A PIC (particle-in-cell)-MC (Monte Carlo) code to model electron beam transport into dense matter is developed. The background target is treated as a cold, stationary fluid and the fast electrons as particles with the...A PIC (particle-in-cell)-MC (Monte Carlo) code to model electron beam transport into dense matter is developed. The background target is treated as a cold, stationary fluid and the fast electrons as particles with the relativistic motions. The process is described by a particle-in-cell method with consideration of the influence of both the self-generated electric and magnetic fields as well as collisions between the fast electrons and the target. The collisional part of the code is solved by the Monte Carlo-type method. Furthermore by assuming that the background current balances with the fast electron current, the electric field is given by the Ohm's law and the magnetic field is calculated from the Faraday's law. Both are solved in a two-dimensional cylindrical geometry. The algorithms implemented in the code are demonstrated and the numerical experiments are performed for monoenergy homogeneous fast electron beam transport in an aluminum target when the fields, collision and angular scattering are switched on and off independently.展开更多
We have developed a three dimensional (3D) PIC (particle-in-cell)-MC (MonteCarlo) code in order to simulate an electron beam transported into the dense matter based onour previous two dimensional code.The relativistic...We have developed a three dimensional (3D) PIC (particle-in-cell)-MC (MonteCarlo) code in order to simulate an electron beam transported into the dense matter based onour previous two dimensional code.The relativistic motion of fast electrons is treated by theparticle-in-cell method under the influence of both a self-generated transverse magnetic field andan axial electric field,as well as collisions.The electric field generated by return current is ex-pressed by Ohm's law and the magnetic field is calculated from Faraday's law.The slowing downof monoenergy electrons in DT plasma is calculated and discussed.展开更多
The low-energy muon facility at PSI provides nearly fully polarized positive muons with tunable energies in the ke V range to carry out muon spin rotation(LE-μSR)experiments with nanometer depth resolution on thin fi...The low-energy muon facility at PSI provides nearly fully polarized positive muons with tunable energies in the ke V range to carry out muon spin rotation(LE-μSR)experiments with nanometer depth resolution on thin films,heterostructures, and near-surface regions. The low-energy muon beam is focused and transported to the sample by electrostatic lenses. In order to achieve a minimum beam spot size at the sample position and to enable the steering of the beam in the horizontal and vertical direction, a special electrostatic device has been implemented close to the sample position. It consists of a cylinder at ground potential followed by four conically shaped electrodes,which can be operated at different electric potential. In LE-μSR experiments, an electric field at the sample along the beam direction can be applied to accelerate/decelerate muons to different energies(0.5–30 keV). Additionally, a horizontal or vertical magnetic field can be superimposed for transverse or longitudinal field μSR experiments. The focusing properties of the conical lens in the presence of these additional electric and magnetic fields have been investigated and optimized by Geant4 simulations. Some experimental tests were also performed and show that the simulation well describes the experimental setup.展开更多
This paper investigates the transverse 3:1 internal resonance of an axially transporting nonlinear viscoelastic Euler-Bernoulli beam with a two-frequency parametric excitation caused by a speed perturbation.The Kelvin...This paper investigates the transverse 3:1 internal resonance of an axially transporting nonlinear viscoelastic Euler-Bernoulli beam with a two-frequency parametric excitation caused by a speed perturbation.The Kelvin-Voigt model is introduced to describe the viscoelastic characteristics of the axially transporting beam.The governing equation and the associated boundary conditions are obtained by Newton’s second law.The method of multiple scales is utilized to obtain the steady-state responses.The RouthHurwitz criterion is used to determine the stabilities and bifurcations of the steady-state responses.The effects of the material viscoelastic coefficient on the dynamics of the transporting beam are studied in detail by a series of numerical demonstrations.Interesting phenomena of the steady-state responses are revealed in the 3:1 internal resonance and two-frequency parametric excitation.The approximate analytical method is validated via a differential quadrature method.展开更多
The accelerator beam transport operator presents the evolution of beam phasespace point with given transport elements and given initial point,while the inverse beamtransport operator presents the evolution of beam pha...The accelerator beam transport operator presents the evolution of beam phasespace point with given transport elements and given initial point,while the inverse beamtransport operator presents the evolution of beam phase space configuration with giveninitial phase space geometry.Therefore,it is necessary to develop a general theory be-tween these two operators.Several concrete examples are worked out in detail to showthe practical applications of such a theory.This paper deals with the linear acceleratorbeam transport operator,and a theorem of finding the inverse linear beam transportoperator for both autonomous and nonautonomous accelerator dynamics is developed.展开更多
