摘要
超短脉冲激光与靶相互作用可产生高能电子以及质子、离子、X/γ射线等次级粒子和射线,这些粒子和射线在惯性约束聚变、激光核物理、实验室天体物理、生物、医学以及材料科学等领域具有广泛的应用前景.高能电子的特征参数测量对理清激光等离子体相互作用过程、优化粒子参数和拓展其应用具有重要意义.本文研究设计了一款紧凑型矩形结构磁谱仪,在永磁铁均匀场中采用前、侧、后三面IP板布局,满足了几十 keV到10 MeV的电子能谱测量需求,并对磁谱仪的特征参数如能量色散、能量色散梯度、能量分辨率、斜入射效应等进行详细分析.基于北京大学DC-SRF-Ⅱ射频超导光阴极电子枪开展了磁谱仪能量刻度实验,在真空条件下实验测量了 0.7～1.8 MeV区间内多个能量的电子能谱,结果显示,磁谱仪的能量测量与监测系统结果基本符合.电子能谱的能量分辨率主要决定于磁谱仪自身分辨能力,为提高能量分辨率,需通过准直系统进一步减小入射孔径和电子发散角.
Abstract
The interactions of ultra-intense lasers with targets can generate relativistic electrons and various secondary particles such as energetic protons,ions,neutrons,X and γ rays.The particles and rays have been used in many fields of science research and applications including inertial confinement fusion(ICF),laser nuclear physics,labora-tory astrophysics,charge particle acceleration,particle imaging,nuclear medicine,biol-ogy,and material science.As the primary particles,the characterization of hot electrons is very essential for understanding laser-plasma physics,optimizing particle parameters,and meeting various application requirements.In previous studies,electron magnetic spectrometer(EMS)is commonly favored because of its simple structure and low cost.The electrons of different energy are directly deflected along different trajectories by the Lorenz force to disperse electron energies.In most designs of EMSs,the magnetic field and energy dispersion were only described.The detailed characteristic parameters and their influencing factors,such as energy resolution,angle divergence broadening,and oblique incidence effects,lack in-depth analysis.Otherwise,most EMSs were used in laser-plasma experiments without calibration.The reliability and uncertainties of electron spectrum data should be further investigated.In the work,a compact and wide-range electron magnetic spectrometer with magnetic strength of 500 Gs were described.The detailed characteristics of the EMS were analyzed,including electron energy disper-sion,energy dispersion gradient,energy resolution,and oblique incident effect.The results indicate that the energy resolution is influenced by electron energy,incident aperture,and divergence angle.Compared to the front and rear panel,the electrons deflected to the side panel have significant advantages in energy dispersion gradient and energy resolution.The energy range of the side panel should be considered as the main work region.The EMS were calibrated by 0.7-2 MeV electrons on the DC-SRF-Ⅱ beam line device.The spectrum peak energy is approximately equal to the corrected energy passing through the 200 μm beryllium window.The electron energy resolution is slightly larger than the EMS energy resolution itself,and it is significantly increased in air compared to that in vacuum.In order to improve the energy resolution,the incident aperture and divergence angle should be further reduced,which are also beneficial for reducing background signals.The EMS will be used to measure hot electrons produced by laser-solid interactions in the following work.The accurate measurement of the electron energy spectrum is of great significance for studying and optimizing the hot electron,proton,and X/γ sources and their applications.
基金项目
国家财政部稳定支持研究经费项目(WDJC-2019-02)
国家财政部稳定支持研究经费项目(BJ20002501)
国家科技期刊平台
NSTL
万方数据