A two-dimensional hybrid code is developed to model the transport of a high-current electron beam in a dense plasma target. The beam electrons are treated as particles and described by particle-in-cell simulation incl...A two-dimensional hybrid code is developed to model the transport of a high-current electron beam in a dense plasma target. The beam electrons are treated as particles and described by particle-in-cell simulation including collisions with the target plasma particles. The background target plasma is assumed to be a stationary fluid with temperature variations. The return current and the self-generated electric and magnetic fields are obtained by combining Amp^re＇s law without the displacement current, the resistive Ohm＇s law and Faraday＇s law. The equations are solved in two-dimensional cylindrical geometry with rotational symmetry on a regular grid, with centered spatial differencing and first-order implicit time differencing. The algorithms implemented in the code are described, and a numerical experiment is performed for an electron beam with Maxwellian distribution ejected into a uniform deuterium-tritium plasma target.展开更多
Electron beam injectors are pivotal components of large-scale scientific instruments,such as synchrotron radiation sources,free-electron lasers,and electron-positron colliders.The quality of the electron beam produced...Electron beam injectors are pivotal components of large-scale scientific instruments,such as synchrotron radiation sources,free-electron lasers,and electron-positron colliders.The quality of the electron beam produced by the injector critically influences the performance of the entire accelerator-based scientific research apparatus.The injectors of such facilities usually use photocathode and thermionic-cathode electron guns.Although the photocathode injector can produce electron beams of excellent quality,its associated laser system is massive and intricate.The thermionic-cathode electron gun,especially the gridded electron gun injector,has a simple structure capable of generating numerous electron beams.However,its emittance is typically high.In this study,methods to reduce beam emittance are explored through a comprehensive analysis of various grid structures and preliminary design results,examining the evolution of beam phase space at different grid positions.An optimization method for reducing the emittance of a gridded thermionic-cathode electron gun is proposed through theoretical derivation,electromagnetic-field simulation,and beam-dynamics simulation.A 50%reduction in emittance was achieved for a 50 keV,1.7 A electron gun,laying the foundation for the subsequent design of a high-current,low-emittance injector.展开更多
The effects of initial spin orientation on the final electron beam polarization in laser wakefield acceleration in a pre-polarized plasma are investigated theoretically and numerically.From the results of variation of...The effects of initial spin orientation on the final electron beam polarization in laser wakefield acceleration in a pre-polarized plasma are investigated theoretically and numerically.From the results of variation of the initial spin direction,the spin dynamics of the electron beam are found to depend on the self-injection mechanism.The effects of wakefields and laser fields are studied using test particle dynamics and particle-in-cell simulations based on the Thomas-Bargmann-Michel-Telegdi equation.Compared with transverse injection,longitudinal injection is found to be preferable for obtaining a highly polarized electron beam.展开更多
In this study,the dosimetric characteristics(thickness applicability,preheating time,temperature and humidity dependence,in-batch uniformity,readout reproducibility,dose linearity,self-decay,and electron energy respon...In this study,the dosimetric characteristics(thickness applicability,preheating time,temperature and humidity dependence,in-batch uniformity,readout reproducibility,dose linearity,self-decay,and electron energy response)of engineered polycarbonate films irradiated with an electron beam(0–600 kGy)were investigated using photoluminescence spectroscopy.The results show a linear relationship between photoluminescence intensity and radiation dose when the thickness of the polycarbonate film is 0.3 mm.A higher fluorescence intensity can be obtained by preheating at 60℃ for 180 min before photoluminescence spectrum analysis.As the temperature during spectral testing and the ambient humidity(during and after irradiation)increased,the photoluminescence intensity of the polycarbonate films decreased.The photoluminescence intensity deviation of the polycarbonate films produced within the same batch at 100 kGy is 2.73%.After ten times of repeated excitations and readouts,the coefficients of variation in photoluminescence intensity are less than 8.6%,and the linear correlation coefficient between photoluminescence intensity and irradiation dose is 0.965 in the dose capture range of 20–600 kGy.Within 60 days of irradiation,the photoluminescence intensity of the polycarbonate film decreased to 60%of the initial value.The response of the 0.3 mm polycarbonate films to electron beams with energies exceeding 3.5 MeV does not differ significantly.This comprehensive analysis indicates the potential of polycarbonate films as a high-radiation dose detection material.展开更多
The microstructural evolution and mechanical properties of a vacuum electron beam welded aerospace 5B70 aluminum alloy joint were studied.Quantitative analyses of the phase composition,microstructural evolution,grain ...The microstructural evolution and mechanical properties of a vacuum electron beam welded aerospace 5B70 aluminum alloy joint were studied.Quantitative analyses of the phase composition,microstructural evolution,grain size,grain boundary density,and texture changes were performed by X-ray diffraction,scanning electron microscopy,and electron backscatter diffraction.The fusion zone(FZ)comprises equiaxed cellular crystals,and a fine~20μm-thick crystal layer forms in the transition zone(TZ)between the FZ and heat affected zone(HAZ).The HAZ closely resembles the base material(BM),retaining the original rolling microstructure.Mechanical property testing shows that the fine-grained layer in the TZ exhibits the highest nanohardness,with the FZ corresponding to the lowest microhardness.The welded-joint sample has lower yield strength,ultimate tensile strength,and elongation after fracture than the BM.These reductions of mechanical properties are primarily influenced by the grain size and distribution of the precipitated phases.展开更多
