Deep neural networks(DNN)are widely used in image recognition,image classification,and other fields.However,as the model size increases,the DNN hardware accelerators face the challenge of higher area overhead and ener...Deep neural networks(DNN)are widely used in image recognition,image classification,and other fields.However,as the model size increases,the DNN hardware accelerators face the challenge of higher area overhead and energy consumption.In recent years,stochastic computing(SC)has been considered a way to realize deep neural networks and reduce hardware consumption.A probabilistic compensation algorithm is proposed to solve the accuracy problem of stochastic calculation,and a fully parallel neural network accelerator based on a deterministic method is designed.The software simulation results show that the accuracy of the probability compensation algorithm on the CIFAR-10 data set is 95.32%,which is 14.98%higher than that of the traditional SC algorithm.The accuracy of the deterministic algorithm on the CIFAR-10 dataset is 95.06%,which is 14.72%higher than that of the traditional SC algorithm.The results of Very Large Scale Integration Circuit(VLSI)hardware tests show that the normalized energy efficiency of the fully parallel neural network accelerator based on the deterministic method is improved by 31%compared with the circuit based on binary computing.展开更多
Superconducting linear accelerators(SCL)have a high acceleration gradient and are capable of operating in a high-duty factor mode.For high-power and high-intensity SCL,the design of beam dynamics generally follows the...Superconducting linear accelerators(SCL)have a high acceleration gradient and are capable of operating in a high-duty factor mode.For high-power and high-intensity SCL,the design of beam dynamics generally follows the principle that the zero-current periodic phase advance(σ0)of each degree of freedom is less than 90°to avoid envelope instability caused by space charge.However,this principle is obtained under the condition of a completely periodic focusing channel,and it is ambiguous for pseudoperiodic structures,such as linear accelerators.Although transverse beam dynamics without acceleration have been studied by other researchers,it appears that there are some connections between pure 2D and 3D beam dynamics.Based on these two points,five focusing schemes for the solenoid and quadrupole doublet channels were designed to simulate the beam behavior with non-constantσ0.Among them,the four schemes follow the characteristics of variation in the zero-current longitudinal phase advance(σ0l)under a constant acceleration gradient and synchronous phase.The zero-current transverse phase advance(σ0t)is consistent withσ0l,based on the equipartition requirement.The initialσ0twas set to 120°,110°,100°,and 90°,and was then gradually decreased to approximately 40°at the end of the channel.The last scheme maintains the maximumσ0tof88°by reducing the acceleration gradient of the corresponding cavities,until the point at whichσ0tequals88°with a normal gradient.Using the stopbands obtained from the linearized envelope equations and multiparticle particle-in-cell(PIC)simulations,the transport properties of both continuous and 3D-bunched beams with the acceleration of the five focusing schemes were studied.It was found that for a CW beam,when tune depression>0.7,σ0tcan break through 90°when the beams were transported in both solenoid and quadrupole doublet periodic focusing channels.When tune depression<0.7,the conclusions were different.For the solenoid focusing system,σ0tcan partially break through 90°,and the beam quality is not significantly affected.For the quadrupole doublet focusing system,a partial breakthrough of 90°has a greater impact on the beam quality.The same conclusions were obtained for a bunched beam with acceleration.展开更多
In this paper, the origin and type of radiation hazards as well as the main aspects of radiation protection for low-energy accelerators are discussed in general, and the problems of radiation protection and the experi...In this paper, the origin and type of radiation hazards as well as the main aspects of radiation protection for low-energy accelerators are discussed in general, and the problems of radiation protection and the experimental results of the operational monitoring of the five accelerators in the institute of Nuclear Science and Technology,Sichuan University, namely, one 1.2 M cyclofron, two Cockroft-waltons and two Van de Graafts, as well as a powerful electron accelerator for industrial irradiation are described. The discussion and evaluation are made according to the requirments of the National standards GB 5172-85.展开更多
Laser wakefield accelerators（LWFAs） are compact accelerators which can produce femtosecond high-energy electron beams on a much smaller scale than the conventional radiofrequency accelerators. It is attributed to th...Laser wakefield accelerators（LWFAs） are compact accelerators which can produce femtosecond high-energy electron beams on a much smaller scale than the conventional radiofrequency accelerators. It is attributed to their high acceleration gradient which is about 3 orders of magnitude larger than the traditional ones. The past decade has witnessed the major breakthroughs and progress in developing the laser wakfield accelerators. To achieve the LWFAs suitable for applications,more and more attention has been paid to optimize the LWFAs for high-quality electron beams. A single-staged LWFA does not favor generating controllable electron beams beyond 1 Ge V since electron injection and acceleration are coupled and cannot be independently controlled. Staged LWFAs provide a promising route to overcome this disadvantage by decoupling injection from acceleration and thus the electron-beam quality as well as the stability can be greatly improved.This paper provides an overview of the physical conceptions of the LWFA, as well as the major breakthroughs and progress in developing LWFAs from single-stage to two-stage LWFAs.展开更多
Dielectric laser accelerators(DLAs)are considered promising candidates for on-chip particle accelerators that can achieve high acceleration gradients.This study explores various combinations of dielectric materials an...Dielectric laser accelerators(DLAs)are considered promising candidates for on-chip particle accelerators that can achieve high acceleration gradients.This study explores various combinations of dielectric materials and accelerated structures based on the inverse Cherenkov effect.The designs utilize conventional processing methods and laser parameters currently in use.We optimize the structural model to enhance the gradient of acceleration and the electron energy gain.To achieve higher acceleration gradients and energy gains,the selection of materials and structures should be based on the initial electron energy.Furthermore,we observed that the variation of the acceleration gradient of the material is different at different initial electron energies.These findings suggest that on-chip accelerators are feasible with the help of these structures and materials.展开更多
