Study of coherent interactions between charged particle beams and crystals for beam steering and intense electromagnetic radiation generation.

Abstract

The work presented in this thesis has been devoted to the investigation of new schemes for beam steering and high-intense electromagnetic radiation generation through coherent interactions of charged particle beams with crystals. A series of experiments was carried out in two different laboratories, i.e., the Super Proton Synchrotron (SPS) at CERN in Geneve and the MAinzer MIkrotron (MAMI) of the University of Mainz in Germany, by different international and national collaborations, namely the UA9 experiment., the European CUTE project and the INFN COHERENT and ICE-RAD experiments. The experimental data have been analysed and critically compared with simulations. First of all, the possibility of combining the efficient deflection and the intense electromagnetic radiation production of ultrarelativistic electrons through channeling or volume reflection in bent silicon crystals was investigated. Interesting results were obtained in a wide range of beam energies, spanning from 0.855 GeV available at MAMI to hundreds of GeV accessible at the H4 extracted beamline of SPS. It has been demonstrated the possibility to use bent crystals for efficient deflection of electron beams in the subGeV energy range. This range of energies was still unexplored due to the lack of properly sized bent crystal for negative beams steering. Secondly, it has been shown that the radiation accompanying single (VR) and multiple (MVROC) volume reflection in a bent crystal has peculiar characteristics, such as higher intensity than for bremsstrahlung in an amorphous material and a wide angular acceptance, that make this kind of radiation quite interesting for applications. On the very high-energy side, crystal-aided collimation through radiation accompanying VR and MVROC has been proposed for the future electronpositron colliders, e.g., the International Linear Collider. On the other hand, in the subGeVGeV energy range, which is accessible by most electron accelerators worldwide, the radiation accompanying VR can be exploited as an high-intensity X- or γ-sourse with poor emittance beams. In addition to the studies carried out with electrons, the investigation of new schemes for manipulation of charged beams trajectories was carried out at the H8 beamline of SPS with the usage of 400 GeV/c protons. Firstly, a periodically bent crystal was realized via the superficial grooving method and tested at the H8 line. The effectiveness of this method in achieving perfectly periodic structures was demonstrated. On the strength of these results, it has been proposed to test the crystal sample as a positron-based crystalline undulator in the energy range of 10-20 GeV, as a source of intense MeV photons. Finally, it has been experimentally demonstrated that even a straight crystal, i.e., a crystal mirror, may be used for the steering of ultrarelativistic protons in place of a bent crystal. Unlike the traditional scheme relying on mm-long curved crystals, particle mirroring enables beam steering in high-energy accelerators via interactions with μm-thin straight crystal. The main advantage of mirroring is the interaction with a minimal amount of material along the beam, thereby decreasing unwanted nuclear interactions. Summarizing, all the experimental studies presented in this thesis lead us to consider crystals, either bent or unbent, as reliable tools in particle accelerator physics for different applications within a wide energy range.