Thesis

Optimisation of energy and brightness transformer stages in a plasma Wakefield accelerator

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Awarding institution
  • University of Strathclyde
Date of award
  • 2024
Thesis identifier
  • T16896
Person Identifier (Local)
  • 201877778
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Qualification Name
Department, School or Faculty
Abstract
  • Capable of sustaining giga-volt-per-metre accelerating gradients, plasma accelerators are a promising technology that offer a path to compact machines for high-energy applications. In the case of a beam-driven plasma Wakefield accelerator (PWFA), energy is transferred from a driver particle beam to an existing bunch trailing in its wake; in this way, the plasma accelerator can be seen as an energy transformer. Alternatively a beam can also be formed directly inside the wake—a so-called plasma cathode. The quality of this new bunch can furthermore be higher than that of the incoming drive beam, where the plasma stage now acts as a brightness transformer.In the case of an energy transformer, this work focuses on an important quantity in plasma acceleration—the energy-transfer efficiency. Here, a new diagnostic was developed based on the light emitted from a beam-interacted plasma that can—in contrast to conventional dipole spectrometers—non-invasively measure the energy-transfer efficiency with longitudinal resolution on a shot-to-shot basis. After benchmarking this method with the spectrometer-based technique, local energy-transfer efficiencies of up to (58 ± 3)% were measured. Furthermore, the potential of this method in diagnosing transverse instabilities was investigated, with this diagnostic seen as being key to the monitoring and optimisation of future plasma accelerators.A PWFA-based plasma cathode stage was then also established and optimised, with the goal of demonstrating the brightness transformation of an input drive beam. Based on optically generated density downramp injection, bunches were internally injected with high reproducibility and accelerated with ∼ GVm−1 accelerating gradients. Thorough characterisation of these bunches yielded O(10pCMeV−1) peak spectral densities, percent level energy spreads and normalised emittances around an order of magnitude less than the drive beam. As a result, the 3D brightness of the injected bunches (i.e. brightness in the horizontal and spectral directions) was shown to be 4.8 times higher than that of the drive beam.Ultimately, both of the themes explored in this thesis are important if plasma accelerators are to meet the demands of future FEL light sources and linear colliders.
Advisor / supervisor
  • Hidding, Bernhard
  • Sheng, Zheng-Ming
Resource Type
DOI
Date Created
  • 2023

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