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 OR3: Atmospheric Discharges: Pulses and Streamers |
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Chair: Peter Bruggerman, University of Minnesota Room: 305 AB |
Thursday, October 15, 2015 10:00AM - 10:30AM |
OR3.00001: 2D fluid simulations of discharges at atmospheric pressure in reactive gas mixtures Invited Speaker: Anne Bourdon Since a few years, low-temperature atmospheric pressure discharges have received a considerable interest as they efficiently produce many reactive chemical species at a low energy cost. This potential is of great interest for a wide range of applications as plasma assisted combustion or biomedical applications. Then, in current simulations of atmospheric pressure discharges, there is the need to take into account detailed kinetic schemes. It is interesting to note that in some conditions, the kinetics of the discharge may play a role on the discharge dynamics itself. To illustrate this, we consider the case of the propagation of He-N$_2$ discharges in long capillary tubes, studied for the development of medical devices for endoscopic applications. Simulation results put forward that the discharge dynamics and structure depend on the amount of N$_2$ in the He-N$_2$ mixture. In particular, as the amount of N$_2$ admixture increases, the discharge propagation velocity in the tube increases, reaches a maximum for about $0.1\%$ of N$_2$ and then decreases, in agreement with experiments. For applications as plasma assisted combustion with nanosecond repetitively pulsed discharges, there is the need to handle the very different timescales of the nanosecond discharge with the much longer (micro to millisecond) timescales of combustion processes. This is challenging from a computational point of view. It is also important to better understand the coupling of the plasma induced chemistry and the gas heating. To illustrate this, we present the simulation of the flame ignition in lean mixtures by a nanosecond pulsed discharge between two point electrodes. In particular, among the different discharge regimes of nanosecond repetitively pulsed discharges, a ``spark'' regime has been put forward in the experiments, with an ultra-fast local heating of the gas. For other discharge regimes, the gas heating is much weaker. We have simulated the nanosecond spark regime and have observed shock waves generated by the discharge, in agreement with experiments. Then, we have studied the production of active species for the different regimes of nanosecond repetitively pulsed discharges. We present the relative importance of gas heating and the production of active species for the ignition of lean H$_2$-air and CH$_4$-air mixtures. [Preview Abstract] |
Thursday, October 15, 2015 10:30AM - 11:00AM |
OR3.00002: Thomson scattering diagnostics of atmospheric pressure plasmas - Pulsed filament discharges and plasma jets Invited Speaker: Kentaro Tomita Recently, non-thermal atmospheric-pressure plasmas have received much attention. Because the characteristics of the plasmas are governed by free electrons, measurements of the electron density ($n_{\mathrm{e}})$ and electron temperature ($T_{\mathrm{e}})$ are a prerequisite for understanding plasma behavior. To contribute to the understanding of non-thermal atmospheric-pressure plasmas, we have been developing a laser Thomson scattering (LTS) technique as a diagnostic method for measuring $n_{\mathrm{e}}$ and $T_{\mathrm{e}}$ of two types of plasmas; a pulsed-filament discharge and He flow plasma jet. The pulsed filament discharge has a short current width (a few tens of ns) and a small size. In order to apply LTS to such plasmas, reproducibility of time and space of the plasmas were improved using a high-speed semiconductor switch. Spatiotemporal evolutions of $n_{\mathrm{e}}$ and $T_{\mathrm{e}}$ of a main discharge have been obtained. Now we try to apply LTS at a time of primary streamer. Regarding to the He flow plasma jet, the discharge was generated with He gas flow with N$_{2}$/O$_{2}$(20{\%}) or N$_{2}$ shielding gas. It was confirmed that the $n_{\mathrm{e}}$ at the center of the plasma with N$_{2}$/O$_{2}$ shielding gas was around 50{\%} higher than that with the N$_{2}$ shielding gas. [Preview Abstract] |
Thursday, October 15, 2015 11:00AM - 11:15AM |