The high-current pulsed electron beam(HCPEB) treatment with current density 6 J/cm^2 was applied on AZ91 Mg alloy to improve its corrosion resistance. Results showed that the net-like Mg_(17)Al_(12) disappeared on the...The high-current pulsed electron beam(HCPEB) treatment with current density 6 J/cm^2 was applied on AZ91 Mg alloy to improve its corrosion resistance. Results showed that the net-like Mg_(17)Al_(12) disappeared on the surface of AZ91 Mg alloy after irradiation by HCPEB, which was instead of supersaturated Al element on the surface. Nevertheless, the application of HCPEB also led to the formation of crater-like and groove-like structures as well as micro-cracks on the surface of AZ91 Mg alloy. After HCPEB treatment by 3, 5 and 10 pulses, the AZ91 Mg alloy exhibited better corrosion resistance.However, the increasing amount of micro-cracks reduced the anti-corrosive properties of AZ91 Mg alloy as the pulse increased to 20 and 30.展开更多
The present paper reports the rapid surface alloying induced by the bombardment of high-current pulsed electron beam. Two kinds of substrate materials were examined to show this effect. The first sample was a pure Al ...The present paper reports the rapid surface alloying induced by the bombardment of high-current pulsed electron beam. Two kinds of substrate materials were examined to show this effect. The first sample was a pure Al metal pre-coated with fine carbon powders prior to the bombardment, and the second alloy is the D2-Crl2MolVl mould steel pre-coated with Cr, Ti, and TiN powders. The surface elements diffuse about several micrometers into the substrate materials only after several bombardments. Tribological behaviors of these samples were characterized and significant improvement in wear resistance was found. Finally, a TEM analysis reveals the presence of stress waves generated by coupled thermal and stress fields, which was considered as the main cause of the enhanced properties.展开更多
Ti–Al surface alloy was fabricated using a cyclic pulsed liquid-phase mixing of predeposited 100 nm Al film with a-Ti substrate by low-energy high-current electron beam. Electron probe micro-analysis（EPMA）,grazing ...Ti–Al surface alloy was fabricated using a cyclic pulsed liquid-phase mixing of predeposited 100 nm Al film with a-Ti substrate by low-energy high-current electron beam. Electron probe micro-analysis（EPMA）,grazing incidence X-ray diffraction analysis（GIXRD）,transmission electron microscopy（TEM）, and nanoindentation were used to investigate the characterization of Ti–Al surface alloy. The experimental results show that the thickness of alloy layer is ＊3 lm, and the content of Al in the ＊1 lm thickness surface layer is ＊60 at%. The tetragonal TiAl and TiAl2intermetallics were synthesized at the top surface, which have nanocrystalline structure.The main phase formed in the ＊2.5 lm thick surface is TiAl, and there are few TiAl2and Ti3Al phase for the alloy.Dislocation is enhanced in the alloyed layer. The nanohardness of Ti–Al surface alloy increased significantly compared with a-Ti substrate due to the nanostructure and enhanced dislocation. Since the e-beam remelted repeatedly, the Ti–Al surface alloy mixed sufficiently with Ti substrate. Moreover, there is no obvious boundary between the alloyed layer and substrate.展开更多
Up-and-coming high-temperature materials,refractory high entropy alloys,are suffering from lower oxidation resistance,restricting their applications in the aerospace field.In this study,two novel treatments of Al-depo...Up-and-coming high-temperature materials,refractory high entropy alloys,are suffering from lower oxidation resistance,restricting their applications in the aerospace field.In this study,two novel treatments of Al-deposited and remelted were developed to refine the microstructure and enhance the oxidation resistance of refractory high entropy alloy using electron beam freeform fabrication(EBF3).Finer and short-range ordering structures were observed in the remelted sample,whereas the Al-deposited sample showcased the formation of silicide and intermetallic phases.High-temperature cyclic and isothermal oxidation tests at 1000℃ were carried out.The total weight gain after 60 h of cyclic oxidation decreased by 17.49%and 30.46%for the remelted and deposited samples,respectively,compared to the as-cast state.Oxidation kinetics reveal an evident lower mass gain and oxidation rate in the treated samples.A multilayer oxide consisting of TiO_(2)+Al_(2)O_(3)+SiO_(2)+AlNbO_(4) was studied for its excellent oxidation resistance.The oxidation behavior of rutile,corundum and other oxides was analyzed using first principles calculations and chemical defect analysis.Overall,this research,which introduces novel treatments,offers promising insights for enhancing the inherent oxidation resistance of refractory high entropy alloys.展开更多
[Background]Traveling-wave tubes(TWTs)are widely applied in radar,imaging,and military systems owing to their excellent amplification characteristics.Miniaturization and integration are critical to the future of TWTs,...[Background]Traveling-wave tubes(TWTs)are widely applied in radar,imaging,and military systems owing to their excellent amplification characteristics.Miniaturization and integration are critical to the future of TWTs,with multi-channel slow-wave structures(SWSs)forming the foundation for their realization in high-power vacuum electronic devices.[Purpose]To provide design insights for multi-channel TWTs and simultaneously enhance their output power,a W-band folded-waveguide TWT with dual electron beams and H-plane power combining was proposed.[Methods]Three-dimensional electromagnetic simulations in CST were conducted to verify the highfrequency characteristics,electric field distribution,and amplification performance of the proposed SWS,thereby confirming the validity of the design.[Results]Results indicate that the designed TWT achieves a transmission bandwidth of 10 GHz.With an electron beam voltage of 17.9 kV and a current of 0.35 A,the output power reaches 450 W at 94 GHz,corresponding to an efficiency of 7.18%and a gain of 23.5 dB.Moreover,under fixed beam voltage and current,the TWT delivers over 200 W output power across 91–99 GHz,with a 3 dB bandwidth of 91–98.5 GHz.The particle voltage distribution after modulation further validates the mode analysis.[Conclusions]These results demonstrate the feasibility of compact dual-beam power-combining structures and provide useful guidance for the design of future multi-channel TWTs.展开更多
