Italian National Agency for New Technologies, Energy and Sustainable Economic Development
Science: First demonstration of plasma particle accelerator-driven free electron laser published in Nature
Steps forward towards the first generation of radiation sources based on plasma particle accelerators, to study the origin of matter and the universe and for numerous applications in the biomedical, pharmaceutical and cultural heritage fields. The results of an experiment conducted by an ENEA-INFN team, which for the first time in the world tested a Free Electron Laser (FEL) driven by a plasma accelerator, obtaining electron beams of a quality comparable to those of conventional accelerators, was published in Nature.
Smaller, more compact, cheaper and capable of obtaining higher energies than the current ones, plasma particle accelerators promise easier use, new application fields, a widespread and capillary use throughout the territory in universities, industries and hospitals.
"In the current FELs, electrons are accelerated by the radiofrequency field with machines that can even be a few kilometers long and have huge construction and operating costs", pointed out Alberto Petralìa at the ENEA Plasma Application and Interdisciplinary Experiments Laboratory. “For this reason - he said - we believe that the experiment provides the evidence that grounds the scheme of this machine and a milestone in the use of plasma-based accelerators, providing an important contribution towards the development of more compact FELs operating at much shorter wavelengths, for new horizons of knowledge and applications, also in the medical and biological fields”.
ENEA, at the forefront in the study of radioactive sources across the entire electromagnetic spectrum, contributed to this experiment in the alignment and transport procedures of the electron beam in the undulator  and in the characterization of the radiation generated, in terms of intensity and spectral content .
INFN, where the pilot experiment was carried out, supervised the work concerning production, acceleration and characterization of the electron beam.
“We conducted the experiment using the beam-driven technique, in which an electron beam is accelerated by an electric field produced in the plasma by the passage of a first particle beam,” explained Petralia. “This allowed to observe both the radiation obtained in the infrared region and its intensity, confirming its suitability for the construction of future machines for generating light pulses comparable to a laser in X-rays, with a small wavelength , capable of investigating matter with a better resolution”, concluded Petralìa.
The result is an important step towards the creation of new X-ray FEL sources based on plasma accelerators, which is also the objective of the European project "EuPRAXIA” –
ENEA participates in the project together with the INFN, Cnr, Rome Universities "Sapienza" and "Tor Vergata", Elettra Sincrotrone Trieste and other prestigious European research centres. It also coordinated the activities related to the definition of the FEL performance within the Conceptual Design Report and is involved in the design of the EuPRAXIA@SPARC_LAB>, which will be the first FEL driven by a plasma accelerator to generate X-ray radiation.
Free Electron Laser (FELS)
They operate in regions of the electromagnetic spectrum not accessible by conventional lasers, i.e. in the TeraHertz and in the extreme ultraviolet up to X-rays. In FELs, electrons are accelerated to nearly the speed of light and subsequently injected into a structure, called an undulator, which has a magnetic field with an amplitude that varies along the direction of motion of the electrons, thus forcing the particles to follow a trajectory similar to a wave (hence the name undulator). In this interaction between the moving electrons and the magnetic field, electromagnetic radiation is produced and then amplified. The most modern X-rays FELs make it possible to investigate the matter and the phenomena that occur on the spatial and temporal scale typical of processes at the molecular level.
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 The structure in which the accelerated electron beam interacts with the magnetic field, generating the radiation which is amplified in the passage, through the entire 12 meters of length.
 A first stage of radiofrequency and the second stage of plasma acceleration.
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