Laser-plasma electron acceleration and X-ray production in capillary tubes*

The dynamics of electron acceleration and X-rays production in capillary tubes are investigated numerically. An ultra-intense ($0.77 \times 10^{18}$ W/cm$^2$) and ultra-short (35 fs) laser pulse can be guided in cm long plasmas with electron densities of the order of $5 \times 10^{18}$cm$^{-3}$. Self-injected electrons are accelerated in the plasma wake, and undergo betatron oscillations giving rise to X-rays emission. We performed cm-long quasi-3D PIC simulations with CALDER-CIRC. The capillary tube was implemented through a non-uniform dielectric function. X-ray production was calculated a posteriori from electron trajectories by classical formulas. We compare numerical results with experimental ones. For cm long propagation, multiple electrons injection and acceleration are observed. The X-ray emission at the output of the tube is calculated in the conditions of the experiment. The effects of the plasma density and of the capillary edge on the X-ray beam divergence are discussed.