An improved indirect scheme for laser positron generation is proposed. The positron yields in high-ZZ metal targets irradiated by laser produced electrons from near-critical density plasmas and underdense plasma are i...An improved indirect scheme for laser positron generation is proposed. The positron yields in high-ZZ metal targets irradiated by laser produced electrons from near-critical density plasmas and underdense plasma are investigated numerically. It is found that the positron yield is mainly affected by the number of electrons of energies up to several hundreds of MeV. Using near-critical density targets for electron acceleration, the number of high energy electrons can be increased dramatically. Through start-to-end simulations, it is shown that up to 6.78×10106.78×1010 positrons can be generated with state-of-the-art Joule-class femtosecond laser systems.展开更多
This study investigates the generation of high energy photons and positrons using focused ultrahigh intensity femtosecond laser pulses on a relativistic electron beam with a set of two-dimensional particle- in-cell si...This study investigates the generation of high energy photons and positrons using focused ultrahigh intensity femtosecond laser pulses on a relativistic electron beam with a set of two-dimensional particle- in-cell simulations. We consider circularly and linearly polarized, single and spatially separated double laser pulses. We model both 500 MeV and 1 GeV electron beams. Higher positron production is obtained using circularly polarized laser pulses. Using double pulses, the focusing effect of the ponderomotive force confines the electrons to a small volume, generating additional energetic photons and positrons. The positron spectral distributions are effectively modified by these variations. When the electron beam energy is doubled, the number of positrons increased, while the cutoff energy remained nearly constant.展开更多
The generation ofγphotons and positrons using an ultrahigh-intensity laser pulse interacting with various plasma solid foils is investigated with a series of quantum electrodynamic particlein-cell(PIC)simulations.Whe...The generation ofγphotons and positrons using an ultrahigh-intensity laser pulse interacting with various plasma solid foils is investigated with a series of quantum electrodynamic particlein-cell(PIC)simulations.When ultrahigh-intensity lasers interact with plasma foils,a large amount of the laser energy is converted intoγphoton energy.The simulation results indicate that for a fixed laser intensity with different foil densities,the conversion efficiency of the laser toγphotons and the number of produced photons are highly related to the foil density.We determine the optimal foil density by PIC simulations for high conversion efficiencies as approximately 250 times the critical plasma density,and this result agrees very well with our theoretical assumptions.Four different foil thicknesses are simulated and the effects of foil thickness onγphoton emission and positron production are discussed.The results indicate that optimal foil thickness plays an important role in obtaining the desiredγphoton and positron production according to the foil density and laser intensity.Further,a relation between the laser intensity and conversion efficiency is present for the optimal foil density and thickness.展开更多
基金Supported by the National Basic Research Program of China under Grant No 2013CBA01502the National Natural Science Foundation of China under Grant Nos 11575011 and 11535001+1 种基金the National Grand Instrument Project under Grant No2012YQ030142the UK EPSRC under Grant Nos EP/G054950/1,EP/G056803/1,EP/G055165/1 and EP/M022463/1
文摘An improved indirect scheme for laser positron generation is proposed. The positron yields in high-ZZ metal targets irradiated by laser produced electrons from near-critical density plasmas and underdense plasma are investigated numerically. It is found that the positron yield is mainly affected by the number of electrons of energies up to several hundreds of MeV. Using near-critical density targets for electron acceleration, the number of high energy electrons can be increased dramatically. Through start-to-end simulations, it is shown that up to 6.78×10106.78×1010 positrons can be generated with state-of-the-art Joule-class femtosecond laser systems.
基金This work was financially supported by the National Natural Science Foundation of China （NSFC） （Grant Nos. 11664039 and 11575150）, and the Doctoral Fund of Xinjiang University （Grant Nos. BS150216 and BS150217）. A. Ablat was supported by NSFC （Grant Nos. 61464010 and 61604126）. The authors are particularly grateful to CFSA at the University of War- wick for allowing us to use the EPOCH.
文摘This study investigates the generation of high energy photons and positrons using focused ultrahigh intensity femtosecond laser pulses on a relativistic electron beam with a set of two-dimensional particle- in-cell simulations. We consider circularly and linearly polarized, single and spatially separated double laser pulses. We model both 500 MeV and 1 GeV electron beams. Higher positron production is obtained using circularly polarized laser pulses. Using double pulses, the focusing effect of the ponderomotive force confines the electrons to a small volume, generating additional energetic photons and positrons. The positron spectral distributions are effectively modified by these variations. When the electron beam energy is doubled, the number of positrons increased, while the cutoff energy remained nearly constant.
基金supported by National Natural Science Foundation of China(No.11664039)The authors are particularly grateful to CFSA at the University of Warwick for allowing us to use the EPOCH code(developed under UK EPSRC Grants(Nos.EP/G054940/1,EP/G055165/1,and EP/G056803/1)).
文摘The generation ofγphotons and positrons using an ultrahigh-intensity laser pulse interacting with various plasma solid foils is investigated with a series of quantum electrodynamic particlein-cell(PIC)simulations.When ultrahigh-intensity lasers interact with plasma foils,a large amount of the laser energy is converted intoγphoton energy.The simulation results indicate that for a fixed laser intensity with different foil densities,the conversion efficiency of the laser toγphotons and the number of produced photons are highly related to the foil density.We determine the optimal foil density by PIC simulations for high conversion efficiencies as approximately 250 times the critical plasma density,and this result agrees very well with our theoretical assumptions.Four different foil thicknesses are simulated and the effects of foil thickness onγphoton emission and positron production are discussed.The results indicate that optimal foil thickness plays an important role in obtaining the desiredγphoton and positron production according to the foil density and laser intensity.Further,a relation between the laser intensity and conversion efficiency is present for the optimal foil density and thickness.
