“天光一号”驱动的聚苯乙烯高压状态方程测量

Equation-of-state measurements for polystyrene under high presure driven by HEAVEN-I laser facility

聚苯乙烯等CH材料的高压状态方程研究对于ICF聚变点火具有重要意义.本文基于"天光一号"长脉冲激光装置开展了聚苯乙烯高压状态方程研究,理论模拟了靶内的冲击动力学过程,采用侧向阴影成像技术实验测量了不同厚度的聚苯乙烯平面靶和飞片靶,获得了靶内的冲击波速度与粒子速度等状态方程参数.结果表明:长脉冲激光驱动下CH平面靶内经历了明显的准等熵加载过程,并逐渐演化为弱冲击加载.实验测量平面靶压力12 GPa,飞片撞击靶压力34 GPa,与模拟结果基本相符.

The equation of state(EOS)for CH material used as an ablator layer at high pressure is important in the study of implosion dynamics and target design for inertial confinement fusion(ICF).At present,most of EOS data are on the Hugoniot line under shock compression.The EOS data below Hugoniot line need further studying for low-entropy pre-compression.In the present article,the EOS of polystyrene is established under quasi-isentropic compression driven by HEAVEN-I KrF laser facility with a long rising edge(~20 ns).The shock dynamic behaviors of three kinds of CH targets are simulated,which are 100μm CH planar target,Al-coated CH planar target(10μm Al,50 or 150μm CH),and flyer-impact target composed of flyer(Al-coated CH),100μm vacuum layer,and 100μm CH layer.The planar targets and flyer-impact targets with different thickness are irradiated by six-focused laser beams with total energy of 50–100J,and the free surface velocity and wave average transit velocity are measured by side-on shadowgraph technique.The simulation results indicate that the initial loading process is quasi-isentropic compression process,and then evolves into a weak shock compression process for the CH planar target in the rising edge stage.Comparing with the CH planar target,the reflected rarefaction waves from the Al-CH interface of Al-coated CH target can suppress the enhancement of compression wave,and delay the formation of shock wave when laser directly irradiates the Al layer.The shock pressure of the CH target layer(the third layer)is significantly higher than those of the former two targets in the flyer-impact target.However,the chasing rarefaction wave can unload the compression state incompletely and reduce the pressure when the CH target layer is much thicker than Al layer.The final pressure is about 15 GPa in the CH planar target,while the final pressure is about 30 GPa in flyer-impact target:both of them are less than the pressure threshold of opacity change for the transparent polystyrene.The quasi-isentropic dynamical process is difficult to measure by the velocity interferometer system for any reflector technique.The experimental results show that the average wave transit velocity is significantly less than the final shock velocity derived from the free surface velocities in the CH and Al-coated CH planar target side-on shadow experiments.They indicate that the compression wave enhancement and quasi-isentropic compression process occur in the propagation of wave front.The shock pressure is about 12 GPa in the CH planar target,and about 34 GPa under shock load in the flyer-impact target.The experimental data and shock dynamic processes are basically consistent with the simulation results.