This paper deals with the theory of nonlinear accelerator beam transport op-erator.For nonautonomous accelerator dynamics,a theorem of finding the inversenonlinear beam transport operator is developed.Several concrete...This paper deals with the theory of nonlinear accelerator beam transport op-erator.For nonautonomous accelerator dynamics,a theorem of finding the inversenonlinear beam transport operator is developed.Several concrete examples are workedout in detail to show the practical applications of this theory.展开更多
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 inclu...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 Ampere'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
The n-ZnO/p-Si heterojunction was fabricated by depositing high quality single crystalline aluminium-doped n-type ZnO film on p-type Si using the laser molecular beam epitaxy technique. The heterojunction exhibited a ...The n-ZnO/p-Si heterojunction was fabricated by depositing high quality single crystalline aluminium-doped n-type ZnO film on p-type Si using the laser molecular beam epitaxy technique. The heterojunction exhibited a good rectifying behavior. The electrical properties of the heterojunction were investigated by means of temperature dependence current density-voltage measurements. The mechanism of the current transport was proposed based on the band structure of the heterojunction. When the applied bias V is lower than 0.15 V, the current follows the Ohmic behavior. When 0.15V<V<0.6 V, the transport property is dominated by diffusion or recombination in the junction space charge region, while at higher voltages (V > 0.6 V), the space charge limited effect becomes the main transport mechanism. The current-voltage characteristic under illumination was also investigated. The photovoltage and the short circuit current density of the heterojunction aproached 270 mV and 2.10 mA/cm 2 , respectively.展开更多
Evolution of an electrostatic plasma wave driven by a low-density ultra-relativistic electron beam in dense inhomogeneous plasma is considered. In particular, the wavelength variation as observed at fixed locations in...Evolution of an electrostatic plasma wave driven by a low-density ultra-relativistic electron beam in dense inhomogeneous plasma is considered. In particular, the wavelength variation as observed at fixed locations in the plasma is analyzed in terms of the wave characteristics. It is shown that for a negative density gradient, the observed local wavelength decreases monotonically with time, but for a positive density gradient, it first increases and then decreases with time, accompanied by reversal of the wave phase. However, in both cases the local wavelength eventually decreases with time since Landau damping becomes significant as the wavelength becomes of the order of the plasma Debye length. Results from particle-in-cell simulations agree well with theoretical analyses of the wavelength variation.展开更多
The focusing and the stable transport of an intense elliptic sheet electron beam in a uniform magnetic field are investigated thoroughly by using the macroscopic cold-fluid model and the single-particle orbit theory.T...The focusing and the stable transport of an intense elliptic sheet electron beam in a uniform magnetic field are investigated thoroughly by using the macroscopic cold-fluid model and the single-particle orbit theory.The results indicate that the envelopes and the tilted angles of the sheet electron beam obtained by the two theories are consistent.The single-particle orbit theory is more accurate due to its treatment of the space-charge fields in a rectangular drift tube.The macroscopic cold-fluid model describes the collective transport process in order to provide detailed information about the beam dynamics,such as beam shape,density,and velocity profile.The tilt of the elliptic sheet beam in a uniform magnetic field is carefully studied and demonstrated.The results presented in this paper provide two complete theories for systemically discussing the transport of the sheet beam and are useful for understanding and guiding the practical engineering design of electron optics systems in high power vacuum electronic devices.展开更多
基金The project supported by the Key Projects of National Natural Science Foundation of China under Grant No. 70431002 and National Natural Science Foundation of China under Grant Nos. 70371068 and 10247005
基金supported by the National High Technology ICF Committee of Chinathe National Natural Science Fund of China(Nos. 10335020, 10375011, 10576007)the Laboratory of Computational Physics (No. 51479050205ZW0905)
文摘A PIC (particle-in-cell)-MC (Monte Carlo) code to model electron beam transport into dense matter is developed. The background target is treated as a cold, stationary fluid and the fast electrons as particles with the relativistic motions. The process is described by a particle-in-cell method with consideration of the influence of both the self-generated electric and magnetic fields as well as collisions between the fast electrons and the target. The collisional part of the code is solved by the Monte Carlo-type method. Furthermore by assuming that the background current balances with the fast electron current, the electric field is given by the Ohm's law and the magnetic field is calculated from the Faraday's law. Both are solved in a two-dimensional cylindrical geometry. The algorithms implemented in the code are demonstrated and the numerical experiments are performed for monoenergy homogeneous fast electron beam transport in an aluminum target when the fields, collision and angular scattering are switched on and off independently.