Laser wakefield accelerators （LWFAs） are considered to be one of the most compeuuve next- generation accelerator candidates. In this paper, we will study the potential high-flux electron beam production of an LWFA d...Laser wakefield accelerators （LWFAs） are considered to be one of the most compeuuve next- generation accelerator candidates. In this paper, we will study the potential high-flux electron beam production of an LWFA driven by petawatt-level laser pulses. In our three-dimensional particle-in-cell simulations, an optimal set of parameters gives -40 nC of charge with 2 PW laser power, thus -400 kA of instantaneous current if we assume the electron beam duration is 100 fs. This high flux and its secondary radiation are widely applicable in nuclear and QED physics, industrial imaging, medical and biological studies.展开更多
We put forward a new design of a compact beam transport system for intense laser-driven proton therapy,where instead of using conventional pulsed solenoids,our design relies on a helical coil irradiated by a nanosecon...We put forward a new design of a compact beam transport system for intense laser-driven proton therapy,where instead of using conventional pulsed solenoids,our design relies on a helical coil irradiated by a nanosecond laser pulse to generate strong magnetic fields for focusing protons.A pair of dipole magnets and apertures are employed to further filter protons with large divergences and low energies.Our numerical studies combine particle-in-cell simulations for laser-plasma interaction to generate high-energy monoenergetic proton beams,finite element analysis for evaluating the magnetic field distribution inside the coil,and MonteCarlo simulations for beam transport and energy deposition.Our results show that with this design,a spread-out Bragg peak in a range of several centimeters to a deep-seated tumor with a dose of approximately 16.5 cGy and fluctuation around 2% can be achieved.The instantaneous dose rate reaches up to 10^(9)Gy/s,holding the potential for future FLASH radiotherapy research.展开更多
In order to support the physical research on the EAST tokamak,a new positive ion source with designed beam energy of 120 keV was proposed to be developed.Accelerator structure is one of the key components of the ion s...In order to support the physical research on the EAST tokamak,a new positive ion source with designed beam energy of 120 keV was proposed to be developed.Accelerator structure is one of the key components of the ion source.Through the finite element analysis method,the electrostatic analyses of insulators and grid plates were carried out,the material and structure parameters of insulators were determined.The maximum electric field around each insulator is about 4 kV/mm,and the maximum electric field between grids is about 14 kV/mm,which can meet the 120 keV withstand voltage holding.The insulation system for the positive ion source accelerator with 120 keV is designed,and the connection and basic parameters of insulators and support flanges are analyzed and determined.展开更多
We report the world-leading performance of a 1.3 GHz cryomodule equipped with eight 9-cell superconducting radio-frequency cavities that underwent a medium-temperature furnace baking process.During continuous wave hor...We report the world-leading performance of a 1.3 GHz cryomodule equipped with eight 9-cell superconducting radio-frequency cavities that underwent a medium-temperature furnace baking process.During continuous wave horizontal testing,these cavities achieved unprecedented average intrinsic quality factors of 4.0×10^(10)at 20 MV/m and 3.2×10^(10)at 29 MV/m,with no instances of field emission.The cryomodule demonstrates near-complete preservation of ultra-high quality factors and ultra-high accelerating gradients from vertical to horizontal testing,marking a significant milestone in continuous-wave superconducting radio-frequency accelerator technology.This letter presents the cryomodule development experience,includ-ing cavity preparation,cryomodule assembly,degaussing,fast cooldown,and performance testing.展开更多
Aqueous zincion batteries are highly favored for grid-level energy storage owing to their low cost and high safety,but their practical application is limited by slow ion migration.To address this,a strategy has been d...Aqueous zincion batteries are highly favored for grid-level energy storage owing to their low cost and high safety,but their practical application is limited by slow ion migration.To address this,a strategy has been developed to create a cation-accelerating electric field on the surface of the cathode to achieve ultrafast Zn^(2+)diffusion kinetics.By employing electrodeposition to coat MoS_(2)on the surface of BaV_(6)O_(16)·3H_(2)O nanowires,the directional builtin electric field generated at the heterointerface acts as a cation accelerator,continuously accelerating Zn^(2+)diffusion into the active material.The optimized Zn^(2+)diffusion coefficient in CC@BaV-V_(6)O_(16)·3H_(2)@MoS_(2)(7.5×10^(8)cm^(2)s^(-1)) surpasses that of most reported V-based cathodes.Simultaneously,MoS_(2)serving as a cathodic armor extends the cycling life of the Zn-CC@BaV_(6)O_(16)·3H_(2)@MoS_(2)full batteries to over 10000 cycles.This work provides valuable insights into optimizing ion diffusion kinetics for high-performance energy storage devices.展开更多
In laser wakefield acceleration,injecting an external electron beam at a certain energy is a promising approach for achieving a high-quality electron beam with low energy spread and low emittance.In this paper,the pro...In laser wakefield acceleration,injecting an external electron beam at a certain energy is a promising approach for achieving a high-quality electron beam with low energy spread and low emittance.In this paper,the process of laser wakefield acceleration with an external injection at 10 pC has been studied in simulations.A Bayesian optimization method is used to optimize the key laser and plasma parameters so that the electron beam is accelerated to the expected energy with a small emittance and energy spread growth.The effect of the rising edge of the plasma on the transverse properties of the electron beam is simulated and optimized in order to ensure that the external electron beam is injected into the plasma without significant emittance growth.Finally,a high-quality electron beam with an energy of 1.5 GeV,a normalized transverse emittance of 0.5 mm·mrad and a relative energy spread of 0.5%at 10 pC is obtained.展开更多
