Bulletin of the American Physical Society
55th Annual Meeting of the APS Division of Plasma Physics
Volume 58, Number 16
Monday–Friday, November 11–15, 2013; Denver, Colorado
Session TO6: Low Temperature Plasma Science, Engineering and Technology |
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Chair: John Foster, University of Michigan Room: Governor's Square 11 |
Thursday, November 14, 2013 9:30AM - 9:42AM |
TO6.00001: Reduced Breakdown Delay in High Power Microwave Dielectric Window Discharges via Penning-Like Mixtures and Patterened Metallizations John Booske, Brian Kupczyk, Abelardo Garcia, Chien-Hao Liu, Xun Xiang, Nader Behdad, John Scharer Development of high power microwave (HPM) distributed discharge limiters relies critically on minimizing the delay time between HPM incidence and diffuse plasma creation. We present a range of pulsed plasma experiments conducted in neon, argon, helium, xenon, and mixtures of these gases, from 50-760 torr. Breakdown is achieved by illuminating a gas cell with a $\sim$25kW, $\sim$700 V/cm, 800ns-long pulse of X-band microwave radiation (9.382 GHz) as well as 41Hz pulse trains. Current results focus on experiments with metamaterial window coatings that provide dramatic reductions in breakdown delay. Results from experiments combining these patterned metallizations with the aforementioned gas mixtures resulting in \textless\ 20ns breakdown, as well as proposed methods for further breakdown delay reduction, are also presented. [Preview Abstract] |
Thursday, November 14, 2013 9:42AM - 9:54AM |
TO6.00002: Rapid Formation of Distributed Plasma Discharges using X-Band Microwaves Xun Xiang, Brian Kupczyk, John Booske, John Scharer Observations of rapidly formed (\textless~50-300 ns) distributed plasma discharges using X-band microwaves are presented. A cylindrical stainless steel chamber is used to observe microwave breakdown in Ar and Ne gas from 10 to 760 torr. The chamber is illuminated by the output of 25 kW, 0.8 $\mu$s pulse-width, 9.382 GHz magnetron. Measured incident and reflected microwave power is used to detect the discharge and attenuation characteristics as the pressure is varied. Reflected power experiments show over 70{\%} power is reflected once plasma is formed and a small amount of Argon in Neon shortens the breakdown time. Additionally, an ICCD provides fast (\textless~50 ns) time-scale optical images of the plasma, revealing the plasma formation and decay processes. Optical emission spectroscopy measurements provide plasma breakdown characteristics including gas temperature, electron temperature, and plasma density. Mixers are used to compare both the amplitude and phase of the reflected signals before and after 90 degrees shift. Together with a 1D plasma model, plasma parameters including the plasma density, collision frequency and electron temperature are estimated. [Preview Abstract] |
Thursday, November 14, 2013 9:54AM - 10:06AM |
TO6.00003: Multipactor-Susceptible RF Windows as Power-Tunable Microwave Limiters G. Greening, M. Franzi, P. Zhang, Y.Y. Lau, R.M. Gilgenbach Multipactor breakdown on a dielectric may provide automatic protective isolation of electronic circuits such as transmitter-receiver (TR) switches in radar. Prior Monte Carlo simulations suggest the application of a DC bias across a dielectric window in a vacuum-gas environment can lower the threshold for the onset of RF-initiated multipactor [1]. Variation of the DC bias may therefore provide a mechanism by which a microwave window might be tuned such that RF powers exceeding a threshold would result in window breakdown. Previous experimental work confirmed that a DC bias was effective at reducing the threshold for window breakdown to 200 W at 2.45 GHz using argon at 15 -- 25 torr as the background gas. Current research is focusing on operation in a multipactor-dominated pressure regime [2] using 50 \textless\ $p$ \textless\ 500 mTorr. Measurement of RF extinction times and the impact of different window materials on performance are of particular interest, especially materials with high secondary electron yields that are resistant to plasma-induced surface degradation. \\[4pt] [1] P. Zhang et al., Phys. Plasmas 18, 053508 (2011).\\[0pt] [2] J. P. Verboncoeur et al., \textit{Power Modulator Symposium Record}, pp. 13-16, 2006. [Preview Abstract] |
Thursday, November 14, 2013 10:06AM - 10:18AM |
TO6.00004: Investigating the Physics of Microwave Induced Breakdown in Metamaterials with Multi-Resonant Constituting Unit Cells Chien-Hao Liu, Joel Neher, John Booske, Nader Behdad Recently, metamaterials are receiving significant attention in the high-power microwave area for applications ranging from amplifier design to HPM spatial filters. In this work, we investigate the impact of microwave-induced breakdown on the responses of high-power metamaterials that exploit multi-resonant constituting unit cells. We recently demonstrated a single-layer metasurface, the unit cell of which consisted of two different resonators, that showed a discrete nonlinear response under HPM illumination. We observed that when breakdown occurred in this structure, both resonators break down simultaneously despite their considerably different expected breakdown power levels. In this structure, breakdown in the resonator that has a lower breakdown threshold level mitigates the breakdown in the second resonator. In this work, we examine VUV radiation and electron diffusion as potential culprits for this phenomenon. We first will shield the two resonators physically using a VUV transparent material to block possible movement of electrons from one resonator to the other. We will subsequently repeat the same breakdown experiments using a VUV opaque material. The results will be used to determine if either of these potential culprits is responsible for this phenomenon or not. [Preview Abstract] |
