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 QR2: High Pressure Discharges I |
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Chair: Anne Bourdon, CNRS, Ecole Polytechnique Room: Century II |
Thursday, October 31, 2019 1:45PM - 2:00PM |
QR2.00001: Time-resolved Characterization of Plasma Jets Formed using a Piezoelectric Transformer Jinyu Yang, Seong-Kyun Im, David Go The time-resolved characteristics of plasma generated by a piezoelectric transformer (PT) have been investigated. A PT is a non-centrosymmetric crystal that converts low-voltage AC input to high-voltage AC output through an electro-mechanically coupled process. The high voltage gain can be several orders of magnitude, such that an atmospheric-pressure plasma jet (APPJ) can be formed off the surface of the PT. PTs are attractive for APPJ generation because of their simple operation and low power consumption. In this work, the temporal evolution of the PT-driven APPJ was visualized using an intensified CCD camera. For time-resolved plasma visualization, one period of the input voltage (\textasciitilde 14.8 \textmu s) has been separated into 60 phases with a time interval of 250 ns, and images are taken for each phase. Results visually demonstrate the APPJ formation within one period. Notably, the plasma formation is a discrete process, appearing at a fixed phase of the sinusoidal input, and the strongest plasma jet appears at the end of the positive cycle. Simultaneous measurements of the current, however, show that the discharge current spikes appear statistically about a half microsecond earlier than the strongest plasma jet images, which indicates that the plasma produces a strong afterglow. [Preview Abstract] |
Thursday, October 31, 2019 2:00PM - 2:15PM |
QR2.00002: Propagation of atmospheric-pressure surface plasmas on multi-layer silicon-based barriers David Pai, Thibault Darny, Frederic Pailloux, David Babonneau, Sophie Camelio Few studies of surface dielectric barrier discharges (SDBDs) have employed barriers not composed of bulk dielectric materials. We explore several forms of `advanced' multi-layer barriers based on a class of material rarely used as propagating surfaces for SDBDs, namely semiconductors, using nanosecond pulsed discharges generated in air at atmospheric pressure. First, the deposition of an alumina film of 40 nm thickness on a silicon substrate enables the filamentary propagation of a surface discharge otherwise localized near the anode when bare silicon is used as a barrier. Second, we consider the case of a 1-micron thick layer of SiO$_{\mathrm{2}}$ deposited on silicon, forming a Si-SiO$_{\mathrm{2}}$ bilayer. Instead of filaments, the plasma propagates in a well-defined symmetric ring pattern. The ring pattern gradually expands on the surface during the positive voltage pulse and demonstrates high pulse-to-pulse reproducibility and stability. Third, the addition of a nanomaterial atop the Si-SiO$_{\mathrm{2}}$ bilayer, namely ultrananocrystalline diamond (UNCD), enhances the propagation of the uniform ionization front. Scanning electron microscopy and Raman spectroscopy are employed ex situ to characterize how the plasma modifies the above surfaces. [Preview Abstract] |
Thursday, October 31, 2019 2:15PM - 2:45PM |
QR2.00003: Scope of low temperature plasma in futuristic agriculture. Invited Speaker: Zaka-ul-Islam Mujahid Low-temperature plasmas are increasingly investigated for agricultural applications. In this presentation, an assessment of plasma treatment as an alternative to two existing agricultural practices of artificial dormancy release and seed scarification will be presented. Crops from cold climates have a cyclic behavior, where in fall they go into a state of slow growth (crudely sleep) called dormancy. Dormancy is present in both annuals (planted every year such as potato and tulips, etc.) and perennials (planted once and harvested yearly such as grape, apples and peaches, etc.). The plant growth cycle resumes once the plant has been through a particular duration of chilling (sub-5$^{\mathrm{o}}$ temperatures). In the absence of the required chilling period, the crop yield is significantly reduced. Growers rely on artificial chilling in refrigerators for annuals, if natural chilling is insufficient. For perennials, a deficiency in natural chilling can be compensated by spraying chemicals (such as hydrogen cyanamide). Using grape buds and seeds as test crops, it was observed that plasma treatment could effectively release the dormancy; similar to or better than the natural chilling. The plant enzymes indicate that the plasma treatment can induce stress in plants identical to the natural chilling and hydrogen cyanamide spray. Seeds with tough coats have a low germination as their outer skin is a barrier for the water and air permeation. Growers traditionally soak these seeds in acids to improve germination; a method known as seed scarification. It was observed that plasma treatment can improve the germination of such seeds similar to the acid scarification. Both the plasma-based alternatives are environmentally friendlier than the existing agricultural practices, which make them promising alternatives for further investigation and development. [Preview Abstract] |
Thursday, October 31, 2019 2:45PM - 3:00PM |
