The polarization effect introduced by electric field deformation is the most important bottleneck of CdZnTe detector in x-ray imaging. Currently, most of studies focus on electric field deformation caused by trapped c...The polarization effect introduced by electric field deformation is the most important bottleneck of CdZnTe detector in x-ray imaging. Currently, most of studies focus on electric field deformation caused by trapped carriers;the perturbation of electric field due to drifting carriers has been rarely reported. In this study, the effect of transient space-charge perturbation on carrier transport in a CdZnTe semiconductor is evaluated by using the laser-beam-induced current(LBIC) technique.Cusps appear in the current curves of CdZnTe detectors with different carrier transport performances under intense excitation, indicating the deformation of electric field. The current signals under different excitations are compared. The results suggest that with the increase of excitation, the amplitude of cusp increases and the electron transient time gradually decreases. The distortion in electric field is independent of carrier transport performance of detector. Transient space-charge perturbation is responsible for the pulse shape and affects the carrier transport process.展开更多
We developed a cubic non-linear theory describing the dynamics of the multiharmonic spacecharge wave（SCW）, with harmonics frequencies smaller than the two-stream instability critical frequency, with different relati...We developed a cubic non-linear theory describing the dynamics of the multiharmonic spacecharge wave（SCW）, with harmonics frequencies smaller than the two-stream instability critical frequency, with different relativistic electron beam（REB） parameters. The self-consistent differential equation system for multiharmonic SCW harmonic amplitudes was elaborated in a cubic non-linear approximation. This system considers plural three-wave parametric resonant interactions between wave harmonics and the two-stream instability effect. Different REB parameters such as the input angle with respect to focusing magnetic field, the average relativistic factor value, difference of partial relativistic factors, and plasma frequency of partial beams were investigated regarding their influence on the frequency spectrum width and multiharmonic SCW saturation levels. We suggested ways in which the multiharmonic SCW frequency spectrum widths could be increased in order to use them in multiharmonic two-stream superheterodyne free-electron lasers, with the main purpose of forming a powerful multiharmonic electromagnetic wave.展开更多
The self-consistent differential equations, which describe a laminar-flow equilibrium state in a magnetically focused intense relativistic electron beam propagating inside a conducting waveguide, are presented. The ca...The self-consistent differential equations, which describe a laminar-flow equilibrium state in a magnetically focused intense relativistic electron beam propagating inside a conducting waveguide, are presented. The canonical angular momentum, Pe, defined under the conditions at the source, uniquely determines the possible solutions of these equations. By numerically solving these equations, the space-charge limited current and the externally applied magnetic field are obtained in a solid beam and a hollow beam in two cases of Pθ= 0 （magnetically shielded source） and Pθ= const. （immersed source） separately. It is shown that the hollow beam is more beneficial to the propagation of the intense relativistic beam through a drift tube than the solid beam.展开更多
The problem of extracting space-charge-limited ion beams from spherical emission boundaries is analyzed for simple,two electrode,parallel-plate and spherical sector electrode systems by application of Langmuir-Blodget...The problem of extracting space-charge-limited ion beams from spherical emission boundaries is analyzed for simple,two electrode,parallel-plate and spherical sector electrode systems by application of Langmuir-Blodgett theory with account taken for the divergent lens effect caused by the aperture in the extraction electrode.Results derived from simulation studies for the three electrode system,designed for use with the Oak Ridge National Laboratory ECR ion source,complement predictions made from elementary analytical theory with or without magnetic field in the extraction region of the source.Under minimum half- angular divergence(minimum emittance)conditions,the plasma emission boundary has an optimum curvature and the perveance,P,(i.e,current density,j+and extraction gap,d),has an optimum value for a given charge- state.From these studies,we find that the optimum perveance for any electrode system can be determined from the Child-Langmuir relation for the parallel-plate electrode system multiplied by a factor,F with value 0.49≤F≤1.展开更多
The linear theory of free-electron laser (FEL) is established by means of the spacecharge wave theory. Equations for space-charge waves in FEL with magnetostatic wiggler have been derived and solved. The space-charge ...The linear theory of free-electron laser (FEL) is established by means of the spacecharge wave theory. Equations for space-charge waves in FEL with magnetostatic wiggler have been derived and solved. The space-charge density waves and the current waves have been obtained, and the differences between these waves and the conventional space-charge waves are discussed in detail. Using these space-charge waves, the dispersion equations of FEL have been derived, and some special cases are analyzed. A new concept and suggestion are presented.展开更多
