Radio Frequency Characterization and Alignment to the Nanometer Scale of a Beam Position Monitor for Particle Accelerators

The Compact LInear Collider (CLIC) study at CERN requires low emittance beam transportation and preservation, thus a precise control of the transverse beam orbit along two separate 20 km-long linacs in the micrometric regime is crucial to achieve high luminosity collisions. A series of resonant cavity Beam Position Monitors (BPMs) is located along the beam line, each near a focusing beam quadrupole. While the BPMs are used to precisely monitor the beam trajectory along the evacuated beam pipe, the quadrupole magnets are essential to focus the particle beam. The two devices are attached in such a way that beam drifts from the magnetic center of the quadrupole will be monitored by the BPM and consequently controlled to avoid emittance blow up. The PACMAN project aims to pre-align the BPM and the Main Beam Quadrupole (MBQ) on a common support in a laboratory environment with micrometric accuracy, this is a mandatory first step to meet the CLIC luminosity and emittance specifications. A dedicated standalone test bench for observing mechanical and electromagnetic misalignments was designed, including nano-positioning stages for beam trajectory adjustments. The electromagnetic offset between the two devices is characterized through stretched and vibrating wire measurements techniques. This doctoral dissertation focuses on the study and the analysis of the cavity BPM designed for the CLIC Test Facility (CTF3). Measurements, RF characterization and final fiducialization of the BPM-MBQ electromagnetic offset are treated with details. Initial studies through EM simulations of the cavity BPM are covered, along with a discussion on the implementation of state-of-the-art RF measurements methods. The RF stretched-wire characterization is implemented on both the Final PACMAN Alignment Bench (FPAB) and the single BPM. The presented experimental results prove the feasibility of the innovative alignment methodology established by the PACMAN team, locating the electromagnetic displacement between the quadrupole and the attached BPM in a micrometric range. As a supplementary challenge, the verification of the nanometric resolution of the position cavity BPM was undertaken through an innovative, wire-based, approach.