Manipulation of charged particle beams through coherent interactions with crystals

In the last years, the field of channeling and related phenomena aimed to particle-beam steering has received a tremendous impulse by the advent of a new generation of silicon crystals, which resulted in significant performance increase and lead to the discovery of novel phenomena. The first key factor was the usage of silicon crystals exploiting secondary deformations, which provide extremely uniform bending an optimal sample thickness across the beam. Moreover, the holder to impart the primary curvature is designed to keep apart all the material but silicon from the trajectory of the beam. A second key factor which lead to performance improvement is the quality of the crystal surfaces by using properly tailored chemical etchings. In particular, the entry face of the crystal plays an important role, because it is the surface accepting incoming beam particles. Lastly, significant contribution was due to the characterization of the samples with a variety of techniques. A thorough characterization allows fine adjustment of the experimental parameters for crystal fabrication and certification of its quality prior to installation in the accelerator. In this thesis it will be shown the procedures for manufacturing of crystal realized at Sensors and Semiconductor Laboratory of Ferrara University. The fabrication methods, based on revisitations of micromachining techniques, allow obtaining high quality crystals, which lead to performance increase as well as to the discovery of new effects in the interaction with positively and negatively charged particle beams at CERN facilities. As it will be shown in this thesis, the geometry and the quality of the realized crystals allowed attaining a record 83% efficiency when operated to deflect a 400 GeV proton beam at the H8 line at CERN by means of planar channeling and contributed to the observation of volume reflection. The same crystal generation enabled to observe multiple volume reflection in both a series and in a single crystal and to successfully achieve deflection of negatively charged particle beams through either channeling or volume reflection. Coherent phenomena in crystals may be the basis for halo collimation for current hadron colliders (e.g. the LHC). An efficient collimation system is a necessary condition to run the accelerator at its top luminosity and to prevent damage of its sophisticated superconductive magnets. This smarted collimation scheme is currently being under investigation in the pilot UA9 experiments, which investigate crystal-assisted schemes for halo collimation in the CERN SPS through channeling of protons. The first and preliminary results of UA9 experiment shows good perspectives on the possibility to collimate the LHC beam by using bent crystals.