In this study,we present an in-depth exploration of charge transport phenomena and variable photo-switching characteristics in a novel double-perovskite-based three-terminal device.The Cs_(2)AgBiBr_(6) thin film(TF)wa...In this study,we present an in-depth exploration of charge transport phenomena and variable photo-switching characteristics in a novel double-perovskite-based three-terminal device.The Cs_(2)AgBiBr_(6) thin film(TF)was synthesized through a three-step thermal evaporation process followed by precise open-air annealing,ensuring superior film quality as confirmed by structural and morphological characterizations.Photoluminescence spectroscopy revealed distinct emissions at 2.28 and 2.07 eV,indicative of both direct and indirect electronic transitions.Our device exhibited space-charge limited current(SCLC)behaviour beyond 0.35 V,aligning with the relationship Current(I)∝Voltage(V)^(m),where the exponent m transitioned from≤1 to>1.Detailed analysis of Schottky parameters within the trap-filled limit(TFL)regime was conducted,accounting for variations in temperature and optical power.Significantly,the self-powered photodetector demonstrated outstanding performance under illumination.The sensitivity of the device was finely tunable via the applied bias voltages at the third terminal.Notably,an optimal bias voltage of±100μV yielded maximum responsivity(R)of 0.48 A/W and an impressive detectivity(D*)of 1.07×10^(9) Jones,highlighting the potential of this double-perovskite-based device for advanced optoelectronic applications.展开更多
Two-dimensional diagnosis of laser-induced zirconium(Zr)plasma has been experimentally performed using the time-of-flight method by employing Faraday cups in addition to electric and magnetic probes.The characteristic...Two-dimensional diagnosis of laser-induced zirconium(Zr)plasma has been experimentally performed using the time-of-flight method by employing Faraday cups in addition to electric and magnetic probes.The characteristic parameters of laser-induced Zr plasma have been evaluated as a function of different laser irradiances ranging from 4.5 to 11.7 GW cm-2 at different axial positions of 1–4 cm with a fixed radial distance of 2 cm.A well-supporting correlation between the plume parameters and the laser-plasma-produced spontaneous electric and magnetic(E and B)fields was established.The measurements of the characteristic parameters and spontaneously induced fields were observed to have an increasing trend with the increasing laser irradiance.However,when increasing the spatial distance in both the axial and radial directions,the plasma parameters(electron/ion number density,temperature and kinetic energy)did not show either continuously increasing or decreasing trends due to various kinetic and dynamic processes during the spatial evolution of the plume.However,the E and B fields were observed to be always diffusing away from the target.The radial component of electron number densities remained higher than the axial number density component,whereas the axial ion number density at all laser irradiances and axial distances remained higher than the radial ion number density.The higher axial self-generated electric field(SGEF)values than radial SGEF values are correlated with the effective charge-separation mechanism of electrons and ions.The generation of a self-generated magnetic field is observed dominantly in the radial direction at increasing laser irradiance as compared to the axial one due to the deflection of fast-moving electrons and the persistence of two-electron temperature on the radial axis.展开更多
This paper presents a three-dimensional time-dependent nonlinear theory of helix traveling wave tubes for beam- wave interaction. The radio frequency electromagnetic fields are represented as the superposition of azim...This paper presents a three-dimensional time-dependent nonlinear theory of helix traveling wave tubes for beam- wave interaction. The radio frequency electromagnetic fields are represented as the superposition of azimuthally sym- metric waves in a vacuum sheath helix. Coupling impedance is introduced to the electromagnetic field equations＇ stimulating sources, which makes the theory easier and more flexible to realize. The space charge fields are calculated by electron beam space-charge waves expressed as the superposition solutions of Helmholtz equations. The focusing forces due to either a solenoidal field or a periodic permanent magnetic field is also included. The dynamical equations of electrons are Lorentz equations associating with electromagnetic fields, focusing fields and space-charge fields. The numerically simulated results of a tube are presented.展开更多
