Trovo, M.
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| THPP001 | SRFEL Linewidth Narrowing in the Ultraviolet | 447 |
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The ELETTRA Storage Ring FEL succeded in operating in the Ultraviolet range, around 350 nm, with an etalon Fabry Perot inserted in the optical cavity. The high vacuum vessel, integrating a totally motorized control system for the principal degrees of freedom of the silica plate, allowed to obtain the laser oscillation, showing a reduction of the spectral linewidth by more than an order of magnitude. Temporal analysis by a double sweep streak camera showed also a broadening of the temporal pulse width. These major results are here exposed and compared with a numerical analysis and the Storage Ring FEL dynamics theory. |
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| THPP007 | Stabilization of the Elettra Storage-Ring Free-Electron Laser using a Derivative Feedback | |
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The possibility of establishing and maintaining a stable operation mode of a storage-ring free electron laser finally resides in a deep understanding of the strongly coupled laser-electron dynamics. Such a dynamics may be affected by electron-beam instabilities whose origin can be traced back either to electromagnetic wake fields or to "external" perturbations (e.g. line-induced modulations, mechanical vibrations, etc.). This is the case of the Elettra storage-ring free-electron laser which is significantly affected by a 50-Hz perturbation of the electron beam density. We have developed a simple theoretical model which has been proved to be able to provide insight into the evolution of the laser intensity. In this framework, we have also proposed the possibility of utilizing a derivative closed-loop feedback to create or enlarge the region of stable signal. A feedback of this type has been implemented on the Elettra storage-ring free-electron laser. The obtained results, which fully confirm our predictions, are discussed in this paper. |
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| WEOA001 | Feedback Control Of Dynamical Instabilities In Classical Lasers And Fels | 391 |
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Dynamical instabilities lead to unwanted full-scale power oscillations in many classical lasers and FEL oscillators. For a long time, applications requiring stable operation were typically performed by working outside the problematic parameter regions. A breakthrough occurred in the nineties [1], when emphasis was made on the practical importance of unstable states (stationary or periodic) that coexist with unwanted oscillatory states. Indeed, although not observable in usual experiments, unstable states can be stabilized, using a feedback control involving arbitrarily small perturbations of a parameter. This observation stimulated a set of works leading to successful suppression of dynamical instabilities (initially chaos) in lasers, sometimes with surprisingly simple feedback devices [2]. We will review a set of key results, including in particular the recent works on the stabilization of mode-locked lasers, and of the super-ACO, ELETTRA and UVSOR FELs [3]. [1] Ott et al. Phys. Rev. Lett., 64, 1196 (1990). [2] Bielawski et al. Phys. Rev. A 47, 327 (1993). [3] Bielawski et al. Phys. Rev. E. 69, 045502 (2004), De Ninno & Fanelli, Phys. Rev. Lett. 92, 094801 (2004), Bruni et al., proc. EPAC 2004. |
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| THPP013 | Operation of the European FEL at ELETTRA Below 190 nm: A Tunable Laser Source for VUV Spectroscopy | 473 |
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Thanks to an intensive technological effort in the framework of the EEC Contract HPRI CT-2001-50025 (EUFELE), the European FEL at ELETTRA was able to break the previous record for the shortest wavelength of an FEL oscillator. Novel solutions were adopted for multilayer mirrors to allow FEL operation in the wavelength region between 160 and 190 nm, which is one of the main targets of the project. The characteristics of the FEL pulses measured at 176 nm (spectral profiles, high intensity, meV bandpass, MHz repetition rate) make it a competitive light source for spectroscopy, in particular for fluorescence studies in the VUV spectral range. Proof of principle experiments have been performed on different types of silica glasses, yielding information on the mechanisms of light absorption in this material. |
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| THPP059 | Frequency Modulation Effects in the Photoinjector for the FERMI @ Elettra FEL | 616 |
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In the framework of the FERMI@ELETTRA project, aimed to build an X-ray FEL source, a crucial role is played by the electron source, which has to produce a very high quality bunch, in terms of low emittance and uncorrelated energy spread. We have investigated the effects of low- (100-300 5m) and high- ( 10-50 5m) frequency modulation of the beam charge deriving from intensity modulation of the laser pulse incident on the photocathode on the downstream beam distribution. Following other proposals, we have investigated the use of a short laser 'heater' to increase the effective incoherent energy spread and reduce the gain in the longitudinal density modulation instability. We present results from simulation of the beam generation at the photocathode, and transport through the photoinjector, initial acceleration modules and the laser heater. |
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| THPP060 | The RF Injector for the FERMI @ Elettra Seeded X-Ray FEL | 620 |
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In the framework of the FERMI@ELETTRA project, aimed to build an x-ray FEL source based on laser-seeded harmonic generation, a crucial role is played by the electron source, which has to produce a very high quality beam, in terms of low emittance and uncorrelated energy spread. A very attractive solution is the SLAC/BNL/UCLA 1.6 cell s-band gun III based upon the demonstrated high performance of this design and its descendants. This paper describes the results of the optimization studies based on the gun III design and carried out with two space charge tracking codes (GPT and ASTRA) for nominal operating parameters. In particular two different bunch charge regimes has been explored: low (few hundreds of pC) and high (~1nC) . In the first case, the limited charge extracted from the photo-cathode allows to propagate a bunch with an initial higher density and to compress it along the linac down to a few hundreds of fs, attaining a high peak current bunch with a very low slice emittance. The second case has been investigated in order to verify the possibility to produce a "1 ps plateau" bunch with acceptable peak current and a slice emittance lower than 2 mm mrad. We present simulation results for both cases. |
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| FROA003 | FERMI @ Elettra: A Seeded Harmonic Cascade FEL for EUV and Soft X-Rays | 682 |
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We describe the machine layout and major performance parameters for the FERMI FEL project funded for construction at Sincrotrone Trieste, Italy. The project will be the first user facility based on seeded harmonic cascade FELs, providing controlled, high peak-power pulses. With a high-brightness rf photocathode gun, and using the existing 1.2 GeV S-band linac, the facility will provide tunable output over a range from ~100 nm to ~10 nm, with pulse duration from 40 fs to ~ 1ps, and with fully variable output polarization. Initially, two FEL cascades are planned; a single-stage harmonic generation to operate > 40 nm, and a two-stage cascade operating from ~40 nm to ~10 nm or shorter wavelength. The output is spatially and temporally coherent, with peak power in the GW range. Lasers provide modulation to the electron beam, as well as driving the photocathode and other systems, and the facility will integrate laser systems with the accelerator infrastructure, including a state-of-the-art optical timing system providing synchronization of rf signals, lasers, and x-ray pulses. Major systems and overall facility layout are described, and key performance parameters summarized. |
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