Z箍缩动态黑腔形成过程和关键影响因素数值模拟研究

在Z箍缩动态黑腔研究中, 认识黑腔形成物理过程及主要特征, 明确优化黑腔辐射的关键参数, 是实验物理设计的重要基础. 本文针对W丝阵填充CH泡沫转换体的负载构型, 利用一维辐射磁流体程序, 在8 MA驱动电流条件下开展了动态黑腔形成过程和关键影响因素的数值模拟研究. 结果表明, 丝阵等离子体与泡沫转换体相互作用产生局部高压力区是驱动冲击波传播和形成动态黑腔的关键物理过程. 由于辐射超声速传播及其与冲击波波阵面的空间分离, 产生了辐射温度较高而物质未受明显压缩的动态黑腔区域. 丝阵等离子体碰撞泡沫转换体前的状态分布决定了动态黑腔辐射场的主要特征, 可以通过改变负载参数调整并优化黑腔辐射波形. 综合考虑黑腔峰值辐射温度和有效维持时间两个参数, 选择匹配质量的丝阵和泡沫, 使丝阵质量略小于泡沫, 可以获得相对优化的动态黑腔辐射波形. 同时, 合适的丝阵/泡沫初始半径比也是优化动态黑腔辐射的重要影响因素.

Numerical studies on the formation process of Z-pinch dynamic hohlruams and key issues of optimizing dynamic hohlraum radiation

Dynamic hohlraum is a possible selection to drive inertial confinement fusion. Currently, the ~8 MA PTS facility in China has been completed, which provides a powerful experimental platform of relatively large drive current for researches of dynamic hohlraums and dynamic hohlraum driven inertial fusion. To understand the formation processes and the main characteristics of the dynamic hohlraum, and explore the most important issues affecting the optimization of hohlraum radiation, is not only fundamental in the research of dynamic hohlraums, especially for the experimental design, but also can provide a physical insight for the experimental diagnosis. In this paper the implosion dynamics of a tungsten wire-array Z-pinch embedded with a CH foam converter, especially the impaction interaction of the wire-array plasma with the converter plasma, is numerically investigated using a one-dimensional non-equilibrium radiation magnetohydrodynamic code. In simulations the tungsten plasma is assumed as a plasma shell with a width of 1 mm, and the CH converter plasma is assumed to be uniform with an initial temperature of 0.1 eV. The overall implosion is driven by an assumed current with a peak value of 8 MA and a rise time of 66.4 ns. It is shown that a local high pressure region, which is generated by the impaction of the tungsten plasma with the converter plasma, is crucial to launch the strongly radiating shock wave and to form the dynamic hohlraum. Due to the supersonic radiation transfer in the low opacity CH converter plasma, which is also produced in the high pressure region, there exists a hohlraum region inside the front of the shock wave, in which the radiation is high. At the same time, the plasma pressure is uniform in this hohlraum region, so the plasma will not be disturbed before the shock arrives. As the shock propagates to the axis, the hohlraum becomes small and the radiation temperature is also increased. Basically, the hohlraum radiation is determined by the detailed profiles of plasma conditions when the wire-array plasma impacts onto the CH converter plasma. And these profiles are determined by many factors, such as the drive current, initial masses and radii of the wire-array and the converter, as well as the material of the converter. When the drive current is fixed, the optimal wire-array can be determined. Firstly, the mass ratio of the wire-array to the CH converter is varied. Numerical calculations show that as this ratio is decreased, the shock velocity is increased and the radiation temperature is increased as well. Additionally, the time duration of the radiation pulse before the shock arrives at the axis is remarkably increased. It is also found that when this mass ratio is slightly lower than unity, for example 0.75, a relative optimal dynamic hohlraum can be produced. Secondly, if the mass ratio is fixed and the initial radius of the converter is decreased, it is found that the shock velocity is just slightly changed. However, the peak hohlraum radiation temperature is increased and the radiation pulse becomes remarkably narrow. A suitable radius ratio of the wire-array to the converter, neither too large to induce strong Magneto-Rayleigh-Taylor (MRT) instability nor too small to gain a small kinetic energy of the wire-array before impacting onto the converter surface, should be selected. In the future we will develop two-dimensional code to investigate the effect of MRT instability on the formation of dynamic hohlraums.