Analysis of stimulated Brillouin scattering in ICF hohlraum excited by multi-color incoherent lights
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摘要: 为研究多色非相干激光入射ICF黑腔的受激布里渊散射（SBS）和受激拉曼散射（SRS）发展情况，建立了一维受激散射稳态谱分析模型，并发展了相应的数值模拟程序。分析了不同频率激光激发的受激散射光通过共用等离子体波耦合的物理图像以及影响背散光谱的物理因素。针对波长差0.3 nm的等强度双色光入射封底金腔的SBS进行了模拟分析，结果表明：采用双色光有效抑制了SBS；SBS光谱劈裂成间距为0.3 nm的两个峰；波长较长的入射光对应的SBS光获得了较大的增益；如果固定激光总强度和总带宽，则存在抑制SBS的最优光束数目。Abstract: To study the stimulated Brillouin scattering (SBS) and stimulated Raman scattering in inertial confinement fusion (ICF) hohlraum excited by multi-color incoherent light, in this paper a one-dimensional steady-state model is introduced and implemented by a numerical program. The physical pictures in which the stimulated scattering excited by individual lightrays can be coupled through sharing electrostatic wave and the physical factors affecting the spectrum of backward scattered light are analyzed. The simulation of SBS in a golden cylinderical hohlraum excited by two-color light with wavelength separation
$ 0.3\;\mathrm{n}\mathrm{m} $ shows that: SBS can be effectively suppressed by the two-color light, the spectrum of SBS splits into two peaks with separation of 0.3 nm, the SBS light corresponding to incident light of longer wavelength gets higher gain, and if the total intensity and bandwidth of lasers are both fixed, there exists a best number of beamlets to suppress SBS. -
图 1 双色光SBS共用离子声波
Figure 1. SBS excited by two individual lightrays are coupled through sharing ion acoustic wave
图 2
$ (351\pm 0.15)\mathrm{n}\mathrm{m} $ 等强度双色光分别和同时入射$ {\text{C}}_{\text{5}}{\text{H}}_{\text{12}} $ 时的耦合系数谱Figure 2. The spectra of coupling coefficient when equal intensity two-color light of wavelength
$ (351\pm 0.15)\mathrm{n}\mathrm{m} $ incident$ {\text{C}}_{\text{5}}{\text{H}}_{\text{12}} $ plasma respectively and simultaneously
图 3
$ (351\pm 0.15)\mathrm{n}\mathrm{m} $ 等强度双色光分别和同时入射高密度$ {\text{C}}_{\text{5}}{\text{H}}_{\text{12}} $ 和低密度$ \mathrm{H}\mathrm{e} $ 的耦合系数谱Figure 3. The spectra of coupling coefficient when equal intensity two-color light of wavelength
$ (351\pm 0.15)\mathrm{n}\mathrm{m} $ incident high density$ {\text{C}}_{\text{5}}{\text{H}}_{\text{12}} $ and low density He plasma respectively and simultaneously
图 4 单色光入射（a）和双色光入射（b）的SBS和SRS背散光强度演化
Figure 4. The intensity evolution of SBS and SRS backscattered by monochromatic light and bichromatic light
图 5 单色光入射和双色光入射的SBS背散光谱随时间演化
Figure 5. Time evolution of SBS back scattering spectra of monochromatic light and bichromatic light
图 6
$ {t}=1.5\;\mathrm{n}\mathrm{s} $ ，单色光入射（a）和双色光入射（b）腔轴光线上的SBS背散光谱随空间演化Figure 6. t =1.5 ns, the spatial evolution of the SBS backscattering spectra of monochromatic light (a) and bichromatic light (b) on the cylindrical axis
图 7
$ {t}=2.5\;\mathrm{n}\mathrm{s} $ ，单色光入射（a）和双色光入射（b）腔轴光线上的SBS背散光谱随空间演化Figure 7. t =2.5 ns, the spatial evolution of the SBS backscattering spectra of monochromatic light (a) and bichromatic light (b) on the cylindrical axis
图 10
$ {t}=1.5\;\mathrm{n}\mathrm{s} $ ，腔轴光线，双色光入射，（a）为入射光和SBS散射光的耦合系数谱随空间变化，红线为流速分布示意；（b）为入射光、SBS散射光和耦合系数的乘积随空间变化，红线为平均电离度$ {{Z}}_{\mathrm{a}\mathrm{v}\mathrm{g}} $ 分布示意图Figure 10. t =1.5 ns, the ray at cylindrical axis, monochromatic light: (a) shows the coupling coefficient between incident light and SBS scattering light, and the red line denotes flow velocity along the ray; (b) shows the convective growth rate of SBS scattering light, and the red line denotes the mean ionization degree
$ {{Z}}_{\mathrm{a}\mathrm{v}\mathrm{g}} $ 
图 11
$ {t}=2.5\;\mathrm{n}\mathrm{s} $ ，腔轴光线，双色光入射，（a）为入射光和SBS散射光的耦合系数谱随空间变化，红线为流速分布示意；（b）为入射光、SBS散射光和耦合系数的乘积随空间变化，红线为平均电离度$ {{Z}}_{\mathrm{a}\mathrm{v}\mathrm{g}} $ 分布示意图Figure 11. t =2.5 ns, the ray at cylindrical axis, monochromatic light: (a) shows the coupling coefficient between incident light and SBS scattering light, and the red line denotes flow velocity along the ray; (b) shows the convective growth rate of SBS scattering light, and the red line denotes the mean ionization degree
$ {{Z}}_{\mathrm{a}\mathrm{v}\mathrm{g}} $ 
图 12
$ {t}=\mathrm{1.5,2.5}\;\mathrm{n}\mathrm{s} $ ，双色的入射光强度和SBS散射光强度随空间变化Figure 12. t =1.5, 2.5 ns, the spatial evolution of intensities of monochromatic incident light and SBS scattering light
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