Bulletin of the American Physical Society
68th Annual Gaseous Electronics Conference/9th International Conference on Reactive Plasmas/33rd Symposium on Plasma Processing
Volume 60, Number 9
Monday–Friday, October 12–16, 2015; Honolulu, Hawaii
Session TF4: Atmospheric Pressure Plasma Jets |
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Chair: Mikhail Benilov, University of Madeira Room: 303 AB |
Friday, October 16, 2015 10:00AM - 10:30AM |
TF4.00001: Computational Modeling and Simulation of Micron-Scale Discharges and Their Interactions with High-Frequency Electromagnetic Waves Invited Speaker: Laxminarayan L. Raja In this work we discuss high-fidelity computational modeling of micron-scale discharges and their interactions with electromagnetic waves in the microwave regime. The study is motivated by applications in plasma metamaterials where large arrays of microdischarge structures are used to manipulate incident micro/terahertz waves. We use a combination of classical particle-in-cell (PIC) modeling and fluid modeling approaches to understand breakdown of individual microdischarge structures due to the electromagnetic wave excitation and the operation of stable microdischarges in the presence of these waves, respectively. The effect of length scale, frequency of excitation, surface electron emission physics on breakdown is addressed in detail with the PIC model. The fluid model represents both plasma physics and wave interaction effects. Self-consistent approach for modeling of plasma-wave interaction and the numerical implementation will be discussed in detail. The manipulation of incident electromagnetic waves as a function of individual microdischarge structure is reported. Also, we study non-linear interactions where sufficiently high-intensity electromagnetic waves modify the structure of the individual microdischarges leading.\\[4pt] In collaboration with Dmitry Levko and Premkumar Paneerchelvam, Department of Aerospace Engineering and Engineering Mechanics, The University of Texas at Austin. [Preview Abstract] |
Friday, October 16, 2015 10:30AM - 10:45AM |
TF4.00002: Temporal evolution of the EVDF in a ns-pulsed APPJ in Helium Uwe Czarnetzki, Christian Schregel, Dirk Luggenh\"olscher The temporal evolution of the EVDF in a ns-pulsed jet-discharge operated in Helium is measured by Thomson scattering. Further, spatially and temporally resolved emission spectra and current and voltage waveforms are measured. The discharge consists of two molybdenum electrodes of 20 mm length which form a 1.5 mm high and 0.95 mm wide gap between two glass plates. A 150 ns long voltage pulse of 1-2 kV (5 kHz) is applied. A Nd:YAG laser provides an 8 ns laser pulse at 532 nm and the scattered light is detected by a gated ICCD camera connected to a TGS. Up to three orders of magnitude dynamic range for the absolutely calibrated EVDF are archived in the range 0.5 eV to 12 eV. A 60 ns Townsend pre-phase is followed by a 90 ns long DC-like discharge showing strong atomic emission lines. The 1,000 ns long afterglow is characterized by initial recombination of cold electrons and Helium excimer formation, predominately in Rydberg states, which slowly relax to lower states radiating in the visible range of the spectrum. Rydberg states are probed by ionization with an intense laser pulse and subsequent detection of the additional free electrons by Thomson scattering. This work was funded by the DFG Research Group FOR1123. [Preview Abstract] |
Friday, October 16, 2015 10:45AM - 11:00AM |
TF4.00003: Influence of HV pulse repetition rate on densities of excited species in atmospheric helium plasma jet Nader Sadeghi, Vincent Puech, Claire Douat Time varying plasma characteristics of a 2 mm diameter atmospheric helium microplasma jet excited by nanosecond high voltage pulses (4-7 kV; 1-50 kHz rep. rate) was studied. Density of helium He(2$^{3}$S$_{1})$ metastable atoms was determined by tunable laser diode absorption. The spatio-temporal dynamics of characteristic plasma jet emissions, such as the 706.5 nm and 587.5 nm He* and 777 nm O* lines, the 337 nm N$_{2}$(C-B), 391 nm N$_{2}^{+}$(B-A) and 308 nm OH* bands were studied by sub-nanosecond time-resolved imaging of the jet with bandpass filters and by nanosecond time-resolved photon-counting behind an spectrograph. Spatial distribution of excited species strongly depends on plasma parameters and HV pulses rep. rate; $e.g.$ hollow shape profiles at 3 kHz become axially centered above 10 kHz. Also, higher is the rep. rate slower are the late afterglow decay times of O* and OH* emissions, reaching about 20 $\mu$s at 20 kHz. This is likely linked to the very slow positive ion-negative ion recombination mechanism, producing these excited species. The two above-mentioned effects are attributed to a memory effect due to formation of negative ions generated from water impurity and air penetration. [Preview Abstract] |
Friday, October 16, 2015 11:00AM - 11:15AM |
