Development of a monochromatic crystal backlight imager for the recent double-cone ignition experiments

We developed a monochromatic crystal backlight imaging system for the double-cone ignition(DCI) scheme, employing a spherically bent quartz crystal. This system was used to measure the spatial distribution and temporal evolution of the head-on colliding plasma from the two compressing cones in the DCI experiments. The influence of laser parameters on the x-ray backlighter intensity and spatial resolution of the imaging system was investigated. The imaging system had a spatial resolution of 10 μm when employing a CCD detector. Experiments demonstrated that the system can obtain time-resolved radiographic images with high quality, enabling the precise measurement of the shape, size, and density distribution of the plasma.

Effect of methane co-feeding on the selectivity of ethylene produced from oxidative dehydrogenation of ethane with CO_2 over a Ni-La/SiO_2 catalyst

A Ni-La/SiO2 catalyst was prepared through the incipient wetness impregnation method and tested in the oxidative dehydrogenation of ethane （ODHE） with CO2. The fresh and used catalysts were characterized by XRD and SEM techniques. The Ni-La/SiO2 catalyst exhibited catalytic activity for the oxidative dehydrogenation of ethane, but with low ethylene selectivity in the absence of methane. The selectivity to ethylene increased with increasing molar ratio of methane in the feed. The carbon deposited on the catalyst surface in the sole ODHE with CO2 was mainly inert carbon, while much more filamentous carbon was formed in the presence of methane. The filamentous carbon was easy to be removed by CO2, which might play a role in improving the conversion of ethane to ethylene. The introduction of methane might affect the equilibrium of the CO2 reforming of ethane and the ODHE with CO2. As a consequence, the synthesis gas produced from CO2 reforming of methane partly inhibited the reaction of ethane and promoted the ODHE with CO2, thus increasing the selectivity of ethylene.

An investigation of the L-shell x-ray conversion efficiency for laser-irradiated tin foils

We have used the ShenguangⅡlaser in third harmonic(351 nm)to investigate the emission of L-shell radiation in the 3.3–4.4 ke V range generated using thin foils of Sn coated onto a parylene substrate with irradiation of order 1015 W cm-2 and nanosecond pulse duration.In our experiment,we have concentrated on assessing the emission on the non-laser irradiated side as this allows an experimental geometry relevant to experiments on photo-ionised plasmas where a secondary target must be placed close to the source,to achieve x-ray fluxes appropriate to astrophysical objects.Overall L-shell conversion efficiencies are estimated to be of order 1%,with little dependence on Sn thickness between 400 and 800 nm.

Effects of Exogenousα-Ketoglutaric Acid on 2-Acetyl-1-Pyrroline,Yield Formation and Grain Quality Characters of Aromatic Rice

The improvement of grain quality in aromatic rice is very important for farmer to increase their income.Present study was conducted with a two-year field experiment and three aromatic rice cultivars in order to study the effects of exogenousα-ketoglutaric acid on yield formation,grain quality characters and the biosynthesis of 2-acetyl-1-pyrroline(2-AP,key component of aromatic rice’s fragrance)in aromatic rice.At heading stage,0.50 mmol L^(-1)(T1)and 1.00 mmol L^(-1)(T2)α-ketoglutaric acid solutions were overhead sprinkle to aromatic rice plants,respectively while the treatment which was overhead sprinkled with distilled water was set as control(CK).The results showed that 17.34%-33.04%and 21.39%-34.74%higher grain 2-AP contents were recorded in T1 and T2 treatments,respectively.Compared with CK,T1 and T2 treatments significantly reduced the transcript level of gene BADH2 which is related to the 2-AP biosynthesis in aromatic rice.3.86%-7.51%higher grain protein contents and 1.15%-3.37%higher head rice rates were also recorded inα-ketoglutaric acid treatments than CK.Moreover,T1 and T2 treatments remarkably decreased the chalky rice rate,chalkiness and grain amylose content.However,there was no remarkable difference in grain yield and related trails(effective panicle number,grain number per panicle,seed-setting rate and 1000-grain weight)among CK,T1 and T2 treatments.In conclusion,application of exogenousα-ketoglutaric acid enhanced 2-AP biosynthesis and improved grain quality of aromatic rice.

Observation of Zeeman splitting effect in a laser-driven coil

The Zeeman splitting effect is observed in a strong magnetic field generated by a laser-driven coil.The expanding plasma from the coil wire surface is concentrated at the coil center and interacts with the simultaneously generated magnetic field.The Cu I spectral lines at wavelengths of 510.5541,515.3235,and 521.8202 nm are detected and analyzed.The splittings of spectral lines are used to estimate the magnetic field strength at the coil center as∼31.4±15.7 T at a laser intensity of∼5.6310^(15) W/cm^(2),which agrees well with measurements using a B-dot probe.Some other plasma parameters of the central plasma disk are also studied.The temperature is evaluated from the Cu I spectral line intensity ratio,while the electron density is estimated from the Stark broadening effect.

