High Energy Density Ion Beam from a Focusing Shaped Target in the Radiation Pressure Regime

Abstract

We report the focusing of a shaped thin target by a circular-polarized laser pulse at 1022 W/cm2 intensity, to a low-emittance, quasi-monoenergetic proton beam. The target shape is designed to be simultaneously deformed and focused into a cubic micron spot by the radiation pressure during its acceleration. A simple model reminiscent of geometric optics of the ions is developed. The model predicts the self-consistent dynamics of the nanostructured thin target, as well as the targets shape that is necessary for focusing without aberrations. Three-dimensional particle-in-cell simulations show that the focal length and the final energy are in good agreement with the scaling laws obtained from the geometric optics model. Extensive scans of the laser and target parameters identify the stable propagation regime where the Rayleigh-Taylor (RT)-like instability is suppressed. Stable focusing is found at different laser powers (from petawatt to multi-petawatt). Focused proton beam with number density of order 1023 cm−3 and energy density up to 2×1013 J/cm3 at the focal point is observed in simulation with laser power 35 PW.