超音速高密度喷流对撞过程中的高效能量转移

Efficient energy transition from kinetic to internal energy in supersonic collision of high-density plasma jets from conical implosions

在双锥对撞点火激光核聚变方案中,两个锥口相距约100μm放置的金锥内氘氚球冠靶在高功率纳秒激光烧蚀驱动下,获得沿金锥的球对称压缩和加速,形成沿着金锥轴向的超音速高密度喷流,出射喷流在两个金锥的几何中心发生对撞减速并形成聚变密度等离子体.在对撞过程中,高速运动喷流的动能转化为内能,实现对等离子体的预加热,与此同时,皮秒拍瓦激光产生的高能快电子从垂直方向入射并加热高密度等离子体,使其快速升温达到聚变温度,实现聚变点火.2020年在中国科学院上海光学精密机械研究所高功率激光联合实验室神光Ⅱ升级激光装置上,我们利用总能量为10 kJ的八路纳秒激光进行了两轮实验.实验利用包括X射线汤姆逊散射、硬X射线单色背光成像、X射线条纹和分幅成像等多种主动、被动诊断方法对超音速高密度喷流对撞过程进行了高时空分辨研究,实验测量发现,在单锥口形成的超音速等离子体喷流密度为5.5—8 g/cm^(3);在对撞过程中形成了阻滞时间约200 ps的高密度等离子体,中心密度达到了(46±24)g/cm3.通过对等离子的温度、速度的分析发现,对撞过程中动能到内能的转换效率高达89.5%.

A collision of supersonic jets in the double-cone ignition scheme is realized experimentally.With a very high deceleration,the supersonic jets merge into a high density plasma core,which will be further fast heated to ignition condition.Both the density and temperature of the plasma core are increased due to nearly 100%of kinetic energy of the jets converted into the internal energy.Some diagnostic tools are used to characterize the plasma,including X-ray Thomson scattering,hard X-ray monochromatic backlighting,X-ray streak imaging and framing imaging.The density of the supersonic jet arrive at about 5.5–8 g/cm3.During colliding,a stagnation phase lasts about 200 ps,and the maximum density of the plasma core is increased to(46±24)g/cm3.By analyzing the velocity and temperature before and after colliding,it is found that 90%of the kinetic energy is converted into thermal energy.