This research examines the dynamics of a cosh-Gaussian laser pulse travelling through a vacuum and its impact on electron acceleration. We examine the impact of several critical factors, such as laser electric field a...This research examines the dynamics of a cosh-Gaussian laser pulse travelling through a vacuum and its impact on electron acceleration. We examine the impact of several critical factors, such as laser electric field amplitude, decentered parameter, beam waist, and laser chirp parameter, on the energy gain of electrons using coupled momentum equations. Our results indicate that the energy acquisition of electrons escalates with the amplitude of the laser electric field, decentered parameter, and chirp parameter. An appropriate beam waist is essential for attaining energyefficient electron acceleration in a vacuum. Through the optimization of these parameters, we get a maximum electron energy gain of 2.80 Ge V. This study highlights the significance of customized laser pulse attributes in improving electron acceleration and aids in the progression of high-energy particle physics.展开更多
The electron energy spectrum is one of the most important characteristics of an electron beam that is extracted from a linear accelerator. The most direct way to determine an electron spectrum would be to use a magnet...The electron energy spectrum is one of the most important characteristics of an electron beam that is extracted from a linear accelerator. The most direct way to determine an electron spectrum would be to use a magnetic spectrometer and this method could also give results with high precision and effectiveness. In this article we describe our design of a new multi-layer absorption method, which is based on the depth-dose curves method that can be used in most irradiation accelerators, and adds the Monte Carlo simulation and iterative algorithm in order to reconstruct the electron energy spectrum. In this article the energy spectrum was measured using these two methods, and good results were acquired. These results could be crosschecked, which made the results more reliable.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
Dynamitron DC1500/25/04 type EBA （Electron beam accelerator）, model JOB 188, was manufactured by IBA Industrial （Radiation Dynamics, Inc.） and installed at IPEN-CNEN/SP, in 1978. The technical specifications of th...Dynamitron DC1500/25/04 type EBA （Electron beam accelerator）, model JOB 188, was manufactured by IBA Industrial （Radiation Dynamics, Inc.） and installed at IPEN-CNEN/SP, in 1978. The technical specifications of the EBA are： energy 0.5 to 1.5 MeV; beam current： 0.3 to 25.0 mA; beam scanning： 60 to 120 cm; beam width： 25.4 mm and frequency： 100 Hz. Nowadays, this accelerator has been used for innumerable applications, such as： For sterilization of medical, pharmaceutical and biological products, treatment of industrial and domestic effluents and sludge, preservation and disinfestations of foods and agricultural products. Other important application are lignocellulosic material irradiation as a pre-treatment to produce ethanol bio-fuel, decontamination of pesticide packing, solid residues remediation, organic compounds removal from wastewater, treatment of effluent from petroleum production units, crosslinking of foams, wires and electric cables. Electron accelerator JOB 188 is, also, very important composite and nanocomposite materials and carbon fibers irradiation, irradiated grafting ion-exchange membranes for fuel cells application, natural polymers and multilayer packages irradiation and biodegradable blends production. The energy of the electron beam is calculated as a function of the current in the accelerator high-voltage divisor, taking into account the thickness and density of the material to be irradiated. This energy is calculated considering the electron through the entire material and the distance from the titanium foil window, so that the absorbed doses at the points of entrance and exit are equivalent on the material. The dose is directly proportional to the beam current and the exposure time of the material under the electron beam and inversely proportional to the scan width. The aim of this paper is to analyze the power system parameters of the EBA Dynamitron DC 1500/25/04, such as, voltage and RMS （Root-mean-square） current in the oscillator system, high voltage generator and waveform. For this purpose software developed in the Radiation Technology Center at IPEN/CNEN-SP to simulate the energy efficiency of this industrial accelerator. Finally, it is also targeted to compare theoretical dosimetry using parameters of energy and beam current with data from the accelerator power system. This knowledge and technology will be very useful and essential for the control system upgrade of EBA, mainly Dynamitron DC 1500/25/04 taking into consideration that radiation processing technology for industrial and environmental applications has been developed and used worldwide.展开更多