TF4.00004: Comparison between micro hollow cathode discharges and atmospheric pressure plasma jets working in Ar/O$_{2}$ Claudia Lazzaroni, Pascal Chabert A global model of a Micro Hollow Cathode Discharge (MHCD) in argon (Ar) with an admixture of oxygen (O$_{2})$, working at several hundreds of Torr, is presented. MHCDs operate in steady state and in self-pulsed mode both captured by the model. This discharge is a source of high reactive oxygen species (ROS) densities, a key parameter in many applications such as medicine. The Atmospheric Pressure Plasma Jet (APPJ), which consists in the application of a radio frequency (RF) voltage across two parallel electrodes separated by one millimeter, is another micro-plasma source which is widely used in medicine. The global model of the MHCD is compared to an analytical-numerical global model of the APPJ. Seventeen species are considered and 130 reactions are taken into account in the plasma volume. The species densities oscillate in time during the self-pulsing regime of the MHCD, following the discharge current oscillations, and we will compare the peak and the time-averaged densities to the APPJ densities. This comparison shows that in both regimes, the MHCD produces preferentially reactive oxygen excited species, O* and O$_{2}$*, whereas the APPJ produces preferentially reactive oxygen stable species, O and O$_{3}$. This is due to the higher plasma densities produced in the MHCD. [Preview Abstract] |
Friday, October 16, 2015 11:15AM - 11:30AM |
TF4.00005: Gas and heat dynamics of a micro-scaled atmospheric pressure plasma jet Judith Golda, Sean Kelly, Miles M. Turner, Volker Schulz-von der Gathen Low temperature atmospheric pressure plasma jets enable the production of reactive species. Therefore, they are used for surface modification and considered for use in bio-medicine. Bio-medical applications demand stability of the discharge and knowledge of the temperature of the plasma effluent and the device components. While treating heat-sensitive biological material, the threshold temperature of the tissue must not be exceeded. Additionally, chemical processes in the discharge strongly depend on the gas temperature. However, heating in such discharges is still poorly understood. To assess this problem, we investigated the geometric design of the microscaled atmospheric pressure plasma jet based on a reference jet which is proposed by the European COST group MP1101. Thermocouple measurements and numerical model data show a bounded exponential temperature growth described by a single characteristic time parameter. Where the carrier gas exits the device, peak temperatures range from 297 K to 381 K in ``alpha mode'' operation for flows of 2 - 0.25 slpm. Spatial profiles of surface heating, obtained by thermal imaging, are found to correlate strongly with the impacting plume where peak temperatures occur in regions of maximum surface helium concentration. [Preview Abstract] |
Friday, October 16, 2015 11:30AM - 11:45AM |
TF4.00006: Properties of DC-Pulsed Microplasma Arrays at Intermediate Pressures Peng Tian, Chenhui Qu, Mark J. Kushner Microplasma arrays are being investigated to manipulate electromagnetic waves due to their ability to change electrical properties with a short response time. In these applications, there are often tradeoffs between a short response time, plasma density and uniformity of the plasma, all of which scale with pressure. Controlling of cross-talk between microdischarges is also an issue when there are no physical isolations between microdischarges in the array. These scalings motivate operation at intermediate pressures, 10s to 100s Torr, which by pd scaling corresponds to sizes of the microcavity of hundreds of microns. In this paper, a computational investigation on the scaling of microplasma arrays excited by pulsed dc-bipolar/unipolar waveforms is discussed using results from a 2-dimensional plasma hydrodynamics model. The goal is to maximize the time averaged electron density in a spatially controllable manner while controlling cross-talk between microplasmas that are not physically isolated. We investigated 1-D and 2-D microplasma arrays of sub-mm cavities operating at 10s-100s Torr in rare gases, excited by ns DC pulses with several MHz pulsing frequency. Plasma densities up to 10$^{\mathrm{14}}$ cm$^{\mathrm{-3}}$ are predicted in Penning mixtures. [Preview Abstract] |
Friday, October 16, 2015 11:45AM - 12:00PM |
TF4.00007: Phase-resolved imaging of the interaction dynamics in rf-driven microplasma arrays at atmospheric pressure Jerome Bredin, Katharina Grosse, Sameer Al-Bataineh, Endre Szili, Rob Short, Deborah O'Connell Atmospheric-pressure microplasmas are under development for future surface processing applications due to their decreased cost and high throughput compared to low-pressure configurations. Microplasma arrays are designed to achieve a large-area homogenous treatment. The investigated plasma source consists of a 7x7 micron-scale dielectric barrier discharges array operated in an atmospheric-pressure helium environment. The discharge is driven by radio-frequency (rf) power at 2 MHz and the power is pulsed at 1 kHz with an on-time of 90 rf cycles. Pulsed rf offers promise of improved control over the plasma properties and long operation lifetimes of the arrays. Nanosecond imaging (head-on and side observation) is used to investigate the spatio-temporal behaviour and the interactions between the cavities throughout the pulse. As a function of time within the pulse, distinct plasma dynamics are observed. This includes the formation of ``glow'' and ``ring'' shaped discharges as well as interactions between discharges. These depend on the dimensions of the cavities and the driving voltage. Through this study, we expect to be able to tailor conditions such as homogeneous operation and optimum species production. [Preview Abstract] |
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