Bulletin of the American Physical Society
66th Annual Gaseous Electronics Conference
Volume 58, Number 8
Monday–Friday, September 30–October 4 2013; Princeton, New Jersey
Session ET2: Microdischarges I |
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Chair: Fumiyoshi Tochikubo, Tokyo Metropolitan University Room: Ballroom II |
Tuesday, October 1, 2013 1:30PM - 1:45PM |
ET2.00001: Electrical Breakdown Characteristics in Fluctuating Fluids near Gas-liquid Critical Point of Helium Hitoshi Muneoka, Keiichiro Urabe, Sven Stauss, Kazuo Terashima In order to unify discharge behavior in gases and liquids, we have experimentally investigated the breakdown voltages near the critical point of helium [critical temperature ($T_{\mathrm{c}})$: 5.20 K, critical pressure ($P_{\mathrm{c}})$: 0.227 MPa], for $T =$ 5.02 - 5.50 K and $P =$ 0.03 - 0.3 MPa, which includes the gaseous, liquid, and supercritical fluid (SCF) states of helium. Detailed measurements of micrometer-gap ($\sim$3 $\mu$m) direct-current discharges in the high density (0.1 -- 27 mol/L) and ultra-pure (due to the very low temperature) medium allowed for the first time a clear observation of a critical anomaly of the breakdown voltage in helium. This anomaly - a local minimum of the breakdown voltage - could only be observed in micrometer gap discharges because the characteristic length of the local fluid structure has to be comparable to the gap distance. We also developed a discharge model that takes into account the local fluid structure in a fluctuating medium and the effect of small discharge volumes. The analysis and model suggest that the critical anomaly is caused by extended acceleration paths inside low density domains generated by the density fluctuation. [Preview Abstract] |
Tuesday, October 1, 2013 1:45PM - 2:00PM |
ET2.00002: Self-Pulsing Non-Equilibrium Plasma Discharge at Atmospheric and Higher Pressures Rajib Mahamud, Tanvir I. Farouk Recently there has been research trust directed towards the development of high pressure non-thermal plasma with a focus to overcome the limitations of their low pressure counter parts. Among the different high pressure non-thermal discharges \textit{micro plasma} continues to be a topic of immense interest. Even though micron sized inter-electrode separation has been successful in attaining non-thermal plasma conditions at atmospheric pressure, the small size cause the effect of other operating parameters to be crucial in stable operation. In this study, simulation of DC micro plasma discharge has been conducted using a hybrid model with detailed helium-nitrogen feed gas kinetics. Simulations were conducted over a broad range of pressure 1 -- 10 atm, and power circuit parameters. The self-pulsing regime was found to operate in the subnormal regime and is triggered when the circuit response time starts becoming comparable and larger than the ion transit time. The simulations further indicated that the oscillation frequency increases as the discharge current increases in the subnormal regime. In this self-pulsing regime of operation insignificant increase in the gas temperature is observed confirming that the self-pulsing is not due thermal instability. Results from the study showed that this self-pulsing mode is more prevalent at higher pressure. The oscillation frequency increased almost in a linear fashion as a function of pressure. Predictions were found to be good agreement with experimental measurements. [Preview Abstract] |
Tuesday, October 1, 2013 2:00PM - 2:15PM |
ET2.00003: A short pulse, high rep-rate microdischarge VUV source Jacob Stephens, Andrew Fierro, James Dickens, Andreas Neuber A MOSFET based high voltage pulser is utilized to excite a microdischarge (MD), or microdischarge array (MDA) with pulsed voltages of up to 1 kV, with risetime and FWHM on the order of 10 ns and 30 ns, respectively. Additionally, the pulser is capable of pulsing at rep-rates in excess of 35 MHz. However, for these experiments the rep-rate was set on the order of 1 MHz, so as to limit excess energy deposition into the background gas and optimize the energy efficiency of VUV generation. Using VUV capable spectral diagnostics, the VUV emission of the MDs for various pressures (50-800$+$ Torr) and gases, focused on argon, argon-hydrogen mixtures, and neon-hydrogen mixtures (all of which provide strong emission at $\lambda $ \textless\ 130 nm) is studied, for pulsed, MHz rep-rated excitation. Using a photomultiplier tube the time dependent behavior of the VUV emission is characterized and compared to results from transient fluid modeling of the MDA. For instance, the MDA turn-on time is recorded to be about 15 ns, which matches the full plasma development time in the model, and the MDA self- capacitance largely determines the turn-off behavior. [Preview Abstract] |
