Ion acceleration in electrostatic collisionless shock: on the optimal density profile for quasi-monoenergetic beams

TL;DR

This study investigates how tailored plasma density profiles can optimize ion acceleration in electrostatic shocks, aiming to produce quasi-monoenergetic ion beams with minimal energy spread in laser-driven systems.

Contribution

It identifies the optimal plasma scale length for minimizing energy spread and proposes a novel layered density profile approach for better control.

Findings

Optimal plasma scale length reduces energy spread

Layered density profiles improve beam control

Engineered profiles achieve low energy spread with high controllability

Abstract

A numerical study on ion acceleration in electrostatic shock waves is presented, with the aim of determining the best plasma configuration to achieve quasi-monoenergetic ion beams in laser-driven systems. It was recently shown that tailored near-critical density plasmas characterized by a long-scale decreasing rear density profile lead to beams with low energy spread [F. Fi\'uza et al., Physical Review Letters 109, 215001 (2012)]. In this work, a detailed parameter scan investigating different plasma scale lengths is carried out. As result, the optimal plasma spatial scale length that allows for minimizing the energy spread while ensuring a significant reflection of ions by the shock is identified. Furthermore, a new configuration where the required profile has been obtained by coupling micro layers of different densities is proposed. Results show that this new engineered approach is a valid alternative, guaranteeing a low energy spread with a higher level of controllability.