The performance of an organic photovoltaic （OPV） cell based on copper phthatocyanine CuPc/C60 with a tris- （8-hydroxyquinolinato） aluminum （Alq3） buffer layer has been investigated. It was found that the power c...The performance of an organic photovoltaic （OPV） cell based on copper phthatocyanine CuPc/C60 with a tris- （8-hydroxyquinolinato） aluminum （Alq3） buffer layer has been investigated. It was found that the power conversion efficiency of the device was 1.51% under illumination with an intensity of 100 mW/cm^2, which was limited by a squareroot dependence of the photocurrent on voltage. The photocurrent optical power density characteristics showed that the OPV cell had a significant space-charge limited photocurrent with a varied saturation voltage and a three quarters power dependence on optical power density. Also, the absorption spectrum was measured by a spectrophotometer, and the results showed that the additional Alq3 layer has a minor effect on photocurrent generation.展开更多
This paper investigates the dielectric properties of （Na0.5K0.5Bi）0.5TiO3 crystal at intermediate frequencies （1kHz〈 f 〈IMHz） in the temperature range of 30-560℃. A pronounced high-temperature diffuse dielectri...This paper investigates the dielectric properties of （Na0.5K0.5Bi）0.5TiO3 crystal at intermediate frequencies （1kHz〈 f 〈IMHz） in the temperature range of 30-560℃. A pronounced high-temperature diffuse dielectric anomaly has been observed. This dielectric anomaly is shown to arise from a Debye-like dielectric dispersion that slows down following an Arrhenius law. The activation energy Er obtained in the fitting process is about 0.69eV. It proposes that the dielectric peak measured at low frequency above 400℃ is not related to the phase transition but to a space-charge relaxation.展开更多
The space-charge layer （SCL） and surface depletion area （SDA） model for beveled p-n junction is presented. The surface space-charge density is calculated for depletion case of beveled p-n junction. Based on the fi...The space-charge layer （SCL） and surface depletion area （SDA） model for beveled p-n junction is presented. The surface space-charge density is calculated for depletion case of beveled p-n junction. Based on the finite difference method, the effect of the equivalent surface charge density on the surface depletion area for positively beveled p-n junction is also studied. Thyristors passivated with polyimide （PI） or polyester improved silicon paint （SP） are fabricated to verify the effect of equivalent surface charge on the peripheral surface of beveled p-n junction. The change of leakage current is sensitive to the surface charges. It indicates that the selection of passivation materials is a significant process to ensure the breakdown voltage capability of beveled devices.展开更多
For a low surface barrier, the energy band, barrier height and width of the space charge region at the surface of relatively large grains of ZnO are presented analytically on condition that the electron distribution o...For a low surface barrier, the energy band, barrier height and width of the space charge region at the surface of relatively large grains of ZnO are presented analytically on condition that the electron distribution obeys the Boltzmann statistics. It is shown that the temperature in the space charge distribution factor has an important effect on the energy band, barrier height and width of the space charge region. The depletion approximation is a model in which the temperature in the space charge distribution factor is zero. Our results are better than the depletion approximation.展开更多
Lanthanum lithium titanate is one of the promising electrolytes for solid-state lithium-ion batteries due to its high bulk ionic conductivity up to∼10^(−3) S/cm.However,the practical application of this material has ...Lanthanum lithium titanate is one of the promising electrolytes for solid-state lithium-ion batteries due to its high bulk ionic conductivity up to∼10^(−3) S/cm.However,the practical application of this material has been bottlenecked by high grain boundary(GB)resistance,while the underlying mechanism is still under debate.Here we report a comprehensive study with direct evidence to reveal the origin of high GB resistance in La_(2/3)–xLi_(3x)TiO_(3)(LLTO).Atomic-scale observations via advanced scanning transmission electron microscopy show that the GBs are uniformly subject to subsurface segregation of La atoms to compensate for the excess surface charges.The La segregation leads to an abrupt decrease of charge carrier concentration neighboring GBs and hence is supposed to have deleterious effect on GB conductivity.The findings suggest a novel mechanism of space-charge-induced cation segregation,which shed lights on the intrinsic origin of low GB ionic conductivity in LLTO.展开更多
In the study of beam dynamics of high intensity linear accelerators,full 3D multiparticle simulations are needed due to numerous nonlinear effects caused by the strong space-charge effects between charged particles.Ho...In the study of beam dynamics of high intensity linear accelerators,full 3D multiparticle simulations are needed due to numerous nonlinear effects caused by the strong space-charge effects between charged particles.However,the use of multiparticle simulations is limited by the speed of the Particle-in-cell(PIC)algorithm.In this work,we modify the PIC algorithm by using the symmetry of beam,the solution procedure is divided into two steps,one is the solution of the symmetric field and the other is the addition of the asymmetric field components.Due to the full use of symmetry,our modified algorithm can significantly improve the computational speed of multiparticle simulations.Results show that the modified algorithm accelerates the process of solving space-charge field by a factor of 4,thus increases the speed of the entire multiparticle simulation by a factor of 1.7,while ensures the accuracy of the simulation.Although our algorithm is modified for linear accelerator,considering that the algorithm is an improvement based on symmetry,it can still speed up the simulation for any accelerator with symmetry.展开更多
