Numerical studies of electron acceleration behind self-modulating proton beam in plasma with a density gradient

A Petrenko,K Lotov,A Sosedkin

doi:10.1016/j.nima.2016.01.063

Abstract

Presently available high-energy proton beams in circular accelerators carry enough momentum to accelerate high-intensity electron and positron beams to the TeV energy scale over several hundred meters of the plasma with a density of about 1015cm−3. However, the plasma wavelength at this density is 100–1000 times shorter than the typical longitudinal size of the high-energy proton beam. Therefore the self-modulation instability (SMI) of a long (~10cm) proton beam in the plasma should be used to create the train of micro-bunches which would then drive the plasma wake resonantly. Changing the plasma density profile offers a simple way to control the development of the SMI and the acceleration of particles during this process. We present simulations of the possible use of a plasma density gradient as a way to control the acceleration of the electron beam during the development of the SMI of a 400GeV proton beam in a 10m long plasma. This work is done in the context of the AWAKE project—the proof-of-principle experiment on proton driven plasma wakefield acceleration at CERN.

Highlights

IntroductionWakefields with GV/m amplitude correspond to the plasma wavelength around 1 mm, the typical proton beam bunches in a storage ring have the longitudinal size in the order of 10 cm
Available high-energy proton beams in circular accelerators carry enough momentum to accelerate high-intensity electron and positron beams to the TeV energy scale over several hundred meters of the plasma with a density of about 1015 cm À 3
We focus on the case of a constant plasma density gradient which is relevant for the AWAKE experiment

Summary

Introduction

Wakefields with GV/m amplitude correspond to the plasma wavelength around 1 mm, the typical proton beam bunches in a storage ring have the longitudinal size in the order of 10 cm. In the original PDPWFA proposal [3] the proton beam was assumed to be compressed by a factor of 1000 down to the longitudinal size of 0.1 mm Such an extreme bunch compression is very challenging ( technically feasible), but the high plasma wakefields can be excited resonantly with a sequence of sub-millimeter long microbunches produced from the long proton beam as a result of the beam self-modulation instability (SMI) [4,5] in plasma. The selected plasma section design is already capable of creating plasma density profiles with a constant gradient along the whole 10 m long section [10,9] This gradient naturally appears if the continuous flow of rubidium vapor through the orifices at the beam entrance and exit is unbalanced.

Effect of density gradient on the plasma wakefields

Findings

Conclusions