Characterisation of plasmas produced in vapour layers in conducting solutions

• Main Author: Kelsey, C. P.
• Published: Queen's University Belfast 2014
• Subjects: 530.4
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.678703

This thesis looks at plasmas produced in vapour layers in electrically conducting solutions, with a particular focus placed on adapting existing diagnostic techniques to the novel environment. An asymmetrical geometry with a 0.5 or 1 mm wire electrode surrounded by a dielectric tube with 0.5 or 1 mm extruded, and a larger area collar or plate electrode is used to generate the plasmas. The discharge is operated with negative voltages on the order of several hundred volts applied to the wire electrode for several hundred microseconds with the larger electrode grounded and both electrodes submerged in solutions with room temperature conductivities ranging between 10 and 40 mS/cm. Due to area asymmetry between the electrodes, vapour layer formation occurs around the wire electrode via Joule heating so that the vapour layer/liquid boundary acts as the effective ground electrode with the resistance of the conductive solution limiting current flow within the plasma. Fast camera imaging, voltage, current and PMT measurements as well as multiphysics modelling are used across a range of pressures to establish that geometric field enhancement is present to the extent that streamer breakdown is the most likely initiation mechanism for the plasma. After this the plasma quickly transitions to an atmospheric pressure glow mode. Diagnostics used to further characterise this mode of the plasma include time resolved Stark broadening measurements of the hydrogen beta line to determine electron density and time averaged measurements of the relative intensities of barium II lines to determine electron temperature. Chemical measurements also performed on the conducting solution surrounding a separate plasma system in a similar operating regime but with a bipolar voltage waveform at kHz frequency to determine the production rate for hydrogen peroxide along with electrical measurements to allow a production efficiency to be calculated.