激光辐照固体靶产生等离子体反冲研究

Plasma recoil induced by laser radiated solid target

提出一种通过诊断等离子体反冲动量来计算激光加载产生冲击压强的方法.当强激光辐照固体靶表面时,所产生的高速喷射的等离子体对靶具有反冲作用,通过诊断等离子体反冲动量的变化可以计算激光辐照固体靶产生的冲击压强变化.本文利用辐射流体力学软件研究了这种诊断方法,模拟采用的激光功率密度为5×10^(12)—5×10^(13)W/cm^2,激光脉宽选取纳秒量级.模拟结果表明该方法是有效且可行的.

Based on the theory of conservation of momentum, a theoretical method of calculating the shock pressure induced by laser loading via diagnosing plasma recoil momentum is presented. When a high-power laser irradiates a solid target surface, the plasma jet with high velocity induced by laser has a recoil effect on the target. Then the plasma recoil momentum induced by laser irradiating solid target can be calculated by the distribution of electron plasma. At the same time, the subcritical electron plasma density could be measured by interferometry and the supercritical plasma density could be fitted into exponential function form. So the variation of shock wave pressure could be calculated via diagnosing plasma recoil momentum. This method does not consider the relationship between D and u, nor uses the window material nor needs the steady shock propagation. It is a useful method of studying the material property under high strain rate and isentropic compression. Numerical simulation results using one-dimensional radiation hydro code called MULTI for laser intensities ranging from 5 × 10^12W/cm^2 to 5 × 10^13W/cm^2 are presented. The electron temperature is nearly equal to the ion temperature for the laser pulse duration τ2 ns but much greater than the ion temperature for τ = 1 ns. This means for that ns pulse duration, the difference between electron and ion temperature could be ignored in general. And in order to fit the shock pressure value more exactly, the density of ablation surface nabl = n0 exp（-1） is used in the simulations. The simulation results indicate that the value of calculating shock pressure obtained via diagnosing plasma recoil momentum is similar to the shock pressure calculated by MULTI simulation for ns pulse duration. And the value of calculating shock pressure is also similar to the experimental value for pulse durationτ = 5 ns. From the simulation results, it is obvious that the method of calculating the shock pressure via diagnosing plasma recoil momentum is effective and feasible.