Nanostructured amorphous silicon nitride （NASN） was obtained by compacting the particles of the order of nanometer. The volume of interfaces occupies a large fraction of the total volume. This type of solid possesse...Nanostructured amorphous silicon nitride （NASN） was obtained by compacting the particles of the order of nanometer. The volume of interfaces occupies a large fraction of the total volume. This type of solid possesses some novel physical properties. The conventional Si<sub>3</sub>N<sub>4</sub> is a kind of excellent insulator, and thus it is展开更多
Nowadays,the demand for advanced functional materials in transducer technology is growing rapidly.Piezoelectric materials transform mechanical variables(displacement or force)into electrical signals(charge or voltage)...Nowadays,the demand for advanced functional materials in transducer technology is growing rapidly.Piezoelectric materials transform mechanical variables(displacement or force)into electrical signals(charge or voltage)and vice versa.They are interesting from both fundamental and application points of view.Ferrooelectrets(also called piezoelectrets)are a relatively young group of piezo-,pyro-and ferroelectric materials.They exhibit ferroic behavior phenomenologically undistinguishable from that of traditional ferroelectrics,although the materials per se are essentially non-polar space-charge electrets with artificial macroscopic dipoles(i.e.,internally charged cavities).A lot of work has been done on ferroelectrets and their applications up to now.In this paper,we review and discuss mostly the work done at University of Potsdam on the research and development of ferroelectrets.We will,however,also mention important results from other teams,and prospect the challenges and future progress trend of the field of ferroelectret research.展开更多
The SSC-linac （a new injector for the Separated Sector Cyclotron） is being designed in the HIRFL （Heavy Ion Research Facility in Lanzhou） system to accelerate 238U34＋ from 3.72 keV/u to 1.008 MeV/u. As a part of ...The SSC-linac （a new injector for the Separated Sector Cyclotron） is being designed in the HIRFL （Heavy Ion Research Facility in Lanzhou） system to accelerate 238U34＋ from 3.72 keV/u to 1.008 MeV/u. As a part of the SSC-linac injector, the HEBT （high energy beam transport） has been designed by using the TRACE-3D code and simulated by the 3D PIC （particle-in-cell） Track code. The total length of the HEBT is about 12 meters and a beam line of about 6 meters are shared with the exiting beam line of the HIRFL system. The simulation results show that the particles can be delivered efficiently in the HEBT and the particles at the exit of the HEBT well match the acceptance of the SSC for further acceleration. The dispersion is eliminated absolutely in the HEBT. The space-charge effect calculated by the Track code is inconspicuous. According to the simulation, more than 60 percent of the particles from the ion source can be transported into the acceptance of the SSC.展开更多
A novel quasi-opitcal resonance system modified axisymmetrical quasi-optical cavity of oblique ratation(MAQCOR)-is proposed using the laplace integral transormation the kinetic theory of the high relativsitic electron...A novel quasi-opitcal resonance system modified axisymmetrical quasi-optical cavity of oblique ratation(MAQCOR)-is proposed using the laplace integral transormation the kinetic theory of the high relativsitic electron cyclotron maser with MAQCORis carried out within the framowrk of the linearized vlasov-mxawel eauations the formulas of beamwave intreaction power starting current and frequency shift have been derived some important plroblems such as high-order harmonic modes competition inflneces of the rationg angle and space charge and space chrage effcet are andlyaed and discussed in detall and a serios fo new condinsions are obtained a theoretical bssia is laid for the design of this novel qussi-optical gyrotron展开更多
The effects of the multimode diluted waveguide on quantum efficiency and saturation behavior of the evanescently coupled uni-traveling carrier （UTC） photodiode structures are reported. Two kinds of evanescently coup...The effects of the multimode diluted waveguide on quantum efficiency and saturation behavior of the evanescently coupled uni-traveling carrier （UTC） photodiode structures are reported. Two kinds of evanescently coupled uni-traveling carrier photodiodes （EC-UTC-PD） were designed and characterized： one is a conventional EC-UTC-PD structure with a multimode diluted waveguide integrated with a UTC-PD; and the other is a compact EC-UTC-PD structure which fused the multimode diluted waveguide and the UTC-PD structure together. The effect of the absorption behavior of the photodiodes on the efficiency and saturation characteristics of the EC-UTC-PDs is analyzed using 3-D beam propagation method, and the results indicate that both the responsivity and saturation power of the compact EC-UTC-PD structures can be further improved by incorporating an optimized compact multimode diluted waveguide.展开更多
