Abstract-Stable coherent terahertz synchrotron radiation from controlled relativistic electron bunches

C. Evain, C. Szwaj, E. Roussel, J. Rodriguez, M. Le Parquier, M.-A. Tordeux, F. Ribeiro, M. Labat, N. Hubert, J.-B. Brubach, P. Roy,  S. Bielawski, 

Fig. 1: Storage ring synchrotron facilities, and the microbunching instability.

https://www.nature.com/articles/s41567-019-0488-6?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+nphys%2Frss%2Fcurrent+%28Nature+Physics+-+Issue%29&utm_content=Google+Feedfetcher

Relativistic electron bunches used in synchrotron light sources are complex media, in which patterns might form spontaneously. These spatial structures were studied over the past decades for very practical reasons. The patterns, which spontaneously appear during an instability, increase the terahertz radiation power by factors exceeding 10,000. However, their irregularity largely prevented applications of this powerful source. Here we show that principles from chaos control theory allow us to generate regular spatio-temporal patterns, stabilizing the emitted terahertz power. Regular unstable solutions are expected to coexist with the undesired irregular solutions, and may thus be controllable using feedback control. We demonstrate the stabilization of such regular solutions in the Synchrotron SOLEIL storage ring. Operation of these controlled unstable solutions enables new designs of high-charge and stable synchrotron radiation sources.

Abstract-Observing microscopic structures of a relativistic object using a time-stretch strategy

• 
  • E. Roussel,
  • C. Evain,
  • M. Le Parquier,
  • C. Szwaj,
  • S. Bielawski,
  • L. Manceron,
  • J.-B. Brubach,
  • M.-A. Tordeux,
  • J.-P. Ricaud,
  • L. Cassinari,
  • M. Labat,
  • M.-E Couprie
  • & P. Roy

http://www.nature.com/srep/2015/150528/srep10330/full/srep10330.html

Emission of light by a single electron moving on a curved trajectory (synchrotron radiation) is one of the most well-known fundamental radiation phenomena. However experimental situations are more complex as they involve many electrons, each being exposed to the radiation of its neighbors. This interaction has dramatic consequences, one of the most spectacular being the spontaneous formation of spatial structures inside electrons bunches. This fundamental effect is actively studied as it represents one of the most fundamental limitations in electron accelerators, and at the same time a source of intense terahertz radiation (Coherent Synchrotron Radiation, or CSR). Here we demonstrate the possibility to directly observe the electron bunch microstructures with subpicosecond resolution, in a storage ring accelerator. The principle is to monitor the terahertz pulses emitted by the structures, using a strategy from photonics, time-stretch, consisting in slowing-down the phenomena before recording. This opens the way to unpreceeded possibilities for analyzing and mastering new generation high power coherent synchrotron sources.

Abstract-Coherent synchrotron radiation for broadband terahertz spectroscopy

J. Barros¹, C. Evain², L. Manceron¹, J.-B. Brubach¹, M.-A. Tordeux¹, P. Brunelle¹, L. Nadolski¹, A. Loulergue¹, M.-E. Couprie¹, S. Bielawski², C. Szwaj², and P. Roy¹

¹Synchrotron SOLEIL, Saint Aubin, BP 48, 91192 Gif-sur-Yvette, Cedex, France
²Laboratoire de Physique des Lasers, Atomes et Molécules, Université des Sciences et Technologies de Lille, F-59655 Villeneuve d’Ascq Cedex, France                        

We present the first high resolution (10⁻³ cm⁻¹) interferometric measurements in the 200–750 GHz range using coherent synchrotron radiation, achieved with a low momentum compaction factor. The effect of microbunching on spectra is shown, depending on the bunch current. A high signal-to-noise ratio is reached thanks to an artifact correction system based on a double detection scheme. Combined to the broad emitted spectral range and high flux (up to 10⁵ times the incoherent radiation), this study demonstrates that coherent synchrotron radiation can now be used for stability-demanding applications, such as gas-phase studies of unstable molecules.

© 2013 American Institute of Physics