Amplitude enhancement of the self-modulated plasma wakefields

TL;DR

This paper introduces a novel plasma density profile that enhances the amplitude of self-modulated plasma wakefields by 30%, while also increasing proton survival rates, addressing phase velocity issues in uniform plasmas.

Contribution

A new plasma density profile is proposed that significantly boosts wakefield amplitude and proton survival compared to previous methods.

Findings

Wakefield amplitude increased by 30% with the new profile.

Approximately 24% of protons survive in micro-bunches after modulation.

The physics behind the density profile's effectiveness is analyzed.

Abstract

Seeded Self-modulation (SSM) has been demonstrated to transform a long proton bunch into many equidistant micro-bunches (e.g., the AWAKE case), which then resonantly excite strong wakefields. However, the wakefields in a uniform plasma suffer from a quick amplitude drop after reaching the peak. This is caused by a significant decrease of the wake phase velocity during self-modulation. A large number of protons slip out of focusing and decelerating regions and get lost, and thus cannot contribute to the wakefield growth. Previously suggested solutions incorporate a sharp or a linear plasma longitudinal density increase which can compensate the backward phase shift and therefore enhance the wakefields. In this paper, we propose a new plasma density profile, which can further boost the wakefield amplitude by 30%. More importantly, almost 24% of protons initially located along one plasma period survive in a micro-bunch after modulation. The underlying physics is discussed.