快预脉冲调控丝阵Z箍缩负载质量分布及对内爆MRT不稳定性的影响研究

Z-pinch is currently the most intense laboratory soft X-ray source and the major challenge in improving the X-ray yield is MRT instability during implosion phase. Based on the situations above, we propose to utilize the snowplow stabilization to mitigate the MRT instability for wire array load, by creating a tailored mass distribution via special design of load configuration and the application of fast-rising prepulse. The proposal contains three main tasks: (1) to deepen the understanding of mass evolution of single wire by studying the spatial and temporal connections between the wire core and corona plasma; and to supplement the “cold starting” model with a semi empirical model of surface breakdown; (2) to understand the relationship between single wire and wire array explosion by studying the expansion and fusion of wire cores and corona plasma in an array; and to apply the cold starting model to wire array by introducing mechanisms such as electric shielding and current dividing; (3) to obtain proper wire array configuration and prepulse parameters for mitigation of MRT instability based on the amplitude, growth rate, and initial seed amplitude of MRT instability reconstructed from experimental results. By completing the tasks above, the technique of generating a tailored mass profile will be developed and the influence of mass distribution on MRT instability will be revealed for wire array load, which is a fulfillment for the methodology of wire array designing, and promisingly will provide new approaches for the optimization of mega-ampere wire array Z-pinches.

Z箍缩是产生高强度软X射线辐射的有效手段，而制约其X射线辐射功率和产额提高的主要因素为内爆阶段磁瑞利-泰勒（MRT）不稳定性的发展。本项目针对丝阵负载，提出利用快前沿预脉冲调控其质量分布，进而通过雪耙致稳效应抑制MRT不稳定性发展的新思路。首先从晕层与丝芯时空关联性的角度深入理解单丝质量分布演化规律，并发展可描述沿面击穿过程的单丝冷启动模型；接着对丝阵从多丝分流、电场屏蔽等机制入手建立与单丝负载实验规律的联系，并重点关注丝芯与晕层的膨胀、融合，进而拓展单丝冷启动模型，实现对丝阵电爆炸过程的自洽描述。在此基础上，以MRT不稳定性幅值、增长率和初始扰动种子幅值为评价指标，探索局部最优的质量分布和相应的负载构型及预脉冲参数。通过研究，掌握利用预脉冲调控负载质量分布的方法及其对MRT不稳定性的影响规律，丰富和发展丝阵负载设计与调控理论，并有望为数十MA大电流Z箍缩负载优化提供科学依据和技术基础。

Z箍缩是产生高强度软X射线辐射的有效手段，而制约其X射线辐射功率和产额提高的主要因素为内爆阶段磁瑞利-泰勒（MRT）不稳定性的发展。本项目针对丝阵负载，提出利用快前沿预脉冲调控其质量分布，进而通过雪耙致稳效应抑制MRT不稳定性发展的思路；围绕预脉冲作用下单丝质量分布演化、丝阵质量分布演化以及主预脉冲作用下丝阵Z箍缩动力学行为三个方面开展研究。.目前，已掌握了利用预脉冲实现典型低熔点（铝）和高熔点（钨）丝阵高汽化率均匀丝爆的方法；并基于“秦1”装置，获得了优化的预脉冲参数和主预脉冲延时，基本掌握了预脉冲调控下丝阵演化规律。实验结果表明，预脉冲的引入可完全改变丝阵Z箍缩动力学过程：随着主预脉冲延时的增大，内爆阶段质量消融流被显著抑制，并最终演变为雪耙内爆。雪耙内爆阶段，由于电流壳层质量不断增大，降低了内爆加速度，从而有效抑制了MRT不稳定的发展；实验中电流壳层到达丝阵主体质量后才观察到MRT不稳定性，推测此时不稳定性种子由电热不稳定性引入。数值模拟方面，掌握了常见金属材料的大范围状态方程数据，发展了基于开源代码FLASH的二维电爆炸“冷启动”磁流体数值模拟方法。.综上所述，通过本项目研究，已经在数百kA电流水平证实了预脉冲调控对抑制MRT不稳定性发展的作用，并具备了通过调控预脉冲参数设计丝阵质量分布的能力，有望为数十MA大电流Z箍缩负载优化提供科学依据。.