This paper discusses the influence of Sb/In ratio on the transport properties and crystal quality of the 200 nm InAs_(x)Sb_(1-x)thin film.The Sb content of InAs_(x)Sb_(1-x)thin film in all samples was verified by HRXR...This paper discusses the influence of Sb/In ratio on the transport properties and crystal quality of the 200 nm InAs_(x)Sb_(1-x)thin film.The Sb content of InAs_(x)Sb_(1-x)thin film in all samples was verified by HRXRD of the symmetrical 004 reflections and asymmetrical 115 reflections.The calculation results show that the Sb component was 0.6 in the InAs_(x)Sb_(1-x)thin film grown under the conditions of Sb/In ratio of 6 and As/In ratio of 3,which has the highest electron mobility(28560 cm^(2)/V·s)at 300 K.At the same time,the influence ofⅤ/Ⅲratio on the transport properties and crystal quality of Al_(0.2)In_(0.8)Sb/InAs_(x)Sb_(1-x)quantum well heterostructures also has been investigated.As a result,the Al_(0.2)In_(0.8)Sb/InAs_(0.4)Sb_(0.6)quantum well heterostructure with a channel thickness of 30 nm grown under the conditions of Sb/In ratio of 6 and As/In ratio of 3 has a maximum electron mobility of 28300 cm^(2)/V·s and a minimum RMS roughness of 0.68 nm.Through optimizing the growth conditions,our samples have higher electron mobility and smoother surface morphology.展开更多
A 4 MeV RF linear accelerator for electron beam irradiation applications has been developed at the PBP-CMU Electron Linac Laboratory,Thailand.The system has been reengineered using a decommissioned medical linear acce...A 4 MeV RF linear accelerator for electron beam irradiation applications has been developed at the PBP-CMU Electron Linac Laboratory,Thailand.The system has been reengineered using a decommissioned medical linear accelerator.The main components include a thermionic DC electron gun,an RF linear accelerator,a beam diagnostic chamber,and a beam exit window for electron beam irradiation.Therefore,reengineering must be performed based on the characteristics of the electron beam and its dynamics throughout the system.In this study,the electron beam current density emitted from the cathode was calculated based on the thermionic emission theory,and the result was used to produce the electron beam distribution in the gun using CST Studio Suite^(■)software.The properties of the electron beam and its acceleration in the linear accelerator and downstream diagnostic section were studied using the ASTRA electron beam dynamics simulation code,with the aim of producing an electron beam with an average energy of 4 MeV at the linear accelerator exit.The transverse beam profile and electron deposition dose in the ambient environment were calculated using Geant4 Monte Carlo simulation software to estimate the beam performance for the irradiation experiments.The parameters studied can be used as guidelines for machine operation and future experimental plans.展开更多
A thermionic gun is endowed with a long bunch tail,which presents challenges for the compact terahertz free electron laser(FEL)facility at the Huazhong University of Science and Technology.Owing to a large energy spre...A thermionic gun is endowed with a long bunch tail,which presents challenges for the compact terahertz free electron laser(FEL)facility at the Huazhong University of Science and Technology.Owing to a large energy spread,the tail particles do not contribute to the radiation.In the original design,an x-direction slit is used in the dispersive section of the transport line to remove the tail particles.This paper presents an improved scheme to remove the tail by introducing an RF beam chopper system at the exit of the electron gun,to prevent a significant number of tail particles from entering the linac.The facility remains compact while effectively removing the tail of the bunch.The parameters of the beam chopper system are designed.Bunch parameters and radiation performance are analyzed via a start-to-end simulation.The findings indicate that 43%of the particles can pass through the beam chopper system for subsequent acceleration and transport,which saves the RF power,reduces beam loss in the linac,reduces background noise,and suppresses the sideband instability.Simultaneously,the beam chopper system causes an increase in beam emittance,energy spread,and an offset in the center of the bunch.These effects can be mitigated by a solenoid,linac,and steering coils.The simulation results for the FEL show that the micro-pulse energy is greater than 1.1μJ in the frequency range of 2.8-9.7 THz,and the maximum micro-pulse energy is 1.28μJ.展开更多
We propose a compact scheme to modulate a relativistic electron beam(REB)into three-dimensional(3D)nanoscale bunches by injecting a rarefied REB into an underdense plasma.This scheme self-consistently integrates the l...We propose a compact scheme to modulate a relativistic electron beam(REB)into three-dimensional(3D)nanoscale bunches by injecting a rarefied REB into an underdense plasma.This scheme self-consistently integrates the lateral focusing and axial modulation of the REB in its self-driven plasma wakefield.The REB first expels the plasma electrons in its path to form a wake,where the lateral force of the chargeseparation field compresses it to higher density,so that more plasma electrons are expelled as it propagates.The positive feedback loop is repeated until the REB becomes a thin electron filament of density a hundred times that of the original.As it continues to propagate in the elongated electron-free wake bubble,the axial electric field induces an energy chirp on the electron filament,and longitudinally modulates it into 3D nanoscale bunches by asynchronous envelope oscillations.The excitation conditions of this scheme with respect to the beam and plasma parameters,as well as the spatial scale of the obtained electron bunches,are analyzed analytically and agree well with particle-in-cell simulations.In addition,our radiation simulations show that coherent extreme ultraviolet radiation can be generated with such 3D nanoscale bunches.展开更多
Terahertz(THz)radiation is rapidly emerging as a powerful tool with diverse applications,including high-speed imaging,laser-driven particle acceleration,and ultra-high frequency(UHF)communications.However,generating m...Terahertz(THz)radiation is rapidly emerging as a powerful tool with diverse applications,including high-speed imaging,laser-driven particle acceleration,and ultra-high frequency(UHF)communications.However,generating multipulse THz radiation with controllable time intervals remains a significant challenge.This study presents an approach to overcome this hurdle by exploiting the interaction between an electron beam and plasma.Using numerical simulations and theoretical analysis,we investigated the behavior of an electron beam within a plasma and its interaction with the longitudinal sheath field.This interaction resulted in the generation of multiple distinct THz pulses.We demonstrated that the plasma length adjustment allows for precise tuning of the interval between THz pulses.Moreover,the radiation intensity could be controlled by the electron beam energy and the electron bunch duration.The proposed scheme can generate multipulse THz radiation in a flexible and precise manner,paving the way for advancements in applications requiring high temporal resolution.展开更多
