The mechanism by which intense X-rays ablate a material surface and generate recoil momentum serves as the physical foundation for major engineering applications such as asteroid defense and X-ray-driven propulsion. Currently, this physical process is well established in the field of plasma physics under laboratory conditions. However, a systematic understanding of the momentum generation mechanisms and their evolution under low specific energy, long-duration, and long-distance conditions—such as those encountered in asteroid defense and ablation propulsion—remains lacking.In this study, we constructed a one-dimensional irradiation-driven model for intense X-rays under such conditions using the FLASH radiation hydrodynamics code. Based on this model, we divided the momentum generation process induced by intense X-ray irradiation into four stages according to their physical characteristics and analyzed the contribution of each stage to the total momentum increase. The results show that the second stage dominates momentum growth.We further propose a correction method for the impulse coupling coefficient based on spontaneous expansion, utilizing Riemann invariants. The results indicate that under conditions where the radiation spectrum is concentrated within 1 keV and the fluence ranges from 50 to 200 J/cm², the impulse coupling coefficient for Al under intense X-ray irradiation lies between 0.3 and 0.7 Pa·s·cm²/J, which agrees well with experimental results and theoretical predictions from the vaporization impulse theory.Through high-precision simulation and a self-consistent numerical correction method, this study achieves an accurate calculation of the impulse coupling coefficient, providing a physical basis for analyzing experimental phenomena in relevant Z-pinch facilities and deepening our understanding of the momentum generation mechanism.
 

Z-pinch， Radiation hydrodynamics simulation， Thermo-mechanical effects， Impulse coupling coefficient