Experimental validation of laser intensity is particularly important for the study of fundamental physics at extremely high intensities.However,reliable diagnosis of the focal spot and peak intensity faces huge challe...Experimental validation of laser intensity is particularly important for the study of fundamental physics at extremely high intensities.However,reliable diagnosis of the focal spot and peak intensity faces huge challenges.In this work,we demonstrate for the firs time that the coherent radiation farfiel patterns from laser–foil interactions can serve as an in situ,real-time,and easy-to-implement diagnostic for an ultraintense laser focus.The laser-driven electron sheets,curved by the spatially varying laser fiel and leaving the targets at nearly the speed of light,produce doughnut-shaped patterns depending on the shapes of the focal spot and the absolute laser intensities.Assisted by particle-in-cell simulations,we can achieve measurements of the intensity and the focal spot,and provide immediate feedback to optimize the focal spots for extremely high intensity.展开更多
In this work,the high-energy-density plasmas(HEDP)evolved from joule-class-femtosecond-laser-irradiated nanowire-array(NWA)targets were numerically and experimentally studied.The results of particle-in-cell simulation...In this work,the high-energy-density plasmas(HEDP)evolved from joule-class-femtosecond-laser-irradiated nanowire-array(NWA)targets were numerically and experimentally studied.The results of particle-in-cell simulations indicate that ions accelerated in the sheath field around the surfaces of the nanowires are eventually confined in a plasma,contributing most to the high energy densities.The protons emitted from the front surfaces of the NWA targets provide rich information about the interactions that occur.We give the electron and ion energy densities for broad target parameter ranges.The ion energy densities from NWA targets were found to be an order of magnitude higher than those from planar targets,and the volume of the HEDP was several-fold greater.At optimal target parameters,8%of the laser energy can be converted to confined protons,and this results in ion energy densities at the GJ/cm^(3) level.In the experiments,the measured energy of the emitted protons reached 4 MeV,and the changes in energy with the NWA’s parameters were found to fit the simulation results well.Experimental measurements of neutrons from 2H(d,n)3He fusion with a yield of(24±18)×10^(6)/J from deuterated polyethylene NWA targets also confirmed these results.展开更多
The newly built Compact Laser Plasma Accelerator-Therapy facility at Peking University will deliver 60 J/1 Hz laser pulses with 30 fs duration.Driven by this petawatt laser facility,proton beams with energy up to 200 ...The newly built Compact Laser Plasma Accelerator-Therapy facility at Peking University will deliver 60 J/1 Hz laser pulses with 30 fs duration.Driven by this petawatt laser facility,proton beams with energy up to 200 MeV are expected to be generated for tumor therapy.During high-repetition operation,both prompt radiation and residual radiation may cause safety problems.Therefore,human radiological safety assessment before commissioning is essential.In this paper,we simulate both prompt and residual radiation using the Geant4 and FLUKA Monte Carlo codes with reasonable proton and as-produced electron beam parameters.We find that the prompt radiation can be shielded well by the concrete wall of the experimental hall,but the risk from residual radiation is nonnegligible and necessitates adequate radiation cooling.On the basis of the simulation results,we discuss the constraints imposed by radiation safety considerations on the annual working time,and we propose radiation cooling strategies for different shooting modes.展开更多
Rational design of hierarchical structures and a dual-interface built-in electric field(BIEF)are vital for enhancing dielectric loss and directional charge transport in microwave absorption materials(MAMs).Herein,we p...Rational design of hierarchical structures and a dual-interface built-in electric field(BIEF)are vital for enhancing dielectric loss and directional charge transport in microwave absorption materials(MAMs).Herein,we propose a dual-interface BIEF engineering strategy to construct a multifunctional MoS_(2)@C/CoS_(x)composites.Inspired by the spiderweb hunting mechanism,magnetic Co-based Prussian blue(PB)is electro spun with polyacrylonitrile to form Co@CoO/C nanofibers,followed by sulfidation to induce ordered array architectures.The structural evolution enables the formation of heterogeneous MoS_(2)-CoS_(x)-C interfaces and modulates the interfacial electric field intensity to enhance dielectric polarization.Density functional theory(DFT)calculations confirm that the work function difference(ΔΦ)of C/CoS_(2)/MoS_(2) is 6.179 eV,which indicates that