OR3.00003: Sub-nanosecond dynamics of atmospheric air discharge under highly inhomogeneous and transient electric field Pierre Tardiveau, Lionel Magne, Stephane Pasquiers, Pascal Jeanney, Blandine Bournonville The effects of the application of extreme overvoltages (\textgreater 500 {\%}) in air gaps over less than a few nanoseconds bring us to reconsider the classical physics of streamer used to describe air discharges at atmospheric pressure. Non equilibrium discharges created by extremely transient and intense electric fields in standard conditions of pressure and temperature exhibit unusual diffuse and large structure. In point-to-plane electrode configurations, a plasma cloud is observed which properties depend on voltage pulses features (amplitude, rise time, length, and frequency) and electrodes properties (material, shape, and gap length). Our parametric experimental study is based on fast electrical characterization and sub-nanosecond imaging and shows the different stages of propagation of the cloud. This work details the conditions to maximize the cloud size without moving towards a multi-channel streamer regime. Based on the analysis and the Abel transform processing of the emission of excited states of nitrogen from the discharge, a focus is made on the structuration of the plasma cloud while it is propagating. It shows how much, according to the experimental conditions, the external electric field can be screened by the plasma and, inversely, how deep and how long a high electric field can be sustained in the gap, that is challenging for pulsed atmospheric plasmas applications. [Preview Abstract] |
Thursday, October 15, 2015 11:15AM - 11:30AM |
OR3.00004: Electric field of streamers propagating along dielectric surfaces Dirk Trienekens, Sander Nijdam, Gerrit Kroesen, Thomas Christen, Ute Ebert In electric power devices for high voltage, the interface between solid and gaseous insulation is usually the most critical part with respect to electric discharges that may lead to breakdown. For a better understanding of the underlying fundamental physics of these discharges, we investigate the streamer propagation along dielectric surfaces, with focus on the streamer electric fields and surface charges deposited on the dielectric material. In particular, we constructed a setup that enables us to study the electric field of the streamer in situ. A positive high voltage pulse is generated using a push-pull switch and supplied to a needle close to a birefringent BSO (Bismuth Silicon Oxide) crystal, along which the streamers can then propagate. Using a power LED and polarizing optics, we are able to visualize via the Pockels effect the electric field caused by the discharge. With this, we are able to quantitatively study streamer electric fields with good temporal and spatial resolution, and can estimate lifetimes of the deposited charges. [Preview Abstract] |
Thursday, October 15, 2015 11:30AM - 11:45AM |
OR3.00005: Experimental investigations of electrodeless streamer inception Anna Chvyreva, Thomas Christen, A.J.M. Pemen Experimental investigations of surface streamer discharges were performed to analyze the conditions of surface streamer inception and determine the important parameters of discharge propagation over a dielectric. The present work is devoted to electrodeless streamer inception in an arrangement typically used in an industrial high voltage device. The process of discharge propagation was investigated under AC and pulsed voltage supplies. The main focus of the work was to determine the velocities of streamer propagation over a dielectric surrounded by nitrogen or air environment. These propagation velocities were estimated by means of time-resolved imaging and current measurements of discharge processes. Other important characteristics of pre-breakdown discharge behavior (such as electric field required for the inception and the values of ionization rates) were obtained. Results demonstrate the influence of a dielectric surface on a process of discharge development; the differences between streamers propagating along a dielectric surface in nitrogen and air environment are analyzed and characteristic parameters are compared to discharge development in bulk gas. [Preview Abstract] |
Thursday, October 15, 2015 11:45AM - 12:00PM |
OR3.00006: Dependence of streamer density on electric field strength on positive electrode Nakamura Koki, Okuyama Takahumi, Douyan Wang, N. Takao, Akiyama Hidenori Pulsed streamer discharge plasma, a type of non-thermal plasma, is known as generation method of reactive radicals and ozone and treatment of exhausted gas. From our previous research, the distance between electrodes has been considered a very important parameter for applications using pulsed streamer discharge. However, how the distance between electrodes affects the pulsed discharge hasn't been clarified. In this research, the propagation process of pulsed streamer discharge in a wire-plate electrode was observed using an ICCD camera for 4 electrodes having different distance between electrodes. The distance between electrodes was changeable at 45 mm, 40 mm, 35 mm, and 30 mm. The results show that, when the distance between electrodes was shortened, applied voltage with a pulse duration of 100 ns decreased from 80 to 60.3 kV. Conversely, discharge current increased from 149 to 190 A. Streamer head velocity became faster. On the other hand, Streamer head density at onset time of streamer head propagation didn't change. This is considered due to the electric field strength of streamer head at that time, in result, it was about 14 kV/mm under each distance between electrodes. [Preview Abstract] |
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