X-ray preheat shield in laser direct-drive ramp compression experiments

Laser drive ramp compression is an important method to achieve an extremely high-pressure but relatively low-temperature material state. In this study, we found VISAR streaks disappearing under high pressure. To solve this problem, the mechanism of probe-laser absorption in laser drive ramp compression experiments has been studied, and X-ray preheat is found to be the main factor in this mechanism. Subsequently, target configuration optimization and code simulation were performed based on previous experiments, and laser drive ramp compression experiments were performed on the SHENGGUANG prototype facility. In the experiments, the probe-laser reflectivity was above 90% at 450 GPa, which is much higher than those in previous experiments, demonstrating that the X-ray preheat was shielded well with the optimized target configuration.