低压多丝正比室的位置分辨研究

低压多丝正比室为放射性束核反应的靶前粒子提供位置和时间信号。本工作用²⁴¹Amα源研究电压、工作气体压强等因素对低压多丝正比室位置分辨的影响。实验结果表明：在不同的气体压强条件下，低压多丝正比室的位置分辨均可达到1mm，但考虑到时间、效率等因素，实验中需尽可能提高气压。     

便携式同步辐射原位激光加热装置研制

同步辐射实验方法在研究材料的结构和物性上具有独特的优势，然而，要实现同步辐射原位高温条件，尤其温度高于2 000 K以上，对很多实验方法来说还是一个挑战。激光加热方法可以实现快速、微区的极端高温条件，已经成为高温物性研究的重要工具。上海同步辐射光源在极端高温研究领域，例如高熵合金、涡轮叶片、航空材料等还欠缺相关的原位高温条件，因此，研制了一种便携式连续激光加热装置，利用光谱仪获得样品的热辐射谱，并通过黑体辐射方法拟合出样品的温度梯度和温度稳定性。利用该装置成功实现真空环境中钨片的快速熔化(熔点约3 695 K)，并在上海同步辐射光源表面衍射线站获得了1 608 K原位条件下的MoS2和CTAB-MoS₂材料X射线衍射图谱。本工作所研制的激光加热方法拓展了上海光源在极端条件下的实验能力，为极端高温条件下的材料物性研究提供了重要手段。     

强激光与固体靶相互作用所致硬X射线剂量的蒙特卡罗模拟

本文利用蒙特卡罗程序FLUKA建立了强激光与固体靶相互作用所致硬X射线剂量估算模型,通过与文献结果进行比较,对计算模型进行了验证。利用该计算模型研究了不同电子温度、不同靶材料(包括金、铜和聚乙烯3种常见靶材)和厚度对X射线剂量的影响。计算结果表明,X射线剂量与电子温度密切相关,并会受到靶参数的影响。相同靶厚情形下,Au靶产生的X射线剂量约为Cu靶产生的X射线剂量的1.2倍,约为PE(聚乙烯)产生的X射线剂量的5倍。另外,相较于其他靶厚,当选取电子的平均射程为靶厚时,产生的X射线剂量较大。这些计算结果将为强激光装置中电离辐射剂量的评估提供相关参考。     

KrF激光受激布里渊散射脉宽压缩的研究

用线宽０．５ｃｍ＾－１，脉宽２３ｎｓ的ＫｒＦ激光在ＳＦ６气体和液体环已烷中进行了受激布时散射脉宽压缩的实验研究。测量了脉宽压缩效果和ＳＢＳ反射率随泵浦光能量，气体气压，透镜焦距，焦点位置等实验条件的变化关系，分析了讨论了气体气压，透镜瑞利范围对ＳＢＳ阈值的影响。     

超短激光与薄膜靶作用加速产生质子初步研究

物理学家利用高能粒子加速器进行了多方面的研究，但高能粒子加速器庞大且耗资巨大。随着超短超强激光的发展，现在的激光的功率密度可达到10^22W／cm^2。许多实验室利用不同功率密度的激光与固体靶、薄膜靶及气体等相互作用，进行加速产生高能粒子的研究。其中，利用超短超强激光与薄膜薄相互作用加速产生质子是一重要的研究课题，利用超热电子加速产生超热电子，     

9 高功率KrF激光性能改进及束靶作用研究进展

采用光束平滑技术和像传递技术，优化建立了“天光一号”装置的6束MOPA系统，激光放大器的输出能量提高到200J，在靶上获得好的激光辐照均匀性，6束激光聚焦到靶的不均匀度达2%，接近美国海军实验室NIKE装置的水平；首次实现6束激光同时打靶，在功率密度2TW／cm^2的条件下，采用飞片增压技术在飞片靶中产生超过200万大气压的冲击波，采用可见光条纹相机测量到冲击波信号，验证了天光装置开展状态方程实验研究的可行性。     

XG-Ⅲ装置ps激光束线所致感生放射性评估研究

利用PIC与蒙特卡罗模拟方法对XG-Ⅲ装置在ps激光束线驱动的X射线源和中子源等多种工作模式下进行了剂量学评估,使用PIC模拟确定了高能电子源项后,将其作为蒙特卡罗软件FLUKA的输入数据,通过模拟计算得到了不同靶材在实验结束后不同时刻的感生放射性核素活度及在靶周围所致的剂量。模拟结果表明,对于激光驱动的轫致辐射X射线源,在每次打靶完成并冷却10 min后,在距靶表面1 cm处的感生放射性剂量率约为4 mSv/h,而在距靶表面30 cm处的感生放射性剂量率则已降低到15 μSv/h。对于激光驱动的光核反应产生的光中子源,冷却10 min后在距靶表面1 cm处的感生放射性剂量率小于10 μSv/h。除了靶的材料,靶厚度也会对靶周围的感生放射性剂量率变化情况产生影响,因此有必要在不同的照射环境下,针对不同的靶材及靶厚采取不同的辐射防护方案。本文研究结果可为超短超强激光设施的辐射风险分析及辐射防护工作提供相关参考。     

