An atmospheric-pressure microgap plasma source for ozone generation

Open Access
Author:
Brubaker, Timothy Ryan
Graduate Program:
Electrical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 20, 2014
Committee Members:
  • Sven G Bilen, Thesis Advisor
Keywords:
  • microplasma
  • microwave
  • ozone
  • atmospheric-pressure
  • microgap
  • microdischarge
  • plasma
Abstract:
Ozone is a powerful oxidant commonly used to remove pollutants in water. Although widely implemented, conventional ozone generators create corona or glow discharges in the air using high-voltage power supplies that present a hazard for those working on or around the devices. In this thesis, we investigate the use of microplasmas to create a low-voltage ozone generator. This thesis presents the design and preliminary characterization of a resonant-cavity microplasma source operating at 2.45 GHz. Microwave-excited microplasmas have been shown to create stable, non-equilibrium plasmas at atmospheric pressure. These plasmas do not require high voltages, vacuum systems, or noble gases, making them an attractive alternative for generating air plasmas. This particular design uses a resonant cavity to create a discharge across two knife-edge electrodes, separated by a ≈ 100-µm gap. A plasma was established across the gap using a hand-held Tesla coil. The plasma spanned 14 mm at 116-W applied power and generated ozone at 0.002 %wt. Through spectral analysis, we found that the N2 first-positive and second-positive systems and the N2+ first negative system dominate the plasma. We also identify the reactive species OH, NO, and O, which might find applications outside of water treatment. A brief overview of laser-based diagnostics that would aid in characterizing microplasma sources will also be presented, along with specifications for laser-induced fluorescence and laser scattering systems. Lastly, we explore the potential benefits and shortcomings of the source design and recommendations for future research using microplasma sources of similar design.