Dottorato in FISICA DEGLI ACCELERATORI

Titolo della tesi: Start to end simulations and beam characterization of the THz Free Electron Laser SABINA at SPARC_LAB

SABINA (Source of Advanced Beam Imaging for Novel Application) is a project developed at the SPARC_LAB research facility at LNF-INFN, with goal of realizing a source of electromagnetic radiation covering an interesting and underdeveloped region of electromagnetic spectrum: that of THz/MIR (Mid-Infrared). The terahertz (THz) spectral region is defined as the region in the frequency range of (0.1–10) THz, which corresponds to a photon energy of (0.4 -40) meV. This frequency range has also been called ``THz-gap" to underline the lack of sources and detectors working at a photon energy (0.1 -30) meV until two decades ago. In any case, although great efforts have been made to fill this gap, a true bridge between THz radiation and MIR is not yet complete, particularly with regard to high picosecond (ps)/sub-picosecond pulsed beams. The SABINA project aims at the realization of a FEL (Free Electron Laser) beamline operating as a user facility that delivers quasi monochromatic light, with high intensity ps/sub-ps photon pulses (up to hundreds of uJ each), in the frequency range between 3 THz (100 um) to 30 THz ($10 um). A crucial feature will be the possibility to control the radiation polarization from linear, to circular, to elliptical. This polarization flexibility will allow to perform exotic studies such as chiral pump-probe spectroscopy on ps time scale, investigating the dynamical properties of chiral molecules through the implementation of multiple colors and polarization. We underline that a facility matching all these requirements at the same time, represents a unique opportunity in the world-wide scenario. The reference technology is that of the FEL, hence the radiation will be produced by an intense ultrarelativistic electron beam traversing an undulator based on the APPLE-X configuration which will allow to generate the radiation with the aforementioned features. This thesis work is carried out in the framework of SABINA and is mainly devoted to the the study and definition of the undulator features and the characteristic of the output radiation, as well as to the study of the electron beam dynamics, from its generation at the photo-cathode, up to the undulator exit. The study extends and includes the electron beam transfer to the undulator, realized with a dogleg, a set of bending magnets and focusing optical elements affecting the electron beam quality during the transport. The study of the dogleg dynamics and the beam quality degradation is therefore an important aspect of the work. The thesis includes a part of experimental work on the characterizations of magnets dedicated to the electron beam transport and matching. The detailed study of the experimental characterization of two PMQs (Permanent Magnet Quadrupoles) triplets, which will be installed on the SPARC_LAB beamline is presented.