Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session UO08: Plasma-Surface Interactions, Interfacial Plasmas, Emerging ApplicationsLive Streamed
|
Hide Abstracts |
Chair: Elijah Thimsen, Washington Univ. St Louis Room: 402 ABC |
Thursday, October 20, 2022 2:00PM - 2:12PM Author not Attending |
UO08.00001: Electron Properties and Reaction Mechanisms in Plasma-Assisted Catalysis of Ammonia Synthesis David D Caron, Bruce E Koel, Ahmed Diallo, Shurik Yatom Ammonia synthesis by the Haber-Bosch process contributes 1-3% of the world’s total energy demand per year. Plasma-assisted catalysis is being investigated as an alternative method for ammonia production, with attractive features of distributed production, ease of on-off operation suitable for intermittent electrical energy supply, and possibly even increasing the energy yield of ammonia. Most studies of plasma-assisted catalysis have either characterized the ammonia production rate, showing the benefits of coupling a catalyst with a plasma environment, or characterized the bulk plasma and particle dynamics. These separate approaches have limited our understanding of important plasma-catalyst interactions such as sheath effects, reaction pathways, and catalyst active sites. Here, we report results from our investigations into the particle dynamics and plasma properties observed in a dielectric barrier discharge (DBD) reactor for ammonia synthesis via plasma-assisted catalysis. The DBD was produced by a nanosecond pulser (NSP), which enables selective heating of electrons and a plasma with tunable properties. To understand the particle dynamics in the plasma adjacent to the catalyst, we used the non-perturbative methods of Thompson scattering for electron density and energy and Raman scattering for molecular vibrational energies, taken concurrently at a given location. This enables us to make correlations between electron dynamics, N2 energy states, and ammonia production rates. Insights from these results for plasma-assisted catalysis of ammonia synthesis will be discussed. |
Thursday, October 20, 2022 2:12PM - 2:24PM |
UO08.00002: In situ investigation of plasma synthesis of ammonia with porous silica catalysts Sophia Gershman, Fnu Gorky, Hoang Nguyen, Maria Carreon Plasma catalytic synthesis of ammonia is a promising component of electrification of manufacturing for green economy and energy storage due to the adaptability of this process to intermittent sources of electricity. Nevertheless, many problems remain in achieving both the output and the efficiency required for practical implementation. Solving these problems will require a detailed understanding of the role of plasma conditions, such as electron temperature and density as well as vibrational excitation temperatures of molecular nitrogen in the requirements for the catalyst design. Our previous experiments with mesoporous silica catalyst in a packed bed reactor showed that this catalyst produces the highest output concentrations of ammonia at high plasma density and hence high power, but at lower plasma density, the addition of a metal catalyst is beneficial to the overall concentration of ammonia. A reactor is designed that allows us to determine plasma conditions and ammonia concentration in the reactor in situ and in real time during plasma catalysis. The new reactor design will aid in the understanding of the role of plasma parameters for the appropriate design of the catalyst composition and structure. |
Thursday, October 20, 2022 2:24PM - 2:36PM |
UO08.00003: Nonequilibrium plasma for the production of hydrogen from methane Elijah J Thimsen Methane is an abundant molecule in the environment that is produced naturally by a variety of biological and nonbiological processes. Natural gas that comes from wells is from 75 to 90 mol. % methane. The production of hydrogen without CO2 emission has regained interest in recent years as urgency for action on climate change is increasing. The production of hydrogen from methane is much less energy intensive than splitting water into hydrogen and oxygen, and so processes to split methane driven by renewable electricity are attractive in this context. Thermal plasmas have been explored for the synthesis of hydrogen and carbon products from methane. These processes operate by heating the gas to very high temperatures on the order of thousands of degrees Celsius, and then rapidly quenching the resulting gas to supress the reverse reaction. Energy efficiency, based on the power input and enthalpy of reaction, for these thermal plasma processes can be as high as 40%. We are exploring the idea that nonequilibrium plasmas may be able to achieve higher energy efficiency for methane splitting because the gas temperature remains much lower than in thermal plasmas. In other words, the idea is that the energy supplied to the nonequilibrium plasma is more effectively focused into the chemical reaction with less going to unwanted gas heating, when compared to thermal plasmas. If this idea is correct, then it should be feasible to realize an energy conversion efficiency greater than the thermal plasma benchmark of 40% for methane splitting to generate hydrogen. Results from experiments conducted by our group will be presented. |
Thursday, October 20, 2022 2:36PM - 2:48PM |
