Beam quality improvement in the later stage of radiation pressure acceleration

Abstract

It is known that high quality proton beams can be produced in the radiation pressure acceleration (RPA) by using a circularly polarized ultraintense super-Gaussian laser. However, a transverse mismatching phenomenon between the laser intensity profile and the particle spatial distribution appears in the later stage of RPA, which leads to a decompression of proton beam and broadening of the energy spectrum. To weaken this effect, a new scheme with an additional plasma channel located behind a thin hydrogen foil is proposed. It is found that a good local matching can be maintained when the laser pulse propagates in the channel, which contributes to a stable RPA for a longer time. Two-dimensional particle-in-cell simulations show that the proton beam has a peak energy of 2.0 GeV and energy spread of 13.8% at t=300 fs. With further acceleration until t=500 fs, a better quality beam with about 40% increase in peak energy and 26.2% improvement in energy conversion efficiency for high-energy protons (≥1.5 GeV) can be obtained finally. Meanwhile, the energy spread drops from 100% to 28.5%. This work may provide a more promising way to generate the high quality proton beam.