Laser-plasma instabilities under ignition conditions for direct-drive inertial confinement fusion are studied using two-dimensional Particle-in-Cell simulations with a combination of in-plane (PP) and out-of-the-plane (SP) lasers. The results show that stimulated Raman side scattering can induce significant pump depletion and form a gap in the Raman scattered light spectra that have been observed in experiments.
As an alternative inertial confinement fusion scheme with predicted high energy gain and more robust designs, shock ignition requires a strong converging shock driven by a shaped pulse with a high-intensity spike at the end to ignite a pre-compressed fusion capsule. Understanding nonlinear laser-plasma instabilities in shock ignition conditions is crucial to assess and improve the laser-shock energy coupling. Recent experiments conducted on the OMEGA-EP laser facility have for the first time demonstrated that such instabilities can $\sim$100\% deplete the first 0.5 ns of the high-intensity las…
Two-dimension Particle-in-cell simulations for laser plasma interaction with laser intensity of $10^{16} W/cm^2$, plasma density range of 0.01-0.28$n_c$ and scale length of $230 -330 μm$ showed significant pump depletion of the laser energy due to stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) in the low density region ($n_e=0.01-0.2 n_c$). The simulations identified hot electrons generated by SRS in the low density region with moderate energy and by two-plasmon-decay (TPD) near $n_e=0.25n_c$ with higher energy. The overall hot electron temperature (46 keV) and con…
We report results and modelling of an experiment performed at the TAW Vulcan laser facility, aimed at investigating laser-plasma interaction in conditions which are of interest for the Shock Ignition scheme to Inertial Confinement Fusion, i.e. laser intensity higher than 10^16 W/cm2 impinging on a hot (T > 1 keV), inhomogeneous and long scalelength preformed plasma. Measurements show a significant SRS backscattering (4 - 20% of laser energy) driven at low plasma densities and no signatures of TPD/SRS driven at the quarter critical density region. Results are satisfactorily reproduced by an ana…
We demonstrate pump-probe techniques, namely the Doppler spectrometry and the reflectometry in detail, which directly capture the time-resolved ultrafast evolution of high intensity femtosecond laser-driven hot, dense plasma. These techniques are capable of capturing ultrafast plasma dynamics on time scales of sub 100 femtosecond. We have shown the dynamics of high intensity femtosecond laser-driven shock like disturbance into the plasma at densities more than 10^22/cc. This can help understanding the physics related to shock ignition, supernova explosion and many other astrophysical scenarios…
The document describes a numerical algorithm to simulate plasmas and fluids in the 3 dimensional space by the Euler method, in which the spatial meshes are fixed to the space. The plasmas and fluids move through the spacial Euler mesh boundary. The Euler method can represent a large deformation of the plasmas and fluids. On the other hand, when the plasmas or fluids are compressed to a high density, the spatial resolution should be ensured to describe the density change precisely. The present 3D Euler code is developed to simulate a nuclear fusion fuel ignition and burning. Therefore, the 3D E…
Spatially combining multiple strong laser beams is a promising concept for achieving ultrahigh laser intensities. Proof-of-principle experiments have been conducted at the National Ignition Facility to report a combination of up to twenty pulses with high energy conversion efficiency. However, the combination process might damage the seed focusability due to mismatch of the seed and pump wavefronts. Here, we investigate the effect of the finite pump beam size on the focusability of the seed pulse. We propose an approach to retain and even improve the seed focusability by specifically arranging…
The success of direct laser-driven inertial confinement fusion (ICF) relies critically on the efficient coupling of laser light to plasma. At ignition scale, the absolute stimulated Raman scattering (SRS) instability can severely inhibit this coupling by redirecting and strongly depleting laser light. This Letter describes a new dynamic saturation regime of the absolute SRS instability. The saturation occurs when spatiotemporal fluctuations in the ion-acoustic density detune the instability resonance. The dynamic saturation mitigates the strong depletion of laser light and enhances its transmi…
Compression of an intense laser pulse using backward Raman amplification (BRA) in plasma, followed by vacuum focusing to a small spot size, can produce unprecedented ultrarelativistic laser intensities. The plasma density inhomogeneity during BRA, however, causes laser phase and amplitude distortions, limiting the pulse focusability. To solve the issue of distortion, we investigate the use of optical phase conjugation as the seed pulse for BRA. We show that the phase conjugated laser pulses can retain focusability in the nonlinear pump-depletion regime of BRA, but not so easily in the linear a…
In its usual implementation, the Raman amplifier features only one pump carrier frequency. However, pulses with well-separated frequencies can also be Raman amplified while compressed in time. Amplification with frequency-separated pumps is shown to hold even in the highly nonlinear, pump-depletion regime, as derived through a fluid model, and demonstrated via particle-in-cell (PIC) simulations. The resulting efficiency is similar to single-frequency amplifiers, but, due to the beat-wave waveform of both the pump lasers and the amplified seed pulses, these amplifiers feature higher seed intens…
Ray-based calculations of backscatter in laser fusion targets
本文提出了一个非均匀等离子体布里渊散射和拉曼散射的一维稳态模型。子等离子体波被处理在强阻尼限制，并具有由（线性）动力学响应的有质动力驱动的振幅。包括泵浦损耗，逆韧致辐射阻尼，韧致辐射发射，汤姆逊散射密度波动，和整个光束聚焦。描述了实现该模型的数字代码DEPPENDIX。该模型与传统的线性增益计算，以及“平面波”模拟与近轴传播代码PF3D。与OMEGA激光装置上布里渊散射实验的比较[T. R. Boehly等人，光学通信133，p.495（1997）]表明，激光散斑大大增强了反射率，超过了DEPTOND结果。由相位共轭激发的这种增强的近似上限，给出了通过加倍的DEPtrons耦合系数。国家点火装置（NIF）点火设计的分析与设计[J. A. Paisner，E. M. Campbell和W. J.Hogan，Fusion Technol.26，p.755（1994）]，峰值辐射温度为285 eV，显示出极低的反射率。拉曼光的再吸收在该设计中被认为是显著的。
We investigate parametric processes in magnetised plasmas, driven by a large-amplitude pump light wave. Our focus is on laser-plasma interactions relevant to high-energy-density (HED) systems, such as the National Ignition Facility and the Sandia MagLIF concept. We derive dispersion relations for three-wave interactions in a multi-species plasma using Maxwell's equations, the warm-fluid momentum equation and the continuity equation. The application of an external B field causes right and left polarised light waves to propagate with differing phase velocities. This leads to Faraday rotation of …
Magnetic island structures in relativistic laser-driven plasma channels
State Key Laboratory of Nuclear Physics and Technology, and Key Laboratory of HEDP of the Ministry of Education, CAPT, School of Physics, Peking University（北京大学物理学院）；Institute of Theoretical Physics, Chinese Academy of Sciences（中国科学院理论物理研究所）；Institute of Modern Physics, Fudan University（复旦大学现代物理研究所）；Beijing Laser Acceleration Innovation Center（北京激光加速创新中心）
Effects of laser-plasma parameters on sub-nanosecond evolution of cross-beam energy transfer
School of Science, Shenzhen Campus of Sun Yat-sen University（中山大学深圳学院理学院）；College of Science, National University of Defense Technology（国防科技大学理学院）；Institute of Applied Physics and Computational Mathematics（应用物理与计算数学研究所）；Zhejiang Institute of Modern Physics, Institute of Astronomy, School of Physics, Zhejiang University（浙江大学物理学院天文系现代物理研究所）；Shanghai Institute of Laser Plasma, China Academy of Engineering Physics（中国工程物理研究院上海激光等离子体研究所）
