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.