Enhancement of Magnetic Vortex Acceleration by Laser Interaction with Near-Critical Density Plasma inside a Hollow Conical Target

The effects of magnetic vortex acceleration (MVA) are investigated with two-dimensional particle-in-cell (PIC) simulations by laser interaction with near-critical density (NCD) plasma inside a hollow conical plasma. Energetic and collimated proton beams can be accelerated by a longitudinal charge-separation field. Energetic protons with a peak energy of 220 MeV are produced in PIC simulations. Compared with a uniform NCD plasma, both the cutoff energy and collimation of proton beams are improved remarkably. Furthermore, the influence of different gap sizes of cone tip is taken into account. For optimizing magnetic vortex acceleration, the gap size of the cone tip is suggested to match the focal spot size of laser pulse.