基金The project supported by the Key Projects of National Natural Science Foundation of China under Grant No. 70431002 and National Natural Science Foundation of China under Grants Nos. 70371068 and 10247005
基金National High Technology ICF Committee in ChinaNational Natural Science Fund of China(Nos.10675024,10335020,10375011,and 10576007)+1 种基金National Basic Research Program of China(973 Program)(No.2007CB815101)the Laboratory of Computational Physics(No.51479050205ZW0905)
文摘We have developed a three dimensional (3D) PIC (particle-in-cell)-MC (MonteCarlo) code in order to simulate an electron beam transported into the dense matter based onour previous two dimensional code.The relativistic motion of fast electrons is treated by theparticle-in-cell method under the influence of both a self-generated transverse magnetic field andan axial electric field,as well as collisions.The electric field generated by return current is ex-pressed by Ohm's law and the magnetic field is calculated from Faraday's law.The slowing downof monoenergy electrons in DT plasma is calculated and discussed.
基金a scholarship from the China Scholarship Council (CSC)financial support from PSI for her stay at PSI
文摘The low-energy muon facility at PSI provides nearly fully polarized positive muons with tunable energies in the ke V range to carry out muon spin rotation(LE-μSR)experiments with nanometer depth resolution on thin films,heterostructures, and near-surface regions. The low-energy muon beam is focused and transported to the sample by electrostatic lenses. In order to achieve a minimum beam spot size at the sample position and to enable the steering of the beam in the horizontal and vertical direction, a special electrostatic device has been implemented close to the sample position. It consists of a cylinder at ground potential followed by four conically shaped electrodes,which can be operated at different electric potential. In LE-μSR experiments, an electric field at the sample along the beam direction can be applied to accelerate/decelerate muons to different energies(0.5–30 keV). Additionally, a horizontal or vertical magnetic field can be superimposed for transverse or longitudinal field μSR experiments. The focusing properties of the conical lens in the presence of these additional electric and magnetic fields have been investigated and optimized by Geant4 simulations. Some experimental tests were also performed and show that the simulation well describes the experimental setup.
基金Project supported by the National Natural Science Foundation of China (Nos.12002142,1187215951976087)+1 种基金the National Natural Science Foundation of Shanghai of China (No.21ZR1462500)the Natural Science Foundation of Shandong Province of China (No.ZR2021QB137)。
文摘This paper investigates the transverse 3:1 internal resonance of an axially transporting nonlinear viscoelastic Euler-Bernoulli beam with a two-frequency parametric excitation caused by a speed perturbation.The Kelvin-Voigt model is introduced to describe the viscoelastic characteristics of the axially transporting beam.The governing equation and the associated boundary conditions are obtained by Newton’s second law.The method of multiple scales is utilized to obtain the steady-state responses.The RouthHurwitz criterion is used to determine the stabilities and bifurcations of the steady-state responses.The effects of the material viscoelastic coefficient on the dynamics of the transporting beam are studied in detail by a series of numerical demonstrations.Interesting phenomena of the steady-state responses are revealed in the 3:1 internal resonance and two-frequency parametric excitation.The approximate analytical method is validated via a differential quadrature method.