In the conventional design of RF linacs, the bunched beams are not in thermal equilibrium. The space charge forces couple the particle motions between the transverse and the longitudinal directions. Furthermore it wil...In the conventional design of RF linacs, the bunched beams are not in thermal equilibrium. The space charge forces couple the particle motions between the transverse and the longitudinal directions. Furthermore it will cause the equipartitioning process which leads to emittance growth and halo formation. In the design of the China Spallation Neutron Source （CSNS） linac, three cases are investigated using the Hofmann stability charts. In this paper, we present the equipartitioning beam study of the CSNS Alvarez DTL linac.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.61874089)the Fund of MIIT(Grant No.MJ-2017-F-05)+2 种基金the 111 Project of China(Grant No.B08040)the NPU Foundation for Fundamental Research,Chinathe Research Found of the State Key Laboratory of Solidification Processing(NWPU),China
文摘The polarization effect introduced by electric field deformation is the most important bottleneck of CdZnTe detector in x-ray imaging. Currently, most of studies focus on electric field deformation caused by trapped carriers;the perturbation of electric field due to drifting carriers has been rarely reported. In this study, the effect of transient space-charge perturbation on carrier transport in a CdZnTe semiconductor is evaluated by using the laser-beam-induced current(LBIC) technique.Cusps appear in the current curves of CdZnTe detectors with different carrier transport performances under intense excitation, indicating the deformation of electric field. The current signals under different excitations are compared. The results suggest that with the increase of excitation, the amplitude of cusp increases and the electron transient time gradually decreases. The distortion in electric field is independent of carrier transport performance of detector. Transient space-charge perturbation is responsible for the pulse shape and affects the carrier transport process.
基金supported by the Ministry of Education and Science of Ukraine under Grant No.0117U002253
文摘We developed a cubic non-linear theory describing the dynamics of the multiharmonic spacecharge wave（SCW）, with harmonics frequencies smaller than the two-stream instability critical frequency, with different relativistic electron beam（REB） parameters. The self-consistent differential equation system for multiharmonic SCW harmonic amplitudes was elaborated in a cubic non-linear approximation. This system considers plural three-wave parametric resonant interactions between wave harmonics and the two-stream instability effect. Different REB parameters such as the input angle with respect to focusing magnetic field, the average relativistic factor value, difference of partial relativistic factors, and plasma frequency of partial beams were investigated regarding their influence on the frequency spectrum width and multiharmonic SCW saturation levels. We suggested ways in which the multiharmonic SCW frequency spectrum widths could be increased in order to use them in multiharmonic two-stream superheterodyne free-electron lasers, with the main purpose of forming a powerful multiharmonic electromagnetic wave.
基金Project supported by the National Natural Science Foundation of China （Grant No 10476004）.
文摘The self-consistent differential equations, which describe a laminar-flow equilibrium state in a magnetically focused intense relativistic electron beam propagating inside a conducting waveguide, are presented. The canonical angular momentum, Pe, defined under the conditions at the source, uniquely determines the possible solutions of these equations. By numerically solving these equations, the space-charge limited current and the externally applied magnetic field are obtained in a solid beam and a hollow beam in two cases of Pθ= 0 （magnetically shielded source） and Pθ= const. （immersed source） separately. It is shown that the hollow beam is more beneficial to the propagation of the intense relativistic beam through a drift tube than the solid beam.
基金Supported by the U.S.Department of Energy under contract DE-AC05-00OR22725 with UT-Battelle,LLC
文摘The problem of extracting space-charge-limited ion beams from spherical emission boundaries is analyzed for simple,two electrode,parallel-plate and spherical sector electrode systems by application of Langmuir-Blodgett theory with account taken for the divergent lens effect caused by the aperture in the extraction electrode.Results derived from simulation studies for the three electrode system,designed for use with the Oak Ridge National Laboratory ECR ion source,complement predictions made from elementary analytical theory with or without magnetic field in the extraction region of the source.Under minimum half- angular divergence(minimum emittance)conditions,the plasma emission boundary has an optimum curvature and the perveance,P,(i.e,current density,j+and extraction gap,d),has an optimum value for a given charge- state.From these studies,we find that the optimum perveance for any electrode system can be determined from the Child-Langmuir relation for the parallel-plate electrode system multiplied by a factor,F with value 0.49≤F≤1.
