus, a compact triple differential pumping chamber (TDPC) based on 3D printing was designed in our preliminary research of GATs to realize a compact, rapid and cost-effective pressure transition. The simulation results reveal that it yields good differential capability with three low-speed scroll pumps (8 L s^-1) and efficient differential performance from 200 Pa to 22.3 Pa, which facilitates operation of the next differential pump (turbomolecular pump). Moreover, the experimental results show a vacuum leakage rate of 1.69 ×10^-12 Pa m³ s^-1 and a relative error of less than 25% compared with the simulated pressure. Furthermore, the gas injection position of the active gas cell and the heating temperature (600°C) near the differential pipe have a negligible effect on the differential performance of the TDPC. This study demonstrates the novel concept of a differential pumping chamber, reflects its application prospects in DPS, and provides a useful reference for the DPS design of GATs.