MgAl(Hx)薄膜的光致等离子体流场特性及驱动效应研究

The shock initiation by a laser-driven flyer is of great importance for the safety of weapon systems since it is intrinsically immune to electromagnetic interference. The ablation layer is the key component in a laser-driven flyer configuration. It absorbs the laser energy and generates high density plasma which accelerates the flyer to a velocity up to several km/s. However, the evident energy loss of the commonly used ablation layer has remarkably constrained the practical application of such technique. Herein, we propose for the first time to utilize the MgAl(Hx) film as the ablation layer. Such film is able to enhance both the laser absorption and ablation reaction. Therefore, the energy efficiency will hopefully be significantly increased. In this study, we intent to dig into the influence of hydrogen in a MgAl(Hx) film on the ion ionization state of the laser-induced plasma. Furthermore, we are about to systematically investigate the flow field of the laser-induced plasma and the performance of the laser-driven flyer. More specifically, MgAl(Hx) films with various hydrogen contents will be prepared by magnetron sputtering and hydrogen adsorption instrument. TEM, neutron reflectometer, spectrophotometer will be used to characterize the microstructure and related parameters of the MgAl(Hx) films. Time-of-flight mass spectrometer, time-resolved spectrometer will be used to analyze the flow field of the laser-induced plasma. Additionally, time-resolve shadowgraph and PDV will be used to study the performance of the laser-driven flyer. Consequently, the flow field parameters of the laser-induced plasma and the performance of the flyer will be elucidated. These results can provide guidance for high-efficiency ablation layer design, which will bring forward the practical utilization of the laser-driven flyer technique.

激光驱动飞片起爆技术可显著提升武器系统的抗强电磁干扰能力，对提升武器装备安全性有重要意义。烧蚀层吸收激光能量并转化为驱动飞片的等离子体势能，是能量转换的重要载体。当前，烧蚀层换能效率低是制约该技术工程应用的瓶颈。为此，本项目创新地采用MgAl(Hx)薄膜作为烧蚀层，在提升薄膜光吸收率的同时，由于氢的引入使得烧蚀反应增强，进而大幅提升驱动效能。本项目围绕氢对MgAl(Hx)薄膜光致电离过程离子价态演变的影响规律这一科学问题，系统地开展MgAl(Hx)的光致等离子流场特性及驱动效应研究。采用磁控溅射和氢气吸附法制备不同氢含量的MgAl(Hx)薄膜，通过TEM、中子反射、分光光度计等表征薄膜基本特性；采用飞行质谱、光谱等方法获得光致等离子体流场特性；采用阴影成像、PDV获得激光驱动效应。本项目研究成果可指导高效能烧蚀层设计，为推进激光驱动飞片起爆技术的工程应用提供支撑。

激光驱动飞片起爆技术可显著提升武器系统的抗强电磁干扰能力，对提升武器装备安全性有重要意义。当前，烧蚀层换能效率低是制约该技术工程应用的瓶颈，为此，本项目创新地采用MgAl(Hx)薄膜作为烧蚀层，通过引入氢增强激光烧蚀反应，进而大幅提升驱动效能。本项目采用反应磁控溅射沉积MgAl(Hx)薄膜，获得了溅射功率、氩氢工作气流量比、工作气压等对薄膜沉积的影响规律，并通过调整氩氢混合工作气体的流量比成功制备了不同氢含量的MgAl(Hx)薄膜样品。采用中子反射、XRD等对MgAl(Hx)薄膜进行了表征，表明MgAl(Hx)薄膜样品的氢含量最高可达11at.%，当氢含量较小时，氢在MgAl(Hx)薄膜中主要以MgH2形式存在，随着氢含量增大，MgAl(Hx)薄膜中将出现MgH2、Mg(AlH4)2等金属氢化物。采用高速摄影和发射光谱法测试了Al、MgAl、MgAlH0.11和MgAlH0.25薄膜的光爆炸过程，表明氢的引入会增强薄膜在激光作用下的电离程度，光爆等离子体电子温度、电子密度、发光强度等随氢的含量增加而升高。利用时间分辨阴影技术获得了四种薄膜的光爆等离子体羽流演变过程，表明MgAlH0.11和MgAlH0.25薄膜的冲击波能量利用率较之MgAl分别提升了18.5%和76.6%。采用飞行时间质谱分析了MgAlH0.25薄膜的光致等离子体的质谱特性，表明光致等离子体中存在MgOH+离子，且在激光烧蚀作用下MgAlH0.25薄膜的离子产率明显大于MgAl薄膜，证实氢参与了薄膜的光爆反应过程。采用PDV测试了不同薄膜驱动飞片速度历程，表明MgAlH0.11和MgAlH0.25薄膜驱动飞片速度较之MgAl薄膜分别提升6%和15%，较之Al薄膜提升38%和50%，氢的引入可显著提高飞片的速度和能量转换效率。本项目研究结果可为激光驱动飞片用高效储氢换能元设计提供支撑。