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Title: Numerical simulations of plasma dynamics and chemistry in dual radio-frequency and pulse driven capacitively coupled atmosphere pressure plasmas
Author: O'Neill, Colm Philip
ISNI:       0000 0004 5992 6561
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2015
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This thesis presents the results of numerical models used to investigate the influence of the operating conditions of a micro atmospheric pressure plasma jet, on the electron dynamics, ionisation/sustainment mechanisms and resultant plasma chemistry. The aim is to determine the, optimum operating conditions of this discharge for enhancing and controlling the underlying plasma processes and production/composition of useful reactive species. Both nonlinear frequency coupling and pulsed excitation have been shown to influence the underlying processes governing the electron dynamics in radio-frequency driven atmospheric pressure plasmas, here the effects of operating a micro atmospheric pressure 'plasma jet (μ-APPJ) using dual frequency (2F) and pulsed excitation are explored. Several multi-scale numerical models based on hydrodynamic equations with a semi-kinetic treatment of the electrons are used to investigate the influence of the operating mode on the plasma dynamics and chemistry. The models consider a helium background gas with a small molecular admixture of either Nitrogen or Oxygen, and range in complexity, with the most complex model accounting for 184 reactions amongst 20 species. Each model is found to agree well with experimental benchmarks. Using 2F excitation, it is found that variations of power density, voltage ratio and phase relationship provide separate control over the electron density, mean electron energy and electro-negativity. Using Pulsed excitation, variations of the pulse width and repetition rate are also found to directly influence the electron density, mean electron energy and electro-negativity. In both cases this is exploited to directly influence the phase dependent and time averaged effective EEPF, which enables tailoring of the EEPF for enhanced control over the plasma chemical kinetics. This is shown to allow control over the production and composition of useful reactive species, namely reactive oxygen species.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available