Electron beam fluorescence technology is an advanced non-contact measurement in rarefied flow fields,and the fluorescence signal intensity is positively correlated with the electron beam current.The ion bombardment se...Electron beam fluorescence technology is an advanced non-contact measurement in rarefied flow fields,and the fluorescence signal intensity is positively correlated with the electron beam current.The ion bombardment secondary emission electron gun is suitable for the technology.To enhance the beam current,COMSOL simulations and analyses were conducted to examine plasma density distribution in the discharge chamber under the effects of various conditions and the electric field distribution between the cathode and the spacer gap.The anode shape and discharge pressure conditions were optimized to increase plasma density.Additionally,an improved spacer structure was designed with the dual purpose of enhancing the electric field distribution between the cathode-spacer gaps and improving vacuum differential effects.This design modification aims to increase the pass rate of secondary electrons.Both simulation and experimental results demonstrated that the performance of the optimized electron gun was effectively enhanced.When the electrode voltage remains constant and the discharge gas pressure is adjusted to around 8 Pa,the maximum beam current was increased from 0.9 mA to 1.6 mA.展开更多
The Cooling Storage Ring(CSR)external-target experiment(CEE)will be the first large-scale nuclear physics experiment at the Heavy Ion Research Facility in Lanzhou(HIRFL).A beam monitor has been developed to monitor th...The Cooling Storage Ring(CSR)external-target experiment(CEE)will be the first large-scale nuclear physics experiment at the Heavy Ion Research Facility in Lanzhou(HIRFL).A beam monitor has been developed to monitor the beam status and to improve the reconstruction resolution of the primary vertex.Custom-designed pixel charge sensors,named TopmetalCEEv1,are employed in the detector to locate the position of each particle.Readout electronics for the beam monitor were designed,including front-end electronics utilizing the Topmetal-CEEv1 sensors,as well as a readout and control unit that communicates with the DAQ,trigger,and clock systems.A series of tests were performed to validate the functionality and performance of the system,including basic electronic verifications and responses toαparticles and heavy-ion beams.The results show that all designed functions of the readout electronics system work well,and this system could be used for beam monitoring in the CEE experiment.展开更多
For a long time,the large loss of the strength and toughness of fusion welded joints for thick nearβtitanium alloys has largely hindered their engineering application,which results from the few precipitations of the ...For a long time,the large loss of the strength and toughness of fusion welded joints for thick nearβtitanium alloys has largely hindered their engineering application,which results from the few precipitations of the strengtheningαphase during welding cooling.In this study,double annealing treatment was designed for electron beam welded joints of 30-mm-thick nearβTi-5Al-5Mo-5V-1Cr-1Fe alloy,with the aim of regulating the proportion of multi-level lamellar microstructures and enhancing the joint properties.Among various annealing temperatures(first annealing at 750–880 ℃+second annealing at 580 ℃),the 750 ℃+580 ℃ annealed joint exhibited simultaneously enhanced strength and toughness,with the increase in tensile strength and impact energy from 844 MPa and 8.8 J for the as-welded joint to 1129 MPa and 14.5 J for annealed joint,respectively,which were superior to those of the joints of Ti5Al-5Mo-5V-1Cr-1Fe alloy as reported.The great increases in the strength and toughness were mainly attributed to the excellent proportion matching of formed multi-level lamellar microstructures(76.1%of primaryα(αp)lamellae and 7.9%of secondaryα(αs)lamellae),among which theαp phase andαs phase mainly affected the joint toughness and strength,respectively.The good coupling ofαp phase andαs phase improved the precipitation strengthening and the resistance to crack propagation.The modified strengthening mechanism models were proposed by introducing the thickness and proportion parameters of the precipitated phase.It was indicated that the theoretical calculation values were in good agreement with the experimental ones,and the solution strengthening and precipitation strengthening provided a large contribution(a sum of about 75%)to the yield strength of the annealed joints.This study provides a novel method via designing proper multi-level lamellar microstructures to simultaneously improve the strength and toughness of nearβtitanium alloy joints.展开更多
1.Introduction Nowadays,lithium-ion batteries(LIBs)have been extensively applied in portable electronic devices,electric vehicles,and energy storage.The increasing demands of energy density and cycle life encourage co...1.Introduction Nowadays,lithium-ion batteries(LIBs)have been extensively applied in portable electronic devices,electric vehicles,and energy storage.The increasing demands of energy density and cycle life encourage considerable research on the mechanisms of battery failure and the synthesis of new materials.Cathodes of LIBs,as the key component determining energy density and capacity,have been widely investigated.Considerable research has been conducted to reveal the degradation mechanisms of LIB cathodes,including bulk structure degradation in the form of phase transformations[1-4],point/extended defect formation[5],cracking[6,7],and cavitation[8-10],surface phase transformation into cationdensified phases[11-14],gassing[15],transition metal dissolution[16,17],and over-growth of the cathode-electrolyte interphases(CEIs)[18,19].展开更多
基金supported by National Natural Science Foundation of China(Nos.11175030,11475030,91230205,11175029 and 11375032)the National High-Tech ICF Committee of Chinathe Science and Technology Foundation of China Academy of Engineering Physics(No.2011A0102008)
文摘A two-dimensional hybrid code is developed to model the transport of a high-current electron beam in a dense plasma target. The beam electrons are treated as particles and described by particle-in-cell simulation including collisions with the target plasma particles. The background target plasma is assumed to be a stationary fluid with temperature variations. The return current and the self-generated electric and magnetic fields are obtained by combining Amp^re＇s law without the displacement current, the resistive Ohm＇s law and Faraday＇s law. The equations are solved in two-dimensional cylindrical geometry with rotational symmetry on a regular grid, with centered spatial differencing and first-order implicit time differencing. The algorithms implemented in the code are described, and a numerical experiment is performed for an electron beam with Maxwellian distribution ejected into a uniform deuterium-tritium plasma target.
