Implementation of Light Diagnostics for Wakefields at AWAKE

TL;DR

This paper details the development and calibration of light diagnostics to study wakefield energy dissipation in plasma caused by a relativistic proton bunch, enabling analysis of plasma density variations and wakefield evolution.

Contribution

It introduces a new light diagnostic setup for measuring energy dissipation in plasma during proton-driven wakefield experiments, applicable to different plasma sources.

Findings

Light emission correlates with energy deposited in plasma.

Calibration enables measurement of plasma density steps.

Diagnostics facilitate ongoing wakefield evolution studies.

Abstract

We describe the implementation of light diagnostics for studying the self-modulation instability of a long relativistic proton bunch in a 10m-long plasma. The wakefields driven by the proton bunch dissipate their energy in the surrounding plasma. The amount of light emitted as atomic line radiation is related to the amount of energy dissipated in the plasma. We describe the setup and calibration of the light diagnostics, configured for a discharge plasma source and a vapor plasma source. For both sources, we analyze measurements of the light from the plasma only (no proton bunch). We show that with the vapor plasma source, the light signal is proportional to the energy deposited in the vapor/plasma by the ionizing laser pulse. We use this dependency to obtain the parameters of an imposed plasma density step. This dependency also forms the basis for ongoing studies, focused on investigating the wakefield evolution along the plasma.