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Title: Techniques for high repetition rate laser wakefield acceleration
Author: Arran, Christopher
ISNI:       0000 0004 7966 1759
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2018
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I present work on three different techniques in order to contribute towards laser wakefield acceleration (LWFA) experiments which could operate at multi-kHz repetition rates and at low plasma densities ne ~ 1017 cm-3, enabling the acceleration of higher energy electrons in a single stage. Together, these techniques would help to make the next generation of LWFA facilities substantially more competitive with conventional accelerators. Firstly, I consider the accuracy required to resonantly excite plasma wakefields with trains of many laser pulses, produced by high average-power but lower peak-power laser systems. Through theory, simulations and experimental results, I show a strong constraint on the systematic error acceptable in the separation of pulses. However, I also explore using chirped trains of laser pulses, where the pulse separation increases over time, to increase the efficacy of resonant excitation when the pulse spacing cannot be perfectly matched to the plasma. Secondly, I describe a recent technique which can measure plasma waves rapidly and sensitively, using temporally encoded spectral shifting (TESS). I generalise the technique to probe pulses with non-Gaussian profiles and demonstrate that it can be extended to measure quasi-linear wakefields which are not sinusoidal. I detail how a TESS analysis can be conducted in practice and present results from a recent experiment using the technique. Thirdly, I outline a proposed all-optical method of creating plasma waveguides which would be capable of operating at low densities and high repetition rates and are in principle immune to damage from laser pulses. Start to end simulations demonstrate that these hydrodynamic optical-field-ionized plasma channels could meet all of the requirements for next generation laser wakefield acceleration experiments and are used to propose some optimum experimental parameters.
Supervisor: Hooker, Simon ; Walczak, Roman Sponsor: Helmholtz VI ; Science and Technology Facilities Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: High power lasers ; Accelerator physics ; Plasma physics