The irradiation of few-nm-thick targets by a finite-contrast high-intensity short-pulse laser results in a strong pre-expansion of these targets at the arrival time of the main pulse.The targets decompress to near and...The irradiation of few-nm-thick targets by a finite-contrast high-intensity short-pulse laser results in a strong pre-expansion of these targets at the arrival time of the main pulse.The targets decompress to near and lower than critical densities with plasmas extending over few micrometers,i.e.multiple wavelengths.The interaction of the main pulse with such a highly localized but inhomogeneous target leads to the generation of a short channel and further self-focusing of the laser beam.Experiments at the Glass Hybrid OPCPA Scaled Test-bed(GHOST)laser system at University of Texas,Austin using such targets measured non-Maxwellian,peaked electron distribution with large bunch charge and high electron density in the laser propagation direction.These results are reproduced in 2D PIC simulations using the EPOCH code,identifying direct laser acceleration(DLA)[1]as the responsible mechanism.This is the first time that DLA has been observed to produce peaked spectra as opposed to broad,Maxwellian spectra observed in earlier experiments[2].This high-density electrons have potential applications as injector beams for a further wakefield acceleration stage as well as for pump-probe applications.展开更多
In layered optimization scheme and solid state cathodoluminescence, silicon oxide plays a very important role in obtaining high energy hot electrons to excite luminescent centers or organic luminescent ma terials. The...In layered optimization scheme and solid state cathodoluminescence, silicon oxide plays a very important role in obtaining high energy hot electrons to excite luminescent centers or organic luminescent ma terials. The acceleration ability of electrons of SiO2 and ZnS was compared through the variation of emission intensity based on ZnS：Er phosphor during the reverse of polarity of sinusoidal voltage. The ratio of maximum emission intensity under positive and negative half period is 2.18. This result not only demonstrates that parts of primary electron comes from electrode, but electrons in conduction band of SiO2 can be heated to higher energy than that of ZnS.展开更多
This paper investigates the properties of the ultrashort pulsed beam aimed to the capture-and-acceleration-scenario （CAS） vacuum electron acceleration. The result shows that the spatiotemporal distribution of the ph...This paper investigates the properties of the ultrashort pulsed beam aimed to the capture-and-acceleration-scenario （CAS） vacuum electron acceleration. The result shows that the spatiotemporal distribution of the phase velocity, the longitudinal component of the electric field and the acceleration quality factor are qualitatively similar to that of the continuous-wave Gaussian beam, and are slightly influenced by the spatiotemporal coupling of the ultrashort pulsed beam. When the pulse is compressed to an ultrashort one in which the pulse duration TFWHM 〈 5T0, the variation of the maximum net energy gain due to the carrier-envelope phase is a crucial disadvantage in the CAS acceleration process.展开更多
Electron acceleration in plasma driven by circular polarized ultraintense laser with asymmetric pulse axe investigated analytically and numerically in terms of oscillation-center Hamiltonian formalism. Studies include...Electron acceleration in plasma driven by circular polarized ultraintense laser with asymmetric pulse axe investigated analytically and numerically in terms of oscillation-center Hamiltonian formalism. Studies include wakefield acceleration, which dominates in blow-out or bubble regime and snow-plow acceleration which dominates in supra-bubble regime. By a comparison with each other it is found that snow-plow acceleration has lower acceleration capability. In wakefield acceleration, there exists an obvious optimum pulse asymmetry or/and pulse lengths that leads to the high net energy gain while in snow-plow acceleration it is insensitive to the pulse lengths. Power and linear scaling laws for wakefield and snow-plow acceleration respetively are observed from the net energy gain depending on laser field amplitude. Moreover, there exists also an upper and lower limit on plasma density for an effective acceleration in both of regimes.展开更多
Within the framework of plane-wave angular spectrum analysis of the electromagnetic field structure, a solution valid for tightly focused radially polarized few-cycle laser pulses propagating in vacuum is presented. T...Within the framework of plane-wave angular spectrum analysis of the electromagnetic field structure, a solution valid for tightly focused radially polarized few-cycle laser pulses propagating in vacuum is presented. The resulting field distribution is significantly different from that based on the paraxial approximation for pulses with either small or large beam diameters. We compare the electron accelerations obtained with the two solutions and find that the energy gain obtained with our new solution is usually much larger than that with the paraxial approximation solution.展开更多
With the development of photocathode rf electron gun, electrons with high-brightness and mono-energy can be obtained easily. By numerically solving the relativistic equations of motion of an electron generated from th...With the development of photocathode rf electron gun, electrons with high-brightness and mono-energy can be obtained easily. By numerically solving the relativistic equations of motion of an electron generated from this facility in laser fields modelled by a circular polarized Gaussian laser pulse, we find the electron can obtain high energy gain from the laser pulse. The corresponding acceleration distance for this electron driven by the ascending part of the laser pulse is much longer than the Rayleigh length, and the light amplitude experienced on the electron is very weak when the laser pulse overtakes the electron. The electron is accelerated effectively and the deceleration can be neglected.For intensities around 1019 W·μm2/cm2,an electron's energy gain near 0.1 GeV can be realized when its initial energy is 4.5 MeV, and the final velocity of the energetic electron is parallel with the propagation axis. The energy gain can be up to 1 GeV if the intensity is about 1021 W·μm2/cm2.The final energy gain of the electron as a function of its initial conditions and the parameters of the laser beam has also been discussed.展开更多
