High efficiency uniform positron beam loading in a hollow channel plasma wakefield accelerator

TL;DR

This paper introduces a new positron beam loading regime in hollow plasma channels that enables high-gradient acceleration with narrow energy spread and high efficiency, verified by simulations and theoretical analysis.

Contribution

The paper presents a novel beam loading regime in hollow plasma channels that achieves efficient, high-gradient positron acceleration with minimal energy spread, supported by explicit beam shaping and theoretical modeling.

Findings

Achieves GV/m gradient with <0.5% energy spread

Simultaneously attains ~50% energy transfer efficiency

Theoretical model agrees with simulation results

Abstract

We propose a novel positron beam loading regime in a hollow plasma channel that can efficiently accelerate $e^+$ beam with high gradient and narrow energy spread. In this regime, the $e^+$ beam coincides with the drive $e^-$ beam in time and space and their net current distribution determines the plasma wakefields. By precisely shaping the beam current profile and loading phase according to explicit expressions, three-dimensional Particle-in-Cell (PIC) simulations show that the acceleration for $e^+$ beam of $\sim$nC charge with $\sim$GV/m gradient, $\lesssim$0.5% induced energy spread and $\sim$50% energy transfer efficiency can be achieved simultaneously. Besides, only tailoring the current profile of the more tunable $e^-$ beam instead of the $e^+$ beam is enough to obtain such favorable results. A theoretical analysis considering both linear and nonlinear plasma responses in hollow plasma channels is proposed to quantify the beam loading effects. This theory agrees very well with the simulation results and verifies the robustness of this beam loading regime over a wide range of parameters.