Near-Infrared noise in intense electron bunches

TL;DR

This paper examines near-infrared noise in intense electron bunches, comparing models with experiments, and explores implications for coherent electron cooling in high-energy physics facilities.

Contribution

It provides a detailed comparison between shot-noise models and experimental measurements of optical transition radiation in electron bunches relevant to EIC.

Findings

Shot-noise model agrees with experimental OTR data

Observed microbunching with up to 100-fold enhancement

Identified limitations of the OTR measurement method

Abstract

This article investigates electron bunch density fluctuations in the 1 - 10 $\mu m$ wavelength range, focusing on their impact on coherent electron cooling (CEC) in hadron storage rings. In this study, we thoroughly compare the shot-noise model with experimental observations of optical transition radiation (OTR) generated by a relativistic electron bunch ($\gamma \approx$ 50), transiting an Aluminium metal surface. The bunch parameters are close to those proposed for a stage in an Electron-Ion Collider (EIC), where the bunch size is much larger than the OTR wavelength being measured. Here we present measurements and particle tracking results of both the low-level noise for the EIC bunch parameters and longitudinal space-charge-induced microbunching for the chicane-compressed bunch with coherent OTR enhancements up to 100 times in the various bandwidth-filtered near-infrared (NIR) OTR photodiode signals. We also discuss the corresponding limitations of the OTR method.