Development of a New Subermerged Entry Nozzle in Thin Slab Caster

The fluid flow in the mould of the thin slab continuous caster has a large intluence on the quality of slabs and its productivity.The fluid flow pattern can be controlled by the SEN (Submerged Entry Nozzle) structure. Traditional SEN can not decrease the surface turbulence and penetration depth at the same time, especially at high casting speed. In order to improve the fluid flow in the mould, a new structure SEN-Dissipation SEN have been invented. The water modeling experiments proved that the dissipation SEN could satisfy, the needs of fluid flow condition in the mould at high casting speed.

Experimental Study of Fluid Flow in Thin Slab Continuous Caster Mould with Water-Model

Model study is an efficient method for optimizing the siructure of the mould and the submerged entry nozzle (SEN). Based on the similarity criteria, a full-scale water model has been established in accordance with the mould of thin-slab caster of the CSP (Compact Strip Production) operation. The effects of SEN structure including outlet area, outflow angle, nozzle width, thick-ness and immersion depth have been studied under high speed casting by measuring the amplitude and the impetus of top waves. By the orthogonal experiment design, not only the influence of the faCtors was estimated, but also the optimum work condition was judged. The rules of the fluid flow phenomena were summarized. The principle for choosing a reasonable structure of SEN was discussed.

麋鹿食物组成及其分析方法研究进展

麋鹿(Elaphurusdavidianus)是国家一级重点保护野生动物。自1980年麋鹿重引入项目开展以来,麋鹿食物组成便一直是科研工作者研究的重点之一。本文总结了北京麋鹿生态实验中心、江苏大丰麋鹿国家级自然保护区和湖北石首麋鹿国家级自然保护区麋鹿采食的主要植物资源,综述了常用动物食物组成研究方法,包括直接观察法、利用法、胃含物分析法、粪便显微分析法、胃含物或粪便DNA分析法和稳定同位素技术,并分析了个体因素、植物营养成分、植物可获得性和人为因素等对麋鹿食物组成的影响。对常用食物组成研究方法的比较分析表明,不同方法在解析食物组成时反映的时间尺度和食物分辨率不同,在麋鹿等大型濒危有蹄类动物研究中有其优势和局限性。现有的麋鹿相关研究表明,个体因素所导致的生理差异和能量需求改变会影响麋鹿的食物组成;植物营养成分包括粗蛋白、可溶性糖、纤维素等是影响麋鹿食物组成的重要因子;植物可获得性和人为因素则通过改变食物多样性和丰富度进一步影响麋鹿的食物组成。今后,建议研究者在明确研究目的和研究对象的基础上,评估可用研究方法的优缺点,选择适宜的样品采集和数据分析方法,构建合理的食物组成研究方案。此外,在今后的研究中,应注重整合麋鹿相关研究结果,利用多种方法相结合分析麋鹿的食物组成,全面解析麋鹿的食物选择机制,为深入研究重引入过程中麋鹿对生境破碎化、湿地退化、人为活动干扰等的响应提供指导,进一步推进麋鹿种群发展和长效保护工作的开展。

A novel multi-shot target platform for laser-driven laboratory astrophysics experiments

A new approach to target development for laboratory astrophysics experiments at high-power laser facilities is presented.With the dawn of high-power lasers,laboratory astrophysics has emerged as a field,bringing insight into physical processes in astrophysical objects,such as the formation of stars.An important factor for success in these experiments is targetry.To date,targets have mainly relied on expensive and challenging microfabrication methods.The design presented incorporates replaceable machined parts that assemble into a structure that defines the experimental geometry.This can make targets cheaper and faster to manufacture,while maintaining robustness and reproducibility.The platform is intended for experiments on plasma flows,but it is flexible and may be adapted to the constraints of other experimental setups.Examples of targets used in experimental campaigns are shown,including a design for insertion in a high magnetic field coil.Experimental results are included,demonstrating the performance of the targets.

