Date of Award

Spring 2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical & Computer Engineering

Program/Concentration

Electrical & Computer Engineering

Committee Director

Chunqi Jiang

Committee Member

Lepsha Vuskovic

Committee Member

Shirshak Dhali

Committee Member

Shu Xiao

Abstract

Non-thermal atmospheric pressure plasma jets attract a lot of attentions due to its growing interest in plasma medicine. In this study, reactive species (e.g. excited He, O, OH) in a helium single-electrode non-thermal atmospheric pressure nanosecond plasma jet (APNPJ) driven by a nanosecond pulsed power supply have been studied via electrical measurements (e.g. voltage, current) and optical emission spectroscopy. It is shown that the gas temperature of the APNPJs remained near 300±50 K by fitting N2(C-B) second positive system and OH(A-X) emission spectrum. Higher excited N2+ (by a factor of 1.3) but less excited N2, He, O, and OH productions are observed when compared two APNPJs driven by a short pulse (5 ns pulse width) and a long pulse (164 ns), respectively. Importantly, comparable or more excited species were produced by the 5-ns pulsed plasma for the first 100 ns which implies shorter rise time of a pulsed voltage can influence the plasma chemistry by boosting the production of excited species. Further studies indicate that enhanced ionization near the single-electrode nozzle, earlier streamer formation and stronger emissions by excited N2, N2+, OH, and O are observed when the 164-ns plasma jet impinges onto the water surface. Interestingly, maximal OH(A-X) emissions are obtained at pulse width of 600 – 800 ns when a plasma jet impinges onto the water surface with examining of pulse widths from 200 ns to 5000 ns at 7 kV, 200 ns at 1 kHz. More importantly, temporally-resolved emission spectroscopy shows that more than 40% OH(A-X) emissions is produced during the first 200 ns of the voltage pulse regardless of the pulse width.

Plume dynamics indicate that increasing both amplitude (ranging from 5 kV to 10 kV) and helium flow rate (from 8 SCCM to 164 SCCM) resulted in faster propagation of ionization fronts iii hence longer plasma plumes, meanwhile, higher repetition rate (from 10 Hz to 4 kHz) and longer pulse width (from 200 ns to 990 μs) created earlier inception of ionization fronts but shorter plume lengths. Study of repeatability of both air corona discharge and plasma jets pertinent to breakdown probability are investigated in further details.

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DOI

10.25777/c38j-st04

ISBN

9798635232491

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