Efficient proton acceleration from laser-driven cryogenic hydrogen target of various shapes

We theoretically investigate high energy, collimated proton beam with three dimensional particle in cell simulations of ultrashort petawatt laser interaction with cryogenic hydrogen target of various shapes. Here we show that under appropriate conditions between the laser and target parameters, the protons are accelerated to high energies mainly due to collisionless shock acceleration mechanism combined with TNSA. The dependence of the protonic energy on the laser field, target shape and thickness is reported. It is demonstrated that the irradiation of intense laser (20fs, 2PW) with cryogenic hydrogen target at optimal thickness allows the efficient generation of high energy proton beam (100 MeV) of small divergence. Our results also indicate that diffracted laser field strongly affects the collimation of ions as it passes beside the mass limited target. This approach predicts a possible pathway to control laser driven ion sources.