In this paper,a radially polarised cosh-Gaussian laser beam(CGLB)is used to study the electron acceleration produced in vacuum.A highly energetic electron beam can be achieved by a CGLB,even with comparatively low-pow...In this paper,a radially polarised cosh-Gaussian laser beam(CGLB)is used to study the electron acceleration produced in vacuum.A highly energetic electron beam can be achieved by a CGLB,even with comparatively low-powered lasers.The properties of a CGLB cause it to focus earlier,over a shorter duration than a Gaussian laser beam,which makes it suitable for obtaining high energies over small durations.It is found that the energy gained by the electrons strongly depends upon the decentering parameter of the laser profile.It is also observed that for a fixed value of energy gain,if the decentering parameter is increased,then the intensity of the laser field decreases.The dependence of the energy gained by electrons on the laser intensity and the laserspot size is also studied.展开更多
We present analytical studies of electron acceleration in the low-density preplasma of a thin solid target byan intense femtosecond laser pulse.Electrons in the preplasma are trapped and accelerated by the ponderomoti...We present analytical studies of electron acceleration in the low-density preplasma of a thin solid target byan intense femtosecond laser pulse.Electrons in the preplasma are trapped and accelerated by the ponderomotive forceas well as the wake field.Two-dimensional particle-in-cell simulations show that when the laser pulse is stopped by thetarget,electrons trapped in the laser pules can be extracted and move forward inertially.The energetic electron bunchin the bubble is unaffected by the reflected pulse and passes through the target with small energy spread and emittance.There is an optimal preplasma density for the generation of the monoenergetic electron bunch if a laser pulse is given.The maximum electron energy is inverse proportion to the preplasma density.展开更多
The magnetic merging process related to pairwise magnetic islands coalescence is investigated by two-dimensional particle-in-cell simulations with a guide field.Owing to the force of attraction between parallel curren...The magnetic merging process related to pairwise magnetic islands coalescence is investigated by two-dimensional particle-in-cell simulations with a guide field.Owing to the force of attraction between parallel currents within the initial magnetic islands,the magnetic islands begin to approach each other and merge into one big island.We find that this newly formed island is unstable and can be divided into two small magnetic islands spontaneously.Lastly,these two small islands merge again.We follow the time evolution of this process,in which the contributions of three mechanisms of electron acceleration at different stages,including the Fermi,parallel electric field,and betatron mechanisms,are studied with the guide center theory.展开更多
The basic physical characteristics of electrons accelerated by two linearly polarized and circularly symmetric crossed Laguerre-Gaussian （LG） laser beams with equal frequency and amplitude in vacuum are studied in d...The basic physical characteristics of electrons accelerated by two linearly polarized and circularly symmetric crossed Laguerre-Gaussian （LG） laser beams with equal frequency and amplitude in vacuum are studied in detail. The condition, under which electrons can be accelerated effectively, and the energy gain are discussed.展开更多
Relativistic magnetic reconnection(MR)driven by two ultra-intense lasers with different spot separation distances is simulated by a three-dimensional(3D)kinetic relativistic particle-in-cell(PIC)code.We find that chan...Relativistic magnetic reconnection(MR)driven by two ultra-intense lasers with different spot separation distances is simulated by a three-dimensional(3D)kinetic relativistic particle-in-cell(PIC)code.We find that changing the separation distance between two laser spots can lead to different magnetization parameters of the laser plasma environment.As the separation distance becomes larger,the magnetization parameterσbecomes smaller.The electrons are accelerated in these MR processes and their energy spectra can be fitted with double power-law spectra whose index will increase with increasing separation distance.Moreover,the collisionless shocks’contribution to energetic electrons is close to the magnetic reconnection contribution withσdecreasing,which results in a steeper electron energy spectrum.Basing on the3D outflow momentum configuration,the energetic electron spectra are recounted and their spectrum index is close to 1 in these three cases because the magnetization parameterσis very high in the 3D outflow area.展开更多