基金supported by the Hundred-person Program of Chinese Academy of Sciences and the National Natural Science Foundation of China(No.11905074).
文摘Electron beam injectors are pivotal components of large-scale scientific instruments,such as synchrotron radiation sources,free-electron lasers,and electron-positron colliders.The quality of the electron beam produced by the injector critically influences the performance of the entire accelerator-based scientific research apparatus.The injectors of such facilities usually use photocathode and thermionic-cathode electron guns.Although the photocathode injector can produce electron beams of excellent quality,its associated laser system is massive and intricate.The thermionic-cathode electron gun,especially the gridded electron gun injector,has a simple structure capable of generating numerous electron beams.However,its emittance is typically high.In this study,methods to reduce beam emittance are explored through a comprehensive analysis of various grid structures and preliminary design results,examining the evolution of beam phase space at different grid positions.An optimization method for reducing the emittance of a gridded thermionic-cathode electron gun is proposed through theoretical derivation,electromagnetic-field simulation,and beam-dynamics simulation.A 50%reduction in emittance was achieved for a 50 keV,1.7 A electron gun,laying the foundation for the subsequent design of a high-current,low-emittance injector.
基金supported by the National Natural Science Foundation of China(Grant Nos.11804348,11775056,11975154,12225505,and 12405281)the Science Challenge(Project No.TZ2018005)+2 种基金supported by the Shanghai Pujiang Program(Grant No.23PJ1414600)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB0890203)supported by the Accelerator Technology Helmholtz Infrastructure consortium ATHENA.
文摘The effects of initial spin orientation on the final electron beam polarization in laser wakefield acceleration in a pre-polarized plasma are investigated theoretically and numerically.From the results of variation of the initial spin direction,the spin dynamics of the electron beam are found to depend on the self-injection mechanism.The effects of wakefields and laser fields are studied using test particle dynamics and particle-in-cell simulations based on the Thomas-Bargmann-Michel-Telegdi equation.Compared with transverse injection,longitudinal injection is found to be preferable for obtaining a highly polarized electron beam.
基金supported by the National Natural Science Foundation of China(No.12305385)Key Projects of Scientific Research of the Hunan Provincial Department of Education(22A0310)the Research Startup Project of University of South China(220XQD025).
文摘In this study,the dosimetric characteristics(thickness applicability,preheating time,temperature and humidity dependence,in-batch uniformity,readout reproducibility,dose linearity,self-decay,and electron energy response)of engineered polycarbonate films irradiated with an electron beam(0–600 kGy)were investigated using photoluminescence spectroscopy.The results show a linear relationship between photoluminescence intensity and radiation dose when the thickness of the polycarbonate film is 0.3 mm.A higher fluorescence intensity can be obtained by preheating at 60℃ for 180 min before photoluminescence spectrum analysis.As the temperature during spectral testing and the ambient humidity(during and after irradiation)increased,the photoluminescence intensity of the polycarbonate films decreased.The photoluminescence intensity deviation of the polycarbonate films produced within the same batch at 100 kGy is 2.73%.After ten times of repeated excitations and readouts,the coefficients of variation in photoluminescence intensity are less than 8.6%,and the linear correlation coefficient between photoluminescence intensity and irradiation dose is 0.965 in the dose capture range of 20–600 kGy.Within 60 days of irradiation,the photoluminescence intensity of the polycarbonate film decreased to 60%of the initial value.The response of the 0.3 mm polycarbonate films to electron beams with energies exceeding 3.5 MeV does not differ significantly.This comprehensive analysis indicates the potential of polycarbonate films as a high-radiation dose detection material.
基金supported by the National Natural Science Foundation of China(Nos.52175206,52205187,52130509)the Science and Technology Planning Project of Guizhou Province,China(No.ZK[2022]013)。
文摘The microstructural evolution and mechanical properties of a vacuum electron beam welded aerospace 5B70 aluminum alloy joint were studied.Quantitative analyses of the phase composition,microstructural evolution,grain size,grain boundary density,and texture changes were performed by X-ray diffraction,scanning electron microscopy,and electron backscatter diffraction.The fusion zone(FZ)comprises equiaxed cellular crystals,and a fine~20μm-thick crystal layer forms in the transition zone(TZ)between the FZ and heat affected zone(HAZ).The HAZ closely resembles the base material(BM),retaining the original rolling microstructure.Mechanical property testing shows that the fine-grained layer in the TZ exhibits the highest nanohardness,with the FZ corresponding to the lowest microhardness.The welded-joint sample has lower yield strength,ultimate tensile strength,and elongation after fracture than the BM.These reductions of mechanical properties are primarily influenced by the grain size and distribution of the precipitated phases.
基金the finacial support from the National Natural Science Foundation of China(Nos.51771128 and 51771129)the Projects of International Cooperation in Shanxi(No.201703D421039)the Natural Science Foundation of Shanxi(No.201601D011034)
文摘The high-current pulsed electron beam(HCPEB) treatment with current density 6 J/cm^2 was applied on AZ91 Mg alloy to improve its corrosion resistance. Results showed that the net-like Mg_(17)Al_(12) disappeared on the surface of AZ91 Mg alloy after irradiation by HCPEB, which was instead of supersaturated Al element on the surface. Nevertheless, the application of HCPEB also led to the formation of crater-like and groove-like structures as well as micro-cracks on the surface of AZ91 Mg alloy. After HCPEB treatment by 3, 5 and 10 pulses, the AZ91 Mg alloy exhibited better corrosion resistance.However, the increasing amount of micro-cracks reduced the anti-corrosive properties of AZ91 Mg alloy as the pulse increased to 20 and 30.