the differencesΔΦamong MoS_(2),CoS_(x)and C components drive the spontaneous formation of dual-interface BIEF.This facilitates directional charge migration and strong dipolar/interface polarization,significantly improving the microwave attenuation capability.Benefiting from this design,the composite achieves a minimum reflection loss(RL_(min))of-63.83 dB and a maximum effective absorption bandwidth(EAB_(max))of 6.96 GHz,covering both C and Ku bands.In addition,the material reveals excellent infrared stealth performance due to its unique spiderweb-inspired ordered array structure.This study provides new insights into interfacial electric field modulation and a generalizable approach for designing multi-band and tunable microwave absorbers with synergistic electromagnetic and thermal stealth functions.展开更多
Carbon nanotube foams(CNFs)have been successfully used as near-critical-density targets in the laser-driven acceleration of high-energy ions and electrons.Here we report the recent advances in the fabrication techniqu...Carbon nanotube foams(CNFs)have been successfully used as near-critical-density targets in the laser-driven acceleration of high-energy ions and electrons.Here we report the recent advances in the fabrication technique of such targets.With the further developed floating catalyst chemical vapor deposition(FCCVD)method,large-area(>25 cm^(2))and highly uniform CNFs are successfully deposited on nanometer-thin metal or plastic foils as double-layer targets.The density and thickness of the CNF can be controlled in the range of 1−13 mg/cm^(3)and 10−200µm,respectively,by varying the synthesis parameters.The dependence of the target properties on the synthesis parameters and the details of the target characterization methods are presented for the first time.展开更多
A novel method of initiating nuclear fusion reactions in a full plasma environment was suggested, and a proof-of-concept experiment was carried out with the D ＋D → n＋3He reaction. In this new approach, two plasma j...A novel method of initiating nuclear fusion reactions in a full plasma environment was suggested, and a proof-of-concept experiment was carried out with the D ＋D → n＋3He reaction. In this new approach, two plasma jets generated by high-intensity lasers collide headon-head. The center-of-mass energy of the nuclei increases accordingly, and therefore, reaction products can be significantly enhanced, especially in the sub-Coulomb barrier ranges. As a result of the fusion reaction, up to - 7.6 ×105 neutrons had been observed. This new type of ＂plasma collider＂ could provide an innovative tool to study nuclear reactions under astrophysical conditions.展开更多
Astrophysical collisionless shocks are amazing phenomena in space and astrophysical plasmas, where supersonic flows generate electromagnetic fields through instabilities and particles can be accelerated to high energy...Astrophysical collisionless shocks are amazing phenomena in space and astrophysical plasmas, where supersonic flows generate electromagnetic fields through instabilities and particles can be accelerated to high energy cosmic rays. Until now, understanding these micro-processes is still a challenge despite rich astrophysical observation data have been obtained. Laboratory astrophysics, a new route to study the astrophysics, allows us to investigate them at similar extreme physical conditions in laboratory. Here we will review the recent progress of the collisionless shock experiments performed at SG-II laser facility in China. The evolution of the electrostatic shocks and Weibel-type/filamentation instabilities are observed. Inspired by the configurations of the counter-streaming plasma flows, we also carry out a novel plasma collider to generate energetic neutrons relevant to the astrophysical nuclear reactions.展开更多
We present laboratory measurement and theoretical analysis of silicon K-shell lines in plasmas produced by Shenguang II laser facility, and discuss the application of line ratios to diagnose the electron density and t...We present laboratory measurement and theoretical analysis of silicon K-shell lines in plasmas produced by Shenguang II laser facility, and discuss the application of line ratios to diagnose the electron density and temperature of laser plasmas.Two types of shots were carried out to interpret silicon plasma spectra under two conditions, and the spectra from 6.6 ?A to6.85 ?A were measured. The radiative-collisional code based on the flexible atomic code(RCF) is used to identify the lines, and it also well simulates the experimental spectra. Satellite lines, which are populated by dielectron capture and large radiative decay rate, influence the spectrum profile significantly. Because of the blending of lines, the traditional G value and R value are not applicable in diagnosing electron temperature and density of plasma. We take the contribution of satellite lines into the calculation of line ratios of He-α lines, and discuss their relations with the electron temperature and density.展开更多