超短脉冲激光与固体靶相互作用的硬X射线能谱

本实验使用高纯锗探测器，运用单光子法，对超短脉冲激光与固体铜靶相互作用产生的硬X射线能谱进行测量。实验结果表明：在激光强度I≈8×10¹⁶W/cm²的P极化光以45°入射角照射5 mm铜靶、探测立体角为4.5×10^－6的实验条件下，产生的硬X射线的能量主要集中在低于100keV能量范围内，超热电子温度分别为(7.4±0.7)keV和(19.5±1.6)keV。     

O^5＋离子入射在金属表面形成L壳层X射线产生截面的研究

迄今为止，K壳层电离的研究已取得了长足的进展。人们已对各不同入射离子轰击各种靶元素，在很大的能区范围内测量了K壳层X射线产生截面，而L壳层的实验数据则不够完善。本实验测量了20-45MeV的O^5＋离子轰击金属元素Au，Nb，Cd，Fe和Ta靶所引起的L亚壳层X射线产生截面。     

实验研究靶对超热电子行为的影响

研究了靶材料及靶厚度对超热电子产生机制及空间行为的影响。研究结果表明,在激光以45°角入射的条件下,靶材料对超热电子产生机制无明显影响,但靶材厚度对激光吸收效率有很大影响,而超热电子的空间行为并不随靶厚度变化,主要集中在靶前后表面的法线方向发射。     

Pulsed laser treatments of polyethylene films

A Nd:Yag pulsed laser, 3 ns pulse width, 150 mJ pulse energy, operating at the second harmonics (532 nm) has been used to irradiate in air polyethylene thin films.The thermal and chemical effects induced by the laser irradiation in the polymer are responsible of the hydrogen and C_xH_y groups emission at long irradiation times. A special study, concerning the welding effect between two different types of polyethylene films, one transparent and the other strong absorbent the laser light, was performed. The welding, at the interface of the two pressed polymers, depends on the optical and micro-structural material properties besides the irradiation time. In particular, polymers with different viscosity, melting temperature and crystalline degree exhibit different mechanical behaviour.Different techniques were employed to investigate on the polymeric welding effects, such as the mass quadrupole spectrometry, the scanning electron microscope, the surface profiler and the mechanical strength measurement.     

Fukushima Daiichi fuel debris retrieval: results of aerosol characterization during laser cutting of non-radioactive corium simulants

ABSTRACT

The production and dispersion of contaminated aerosols during the laser cutting of corium can potentially provide useful insights into the dispersion of contamination during the evacuation of damaged reactors during decommissioning. Quantitative assessments of contamination dispersion are fundamental to the development of a safety case for the decommissioning of the Fukushima Daiichi plant. This collaborative work between IRSN, ONET Technologies and CEA, managed by the Mitsubishi Research Institute on behalf of the Japanese Ministry of Economy, Trade and Industry, presents the characterization of aerosols generated during laser cutting of corium simulants both in air and under water.

The objective is to obtain quantitative data for risk assessment related to the contamination released and disseminated when implementing this technique, over the next few years, in the process of decommissioning the damaged reactors. This paper presents a part of the results stemming from this project, focused on the characterization of aerosols produced during laser cutting of two representative corium simulants in air and underwater conditions. The experimental configuration also enabled investigation of the production of other material residues such as particle dross and water purity on the particulate composition of the aerosols. Ultimately, the radioisotope concentration distribution in the aerosols are transposed to radioactivity in order to assess the risk to radiation workers during decommissioning.     

Plasma ignition threshold disparity between silver nanoparticle-based target and bulk silver target at different laser wavelengths

Plasma ignition threshold of nanoparticle-based and bulk silver targets was measured in air. The plasma was initiated by a Nd:YAG laser at wavelengths of 355, 532, and 1064 nm. The plasma ignition was monitored utilizing the prominent Ag I line at 546.5 nm. Lower ignition thresholds of the nanoparticle-based silver target were estimated at 0.4?±?0.02, 0.34?±?0.04, and 0.27?±?0.035 J cm~(-2) coupled with the different laser wavelengths, respectively. In contrast, the bulk silver target plasma exhibited an order of magnitude higher ignition threshold. A three orders of magnitude enhanced emission intensity from the nano-based target over the bulk target was achieved at lower levels of laser irradiation. A reduction of the thermal diffusion length of the nanosilver was assumed in order to theoretically predict this reduction in the plasma threshold. In addition, the effect of self-reversal on the resonance lines was taken into consideration.     

