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Improving laser-accelerated proton beam divergence by electric and magnetic fields induced in flat channel-like targets

Improving parameters of laser-driven proton and ion beams becomes one of the most important goals in the field of laser acceleration in order to fulfill requirements of foreseen applications. This work presents parametric 2D and 3D particle-in-cell simulations of various target designs in order to reduce proton beam divergence without significant drop in maximum energies or in proton number. The optimal target design proved to be a channel-like target which produces not only a long-lasting focusing transverse electric field in contrast to a flat foil, but also a magnetic quadrupole with strong octupole component inside the guiding channel. A combination of both electric and magnetic features results in a strong proton beam divergence reduction, accompanied by a higher uniformity of the beam, which is studied as a function of proton energy.