Author Affiliations
Abstract
1 State Key Laboratory of Nuclear Physics and Technology, and Key Laboratory of HEDP of the Ministry of Education, CAPT, Peking University, Beijing, China
2 Beijing Laser Acceleration Innovation Center, Beijing, China
3 Institute of Guangdong Laser Plasma Technology, Guangzhou, China
The discharged capillary plasma channel has been extensively studied as a high-gradient particle acceleration and transmission medium. A novel measurement method of plasma channel density profiles has been employed, where the role of plasma channels guiding the advantages of lasers has shown strong appeal. Here, we have studied the high-order transverse plasma density profile distribution using a channel-guided laser, and made detailed measurements of its evolution under various parameters. The paraxial wave equation in a plasma channel with high-order density profile components is analyzed, and the approximate propagation process based on the Gaussian profile laser is obtained on this basis, which agrees well with the simulation under phase conditions. In the experiments, by measuring the integrated transverse laser intensities at the outlet of the channels, the radial quartic density profiles of the plasma channels have been obtained. By precisely synchronizing the detection laser pulses and the plasma channels at various moments, the reconstructed density profile shows an evolution from the radial quartic profile to the quasi-parabolic profile, and the high-order component is indicated as an exponential decline tendency over time. Factors affecting the evolution rate were investigated by varying the incentive source and capillary parameters. It can be found that the discharge voltages and currents are positive factors quickening the evolution, while the electron-ion heating, capillary radii and pressures are negative ones. One plausible explanation is that quartic profile contributions may be linked to plasma heating. This work helps one to understand the mechanisms of the formation, the evolutions of the guiding channel electron-density profiles and their dependences on the external controllable parameters. It provides support and reflection for physical research on discharged capillary plasma and optimizing plasma channels in various applications.
channel-guided laser discharge capillary plasma density profile High Power Laser Science and Engineering
2023, 11(6): 06000e85
南华大学 核科学技术学院，湖南 衡阳 421001
提出了一种基于激光尾波场加速电子诱导光核嬗变的优化方案并开展了135Cs光核嬗变的数值模拟研究。蒙特卡罗模拟研究发现随着电子能量的增加，嬗变产额逐渐趋于饱和，单位能量电子的嬗变效率在40 MeV附近时存在峰值，半高处能量为20、120 MeV。为了提升半高处能量内的电子电量从而优化嬗变产额，使用粒子模拟程序研究了超短超强激光在气体等离子体中的传输过程。研究结果发现，随着等离子体密度的降低，尾波场加速的电子能量逐渐升高，但是电荷量逐渐减少，并且圆偏振激光加速的电子能量和电荷量均优于线偏振激光。通过调整等离子体密度和激光偏振，发现在圆偏振激光和特定等离子体密度条件下，存在嬗变产额的最优值。利用电导率等效方法对345 GHz折叠波导行波管中的电磁信号的传输损耗进行了仿真研究，考察了流通管孔径、加工粗糙度等对冷腔传输损耗的影响，流通管孔径较大或加工粗糙度较大都会导致电磁信号传输衰减严重。还模拟分析了热腔中电磁信号衰减对慢波结构净增益、带宽、最佳周期数等器件特征参数的影响，结果显示，电磁信号衰减会使得增益下降和带宽降低。
光核嬗变 激光尾波场加速 长寿命裂变产物 气体等离子体密度 photo-transmutation laser wavefield acceleration long-lived fission products plasma density 强激光与粒子束
2023, 35(9): 091006
Author Affiliations
Abstract
1 Key Laboratory for Laser Plasmas (MoE), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, China
2 Collaborative Innovation Center of IFSA, Shanghai Jiao Tong University, Shanghai, China
3 Research Center of Laser Fusion of China Academy of Engineering Physics, Mianyang, China
4 College of Physics and Electronics Engineering, Northwest Normal University, Lanzhou, China
5 Tsung-Dao Lee Institute, Shanghai Jiao Tong University, Shanghai, China
As a typical plasma-based optical element that can sustain ultra-high light intensity, plasma density gratings driven by intense laser pulses have been extensively studied for wide applications. Here, we show that the plasma density grating driven by two intersecting driver laser pulses is not only nonuniform in space but also varies over time. Consequently, the probe laser pulse that passes through such a dynamic plasma density grating will be depolarized, that is, its polarization becomes spatially and temporally variable. More importantly, the laser depolarization may spontaneously take place for crossed laser beams if their polarization angles are arranged properly. The laser depolarization by a dynamic plasma density grating may find application in mitigating parametric instabilities in laser-driven inertial confinement fusion.
