Absolute energy calibration for relativistic electron beams with pointing instability from a laser-plasma accelerator

Abstract

The pointing instability of energetic electron beams generated from a laser-driven accelerator can cause a serious error in measuring the electron spectrum with a magnetic spectrometer. In order to determine a correct electron spectrum, the pointing angle of an electron beam incident on the spectrometer should be exactly defined. Here, we present a method for absolutely calibrating the electron spectrum by monitoring the pointing angle using a scintillating screen installed in front of a permanent dipole magnet. The ambiguous electron energy due to the pointing instability is corrected by the numerical and analytical calculations based on the relativistic equation of electron motion. It is also possible to estimate the energy spread of the electron beam and determine the energy resolution of the spectrometer using the beam divergence angle that is simultaneously measured on the screen. The calibration method with direct measurement of the spatial profile of an incident electron beam has a simple experimental layout and presents the full range of spatial and spectral information of the electron beams with energies of multi-hundred MeV level, despite the limited energy resolution of the simple electron spectrometer.

Demonstration of self-truncated ionization injection for GeV electron beams

“…A particle trajectory code was used to calculate the electron energy shot-to-shot taking into account the beam pointing angle (at DRZ1) before the magnet and the code was written based on the method adapted from ref. 41 . To get the electron beam energy-spread, a computer code was written to deconvlove the spectrum after the magnet from the beam size for each shot.…”

Generation of high-quality electron beams by ionization injection in a single acceleration stage

“…A MATLAB electron trajectory code was written to calculate the electron energy shot to shot, taking into consideration the beam’s pointing angle before magnet based on the method presented in Ref. [36]. To measure the electron beam energy spread, a computer code was used to deconvolve the energy spectrum from the beam size for each shot.…”

A flexible, on-line magnetic spectrometer for ultra-intense laser produced fast electron measurement

“…Trapezoidal-shaped (truncated square) magnets (marked by dashed-line in is not inside the uniform region and there is no collimator at the entrance, the electron trajectories and energy dispersions need to be precisely simulated using a particle tracing program [12] in order to include the effects of fringe fields.…”

“…The scintillator fibers [8][9][10][11] are normally placed parallel to the magnetic lines along the sides of both plates. The effects of fringe field on electron deflection trajectory are inevitable [12]. In addition, the effective fiber length which produces scintillating light is only a small portion of the fiber.…”