Energy-chirp compensation of laser-driven ion beams enabled by structured targets

TL;DR

This paper demonstrates through 3D simulations that structured targets can effectively compensate for energy chirp in laser-driven ion beams, resulting in high-quality, mono-energetic proton beams with high charge and low divergence.

Contribution

The study introduces a novel structured target design that reverses ion energy chirp, enhancing mono-energetic ion beam quality in laser acceleration.

Findings

Achieved a mono-energetic proton peak at 200 MeV.

Produced ion beams with several nanocoulombs of charge.

Maintained low divergence below 10 degrees.

Abstract

We show using 3D simulations that the challenge of generating dense mono-energetic laser-driven ion beams with low angular divergence can be overcome by utilizing structured targets with a relativistically transparent channel and an overdense wall. In contrast to a uniform target that produces a chirped ion beam, the target structure facilitates formation of a dense electron bunch whose longitudinal electric field reverses the energy chirp. This approach works in conjunction with existing acceleration mechanisms, augmenting the ion spectra. For example, our 3D simulations predict a significant improvement for a 2 PW laser pulse with a peak intensity of $5 \times 10^{22}$ W/cm$^2$. The simulations show a mono-energetic proton peak in a highly desirable energy range of 200 MeV with an unprecedented charge of several nC and relatively low divergence that is below 10$^{\circ}$.