Thursday, November 14, 2013 10:18AM - 10:30AM |
TO6.00005: Collisionless acceleration of plasma electrons by intense electron beam D. Sydorenko, I.D. Kaganovich, A.V. Khrabrov, P.L.G. Ventzek, L. Chen Experimental measurements of electron energy distribution function in a rf dc discharge with 800 V dc voltage reveal the presence of a peak of super-thermal electrons with energy in the range of 40-400 eV [1]. The cathode in the experimental device could emit electrons thus producing an electron beam. We used a particle-in-cell code [2] to investigate acceleration of plasma electrons by an electron beam in a dc discharge with parameters close to those of Ref. [1]. The beam excites electron plasma waves via the two-stream instability. Simulations show that the two-stream instability is intermittent, with quiet and active periods. During the quiet periods, the beam propagates through the plasma with minimal perturbations. During the periods of activity of two-stream instability, the beam interacts with the plasma most intensively at locations where the global frequency of instability matches the local electron plasma frequency. There may be two resonance areas with intense oscillations usually near the edges of the plasma. These intense localized plasma oscillations produce peaks in the velocity distribution function similar to the ones measured in the experiment. \\[4pt] [1] L. Xu et al., Appl. Phys. Lett. 93, 261502 (2008).\\[0pt] [2] D. Sydorenko et al., Phys. Plasmas 13, 014501 (2006). [Preview Abstract] |
Thursday, November 14, 2013 10:30AM - 10:42AM |
TO6.00006: Analysis of Secondary Chemistry and Treatment of Burn Wounds with Nonthermal Plasma Induced Effluent Mark Golkowski, S. Reed Plimpton, Czeslaw Golkowski Exploitation of non-thermal plasmas in the biomedical setting is a rapidly growing field with a large number of diverse technologies under investigation. Potential applications of such devices range from instrument sterilization to clinical therapy. One of the key hurdles to the implementation of non-thermal plasma technologies in the relatively poor understanding of the chemical processes taking place. Our group has recently completed precise analysis of chemical species created by our indirect exposure non-thermal plasma device with hydrogen peroxide additives. Reactive nitrogen and oxygen species are observed using optical absorption spectroscopy. We report the unique detection of short lived hydroxyl radicals at a significant distance from the discharge using electron paramagnetic spin resonance trapping. The hydroxyl radicals are shown to be generated in secondary ozonide based chemical processes away from the discharge. The plasma device is applied to a porcine model of infected full thickness burn wounds. The bacteria load reduction after treatment with our device is shown to be 10-100 fold improvement over Silvadene which is the main treatment currently used in the clinic. [Preview Abstract] |
Thursday, November 14, 2013 10:42AM - 10:54AM |
TO6.00007: Characterization of Liquid Lithium Wetting and Thermoelectric Properties for Nuclear Fusion Applications Peter Fiflis, Wenyu Xu, Michael Christenson, Daniel Andruczyk, Davide Curreli, David Ruzic Critical to the implementation of flowing liquid lithium plasma facing components is understanding the interactions of liquid lithium with various surfaces. Presented here are experiments investigating the material compatibility, wetting characteristics, and relative thermopower of liquid lithium with a variety of potential substrate candidates for the LiMIT concept [D.N. Ruzic et al 2011 Nucl. Fusion 51 102002]. Wetting experiments with lithium used the contact angle as a metric. Among those materials investigated are 316 SS,~Mo, Ta, and W. The contact angle, as well as its dependence on temperature was measured. For example, at 200 C, tungsten registers a contact angle of 130$^{\circ}$, whereas above its wetting temperature of 350 C, the contact angle is less than 80$^{\circ}$. Several methods were found to decrease the critical wetting temperature of various materials and are presented here. The thermopower of W, Mo, Ta, Li, Ga, Wood's metal and Sn has been measured relative to stainless steel, and the Seebeck coefficient of has then been calculated. For molybdenum the Seebeck coefficient has a linear rise with temperature from S$_{\mathrm{Mo}}=$3.9$\mu $VK$^{-1}$ at 30 $^{\circ}$C to 7.5$\mu $VK$^{-1}$ at 275 $^{\circ}$C. [Preview Abstract] |
Thursday, November 14, 2013 10:54AM - 11:06AM |
TO6.00008: Research the Length of the Positive Corona Glow Using the Digital Image Processing Technology Qizheng Ye, Yu Hu, Yi Sun A digital image processing technology presented in our previously paper---gray level histogram obtained by image processing of the discharge---is used to calculate the length of the positive corona glow. The calculated results of the mean gray level, the standard deviation of the gray levels and the coefficient of variation which is the ratio of the standard deviation to the mean gray level, show that the jump location of the coefficient of variation is the end point of the glow and can be used as an index of the length of glow. With an increase of the voltage, the length of glow increases and the positive glow mingles with the negative glow at last. Compared with the other methods, the method is not only effective but also simple in the quantitative analysis the length of the glow. [Preview Abstract] |
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