Three-dimensional dynamics of breakout afterburner ion acceleration using high-contrast short-pulse laser and nanoscale targets

Breakout afterburner (BOA) laser-ion acceleration has been demonstrated for the first time in the laboratory. In the BOA, an initially solid-density target undergoes relativistically induced transparency, initiating a period of enhanced ion acceleration. First-ever kinetic simulations of the BOA in three dimensions show that the ion beam forms lobes in the direction orthogonal to laser polarization and propagation. Analytic theory presented for the electron dynamics in the laser ponderomotive field explains how azimuthal symmetry breaks even for a symmetric laser intensity profile; these results are consistent with recent experiments at the Trident laser facility.     

周期量级激光脉冲驱动下非次序双电离的三维经典系综模拟

利用三维经典系综模型研究了周期量级激光脉冲驱动的氩原子非次序双电离,所得结果表明,Ar2+离子的纵向动量分布与载波包络相位有很强的依赖关系,随载波包络相位φ的增加,具有不对称双峰结构的离子纵向动量分布重心从负动量转移到正动量,并且φ每改变π时Ar2+离子的纵向动量呈现相反的分布.在重碰撞过程中核与电子之间的库仑势发生变化后,计算得到的Ar2+离子纵向动量分布随载波包络相位的变化与实验结果定量上一致.     

Three-dimensional imaging simulation of active laser detection based on DLOS method

The technology of active laser detection is widely used in many different fields nowadays. With the development of computer technology, programmable software simulation can provide reference for the design of active laser detection. The characteristics of the active laser detecting systems also can be judged more visual. Based on the features of the active laser detection, an improved method of radiative transfer calculation (Double Line Of Sight) was developed, and the simulation models of complete active laser detecting imaging were founded. Compared with the results calculated by the Monte Carlo method, the correctness of the improved method was verified. The results of active laser detecting imaging of complex three-dimensional targets in different atmospheric scenes were compared. The influence of different atmospheric dielectric property were analyzed, which provides effective reference for the design of active laser detection.     

Three-dimensional simulation of the temperature field in high-power double-clad fiber laser

The 3D temperature distribution in high-power double-clad fiber laser (DCFL) and the evolution of the temperature field in the fiber are analyzed, according to the transient heat conduction equation. The temperature in the fiber reaches the maximum after opening the pump light about 20 s, and cools down to the room temperature after shutting down for also about 20 s. The shape of the inner-clad can only affect the spacial distribution of the temperature outside of the core, but have no effect on the maximum temperature in the core.     

Electrical characteristics of a small active volume (1 cm3) discharge-pumped XeCl laser

Through the use of a PFL (pulse-forming line) of conveniently changeable output impedance Z_O, the electrical characteristics of a small volume-discharge of standard XeCl laser gas mix was studied. The impedance Z_D from a 2×0.5×1(=1) cm³ discharge was found to be about 10. A PFL of very low impedance is therefore rather inefficient in driving the discharge, because of the impedance mismatch and the slower current rise time. The data presented will be useful for the design of excimer lasers of small discharge volume, which find applications in serving as master oscillator or in high repetition rate operation.     

Instability and mode transition analysis of a hydrogen-rich combustion in a model afterburner

Combustion instabilities were investigated experimentally for a hydrogen-rich combustion in a model afterburner installed at the end of a high-enthalpy wind tunnel. Air was supplied at 0.3 MPa and 950 K. The combustion instabilities were studied with the time-resolved measurements of a near-infrared (NIR) emission from water molecules over 780 nm using a high-speed video camera. Pressure was also measured in the combustor. The pressure and the NIR images were analyzed by data-driven approach, which include the fast Fourier transform (FFT), the wavelet transform, the dynamic mode decomposition (DMD) and the Gaussian process latent variable methods (GP-LVM). Thermoacoustic instability was observed under a rich condition, and the amplitude of the pressure oscillation was the maximum at the overall equivalence ratio of approximately 2.4 or 2.7 as a result of the FFT. The combustion dynamics were investigated in detail for an experimental run at the equivalence ratio of 2.4. A pressure spectrogram indicated a flame–vortex interaction with a Strouhal number of 0.5 (2300 Hz), thermoacoustic instability (560 Hz), and their transitions with the wavelet transform. For NIR images, the same tendency was also observed in the spectrogram of the modes obtained by the Gabor-filtered DMD, which could clearly resolve the high-order harmonic modes of the flame–vortex interaction and the thermoacoustic instability. Furthermore, NIR images were analyzed with GP-LVM to study the evolution of the combustion dynamics in a three-dimensional latent space. Recurrence plots with the Euclidean distance function were used to visualize the evolutions of the combustion dynamics. A limit cycle behavior of the flame–vortex interaction was clearly observed, whereas the limit cycle of the thermoacoustic instability showed more complicated behaviors. The transition behaviors of the instabilities were observed in the recurrence plots in detail, indicating that the flame–vortex interaction excited the fourth harmonic mode of the thermoacoustic instability, followed by the basic mode.     