Electrospun nanofibers with highly efficient photothermal/electrothermal performance are extremely popular because of their great potential in wearable heaters.However,the lack of necessary wearable properties such as...Electrospun nanofibers with highly efficient photothermal/electrothermal performance are extremely popular because of their great potential in wearable heaters.However,the lack of necessary wearable properties such as high mechanical strength and quick response of electrospun micro/nanofibers seriously affects their practical application.In this work,a technical route combining electrospinning and surface modification technology is proposed.The 3-triethoxysilylpropylamine-polyacrylonitrile@copper sulfide(K-PAN@CuS)composite fabric was achieved by modifying the original electrospinning PAN fiber and subsequently loading CuS nanoparticles.The results show that the break strength of the K-PAN@CuS fabric was increased by 10 times compared to that of the original PAN@CuS fabric.Furthermore,the saturated temperature of the K-PAN@CuS fabric heater could reach 116℃within 15 s at a relatively low voltage of 3 V and 120.3℃within 10 s under an infrared therapy lamp(100 W).In addition,due to its excellent conductivity,such a unique structural design enables the fiber to be closely attached to the human skin and helps to monitor human movements.This K-PAN@CuS fabric shows great potential in wearable heaters,hyperthermia,all-weather thermal management,and in vitro physical therapy.展开更多
Post-acceleration of protons in helical coil targets driven by intense,ultrashort laser pulses can enhance ion energy by utilizing the transient current from the targets’self-discharge.The acceleration length of prot...Post-acceleration of protons in helical coil targets driven by intense,ultrashort laser pulses can enhance ion energy by utilizing the transient current from the targets’self-discharge.The acceleration length of protons can exceed a few millimeters,and the acceleration gradient is of the order of GeV/m.How to ensure the synchronization between the accelerating electric field and the protons is a crucial problem for efficient post-acceleration.In this paper,we study how the electric field mismatch induced by current dispersion affects the synchronous acceleration of protons.We propose a scheme using a two-stage helical coil to control the current dispersion.With optimized parameters,the energy gain of protons is increased by four times.Proton energy is expected to reach 45 MeV using a hundreds-of-terawatts laser,or more than 100 MeV using a petawatt laser,by controlling the current dispersion.展开更多
To meet the demands of laser-ion acceleration at a high repetition rate,we have developed a comprehensive diagnostic system for real-time and in situ monitoring of liquid sheet targets(LSTs).The spatially resolved rap...To meet the demands of laser-ion acceleration at a high repetition rate,we have developed a comprehensive diagnostic system for real-time and in situ monitoring of liquid sheet targets(LSTs).The spatially resolved rapid characterizations of an LST’s thickness,flatness,tilt angle and position are fulfilled by different subsystems with high accuracy.With the help of the diagnostic system,we reveal the dependence of thickness distribution on collision parameters and report the 238-nm liquid sheet generated by the collision of two liquid jets.Control methods for the flatness and tilt angle of LSTs have also been provided,which are essential for applications of laser-driven ion acceleration and others.展开更多
基金supported by the Guangdong High Level Innovation Research Institute(Grant No.2021B0909050006)the National Grand Instrument Project(Grant No.2019YFF01014402)+1 种基金the National Natural Science Foundation of China(Grant No.12205008)support from the National Science Fund for Distinguished Young Scholars(Grant No.12225501)。
文摘Experimental validation of laser intensity is particularly important for the study of fundamental physics at extremely high intensities.However,reliable diagnosis of the focal spot and peak intensity faces huge challenges.In this work,we demonstrate for the firs time that the coherent radiation farfiel patterns from laser–foil interactions can serve as an in situ,real-time,and easy-to-implement diagnostic for an ultraintense laser focus.The laser-driven electron sheets,curved by the spatially varying laser fiel and leaving the targets at nearly the speed of light,produce doughnut-shaped patterns depending on the shapes of the focal spot and the absolute laser intensities.Assisted by particle-in-cell simulations,we can achieve measurements of the intensity and the focal spot,and provide immediate feedback to optimize the focal spots for extremely high intensity.