We study the dynamics of single electron in an inhomogeneous cylindrical plasma channel during the direct acceleration by linearly polarized chirped laser pulse.By adjusting the parameters of the chirped laser pulse a...We study the dynamics of single electron in an inhomogeneous cylindrical plasma channel during the direct acceleration by linearly polarized chirped laser pulse.By adjusting the parameters of the chirped laser pulse and the plasma channel,we obtain the energy gain,trajectory,dephasing rate and unstable threshold of electron oscillation in the channel.The influences of the chirped factor and inhomogeneous plasma density distribution on the electron dynamics are discussed in depth.We find that the nonlinearly chirped laser pulse and the inhomogeneous plasma channel have strong coupled influence on the electron dynamics.The electron energy gain can be enhanced,the instability threshold of the electron oscillation can be lowered,and the acceleration length can be shortened by chirped laser,while the inhomogeneity of the plasma channel can reduce the amplitude of the chirped laser.展开更多
In this study,we investigate the generation of parametric decay instability,Langmuir turbulence formation,and electron acceleration in ionospheric heating via a two-fluid model using the Fokker-Planck equation and Vla...In this study,we investigate the generation of parametric decay instability,Langmuir turbulence formation,and electron acceleration in ionospheric heating via a two-fluid model using the Fokker-Planck equation and Vlasov-Poisson system simulations.The simulation results of both the magnetofluid model and the kinetic model demonstrate the dynamics of electron acceleration.Further,the results of the Vlasov-Poisson simulations suggest the formation of electron holes in phase space at the same spatial scale as the Langmuir wave,which are shown to be related to electron acceleration.In addition,electron acceleration is enhanced through the extension of the wavenumber spectrum caused by strong Langmuir turbulence,leading to more electron holes in phase space.展开更多
The direct acceleration of electrons by using two linearly polarized crossed Bessel-Gaussian （BG） beams with equal frequency and amplitude in vacuum is proposed and studied. It is shown that two linearly polarized B...The direct acceleration of electrons by using two linearly polarized crossed Bessel-Gaussian （BG） beams with equal frequency and amplitude in vacuum is proposed and studied. It is shown that two linearly polarized BG beams of the same order （0 or 1） with a π-rad phase difference have a resultant non-zero longitudinal electric field on the z-axis and can be used, in principle, to accelerate electrons.展开更多
By numerically solving the relativistic equations of motion of a single electron in laserfields modeled by a Gaussian laser beam, we get the trajectory and energy of the electron. Whenthe drifting distance is comparab...By numerically solving the relativistic equations of motion of a single electron in laserfields modeled by a Gaussian laser beam, we get the trajectory and energy of the electron. Whenthe drifting distance is comparable to or even longer than the corresponding Rayleigh length, theevolution of the beam waist cannot be neglected. The asymmetry of intensity in acceleration anddeceleration leads to the conclusion that the electron can be accelerated effectively and extracted bythe longitudinal ponderomotive force. For intensities above 10～(19) Wμm～2/cm～2, an electron's energygain about MeV can be realized, and the energetic electron is parallel with the propagation axis.展开更多
Electron dynamics in the fields associated with a transverse magnetic （TM） wave propagating inside a rectangular waveguide is analytically studied. The relativistic momentum and energy equations for an electron are ...Electron dynamics in the fields associated with a transverse magnetic （TM） wave propagating inside a rectangular waveguide is analytically studied. The relativistic momentum and energy equations for an electron are solved, which was injected initially along the propagation direction of the microwave. Expressions of the acceleration gradient and deflection angle are obtained. In principle, it is shown that the electron can be accelerated in this condition and there is no deflection when the electron is injected from the centre of the waveguide front. However, it is found that the acceleration gradient and deflection angle depend strongly on the parameters of the microwave （intensity, frequency, etc.） and the dimensions of the waveguide.展开更多
文摘This research examines the dynamics of a cosh-Gaussian laser pulse travelling through a vacuum and its impact on electron acceleration. We examine the impact of several critical factors, such as laser electric field amplitude, decentered parameter, beam waist, and laser chirp parameter, on the energy gain of electrons using coupled momentum equations. Our results indicate that the energy acquisition of electrons escalates with the amplitude of the laser electric field, decentered parameter, and chirp parameter. An appropriate beam waist is essential for attaining energyefficient electron acceleration in a vacuum. Through the optimization of these parameters, we get a maximum electron energy gain of 2.80 Ge V. This study highlights the significance of customized laser pulse attributes in improving electron acceleration and aids in the progression of high-energy particle physics.
