Author: Michael G. Hogg

Publisher:

Published: 2015

Total Pages: 0

ISBN-13:

Gas filled spark switches are used extensively in pulsed power systems for their high rate of dV/dt, dI/dt, fast closing times with low jitter, and their high voltage and current capability. Recently there has been a renewed interest in designing spark switches that can operate with environmentally friendly gases such as air. This thesis presents an investigation into gas filled plasma closing (spark) switches. Investigating the utilisation of pre-breakdown corona discharge to increase the performance of spark switches operating in environmentally friendly gases is a re-occurring novelty throughout this study. To achieve the aim of this thesis, a number of separate approaches were adopted. In Chapter 2 a comprehensive literature review of pulsed power and plasma switches is presented. Breakdown voltage, time delay to breakdown and its jitter are compared as are different electrode topologies and triggering mechanisms. Chapter 3 describes the experimental systems that were specially designed and built, including the design of a computer (LabVIEW) controlled high voltage system and a precision pneumatic control system. Chapter 4 presents a comprehensive unique investigation into a range of topologies: plane-plane, sphere-sphere, and cone-plane filled with air, nitrogen, and a 60%/40% nitrogen/oxygen mixture. Building on Chapter 4, Chapter 5 presents an investigation of the breakdown voltage of point-plane topologies with varying point radii and for the first time a new parameter "critical electrode separation", dcrit, was identified where positive and negative have equal breakdown voltages. A standalone investigation into the corona discharge in point-plane topology is analysed in Chapter 6 to explain the effects of corona discharge on the self-breakdown voltage. Triggered switches are used extensively in pulsed power systems such as high-voltage pulse generators. A new approach to triggering a switch is investigated in Chapter 7, where a triggering impulse is superimposed on to a DC energised spark switch to initiate breakdown, with breakdown time delays of ~20 ns and jitter of ~1-2 ns. In Chapter 8, a multi-stage spark switch was designed with point-plane topology from the results in Chapter 5, to investigate the impact of multi-stages on the breakdown voltage, corona discharge, time delay, and its jitter. It was established that, with negative energisation, a range of DC energisation levels could be identified that would allow the switches to operate with jitter of ~1-2 ns in a corona stabilised region with increased breakdown voltage. The final section of this thesis in Chapter 9 introduces post-breakdown plasma resistance and inductance consideration. A new method of simulating transient plasma resistance and inductance of plasma channel using PSpice software is presented. This new approach to simulating plasma resistance and inductance can lead to the development of much more accurate plasma resistance models and more accurate modelling of pulsed power systems with multiple spark switches such as pulse generators.