Neutral beam injection(NBI)has been proven as a reliable heating and current drive method for fusion plasma.For the high-energy NBI system(particle energy>150 ke V)of large-scale fusion devices,the negative ion sou...Neutral beam injection(NBI)has been proven as a reliable heating and current drive method for fusion plasma.For the high-energy NBI system(particle energy>150 ke V)of large-scale fusion devices,the negative ion source neutral beam injection(NNBI)system is inevitable,which can obtain an acceptable neutralization efficiency(>55%).But the NNBI system is very complex and challengeable.To explore and master the key NNBI technology for future fusion reactor in China,an NNBI test facility is under development in the framework of the Comprehensive Research Facility for Fusion Technology(CRAFT).The initial goal of CRAFT NNBI facility is to achieve a 2 MW hydrogen neutral beam at the energy of 200–400 ke V for lasting 100 s.In the first operation of the CRAFT NNBI facility,a negative ion source with dual RF drivers was developed and tested.By using the 50 keV accelerator,the long-pulse and highcurrent extractions of negative hydrogen ions have been achieved and the typical values were 55.4 keV,7.3 A(~123 A/m^(2)),105 s and 55.0 keV,14.7 A(~248 A/m^(2)),30 s,respectively.By using the 200 keV accelerator,the megawatt-class negative hydrogen beam has also been achieved(135.9 keV,8.9 A,8 s).The whole process of the gas neutralization of negative ion beam,electric removal of residual ions,and beam transport have been demonstrated experimentally.展开更多
西南艰险山区分布着大量的不同倾向的层状碎裂结构斜坡,地震作用下极易发生崩塌、滑坡等灾害,对在建的川藏铁路造成严重威胁。通过大型振动台模型试验,研究了强震条件下顺倾、反倾层状碎裂结构斜坡的动力响应、失稳破坏模式以及能量传...西南艰险山区分布着大量的不同倾向的层状碎裂结构斜坡,地震作用下极易发生崩塌、滑坡等灾害,对在建的川藏铁路造成严重威胁。通过大型振动台模型试验,研究了强震条件下顺倾、反倾层状碎裂结构斜坡的动力响应、失稳破坏模式以及能量传递规律。试验结果表明:反倾斜坡的抗震性能显著优于顺倾斜坡;顺倾斜坡的破坏模式主要为拉裂-剪切-隆起-滑移型破坏,反倾斜坡的破坏模式主要为拉伸-弯曲-倾倒-崩塌型破坏;反倾斜坡的自振频率高于顺倾斜坡,顺倾斜坡的自振频率随震级的增加而逐渐降低,而反倾斜坡的自振频率在地震波幅值为0.4g~0.7g时出现反复震荡现象;顺倾斜坡存在明显的高程放大效应和趋表效应,反倾斜坡存在高程放大效应,其内部的加速度响应大于坡表。边际谱识别显示:顺倾斜坡的边际谱幅值(peak of marginal spectrum amplitude,简称PMSA)突变在坡腰上部最显著,说明该位置附近地震波的能量损失最大,反映出顺倾斜坡在坡腰上部附近形成了滑动破坏面;反倾斜坡的PMSA在坡肩处降低得最为显著,反映出坡肩部位损伤最为严重,易发生局部崩塌破坏。分析结果与试验现象能够较好地吻合,进一步揭示了不同结构类型层状碎裂结构斜坡在强震作用下的动力响应与失稳破坏模式,为川藏铁路的安全建设提供了依据。展开更多
The Moon provides a unique environment for investigating nearby astrophysical events such as supernovae.Lunar samples retain valuable information from these events,via detectable long-lived“fingerprint”radionuclides...The Moon provides a unique environment for investigating nearby astrophysical events such as supernovae.Lunar samples retain valuable information from these events,via detectable long-lived“fingerprint”radionuclides such as^(60)Fe.In this work,we stepped up the development of an accelerator mass spectrometry(AMS)method for detecting^(60)Fe using the HI-13tandem accelerator at the China Institute of Atomic Energy(CIAE).Since interferences could not be sufficiently removed solely with the existing magnetic systems of the tandem accelerator and the following Q3D magnetic spectrograph,a Wien filter with a maximum voltage of±60 kV and a maximum magnetic field of 0.3 T was installed after the accelerator magnetic systems to lower the detection background for the low abundance nuclide^(60)Fe.A 1μm thick Si_(3)N_(4) foil was installed in front of the Q3D as an energy degrader.For particle detection,a multi-anode gas ionization chamber was mounted at the center of the focal plane of the spectrograph.Finally,an^(60)Fe sample with an abundance of 1.125×10^(-10)was used to test the new AMS system.These results indicate that^(60)Fe can be clearly distinguished from the isobar^(60)Ni.The sensitivity was assessed to be better than 4.3×10^(-14)based on blank sample measurements lasting 5.8 h,and the sensitivity could,in principle,be expected to be approximately 2.5×10^(-15)when the data were accumulated for 100 h,which is feasible for future lunar sample measurements because the main contaminants were sufficiently separated.展开更多
The acceleration of electrons near three-dimensional(3D)magnetic nulls is crucial to the energy conversion mechanism in the 3D magnetic reconnection process.To explore electron acceleration in a 3D magnetic null topol...The acceleration of electrons near three-dimensional(3D)magnetic nulls is crucial to the energy conversion mechanism in the 3D magnetic reconnection process.To explore electron acceleration in a 3D magnetic null topology,we constructed a pair of 3D magnetic nulls in the PKU Plasma Test(PPT)device and observed acceleration of electrons near magnetic nulls.This study measured the plasma floating potential and ion density profiles around the 3D magnetic null.The potential wells near nulls may be related to the energy variations of electrons,so we measured the electron distribution functions(EDFs)at different spatial positions.The axial variation of EDF shows that the electrons deviate from the Maxwell distribution near magnetic nulls.With scanning probes that can directionally measure and theoretically analyze based on curve fitting,the variations of EDFs are linked to the changes of plasma potential under 3D magnetic null topology.The kinetic energy of electrons accelerated by the electric field is 6 eV(v_(e)~7v_(Alfvén-e))and the scale of the region where accelerating electrons exist is in the order of serval electron skin depths.展开更多
Metal-halide perovskites are revolutionizing the world of X-ray detectors,due to the development of sensitive,fast,and cost-effective devices.Self-powered operation,ensuring portability and low power consumption,has a...Metal-halide perovskites are revolutionizing the world of X-ray detectors,due to the development of sensitive,fast,and cost-effective devices.Self-powered operation,ensuring portability and low power consumption,has also been recently demonstrated in both bulk materials and thin films.However,the signal stability and repeatability under continuous X-ray exposure has only been tested up to a few hours,often reporting degradation of the detection performance.Here it is shown that self-powered direct X-ray detectors,fabricated starting from a FAPbBr_(3)submicrometer-thick film deposition onto a mesoporous TiO_(2)scaffold,can withstand a 26-day uninterrupted X-ray exposure with negligible signal loss,demonstrating ultra-high operational stability and excellent repeatability.No structural modification is observed after irradiation with a total ionizing dose of almost 200 Gy,revealing an unexpectedly high radiation hardness for a metal-halide perovskite thin film.In addition,trap-assisted photoconductive gain enabled the device to achieve a record bulk sensitivity of 7.28 C Gy^(−1)cm^(−3)at 0 V,an unprecedented value in the field of thin-film-based photoconductors and photodiodes for“hard”X-rays.Finally,prototypal validation under the X-ray beam produced by a medical linear accelerator for cancer treatment is also introduced.展开更多
We present a first on-chip positron accelerator based on dielectric laser acceleration.This innovative approach significantly reduces the physical dimensions of the positron acceleration apparatus,enhancing its feasib...We present a first on-chip positron accelerator based on dielectric laser acceleration.This innovative approach significantly reduces the physical dimensions of the positron acceleration apparatus,enhancing its feasibility for diverse applications.By utilizing a stacked acceleration structure and far-infrared laser technology,we are able to achieve a seven-stage acceleration structure that surpasses the distance and energy gain of using the previous dielectric laser acceleration methods.Additionally,we are able to compress the positron beam to an ultrafast sub-femtosecond scale during the acceleration process,compared with the traditional methods,the positron beam is compressed to a greater extent.We also demonstrate the robustness of the stacked acceleration structure through the successful acceleration of the positron beam.展开更多