depolarization high-power laser plasma density grating High Power Laser Science and Engineering
2023, 11(3): 03000e37
针对采用氩气放电方式产生等离子体的离子引出模拟研究需求，提出一种等离子体密度及电子温度等关键特征参数的光谱测量方法。根据氩等离子体状态建立反映其粒子间动力学反应过程的粒子布居平衡模型，并通过对比分析实验测得的发射光谱获取等离子体相关特征参数信息。实验结果表明，该光谱测量方法可获取典型工况下射流区内氩等离子体的密度及电子温度等关键参数信息，为离子引出过程的模拟研究提供一种可靠和实用的等离子体参数测量手段。
光谱学 等离子体密度 电子温度 氩气放电 发射光谱 粒子布居平衡模型 激光与光电子学进展
2022, 59(17): 1730002
1 长春理工大学光电工程学院, 吉林 长春 130022
2 光驰科技(上海)有限公司, 上海 200444
磁控溅射系统中薄膜厚度的均匀性是关键指标之一。通过分析磁场强度、靶材与基板的距离和气体压强对Si3N4和SiO2两种薄膜厚度均匀性的影响,借助Langmuir探针分析等离子体的密度,并采用二进制阶梯式充气方式调整纵向的均匀性。通过对靶材加载正弦半波电压并使用MATLAB软件确定振幅及相位参数,从而调整横向的均匀性。实验结果表明,对于Si3N4膜层,其在横向上、中和下的均匀性分别为±1.27%、±0.62%和±1.33%,纵向的均匀性为±0.33%;对于SiO2膜层,其在横向上、中和下的均匀性分别为±1.12%、±0.42%和±1.23%,纵向的均匀性为±0.25%。
薄膜 厚度均匀性 磁控溅射 孪生靶 等离子体密度 二进制梯度充气方式 正弦半波
华中科技大学 武汉光电国家实验室, 武汉 430074
为了研究高能脉冲CO2激光诱导空气等离子体放电通道的特性, 建立了高压电容充放电实验平台, 激光束经离轴抛物聚焦镜汇聚, 引发间距可调的盘状电极和针状电极之间的等离子体放电通道。利用电气参量测量、发射光谱测量等手段, 分析了等离子体放电通道的启动特性、阻抗特性和等离子体密度。结果表明, 激光束与放电方向同轴的结构以及较大的脉冲能量, 使得激光诱导等离子体放电通道的启动时间大幅缩短, 50mm间距的等离子体通道, 启动时间约为2μs; 激光诱导等离子体放电通道的阻抗很小, 约1Ω~2Ω, 并且阻抗值随放电电压的增加有减小的趋势, 而与等离子体通道长度的关系不明显; 由谱线的Stark展宽计算获得的空气击穿之后、放电启动之前的等离子体电子密度约为1019cm-3, 尽管放电启动时等离子体辐射显著增强, 但等离子体密度近乎单调下降。这些结果将有利于高能脉冲CO2激光诱导空气等离子体放电通道的应用研究。
激光技术 等离子体通道 等离子体阻抗 等离子体密度 laser technique plasma channel plasma impedance plasma density
Author Affiliations
Abstract
1 Lawrence Livermore National Laboratory, Livermore, CA 94551, USA
2 University of California, Davis, CA 95616, USA
We present an interferometry setup and the detailed fringe analysis method for intense short pulse (SP) laser experiments. The interferometry scheme was refined through multiple campaigns to investigate the effects of pre-plasmas on energetic electrons at the Jupiter Laser Facility at Lawrence Livermore National Laboratory. The interferometer used a frequency doubled ( D 0:527 mm) 0.5 ps long optical probe beam to measure the pre-plasma density, an invaluable parameter tobetter understand how varying pre-plasma conditions affect the characteristics of the energetic electrons. The hardware of the diagnostic, data analysis and example data are presented. The diagnostic setup and the analysis procedure can be employed for any other SP laser experiments and interferograms, respectively.finish the manuscript. This work was performed under the auspices of the US DOE by LLNL under contract no. DEAC52-07NA27344 and funded by the LDRD (12-ERD-062) program.
