Statistical properties of undulator radiation in the IOTA storage ring

TL;DR

This paper investigates the statistical fluctuations of undulator radiation in the IOTA storage ring, combining theoretical modeling with experiments to understand photon shot noise and its implications for beam diagnostics and lifetime.

Contribution

It presents a new theoretical model for photon emission fluctuations and validates it with experiments at IOTA, enhancing understanding of radiation noise in high-mode regimes.

Findings

Model accurately predicts photon number fluctuations.

Photon shot noise is significant in high-mode regimes.

Insights into beam size diagnostics and lifetime improvements.

Abstract

We study turn-by-turn fluctuations in the number of spontaneously emitted photons from an undulator, installed in the Integrable Optics Test Accelerator (IOTA) electron storage ring at Fermilab. A theoretical model is presented, showing the relative contributions due to the discrete nature of light emission and to the incoherent sum of fields from different electrons in the bunch. The model is compared with a previous experiment at Brookhaven and with new experiments we carried out at IOTA. Our experiments focused on the case of a large number of longitudinal and transverse radiation modes, a regime where photon shot noise is significant and the total magnitude of the fluctuations is very small. The experimental and data analysis techniques, required to reach the desired sensitivity, are detailed. We discuss how the model and the experiment provide insights into this emission regime, enable diagnostics of small beam sizes, and improve our understanding of beam lifetime in IOTA.