Betatron x-ray production in mixed gases

Betatron x-rays with multi-keV photon energies have been observed from a GeV-class laser-plasma accelerator. The experiment was performed using the 200 TW Callisto laser system at LLNL to produce and simultaneously observe GeV-class electron beams and keV Betatron x-rays. The laser was focused with two different optics (f/8 and f/20), and into various gas cells with sizes ranging from 3 to 10 mm, and containing mixed gases (He, N, CO2, Ar, Ne) to accelerate large amounts of charge in the ionization induced trapping regime. KeV betatron x-rays were observed for various concentrations of gases. Electron spectra were measured on large image plates with the two-screen method after being deflected by a large 0.42 Tesla magnet spectrometer. Betatron oscillations observed on the electron spectra can be benchmarked against a simple analytical model (Runge-Kutta algorithm solving the equation of motion of an electron in the wakefield), in order to retrieve the electron injection conditions into the wake