Characterisation of beam driven ionisation injection in the blowout regime of Plasma Acceleration

TL;DR

This paper characterizes beam-driven ionisation injection in plasma acceleration, analyzing how dopant properties and injection position affect the quality of the resulting electron bunches using 3D PIC simulations.

Contribution

It provides a systematic analysis of ionisation injection mechanisms and the influence of dopant properties on beam quality in the blowout regime.

Findings

Electron capture position influences bunch quality.

Dopant density and ionisation state affect emittance and energy spread.

High transformer ratio confines ionisation to bubble closure.

Abstract

Beam driven ionisation injection is characterised for a variety of high-Z dopant. We discuss the region of extraction and why the position where electrons are captured influences the final quality of the internally-injected bunch. The beam driven ionisation injection relies on the capability to produce a high gradient fields at the bubble closure, with magnitudes high enough to ionise by tunnelling effect the still bounded electrons (of a high-Z dopant). The ionised electrons are captured by the nonlinear plasma wave at the accelerating and focusing wake phase leading to high-brightness trailing bunches. The high transformer ratio guarantees that the ionisation only occurs at the bubble closure. The quality of the ionisation-injected trailing bunches strongly and non-linearly depends on the properties of the dopant gas (density and initial ionisation state). We use the full 3D PIC code ${\tt ALaDyn}$ to consider the highly three-dimensional nature of the effect. By means of a systematic approach we have investigated the emittance and energy spread formation and the evolution for different dopant gases and configurations.