The interaction of high energy lepton jets composed of electrons and positrons with background electron–proton plasma is investigated numerically based upon particle-in-cell simulation,focusing on the acceleration pr...The interaction of high energy lepton jets composed of electrons and positrons with background electron–proton plasma is investigated numerically based upon particle-in-cell simulation,focusing on the acceleration processes of background protons due to the development of electromagnetic turbulence.Such interaction may be found in the universe when energetic lepton jets propagate in the interstellar media.When such a jet is injected into the background plasma,theWeibel instability is excited quickly,which leads to the development of plasma turbulence into the nonlinear stage.The turbulent electric and magnetic fields accelerate plasma particles via the Fermi II type acceleration,where the maximum energy of both electrons and protons can be accelerated to much higher than that of the incident jet particles.Because of background plasma acceleration,a collisionless electrostatic shock wave is formed,where some pre-accelerated protons are further accelerated when passing through the shock wave front.Dependence of proton acceleration on the beam-plasma density ratio and beam energy is investigated.For a given background plasma density,the maximum proton energy generally increases both with the density and kinetic energy of the injected jet.Moreover,for a homogeneous background plasma,the proton acceleration via both turbulent fields and collisionless shocks is found to be significant.In the case of an inhomogeneous plasma,the proton acceleration in the plasma turbulence is dominant.Our studies illustrate a scenario where protons from background plasma can be accelerated successively by the turbulent fields and collisionless shocks.展开更多
The aim of this study is to create a fast and stable iterative technique for numerical solution of a quasi-linear elliptic pressure equation. We developed a modified version of the Anderson acceleration(AA)algorithm t...The aim of this study is to create a fast and stable iterative technique for numerical solution of a quasi-linear elliptic pressure equation. We developed a modified version of the Anderson acceleration(AA)algorithm to fixed-point(FP) iteration method. It computes the approximation to the solutions at each iteration based on the history of vectors in extended space, which includes the vector of unknowns, the discrete form of the operator, and the equation's right-hand side. Several constraints are applied to AA algorithm, including a limitation of the time step variation during the iteration process, which allows switching to the base FP iterations to maintain convergence. Compared to the base FP algorithm, the improved version of the AA algorithm enables a reliable and rapid convergence of the iterative solution for the quasi-linear elliptic pressure equation describing the flow of particle-laden yield-stress fluids in a narrow channel during hydraulic fracturing, a key technology for stimulating hydrocarbon-bearing reservoirs. In particular, the proposed AA algorithm allows for faster computations and resolution of unyielding zones in hydraulic fractures that cannot be calculated using the FP algorithm. The quasi-linear elliptic pressure equation under consideration describes various physical processes, such as the displacement of fluids with viscoplastic rheology in a narrow cylindrical annulus during well cementing,the displacement of cross-linked gel in a proppant pack filling hydraulic fractures during the early stage of well production(fracture flowback), and multiphase filtration in a rock formation. We estimate computational complexity of the developed algorithm as compared to Jacobian-based algorithms and show that the performance of the former one is higher in modelling of flows of viscoplastic fluids. We believe that the developed algorithm is a useful numerical tool that can be implemented in commercial simulators to obtain fast and converged solutions to the non-linear problems described above.展开更多
X-ray sources with tunable energy spectra have a wide range of applications in different scenarios due to their different penetration depths.However,existing x-ray sources face difficulties in terms of energy regulati...X-ray sources with tunable energy spectra have a wide range of applications in different scenarios due to their different penetration depths.However,existing x-ray sources face difficulties in terms of energy regulation.In this paper,we present a scheme for tuning the energy spectrum of a betatron x-ray generated from a relativistic electron bunch oscillating in a plasma wakefield.The center energy of the x-ray source can be tuned from several keV to several hundred keV by changing the plasma density,thereby extending the control range by an order of magnitude.At different central energies,the brightness of the betatron radiation is in the range of 3.7×10^(22)to 5.5×10^(22)photons/(0.1%BW·s·mm^(2)·mrad^(2))and the photon divergence angle is about 2 mrad.This high-brightness,energy-controlled betatron source could pave the way to a wide range of applications requiring photons of specific energy,such as phase-contrast imaging in medicine,non-destructive testing and material analysis in industry,and imaging in nuclear physics.展开更多
文摘Deep neural networks(DNN)are widely used in image recognition,image classification,and other fields.However,as the model size increases,the DNN hardware accelerators face the challenge of higher area overhead and energy consumption.In recent years,stochastic computing(SC)has been considered a way to realize deep neural networks and reduce hardware consumption.A probabilistic compensation algorithm is proposed to solve the accuracy problem of stochastic calculation,and a fully parallel neural network accelerator based on a deterministic method is designed.The software simulation results show that the accuracy of the probability compensation algorithm on the CIFAR-10 data set is 95.32%,which is 14.98%higher than that of the traditional SC algorithm.The accuracy of the deterministic algorithm on the CIFAR-10 dataset is 95.06%,which is 14.72%higher than that of the traditional SC algorithm.The results of Very Large Scale Integration Circuit(VLSI)hardware tests show that the normalized energy efficiency of the fully parallel neural network accelerator based on the deterministic method is improved by 31%compared with the circuit based on binary computing.
