Experimental study of extended timescale dynamics of a plasma wakefield driven by a self-modulated proton bunch

TL;DR

This study experimentally investigates plasma wakefield dynamics driven by a self-modulated proton bunch over extended timescales, revealing the development of wakefield amplitude and associated potentials through measurements and simulations.

Contribution

It provides the first experimental measurements of plasma wakefield evolution over 800 ps and links these observations to simulation predictions of electron trajectories and potential formation.

Findings

Wakefield amplitude develops over 800 ps

Resonant excitation causes plasma electron crossing

Potential outside plasma boundary observed

Abstract

Plasma wakefield dynamics over timescales up to 800 ps, approximately 100 plasma periods, are studied experimentally at the Advanced Wakefield Experiment (AWAKE). The development of the longitudinal wakefield amplitude driven by a self-modulated proton bunch is measured using the external injection of witness electrons that sample the fields. In simulation, resonant excitation of the wakefield causes plasma electron trajectory crossing, resulting in the development of a potential outside the plasma boundary as electrons are transversely ejected. Trends consistent with the presence of this potential are experimentally measured and their dependence on wakefield amplitude are studied via seed laser timing scans and electron injection delay scans.