基金This work was supported by the NSFC innovation group project(Grant No.11921006)the National Grand Instrument Project(Grant No.2019YFF01014402)+1 种基金the United States Department of Energy(Grant No.DE-FG03-93ER40773)the NNSA(Grant No.DENA0003841)(CENTAUR).The PIC simulations were carried out using the High-Performance Computing Platform of Peking University。
文摘In this work,the high-energy-density plasmas(HEDP)evolved from joule-class-femtosecond-laser-irradiated nanowire-array(NWA)targets were numerically and experimentally studied.The results of particle-in-cell simulations indicate that ions accelerated in the sheath field around the surfaces of the nanowires are eventually confined in a plasma,contributing most to the high energy densities.The protons emitted from the front surfaces of the NWA targets provide rich information about the interactions that occur.We give the electron and ion energy densities for broad target parameter ranges.The ion energy densities from NWA targets were found to be an order of magnitude higher than those from planar targets,and the volume of the HEDP was several-fold greater.At optimal target parameters,8%of the laser energy can be converted to confined protons,and this results in ion energy densities at the GJ/cm^(3) level.In the experiments,the measured energy of the emitted protons reached 4 MeV,and the changes in energy with the NWA’s parameters were found to fit the simulation results well.Experimental measurements of neutrons from 2H(d,n)3He fusion with a yield of(24±18)×10^(6)/J from deuterated polyethylene NWA targets also confirmed these results.
基金supported by the National Natural Science Foundation of China(Grant No.12205008)the NSFC Innovation Group Project(Grant No.11921006)+1 种基金the National Grand Instrument Project(Grant Nos.2019YFF01014402 and 2019YFF01014403)the National Science Fund for Distinguished Young Scholars(Grant No.12225501).
文摘The newly built Compact Laser Plasma Accelerator-Therapy facility at Peking University will deliver 60 J/1 Hz laser pulses with 30 fs duration.Driven by this petawatt laser facility,proton beams with energy up to 200 MeV are expected to be generated for tumor therapy.During high-repetition operation,both prompt radiation and residual radiation may cause safety problems.Therefore,human radiological safety assessment before commissioning is essential.In this paper,we simulate both prompt and residual radiation using the Geant4 and FLUKA Monte Carlo codes with reasonable proton and as-produced electron beam parameters.We find that the prompt radiation can be shielded well by the concrete wall of the experimental hall,but the risk from residual radiation is nonnegligible and necessitates adequate radiation cooling.On the basis of the simulation results,we discuss the constraints imposed by radiation safety considerations on the annual working time,and we propose radiation cooling strategies for different shooting modes.
基金supported by the National Natural Science Foundation of China(No.52462026)Postdoctoral Research Foundation of China(No.2018M643699)Shaanxi Province Postdoctoral Science Foundation(No.2018BSHEDZZ 101).