基金the National Natural Science Foundation of China(Nos.11375122 and 11875197).
文摘Superconducting linear accelerators(SCL)have a high acceleration gradient and are capable of operating in a high-duty factor mode.For high-power and high-intensity SCL,the design of beam dynamics generally follows the principle that the zero-current periodic phase advance(σ0)of each degree of freedom is less than 90°to avoid envelope instability caused by space charge.However,this principle is obtained under the condition of a completely periodic focusing channel,and it is ambiguous for pseudoperiodic structures,such as linear accelerators.Although transverse beam dynamics without acceleration have been studied by other researchers,it appears that there are some connections between pure 2D and 3D beam dynamics.Based on these two points,five focusing schemes for the solenoid and quadrupole doublet channels were designed to simulate the beam behavior with non-constantσ0.Among them,the four schemes follow the characteristics of variation in the zero-current longitudinal phase advance(σ0l)under a constant acceleration gradient and synchronous phase.The zero-current transverse phase advance(σ0t)is consistent withσ0l,based on the equipartition requirement.The initialσ0twas set to 120°,110°,100°,and 90°,and was then gradually decreased to approximately 40°at the end of the channel.The last scheme maintains the maximumσ0tof88°by reducing the acceleration gradient of the corresponding cavities,until the point at whichσ0tequals88°with a normal gradient.Using the stopbands obtained from the linearized envelope equations and multiparticle particle-in-cell(PIC)simulations,the transport properties of both continuous and 3D-bunched beams with the acceleration of the five focusing schemes were studied.It was found that for a CW beam,when tune depression>0.7,σ0tcan break through 90°when the beams were transported in both solenoid and quadrupole doublet periodic focusing channels.When tune depression<0.7,the conclusions were different.For the solenoid focusing system,σ0tcan partially break through 90°,and the beam quality is not significantly affected.For the quadrupole doublet focusing system,a partial breakthrough of 90°has a greater impact on the beam quality.The same conclusions were obtained for a bunched beam with acceleration.
文摘In this paper, the origin and type of radiation hazards as well as the main aspects of radiation protection for low-energy accelerators are discussed in general, and the problems of radiation protection and the experimental results of the operational monitoring of the five accelerators in the institute of Nuclear Science and Technology,Sichuan University, namely, one 1.2 M cyclofron, two Cockroft-waltons and two Van de Graafts, as well as a powerful electron accelerator for industrial irradiation are described. The discussion and evaluation are made according to the requirments of the National standards GB 5172-85.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11127901,11425418,and 61221064)the National Basic Research Program of China(Grant No.2011CB808100)the Science and Technology Talent Project of Shanghai City,China(Grant Nos.12XD1405200 and 12ZR1451700)
文摘Laser wakefield accelerators（LWFAs） are compact accelerators which can produce femtosecond high-energy electron beams on a much smaller scale than the conventional radiofrequency accelerators. It is attributed to their high acceleration gradient which is about 3 orders of magnitude larger than the traditional ones. The past decade has witnessed the major breakthroughs and progress in developing the laser wakfield accelerators. To achieve the LWFAs suitable for applications,more and more attention has been paid to optimize the LWFAs for high-quality electron beams. A single-staged LWFA does not favor generating controllable electron beams beyond 1 Ge V since electron injection and acceleration are coupled and cannot be independently controlled. Staged LWFAs provide a promising route to overcome this disadvantage by decoupling injection from acceleration and thus the electron-beam quality as well as the stability can be greatly improved.This paper provides an overview of the physical conceptions of the LWFA, as well as the major breakthroughs and progress in developing LWFAs from single-stage to two-stage LWFAs.
基金the National Natural Science Foundation of China(Grant No.11975214)。
文摘Dielectric laser accelerators(DLAs)are considered promising candidates for on-chip particle accelerators that can achieve high acceleration gradients.This study explores various combinations of dielectric materials and accelerated structures based on the inverse Cherenkov effect.The designs utilize conventional processing methods and laser parameters currently in use.We optimize the structural model to enhance the gradient of acceleration and the electron energy gain.To achieve higher acceleration gradients and energy gains,the selection of materials and structures should be based on the initial electron energy.Furthermore,we observed that the variation of the acceleration gradient of the material is different at different initial electron energies.These findings suggest that on-chip accelerators are feasible with the help of these structures and materials.
