SRS与TPD产生超热电子特性研究  

Characterization of Suprathermal Electrons Produced by SRS and TPD

作　　者：刘会亚 康宁 冀胜哲 赵耀 周申蕾[1] 雷安乐[1,2] Liu Huiya;Kang Ning;Ji Shengzhe;Zhao Yao;Zhou Shenlei;Lei Anle(Joint Laboratory on High Power Laser and Physics,Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences,Shanghai 201800,China;Shanghai Institute of Laser Plasma,China Academy of Engineering Physics,Shanghai 201800,China)

机构地区：[1]中国科学院上海光学精密机械研究所高功率激光物理联合实验室,上海201800 [2]中国工程物理研究院上海激光等离子体研究所,上海201800

出　　处：《中国激光》2021年第23期113-121,共9页Chinese Journal of Lasers

基　　金：国家自然科学基金(11905280,12005287);中国科学院重点实验室创新基金(CXJJ20S015);上海市软科学研究计划项目(20692114101)。

摘　　要：高功率激光与等离子体相互作用(LPI)产生的超热电子能谱与空间分布是激光惯性约束聚变(ICF)中评估预热增熵、优化靶参数设计的关键依据,因此是研究上的重要内容。基于神光Ⅱ激光装置,研究了不同条件的激光与碳氢平面靶作用产生超热电子的能谱与空间分布。实验结果表明,超热电子能谱符合麦克斯韦分布,拟合温度处于30~65 keV范围,靶前方向得到的超热电子温度和强度均高于靶后方向。在靶后方向探测到的超热电子空间分布近似高斯分布,峰值方向在靶背法线方向。靶前散射光谱上有较强的对流受激拉曼散射(SRS)信号及具有双峰分布特点的双等离子体衰变(TPD)信号。理论结合实验数据分析表明,在高温大尺度等离子体条件下,SRS产生的超热电子相比TPD占据主导地位。此外,分析了由SRS产生的电子等离子体(EPW)波加速的电子动能与散射光波长的关系,发现加速后电子的动能随着散射光波长的增加而增加,与实验结果相符。Objective In laser inertial confinement fusion(ICF)research,the suprathermal electrons generated by the highpower laser and plasma interaction(LPI)have always been a research hotspot.Whether using a direct or indirect drive central ignition scheme,suprathermal electrons with energies greater than 50 keV will deposit some of their energy in the fuel,resulting in preheating and a reduction in implosion performance.It is discovered in the shock ignition scheme that suprathermal electrons with energies less than 100 keV generated by the spike pulse can help enhance the intensity of the shock wave and increase the energy gain.The suprathermal electrons are generally considered to be accelerated by the electron plasma waves,which are generated by LPI instability,such as stimulated Raman scattering(SRS),two plasmon decay(TPD),and resonance absorption.However,it is still unknown which instability dominates the generation of hot electrons.As a result,experimental research on suprathermal electrons’spatial energy spectrum distribution,obtaining the main sources of suprathermal electrons,and exploring ways to control suprathermal electron generation is critical for ICF research.Methods The experiment was carried out at the ShenGuang II high-power laser facility.The schematic of the experimental setup is shown in Fig.1.The four north laser beams(5 th,6 th,7 th,and 8 th beams)were used and irradiated on the 10-μm thick CH foil at 45°and P polarization direction.The wavelength of the laser is 351 nm,the pulse is a 1-ns square wave,and the energy of one beam is 250 J.The diameters of laser focal spots with or without continuous phase plate are approximately 250μm and 120μm,respectively.One laser beam’s corresponding average power density is 5.1×10^(14) and 2.2×10^(15) W/cm^(2).In the experiment,the plasma density distribution was measured with a Normaski interferometry system,and the probe beam was an 80-ps duration pulse with a wavelength of527 nm.The suprathermal electrons were measured by two calibrated electron sp

关 键 词：激光技术 惯性约束聚变 超热电子 受激拉曼散射 双等离子体衰变 

分 类 号：O534[理学—等离子体物理]