Proton beam self-modulation seeded by electron bunch in plasma with density ramp

TL;DR

This paper numerically investigates how plasma density profiles affect proton beam self-modulation seeded by electron bunches, optimizing wakefield stability for the AWAKE experiment at CERN.

Contribution

It identifies optimal plasma density ramp profiles for seeded self-modulation, enhancing wakefield stability and efficiency in proton-driven plasma wakefield acceleration.

Findings

Optimal density profiles can stabilize wakefields at half wavebreaking level.

Low-energy electron bunches are more effective seeds than high-energy ones.

Proper density ramp design is crucial for efficient self-modulation.

Abstract

Seeded self-modulation in a plasma can transform a long proton beam into a train of micro-bunches that can excite a strong wakefield over long distances, but this needs the plasma to have a certain density profile with a short-scale ramp up. For the parameters of the AWAKE experiment at CERN, we numerically study which density profiles are optimal if the self-modulation is seeded by a short electron bunch. With the optimal profiles, it is possible to "freeze" the wakefield at approximately half the wavebreaking level. High-energy electron bunches (160 MeV) are less efficient seeds than low-energy ones (18 MeV), because the wakefield of the former lasts longer than necessary for efficient seeding.