Direct observation of spatio-temporal dynamics of short electron bunches in storage rings

TL;DR

This paper presents the first direct, high-resolution observations of short electron bunch dynamics in storage rings, revealing physical process interplay and self-organization phenomena in THz pulse emissions.

Contribution

It introduces a novel high-sensitivity photonic time stretch detector enabling direct observation of electron bunch behavior in storage rings.

Findings

Below a critical charge, a THz pulse train is observed.

Above the threshold, drifting structures and self-organization occur.

The observations confirm theoretical predictions about bunch dynamics.

Abstract

In recent synchrotron radiation facilities, the use of short (picosecond) electron bunches is a powerful method for producing giant pulses of Terahertz Coherent Synchrotron Radiation (THz CSR). Here we report on the first direct observation of these pulse shapes with a few picoseconds resolution, and of their dynamics over a long time. We thus confirm in a very direct way the theories predicting an interplay between two physical processes. Below a critical bunch charge, we observe a train of identical THz pulses (a broadband Terahertz comb) stemming from the shortness of the electron bunches. Above this threshold, a large part of the emission is dominated by drifting structures, which appear through spontaneous self-organization. These challenging single-shot THz recordings are made possible by using a recently developed photonic time stretch detector with a high sensitivity. The experiment has been realized at the SOLEIL storage ring.