Author: Giannessi, L.
Paper Title Page
MOD04 Status and Perspectives of the FERMI FEL Facility 1
  • L. Giannessi, E. Allaria, L. Badano, F. Bencivenga, C. Callegari, F. Capotondi, F. Cilento, P. Cinquegrana, M. Coreno, I. Cudin, G. D'Auria, M.B. Danailov, R. De Monte, G. De Ninno, P. Delgiusto, A.A. Demidovich, M. Di Fraia, S. Di Mitri, B. Diviacco, A. Fabris, R. Fabris, W.M. Fawley, M. Ferianis, P. Furlan Radivo, G. Gaio, D. Gauthier, F. Gelmetti, F. Iazzourene, S. Krecic, M. Lonza, N. Mahne, M. Malvestuto, C. Masciovecchio, M. Milloch, N.S. Mirian, F. Parmigiani, G. Penco, A. Perucchi, L. Pivetta, O. Plekan, M. Predonzani, E. Principi, L. Raimondi, P. Rebernik Ribič, F. Rossi, E. Roussel, L. Rumiz, C. Scafuri, C. Serpico, P. Sigalotti, S. Spampinati, C. Spezzani, M. Svandrlik, M. Trovò, A. Vascotto, M. Veronese, R. Visintini, D. Zangrando, M. Zangrando
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  FERMI is the seeded Free Electron Laser (FEL) user facility at the Elettra laboratory in Trieste, operating in the VUV to EUV and soft X-rays spectral range; the radiation produced by the seeded FEL is characterised by a number of desirable properties, such as wavelength stability, low temporal jitter and longitudinal coherence. In this paper, after an overview of the FELs performances, we will present the development plans under consideration for the next 3 to 5 years. These include an upgrade of the LINAC and of the existing FEL lines, the possibility to perform multi-pulse experiments in different configurations and an Echo Enabled Harmonic Generation experiment on FEL-2, the FEL line extending to 4 nm (310 eV).  
Towards the Demonstration of Soft X-Ray Echo-Enabled Harmonic Generation at Fermi  
  • E. Allaria, R. Bracco, D. Castronovo, I. Cudin, M.B. Danailov, G. De Ninno, S. Di Mitri, B. Diviacco, W.M. Fawley, M. Ferianis, L. Giannessi, M. Lonza, G. Penco, P. Rebernik Ribič, E. Roussel, S. Spampinati, C. Spezzani, L. Sturari, M. Svandrlik, M. Veronese, R. Visintini, M. Zaccaria, D. Zangrando
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • H.-H. Braun, E. Prat, S. Reiche
    PSI, Villigen PSI, Switzerland
  • G. De Ninno
    University of Nova Gorica, Nova Gorica, Slovenia
  • B.W. Garcia, J.B. Hastings, E. Hemsing, T.O. Raubenheimer, G. Stupakov, J.J. Welch
    SLAC, Menlo Park, California, USA
  • G. Penn
    LBNL, Berkeley, California, USA
  • E. Roussel
    SOLEIL, Gif-sur-Yvette, France
  • A. Zholents
    ANL, Argonne, Illinois, USA
  The echo-enabled harmonic generation seeding scheme is based on an echo mechanism that develops in the electron beam phase-space interacting with two seed lasers before and after a strong dispersive region. It has been proposed for extending the capabilities of externally seeded free electron lasers to reach short wavelengths. After the original proposal, a few experiments have confirmed the capabilities of efficient bunching generation at very high harmonics. However, up to now none of the experiments demonstrated FEL amplification from high harmonic bunching produced at 10 nm wavelengths or shorter. In this work, we report about our plans for performing an EEHG experiment at FERMI. The experiment will be done at the FEL-2 line normally operated in the double stage high-gain harmonic generation configuration in the wavelength range 20-4 nm. After the modification of a few hardware components planned for the first semester of 2018, the FEL-2 layout will be suitable for EEHG at wavelengths down to approximately 6 nm.  
MOP005 FEL Pulse Shortening by Superradiance at FERMI 1
  • N.S. Mirian, L. Giannessi
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • S. Spampinati
    Private Address, warrigton, United Kingdom
  Explorations of saturated superradiant regime is one of the methods that could be used to reduce the duration of the pulses delivered by FERMI. Here we present simulation studies that show the possible application of a superradiant cascade leading to a minimum pulse duration below 8 fs and to a peak power exceeding the GW level in both FEL lines FEL-1 and FEL-2.  