基金supported by Extreme Light Infrastructure- Nuclear Physics (ELI-NP) Phase Ⅱa project co-financed by the Romanian Government and European Union through the European Regional Development FundThe EPOCH code project was funded by the UK EPSRC grants EP/G054950/1, EP/ G056803/1, EP/G055165/1 and EP/ M022463/1
文摘Laser wakefield accelerators （LWFAs） are considered to be one of the most compeuuve next- generation accelerator candidates. In this paper, we will study the potential high-flux electron beam production of an LWFA driven by petawatt-level laser pulses. In our three-dimensional particle-in-cell simulations, an optimal set of parameters gives -40 nC of charge with 2 PW laser power, thus -400 kA of instantaneous current if we assume the electron beam duration is 100 fs. This high flux and its secondary radiation are widely applicable in nuclear and QED physics, industrial imaging, medical and biological studies.
基金supported by the National Key R&D Program of China(Nos.2022YFA1603200 and 2022YFA1603201)National Natural Science Foundation of China(Nos.12135001,11921006,12475243 and 11825502)+1 种基金Strategic Priority Research Program of CAS(No.XDA25050900)support from the National Natural Science Funds for Distinguished Young Scholar(No.11825502)。
文摘We put forward a new design of a compact beam transport system for intense laser-driven proton therapy,where instead of using conventional pulsed solenoids,our design relies on a helical coil irradiated by a nanosecond laser pulse to generate strong magnetic fields for focusing protons.A pair of dipole magnets and apertures are employed to further filter protons with large divergences and low energies.Our numerical studies combine particle-in-cell simulations for laser-plasma interaction to generate high-energy monoenergetic proton beams,finite element analysis for evaluating the magnetic field distribution inside the coil,and MonteCarlo simulations for beam transport and energy deposition.Our results show that with this design,a spread-out Bragg peak in a range of several centimeters to a deep-seated tumor with a dose of approximately 16.5 cGy and fluctuation around 2% can be achieved.The instantaneous dose rate reaches up to 10^(9)Gy/s,holding the potential for future FLASH radiotherapy research.
基金supported by National Natural Science Foundation of China(No.11975261)。
文摘In order to support the physical research on the EAST tokamak,a new positive ion source with designed beam energy of 120 keV was proposed to be developed.Accelerator structure is one of the key components of the ion source.Through the finite element analysis method,the electrostatic analyses of insulators and grid plates were carried out,the material and structure parameters of insulators were determined.The maximum electric field around each insulator is about 4 kV/mm,and the maximum electric field between grids is about 14 kV/mm,which can meet the 120 keV withstand voltage holding.The insulation system for the positive ion source accelerator with 120 keV is designed,and the connection and basic parameters of insulators and support flanges are analyzed and determined.
基金supported by Zhangjiang Laboratory,the SHINE R&D project(No.2017SHZDZX02)the SHINE projectthe National Natural Science Foundation of China(No.12125508).
文摘We report the world-leading performance of a 1.3 GHz cryomodule equipped with eight 9-cell superconducting radio-frequency cavities that underwent a medium-temperature furnace baking process.During continuous wave horizontal testing,these cavities achieved unprecedented average intrinsic quality factors of 4.0×10^(10)at 20 MV/m and 3.2×10^(10)at 29 MV/m,with no instances of field emission.The cryomodule demonstrates near-complete preservation of ultra-high quality factors and ultra-high accelerating gradients from vertical to horizontal testing,marking a significant milestone in continuous-wave superconducting radio-frequency accelerator technology.This letter presents the cryomodule development experience,includ-ing cavity preparation,cryomodule assembly,degaussing,fast cooldown,and performance testing.
基金National Natural Science Foundation of China (61761047 and 41876055)Program for Innovative Research Team (in Science and Technology) in University of Yunnan Province。
文摘Aqueous zincion batteries are highly favored for grid-level energy storage owing to their low cost and high safety,but their practical application is limited by slow ion migration.To address this,a strategy has been developed to create a cation-accelerating electric field on the surface of the cathode to achieve ultrafast Zn^(2+)diffusion kinetics.By employing electrodeposition to coat MoS_(2)on the surface of BaV_(6)O_(16)·3H_(2)O nanowires,the directional builtin electric field generated at the heterointerface acts as a cation accelerator,continuously accelerating Zn^(2+)diffusion into the active material.The optimized Zn^(2+)diffusion coefficient in CC@BaV-V_(6)O_(16)·3H_(2)@MoS_(2)(7.5×10^(8)cm^(2)s^(-1)) surpasses that of most reported V-based cathodes.Simultaneously,MoS_(2)serving as a cathodic armor extends the cycling life of the Zn-CC@BaV_(6)O_(16)·3H_(2)@MoS_(2)full batteries to over 10000 cycles.This work provides valuable insights into optimizing ion diffusion kinetics for high-performance energy storage devices.
基金supported by Science and Technology Major Project of Hubei Province in China(No.2021AFB001)。
文摘In laser wakefield acceleration,injecting an external electron beam at a certain energy is a promising approach for achieving a high-quality electron beam with low energy spread and low emittance.In this paper,the process of laser wakefield acceleration with an external injection at 10 pC has been studied in simulations.A Bayesian optimization method is used to optimize the key laser and plasma parameters so that the electron beam is accelerated to the expected energy with a small emittance and energy spread growth.The effect of the rising edge of the plasma on the transverse properties of the electron beam is simulated and optimized in order to ensure that the external electron beam is injected into the plasma without significant emittance growth.Finally,a high-quality electron beam with an energy of 1.5 GeV,a normalized transverse emittance of 0.5 mm·mrad and a relative energy spread of 0.5%at 10 pC is obtained.
