Characteristic Analysis and Calibration Experiment of A Compact Magnetic Spectrometer

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, laboratory astrophysics, charge particle acceleration, particle imaging, nuclear medicine, biology, 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 dispersion, 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.

Keywords

• electron magnetic spectrometer
• electron energy spectrum
• energy dispersion
• energy resolution