文摘The electron energy spectrum is one of the most important characteristics of an electron beam that is extracted from a linear accelerator. The most direct way to determine an electron spectrum would be to use a magnetic spectrometer and this method could also give results with high precision and effectiveness. In this article we describe our design of a new multi-layer absorption method, which is based on the depth-dose curves method that can be used in most irradiation accelerators, and adds the Monte Carlo simulation and iterative algorithm in order to reconstruct the electron energy spectrum. In this article the energy spectrum was measured using these two methods, and good results were acquired. These results could be crosschecked, which made the results more reliable.
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.
文摘Dynamitron DC1500/25/04 type EBA （Electron beam accelerator）, model JOB 188, was manufactured by IBA Industrial （Radiation Dynamics, Inc.） and installed at IPEN-CNEN/SP, in 1978. The technical specifications of the EBA are： energy 0.5 to 1.5 MeV; beam current： 0.3 to 25.0 mA; beam scanning： 60 to 120 cm; beam width： 25.4 mm and frequency： 100 Hz. Nowadays, this accelerator has been used for innumerable applications, such as： For sterilization of medical, pharmaceutical and biological products, treatment of industrial and domestic effluents and sludge, preservation and disinfestations of foods and agricultural products. Other important application are lignocellulosic material irradiation as a pre-treatment to produce ethanol bio-fuel, decontamination of pesticide packing, solid residues remediation, organic compounds removal from wastewater, treatment of effluent from petroleum production units, crosslinking of foams, wires and electric cables. Electron accelerator JOB 188 is, also, very important composite and nanocomposite materials and carbon fibers irradiation, irradiated grafting ion-exchange membranes for fuel cells application, natural polymers and multilayer packages irradiation and biodegradable blends production. The energy of the electron beam is calculated as a function of the current in the accelerator high-voltage divisor, taking into account the thickness and density of the material to be irradiated. This energy is calculated considering the electron through the entire material and the distance from the titanium foil window, so that the absorbed doses at the points of entrance and exit are equivalent on the material. The dose is directly proportional to the beam current and the exposure time of the material under the electron beam and inversely proportional to the scan width. The aim of this paper is to analyze the power system parameters of the EBA Dynamitron DC 1500/25/04, such as, voltage and RMS （Root-mean-square） current in the oscillator system, high voltage generator and waveform. For this purpose software developed in the Radiation Technology Center at IPEN/CNEN-SP to simulate the energy efficiency of this industrial accelerator. Finally, it is also targeted to compare theoretical dosimetry using parameters of energy and beam current with data from the accelerator power system. This knowledge and technology will be very useful and essential for the control system upgrade of EBA, mainly Dynamitron DC 1500/25/04 taking into consideration that radiation processing technology for industrial and environmental applications has been developed and used worldwide.
基金supported by NNSA cooperative agreement DE-NA0002008the Defense Advanced Research Projects Agency's PULSE program(12-63-PULSE-FP014)the Air Force Office of Scientific Research(FA9550-14-1-0045).
