Pre-plasma effect on laser beam energy transfer to a dense target under conditions relevant to shock ignition
Pre-plasma effect on laser beam energy transfer to a dense target under conditions relevant to shock ignition
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在与冲击点火相关的条件下，前等离子体效应对激光束能量转移到致密目标的影响
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发表时间：
2015
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影响因子：
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通讯作者：
P. Pisarczyk
中科院分区：
文献类型：
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作者：
T. Pisarczyk;S. Gus’kov;O. Renner;N. Demchenko;Z. Kalinowska;T. Chodukowski;M. Rosiński;P. Parys;M. Šmíd;J. Dostál;J. Badziak;D. Batani;L. Volpe;E. Krousky;R. Dudzak;J. Ullschmied;H. Turčičova;J. Hrebicek;T. Medřík;M. Pfeifer;J. Skála;A. Zaraś;L. Antonelli;Y. Maheut;S. Borodziuk;A. Kasperczuk;P. Pisarczyk
本文模拟冲击点火惯性约束聚变靶的辐照条件，研究了两束激光先后作用于平板靶所形成的等离子体的性质。实验中使用的平面靶是由一个镀有薄塑料（CH）层的大块铜（Cu）板组成的，用1ω帕尔斯激光束（λ = 1.315 μm）以250 J的能量辐照该板。通过改变焦斑半径来缩放固定能量激光束的强度。为了模拟激波点火条件，低强度辅助1ω束产生CH预等离子体，主束延迟1.2ns照射CH预等离子体，从而在靶的大质量部分产生激波。为了研究通过靶的双束照射处理的等离子体的参数，应用了一组各种诊断，即：（i）飞秒激光（~40 fs）照射的双通道偏振干涉系统，（ii）X射线范围内的光谱测量，（iii）Cu的K α线发射的二维（2D）分辨成像，（iv）通过离子收集器测量离子发射，以及（v）测量在大质量目标中产生的坑的体积，提供关于激光能量转移到冲击波的效率的信息。二维数值模拟已被用来支持实验数据的解释。一般的结论是，沉积到块状铜在双光束照射的主激光束能量的分数相比，预等离子体的情况下减少。原因是预形成和膨胀的等离子体降低了借助于快电子和电子热导率波从主激光脉冲到靶的固体部分的能量传递的效率。
This paper reports on properties of a plasma formed by sequential action of two laser beams on a flat target, simulating the conditions of shock-ignited inertial confinement fusion target exposure. The experiments were performed using planar targets consisting of a massive copper (Cu) plate coated with a thin plastic (CH) layer, which was irradiated by the 1ω PALS laser beam ( λ = 1.315 μm) at the energy of 250 J. The intensity of the fixed-energy laser beam was scaled by varying the focal spot radius. To imitate shock ignition conditions, the lower-intensity auxiliary 1ω beam created CH-pre-plasma which was irradiated by the main beam with a delay of 1.2 ns, thus generating a shock wave in the massive part of the target. To study the parameters of the plasma treated by the two-beam irradiation of the targets, a set of various diagnostics was applied, namely: (i) Two-channel polaro-interferometric system irradiated by the femtosecond laser (~40 fs), (ii) spectroscopic measurements in the X-ray range, (iii) two-dimensional (2D)-resolved imaging of the K α line emission from Cu, (iv) measurements of the ion emission by means of ion collectors, and (v) measurements of the volume of craters produced in a massive target providing information on the efficiency of the laser energy transfer to the shock wave. The 2D numerical simulations have been used to support the interpretation of experimental data. The general conclusion is that the fraction of the main laser beam energy deposited into the massive copper at two-beam irradiation decreases in comparison with the case of pre-plasma. The reason is that the pre-formed and expanding plasma deteriorates the efficiency of the energy transfer from the main laser pulse to a solid part of the targets by means of the fast electrons and the wave of an electron thermal conductivity.