Effects of target parameters on electron energy gain during laser-driven acceleration in a hollow-core target*

The structure of the hollow-core target exhibits the ability to prevent laser diffraction which allows the focusing effect to enhance the laser longitudinal electric field. When the laser propagates inside the target, electrons can be injected into the channel by the transverse laser electric field. For forward moving electrons, the force from the self-generated quasi-static transverse electric field is compensated by the force of the azimuthal magnetic field, allowing for purely longitudinal acceleration. This process will terminate once electrons slide out of the favorable accelerating phase due to the difference between phase velocity (v_ph) and longitudinal velocity of the electrons, where v_ph depends on the density of injected electrons and the size of the channel. We have performed a series of 2D particle-in-cell simulations for different hollow-core radii to self-consistently determine the phase velocity and corresponding maximum electron energy. The considered setup offers an attractive possibility of generating beams of highly collimated energetic electrons with near-critical density.