文摘The present paper reports the rapid surface alloying induced by the bombardment of high-current pulsed electron beam. Two kinds of substrate materials were examined to show this effect. The first sample was a pure Al metal pre-coated with fine carbon powders prior to the bombardment, and the second alloy is the D2-Crl2MolVl mould steel pre-coated with Cr, Ti, and TiN powders. The surface elements diffuse about several micrometers into the substrate materials only after several bombardments. Tribological behaviors of these samples were characterized and significant improvement in wear resistance was found. Finally, a TEM analysis reveals the presence of stress waves generated by coupled thermal and stress fields, which was considered as the main cause of the enhanced properties.
基金financially supported by the National Natural Science Foundation of China and the Russian Foundation for Basic Research (No. 11011120081)Large Scientific Facilities of the National Natural Science Foundation of China and of the Chinese Academy of Sciences (No. 11079012)the National Natural Science Foundation of China (No. 10875021)
文摘Ti–Al surface alloy was fabricated using a cyclic pulsed liquid-phase mixing of predeposited 100 nm Al film with a-Ti substrate by low-energy high-current electron beam. Electron probe micro-analysis（EPMA）,grazing incidence X-ray diffraction analysis（GIXRD）,transmission electron microscopy（TEM）, and nanoindentation were used to investigate the characterization of Ti–Al surface alloy. The experimental results show that the thickness of alloy layer is ＊3 lm, and the content of Al in the ＊1 lm thickness surface layer is ＊60 at%. The tetragonal TiAl and TiAl2intermetallics were synthesized at the top surface, which have nanocrystalline structure.The main phase formed in the ＊2.5 lm thick surface is TiAl, and there are few TiAl2and Ti3Al phase for the alloy.Dislocation is enhanced in the alloyed layer. The nanohardness of Ti–Al surface alloy increased significantly compared with a-Ti substrate due to the nanostructure and enhanced dislocation. Since the e-beam remelted repeatedly, the Ti–Al surface alloy mixed sufficiently with Ti substrate. Moreover, there is no obvious boundary between the alloyed layer and substrate.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFF0609000)National Natural Science Foundation of China(Grant Nos.52171034 and 52101037)Postdoctoral Fellowship Program of CPSFara(No.GZB20230944).
文摘Up-and-coming high-temperature materials,refractory high entropy alloys,are suffering from lower oxidation resistance,restricting their applications in the aerospace field.In this study,two novel treatments of Al-deposited and remelted were developed to refine the microstructure and enhance the oxidation resistance of refractory high entropy alloy using electron beam freeform fabrication(EBF3).Finer and short-range ordering structures were observed in the remelted sample,whereas the Al-deposited sample showcased the formation of silicide and intermetallic phases.High-temperature cyclic and isothermal oxidation tests at 1000℃ were carried out.The total weight gain after 60 h of cyclic oxidation decreased by 17.49%and 30.46%for the remelted and deposited samples,respectively,compared to the as-cast state.Oxidation kinetics reveal an evident lower mass gain and oxidation rate in the treated samples.A multilayer oxide consisting of TiO_(2)+Al_(2)O_(3)+SiO_(2)+AlNbO_(4) was studied for its excellent oxidation resistance.The oxidation behavior of rutile,corundum and other oxides was analyzed using first principles calculations and chemical defect analysis.Overall,this research,which introduces novel treatments,offers promising insights for enhancing the inherent oxidation resistance of refractory high entropy alloys.
基金National Key Research and Development Program of China(2022YFF0707602)National Natural Science Foundation of China(62471097,62471115,62471101)National Natural Science Foundation of Sichuan(2025ZNSFSC0537)。
文摘[Background]Traveling-wave tubes(TWTs)are widely applied in radar,imaging,and military systems owing to their excellent amplification characteristics.Miniaturization and integration are critical to the future of TWTs,with multi-channel slow-wave structures(SWSs)forming the foundation for their realization in high-power vacuum electronic devices.[Purpose]To provide design insights for multi-channel TWTs and simultaneously enhance their output power,a W-band folded-waveguide TWT with dual electron beams and H-plane power combining was proposed.[Methods]Three-dimensional electromagnetic simulations in CST were conducted to verify the highfrequency characteristics,electric field distribution,and amplification performance of the proposed SWS,thereby confirming the validity of the design.[Results]Results indicate that the designed TWT achieves a transmission bandwidth of 10 GHz.With an electron beam voltage of 17.9 kV and a current of 0.35 A,the output power reaches 450 W at 94 GHz,corresponding to an efficiency of 7.18%and a gain of 23.5 dB.Moreover,under fixed beam voltage and current,the TWT delivers over 200 W output power across 91–99 GHz,with a 3 dB bandwidth of 91–98.5 GHz.The particle voltage distribution after modulation further validates the mode analysis.[Conclusions]These results demonstrate the feasibility of compact dual-beam power-combining structures and provide useful guidance for the design of future multi-channel TWTs.
基金Supported by the Natural Science Basic Research Program of Shaanxi Province(2023-JC-QN-0758)Shaanxi University of Science and Technology Research Launch Project(2020BJ-26)Doctoral Research Initializing Fund of Hebei University of Science and Technology,China(1181476).