文摘The accelerator beam transport operator presents the evolution of beam phasespace point with given transport elements and given initial point,while the inverse beamtransport operator presents the evolution of beam phase space configuration with giveninitial phase space geometry.Therefore,it is necessary to develop a general theory be-tween these two operators.Several concrete examples are worked out in detail to showthe practical applications of such a theory.This paper deals with the linear acceleratorbeam transport operator,and a theorem of finding the inverse linear beam transportoperator for both autonomous and nonautonomous accelerator dynamics is developed.
文摘This paper deals with the theory of nonlinear accelerator beam transport op-erator.For nonautonomous accelerator dynamics,a theorem of finding the inversenonlinear beam transport operator is developed.Several concrete examples are workedout in detail to show the practical applications of this theory.
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 Ampere'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Project supported by the Postdoctor Foundation of Hebei Province, Chinathe Natural Science Foundation of Hebei Province,China (Grant No. F2012201093)the Natural Science Foundation of Hebei University, China (Grant No. 2008127)
文摘The n-ZnO/p-Si heterojunction was fabricated by depositing high quality single crystalline aluminium-doped n-type ZnO film on p-type Si using the laser molecular beam epitaxy technique. The heterojunction exhibited a good rectifying behavior. The electrical properties of the heterojunction were investigated by means of temperature dependence current density-voltage measurements. The mechanism of the current transport was proposed based on the band structure of the heterojunction. When the applied bias V is lower than 0.15 V, the current follows the Ohmic behavior. When 0.15V<V<0.6 V, the transport property is dominated by diffusion or recombination in the junction space charge region, while at higher voltages (V > 0.6 V), the space charge limited effect becomes the main transport mechanism. The current-voltage characteristic under illumination was also investigated. The photovoltage and the short circuit current density of the heterojunction aproached 270 mV and 2.10 mA/cm 2 , respectively.
基金supported by the National Key R&D Program of China (No. 2016YFA0401100)National Natural Science Foundation of China (Nos. 12175154, 11875092, and 12005149)the Natural Science Foundation of Top Talent of Shenzhen Technology University (Nos. 2019010801001 and 2019020801001)。
文摘Evolution of an electrostatic plasma wave driven by a low-density ultra-relativistic electron beam in dense inhomogeneous plasma is considered. In particular, the wavelength variation as observed at fixed locations in the plasma is analyzed in terms of the wave characteristics. It is shown that for a negative density gradient, the observed local wavelength decreases monotonically with time, but for a positive density gradient, it first increases and then decreases with time, accompanied by reversal of the wave phase. However, in both cases the local wavelength eventually decreases with time since Landau damping becomes significant as the wavelength becomes of the order of the plasma Debye length. Results from particle-in-cell simulations agree well with theoretical analyses of the wavelength variation.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60501019,10775139 and 60971073)
文摘The focusing and the stable transport of an intense elliptic sheet electron beam in a uniform magnetic field are investigated thoroughly by using the macroscopic cold-fluid model and the single-particle orbit theory.The results indicate that the envelopes and the tilted angles of the sheet electron beam obtained by the two theories are consistent.The single-particle orbit theory is more accurate due to its treatment of the space-charge fields in a rectangular drift tube.The macroscopic cold-fluid model describes the collective transport process in order to provide detailed information about the beam dynamics,such as beam shape,density,and velocity profile.The tilt of the elliptic sheet beam in a uniform magnetic field is carefully studied and demonstrated.The results presented in this paper provide two complete theories for systemically discussing the transport of the sheet beam and are useful for understanding and guiding the practical engineering design of electron optics systems in high power vacuum electronic devices.