Collimated gamma beams with high peak flux driven by laser-accelerated electrons

Laser-accelerated electrons are promising in producing gamma-photon beams of high peak flux for the study of nuclear photonics,obtaining copious positrons and exploring photon–photon interaction in vacuum.We report on the experimental generation of brilliant gamma-ray beams with not only high photon yield but also low divergence,based on picosecond laser-accelerated electrons.The 120 J 1 ps laser pulse drives self-modulated wakefield acceleration in a high-density gas jet and generates tens-of-MeV electrons with 26 nC and divergence as small as 1.51◦.These collimated electrons produce gamma-ray photons through bremsstrahlung radiation when transversing a high-Z solid target.We design a high-energy-resolution Compton-scattering spectrometer and find that a total photon number of 2.2×10^(9)is captured within an acceptance angle of 1.1°for photon energies up to 16 MeV.Comparison between the experimental results and Monte Carlo simulations illustrates that the photon beam inherits the small divergence from electrons,corresponding to a total photon number of 2.2×10^(11)and a divergence of 7.73°.

Demonstration of a petawatt-scale optical parametric chirped pulse amplifier based on yttrium calcium oxyborate

As optical parametric chirped pulse amplification has been widely adopted for the generation of extreme intensity laser sources,nonlinear crystals of large aperture are demanded for high-energy amplifiers.Yttrium calcium oxyborate(YCa_(4)O(BO_(3))_(3),YCOB)is capable of being grown with apertures exceeding 100 mm,which makes it possible for application in systems of petawatt scale.In this paper,we experimentally demonstrated for the first time to our knowledge,an ultra-broadband non-collinear optical parametric amplifier with YCOB for petawatt-scale compressed pulse generation at 800 nm.Based on the SG-II 5 PW facility,amplified signal energy of approximately 40 J was achieved and pump-to-signal conversion efficiency was up to 42.3%.A gain bandwidth of 87 nm was realized and supported a compressed pulse duration of 22.3 fs.The near-field and wavefront aberration represented excellent characteristics,which were comparable with those achieved in lithium triborate-based amplifiers.These results verified the great potential for YCOB utilization in the future.

Petawatt and exawatt class lasers worldwide

In the 2015 review paper‘Petawatt Class Lasers Worldwide’a comprehensive overview of the current status of highpower facilities of>200 TW was presented.This was largely based on facility specifications,with some description of their uses,for instance in fundamental ultra-high-intensity interactions,secondary source generation,and inertial confinement fusion(ICF).With the 2018 Nobel Prize in Physics being awarded to Professors Donna Strickland and Gerard Mourou for the development of the technique of chirped pulse amplification(CPA),which made these lasers possible,we celebrate by providing a comprehensive update of the current status of ultra-high-power lasers and demonstrate how the technology has developed.We are now in the era of multi-petawatt facilities coming online,with 100 PW lasers being proposed and even under construction.In addition to this there is a pull towards development of industrial and multi-disciplinary applications,which demands much higher repetition rates,delivering high-average powers with higher efficiencies and the use of alternative wavelengths:mid-IR facilities.So apart from a comprehensive update of the current global status,we want to look at what technologies are to be deployed to get to these new regimes,and some of the critical issues facing their development.

Analysis and construction status of SG-Ⅱ 5PW laser facility

We present a recent progress of the SG-II 5 PW facility, which designed a multi-petawatt ultrashort pulse laser based on optical parametric chirped-pulse amplification(OPCPA). The prior two optical parametric amplifiers have been accomplished and chirped pulses with an energy of 49.7 J and a full-width-at-half-maximum(FWHM) spectrum bandwidth of 85 nm have been achieved. In the PW-scale optical parametric amplification(OPA), with the pump pulse that has an energy of 118 J from the second harmonic generation of the SG-II 7 th beam, the pump-to-signal conversion efficiency is up to 41.9%, which to the best of our knowledge is the highest among all of the reported values for OPCPA systems. The compressed pulse is higher than 37 J in 21 fs(1.76 PW), and the focal spot is ～10 μm after the closed-loop corrections by the adaptive optics. Limited by the repetition of the pump laser, the SG-II 5 PW facility operates one shot per hour. It has successfully been employed for high energy physics experiments.

Status and development of high-power laser facilities at the NLHPLP

In this paper, we review the status of the multifunctional experimental platform at the National Laboratory of High Power Laser and Physics(NLHPLP). The platform, including the SG-II laser facility, SG-II 9th beam, SG-II upgrade(SG-II UP) facility, and SG-II 5 PW facility, is operational and available for interested scientists studying inertial confinement fusion(ICF) and a broad range of high-energy-density physics. These facilities can provide important experimental capabilities by combining different pulse widths of nanosecond, picosecond, and femtosecond scales. In addition, the SG-II UP facility, consisting of a single petawatt system and an eight-beam nanosecond system, is introduced including several laser technologies that have been developed to ensure the performance of the facility. Recent developments of the SG-II 5 PW facility are also presented.