文摘The irradiation of few-nm-thick targets by a finite-contrast high-intensity short-pulse laser results in a strong pre-expansion of these targets at the arrival time of the main pulse.The targets decompress to near and lower than critical densities with plasmas extending over few micrometers,i.e.multiple wavelengths.The interaction of the main pulse with such a highly localized but inhomogeneous target leads to the generation of a short channel and further self-focusing of the laser beam.Experiments at the Glass Hybrid OPCPA Scaled Test-bed(GHOST)laser system at University of Texas,Austin using such targets measured non-Maxwellian,peaked electron distribution with large bunch charge and high electron density in the laser propagation direction.These results are reproduced in 2D PIC simulations using the EPOCH code,identifying direct laser acceleration(DLA)[1]as the responsible mechanism.This is the first time that DLA has been observed to produce peaked spectra as opposed to broad,Maxwellian spectra observed in earlier experiments[2].This high-density electrons have potential applications as injector beams for a further wakefield acceleration stage as well as for pump-probe applications.
文摘In layered optimization scheme and solid state cathodoluminescence, silicon oxide plays a very important role in obtaining high energy hot electrons to excite luminescent centers or organic luminescent ma terials. The acceleration ability of electrons of SiO2 and ZnS was compared through the variation of emission intensity based on ZnS：Er phosphor during the reverse of polarity of sinusoidal voltage. The ratio of maximum emission intensity under positive and negative half period is 2.18. This result not only demonstrates that parts of primary electron comes from electrode, but electrons in conduction band of SiO2 can be heated to higher energy than that of ZnS.
基金Project supported by the Natural Science Foundation of China （Grant Nos 60538010, 10335030 and 10376009）, the Science and Technology Commission of Shanghai, China （Grant Nos 05JC14005 and 05SG02）, and the Graduate Science and Technology Innovation Foundation of Fudan University, China.
文摘This paper investigates the properties of the ultrashort pulsed beam aimed to the capture-and-acceleration-scenario （CAS） vacuum electron acceleration. The result shows that the spatiotemporal distribution of the phase velocity, the longitudinal component of the electric field and the acceleration quality factor are qualitatively similar to that of the continuous-wave Gaussian beam, and are slightly influenced by the spatiotemporal coupling of the ultrashort pulsed beam. When the pulse is compressed to an ultrashort one in which the pulse duration TFWHM 〈 5T0, the variation of the maximum net energy gain due to the carrier-envelope phase is a crucial disadvantage in the CAS acceleration process.
基金Supported by the National Natural Science Foundation of China(NSFC)under Grant Nos.10875015 and 10834008
文摘Electron acceleration in plasma driven by circular polarized ultraintense laser with asymmetric pulse axe investigated analytically and numerically in terms of oscillation-center Hamiltonian formalism. Studies include wakefield acceleration, which dominates in blow-out or bubble regime and snow-plow acceleration which dominates in supra-bubble regime. By a comparison with each other it is found that snow-plow acceleration has lower acceleration capability. In wakefield acceleration, there exists an obvious optimum pulse asymmetry or/and pulse lengths that leads to the high net energy gain while in snow-plow acceleration it is insensitive to the pulse lengths. Power and linear scaling laws for wakefield and snow-plow acceleration respetively are observed from the net energy gain depending on laser field amplitude. Moreover, there exists also an upper and lower limit on plasma density for an effective acceleration in both of regimes.
基金supported by the National Natural Science Foundation of China (Grant Nos.10734130,10935002,and 11075105)the National Basic Research Program of China (Grant No.2009GB105002)
文摘Within the framework of plane-wave angular spectrum analysis of the electromagnetic field structure, a solution valid for tightly focused radially polarized few-cycle laser pulses propagating in vacuum is presented. The resulting field distribution is significantly different from that based on the paraxial approximation for pulses with either small or large beam diameters. We compare the electron accelerations obtained with the two solutions and find that the energy gain obtained with our new solution is usually much larger than that with the paraxial approximation solution.