文摘This paper discusses the influence of Sb/In ratio on the transport properties and crystal quality of the 200 nm InAs_(x)Sb_(1-x)thin film.The Sb content of InAs_(x)Sb_(1-x)thin film in all samples was verified by HRXRD of the symmetrical 004 reflections and asymmetrical 115 reflections.The calculation results show that the Sb component was 0.6 in the InAs_(x)Sb_(1-x)thin film grown under the conditions of Sb/In ratio of 6 and As/In ratio of 3,which has the highest electron mobility(28560 cm^(2)/V·s)at 300 K.At the same time,the influence ofⅤ/Ⅲratio on the transport properties and crystal quality of Al_(0.2)In_(0.8)Sb/InAs_(x)Sb_(1-x)quantum well heterostructures also has been investigated.As a result,the Al_(0.2)In_(0.8)Sb/InAs_(0.4)Sb_(0.6)quantum well heterostructure with a channel thickness of 30 nm grown under the conditions of Sb/In ratio of 6 and As/In ratio of 3 has a maximum electron mobility of 28300 cm^(2)/V·s and a minimum RMS roughness of 0.68 nm.Through optimizing the growth conditions,our samples have higher electron mobility and smoother surface morphology.
基金supported by Chiang Mai University for providing infrastructure and the NSRF via the Program Management Unit for Human Resources&Institutional Development,Research and Innovation[grant number B05F650022]for the software CST Studio Suite^(■)2023Financial support for the reengineering and commissioning of the accelerator system was provided by the Thailand Center of Excellence in Physics(ThEP Center),Science and Technology Park Chiang Mai University(CMU STeP)。
文摘A 4 MeV RF linear accelerator for electron beam irradiation applications has been developed at the PBP-CMU Electron Linac Laboratory,Thailand.The system has been reengineered using a decommissioned medical linear accelerator.The main components include a thermionic DC electron gun,an RF linear accelerator,a beam diagnostic chamber,and a beam exit window for electron beam irradiation.Therefore,reengineering must be performed based on the characteristics of the electron beam and its dynamics throughout the system.In this study,the electron beam current density emitted from the cathode was calculated based on the thermionic emission theory,and the result was used to produce the electron beam distribution in the gun using CST Studio Suite^(■)software.The properties of the electron beam and its acceleration in the linear accelerator and downstream diagnostic section were studied using the ASTRA electron beam dynamics simulation code,with the aim of producing an electron beam with an average energy of 4 MeV at the linear accelerator exit.The transverse beam profile and electron deposition dose in the ambient environment were calculated using Geant4 Monte Carlo simulation software to estimate the beam performance for the irradiation experiments.The parameters studied can be used as guidelines for machine operation and future experimental plans.
基金supported by the National Natural Science Foundation of China(No.12175077).
文摘A thermionic gun is endowed with a long bunch tail,which presents challenges for the compact terahertz free electron laser(FEL)facility at the Huazhong University of Science and Technology.Owing to a large energy spread,the tail particles do not contribute to the radiation.In the original design,an x-direction slit is used in the dispersive section of the transport line to remove the tail particles.This paper presents an improved scheme to remove the tail by introducing an RF beam chopper system at the exit of the electron gun,to prevent a significant number of tail particles from entering the linac.The facility remains compact while effectively removing the tail of the bunch.The parameters of the beam chopper system are designed.Bunch parameters and radiation performance are analyzed via a start-to-end simulation.The findings indicate that 43%of the particles can pass through the beam chopper system for subsequent acceleration and transport,which saves the RF power,reduces beam loss in the linac,reduces background noise,and suppresses the sideband instability.Simultaneously,the beam chopper system causes an increase in beam emittance,energy spread,and an offset in the center of the bunch.These effects can be mitigated by a solenoid,linac,and steering coils.The simulation results for the FEL show that the micro-pulse energy is greater than 1.1μJ in the frequency range of 2.8-9.7 THz,and the maximum micro-pulse energy is 1.28μJ.
基金supported by the National Key R&D Program of China(Grant No.2024YFA1613400)the National Natural Science Foundation of China(Grant Nos.12475238,12175154,12205201,and 12475248)+5 种基金the Financial Support for Outstanding Talents Training Fund in Shenzhen(Project No.202101)the Shenzhen Science and Technology Program(Grant No.RCYX20221008092851073)the Guangdong Province Key Construction Discipline Scientific Research Capacity Improvement Project(Grant No.2021ZDJS107)the Natural Science Foundation of Guangdong(Grant No.2025A1515012853)the Natural Science Foundation of Top Talent of SZTU(Grant Nos.GDRC202310 and GDRC202423)the Guangdong Basic and Applied Basic Research Foundation(Grant No.2025A1515010791).
文摘We propose a compact scheme to modulate a relativistic electron beam(REB)into three-dimensional(3D)nanoscale bunches by injecting a rarefied REB into an underdense plasma.This scheme self-consistently integrates the lateral focusing and axial modulation of the REB in its self-driven plasma wakefield.The REB first expels the plasma electrons in its path to form a wake,where the lateral force of the chargeseparation field compresses it to higher density,so that more plasma electrons are expelled as it propagates.The positive feedback loop is repeated until the REB becomes a thin electron filament of density a hundred times that of the original.As it continues to propagate in the elongated electron-free wake bubble,the axial electric field induces an energy chirp on the electron filament,and longitudinally modulates it into 3D nanoscale bunches by asynchronous envelope oscillations.The excitation conditions of this scheme with respect to the beam and plasma parameters,as well as the spatial scale of the obtained electron bunches,are analyzed analytically and agree well with particle-in-cell simulations.In addition,our radiation simulations show that coherent extreme ultraviolet radiation can be generated with such 3D nanoscale bunches.
