Ph.d. degree
EPFL, Switzerland, 2018

Inaki Ortega Ruiz

Supervisor:Aurelio Bay

Accurate Profile Measurement of the Low Intensity Beams in the CERN Experimental Areas

Keywords:

• Beam-line instrumentation (beam position and profile monitors; beam-intensity monitors; bunch length monitors)
• Particle tracking detectors
• Scintillators and scintillating fibres and light guides
• Instrumentation and methods for time-of-flight (TOF) spectroscopy

Abstract:

The CERN accelerators deliver a wide spectrum of secondary beams to the Experimental Areas. These beams are composed of hadrons, leptons, and heavy ions that can vary greatly in momentum (1GeV/c to 400 GeV/c) and intensity (10^2 to 10^8 particles per second). The profile, position, and intensity of these beams are measured using particle detectors. However, the current systems show several problems that limit the quality of this kind of monitoring.
The aim of this doctoral thesis is to investigate the best detector technology that could replace the existing monitors and build a first prototype of it. A review of the existing detection techniques has led to the choice of Scintillating Fibres (SciFi) read-out with Silicon Photomultipliers (SiPM). This detection technology has the potential to perform better in terms of material budget, range of intensities measured, and active area size. In addition, it has particle counting capabilities, which could extend its application to momentum spectrometry or Time-of-Flight (ToF) measurements. Its resistance to radiation damage offers good potential for longevity of use.
A first prototype of a SciFi-SiPM monitor has been successfully tested with different particle beams at CERN, giving accurate profile measurements over a wide range of energies and intensities. It has only shown problems during use with lead ion beams, whose origin is believed to be crosstalk between the fibres.
A Geant4 simulation of a single scintillating fibre has been performed to estimate its signal generation. This simulation is verified by real measurements of the light yield of scintillating fibres. Similarly, another Geant4 simulation of a full SciFi monitor has been developed to characterise the perturbation of the beam by the monitor.
The future beam instrumentation for the Neutrino Platform at CERN is also described here, which is being developed as a continuation of the work conducted during this thesis.