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Title: Numerical models for the simulation of Raman amplification in plasma
Author: Farmer, John
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2012
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Raman amplification in plasma is a potential method of producing ultra-short, ultra-intense laser pulses. As amplification in realistic systems involves many competing nonlinear processes, numerical simulations are often used to better understand the associated complex behaviour. Different models offer different advantages and limitations. This work presents a study of three distinct numerical models: a particle-in-cell (PIC) code, a threewave model derived from a fluid treatment of plasma, and the envelope-PIC code aPIC. PIC codes are known to incur large computational overheads. A new numerical instability associated with nonlinear plasma waves has been identified, which can result in a significant increase in the computational overhead required to achieve convergent results for the simulation of Raman amplification. The absence of collisional damping in available PIC codes is found to limit the parameter spaces within which simulations can be carried out. The conventional three-wave model has been extended to improve its accuracy, and to include the effects of plasma wave harmonics. In warm plasma, a new model is developed to estimate the fraction of trapped electrons, and their influence on the effective modulation depth of the plasma wave. Benchmarking against PIC codes shows strong agreement in regimes where the linearisation of the plasma response and Landau damping rates is valid. aPIC, an envelope-PIC implementation suitable for the investigation of Raman amplification, has been further developed to give improved numerical accuracy, allow the use of chirped pulses, and approximate the dispersive action of the plasma on the laser pulses. Benchmarking against full PIC codes shows good agreement. The code is used to identify a new regime of broad-bandwidth Raman amplification, with nonlinearity arising through high-amplitude plasma waves. Possible future improvements to the model and numerical implementation are outlined. The applicability of these models to the simulation of current experimental work at the University of Strathclyde is also considered.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available