文摘The linear theory of free-electron laser (FEL) is established by means of the spacecharge wave theory. Equations for space-charge waves in FEL with magnetostatic wiggler have been derived and solved. The space-charge density waves and the current waves have been obtained, and the differences between these waves and the conventional space-charge waves are discussed in detail. Using these space-charge waves, the dispersion equations of FEL have been derived, and some special cases are analyzed. A new concept and suggestion are presented.
基金Research Board(SERB),a statutory entity of the Department of Science and Technology(DST),Ministry of Science and Technology,India(File No:CRG/2021/000255)provided financial support to one of the authors.
文摘In this study,we present an in-depth exploration of charge transport phenomena and variable photo-switching characteristics in a novel double-perovskite-based three-terminal device.The Cs_(2)AgBiBr_(6) thin film(TF)was synthesized through a three-step thermal evaporation process followed by precise open-air annealing,ensuring superior film quality as confirmed by structural and morphological characterizations.Photoluminescence spectroscopy revealed distinct emissions at 2.28 and 2.07 eV,indicative of both direct and indirect electronic transitions.Our device exhibited space-charge limited current(SCLC)behaviour beyond 0.35 V,aligning with the relationship Current(I)∝Voltage(V)^(m),where the exponent m transitioned from≤1 to>1.Detailed analysis of Schottky parameters within the trap-filled limit(TFL)regime was conducted,accounting for variations in temperature and optical power.Significantly,the self-powered photodetector demonstrated outstanding performance under illumination.The sensitivity of the device was finely tunable via the applied bias voltages at the third terminal.Notably,an optimal bias voltage of±100μV yielded maximum responsivity(R)of 0.48 A/W and an impressive detectivity(D*)of 1.07×10^(9) Jones,highlighting the potential of this double-perovskite-based device for advanced optoelectronic applications.
文摘Two-dimensional diagnosis of laser-induced zirconium(Zr)plasma has been experimentally performed using the time-of-flight method by employing Faraday cups in addition to electric and magnetic probes.The characteristic parameters of laser-induced Zr plasma have been evaluated as a function of different laser irradiances ranging from 4.5 to 11.7 GW cm-2 at different axial positions of 1–4 cm with a fixed radial distance of 2 cm.A well-supporting correlation between the plume parameters and the laser-plasma-produced spontaneous electric and magnetic(E and B)fields was established.The measurements of the characteristic parameters and spontaneously induced fields were observed to have an increasing trend with the increasing laser irradiance.However,when increasing the spatial distance in both the axial and radial directions,the plasma parameters(electron/ion number density,temperature and kinetic energy)did not show either continuously increasing or decreasing trends due to various kinetic and dynamic processes during the spatial evolution of the plume.However,the E and B fields were observed to be always diffusing away from the target.The radial component of electron number densities remained higher than the axial number density component,whereas the axial ion number density at all laser irradiances and axial distances remained higher than the radial ion number density.The higher axial self-generated electric field(SGEF)values than radial SGEF values are correlated with the effective charge-separation mechanism of electrons and ions.The generation of a self-generated magnetic field is observed dominantly in the radial direction at increasing laser irradiance as compared to the axial one due to the deflection of fast-moving electrons and the persistence of two-electron temperature on the radial axis.
基金supported by the National Natural Science Foundation of China (Grant Nos. 60601004,60801029,10876005,and60931001)
文摘This paper presents a three-dimensional time-dependent nonlinear theory of helix traveling wave tubes for beam- wave interaction. The radio frequency electromagnetic fields are represented as the superposition of azimuthally sym- metric waves in a vacuum sheath helix. Coupling impedance is introduced to the electromagnetic field equations＇ stimulating sources, which makes the theory easier and more flexible to realize. The space charge fields are calculated by electron beam space-charge waves expressed as the superposition solutions of Helmholtz equations. The focusing forces due to either a solenoidal field or a periodic permanent magnetic field is also included. The dynamical equations of electrons are Lorentz equations associating with electromagnetic fields, focusing fields and space-charge fields. The numerically simulated results of a tube are presented.