Design and experimental demonstration of a high conversion efficiency OPCPA pre-amplifier for petawatt laser facility

We present the design and experiment of a broadband optical parametric chirped-pulse amplifier(OPCPA) which provides high conversion efficiency and good beam quality at 808 nm wavelength. Using a three-dimensional spatial and temporal numerical model, several design considerations necessary to achieve high conversion efficiency, good beam quality and good output stability are discussed. To improve the conversion efficiency and broaden the amplified signal bandwidth simultaneously, the nonlinear crystal length and OPCPA parameters are analyzed and optimized with the concept of dissipating amplified idler between optical parametric amplification(OPA) of two crystals configuration.In the experiment, an amplifier consisting of two OPCPA stages of ‘L’ type configuration was demonstrated by using the optimized parameters. An amplified signal energy of 160 mJ was achieved with a total pump-to-signal efficiency of 35%(43% efficiency for the OPCPA stage 2). The output bandwidth of signal pulse reached 80 nm and the signal pulse was compressed to 24 fs. The energy stability reached 1.67% RMS at 3% pump energy variation. The optimized OPCPA amplifier operates at a repetition rate of 1 Hz and is used as a front-end injection for the main amplifier of SG-II 5PW laser facility.

Laser-driven plasma collider for nuclear studies

A novel method of initiating nuclear fusion reactions in a full plasma environment was suggested, and a proof-of-concept experiment was carried out with the D t D ! n t3 He reaction. In this new approach, two plasma jets generated by high-intensity lasers collide headon-head. The center-of-mass energy of the nuclei increases accordingly, and therefore, reaction products can be significantly enhanced, especially in the sub-Coulomb barrier ranges. As a result of the fusion reaction, up to 7:6 105 neutrons had been observed. This new type of ‘‘plasma collider'' could provide an innovative tool to study nuclear reactions under astrophysical conditions.

Spatio-temporal evolution of the optical field on a hohlraum wall at the rising edge of a flat-topped pulse

Considering the time delay in different hohlraum wall positions caused by oblique incidence,the spatio-temporal optical field distribution characteristics of a hohlraum wall,especially during the rising edge of a flat-topped pulse,is simulated by a fast Fourier transform method together with chromatography.Results demonstrate that beam propagation along the hohlraum wall is a push-broom process with complex dynamic spatial–temporal evolution.In the first few picoseconds,the optical intensity of the front position increases rapidly,while that of the rear position is relatively weak.The ratio R of the optical intensity during the rising edge is smaller than that of the steady state.R gradually increases and finally tends to the value of the steady state with time.Calculation also shows that,with shorter total width of the rising edge,R of the optical field decreases and the difference compared to the steady state becomes larger.The evolution is more severe with smaller angle of inclination.

Progress of the injection laser system of SG-Ⅱ

A high power laser system was used to drive the ignition of inertial confinement fusion(ICF), of which the high energy,the uniform focal spot, the accurate laser waveform, and the synchronization between the laser beams are key parameters.To accomplish this, global laser characteristics control should be assured, which was the main purpose of the injection laser system. In this paper, the key technological progress involved in the improvement of the performance of the injection laser of SG-II is reported, including frequency domain control, time domain control, near-field spatial shaping, preamplifier technology, and the optical parametric chirped pulse amplification pump source.

Optimization of compensation for high spatial frequency in distorted wavefront using optical phase conjugation

A method is proposed to optimize the recording structure of the photorefractive volume grating to compensate high spatial frequency in the distorted wavefront by optical phase conjugation.Based on the coupled-wave equation, the diffraction efficiency of the recorded grating formed by the scattered beams in different recording structures is simulated.The theoretical results show that the recorded modulations with high spatial frequency can be significantly improved in the small recording angle.In the experiment, three recording structures with the recording angles of 7.5°, 30°, and 45° are chosen to verify the compensation effect.Compared with the reconstructed image in the large recording angle of 45°, the signal to noise ratio of the image recorded at 7.5° increases to 3.2 times of that at 45°.

Absolute instability modes due to rescattering of stimulated Raman scattering in a large nonuniform plasma

Absolute instability modes due to secondary scattering of stimulated Raman scattering (SRS) in a large nonuniform plasma are studied theoretically and numerically. The backscattered light of convective SRS can be considered as a pump light with a finite bandwidth. The different frequency components of the backscattered light can be coupled to develop absolute SRS instability near their quarter-critical densities via rescattering process. The absolute SRS mode develops a Langmuir wave with a high phase velocity of about c/■ with c the light speed in vacuum. Given that most electrons are at low velocities in the linear stage, the absolute SRS mode grows with very weak Landau damping. When the interaction evolves into the nonlinear regime, the Langmuir wave can heat abundant electrons up to a few hundred ke V via the SRS rescattering. Our theoretical model is validated by particle-in-cell simulations. The absolute instabilities may play a considerable role in the experiments of inertial confinement fusion.