等容预压缩等离子体中的快点火热斑形成与燃烧波传播

Formation of fast-ignition hotspots and propagartion of burning waves in pre-compressed isochoric plasmas

研究热斑点火物理过程对于实现聚变点火和高增益聚变放能具有重要意义,但是,迄今为止的大部分相关研究都是针对等压构型预压缩等离子体进行的,对等容构型预压缩等离子体中的热斑点火过程研究尚不充分.本文针对双锥对撞点火方案产生的等容预压缩高密度等离子体,建立了描述热斑边界演化和核聚变燃烧的半解析模型.该模型表明,在等容预压缩高密度等离子体中的热斑边界,可以用对热斑产生的α粒子具有强烈吸收作用的激波波峰的位置来定义,且等容预压缩等离子体中的热斑点火过程也存在α粒子射程主导的自调节现象.通过考虑α粒子的空间不均匀沉积效应,可以利用该模型描述等容预压缩等离子体中热斑内部的温度和密度演化.使用该模型分析热斑在点火初期时刻的劳森参数和平均热斑温度发现,在快电子总能量相同情况下,能量较低的快电子束更有利于实现点火.辐射流体模拟程序O-SUKI-N的验证计算表明,本文提出的半解析模型的计算结果具有较强的合理性.

The formation and evolution of hotspots is important for achieving ignition and high energy gain in inertial fusion process.However,most of relevant studies are carried out on pre-compressed plasmas with an isobaric configuration,the evolution of the hotspot in a plasma with an isochoric configuration is rarely studied.In this paper,a semi-analytical model is developed to describe the evolution of the hotspot boundary and propagation of fusion burning waves for a high-density pre-compressed plasma with an isochoric configuration in the double-cone ignition scheme.For the shock wave,the strong shock wave approximation and the quasi-isobaric approximation are reasonable.The quasi-isobaric approximation shows that as the plasma density behind the shock wave increases,the plasma temperature decreases.Because of these,the range ofα-particles decreases rapidly behind the shock wave,forming anα-particle absorption peak.Therefore,considering that the hotspot is the main region whereα-particles are produced and deposited,the position of the shock peak can be used to identify the boundary of the hotspot in a high-density plasma with an isochoric configuration.It also shows that a“self-regulating burning process”exists in the burning process of the isochoric hotspot,most ofα-particles are deposited in the stable region and behind the shock,and finally,transport through the shock peak and heat the cold fuel,resulting in the temperature rising.In the high-density hotspots of plasma with an isochoric configuration,the deposition ofα-particles behaves as an obvious non-uniform distribution effect.By analyzing the non-uniform deposition ofα-particles,the deposition rate ofα-particles at the edge of spherical uniform hotspot is calculated,then the temperature and density evolution of the isochoric hotspot can be well described.The model can be used to estimate the Lawson parameter of the hotspots at the end of the early stage of ignition.It is found that a lower fast electron energy is more beneficial to ignition and high gain operation of fusion plasma.It is also shown that the high density of the hotspots in the isochoric plasma will lead to a higher fusion burning rate,which can offset the negative influence of the shock wave and even achieve higher energy gain.The semi-analytical model is verified by the hydrodynamic simulations of O-SUKI-N.