文摘Rational design of hierarchical structures and a dual-interface built-in electric field(BIEF)are vital for enhancing dielectric loss and directional charge transport in microwave absorption materials(MAMs).Herein,we propose a dual-interface BIEF engineering strategy to construct a multifunctional MoS_(2)@C/CoS_(x)composites.Inspired by the spiderweb hunting mechanism,magnetic Co-based Prussian blue(PB)is electro spun with polyacrylonitrile to form Co@CoO/C nanofibers,followed by sulfidation to induce ordered array architectures.The structural evolution enables the formation of heterogeneous MoS_(2)-CoS_(x)-C interfaces and modulates the interfacial electric field intensity to enhance dielectric polarization.Density functional theory(DFT)calculations confirm that the work function difference(ΔΦ)of C/CoS_(2)/MoS_(2) is 6.179 eV,which indicates that the differencesΔΦamong MoS_(2),CoS_(x)and C components drive the spontaneous formation of dual-interface BIEF.This facilitates directional charge migration and strong dipolar/interface polarization,significantly improving the microwave attenuation capability.Benefiting from this design,the composite achieves a minimum reflection loss(RL_(min))of-63.83 dB and a maximum effective absorption bandwidth(EAB_(max))of 6.96 GHz,covering both C and Ku bands.In addition,the material reveals excellent infrared stealth performance due to its unique spiderweb-inspired ordered array structure.This study provides new insights into interfacial electric field modulation and a generalizable approach for designing multi-band and tunable microwave absorbers with synergistic electromagnetic and thermal stealth functions.
基金National Grand Instrument Project(No.2019YFF01014402)NSFC innovation group project(No.11921006)National Natural Science Foundation of China(Nos.11775010,11535001,and 61631001).
文摘Carbon nanotube foams(CNFs)have been successfully used as near-critical-density targets in the laser-driven acceleration of high-energy ions and electrons.Here we report the recent advances in the fabrication technique of such targets.With the further developed floating catalyst chemical vapor deposition(FCCVD)method,large-area(>25 cm^(2))and highly uniform CNFs are successfully deposited on nanometer-thin metal or plastic foils as double-layer targets.The density and thickness of the CNF can be controlled in the range of 1−13 mg/cm^(3)and 10−200µm,respectively,by varying the synthesis parameters.The dependence of the target properties on the synthesis parameters and the details of the target characterization methods are presented for the first time.
基金supported by the National Basic Research Program of China(2013CBA01501 and2013CB834401)the National Natural Science Foundation of China(11135012 and 11135005)+1 种基金the Doctoral Fund of Ministry of Education of China(20120073110065)Shanghai Municipal Science and Technology Commission(11DZ2260700)for the supports
文摘A novel method of initiating nuclear fusion reactions in a full plasma environment was suggested, and a proof-of-concept experiment was carried out with the D ＋D → n＋3He reaction. In this new approach, two plasma jets generated by high-intensity lasers collide headon-head. The center-of-mass energy of the nuclei increases accordingly, and therefore, reaction products can be significantly enhanced, especially in the sub-Coulomb barrier ranges. As a result of the fusion reaction, up to - 7.6 ×105 neutrons had been observed. This new type of ＂plasma collider＂ could provide an innovative tool to study nuclear reactions under astrophysical conditions.
基金supported by the Science Challenge Project (No. TZ2016005)the National Basic Program of China (No. 2013CBA01501/03)+2 种基金the National Natural Science Foundation of China (Nos. 11503041, 11522326, 11622323, and 11573040)the Strategic Priority Research Program of the Chinese Academy of Sciences (Nos. XDB16010200 and XDB07030300)the Project Funded by China Postdoctoral Science Foundation (No. 2015M571124)
文摘Astrophysical collisionless shocks are amazing phenomena in space and astrophysical plasmas, where supersonic flows generate electromagnetic fields through instabilities and particles can be accelerated to high energy cosmic rays. Until now, understanding these micro-processes is still a challenge despite rich astrophysical observation data have been obtained. Laboratory astrophysics, a new route to study the astrophysics, allows us to investigate them at similar extreme physical conditions in laboratory. Here we will review the recent progress of the collisionless shock experiments performed at SG-II laser facility in China. The evolution of the electrostatic shocks and Weibel-type/filamentation instabilities are observed. Inspired by the configurations of the counter-streaming plasma flows, we also carry out a novel plasma collider to generate energetic neutrons relevant to the astrophysical nuclear reactions.