Critical elements of high gain laser fusion

Progress toward high laser fusion can be measured by a set of five critical elements. They are: (1) the laser-to-fuel coupling efficiency, (2) the cold fuel isentrope, (3) the implosion symmetry, (4) the ablation pressure, and (5) the ignition concept.     

Development of an HCN dual laser for the interferometer on EAST

A two-color continuous wave(CW) discharge-pumped far-infrared(FIR) hydrogen cyanide(HCN) laser was developed as the source of an interferometer for measuring the line-averaged electron density in the Experimental Advanced Superconducting Tokamak(EAST). The output power of the dual laser system was about 120 m W from each laser on the 337 μm(0.89 THz)line. The polarization of each output beam was fixed using thin tungsten filaments and oscillated in the EH11 mode. Different megahertz intermediate frequencies(IF) and a slight frequency offset(～1 MHz) were generated in this system to replace the traditional rotating grating with～10 k Hz IF, and this can improve the time resolution of the interferometer significantly. The experimental result showed that different IF signals were obtained by successfully adjusting the cavity length. In particular, the beat frequency was captured at ～1.3 MHz by a Schottky mixer when the length of the resonant cavities was changed by 5 μm by an automatic adjustment system. In order to study the character of IF, a long time record of the IF signal was carried out,and the IF signal could be stabilized for a few minutes in the range of 2 MHz to 3 MHz. A realtime IF stability control system was initially designed for long pulse discharge experiments on the EAST. The ～MHz frequency response and good phase sensitivity of the dual laser HCN interferometer will allow the system to track fast density profiles and resolve fast MHD events,such as tearing/neoclassical tearing, disruptions, etc.     

Impacts of laser pulse width and target thickness on laser micro-propulsion performance

In order to optimize the laser ablation performance of a micro-thruster with 1U dimensions, which employs a micro semiconductor laser, the impacts of pulse width and glycidyl azide polymer (GAP) thickness on thrust performance were researched. The results showed that with a GAP thickness of 200 μm, the single-pulse impulse (I) increased gradually with the increase in the laser pulse width from 50 to 800 μs, while the specific impulse (Isp), impulse coupling coefficient (Cm) and ablation efficiency (η) all reached optimal values with a 200 μs pulse width. It is worth noting that the optimal pulse width is identical to the ignition delay time. Both Cm and η peaked with a pulse width of 200 μs, reaching 242.22 μN W−1 and 35.4%, respectively. With the increase in GAP thickness, I and Cm increased gradually. GAP of different thicknesses corresponded to different optimal laser pulse widths. Under a certain laser pulse width, the optimal GAP thickness should be the most vertical thickness of the ablation pit, and the various propulsion performance parameters at this time were also optimal. With the current laser parameters, the optimal GAP thickness was approximately 150 μm, Isp was approximately 322.22 s, and η was approximately 34.94%.     

Ablation characteristics of carbon-doped glycerol irradiated by a 1064 nm nanosecond pulse laser

The ablation characteristics of carbon-doped glycerol were investigated in laser plasma propulsion using a pulse laser with 10 ns pulse width and 1064 nm wavelength.The results showed that with the incident laser intensity increasing,the target momentum decreased.Results still indicated that the strong plasma shielded the consumption loss and resulted in a low coupling coefficient.Furthermore,the carbon-doping gave rise to variations in the laser focal position and laser intensity,which in turn reduced the glycerol splashing.Based on the glycerol viscosity and the carbon doping,a high specific impulse is anticipated.     

CO2 laser collective Thomson scattering diagnostics on the HT-7 tokamak

A CW CO2 laser collective Thomson scattering diagnostics was developed to measure plasma density fluctuations on the HT-7 tokamak. The design and construction of CO2 laser scattering apparatus is described. The laser source is a continuous-wave CO2 laser with a cavity length of 1.9 m and a power output of about 10 W at 10.6 μm. The k-resolution of the system is △k ≈ 3.2 cm^-1. The preliminary data from the diagnostic is presented.     

Commissioning of a high-resolution collinear laser spectroscopy apparatus with a laser ablation ion source

Collinear laser spectroscopy is a powerful tool for studying the nuclear spins,electromagnetic moments,and charge radii of exotic nuclei.To study the nuclear properties of unstable nuclei at the Beijing Radioactive Ion-beam Facility （BRIF） and the future High Intensity Heavy-ion Accelerator Facility （HIAF）,we developed a collinear laser spectroscopy apparatus integrated with an offline laser ablation ion source and a laser system.The overall performance of this state-of-the-art technique was eva...     

Improved density measurement by FIR laser interferometer on EAST tokamak

A three-channel far-infrared (FIR) hydrogen cyanide (HCN) laser interferometer is in operation since 2010 to measure the line averaged electron density on experimental advanced superconducting tokamak (EAST). The HCN laser signal is improved by means of a new schottky barrier diode (SBD) detector. The improved measurement and latest experiment results of the three-channel FIR laser interferometer on EAST tokamak are reported.