Mach–Zehnder interferometer Mach–Zehnder interferometer optical interferometry optical interferometry picosecond probe picosecond probe plasma density plasma density short pulse laser short pulse laser High Power Laser Science and Engineering
2016, 4(3): 03000e26
1 强脉冲辐射环境模拟与效应国家重点实验室, 西安 710024
2 西北核技术研究所, 西安 710024
在杆箍缩二极管工作前预先填充一定密度的等离子体，可以改善二极管特性，从而提高二极管出射X射线的剂量率。建立了预充等离子体的杆箍缩二极管的粒子模拟模型，通过收集轰击到阳极上的电子，诊断其轴向分布，可以给出不同时刻的束流箍缩特性。利用“剑光一号”加速器低阻抗状态(1 MV/9 Ω/40 ns)开展了预充等离子体的杆箍缩二极管实验研究。预充适当密度的等离子体后，二极管阻抗降低到10 Ω，X射线辐射剂量从0.76 mGy提高到3.19 mGy，侧向焦斑从9 mm降到4 mm。模拟结果和实验基本符合。
预充等离子体杆箍缩二极管 等离子体密度 数值模拟 电子沉积密度轴向分布 侧向焦斑 plasma filled rod pinch diode plasma density numerical simulation axial distribution of electron deposition density axial spot 强激光与粒子束
2014, 26(11): 115009
西北核技术研究所 强脉冲辐射环境模拟及效应国家重点实验室, 西安 710024
“强光一号”等离子体断路开关(POS)及负载二极管系统工作性能不够稳定, 通过分析数据指出POS等离子体源参数差异性是导致系统不稳定的主要原因。POS等离子体源参数重复性测量结果表明, 在开关断路时刻等离子体源瞬时发射等离子体密度重复性极差在10%左右, 而开关区间累积等离子体密度极差超过100 %。开关区间累积等离子体密度和阴极重粒子发射会对POS断路性能产生显著影响。计算表明开关区间累积等离子体密度差异对POS断路电流阈值影响达到200 kA, 与运行数据统计结果一致; 在断路电流阈值相同的条件下, 阴极物质逸出对二极管电压影响显著, MCNP程序计算结果表明, 产生辐射剂量差别可以达到80%, 与统计数据相当。
等离子体断路开关 稳定性 等离子体密度 阴极物质逸出 plasma opening switch stability plasma density cathode matter ejection 强激光与粒子束
2014, 26(8): 085104
采用放电电流为100~300 A、持续时间为13 μs的单脉冲电源，设计了两种同轴电极结构作为放电阳极，分别为筒状电极、喷嘴状电极。利用MAXWELL 3D电场仿真软件对两种电极结构下的电场分布进行了仿真分析，并采用探针法对放电生成的等离子体的参数进行了测量，分析讨论了同轴电极结构对真空放电等离子体生成特性的影响。选取喷嘴状电极结构作为阳极，分别测量了采用铅、铝、铜三种材质的阴极时生成的等离子体的扩散速度及能量。实验与仿真结果表明：当阳极为喷嘴状电极时阴极尖端的电场强度较大，测得放电电流较大，击穿电压较低，等离子体密度也较大；采用铝材质阴极时生成的等离子体扩散速度最快，采用铅材质阴极时生成的等离子体的离子动能最大。
电极结构 真空放电 朗缪尔探针法 等离子体密度 离子动能 electrode configuration vacuum discharge Langmuir probe method plasma density ion kinetic energy
