低密度泡沫金激光-X射线转换特性模拟研究

在激光间接驱动惯性约束聚变中, 激光首先与黑腔壁高Z等离子体相互作用转换成强X射线辐射, 再通过高Z腔壁的X射线再辐射而在靶丸表面产生对称辐射以驱动其内爆, 改善腔中激光–X射线转换特性非常重要. 利用一维辐射流体程序模拟研究了低密度泡沫金对激光–X射线转换特性的影响, 结果表明: 在固定激光参数条件下, 随着Au材料密度降低, 激光–X射线转换效率提高, 当泡沫Au密度为0.1 g/cm³时, 转换效率相对提高19%; 同时, 金M带辐射份额随之减少; 对于发光区运动, 存在合适的泡沫Au密度使其得到有效抑制. 从能量平衡的角度分析了转换效率提高的原因: 在激光与低密度泡沫Au作用时, 转换为流体力学动能损耗的能量份额与固体Au相比有所降低, 因而相应的辐射能份额增加. 低密度泡沫Au改善激光–X射线转换特性是实现黑腔腔壁优化的一种途径, 模拟结果为进一步开展相应实验研究提供了依据.关键词：泡沫金激光-X射线转换辐射谱等离子体运动

Simulation of laser to X-ray conversion features influenced by low density gold foam

In the laser indirect-driven inertial confinement fusion, laser light is converted into X-rays by laser-plasma interactions in the hohlraum, then at the surface of the capsule the re-emission of hohlraum inner wall would drive a symmetrical radiation source to motivate implosion. It is of great importance to improve the features of laser to X-ray conversion in the hohlraum. The influence of low density gold foam on conversion features was investigated numerically with the help of one-dimensional hydrodynamics code. The numerical simulation results show that conversion efficiency increases with the decrease in gold density under the given laser condition. In particular, it can indeed have more than 19% extra conversion efficiency relatively when solid gold is replaced by gold foam of 0.1 g/cm³ density. In addition, the percentage of M-band decreases. There is an appropriate density of gold foam, at which the movement of plasma are restrained. According to the simulation results of energy balance, we get a higher radiation energy proportion when low density gold foam is selected as the target, and this is due to the decrease of kinetic energy losses compared with solid gold. Anyway, it is an effective approach to optimize the hohlraum by using low density gold foam to improve the features of laser to X-ray conversion, and these simulations would provide a scientific basis for further attempting correlative experiments.