Milestones

In the first days of July 2014, a team of scientists carried out a transient grating experiment on the DiProI beamline. In this successful experiment, the scientists split a FEL pulse in two and recombine it at the sample with a finite crossing angle. “This generates a dynamic XUV grating”, says team leader Filippo Bencivenga, “which we then probe by an optical pulse coming from the seed laser of the FEL in a pump-probe, four-wave-mixing scheme. The coherent, non-linear, interaction of the three pulses originated a detectable coherent beam propagating along the phase matching direction.” Such kind of non-linear XUV/soft x-ray wave-mixing experiments will be further developed at FERMI in a dedicated beamline (EIS-TIMER), also exploiting the unique capability of FERMI to radiate multi-colour seeded FEL pulses. A multi-colour transient grating approach would enable, for instance, to follow charge flows between constituent elements in molecules with femtosecond resolution, or to study energy transfer processes at the molecular scale.

During the FEL-2 commisiong time, the average energy per pulse of 10 micro-Joule was achieved during the operation at 4 nm. With so intense ligth, it was also possible to observe the 3^rd harmonic at 1.3 nm.

The bunch charge has been increased in order to reach the desired peak current of 800 A alogn the final bunch of about 1 ps. The figure  shows the  measurement of the bunch profile performed by the RF trasnverse deflector.

The Linac had been set at maximum energy gain and the electron beam reached a final energy of 1548 MeV.

During the RUN 16 the FEL 2 reached the wavelength of 4 nm. The machine operated @1.45 GeV and with a 'flat' longitudinal phase space obtained with a ramped photo injector laser profile.

During the shutdown the new PC-Gun was installed and its functioning enables the machine operation at 50 Hz.

15.02.2013 First FEL-external laser pump-probe signal has been obtained at the DIPROI beamline. The transient reflectivity change induced by the FEL light on GaAs and Si3N4 samples was measured by the use of a fraction of IR seed laser pulse propagated to the experimental hall. The measurement demonstrated excellent short- and long term stability of the signal, indicated an upper limit for the timing jitter of 25 fs RMS and provided a way to find the fine zero tuning of the delay for the following user pump-probe experiments.

The electron bunch has been seeded with two optical pulses, slightly different in time and wavelength: two FEL pulses were obtained, separated by 0.2 nm in wavelength and few hundred femtoseconds in time.

On October 11, 2012 the beam line FERMI FEL-2 has generated its first coherent photons. This is the first experimental demonstration of a seeded free electron laser configured as a two stages cascade operating in the "fresh bunch injection” mode. In this configuration the photons in the second stage are generated from a fresh portion of the electron bunch, which has not been heated by the seed of the first stage.

The first commissioning experiments were done at a final wavelength of 14.4 nm in planar polarization. This wavelength is the result of an harmonic conversion to the 6th harmonic (43.33 nm) in the first stage and the 3rd harmonic in the second (i.e., 18th harmonic of the seed laser). The FEL pulse energy has been optimized to increase the flux to about 20-30uJ. The figure shows one of the single mode spectra obtained from FEL-2 at 14.4 nm.

FEL spectrum

X-band section picture

After the commissioning, the X-band section is routinely used to control the longitudinal e-beam phase space and to improve the magnetic compressor efficiency. The right figure shows a phase space measurement by means of the RF deflector in the linac end with the energy dispersion in horizontal and the temporal distribution in vertical.

Seeded coherent emission from FEL-2 first stage measured by means of a YAG screens located downstream in the FERMI@Elettra udulator hall. The image shows the FEL spot.

The Laser Heater device increases the uncorrelated slice energy spread of the e-beam in controlled way. Figures show the longitudinal phase space of the heated/normal beam, vertically dispersed by the RF deflector, measured in the spectrometer.

The FEL-2 undulators installed. The new undulators (blue-yellow) are now in front of the FEL-1 devices (red).
During the next run (#11), the FEL-2 first stage will be testested.