基金中国科学院特别支持项目，国家自然科学基金，National High-Technology ICF Committee of China，the State Key Basic Research Special Foundation
文摘With the development of photocathode rf electron gun, electrons with high-brightness and mono-energy can be obtained easily. By numerically solving the relativistic equations of motion of an electron generated from this facility in laser fields modelled by a circular polarized Gaussian laser pulse, we find the electron can obtain high energy gain from the laser pulse. The corresponding acceleration distance for this electron driven by the ascending part of the laser pulse is much longer than the Rayleigh length, and the light amplitude experienced on the electron is very weak when the laser pulse overtakes the electron. The electron is accelerated effectively and the deceleration can be neglected.For intensities around 1019 W·μm2/cm2,an electron's energy gain near 0.1 GeV can be realized when its initial energy is 4.5 MeV, and the final velocity of the energetic electron is parallel with the propagation axis. The energy gain can be up to 1 GeV if the intensity is about 1021 W·μm2/cm2.The final energy gain of the electron as a function of its initial conditions and the parameters of the laser beam has also been discussed.
文摘In this paper,a radially polarised cosh-Gaussian laser beam(CGLB)is used to study the electron acceleration produced in vacuum.A highly energetic electron beam can be achieved by a CGLB,even with comparatively low-powered lasers.The properties of a CGLB cause it to focus earlier,over a shorter duration than a Gaussian laser beam,which makes it suitable for obtaining high energies over small durations.It is found that the energy gained by the electrons strongly depends upon the decentering parameter of the laser profile.It is also observed that for a fixed value of energy gain,if the decentering parameter is increased,then the intensity of the laser field decreases.The dependence of the energy gained by electrons on the laser intensity and the laserspot size is also studied.
基金Supported by the National Natural Science Foundation of China under Grant Nos.10875015,10834008,10963002the 973 Program under Grant No.2006CB806004Educational Commission of Jiangxi Province of China under Grant No.GJJ10052
文摘We present analytical studies of electron acceleration in the low-density preplasma of a thin solid target byan intense femtosecond laser pulse.Electrons in the preplasma are trapped and accelerated by the ponderomotive forceas well as the wake field.Two-dimensional particle-in-cell simulations show that when the laser pulse is stopped by thetarget,electrons trapped in the laser pules can be extracted and move forward inertially.The energetic electron bunchin the bubble is unaffected by the reflected pulse and passes through the target with small energy spread and emittance.There is an optimal preplasma density for the generation of the monoenergetic electron bunch if a laser pulse is given.The maximum electron energy is inverse proportion to the preplasma density.
基金supported by the National Natural Science Foundation of China(Grant Nos.41804159 and 41774169)the Key Research Program of Frontier Sciences,Chinese Academy of Sciences(Grant No.QYZDJ-SSW-DQC010)。
文摘The magnetic merging process related to pairwise magnetic islands coalescence is investigated by two-dimensional particle-in-cell simulations with a guide field.Owing to the force of attraction between parallel currents within the initial magnetic islands,the magnetic islands begin to approach each other and merge into one big island.We find that this newly formed island is unstable and can be divided into two small magnetic islands spontaneously.Lastly,these two small islands merge again.We follow the time evolution of this process,in which the contributions of three mechanisms of electron acceleration at different stages,including the Fermi,parallel electric field,and betatron mechanisms,are studied with the guide center theory.
基金Project supported by the National Natural Science Foundation of China （Grant No 10574097）.
文摘The basic physical characteristics of electrons accelerated by two linearly polarized and circularly symmetric crossed Laguerre-Gaussian （LG） laser beams with equal frequency and amplitude in vacuum are studied in detail. The condition, under which electrons can be accelerated effectively, and the energy gain are discussed.
基金supported by the National Natural Science Foundation of China(Grant Nos.U1930108,12175018,12135001,12075030,and 11903006)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA25030700)。
文摘Relativistic magnetic reconnection(MR)driven by two ultra-intense lasers with different spot separation distances is simulated by a three-dimensional(3D)kinetic relativistic particle-in-cell(PIC)code.We find that changing the separation distance between two laser spots can lead to different magnetization parameters of the laser plasma environment.As the separation distance becomes larger,the magnetization parameterσbecomes smaller.The electrons are accelerated in these MR processes and their energy spectra can be fitted with double power-law spectra whose index will increase with increasing separation distance.Moreover,the collisionless shocks’contribution to energetic electrons is close to the magnetic reconnection contribution withσdecreasing,which results in a steeper electron energy spectrum.Basing on the3D outflow momentum configuration,the energetic electron spectra are recounted and their spectrum index is close to 1 in these three cases because the magnetization parameterσis very high in the 3D outflow area.