UO08.00004: Evidence of nanodiamond forming in the gas phase: experiment and activation energy analysis Tanvi Nikhar, Shengyuan Bai, Sergey V Baryshev The mechanism of ballas like nano diamond (ND) formation still remains elusive, and this work attempts to analyze its formation in the framework of activation energy (Ea). ND thin films were grown from H2/CH4/N2 plasma in a 2.45 GHz chemical vapor deposition system. The Ea is calculated corresponding to the thickness and mass growth rate, and renucleation rate, while using substrate temperature (~1000-1300 K) in all the calculations. While these values of ~10 kcal/mol match with the Ea for ND formation throughout literature, they are far off compared to ~50 kcal/mol for single crystal diamond (SCD) formation, concluding thus far, that the processes involved are different. To further elaborate this, we modified the substrate preparation and sample collection method while keeping the growth parameters constant. Electron microscopy and Raman spectroscopy of the collected sample found that ND self nucleates in the plasma and flows to the substrate which acts as a mere collection plate. The Ea values for all the ND films are now re-calculated using the approximated gas temperature (~2000-3000 K), giving values closer to SCD formation. It suggests that the formation process for ND and SCD could be the same, but it happens in the gas phase for ND and directly on the substrate for SCD. |
Thursday, October 20, 2022 2:48PM - 3:00PM |
UO08.00005: Research and Development of Microwave Plasma Enhanced Chemical Vapor Deposition System Using the Fluid Modeling based on the Finite Element Method Kaviya Aranganadin, Yilang Jiang, Jing-Shyang Yen, Jwo-Shiun Sun, Hua-Yi Hsu, Ming-Chieh Lin Microwave Plasma Enhanced Chemical Vapor Deposition (MPECVD) is one of the commonly used thin film manufacturing methods for diamond, graphene, etc. In an MPECVD system, the plasma is confined to the center of the deposition chamber as a ball and uniformly distributed, preventing carbon deposition onto the walls of the chamber and microwave deposition is an electrode-less process hence contamination of the films due to electrode erosion is avoided, making it a best technique for diamond film growth. This paper discusses the design of a 3-D MPECVD chamber connected by slots to a coaxial waveguide and operated at a 2.45 GHz of frequency to produce TM011 mode using the fluid modeling based on finite element method (FEM) that incorporates many physical interfaces such as laminar flow, heat transfer in fluids, plasma, and electromagnetic waves to give more self-consistent and accurate simulation results. The plasma discharge is modeled by coupling drift-diffusion, heavy species transport, and electric fields into a single multiphysics model and the conservation of mass and momentum by solving continuity and Navier-strokes equation, respectively. At an input power of 1 kW with the argon pressure varied from 600 to 1400 Torr, the plasma density increases from 2.35e17 to 4.09e17 1/m^3, reaching steady-state at around 0.1 seconds and a uniform argon plasma is excited by the TM011 microwave resonance. The model is also tested at constant presure of 1,000 Torr and 760 Torr for different power levels, ranging from 800 W to 1 kW which produced a steady state plasma density in the range of 3.17e17 to 3.41e17 1/m^3 and 2.66e17 to 2.80e17 1/m^3, respectively. |
Thursday, October 20, 2022 3:00PM - 3:12PM |
UO08.00006: Atmospheric pressure plasma jets operated by shielded and unshielded high voltage electrodes: Physicochemical characteristics and application to bacterial killing Bhagirath Ghimire, Lanie Briggs, Tanya Sysoeva, John Mayo, Gabe Xu This study investigates how the shielding of a high voltage (HV) electrode influences the physicochemical properties and the bacterial inactivation efficacy of an atmospheric pressure plasma jet. The plasma jet is comprised of a tungsten electrode inserted inside either a single closed end quartz capillary tube (termed as shielded) or double open end quartz capillary tube (termed as unshielded). A second double open end quartz tube surround the capillary tube to create an annulus area where gas flows. The entire assembly is held inside a plastic Swagelok Tee fitting. Plasma is generated by flowing helium gas through the annulus between the quartz tubes and applying a pulsed DC voltage of 8 kV, 1 µs pulse width, and 6 kHz between the HV tungsten electrode, and a copper ring placed near the end of the outer quartz tube that serves as the ground. Results from fast imaging reveal that the plasma bullets in an unshielded jet has a higher velocity by an order of magnitude, and propagates twice as far as the shielded jet. The higher propagation speed and longer plume length for the unshielded configuration are due to higher accumulation of surface charges which also induce higher electric field. These physical characteristics of the unshielded jet also result in the production of more than two times higher concentration of hydrogen peroxide in plasma activated water. Measurement of rotational temperature for both plasma jets showed that they operate at room temperature facilitating their use in real-world applications. The importance of the study for practical application has been demonstrated by treating Escherichia coli, a bacterial pathogen commonly found in the human body. |
Thursday, October 20, 2022 3:12PM - 3:24PM |
