Electron beam and betatron x-ray generation in a hybrid electron accelerator driven by high intensity picosecond laser pulses

We experimentally studied electron beams and synchrotron x-ray radiation generated from the interaction of high-intensity picosecond laser pulses of 1–3 × 1019 W/cm2 with underdense plasmas of 1–8 × 1019 cm−3. Electron beams with maximum energy over 120 MeV, hundreds mrad divergence and tens of nC charge were generated in the experiments. The measured x-ray spectra were fit well with a synchrotron radiation spectrum combination with a bremsstrahlung spectrum. When laser pulses with intensity of 2.38 × 1019 W/cm2 interacting with pure Nitrogen gas with density of 2.35 × 1018 cm−3, we obtained betatron x-ray radiation with critical energy 3–4 keV and photon number up to 1013 photons/Sr per shot, the energy conversion efficiency is about 3 × 10−5. The high photon yield and large energy conversion efficiency are due to large amounts of electrons trapped by self-modulated laser wakefield and mainly accelerated by direct-laser-acceleration mechanism. Such high yield betatron x-ray sources have widely application prospect as backlight or probe in large scale of laser facilities used for high energy density or fusion sciences.