From self-organization in relativistic electron bunches to coherent synchrotron light: observation using a photonic time-stretch digitizer

Serge Bielawski,Patrik Schönfeldt,Clément Evain,Christophe Szwaj,Sophie Walther,Michael J Nasse,Nicole Hiller,Anke-Susanne Müller,Gudrun Niehues,Stefan Funkner,Manuel Schedler,Erik Bründermann,Edmund Blomley,Eva Burkard,Eléonore Roussel,Johannes L Steinmann,Miriam Brosi

doi:10.1038/s41598-019-45024-2

Abstract

In recent and future synchrotron radiation facilities, relativistic electron bunches with increasingly high charge density are needed for producing brilliant light at various wavelengths, from X-rays to terahertz. In such conditions, interaction of electron bunches with their own emitted electromagnetic fields leads to instabilities and spontaneous formation of complex spatial structures. Understanding these instabilities is therefore key in most electron accelerators. However, investigations suffer from the lack of non-destructive recording tools for electron bunch shapes. In storage rings, most studies thus focus on the resulting emitted radiation. Here, we present measurements of the electric field in the immediate vicinity of the electron bunch in a storage ring, over many turns. For recording the ultrafast electric field, we designed a photonic time-stretch analog-to-digital converter with terasamples/second acquisition rate. We could thus observe the predicted link between spontaneous pattern formation and giant bursts of coherent synchrotron radiation in a storage ring.

Highlights

Synchrotron Radiation (CSR) and the microbunching instability has nowadays become a central open question in the development of synchrotron radiation facilities
Electron bunch shapes have been indirectly characterized in single-shot by using new detectors based on thin films of superconducting YBCO41, and high repetition rate electro-optic sampling, using photonic time-stretch[37]
By carefully designing the experimental setup[42,43], we could demonstrate the possibility to operate the synchrotron facility with an electro-optic crystal at 2–18 millimeters from the electron bunch. This pioneer experiment at the ANKA ( KArlsruhe Research Accelerator – KARA) storage ring opened the way to real-time investigations of storage ring electron bunch shapes, under the condition that a suitable photonic ultrafast readout system can be designed

Summary

Introduction

Synchrotron Radiation (CSR) and the microbunching instability has nowadays become a central open question in the development of synchrotron radiation facilities. Electron bunch shapes have been indirectly characterized in single-shot by using new detectors based on thin films of superconducting YBCO41, and high repetition rate electro-optic sampling, using photonic time-stretch[37]. This progress enabled to record structures in single-shot up to the THz range, the obtained information concerned only the far-field (i.e., the synchrotron radiation) emitted by the microstructures[37,39,40]. We present a photonic system that enables to observe microstructures and their evolution in a direct way, by monitoring the electric field in the immediate vicinity of the electrons

Methods

Results

Conclusion