Characterization of the Polarization of the First and Second Stage of FERMI FEL-2  
  • E. Roussel, E. Allaria, C. Callegari, M. Coreno, R. Cucini, S. Di Mitri, B. Diviacco, E. Ferrari, P. Finetti, D. Gauthier, L. Giannessi, G. Penco, L. Raimondi, C. Svetina, M. Zangrando
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • A. Beckmann
    XFEL. EU, Hamburg, Germany
  • L. Giannessi
    ENEA C.R. Frascati, Frascati (Roma), Italy
  • L. Glaser, G. Hartmann, F. Scholz, J. Seltmann, I. Shevchuk, J. Viefhaus
    DESY, Hamburg, Germany
  • M. Zangrando
    IOM-CNR, Trieste, Italy
  The FERMI free-electron laser (FEL) is nowadays the only user facility equipped with Apple-II type undulators that permit to produce either elliptical, circular or linearly polarized light within the extreme ultraviolet and soft x-ray wavelength range. The FERMI FEL-2 line is based on a two-stage "fresh-bunch" high-gain harmonic generation (HGHG) scheme, where the light emitted by a first HGHG stage seeds a fresh portion of the electron bunch in a second FEL stage. Both FEL lights, from the first and second stages, can be tuned separately to linear horizontal, vertical or circular left and right polarization. We report on a systematic characterization of the polarization state of the two stages of FERMI FEL-2 by using an electron Time-Of-Flight based polarimeter. Our results show a good independent control of the polarization of the two stages, with a high degree of polarization typically higher than 95%*
* E. Roussel et al., Polarization Characterization of Soft X-Ray Radiation at FERMI FEL-2. Photonics 2017, 4, 29.
First Demonstration of Fully Coherent Super-Radiant Pulses From a Short-Pulse Seeded FEL  
  • X. Yang
    BNL, Upton, Long Island, New York, USA
  • L. Giannessi
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  The generation of a single X-ray isolated spike of radiation with peak power at the GW level and femtosecond temporal duration represents an almost unique opportunity for time-resolved non-linear spectroscopy. Such a condition is met by an FEL operating in superradiance. The resulting pulse has a self-similar shape deriving from the combined dynamics of saturation and slippage of the radiation over fresh electrons. The pulse is followed by a long pedestal, resulting from the complex dynamics occurring in the tail after saturation. This tail consists of a train of pulses with both transverse and longitudinal coherence and decaying amplitudes. We analyze the dynamical conditions on slippage and pulse length leading to the formation of the main pulse and the following tail. We study the correlation of the tail structure with the longitudinal phase space of the e-beam and provide recipes to partially suppress it near the background level leading to the fully coherent super-radiant pulse. Our analytical prediction of the intensity peak of the leading pulse evolving along the undulator before, during, and after becoming a super-radiant pulse agrees well with the simulations.  
Passive Linearization of the Magnetic Bunch Compression Using Self-Induced Field and Without Any Active Higher Harmonic RF Structure  
  • G. Penco, E. Allaria, I. Cudin, S. Di Mitri, D. Gauthier, L. Giannessi, E. Roussel, S. Spampinati, M. Trovò
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • S. Bettoni, P. Craievich, E. Ferrari
    PSI, Villigen PSI, Switzerland
  • L. Giannessi
    ENEA C.R. Frascati, Frascati (Roma), Italy
  • E. Roussel
    SOLEIL, Gif-sur-Yvette, France
  In linac-driven free-electron lasers, colliders and energy recovery linacs, a common way to compress the electron bunch to kA level is based upon the implementation of a magnetic dispersive element that converts the bunch energy deviation in path-length difference. The non-linearities of such a process are usually compensated by enabling a high harmonic rf structure properly tuned in amplitude and phase. This approach is however not straightforward for foreseen C and X-band linacs. In this work we report the experiment performed on the FERMI linac that has demonstrated the possibility to exploit the longitudinal self-induced field excited by the electron beam itself to passively linearize the compression process without any active higher harmonic rf structure. In this novel configuration, the FERMI electron bunch was compressed up to 700 A as in the nominal case and driven along the FERMI FEL-1 undulators, generating intense extreme-ultraviolet pulses that were provided to users for experiments.  
THB02 Non-Standard Use of Laser Heater for FEL Control and THz Generation 1
  • E. Allaria, L. Badano, M.B. Danailov, A.A. Demidovich, S. Di Mitri, D. Gauthier, L. Giannessi, G. Penco, E. Roussel, P. Sigalotti, S. Spampinati, M. Trovò, M. Veronese
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • E. Roussel
    SOLEIL, Gif-sur-Yvette, France
  The laser heater system is currently used at various FEL facilities for an accurate control of the electron beam energy spread in order to suppress the micro-bunching instabilities that can develop in high brightness electron beams. More recently, studies and experiments have shown that laser-electron interaction developing in the laser heater can open new possibilities for tailoring the electron beam properties to meet special requirements. A suitable time-shaping of the laser heater pulse opened the door to the generation of (tens of) femtosecond-long FEL pulses. Using standard laser techniques it is also possible to imprint onto the electron bunch, energy and density modulations in the THz frequency range that, properly sustained through the accelerator, can be exploited for generation of coherent THz radiation at GeV beam energies. Such recent results at the FERMI FEL are here reported, together with near future plans.