Collective effects and experimental verification of the CLIC drive beam and decelerator

The Compact Linear Collider (CLIC) is a potential next-generation particle collider, in which electrons and positrons collide at a center-of-mass energy of up to 3 TeV. In order to reach a high accelerating gradient and reduce the length of the machine, CLIC uses a novel two-beam scheme. Here, the acceleration energy for the main beam is provided by energy extraction from a secondary electron drive beam, by the use of Power Extraction and Transfer Structures (PETS). This Ph.D. thesis describes deceleration measurements from the CLIC Test Facility 3 at CERN, from a beam that had up to 37 % of its kinetic energy converted into 12 GHz rf power. The results are part of the feasibility demonstration of the CLIC scheme. The measured difference in beam energy of the decelerated beam is correlated with particle tracking simulations and with predictions based on analytical formulae, and a very good agreement is demonstrated. The evolution of the transverse emittance was also studied, since it is critical to contain the large drive beam within the limited available aperture. The emittance was not found to increase from other effects than adiabatic undamping. In order to reach consistency between measurements, theory and simulations, it is important to take the bunch phase into account, which affects the rf field produced in the PETS. New formulae have been derived to take this effect into account. Also longitudinal space charge in the CLIC decelerator has been studied. It has been a concern that, despite the high energy of the CLIC drive beam, longitudinal space charge may lead to a violation of the strict bunch length tolerance. However, it is shown that the space charge effect is still negligible. For this a new Particle-in-Cell written in Octave was developed, and is described in the thesis.