Date of Award
Doctor of Philosophy (PhD)
Shirshak K. Dhali
Frederic D. McKenzie
Atmospheric pressure low temperature plasma jets (APLTPJs) driven by short pulses have recently received great attention because of their potential in biomedical and environmental applications. This potential is due to their user-friendly features, such as low temperature, low risk of arcing, operation at atmospheric pressure, easy handheld operation, and low concentration of ozone generation. Recent experimental observations indicate that an ionization wave exists and propagates along the plasma jet. The plasma jet created by this ionization wave is not a continuous medium but rather consists of a bullet-like-structure known as "Plasma Bullet". More interestingly, these plasma bullets actually have a donut-shaped makeup. The nature of the plasma bullet is especially interesting because it propagates in the ambient air at supersonic velocities without any externally applied electric field. In this dissertation, experimental insights are reported regarding the physical and chemical characteristics of the APLTPJs. The dynamics of the plasma bullet are investigated by means of a high-speed ICCD camera. A plasma bullet propagation model based on the streamer theory is confirmed with adequate explanations. It is also found that a secondary discharge, ignited by the charge accumulation on the dielectric electrode surfaces at the end of the applied voltage, interrupts the plasma bullet propagation due to an opposing current along the ionization channel. The reason for this interesting phenomenon is explained in detail. The plasma bullet comes to an end when the helium mole fraction along the ionization channel, or applied voltage, or both, are less than some critical values. The presence of an inert gas channel in the surrounding air, such as helium or argon, has a critical role in plasma bullet formation and propagation. For this reason, a fluid dynamics study is employed by a commercially available simulation software, COMSOL, based on finite element method. Spatio-temporally resolved optical emission spectroscopy (OES) gives the evolution of excited species along the trajectory of the plasma bullets. The APLTPJs' chemical composition includes short-lived species, such as He, N2, N+2, and long-lived species, such as Hem (helium metastable), O3, NO, NO2. It is worth noting that metastable level excited atoms play an important role in promoting an enhanced chemistry along the plasma jet. Some of the APLTPJs' biomedical applications, such as dental hygiene applications and destruction of amyloid fibrils underlying Parkinson's disease, are explored along with an important discussion showing that the APLTPJs do not have a cytotoxic effect on living cells.
"Characterizations of Atmospheric Pressure Low Temperature Plasma Jets and Their Applications"
(2011). Doctor of Philosophy (PhD), Dissertation, Electrical/Computer Engineering, Old Dominion University, DOI: 10.25777/yfbs-rj14