基金supported by the National Natural Science Foundation of China(Grant No.12175058)the National Science Fund of Hunan Province for Distinguished Young Scholars(Grant No.2024JJ2009)。
文摘Terahertz(THz)radiation is rapidly emerging as a powerful tool with diverse applications,including high-speed imaging,laser-driven particle acceleration,and ultra-high frequency(UHF)communications.However,generating multipulse THz radiation with controllable time intervals remains a significant challenge.This study presents an approach to overcome this hurdle by exploiting the interaction between an electron beam and plasma.Using numerical simulations and theoretical analysis,we investigated the behavior of an electron beam within a plasma and its interaction with the longitudinal sheath field.This interaction resulted in the generation of multiple distinct THz pulses.We demonstrated that the plasma length adjustment allows for precise tuning of the interval between THz pulses.Moreover,the radiation intensity could be controlled by the electron beam energy and the electron bunch duration.The proposed scheme can generate multipulse THz radiation in a flexible and precise manner,paving the way for advancements in applications requiring high temporal resolution.
文摘Electron beam fluorescence technology is an advanced non-contact measurement in rarefied flow fields,and the fluorescence signal intensity is positively correlated with the electron beam current.The ion bombardment secondary emission electron gun is suitable for the technology.To enhance the beam current,COMSOL simulations and analyses were conducted to examine plasma density distribution in the discharge chamber under the effects of various conditions and the electric field distribution between the cathode and the spacer gap.The anode shape and discharge pressure conditions were optimized to increase plasma density.Additionally,an improved spacer structure was designed with the dual purpose of enhancing the electric field distribution between the cathode-spacer gaps and improving vacuum differential effects.This design modification aims to increase the pass rate of secondary electrons.Both simulation and experimental results demonstrated that the performance of the optimized electron gun was effectively enhanced.When the electrode voltage remains constant and the discharge gas pressure is adjusted to around 8 Pa,the maximum beam current was increased from 0.9 mA to 1.6 mA.
基金supported by the National Natural Science Foundation of China(Nos.11927901,12105110,U2032209,12275105)the National Key Research and Development Program of China(Nos.2020YFE0202002,2022YFA1602103)the Fundamental Research Funds for the Central Universities(No.CCNU22QN005)。
文摘The Cooling Storage Ring(CSR)external-target experiment(CEE)will be the first large-scale nuclear physics experiment at the Heavy Ion Research Facility in Lanzhou(HIRFL).A beam monitor has been developed to monitor the beam status and to improve the reconstruction resolution of the primary vertex.Custom-designed pixel charge sensors,named TopmetalCEEv1,are employed in the detector to locate the position of each particle.Readout electronics for the beam monitor were designed,including front-end electronics utilizing the Topmetal-CEEv1 sensors,as well as a readout and control unit that communicates with the DAQ,trigger,and clock systems.A series of tests were performed to validate the functionality and performance of the system,including basic electronic verifications and responses toαparticles and heavy-ion beams.The results show that all designed functions of the readout electronics system work well,and this system could be used for beam monitoring in the CEE experiment.
基金supported by the National Key Re-search and Development Program of China(No.2023YFC2810700)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(No.2021193)+2 种基金Liaoning Province Excellent Youth Foundation(No.2024JH3/10200021)the Liaoning Revital-ization Talents Program(No.XLYC2403094)the Scientific In-strument Developing Project of the Chinese Academy of Sciences(No.PTYQ2024YZ0009).
文摘For a long time,the large loss of the strength and toughness of fusion welded joints for thick nearβtitanium alloys has largely hindered their engineering application,which results from the few precipitations of the strengtheningαphase during welding cooling.In this study,double annealing treatment was designed for electron beam welded joints of 30-mm-thick nearβTi-5Al-5Mo-5V-1Cr-1Fe alloy,with the aim of regulating the proportion of multi-level lamellar microstructures and enhancing the joint properties.Among various annealing temperatures(first annealing at 750–880 ℃+second annealing at 580 ℃),the 750 ℃+580 ℃ annealed joint exhibited simultaneously enhanced strength and toughness,with the increase in tensile strength and impact energy from 844 MPa and 8.8 J for the as-welded joint to 1129 MPa and 14.5 J for annealed joint,respectively,which were superior to those of the joints of Ti5Al-5Mo-5V-1Cr-1Fe alloy as reported.The great increases in the strength and toughness were mainly attributed to the excellent proportion matching of formed multi-level lamellar microstructures(76.1%of primaryα(αp)lamellae and 7.9%of secondaryα(αs)lamellae),among which theαp phase andαs phase mainly affected the joint toughness and strength,respectively.The good coupling ofαp phase andαs phase improved the precipitation strengthening and the resistance to crack propagation.The modified strengthening mechanism models were proposed by introducing the thickness and proportion parameters of the precipitated phase.It was indicated that the theoretical calculation values were in good agreement with the experimental ones,and the solution strengthening and precipitation strengthening provided a large contribution(a sum of about 75%)to the yield strength of the annealed joints.This study provides a novel method via designing proper multi-level lamellar microstructures to simultaneously improve the strength and toughness of nearβtitanium alloy joints.
基金supported by the National Natural Science Foundat ion of China(52388201 and 51525102)。
文摘1.Introduction Nowadays,lithium-ion batteries(LIBs)have been extensively applied in portable electronic devices,electric vehicles,and energy storage.The increasing demands of energy density and cycle life encourage considerable research on the mechanisms of battery failure and the synthesis of new materials.Cathodes of LIBs,as the key component determining energy density and capacity,have been widely investigated.Considerable research has been conducted to reveal the degradation mechanisms of LIB cathodes,including bulk structure degradation in the form of phase transformations[1-4],point/extended defect formation[5],cracking[6,7],and cavitation[8-10],surface phase transformation into cationdensified phases[11-14],gassing[15],transition metal dissolution[16,17],and over-growth of the cathode-electrolyte interphases(CEIs)[18,19].