During the night between March 14 and March 15, 2012, a single shot diffraction image (left) of real holo-object (right) was taken at the DiProI beamline, with the FEL pulse of about 30 µJ @32 nm in planar polarization.

The installation of the FEL-02 transport line was completed during the winter shutdown. In the following run (the 10^th) the e-bunch reached the main dump without charge losses and the trajectory control was established. The side figure shows the beam size along the transport.

He fluorescence is detected over thousands of shots, normalized by FEL intensity, and plotted versus seed wavelength (5×FEL wavelength)

The result is the FEL linewidth, as probed by the much narrower He 1s-4p atomic line (top)
Compare to single-shot line detected by PADRES spectrometer (bottom)

First FERMI spectrum:
A_r photoelectron spectrum was acquired by the LDM detector
with the FEL @ wavelength =65 nm, horizontal polarization.

Seeded coherent emission from FEL-1 measured by means of a fast photodiode located in the FERMI@Elettra experimental hall. The undulators were tuned at 43 nm. The green trace shows the time profile of a single pulse with the photodiode in saturation. The yellow trace shows a series o seeded FEL pulses being turned on (left) and off (center-right) by changing the superposition between SEED laser pulses and electron pulses.
During the night between December 13 and December 14, 2010, the new free-electron laser (FEL) source FERMI@Elettra seeded at 260 nanometers with an external laser has produced the first coherent emission from the FEL-1 undulator chain tuned at wavelengths of 65 nanometers (fourth harmonic of the seed laser) and 43 nanometers (sixth harmonic).
Sample results are shown in the figure for 43 nanometers. The plot shows in green the signal trace of a fast photodiode located on a beamline in the FERMI experimental hall observing the FEL output. Saturation of the photodiode signal affects the measured profile. The yellow trace shows a wider scan with seeded FEL pulses being turned on and off by varying the superposition of seed laser pulses and electron pulses.
This marks the first successful operation of FERMI@Elettra in its planned configuration, i.e., as a next-generation seeded free-electron laser source.

  Experimental Hall (left picture: inside view; right picture: external view) ready to receive the photon distribution systems and the end stations.

The 7 FEL-1 undulators installed and ready to be used!

The FEL-1 beamline gets equipped with two optical fibers that allow to measure the position and magnitude of beam losses. The system locates the position of the beam loss with a resolution of 50 cm. The machine protection system can disable the electron beam if the losses are too high.

Following the installation in December 2009 just beyond the first Bunch Compressor, the conditioning and commissioning of the Low Energy Deflecting Cavity have taken place in spring 2010.

This Device allows bunch length measurements, arrival time jitters estimation, slice emittance and reconstruction of longitudinal phase space.

(left figure: 3D model;
right picture: installed device)

This figure is a Screen Image of the electron beam after the spectrometer dipole and represents the longitudinal Phase Space of the e-beam with the energy dispersion in horizontal and the temporal distribution in vertical.

During the 4^th machine run the electron beam reaches the linac end passing
through the all 17 accelerating sections gaining the nominal energy equal to 1.2 GeV .
The figure shows the software panel that measure the electron beam energy by means of the dipole spectrometer.

The machine protection system (MPS) prevents the accelerator from damaging itself with its own beam. In this first stage, the MPS makes sure that the electron beam cannot hit the supports of diagnostic screens while they are being moved into the beam tube. The system also monitors the main dipole magnets to guarantee that the beam can safely reach a beam dump on one of the predefined paths (see picture).

During the last shift of 19 August, the copper cathode of the RF gun was fed at a level that has generated on the cathode surface an Electric Field of about 80 MV / m, the cathode was then illuminated by a UV pulsed laser at 260 nm which provides the cathode the same few dozen μJoules per pulse. The first photoelectron FERMI have been clearly shown to be both integrated current transformer (ICT) scintillation screen YAG: Ce. The image shows the captured electron beam on the screen.