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 KW4: Atmospheric & Thermal Plasmas |
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Chair: Jochen Schein, Universität der Bundeswehr Room: 303 AB |
Wednesday, October 14, 2015 1:30PM - 2:00PM |
KW4.00001: Modelling for turbulent transport of nanoparticles growing around a thermal plasma jet Invited Speaker: Masaya Shigeta Modelling works for expressing the simultaneous processes of growth and transport of nanoparticles around a turbulent-like thermal plasma jet are presented. From the physical aspect, extending the previous model, a simple-but-consistent model which requires less computational costs is developed to describe the nanoparticles' birth and collective growth through homogeneous nucleation, heterogeneous condensation, and coagulation among themselves as well as transports by convection, diffusion, and thermophoresis. From the mathematical aspect, an original simulation code with higher accuracy is developed to express thermal plasma turbulence and to capture steep gradients in the spatial distribution of nanoparticles. As a base case, an argon thermal plasma jet is ejected at 1.5 slm from the nozzle, and iron vapor is supplied at 0.1 g/min with the plasma jet. The computation shows that the high-temperature plasma jet entrains the surrounding non-ionized gas because of Kelvin-Helmholtz instability at their interface. The instability waves grow up and then the interface rolls up to eddies. As the jet goes downstream, the eddies break to smaller ones, which lead to turbulence transition. This feature has also been reported in the experimental study. The iron vapor is transported with the plasma flow and simultaneously diffuses across the plasma's fringe where the vapor experiences the temperature decrease. As a result, the vapor changes its phase to nanoparticles through nucleation and condensation. The nanoparticles are also transported by convection and diffusion. The regions of large diameters coincide with those of low number densities of nanoparticles, because the size of nanoparticles increases through coagulation among themselves decreasing their own numbers. [Preview Abstract] |
Wednesday, October 14, 2015 2:00PM - 2:30PM |
KW4.00002: Diagnostics of transient non-equilibrium atmospheric pressure plasmas Invited Speaker: Peter Bruggeman Atmospheric pressure plasmas have received a renewed interest in last decades for a variety of applications ranging from environmental remediation, material processing and synthesis to envisioned medical applications such as wound healing. While most low pressure plasmas are diffuse, atmospheric pressure plasmas are often filamentary in nature. The existence of these filaments is correlated with strong gradients in plasma properties both in space and time that can significantly affect the plasma chemistry. As these filaments are often randomly appearing in space and time, it poses great challenges for diagnostics often requiring the stabilization of the filament to study the in situ plasma kinetics. In this contribution, diagnostics of a stabilized nanosecond pulsed plasma filament in a pin-pin geometry and a filament in a nanosecond pulsed atmospheric pressure plasma jet will be presented. We will focus on electron kinetics and OH and H radical production in water containing plasmas. The extension of these diagnostics to plasmas in liquids will also be discussed. [Preview Abstract] |
Wednesday, October 14, 2015 2:30PM - 2:45PM |
KW4.00003: MHD Simulations of Thermal Plasma Jets in Coaxial Plasma Accelerators Vivek Subramaniam, Laxminarayan Raja The development of a magneto-hydrodynamics (MHD) numerical tool to study high energy density thermal plasma in coaxial plasma accelerators is presented. The coaxial plasma accelerator is a device used simulate the conditions created at the confining wall of a thermonuclear fusion reactor during an edge localized mode (ELM) disruption event. This is achieved by creating magnetized thermal plasma in a coaxial volume which is then accelerated by the Lorentz force to form a high velocity plasma jet. The simulation tool developed solves the resistive MHD equation using a finite volume method (FVM) framework. The acceleration and subsequent demagnetization of the plasma as it travels down the length of the accelerator is simulated and shows good agreement with experiments [1]. Additionally, a model to study the thermalization of the plasma at the inlet is being developed in order to give self-consistent initial conditions to the MHD solver. \\[4pt] [1] H Sitaraman and L.L. Raja. Magneto-hydrodynamics simulation Study of deflagration mode in co-axial plasma accelerators. Physics of Plasmas,:012104, 2014 [Preview Abstract] |