激光辐照柱体铝靶的三维光滑粒子流体动力学仿真

在现有光滑粒子流体动力学方法基础上,提出了结合差分方法处理激光辐照边界条件的方法,并利用此方法自编程序模拟计算了功率密度为5.0109 W/cm2的强连续激光辐照铝靶时的热-力学效应,准确给出了与激光作用的边界粒子的分布和飞散情况,同时给出了不同时刻靶体的温度场,得到了温度分布规律,并对结果进行了分析。     

3维并行全电磁粒子模拟软件UNIPIC-3D

介绍了自行研制的3维并行全电磁粒子模拟软件UNIPIC-3D。在该软件中,电磁场量用二阶精度的时域有限差分方法迭代,粒子用相对论牛顿-洛仑兹力方程推进。该软件拥有复杂器件的几何建模和网格自动剖分的功能,具有模拟相对论返波管、虚阴极振荡器、磁绝缘线振荡器等高功率微波器件的能力。且该软件具有强大的后处理功能,可以显示电场、磁场、电流、电压、功率、频谱、粒子相空间等。在高性能并行计算机上对软件的并行效率进行了测试。通过与2.5维UNIPIC软件的结果进行比较,验证了UNIPIC-3D软件的正确性。     

A megawatt excimer laser of small discharge volume (3.8 cm3)

We demonstrated intense laser action form a 14 cm gain length, 3.8 cm³ active volume XeCl laser. The laser peak power of 1.3 MW was comparable with the best results obtained from a similar small active volume excimer laser, and the laser energy of 40 mJ per pulse obtained from our device was considerably higher.     

3维并行全电磁粒子模拟软件UNIPIC-3D

介绍了自行研制的3维并行全电磁粒子模拟软件UNIPIC-3D。在该软件中,电磁场量用二阶精度的时域有限差分方法迭代,粒子用相对论牛顿-洛仑兹力方程推进。该软件拥有复杂器件的几何建模和网格自动剖分的功能,具有模拟相对论返波管、虚阴极振荡器、磁绝缘线振荡器等高功率微波器件的能力。且该软件具有强大的后处理功能,可以显示电场、磁场、电流、电压、功率、频谱、粒子相空间等。在高性能并行计算机上对软件的并行效率进行了测试。通过与2.5维UNIPIC软件的结果进行比较,验证了UNIPIC-3D软件的正确性。     

Neutron production in a picosecond laser plasma at a radiation intensity of 3×1017W/cm2

Neutron production as a result of the reaction ²H(d, n)³He in a picosecond laser plasma is reported. A considerable neutron yield of 5×10⁴ per pulse is obtained for the first time in a picosecond laser plasma on the surface of a solid deuterated target at laser radiation intensity of 3×10¹⁷ W/cm².     

Three-dimensional simulation on explosions of hydrogen atomic clusters irradiated by an intense femtosecond laser pulse

Using classic particle dynamics simulations, the interaction process between an intense femtosecond laser pulse and icosahedral hydrogen atomic clusters H_{13}, H_{55} and H_{147} has been studied. It is revealed that with increasing number of atoms in the cluster, the kinetic energy of ions generated in the Coulomb explosion of the ionized hydrogen clusters increases. The expansion process of the clusters after laser irradiation has also been examined, showing that the expansion scale decreases with increasing cluster size.     

