Overcritical electron acceleration and betatron radiation in the bubble-like structure formed by re-injected electrons in a tailored transverse plasma

We present a novel scheme for dense electron acceleration driven by the laser irradiation of a near-critical-density plasma.The electron reflux effect in a transversely tailored plasma is particularly enhanced in the area of peak density.We observe a bubble-like distribution of re-injected electrons,which forms a strong quasistatic electromagnetic field that can accelerate electrons longitudinally while also preserving the electron transverse emittance.Simulation results demonstrate that over-dense electrons could be trapped in such an artificial bubble and accelerated to an energy of ~500 MeV.The obtained relativistic electron beam can reach a total charge of up to 0.26 nC and is well collimated with a small divergence of 17 mrad.Moreover,the wavelength of electron oscillation is noticeably reduced due to the shaking of the bubble structure in the laser field.As a result,the energy of the produced photons is substantially increased to the range.This new regime provides a path to generating high-charge electron beams and high-energy-ray sources.

Damage mechanism and evaluation model of compressor impeller remanufacturing blanks:A review

The theoretical and technological achievements in the damage mechanism and evaluation model obtained through the national basic research program“Key Fundamental Scientific Problems on Mechanical Equipment Remanufacturing”are reviewed in this work.Large centrifugal compressor impeller blanks were used as the study object.The materials of the blanks were FV520B and KMN.The mechanism and evaluation model of ultra-high cycle fatigue,erosion wear,and corrosion damage were studied via theoretical calculation,finite element simulation,and experimentation.For ultra-high cycle fatigue damage,the characteristics of ultra-high cycle fatigue of the impeller material were clarified,and prediction models of ultra-high cycle fatigue strength were established.A residual life evaluation technique based on the“b-HV-N”(where b was the nonlinear parameter,HV was the Vickers hardness,and N was the fatigue life)double criterion method was proposed.For erosion wear,the flow field of gas-solid two-phase flow inside the impeller was simulated,and the erosion wear law was clarified.Two models for erosion rate and erosion depth calculation were established.For corrosion damage,the electrochemical and stress corrosion behaviors of the impeller material and welded joints in H2S/CO2 environment were investigated.KISCC(critical stress intensity factor)and da/dt(crack growth rate,where a is the total crack length and t is time)varied with H2S concentration and temperature,and their variation laws were revealed.Through this research,the key scientific problems of the damage behavior and mechanism of remanufacturing objects in the multi-strength field and cross-scale were solved.The findings provide theoretical and evaluation model support for the analysis and evaluation of large centrifugal compressor impellers before remanufacturing.

Interlayer engineering of molybdenum disulfide toward efficient electrocatalytic hydrogenation

Electrocatalytic hydrogenation(ECH)enables the sustainable production of chemicals under ambient condition;however,suffers from serious competition with hydrogen(H2)evolution and the use of precious metals as electrocatalysts.Herein,molybdenum disulfide is for the first time developed as an efficient and noble-metal-free catalyst for ECH via in situ intercalation of ammonia or alkyl-amine cations.This interlayer engineering regulates phase transition(2H→1 T),and effectively ameliorates electronic configurations and surface hydrophobicity to promote the ECH of biomass-derived oxygenates,while prohibiting H2 evolution.The optimal one intercalated by dimethylamine(MoS_(2)-DMA)is capable of hydrogenating furfural(FAL)to furfuryl alcohol with high Faradaic efficiency of 86.3%–73.3%and outstanding selectivity of>95.0%at−0.25 to−0.65 V(vs.RHE),outperforming MoS_(2) and other conventional metals.Such prominent performance stems from the enhanced chemisorption and surface hydrophobicity.The chemisorption of H intermediate and FAL,synchronously strengthened on the edge-sites of MoS_(2)-DMA,accelerates the surface elementary step following Langmuir-Hinshelwood mechanism.Moreover,the improved hydrophobicity benefits FAL affinity to overcome diffusion limitation.Discovering the effective modulation of MoS_(2) from a typical H2 evolution electrocatalyst to a promising candidate for ECH,this study broadens the scope to exploit catalysts used for electrochemical synthesis.

宽能谱激光驱动质子束的传输与均匀化

激光加速器在几十年的发展中不断进步.激光等离子体作用产生的加速电场能够在微米尺度将质子加速到数十甚至百兆电子伏能量,有望成为新一代广泛应用的紧凑加速器.激光驱动质子束具有微米量级尺寸(点源)、安培量级的峰值电流、大能散、大散角等特点,具有广阔的应用前景.辐照应用要求质子束在较大面积上具有均匀分布剂量,因而需要在传输中完成从点源到较大面积、剂量均匀的质子束变换.为提高激光加速质子束的利用效率,要求传输的质子束能散范围尽可能大.而色差效应对大能散质子束的传输和均匀化提出了挑战.常梯度磁场的弱聚焦作用可以在水平和竖直方向同时聚焦,在水平方向分析能量;聚焦和能量分析一体化的光学特点能够实现消色差,或者显著降低色差的影响.本文研究了弱聚焦磁场用于大能散质子束传输和均匀化的特点和可行性,实现了20%能散质子束的均匀化传输.通过加入特殊的导向磁铁修正散角,减小色差效应在位置消色差中的影响,使得80%能散质子束传输后可保持较好的均匀性.对比质子束在强聚焦元件四极透镜中的传输,展示了弱聚焦磁场用于大能散质子束均匀化的优势.