Seeding of the Self-Modulation in a Long Proton Bunch by Charge Cancellation with a Short Electron Bunch

TL;DR

This paper proposes a novel self-modulation seeding method in plasma wakefield accelerators using charge cancellation with a short electron bunch, offering an alternative to laser ionization methods and analyzing its feasibility for AWAKE Run 2.

Contribution

It introduces a new seeding mechanism based on electron injection and provides 2D linear theory calculations to evaluate its effectiveness.

Findings

Effective wakefield generation through charge cancellation

Potential for controlled self-modulation growth

Feasibility analysis for AWAKE Run 2

Abstract

In plasma wakefield accelerators (e.g. AWAKE) the proton bunch self-modulation is seeded by the ionization front of a high-power laser pulse ionizing a vapour and by the resulting steep edge of the driving bunch profile inside the created plasma. In this paper, we present calculations in 2D linear theory for a concept of a different self-modulation seeding mechanism based on electron injection. The whole proton bunch propagates through a preformed plasma and the effective beam current is modulated by the external injection of a short electron bunch at the centre of the proton beam. The resulting sharp edge in the effective beam current in the trailing part of the proton bunch is driving large wakefields that can lead to a growth of the seeded self-modulation (SSM). Furthermore, we discuss the feasibility for applications in AWAKE Run 2.