Experimental optimisation of CERN 750MHz proton Radio-Frequency-Quadrupole for Surface Analysis

The present thesis deals with the experimental optimisation of an accelerating structure named ELISA-RFQ. All the experimental work was carried out by the author at the CERN laboratories in Geneva, Switzerland. The branch of application is Radio-Frequency engineering applied to particle accelerators, having had the opportunity to study, perform and apply electro-magnetic characterization, analysis and RF measurement techniques on RF devices. The work is centered around the tuning and RF measurements of a particular typology of resonant cavity, called Radio-Frequency-Quadrupole (RFQ), operating at 750 MHz. The name of the project is ELISA-RFQ, that stands for Experimental Linac for Surface Analysis, and it is a stand-alone accelerator with a length of only one meter that provides protons for ion beam analysis of cultural heritage artwork. The Radio-Frequency-Quadrupole is a special type of accelerator that accelerates protons or ions at low energies, and represents a crucial component of modern linear accelerator designs. Working at high operating frequency allows for compact and economic RFQ designs, opening up a broad variety of applications in industry and in medicine. A list of possible fields of application are: fusion research, semiconductor industry, radiography, ion implantation, ion beam analysis, isotope production, chemistry, material science, radiotherapy and more. Since the twentieth-century particle accelerators constitute crucial high-technological structures, whose development and improvement over the years has led to important advances in science and technology. Their purpose is to accelerate charged particles to relativistic velocities (near speed of light) and at high energies using electro-magnetic fields. In particular the RFQ are part of the category of linear accelerators, in which time-dependent electro-magnetic fields accelerate charged particles along a straight line. An RFQ accelerates hadrons, i.e. protons or ions, at low energies and they were introduced in 1969 by Kapchinsky and Teplyakov first presented the RFQ principle. One of the main advantages of the RFQ over other low-energy RF accelerators is the capability to perform adiabatic bunching converting a large portion of a continuous input beam into a train of stable bunches while minimizing space-charge effects, maintaining high beam quality. The RFQ is considered a major innovation in the field of linear accelerators. In the present days, it is employed often as the first RF accelerating structure in a hadron accelerator complex, as the beam quality achieved at low energies is a fundamental contributor to the overall accelerator performance.