Study of space charge force for a laser-accelerated proton beam

TL;DR

This paper investigates the impact of space charge forces on laser-accelerated proton beams, revealing how high peak currents cause transmission issues and how these effects diminish over time and distance.

Contribution

It provides a detailed analysis of space charge effects using particle-in-cell simulations and ellipsoid models, highlighting thresholds for beam transmission failure.

Findings

Space charge significantly affects beam transmission at high proton counts.

Effects diminish notably after 20 ps or 1.2 mm from the target.

Transmission failure occurs when proton count exceeds 10^10 per pulse.

Abstract

Laser accelerators can provide proton beams with unique qualities, such as micron size, picosecond pulse duration and high peak current, and have been demonstrated for various applications and for scientific research purposes. The effect of the space charge force in high peak current beams is strong and raises challenges for application after beam transportation. We performed two-dimensional particle-in-cell simulations and studied the influence of electrons that have velocities close to that of the protons after laser acceleration. We employed ellipsoid models with different charge distributions to estimate the effects of the space charge force. Results demonstrate that space charge will affect beam transmission, and even lead to complete transmission failure if the number of protons per pulse exceeds 1010. The influence of the space charge force diminishes greatly after 20 ps, which corresponds to approximately 1.2 mm from the target.