Bulletin of the American Physical Society
72nd Annual Gaseous Electronics Conference
Volume 64, Number 10
Monday–Friday, October 28–November 1 2019; College Station, Texas
Session CT1: Plasmas in Liquids I |
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Chair: Sergey Leonov, University of Notre Dame Room: Century I |
Tuesday, October 29, 2019 8:00AM - 8:30AM |
CT1.00001: Correlation between OH density in gas and intensity of luminol chemiluminescence in liquid interacting with atmospheric-pressure DC glow discharge Invited Speaker: Naoki Shirai The relationship between the density of OH radicals in the gas and the intensity of luminol chemiluminescence was investigated using an atmospheric-pressure plasma system in contact with liquid. The luminol chemiluminescence with a thin thickness was observed just below the plasma-liquid interface when the plasma was generated on the aqueous solution surface with luminol. The radial region with the chemiluminescence was approximately 2.6 times larger than that of the plasma with the optical emission, and was similar to the diameter of the region with OH radicals in the gas phase. The decay time constant of the intensity of the luminol chemiluminescence in the afterglow phase of the DC pulsed discharge was approximately 100 $\mu$s, while the optical emission intensity at the second positive system of molecular nitrogen decayed immediately after the termination of the discharge current. On the other hand, the decay time constant of the OH radical density was approximately 100 $\mu$s in the afterglow phase. In addition, we used other atmospheric pressure plasma source using helium crossed gas flow. We confirmed that OH radicals were transported to downstream of crossed gas flow. When this downstream region contacts with luminol, blue chemiluminescence is observed. These experimental results indicate that the luminol chemiluminescence is induced by the transport of OH radicals to the plasma-liquid interface. [Preview Abstract] |
Tuesday, October 29, 2019 8:30AM - 8:45AM |
CT1.00002: Pulsed plasma discharge in liquids at ultra-high pressures Jacob Mallams, Xin Tang, Mirza Akhter, Dr. David Staack Plasmas are used regularly in applications found within geosciences, sanitation, and more. These techniques may also have applications within high pressure fluids. One of these applications is rock drilling where downhole pressures can reach up to 10000 psi. In order to observe the effect of plasma in these conditions, plasma have been studied within fluid in the range of 14.7 psi to 5000 psi. This study investigates potential changes in mechanisms and effects of plasma breakdown in liquids of this factor 300 variation in initial pressure. To achieve said pressures, a pressure vessel was created using pipe fittings available off the shelf, a high pressure pump, viewing glasses, electrical feedthrough, and a 3D printed testing fixture. Plasma discharges have been studied at a variety of voltages ranging from 5kV to 15kV across a 1-3 mm spark gap. 80J, nanosecond pulsed plasma discharges were carried out at different pressures. Testing was recorded with a high speed camera and electrical diagnostics in order to fully identify the breakdown, plasma discharge, and induced bubble activity within the vessel. Preliminary tests show that plasma creation at high pressures is possible but that it requires an increasingly small gap to create breakdown. It is expected that these tests will provide insight to the feasibility of plasma use in other extreme environments. [Preview Abstract] |
Tuesday, October 29, 2019 8:45AM - 9:00AM |
CT1.00003: High Frequency Plasma Electrolytic Oxidation (PEO): Diagnostics and Control of Microdischarges Patrick Hermanns, Vera Bracht, Simon Boeddeker, Peter Awakowicz Plasma Electrolytic Oxidation of aluminum is a promising approach for three dimensional coatings with high growth rates. Individual lifetime, size and current density per microdischarge changes with processing time and oxide layer thickness. Due to the microdischarges being the main reason for coating growth, it is desirable to understand and control their properties. In this work, the lifetime of microdischarges is estimated by wavelet transform of the electrical current signal. Results show a rise in lifetime from 10 us to 100 us with processing time. Therefore, a pulsing frequency between 2 kHz and 100 kHz was chosen. Fast optical measurements, with multiple ICCD cameras triggered individually, show the intensity evolution of microdischarges during individual pulses. Increasing the pulse pause leads to a smaller probability of discharge reignition on the same spot and a further decay of microdischarge intensity during the pulse off time. As a result, the mean current and energy per discharge is reduced. These findings are implemented in a control loop setup, where duty-cycle and current density are used as control values to control the mean discharge size and discharge number density. [Preview Abstract] |
Tuesday, October 29, 2019 9:00AM - 9:15AM |
CT1.00004: On the source of primary electrons at the initial stage of nanosecond breakdown in water Xuewei Zhang, Mikhail Shneider Recent studies have proposed cavitation due to negative pressure created by electrostriction in inhomogeneous field as the mechanism of nanosecond breakdown initiation in water. Initial plasma channel formation results from the multiplication of collisionless electrons in the nanovoids. Here we discuss possible sources of primary electrons that trigger the multiplication process. It is estimated that cosmic background radiation and field ionization of water molecules are unlikely to produce enough electrons even in a field of 5 V/nm, while electron detachment from hydroxide can generate much more electrons. Considering a spherical nanovoid in water, this work shows how the processes in and out of the nanovoid interact and seed the electron multiplication. Solving a fully coupled Poisson-Nernst-Planck model of charge migration, we find that the hydroxide concentration on the cathode-side wall of the void will be enhanced from its equilibrium level without field, which may increase electron generation under realistic field of 0.5 V/nm. The emission of electrons into the nanovoid will shift the equilibrium of water autoionization rightwards. The emitted electron will gain energy before hitting the anode-side wall of the void to release more charges. This mechanism of primary electron generation can be self-sustained depending on the background field and nanovoid size. This work only considers one nanovoid and its vicinity; further studies can be conducted in scenarios involving multiple nanovoids. [Preview Abstract] |
Tuesday, October 29, 2019 9:15AM - 9:30AM |
CT1.00005: Irrigation water enrichment using atmospheric pressure dielectric barrier discharge Edgar Perez-Lopez, Venkattraman Ayyaswamy Low temperature plasmas ignited above the surface of water has been studied for years due to their importance in practical applications in biology, chemistry, and electrochemistry. Specifically, the application of strong electric fields on the surface have been investigated and developed for use in wastewater treatment and environmental applications. The current work deals with the injection of nitrate ions into irrigation water. Several dielectric barrier discharge based plasma ignition configurations that ignite the plasma in ambient air (as opposed to underwater) are considered and the rate of nitrate ion injection and energy requirements are quantified for each configuration. The charge acquired by a 10,000 pf capacitor connected in series with the reactor in conjunction with the voltage across the reactor electrodes is used to measure the input power. The nitrate ion concentration as a function of time is measured and in combination with the energy input to the reactor is used to assess the energy efficiency of each reactor configuration.Based on the results obtained for the configurations considered here, recommendations are made for the optimal set-up for injecting nitrate in flowing water. [Preview Abstract] |
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