An experimental and GEANT4 simulation study on design of a broad energy-range magnetic spectrograph for laser plasma accelerator

Abstract

The design and development of a magnetic spectrograph covering a broad electron energy range (few MeV to 1 GeV) for laser plasma accelerators are presented. Two phosphor screens, one in the forward and other in the side direction, were used to record electrons spectra after the dispersion from the magnet. The third phosphor screen was kept in front of the magnet to simultaneously record the electron beam profile. GEANT4 simulations were performed to estimate extra divergence in the electron beam introduced by the phosphor screen kept in front of the magnet. In the magnetic spectrograph setup, the electron beam was transported through a Ti foil of thickness 54 μm from the vacuum chamber, therefore, GEANT4 simulation was performed to estimate the contribution of secondary particles emitted in the front phosphor signal to correctly measure the beam charge. Next, it was used to simulate and design a suitable electron beam dump. Finally, the spectrograph was used to characterize electron beams generated in laser plasma accelerator driven by 120 fs Ti: Sapphire laser pulse and He and Ar gas jet targets.