Tuesday, October 1, 2013 2:15PM - 2:30PM |
ET2.00004: Laser-spectroscopic electric field measurements in a ns-pulsed microplasma in nitrogen Patrick Boehm, Dirk Luggenhoelscher, Uwe Czarnetzki In this work for the first time ns-pulsed discharges in nitrogen at near atmospheric pressures are investigated by laser-spectroscopic electric field measurements, ultra-fast optical emission spectroscopy, current and voltage measurements. The discharge is operated with kV-pulses of about 150 ns duration between two parallel plate electrodes with a 1.2 mm gap. The laser technique for electric field measurement is based on a four-wave mixing process similar to Coherent anti-Stokes Raman Scattering (CARS). Here the static electric field acts effectively as the third wave with a zero frequency. The frequency of the generated anti-Stokes wave is in the IR regime and the amplitude is proportional to the electric field strength. By measuring the intensity of the IR- and anti-Stokes-signal it is now possible to determine the static electric field. Due to the short pulse-length of the lasers a temporal resolution in the ns range and a typical sensitivity of 50 - 100 V/mm in pure nitrogen is achieved (p \textgreater 50 mbar). Field-measurements are accompanied by emission measurements using a streak-camera with sub-ns resolutions. Further, current and voltage measurements combined with the electric field measurements allow determination of the plasma density. [Preview Abstract] |
Tuesday, October 1, 2013 2:30PM - 2:45PM |
ET2.00005: Implementation of a 3D PIC/MCC Simulation to Investigate Plasma Initiation in Nitrogen at Atmospheric Pressure Andrew Fierro, James Dickens, Andreas Neuber The particle-particle interactions involved in plasma formation are well suited to implement in a parallel environment due to the identical computations done for each particle. Specifically, a 3D PIC/MCC simulation was accelerated on an NVIDIA graphics processing unit (GPU) using the CUDA framework for a developing plasma in nitrogen gas at atmospheric pressure to study the initial phase of breakdown. For this simulation, the computational volume was $\sim$220 mm$^{3}$ with 15 $\mu$m spatial resolution containing two parabolic electrodes. The plasma development is typically characterized by the development of positive ion space charge creating a localized field enhancement thus accelerating ionization processes in this region. For instance, with the application of an 8 kV/cm electric field amplitude, after 1 ns into the simulation, the development of positive ion space charge near both anode and cathode is observed with the densities of $\sim$10$^{16}$ cm$^{-3}$ and $\sim$10$^{14}$ - 10$^{15}$ cm$^{-3}$, respectively, while the electron density sits at $\sim$10$^{11}$ cm$^{-3}$. Already 100 ps into the simulation, the distribution of electron energies exhibits non-thermal characteristics with an average electron energy of 0.98 eV that increases to $\sim$10 eV at 1 ns. [Preview Abstract] |
Tuesday, October 1, 2013 2:45PM - 3:00PM |
ET2.00006: DC Pulsed Atmospheric Micro Plasma using a Voltage Doubled Capacitive Ballast Chang-Seung Ha, Je-Hyun Lee, Eui-Jeong Son, Dong-Hyun Kim, Hae June Lee, Ho-Jun Lee An atmospheric plasma driven by the capacitive ballast circuit with voltage doubler has been developed. At first, the capacitors are charged and then the stored energy is injected into the electrode. At that time, the voltage is doubled by means of series connection switching. The switching device isolate the power from the plasma, therefore the discharge energy is effectively controlled by the stored energy in the capacitor. The role of voltage doubler is maintaining the charging voltage less than the firing voltage of the electrodes and providing sufficiently high voltage during the plasma generation. It eliminates parasitic discharge due to capacitive coupling between isolation switch and plasma electrodes. Proposed method allows stable operation of the $\mu $-plasma under dielectric-free electrode as well as independent control of discharge voltage and energy. When the applied capacitance is varied as 1.2 nF, 10 nF and 22 nF at the voltage of 600V, the corresponding discharge energy per pulse is 168 $\mu $J, 971 $\mu $J, and 1.126 mJ respectively. For the fixed capacitance value, discharge duration decreases and peak current increases with the discharge voltage. The characteristics of the micro plasma are analyzed in terms of time-resolved images, spatio-temporally resolved OES and fluid simulations. [Preview Abstract] |
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