基金supported by the Science Challenge Project(No.TZ2016005)the National Basic Research Program of China(No.2013CBA01503)+1 种基金the National Natural Science Foundation of China(Nos.10905004,11220101002,and11622323)the Fundamental Research Funds for the Central Universities
文摘We present laboratory measurement and theoretical analysis of silicon K-shell lines in plasmas produced by Shenguang II laser facility, and discuss the application of line ratios to diagnose the electron density and temperature of laser plasmas.Two types of shots were carried out to interpret silicon plasma spectra under two conditions, and the spectra from 6.6 ?A to6.85 ?A were measured. The radiative-collisional code based on the flexible atomic code(RCF) is used to identify the lines, and it also well simulates the experimental spectra. Satellite lines, which are populated by dielectron capture and large radiative decay rate, influence the spectrum profile significantly. Because of the blending of lines, the traditional G value and R value are not applicable in diagnosing electron temperature and density of plasma. We take the contribution of satellite lines into the calculation of line ratios of He-α lines, and discuss their relations with the electron temperature and density.
基金the Key Science and Technology Project of Henan Province(Grant No.222102230093).
文摘Electrospun nanofibers with highly efficient photothermal/electrothermal performance are extremely popular because of their great potential in wearable heaters.However,the lack of necessary wearable properties such as high mechanical strength and quick response of electrospun micro/nanofibers seriously affects their practical application.In this work,a technical route combining electrospinning and surface modification technology is proposed.The 3-triethoxysilylpropylamine-polyacrylonitrile@copper sulfide(K-PAN@CuS)composite fabric was achieved by modifying the original electrospinning PAN fiber and subsequently loading CuS nanoparticles.The results show that the break strength of the K-PAN@CuS fabric was increased by 10 times compared to that of the original PAN@CuS fabric.Furthermore,the saturated temperature of the K-PAN@CuS fabric heater could reach 116℃within 15 s at a relatively low voltage of 3 V and 120.3℃within 10 s under an infrared therapy lamp(100 W).In addition,due to its excellent conductivity,such a unique structural design enables the fiber to be closely attached to the human skin and helps to monitor human movements.This K-PAN@CuS fabric shows great potential in wearable heaters,hyperthermia,all-weather thermal management,and in vitro physical therapy.
基金the NSFC Innovation Group Project(No.11921006)the National Grand Instrument Project(No.2019YFF01014402)+1 种基金the Guangdong Provincial Science and Technology Plan Project(No.2021B0909050006)the National Science Fund for Distinguished Young Scholars(No.12225501).
文摘Post-acceleration of protons in helical coil targets driven by intense,ultrashort laser pulses can enhance ion energy by utilizing the transient current from the targets’self-discharge.The acceleration length of protons can exceed a few millimeters,and the acceleration gradient is of the order of GeV/m.How to ensure the synchronization between the accelerating electric field and the protons is a crucial problem for efficient post-acceleration.In this paper,we study how the electric field mismatch induced by current dispersion affects the synchronous acceleration of protons.We propose a scheme using a two-stage helical coil to control the current dispersion.With optimized parameters,the energy gain of protons is increased by four times.Proton energy is expected to reach 45 MeV using a hundreds-of-terawatts laser,or more than 100 MeV using a petawatt laser,by controlling the current dispersion.
文摘To meet the demands of laser-ion acceleration at a high repetition rate,we have developed a comprehensive diagnostic system for real-time and in situ monitoring of liquid sheet targets(LSTs).The spatially resolved rapid characterizations of an LST’s thickness,flatness,tilt angle and position are fulfilled by different subsystems with high accuracy.With the help of the diagnostic system,we reveal the dependence of thickness distribution on collision parameters and report the 238-nm liquid sheet generated by the collision of two liquid jets.Control methods for the flatness and tilt angle of LSTs have also been provided,which are essential for applications of laser-driven ion acceleration and others.
