Date of Award

Summer 2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical/Computer Engineering

Committee Director

Mounir Laroussi

Committee Member

Sylvain Marsillac

Committee Member

Rick McKenzie

Committee Member

Jiang Li

Abstract

A non-thermal transient diffuse plasma can be generated remotely in a nonconductive reduced pressure chamber by an external guided fast ionization wave (FIW). We found that an atmospheric-pressure low-temperature plasma jet (APPJ) can be a source of FIW which transfers an enhanced electric field at the wave front across a reduced pressure Pyrex glass chamber with no electrical connection to the chamber. Here, we studied the formation and propagation of the APPJ plasma, the interaction of atmospheric-pressure guided FIW with a dielectric surface which forms the wall of the reduced-pressure system, and the formation and propagation of the reduce-pressure FIW inside a chamber. In this study, key characteristics of the transient diffuse plasma are discussed.

The reduced pressure plasma parameters were measured by Langmuir probe and APPJ electrical measurements were carried out to elucidate the operational mechanisms of the guided FIW as an igniter of the reduced-pressure transient diffuse plasma. It was shown that the transient discharge in the reduced-pressure chamber was generated by an enhanced electric field (18.5 kV/cm when the APPJ applied voltage was 8.5 kV) inside the chamber that generated a bulk plasma with negative potential due to the nonconductive boundary.

We used fast imaging of both APPJ plasma plume and the transient reduced-pressure FIW inside the Pyrex chamber. Fast images were taken by an intensified CCD to study the launching and propagation phases of both APPJ plasma and the transient reduced-pressure diffuse plasma as well as the incidence of the guided FIW on a dielectric surface. The APPJ plasma plume images revealed that the plasma plume created by guided FIW was in fact made of two discrete volumetric discharges (known as plasma bullet) per applied high-voltage pulse traveling at supersonic velocities up to 170 km/s. Since such a volumetric discharge was initiated by a surface discharge inside the APPJ hollow tube, it had a donut-shaped structure.

We also used Optical emission spectroscopy (OES) to determine the physical and chemical characteristics of the APPJ plasma and the transient diffuse plasma. It was shown that the diffuse plasma was capable of producing first and second ionized nitrogen (N+ and N++), atomic oxygen (O), ionized nitrogen molecule (N2+), and OH radicals in helium diffuse plasma (with air impurities) and in air diffuse plasma.

The present research shows that this type of electrodeless non-thermal, large-volume diffuse plasma resembles a fast-growing transient glow discharge that lasts for several hundreds of nanoseconds. The electron density in such a plasma with the admixture of helium and air can reach up to 1012 cm-3 at a pressure around 1 Torr. A promising application of the large-volume diffuse plasma is in surface processing such as plasma-aided coating and etching processes with minimal contamination due to the clean environment inside the reduced-pressure system.

DOI

10.25777/3cee-ma27

ISBN

9780438712577

ORCID

0000-0003-2779-8270

Available for download on Saturday, December 12, 2020

Share

COinS