QR2.00004: Multiple gas discharges in a dielectric barrier discharge for large-scale plasma jets Duc Ba Nguyen, Young Sun Mok In recent years, there has been an increasing interest in bio-applications of atmospheric pressure plasma jet (APPJ), namely cancer treatment, sterilization, skin treatment, and wound healing. A common APPJ used to bio-applications has a confined area and considerable consumption of noble gases (Ar/He) during the plasma process, due to require room-temperature plasma. Thus, this is costly process and limited commercial capabilities. Since plasma jets spread area during interaction with a non-conductive surface (e.g. human skin), multiple plasma jets would generate in multi-bore tubing instead of one large diameter tube, the effect plasma area will be similar while reducing noble gas consumption. Moreover, the surface discharge in multi-bore tubing has a large area, suggesting more strong internal plasma. Consequently, in this study, multiple gas discharges will be investigated in a two-ring dielectric barrier discharge reactor, the dielectric is a multi-bore tubing and He as plasma gas. The effects of applied voltage, flow rate, and electrodes gap on the plasma jet will be examined in terms of jet length, jet temperature, and gas emission. Optical emission spectra of the plasma jet will be analyzed to evaluate activated chemical species by the plasma source. [Preview Abstract] |
Thursday, October 31, 2019 3:00PM - 3:15PM |
QR2.00005: Quantitative characterization of streamer branching in air through 3D simulations Ute Ebert, Jannis Teunissen, Behnaz Bagheri Branching is an essential element in the evolution of space charge driven streamer discharges; it creates the corona of streamer channels that decreases the electric field in the streamer filled region. We investigate branching of positive streamers in air through 3D simulations with the afivo-streamer code [https://gitlab.com/MD-CWI-NL/afivo-streamer]. Here electrons and ions are treated as densities, but the fewer and far traveling photons (that cause photo-ionization) are treated as quantized entities, i.e., discretely. Their inherent randomness accelerates the dynamic destabilization of wide streamer tips and causes branching, in a stochastic manner. We characterize the distribution of streamer branching: the length of the parent streamer till branching, the diameter ratio of the daughter streamers, their angles relative to each other and to the parent, and their velocities, and we compare our predictions with experimental observations. [Preview Abstract] |
Thursday, October 31, 2019 3:15PM - 3:30PM |
QR2.00006: Gasdynamic Diode: How to Stop 100-kV Streamer Andrey Starikovskiy, Nickolay Aleksandrov The results of a two-dimensional numerical simulation of a streamer discharge developing through a shock wave in air were presented for various neutral density discontinuities across the wave. The focus was on the case when the streamer propagated from a low-density region to a high-density region. Streamer characteristics changed greatly after intersecting the shock wave. It was shown that the streamer failed to penetrate into the high-density region when the ratio between the densities in these regions was sufficiently high (\textgreater 1.2). In this case, the discharge developed along the surface between these regions after reaching the boundary between them. Thus, the gaseous medium demonstrates a unidirectional conductivity on a short time scale; a gas density discontinuity forms a kind of ``gas-dynamic diode'' that allows the plasma channel to propagate in one direction and blocks its development in another. Streamers could penetrate into any of the high-density and low-density regions when a neutral particle density discontinuity was replaced by a gradual density change. [Preview Abstract] |
Thursday, October 31, 2019 3:30PM - 3:45PM |
QR2.00007: Temporal Imaging and Measurement of a High Pressure He/Ar Microplasma for DPRGL Andrew Walsten, Gabe Xu, Carl Sanderson, Charles Ballmann, Daniel Matyas Diode-pumped rare gas lasers (DPRGLs) are being researched and developed due to their ability to operate at high power with high quantum efficiencies. DPRGLs use a rare gas plasma mixture for the gain medium which operates at near atmospheric pressure for efficient lasing. Their performance is dependent on the metastable population of the lasing species. Thus, a stable plasma that is capable of sustaining the metastables for sufficient periods of time is needed. This work seeks to use temporal imaging and measurements of a high pressure He/Ar microplasma in order to better understand the behavior of the plasma. The plasma was generated in a vacuum chamber between two parallel plate style electrodes with a dielectric material covering one electrode. Imaging was done with an ICCD camera. An ICCD spectrometer and diode laser were used to perform OES techniques and absorption spectroscopy in order to measure the temperature and density. The plasma is generated by an initial ionization wave that propagates from one electrode to the other and is followed by a secondary return stroke. The occurrence of this return stroke is controlled by the electric field. The electron temperature remains nearly constant throughout the plasma's lifetime. The results show that maximizing the electric field and voltage increases the plasma peak intensity and duration leading to increased metastable population and improved DPRGL performance. [Preview Abstract] |
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