Amplitude enhancement of the self-modulated plasma wakefields

Y Li,A P Sosedkin,Y Zhao,G Xia,S J Gessner,K V Lotov

doi:10.1088/1742-6596/1067/4/042009

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.

Highlights

Proton bunches with huge energies have been proposed to drive electrons to TeV energies in a single plasma stage [1]
Successful exploitation of the effect assumes the proton bunch to be as short as hundreds of μm while currently producible ones are dozens of cm long
In this paper, we propose and investigate a slightly more complicated plasma profile than the usual steep or linear density increase

Summary

Introduction

Proton bunches with huge energies have been proposed to drive electrons to TeV energies in a single plasma stage [1]. In 2010 Kumar et al [2] proposed that with proper seeding the long bunch will see an efficient growth of the transverse wakefields generated by itself and be modulated by the periodically focusing and defocusing forces. This self-modulation chops the long proton bunch into many equidistant micro-bunches which are one plasma wavelength apart.

Results

Conclusion