神光Ⅱ大型固体高功率激光装置是我国激光驱动器发展历史的里程碑, 其成功研制使我国高功率固体激光工程与技术、聚变物理与基础物理研究实现了全面且本质的跨越式发展。简要概述了神光Ⅱ激光装置研制中创新发展的大量工程方案与技术手段, 举例介绍了神光Ⅱ激光装置在近20年来的高质量运行中取得的众多有国际影响力的研究成果。经多方支持和多年持续发展, 已经形成数万焦耳级纳秒激光装置、皮秒拍瓦以及飞秒拍瓦激光装置等, 这些装置是我国惯性约束核聚变、强场物理、高能量密度物理等研究领域中重要的物理实验核心平台之一。

Direct-drive and indirect-drive inertial confinement fusion (ICF) targets use temporally shaped drive pulses to optimize target performance. The timing of multiple shock waves is crucial to the performance of ICF ignition targets. Velocity interferometer system for any reflector (VISAR) is the principal diagnostic tool for shock-timing experiments. We present velocity measurements from the shock waves in polystyrene targets driven by two 200-ps pulses separated by 1–2 ns. These pulses drive two shock waves that coalescence in the target. Coalescence time and transit times are observed by VISAR.

介绍了神光-Ⅱ装置配套线成像速度干涉仪光路排布、用于任意反射面的速度干涉仪系统中干涉仪结构的选择及干涉仪的调节。该仪器可以用于测量自由面速度、界面速度和透明材料中冲击波波阵面速度。该仪器的最小时间分辨力可达约20 ps, 空间分辨力高于10 μm。并在神光-Ⅱ装置上进行了动态打靶实验,实验用靶为Al-CH靶,获得了较好的实验图像,测得了CH中冲击波的平均传播速度为24.67 km/s。

建立了一套激光驱动瑞利泰勒(R-T)不稳定性正向诊断实验数据的处理流程和方法,主要包括:利用拟合背光曲线的方法扣除背光的不均匀性;采用快速傅里叶变换(FFT)方法对数据进行光滑化处理(去除高频噪声)后得到探针穿越调制靶后的强度信息;结合R-T不稳定性的物理模型,给出R-T不稳定性随时间演化的一些物理规律。并使用这套方法,对神光II装置上取得的直接驱动铝平面调制靶动态诊断实验原始数据进行了处理,并从中得到了光学厚度和增长振幅等物理量随时间的演化规律。

系统介绍了“神光Ⅱ”装置上线成像速度干涉仪的研制情况。根据“神光Ⅱ”靶场实际情况制定了光路排布方案,完成了成像系统的设计;根据物理需求、光路调节的难易情况、光学元件的加工难易度和加工成本等因素确定了干涉系统的结构,制定了干涉仪等光程调节方案,并获得了对比度较高的静态白光干涉条纹图像。通过调研和分析确定了任意反射速度干涉仪(VISAR)干涉图像的处理方法。

结合快点火靶丸预压缩涉及的基本物理问题,分析了驱动激光脉冲波形对材料压缩过程的影响,并利用辐射流体力学程序MULTI模拟了不同激光波形下的材料压缩情况。结果表明:通过调节激光脉冲波形,优化激光初始强度、激光强度开始上升时间和上升速度,控制压缩过程中的熵增,可以获得更高的材料压缩度。

The supersonic jets and the interaction of strong shock waves are ubiquitous features of the nonlinear hydrodynamics of inertial-confinement fusion, astrophysic, and related fields of high energy-density science, so very important value have their studies in laboratory. A laboratories experimental study on jets is reported. The plasma jets were created by an ns laser pulse irradiating a special circular hole target, and the shadow of jets were recorded by using an X-ray laser probe with wavelength of 13.9 nm. Legible shadow images of plasma jets were obtained. The experimental results and theoretical simulation were in qualitative agreement.

Pinhole-assisted point projection (PAPP) backlight scheme is a newly developed diagnostic technique for laser-plasma experiments in foreign laboratories, which will play an important role in diagnostic experiments of inertial confinement fusion (ICF) physics. Experiments have been carried out on the additional beam of “Shenguang-Ⅱ” laser facility, to test the practicability of PAPP scheme. The K-shell X rays (～4.7 keV) emitted from laser-produced planar Ti targets pass through the pinhole aperture with diameter of 10～40 μm, then cast the shadow of the Au sample on CCD. Time-integrated two-dimensional (2D) pictures of the samples are obtained in the experiments with the resolution better than 16.1 μm. The merits, such as high resolution, large field-of-view, high contrast, have been found in the experimental results, and PAPP will become one of the most important diagnostic methods for Rayleigh-Taylor instability research, equation of state (EOS) research and so on.

针孔辅助点投影背光成像是近几年国外新兴的等离子体诊断技术,在惯性约束聚变相关物理实验诊断中具有重要的应用前景。为验证这一诊断方法的实用性,在神光Ⅱ第九路平台上开展了演示实验。利用激光驱动平面Ti靶获得约4.7 keV的Ti K壳层X射线,在十几微米的针孔约束下作为次级点源并对Au栅格样品投影成像,并用CCD记录。实验成功获得了清晰的样品二维空间分辨的时间积分图像,空间分辨力优于16.1 μm。实验结果表明针孔辅助点投影具有较高的空间分辨力、较大的视场、较高的图像对比度,将成为瑞利-泰勒不稳定性研究、激光状态方程研究等物理实验的重要诊断方法之一。

Equation of state (EOS) experiments were performed using a double-frequency (2ω) laser pulse, which exported from the ninth beam of “SG-Ⅱ” laser facility. The ninth laser beam was smoothed by lens-array (LA) uniform illumination technique to generate a flat-top intensity distribution at the target plane and planar shock fronts in targets, which was validated by the plane-target experiments. The shockwave stabilities were experimentally measured by the multi-step target technique. The results showed that the shocks were steady enough during the target thickness range in which the shock velocity was measured. Also, the results were consistent with the numerical simulation results. On this base, the Au EOS was measured by using the impedance-matching technique. Shock pressure higher than 2.7 TPa was achieved in Au, and the relative expanded uncertainties of the measured shockwave velocity were 2% (K=2). Moreover, the experimental data were compared with existing experimental data and EOS models.