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Stable coherent terahertz synchrotron radiation from controlled relativistic electron bunches


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 10,0001,2. However, their irregularity1,2,3,4,5,6,7 largely prevented applications of this powerful source. Here we show that principles from chaos control theory8,9,10 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.

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This work has been partially supported by the LABEX CEMPI (ANR-11-LABX-0007) and the Equipex Flux (ANR-11-EQPX-0017), as well as by the Ministry of Higher Education and Research, Hauts de France council and the European Regional Development Fund through the Contrat de Projets Etat-Region (CPER Photonics for Society P4S). The project used HPC resources from GENCI TGCC/IDRIS (i2016057057, A0040507057).

Author information

S.B. and C.E. carried out the numerical simulations. C.E., S.B. and C.S. led the experimental realization. C.E., S.B. and J.R. developed the FPGA software. The experiments at SOLEIL were designed and performed by M.-A.T. (ring configuration and operation), F.R. (RF system configuration and settings), M.L. and N.H. (interlock and diagnostic systems), J.-B.B. and P.R. (AILES beamline), and M.L., E.R., S.B., C.E. and C.S. (electro-optics sampling detection system and feedback system). The experimental data were analysed by C.S. and C.E. All of the authors participated in the redaction.

Competing interests

The authors declare no competing interests.

Correspondence to C. Evain.

Supplementary information

Supplementary Information

Supplementary Figures.

Supplementary Video 1

Video demonstrating feedback control.

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Fig. 1: Storage ring synchrotron facilities, and the microbunching instability.
Fig. 2: Control of the microbunching instability, experimental set-up and results expected numerically.
Fig. 3: Experimental results on the feedback control.
Fig. 4: Evolution of the coherent terahertz pulse shapes with and without control.