Three-dimensional simulation of primary break-up in a close-coupled atomizer

Until now much of the modelling activity around close-coupled gas atomization has been mainly focused on gas-only flow with discrete phase interaction using Lagrangian-based models. However, this approach is unable to supply valuable information regarding the primary break-up mechanism of the melt being injected. Furthermore, much of existing numerical work is based on two-dimensional axisymmetric geometries, and therefore suffers the absence of three-dimensional flow features. In order to overcome these aspects the authors have carried out an analysis using a three-dimensional geometry by means of an Eulerian, Volume of Fluid, model to accurately present the early stages of melt stream behaviour at the atomizer’s melt inlet. The study investigates the mechanisms associated with primary break-up, and the results obtained highlight three modes under which a close-coupled atomizer may operate.     

Flexural motion in laser evaporative heated cantilever workpiece: Three-dimensional analysis

Laser evaporative heating of metallic surfaces generates a recoil pressure at liquid–vapor interface. Since the magnitude of recoil pressure is considerably high, despite the small evaporative area, the pressure force generated normal to the workpiece surface is considerably high. Consequently, pressure force initiates a flexural motion of the workpiece subjected to a laser evaporative heating. In the present study, flexural motion of a steel plate, with a cantilever arrangement, due to laser evaporative heating is considered. Stress field in the workpiece is also taken into account. Three-dimensional motion of the workpiece is modeled and governing equations of motion and stress field are solved numerically using the finite element method. It is found that surface displacement in the order of 20 m is predicted and the maximum equivalent stress in the order of 700 kPa is obtained. Additional copper element in the workpiece alters the temporal variation of stress levels.     

Boltzmann simulation of a storage ring laser

A numerical technique is described, which follows the motion of the entire electron distribution in a storage ring laser. The laser gain and electron distribution parameters such as energy spread, bunch length, damping rates, and containment time are discussed, both with and without the use of the gain expansion technique. The limits of validity of the onedimensional approximation are defined.     

20cm口径离子推力器力学特性模拟分析

为了提升20 cm离子推力器的抗冲击性能,对现有结构开展了力学分析和试验验证。对栅极组件进行结构等效处理后,采用有限元方法分析了整机的模态和冲击响应谱。分析结果显示,栅极组件结构等效前后的分析结果对比差距8.3%～11.9%;推力器的3个轴向基频分别为246,248,336 Hz,栅极组件和中间极靴是离子推力器的力学薄弱环节并对整体结构稳定性具有重要影响;在冲击载荷1600 g下,栅极组件表面应力主要集中在小孔区边缘处,且形变也主要发生在小孔区;在采取刚度为1000 kN/m的减振措施后,栅极组件的整体形变位移降低了60%～82%。试验结果显示,在10～1200 Hz的低频扫描过程中,推力器3个轴向的基频分别为256,258,348 Hz,与仿真结果基本一致,采用减振措施后的20 cm口径离子推力器通过了1600 g的冲击试验。     

S波段宽带大功率连续波耦合腔行波管3维模拟设计

使用3维PIC粒子模拟软件定量分析了耦合腔行波管的大信号注波互作用行为。使用完整的仿真模型完成了S波段连续波管型的设计,达到如下设计指标：工作频率2.0~2.3 GHz,输出功率4.3 kW,频带内增益波动±0.7 dB。提出了使用大介电常数微扰介质棒减小耦合阻抗计算误差的方法,研究了行波管的冷腔特性,给出了色散、耦合阻抗等参数。     

Three-dimensional simulation of a positive streamer in air near curved anode

We report the results of the first fully three-dimensional numerical simulation of a positive streamer in air in a 5 cm gap between a curved anode and a plane cathode. The formation of a negative radial field ahead of the streamer is found. This field leads to the formation of a current-free region in the streamer channel. The origin of the effect is discussed and the characteristic radius of this region is obtained.     

S波段宽带大功率连续波耦合腔行波管3维模拟设计

 使用3维PIC粒子模拟软件定量分析了耦合腔行波管的大信号注波互作用行为。使用完整的仿真模型完成了S波段连续波管型的设计,达到如下设计指标：工作频率2.0~2.3 GHz,输出功率4.3 kW,频带内增益波动±0.7 dB。提出了使用大介电常数微扰介质棒减小耦合阻抗计算误差的方法,研究了行波管的冷腔特性,给出了色散、耦合阻抗等参数。