基金the National Natural Science Foundation of China(Grant Nos.11865014,11765017,11764039,11475027,11274255,and 11305132)the Natural Science Foundation of Gansu Province of China(Grant No.17JR5RA076)+2 种基金the Scientific Research Project of Gansu Higher Education of China(Grant No.2016A-005)the Natural Science Foundation of Education Department of Guizhou Province of China(Grant No.Qianjiaohe-KY-[2017]301)the Science and Technology Project of Guizhou Province of China(Grant No.Qiankehe-LH-[2017]7008).
文摘We study the dynamics of single electron in an inhomogeneous cylindrical plasma channel during the direct acceleration by linearly polarized chirped laser pulse.By adjusting the parameters of the chirped laser pulse and the plasma channel,we obtain the energy gain,trajectory,dephasing rate and unstable threshold of electron oscillation in the channel.The influences of the chirped factor and inhomogeneous plasma density distribution on the electron dynamics are discussed in depth.We find that the nonlinearly chirped laser pulse and the inhomogeneous plasma channel have strong coupled influence on the electron dynamics.The electron energy gain can be enhanced,the instability threshold of the electron oscillation can be lowered,and the acceleration length can be shortened by chirped laser,while the inhomogeneity of the plasma channel can reduce the amplitude of the chirped laser.
基金supported by the National Natural Science Foundation of China (NSFC Grant Nos. 42104150, 42074187, 41774162, and 41704155)the Foundation of the National Key Laboratory of Electromagnetic Environment (Grant No. 6142403200303)+3 种基金the Chinese Academy of Sciences, Key Laboratory of Geospace Environmentthe University of Science & Technology of China (Grant No. GE2020-01)the Fundamental Research Funds for the Central Universities (Grant No. 2042021kf0020)the Excellent Youth Foundation of Hubei Provincial Natural Science Foundation (Grant No. 2019CFA054)
文摘In this study,we investigate the generation of parametric decay instability,Langmuir turbulence formation,and electron acceleration in ionospheric heating via a two-fluid model using the Fokker-Planck equation and Vlasov-Poisson system simulations.The simulation results of both the magnetofluid model and the kinetic model demonstrate the dynamics of electron acceleration.Further,the results of the Vlasov-Poisson simulations suggest the formation of electron holes in phase space at the same spatial scale as the Langmuir wave,which are shown to be related to electron acceleration.In addition,electron acceleration is enhanced through the extension of the wavenumber spectrum caused by strong Langmuir turbulence,leading to more electron holes in phase space.
基金Project supported by the National Natural Science Foundation of China （Grant No 10574097）.
文摘The direct acceleration of electrons by using two linearly polarized crossed Bessel-Gaussian （BG） beams with equal frequency and amplitude in vacuum is proposed and studied. It is shown that two linearly polarized BG beams of the same order （0 or 1） with a π-rad phase difference have a resultant non-zero longitudinal electric field on the z-axis and can be used, in principle, to accelerate electrons.
基金The project supported by the Special Foundation for P. Lu from Chinese Academy of Science, the National Natural Science Foundation of China (No.10375083), the National High-Technology ICF Committee in China, and the National key Basic Research Special Fo
文摘By numerically solving the relativistic equations of motion of a single electron in laserfields modeled by a Gaussian laser beam, we get the trajectory and energy of the electron. Whenthe drifting distance is comparable to or even longer than the corresponding Rayleigh length, theevolution of the beam waist cannot be neglected. The asymmetry of intensity in acceleration anddeceleration leads to the conclusion that the electron can be accelerated effectively and extracted bythe longitudinal ponderomotive force. For intensities above 10～(19) Wμm～2/cm～2, an electron's energygain about MeV can be realized, and the energetic electron is parallel with the propagation axis.
文摘Electron dynamics in the fields associated with a transverse magnetic （TM） wave propagating inside a rectangular waveguide is analytically studied. The relativistic momentum and energy equations for an electron are solved, which was injected initially along the propagation direction of the microwave. Expressions of the acceleration gradient and deflection angle are obtained. In principle, it is shown that the electron can be accelerated in this condition and there is no deflection when the electron is injected from the centre of the waveguide front. However, it is found that the acceleration gradient and deflection angle depend strongly on the parameters of the microwave （intensity, frequency, etc.） and the dimensions of the waveguide.
