Hole-boring radiation pressure acceleration as a basis for producing high-energy proton bunches

The production of high-energy protons by the 'hole-boring' radiation pressure acceleration (HB-RPA) mechanism of laser-driven ion acceleration is examined in the case where the plasma has a density less than a(0)n(c) in 2D. Previously this was examined in 1D (Robinson 2011 Phys. Plasmas 18 056701) and was motivated by previous predictions of the non-linear criterion for an ultra-intense laser pulse to penetrate a dense plasma. By reducing the density well below a(0)n(c) the proton energies achieved increases considerably, thus leading to proton energies > 100 MeV at laser intensities close to current capabilities. The results show that good quality proton beams with proton energies > 100 MeV can be obtained via HB-RPA using targets with densities in the range 12-20n(c) and laser intensities in the range 5 x 10(21)-3 x 10(22) W cm(-2).