Accelerating and guiding of electron beams in a cone target filled with near-critical-density plasmas

Direct laser acceleration is one of the mechanisms for producing electron bunches carrying up to μC charge, which has attracted much attention in recent decades. Currently, one major challenge for its applications to high-flux x-ray beams and Compton γ-ray sources is the relatively large divergence angle (hundreds of mrad). In this work, a scheme to guide and focus the incident laser and the accelerated electrons is proposed and tested through two-dimensional (2D) particle-in-cell (PIC) simulations. The scheme is based on a hollow cone target (made of aluminum or gold) filled with near-critical-density (NCD) plasmas (pre-ionized polymer foams). Instead of separating the acceleration and focusing processes, it is convenient to simultaneously realize both requirements in such an NCD plasma-filled cone target. PIC simulations reveal that the laser, electrons, and emitted photons can be well-guided along the cone axis in the NCD plasma-filled cone target, preserving the characteristic of high beam charge. Detailed PIC simulations are also performed to show the dependence of the electron energy and charge on the plasma density for a given laser.