Numerical simulation of attenuation performance of the gas attenuator using argon as working medium of SHINE

The performance of the gas attenuator (GAT) with argon as the working medium for the high repetition frequency free electron laser facility (SHINE) is simulated and investigated by means of the finite element numerical simulation method, and the results of the temperature and normalized density distribution of the gas inside the active gas cell at steady state are obtained, demonstrating the density depression effect of the internal gas and the corresponding attenuation results. Under the assumption of equivalent continuous-wave (CW) power input, the gas pressures are obtained for photon intensity attenuation of 103 at different photon energy (0.4-7 keV) and repetition frequencies (1 kHz, 10 kHz, 100 kHz), and compared with the theoretical calculations. The results show that the density depression is gradually enhanced with the increase in the repetition frequency, and the nonlinear deviation of the simulation attenuation gas pressure relative to the theoretical value is also gradually increased. The thermal outflux on the wall of the active gas cell gradually decreases along the beam path, so the cooling system needs extra attention to the inlet region of the cell. According to the simulation results, at the highest operating repetition frequency of 100 kHz, the attenuation gas pressure varies from 0.0767 to 17 Torr, and the highest wall thermal outflux value reaches 52.1 W/m2. The study provides a useful reference for the performance prediction and subsequent optimization design of the gas attenuator.