神光Ⅲ主机上球腔辐射场实验的三维数值模拟与分析

摘要

2015年在神光III激光装置上开展了两孔球腔物理实验.利用三维隐式蒙特卡罗数值模拟程序模拟两孔球腔中的辐射输运问题,研究辐射场分布及其动态演化过程.数值模拟结果大多数与实验结果符合较好,但局部位置存在明显差异.分析了产生差异的可能原因,提出解决措施及未来发展方向.综合数值模拟结果及其与实验结果的对比可知,三维隐式蒙特卡罗数值模拟程序具备较好的黑腔三维辐射输运数值模拟能力.%A new type of laser fusion indirect drive octahedral spherical hohlraum has been built up by Chinese researchers in recent years. The hohlraum with 6 laser entrance holes(LEHs)has superiority over other hohlraum configurations in both robust inherent high symmetry and high coupling energy efficiency from laser to hotspot for inertial confinement fusion study. Recently,an experimental investigation on radiation emission from the spherical hohlraum with two LEHs has been performed on the SGIII laser facility. In this experiment,32 laser beams(24 beams from the top,8 beams from the bottom) are injected into the hohlraum within 3 ns, and the total laser energy is 86.4 kJ. The hohlraum radius is 1.8 mm,and the radius of laser entrance hole is 0.6 mm. The experiments are conducted under two conditions: one is that a 0.48-radius capsule is located at the center of the hohlraum,and the other is that nothing is located in the hohlraum. Some flat response X-ray detectors (FXRDs) are installed at different angles on the target wall to collect the radiation energy. We carry out three-dimensional (3D) simulations of the experiment by using our 3D radiation implicit Monte Carlo code IMC3D. This code was developed in recent years based on fleck and Cumming's ideas. The hydrodynamics is not taken into consideration in the simulations, so we deduct 30% laser energy lost to hohlraum wall movements and back scattered by laser plasma instabilities. Based on the approximation, the simulation results are reasonable in principle. As a result,the radiation temperature of the hohlraum with capsule is 230 eV,and the radiation temperature of the hohlraum without capsule is 238 eV. At the end of laser injection, the capsule reflection ratio is 0.83. Compared with the experimental data, most of the simulation data agree well with the detector observations, except the data at 0?angle. The possible reasons for the difference are analyzed. The flux at 0?angle is more sensitive to the wall plasma movements than at the other angles. So if we ignore this phenomenon, then the witch will occur both in experiment and in simulation, yielding obvious differences for those quantities which strongly relate to the hydrodynamics of wall plasma. Finally,the methods of eliminating the difference are proposed and the prospect of IMC3D is presented.