“聚龙一号”装置磁驱动准等熵压缩实验的一维磁流体力学模拟

国内首台多路并联超高功率脉冲装置"聚龙一号"(PTS)已被用于磁驱动准等熵实验研究,其分时分组放电特点为开展材料的动高压可控路径加载研究提供了便利.磁驱动准等熵实验的物理设计和结果分析需要依赖可靠的数值模拟平台.本文介绍了含强度计算的一维磁流体力学程序MADE1D的物理模型和程序特点,讨论了"聚龙一号"装置两种不同电流波形驱动条件下准等熵实验的模拟情况.结果显示,MADE1D程序能够较好地反映电磁力引起的压缩波在样品内部的产生、传播及发展过程,计算获得的"样品/窗口"界面速度同实验测量结果符合较好.分析发现,电流波形是影响加载过程的重要因素.对于目前使用的带状电极,电流上升率不宜超过40 k A/ns,否则可能在厚度1.2 mm以上的铝样品中产生冲击.

One-dimensional magneto-hydrodynamic simulation of the magnetic drive isentropic compression experiments on primary test stand

The 10 MA primary test stand (PTS), the most powerful pulse power generator in China, is used to obtain isentropic compression of Al samples under a pressure of about 100 GPa. The high performance of laser-triggered gas switches enables the precise synchronization of the 24 modules according to the required timing sequence. This advantage makes the PTS a very good platform for dynamic material compression with fundamental capability of pulse shaping. Tens of isentropic compression experiments have been conducted on the PTS, among which two distinct loading profiles were designed and used to obtain distinct compression processes. The first current, which is used to obtain a shockless compression, has a relatively smooth rise, and the rise-rate keeps almost constant during the 400 ns-long compression. The second current shape has a mild rise but a sharp ends, which is designed to make an artificial “turn-point” in the velocity history, which is helpful for the numerical code verification. The current profile, as well as the sample thickness, is optimized by a one-dimensional magneto-hydrodynamic (1D MHD) code MADE1D coupled with a full circuit model for the PTS. The equation of state and conductivity model used here have a wide coverage in the density, temperature and pressure range. The strength of material and its constitution model are also taken into consideration to simulate the elastic and plastic flow of metal at relatively low pressure and temperature. Compared with the experimental results, the simulated velocity at the sample/window interface is found to agree well with the measurement for most of the cases. This suggests that the MHD simulations with the circuit model are able to reflect the main process of the loading history, and help to analyze and elucidate the phenomena contributing to the compression. It shows that the current waveform is one of the most important factors that affect the loading process. For the PTS and strip-line electrodes it uses, a current rise ratio less than 15 kA/ns helps to obtain a smooth off-Hugoniot pressure rise. The temperature rise due to the pdV work is very small, and most of the sample material, except those in the skin layer where current passes through, keeps solid during the compression. However, for a current rises at 40 kA/ns or more, the ramp loading wave could be sharpened into a shock within the sample thicker than 1.2 mm. Based on the PTS flexibility of pulse shaping, a wide range of desired load processes can be gained by designing and controlling the load current and sample thickness precisely.