基金supported by the Comprehensive Research Facility for Fusion Technology Program of China(No.2018-000052-73-01-001228)。
文摘Neutral beam injection(NBI)has been proven as a reliable heating and current drive method for fusion plasma.For the high-energy NBI system(particle energy>150 ke V)of large-scale fusion devices,the negative ion source neutral beam injection(NNBI)system is inevitable,which can obtain an acceptable neutralization efficiency(>55%).But the NNBI system is very complex and challengeable.To explore and master the key NNBI technology for future fusion reactor in China,an NNBI test facility is under development in the framework of the Comprehensive Research Facility for Fusion Technology(CRAFT).The initial goal of CRAFT NNBI facility is to achieve a 2 MW hydrogen neutral beam at the energy of 200–400 ke V for lasting 100 s.In the first operation of the CRAFT NNBI facility,a negative ion source with dual RF drivers was developed and tested.By using the 50 keV accelerator,the long-pulse and highcurrent extractions of negative hydrogen ions have been achieved and the typical values were 55.4 keV,7.3 A(~123 A/m^(2)),105 s and 55.0 keV,14.7 A(~248 A/m^(2)),30 s,respectively.By using the 200 keV accelerator,the megawatt-class negative hydrogen beam has also been achieved(135.9 keV,8.9 A,8 s).The whole process of the gas neutralization of negative ion beam,electric removal of residual ions,and beam transport have been demonstrated experimentally.
文摘西南艰险山区分布着大量的不同倾向的层状碎裂结构斜坡,地震作用下极易发生崩塌、滑坡等灾害,对在建的川藏铁路造成严重威胁。通过大型振动台模型试验,研究了强震条件下顺倾、反倾层状碎裂结构斜坡的动力响应、失稳破坏模式以及能量传递规律。试验结果表明:反倾斜坡的抗震性能显著优于顺倾斜坡;顺倾斜坡的破坏模式主要为拉裂-剪切-隆起-滑移型破坏,反倾斜坡的破坏模式主要为拉伸-弯曲-倾倒-崩塌型破坏;反倾斜坡的自振频率高于顺倾斜坡,顺倾斜坡的自振频率随震级的增加而逐渐降低,而反倾斜坡的自振频率在地震波幅值为0.4g~0.7g时出现反复震荡现象;顺倾斜坡存在明显的高程放大效应和趋表效应,反倾斜坡存在高程放大效应,其内部的加速度响应大于坡表。边际谱识别显示:顺倾斜坡的边际谱幅值(peak of marginal spectrum amplitude,简称PMSA)突变在坡腰上部最显著,说明该位置附近地震波的能量损失最大,反映出顺倾斜坡在坡腰上部附近形成了滑动破坏面;反倾斜坡的PMSA在坡肩处降低得最为显著,反映出坡肩部位损伤最为严重,易发生局部崩塌破坏。分析结果与试验现象能够较好地吻合,进一步揭示了不同结构类型层状碎裂结构斜坡在强震作用下的动力响应与失稳破坏模式,为川藏铁路的安全建设提供了依据。
基金supported by the National Natural Science Foundation of China(Nos.12125509,12222514,11961141003,and 12005304)National Key Research and Development Project(No.2022YFA1602301)+1 种基金CAST Young Talent Support Planthe CNNC Science Fund for Talented Young Scholars Continuous support for basic scientific research projects。
文摘The Moon provides a unique environment for investigating nearby astrophysical events such as supernovae.Lunar samples retain valuable information from these events,via detectable long-lived“fingerprint”radionuclides such as^(60)Fe.In this work,we stepped up the development of an accelerator mass spectrometry(AMS)method for detecting^(60)Fe using the HI-13tandem accelerator at the China Institute of Atomic Energy(CIAE).Since interferences could not be sufficiently removed solely with the existing magnetic systems of the tandem accelerator and the following Q3D magnetic spectrograph,a Wien filter with a maximum voltage of±60 kV and a maximum magnetic field of 0.3 T was installed after the accelerator magnetic systems to lower the detection background for the low abundance nuclide^(60)Fe.A 1μm thick Si_(3)N_(4) foil was installed in front of the Q3D as an energy degrader.For particle detection,a multi-anode gas ionization chamber was mounted at the center of the focal plane of the spectrograph.Finally,an^(60)Fe sample with an abundance of 1.125×10^(-10)was used to test the new AMS system.These results indicate that^(60)Fe can be clearly distinguished from the isobar^(60)Ni.The sensitivity was assessed to be better than 4.3×10^(-14)based on blank sample measurements lasting 5.8 h,and the sensitivity could,in principle,be expected to be approximately 2.5×10^(-15)when the data were accumulated for 100 h,which is feasible for future lunar sample measurements because the main contaminants were sufficiently separated.
基金supported by National Natural Science Foundation of China(No.11975038)the National Key Research and Development Program of China(No.2022YFA1604600)。
文摘The acceleration of electrons near three-dimensional(3D)magnetic nulls is crucial to the energy conversion mechanism in the 3D magnetic reconnection process.To explore electron acceleration in a 3D magnetic null topology,we constructed a pair of 3D magnetic nulls in the PKU Plasma Test(PPT)device and observed acceleration of electrons near magnetic nulls.This study measured the plasma floating potential and ion density profiles around the 3D magnetic null.The potential wells near nulls may be related to the energy variations of electrons,so we measured the electron distribution functions(EDFs)at different spatial positions.The axial variation of EDF shows that the electrons deviate from the Maxwell distribution near magnetic nulls.With scanning probes that can directionally measure and theoretically analyze based on curve fitting,the variations of EDFs are linked to the changes of plasma potential under 3D magnetic null topology.The kinetic energy of electrons accelerated by the electric field is 6 eV(v_(e)~7v_(Alfvén-e))and the scale of the region where accelerating electrons exist is in the order of serval electron skin depths.
基金supported by the project“PARIDE”(Perovskite Advanced Radiotherapy&Imaging Detectors),funded under the Regional Research and Innovation Programme POR-FESR Lazio 2014-2020(project number:A0375-2020-36698).