基金Project supported by the National Natural Science Foundation of China (NSFC) (Grant Nos. 60736005 and 60425101-1)the Foundation for Innovative Research Groups of the NSFC (Grant No. 60721001),Provincial Project (Grant No. 9140A02060609DZ0208)+1 种基金Program for New Century Excellent Talents in University (Grant No. NCET-06-0812),SRF for ROCS,SEM (Grant No. GGRYJJ08-05)Young Excellent Project of Sichuan Province (Grant No. 09ZQ026-074)
文摘The performance of an organic photovoltaic （OPV） cell based on copper phthatocyanine CuPc/C60 with a tris- （8-hydroxyquinolinato） aluminum （Alq3） buffer layer has been investigated. It was found that the power conversion efficiency of the device was 1.51% under illumination with an intensity of 100 mW/cm^2, which was limited by a squareroot dependence of the photocurrent on voltage. The photocurrent optical power density characteristics showed that the OPV cell had a significant space-charge limited photocurrent with a varied saturation voltage and a three quarters power dependence on optical power density. Also, the absorption spectrum was measured by a spectrophotometer, and the results showed that the additional Alq3 layer has a minor effect on photocurrent generation.
基金Project supported by the National Nature Science Foundation of China （Grant No 50572056）.
文摘This paper investigates the dielectric properties of （Na0.5K0.5Bi）0.5TiO3 crystal at intermediate frequencies （1kHz〈 f 〈IMHz） in the temperature range of 30-560℃. A pronounced high-temperature diffuse dielectric anomaly has been observed. This dielectric anomaly is shown to arise from a Debye-like dielectric dispersion that slows down following an Arrhenius law. The activation energy Er obtained in the fitting process is about 0.69eV. It proposes that the dielectric peak measured at low frequency above 400℃ is not related to the phase transition but to a space-charge relaxation.
基金Project supported by the National Natural Science Foundation of China （Grant No.60036010）
文摘The space-charge layer （SCL） and surface depletion area （SDA） model for beveled p-n junction is presented. The surface space-charge density is calculated for depletion case of beveled p-n junction. Based on the finite difference method, the effect of the equivalent surface charge density on the surface depletion area for positively beveled p-n junction is also studied. Thyristors passivated with polyimide （PI） or polyester improved silicon paint （SP） are fabricated to verify the effect of equivalent surface charge on the peripheral surface of beveled p-n junction. The change of leakage current is sensitive to the surface charges. It indicates that the selection of passivation materials is a significant process to ensure the breakdown voltage capability of beveled devices.
文摘For a low surface barrier, the energy band, barrier height and width of the space charge region at the surface of relatively large grains of ZnO are presented analytically on condition that the electron distribution obeys the Boltzmann statistics. It is shown that the temperature in the space charge distribution factor has an important effect on the energy band, barrier height and width of the space charge region. The depletion approximation is a model in which the temperature in the space charge distribution factor is zero. Our results are better than the depletion approximation.
基金This work was supported by the National Natural Science Foundation of China(U2030206,22075003).
文摘Lanthanum lithium titanate is one of the promising electrolytes for solid-state lithium-ion batteries due to its high bulk ionic conductivity up to∼10^(−3) S/cm.However,the practical application of this material has been bottlenecked by high grain boundary(GB)resistance,while the underlying mechanism is still under debate.Here we report a comprehensive study with direct evidence to reveal the origin of high GB resistance in La_(2/3)–xLi_(3x)TiO_(3)(LLTO).Atomic-scale observations via advanced scanning transmission electron microscopy show that the GBs are uniformly subject to subsurface segregation of La atoms to compensate for the excess surface charges.The La segregation leads to an abrupt decrease of charge carrier concentration neighboring GBs and hence is supposed to have deleterious effect on GB conductivity.The findings suggest a novel mechanism of space-charge-induced cation segregation,which shed lights on the intrinsic origin of low GB ionic conductivity in LLTO.
文摘In the study of beam dynamics of high intensity linear accelerators,full 3D multiparticle simulations are needed due to numerous nonlinear effects caused by the strong space-charge effects between charged particles.However,the use of multiparticle simulations is limited by the speed of the Particle-in-cell(PIC)algorithm.In this work,we modify the PIC algorithm by using the symmetry of beam,the solution procedure is divided into two steps,one is the solution of the symmetric field and the other is the addition of the asymmetric field components.Due to the full use of symmetry,our modified algorithm can significantly improve the computational speed of multiparticle simulations.Results show that the modified algorithm accelerates the process of solving space-charge field by a factor of 4,thus increases the speed of the entire multiparticle simulation by a factor of 1.7,while ensures the accuracy of the simulation.Although our algorithm is modified for linear accelerator,considering that the algorithm is an improvement based on symmetry,it can still speed up the simulation for any accelerator with symmetry.
