Fermi Machine Description

The FERMI single-pass linac-based FEL at the Elettra Laboratory is one of the European FELs, an international user facility in Italy for scientific investigations of ultra-fast and ultra-high resolution processes in material science and physical biosciences with ultra high brilliance X-ray pulses. With a peak brightness of about 6 orders of magnitude higher than third generation sources, full transverse coherence, (close to) transform limited bandwidth, pulse lengths of the order of a picosecond or less, variable polarization and energy tunability, the FERMI source is a powerful tool for scientific exploration in a wide spectrum of disciplines.

The seed laser provides a reference signal throughout the FERMI facility (including the experimental beamlines) to facilitate the femtosecond level precision timing and synchronization of all systems.

The main machine characteristics are:

  • High peak power (~ GW) optical pulses with synchronization to external laser sources. Generation of shorter pulses (sub fs) will also be explored.
  • APPLE II type undulators to enable flexible tuning of both photon wavelength and polarization.
  • Implementation of seeded harmonic cascade FEL schemes for tunable and controlled short-wavelength photon pulse production.
  • Advanced feedback and feed-forward systems to improve output stability.


A general layout of the facility is shown in the above Figure. The accelerator and FEL complex comprises the following parts: a photoinjector and two short linac sections (LINAC 0) generating a bright ~ 100 MeV electron beam (first 10 meters), the main linear accelerator (LINAC 1-4) in which the beam is time-compressed and accelerated up to ~ 1.5 GeV (170 meters), the system to transport the beam to the undulators (SPREADER), the undulator complex generating the FEL radiation (270 meters), the photon beamlines taking the radiation from the undulator to the experimental area (320 meters) and the experimental area itself.

After leaving the undulators, while the FEL radiation is transported to the experimental areas, the electron beam is brought to a beam dump by a sequence of bending magnets. The FEL radiation transport system, designed to handle the high peak power of up to 10 GW in the sub-ps long pulse, includes a differentially pumped windowless vacuum system and low-Z material beam-line components operating at grazing incidence angles. The photon beam transport system incorporates all provisions and equipment necessary to ensure pulse length and energy resolution preservation, monochromatization, 

source shift compensation, beam splitting and focusing into the experimental chambers.

As above mentioned, the FERMI facility comprises two separate coherent radiation sources, FEL-1 and FEL-2, that are being brought online sequentially. FEL-1, currently in the final stages of commissioning, will operate in the wavelength range between 100 and 20 nm via a single cascade harmonic generation, while the FEL-2, currently in the early stages of installation and commissioning, is designed to operate at shorter wavelengths (20-4 nm) via a double cascade mechanism.

Last Updated on Thursday, 17 July 2014 09:44