Wednesday, October 14, 2015 2:45PM - 3:00PM |
KW4.00004: Application of Atmospheric-Pressure Microwave Line Plasma for Low Temperature Process Haruka Suzuki, Suguru Nakano, Hitoshi Itoh, Makoto Sekine, Masaru Hori, Hirotaka Toyoda Atmospheric pressure (AP) plasmas have been given much attention because of its high cost benefit and a variety of possibilities for industrial applications. In various kinds of plasma production technique, pulsed-microwave discharge plasma using slot antenna is attractive due to its ability of high-density and stable plasma production. In this plasma source, however, size of the plasma has been limited up to a few cm in length due to standing wave inside a waveguide. To solve this, we have proposed a newly-developed AP microwave plasma source that utilizes not standing wave but travelling wave. By using this plasma source, spatially-uniform AP line plasma with 40 cm in length was realized by pure helium discharge in 60 cm slot and with nitrogen gas additive of 1{\%}. Furthermore, gas temperature as low as 400 K was realized in this device. In this study, as an example of low temperature processes, hydrophilic treatment of PET films was performed. Processing speed increased with pulse frequency and a water contact angle of $\sim$ 20$^{\circ}$ was easily obtained within 5 s with no thermal damage to the substrate. To evaluate treatment-uniformity of long line length, PET films were treated by 90 cm slot-antenna plasma and uniform treatment performance was confirmed. [Preview Abstract] |
Wednesday, October 14, 2015 3:00PM - 3:15PM |
KW4.00005: High-Speed Visualization of Evaporation Phenomena from Tungsten Based Electrode in Multi-Phase AC Arc Manabu Tanaka, Taro Hashizume, Tomoyuki Imatsuji, Yushi Nawata, Takayuki Watanabe A multi-phase AC arc has been developed for applications in various fields of engineering because it possesses unique advantages such as high energy efficiency. However, understanding of fundamental phenomena in the multi-phase AC arc is still insufficient for practical use. Purpose of this study is to investigate electrode erosion mechanism by high-speed visualization of the electrode metal vapor in the arc. Results indicated that the electrode mainly evaporated at anodic period, leading to the arc constriction. Moreover, evaporation of W electrode with 2wt{\%} La$_{\mathrm{2}}$O$_{\mathrm{3}}$ at the anodic period was much higher than that with 2wt{\%} ThO$_{\mathrm{2}}$. This can be explained by different properties of these oxide additives. Evaporation of the oxide additive resulted in the arc constriction, which accelerated the evaporation of W electrode. Therefore, addition of La$_{\mathrm{2}}$O$_{\mathrm{3}}$ with lower melting and boiling point than ThO$_{\mathrm{2}}$ lead to stronger arc constriction, resulting in severer evaporation of W electrode. [Preview Abstract] |
Wednesday, October 14, 2015 3:15PM - 3:30PM |
KW4.00006: Comparative Study on Extinction Process of Gas-Blasted Air and CO2 Arc Discharge Using Two-Dimensional Electron Density Imaging Sensor Yuki Inada, Tomoki Kamiya, Shigeyasu Matsuoka, Akiko Kumada, Hisatoshi Ikeda, Kunihiko Hidaka, Tomoyuki Nakano, Kosuke Murai, Yasunori Tanaka, Takeshi Shinkai Systematic comparison of the electron density images for various kinds of arc-quenching gas media inside high-voltage circuit breakers is a promising method for the effective search and development of SF6-alternative gases. However, electron density imaging over the decaying arcs around the nozzle throat of the circuit breakers is extremely difficult by using the conventional arc generation setup and localized type sensing systems, due to the nozzle opaqueness and spatiotemporal instability of long-gap arc discharges around current zero. Here, we achieved two-dimensional electron density imaging over the decaying arcs around the nozzle throat first in the world, by a combination of the development of a unique gas flow nozzle integrating a cubic quartz cell and the single-shot recordings using Shack-Hartmann sensors. Shack-Hartmann sensors were applied to gas-blasted air and CO2 arc discharges under current-zero phases after sudden switch-off of stationary arc currents. These experimental results showed that the electron densities and arc diameters took the minimums in the upper stream nozzle regions with the maximum blasting gas speeds. In addition, CO2 had a shorter electron density decaying time constant than air, which is consistent with the previous theoretical studies on higher interruption performance of CO2 compared with air. [Preview Abstract] |
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