Bright betatron x-rays generation from picosecond laser interactions with long-scale near critical density plasmas

Abstract

Our previous experimental and three-dimensional (3D) particle-in-cell (PIC) simulation results demonstrated that a well-directed electron beam with space charge of about μC and maximum energy of 100\u2009MeV can be generated via a sub-petawatt, picosecond laser pulse interacting with a long-scale near-critical-density plasma. Effective laser energy coupling into hot electrons occurs in the presence of strong self-generated quasistatic electric and magnetic fields that confine fast electrons in relativistic ion channels. Here, we report results of 3D PIC simulations, which show that this direct laser accelerated electron beam can work as a compact high-brightness source of x rays. The relativistic electrons make betatron oscillations in the transverse fields of the ion channel and emit a bright broadband x-ray radiation with the critical energy of about 5\u2009keV. Due to the huge number of accelerated electrons, our simulation shows that with a picosecond, 20\u2009J laser pulse, an x-ray spectrum with a photon number of 7 × 10 11 (>1\u2009keV) can be generated, resulting into a peak flux of 2 × 1 0 8 photons/eV and a brilliance of 3.3 × 10 20 photons/s/mm2/mrad2/0.1%BW.