Accurate single-shot measurement technique for the spectral distribution of GeV electron beams from a laser wakefield accelerator.

We present a technique, based on a dipole magnet spectrometer containing multiple scintillation screens, to accurately characterize the spectral distribution of a GeV electron beam generated by laser wakefield acceleration (LWFA). An optimization algorithm along with a numerical code was developed for trajectory tracing and reconstructing the electron beam angle, divergence, and energy spectrum with a single-shot measurement. The code was validated by comparing the results with the Monte-Carlo simulation of electron beam trajectories. We applied the method to analyze data obtained from laser wakefield acceleration experiments performed using a multi-Petawatt laser to accelerate electron beams to multi-GeV energy. Our technique offers improved accuracy to faithfully characterize electron beams with non-negligible shot-to-shot beam pointing fluctuations, particularly in the state-of-the-art multi-GeV LWFA experiments performed to push the energy frontier.