Linear optics control of sideband instability for improved free-electron laser spectral brightness

G. Perosa , E. m. Allaria , L. Badano , N. Bruchon , P. Cinquegrana , M. b. Danailov , A. Demidovich , G. de Ninno (1) , L. Giannessi (2) , N. Mirian , G. m. Penco , P. Rebernik , Eléonore Roussel (3, 4) , P. Sigalotti , S. Spampinati , M. Veronese , M. Trovò , S. Di Mitri

1 Elettra Sincrotrone Trieste
2 ENEA C.R. Frascati, Via E. Fermi, 45, 00044 Frascati, Roma, Italy
3 DYSCO - DYnamique des Systèmes COmplexes
4 PhLAM - Laboratoire de Physique des Lasers, Atomes et Molécules - UMR 8523

Extension of stable longitudinal coherence from vacuum ultraviolet to x rays is highly sought after in the free-electron laser (FEL) community, but it is often prevented by bandwidth broadening originated in the electron beam microbunching instability. We demonstrate that a proper tuning of the linear optics before the beam enters the undulator mitigates the microbunching-induced sideband instability. The experiment was conducted at the Fermi FEL operated in echo-enabled harmonic generation mode, where the spectral brightness at 7 nm wavelength was doubled. The FEL performance is compared to nonoptimized optics solutions and characterized in terms of peak intensity and spectral bandwidth shot-to-shot stability. The technique has straightforward implementation, because it uses quadrupole magnets routinely adopted for beam transport, and it applies to any FEL architecture, so paving the way to the production of high-intensity Fourier-transform limited x-ray pulses in existing and planned FEL facilities.

Mots clés: Synchrotron Radiation and Free-Electron Lasers

Domaines: Physique [physics]

G. Perosa, E. m. Allaria, L. Badano, N. Bruchon, P. Cinquegrana, et al.. Linear optics control of sideband instability for improved free-electron laser spectral brightness. Physical Review Accelerators and Beams, 2020, 23 (11), pp.110703. ⟨10.1103/PhysRevAccelBeams.23.110703⟩. ⟨hal-03090361⟩