基金National Natural Science Foundation of Chinathe State ScienceTechnology Committee
文摘Nanostructured amorphous silicon nitride （NASN） was obtained by compacting the particles of the order of nanometer. The volume of interfaces occupies a large fraction of the total volume. This type of solid possesses some novel physical properties. The conventional Si<sub>3</sub>N<sub>4</sub> is a kind of excellent insulator, and thus it is
基金Financial support from the National Natural Science Foundation of China(No.12174102)the National Key Research and Development Program of China(No.2021YFC3001802)the Shanghai Program for Professor of Special Appointment(Eastern Scholar)at Shanghai Institutions of Higher Learning,and Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology is gratefully acknowledged.
文摘Nowadays,the demand for advanced functional materials in transducer technology is growing rapidly.Piezoelectric materials transform mechanical variables(displacement or force)into electrical signals(charge or voltage)and vice versa.They are interesting from both fundamental and application points of view.Ferrooelectrets(also called piezoelectrets)are a relatively young group of piezo-,pyro-and ferroelectric materials.They exhibit ferroic behavior phenomenologically undistinguishable from that of traditional ferroelectrics,although the materials per se are essentially non-polar space-charge electrets with artificial macroscopic dipoles(i.e.,internally charged cavities).A lot of work has been done on ferroelectrets and their applications up to now.In this paper,we review and discuss mostly the work done at University of Potsdam on the research and development of ferroelectrets.We will,however,also mention important results from other teams,and prospect the challenges and future progress trend of the field of ferroelectret research.
基金Supported by National Natural Science Foundation of China(10635090)
文摘The SSC-linac （a new injector for the Separated Sector Cyclotron） is being designed in the HIRFL （Heavy Ion Research Facility in Lanzhou） system to accelerate 238U34＋ from 3.72 keV/u to 1.008 MeV/u. As a part of the SSC-linac injector, the HEBT （high energy beam transport） has been designed by using the TRACE-3D code and simulated by the 3D PIC （particle-in-cell） Track code. The total length of the HEBT is about 12 meters and a beam line of about 6 meters are shared with the exiting beam line of the HIRFL system. The simulation results show that the particles can be delivered efficiently in the HEBT and the particles at the exit of the HEBT well match the acceptance of the SSC for further acceleration. The dispersion is eliminated absolutely in the HEBT. The space-charge effect calculated by the Track code is inconspicuous. According to the simulation, more than 60 percent of the particles from the ion source can be transported into the acceptance of the SSC.
基金the National Natural Science Foundation of China the Doctoral Fund of Education Committee of China
文摘A novel quasi-opitcal resonance system modified axisymmetrical quasi-optical cavity of oblique ratation(MAQCOR)-is proposed using the laplace integral transormation the kinetic theory of the high relativsitic electron cyclotron maser with MAQCORis carried out within the framowrk of the linearized vlasov-mxawel eauations the formulas of beamwave intreaction power starting current and frequency shift have been derived some important plroblems such as high-order harmonic modes competition inflneces of the rationg angle and space charge and space chrage effcet are andlyaed and discussed in detall and a serios fo new condinsions are obtained a theoretical bssia is laid for the design of this novel qussi-optical gyrotron
基金supported by the National High Technology Research and Development Program of China (Nos. 2006AA01Z256, 2007AA03Z419,2007AA03Z417)the State Key Development Program for Basic Research of China (Nos. 2006CB604901,2006CB604902)the Nati-onal Natural Science Foundation of China (Nos. 90401025,60736036,60706009, 60777021)
文摘The effects of the multimode diluted waveguide on quantum efficiency and saturation behavior of the evanescently coupled uni-traveling carrier （UTC） photodiode structures are reported. Two kinds of evanescently coupled uni-traveling carrier photodiodes （EC-UTC-PD） were designed and characterized： one is a conventional EC-UTC-PD structure with a multimode diluted waveguide integrated with a UTC-PD; and the other is a compact EC-UTC-PD structure which fused the multimode diluted waveguide and the UTC-PD structure together. The effect of the absorption behavior of the photodiodes on the efficiency and saturation characteristics of the EC-UTC-PDs is analyzed using 3-D beam propagation method, and the results indicate that both the responsivity and saturation power of the compact EC-UTC-PD structures can be further improved by incorporating an optimized compact multimode diluted waveguide.
文摘In the conventional design of RF linacs, the bunched beams are not in thermal equilibrium. The space charge forces couple the particle motions between the transverse and the longitudinal directions. Furthermore it will cause the equipartitioning process which leads to emittance growth and halo formation. In the design of the China Spallation Neutron Source （CSNS） linac, three cases are investigated using the Hofmann stability charts. In this paper, we present the equipartitioning beam study of the CSNS Alvarez DTL linac.