文摘Metal-halide perovskites are revolutionizing the world of X-ray detectors,due to the development of sensitive,fast,and cost-effective devices.Self-powered operation,ensuring portability and low power consumption,has also been recently demonstrated in both bulk materials and thin films.However,the signal stability and repeatability under continuous X-ray exposure has only been tested up to a few hours,often reporting degradation of the detection performance.Here it is shown that self-powered direct X-ray detectors,fabricated starting from a FAPbBr_(3)submicrometer-thick film deposition onto a mesoporous TiO_(2)scaffold,can withstand a 26-day uninterrupted X-ray exposure with negligible signal loss,demonstrating ultra-high operational stability and excellent repeatability.No structural modification is observed after irradiation with a total ionizing dose of almost 200 Gy,revealing an unexpectedly high radiation hardness for a metal-halide perovskite thin film.In addition,trap-assisted photoconductive gain enabled the device to achieve a record bulk sensitivity of 7.28 C Gy^(−1)cm^(−3)at 0 V,an unprecedented value in the field of thin-film-based photoconductors and photodiodes for“hard”X-rays.Finally,prototypal validation under the X-ray beam produced by a medical linear accelerator for cancer treatment is also introduced.
基金supported by the National Natural Science Foundation of China(Grant No.11975214).
文摘We present a first on-chip positron accelerator based on dielectric laser acceleration.This innovative approach significantly reduces the physical dimensions of the positron acceleration apparatus,enhancing its feasibility for diverse applications.By utilizing a stacked acceleration structure and far-infrared laser technology,we are able to achieve a seven-stage acceleration structure that surpasses the distance and energy gain of using the previous dielectric laser acceleration methods.Additionally,we are able to compress the positron beam to an ultrafast sub-femtosecond scale during the acceleration process,compared with the traditional methods,the positron beam is compressed to a greater extent.We also demonstrate the robustness of the stacked acceleration structure through the successful acceleration of the positron beam.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12135009,11991074,11975154,and 12005287).
文摘The interaction of high energy lepton jets composed of electrons and positrons with background electron–proton plasma is investigated numerically based upon particle-in-cell simulation,focusing on the acceleration processes of background protons due to the development of electromagnetic turbulence.Such interaction may be found in the universe when energetic lepton jets propagate in the interstellar media.When such a jet is injected into the background plasma,theWeibel instability is excited quickly,which leads to the development of plasma turbulence into the nonlinear stage.The turbulent electric and magnetic fields accelerate plasma particles via the Fermi II type acceleration,where the maximum energy of both electrons and protons can be accelerated to much higher than that of the incident jet particles.Because of background plasma acceleration,a collisionless electrostatic shock wave is formed,where some pre-accelerated protons are further accelerated when passing through the shock wave front.Dependence of proton acceleration on the beam-plasma density ratio and beam energy is investigated.For a given background plasma density,the maximum proton energy generally increases both with the density and kinetic energy of the injected jet.Moreover,for a homogeneous background plasma,the proton acceleration via both turbulent fields and collisionless shocks is found to be significant.In the case of an inhomogeneous plasma,the proton acceleration in the plasma turbulence is dominant.Our studies illustrate a scenario where protons from background plasma can be accelerated successively by the turbulent fields and collisionless shocks.
基金partial financial support from Gazpromneft Science and Technology Center。
文摘The aim of this study is to create a fast and stable iterative technique for numerical solution of a quasi-linear elliptic pressure equation. We developed a modified version of the Anderson acceleration(AA)algorithm to fixed-point(FP) iteration method. It computes the approximation to the solutions at each iteration based on the history of vectors in extended space, which includes the vector of unknowns, the discrete form of the operator, and the equation's right-hand side. Several constraints are applied to AA algorithm, including a limitation of the time step variation during the iteration process, which allows switching to the base FP iterations to maintain convergence. Compared to the base FP algorithm, the improved version of the AA algorithm enables a reliable and rapid convergence of the iterative solution for the quasi-linear elliptic pressure equation describing the flow of particle-laden yield-stress fluids in a narrow channel during hydraulic fracturing, a key technology for stimulating hydrocarbon-bearing reservoirs. In particular, the proposed AA algorithm allows for faster computations and resolution of unyielding zones in hydraulic fractures that cannot be calculated using the FP algorithm. The quasi-linear elliptic pressure equation under consideration describes various physical processes, such as the displacement of fluids with viscoplastic rheology in a narrow cylindrical annulus during well cementing,the displacement of cross-linked gel in a proppant pack filling hydraulic fractures during the early stage of well production(fracture flowback), and multiphase filtration in a rock formation. We estimate computational complexity of the developed algorithm as compared to Jacobian-based algorithms and show that the performance of the former one is higher in modelling of flows of viscoplastic fluids. We believe that the developed algorithm is a useful numerical tool that can be implemented in commercial simulators to obtain fast and converged solutions to the non-linear problems described above.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.11921006 and 12175058)the Beijing Distinguished Young Scientist Program and National Grand Instrument Project (Grant No.SQ2019YFF01014400)+1 种基金the Beijing Municipal Science&Technology Commission,Administrative Commission of Zhongguancun Science Park (Grant No.Z231100006023003)in part funded by United Kingdom EPSRC (Grant Nos.EP/G054950/1,EP/G056803/1,EP/G055165/1,and EP/M022463/1)。
文摘X-ray sources with tunable energy spectra have a wide range of applications in different scenarios due to their different penetration depths.However,existing x-ray sources face difficulties in terms of energy regulation.In this paper,we present a scheme for tuning the energy spectrum of a betatron x-ray generated from a relativistic electron bunch oscillating in a plasma wakefield.The center energy of the x-ray source can be tuned from several keV to several hundred keV by changing the plasma density,thereby extending the control range by an order of magnitude.At different central energies,the brightness of the betatron radiation is in the range of 3.7×10^(22)to 5.5×10^(22)photons/(0.1%BW·s·mm^(2)·mrad^(2))and the photon divergence angle is about 2 mrad.This high-brightness,energy-controlled betatron source could pave the way to a wide range of applications requiring photons of specific energy,such as phase-contrast imaging in medicine,non-destructive testing and material analysis in industry,and imaging in nuclear physics.
