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| MOPPH057 | Design and Performance of the FERMI at Elettra FEL | 174 |
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The FERMI project* at Sincrotrone Trieste is the first user facility based on seeded, harmonic cascade FELs. The second stage FEL will produce tunable output in the 10-40nm wavelength range and will rely upon two stages of harmonic up-conversion. A major goal for this FEL is good longitudinal output coherence (i.e., small spectral bandwidth). At present, we are examining the performance characteristics of two possible configurations. The first "fresh bunch" option is a classic harmonic cascade, where the output radiation from the first radiator is used to seed a fresh part of the electron bunch in the second-stage modulator. The second "whole bunch" scheme seeds the entire e-beam pulse, uses a much shorter first radiator and completely eliminates the second modulator, with the second radiator involving many e-folds of gain. Relying both upon time-steady input parameter sensitivity studies and full start-to-end time-dependent simulations**, we examine the predicted performance of the two configurations and compare with users requirements.
* C. Bocchetta et al., this meeting ** S. Di Mitri et al., this meeting |
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| TUBAU01 | Prospects of Cascaded Harmonic Generation FELs | 281 |
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Harmonic generation in Free Electron Lasers (FELs) encompasses many techniques for using an input seed laser to produce FEL radiation at a frequency that is multiples above that of the seed laser itself. This allows for the advantages of seeded FELs to be preserved, while extending the reach of these FELs to photon energies far above those produced by conventional laser sources. Many new projects are underway to make use of these methods, including the FERMI@Elettra* facility which envisions the use of two harmonic generation stages to reach photon energies above 100 eV. Different methods of harmonic generation are discussed, as well as the technical challenges to overcome in attempting to chain together multiple harmonic stages in an FEL.
* C. Bocchetta et al., Proceedings of the 2005 FEL Conference, (2005) 682. |
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| MOPPH054 | FERMI @ Elettra: A Seeded FEL Facility for EUV and Soft X-Rays | 166 |
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| We describe the conceptual design and major performance parameters for the FERMI FEL project funded for construction at the Sincrotrone Trieste, Italy. This user facility complements the existing storage ring light source at Sincrotrone Trieste, and will be the first facility to be based on seeded harmonic cascade FELs. Seeded FELs provide high peak-power pulses, with controlled temporal duration of the coherent output allowing tailored x-ray output for time-domain explorations with short pulses of 100 fs or less, and high resolution with output bandwidths of the order of meV. The facility uses the existing 1.2 GeV S-band linac, driven by electron beam from a new high-brightness rf photocathode gun, and will provide tunable output over a range from ~100 nm to ~10 nm, and APPLE undulator radiators allow control of x-ray polarization. Initially, two FEL cascades are planned, a single-stage harmonic generation to operate over ~100 nm to ~40 nm, and a two-stage cascade operating from ~40 nm to ~10 nm or shorter wavelengh, each with spatially and temporally coherent output, and peak power in the GW range. | ||
| THAAU01 | Output Bandwidth Effects in Seeded, Harmonic Cascade FELs | 500 |
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| A number of laboratories are studying and/or proposing seeded Harmonic Cascade (HC) FELs as a means both to reach soft x-ray output wavelengths and to provide a degree of longitudinal coherence much greater than that normally possible with SASE devices. While theoretically the output bandwidth of a HC FEL can approach the transform limit given a high quality input seed of reasonable power, there appear to be a number of practical considerations that in many cases can increase the output bandwidth many-fold. In particular, designs that employ dispersive sections following modulator sections in order to increase the amount of coherent harmonic microbunching, can be very sensitive to temporal variations in the electron beam energy, resulting in an output wavelength chirp. Unwanted microbunching induced by the combination of longitudinal space charge instability growth in the linac and CSR in compression sections also can lead to variations in the output radiation phase and amplitude, thus increasing the bandwidth. We give some semi-analytical results for the predicted bandwidth increase for HC configurations and also some detailed numerical simulation results. | ||
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