UO08.00007: Reduced-order Neural Operators for Accelerating Low-Temperature Plasma Chemistry Simulations Tiernan Casey, Simone Venturi, Cem Gormezano In many real-world applications, the simulation of plasma systems for the purposes of design, optimization, or quantification of uncertainty requires a large number of independent computations, which is often limited by computational cost. In this work, we explore the combination of dimensionality reduction techniques and neural operator surrogates to mitigate this expense. Firstly, we test multiple approaches for projecting the plasma dynamics into low-dimensional subspaces. These include both linear techniques (e.g., principal component analysis), which have the advantage of preserving the underlying equations’ form, and non-linear manifold learning approaches (e.g., diffusion maps), which permit a more effective compression of the trajectories at the expense of interpretability. Secondly, we accelerate the simulation of the plasma dynamics in in the reduced order space via emulation through neural operators. These computational objects are machine learning-based surrogates characterized by two main advantages: i) they bypass the numerical integration of the typically stiff underlying equations, and ii) they can predict the dynamical system’s evolution given initial conditions and/or operator parameters unseen during the training phase. We demonstrate these techniques in the context of global chemistry models for low-temperature plasma systems. |
Thursday, October 20, 2022 3:24PM - 3:36PM |
UO08.00008: Magnetron Sputtering Simulations with Enhanced Particle-in-Cell Techniques Joseph G Theis, Gregory R Werner, Thomas G Jenkins, Daniel Main, John R Cary Variable grid spacing, energy-conserving particle-in-cell (EPIC), and speed-limited particle-in-cell (SLPIC) techniques are explored to speed up fully-kinetic simulations of magnetron sputtering. Fully-kinetic simulations of magnetron sputtering are needed to optimize the sputter-coating of thin films. Traditional PIC simulations of magnetron sputtering are computationally slow because the Debye length (~10-5 m) is much smaller than the centimeter size device, and the plasma period (~10-11 s-1) is much shorter than the microsecond long dynamics. Variable grid spacing speeds up simulations by resolving the bulk of the plasma with larger cells and the thin cathode sheath with small cells. EPIC speeds up simulations by relaxing the requirement to resolve the Debye length, which enables larger grid cells. SLPIC speeds up simulations by limiting the speeds of the fastest electrons, which enables larger timesteps. We have shown that SLPIC can quickly simulate electric discharge, collisions, and wall interactions, which are relevant to magnetron sputtering. We plan to compare and possibly combine these different PIC techniques and benchmark our results to both simulation and experimental data before exploring device optimization. |
Thursday, October 20, 2022 3:36PM - 3:48PM |
UO08.00009: Persistent Sputtering Yield Reduction in Plasma-Infused Materials for Plasma Propulsion and Fusion angelica ottaviano, Richard E Wirz, Gary Wan, Graeme T Sabiston, Mary F Konopliv, Anirudh Thuppul Material sputtering provides challenges for plasma devices from space propulsion to fusion. In this talk, Prof. Wirz will discuss plasma-material interactions for plasma thrusters and recent developments towards fusion plasma materials. Plasma thrusters are predominantly driven by thruster component lifetime through erosion and ion and electron induced “facility effects” during ground testing that obfuscate the thruster’s anticipated on-orbit performance. Recent developments in these areas have revealed material approaches that may help fusion devices, which must address both component lifetime and plasma performance via reduction of contaminants. |
Thursday, October 20, 2022 3:48PM - 4:00PM |
UO08.00010: An electron multiplication mechanism at the early stage of nanosecond pulsed breakdown in water Xuewei Zhang, Mikhail N Shneider Nanosecond and subnanosecond pulsed breakdown in water as potential plasma sources have attracted research attention in the past decade. In previous studies, electrostrictive cavitation has been established as the mechanism for breakdown initiation at nanosecond timescale, and electron dissociation from hydroxide has been demonstrated to be the most probable source of primary electrons in bulk pure water. A missing link between the cavitation inception and the formation of the first plasma channel is how the primary electrons multiply in the system. To answer this question, a clearer picture of the cavitation zone that sets the stage for electron multiplication would be needed. In this work, we present a new modeling framework and some numerical results of cavitation dynamics within the first nanosecond. The typical radius and number density of the generated cavities are calculated. The results are in support of the following hypothesis of electron multiplication: an electron gains energy while collisionlessly traversing a cavity under electric field; it causes collisional ionization at the opposite side of the cavity; the two resulting hydrated electrons migrate toward the next cavity and are released into the cavity upon arrival, thus completing one multiplication step. |
Thursday, October 20, 2022 4:00PM - 4:12PM |
UO08.00011: Coupling between thermodynamics and self-organized pattern on the liquid anode of an atmospheric pressure DC glow discharge Zimu Yang, Yao E Kovach, John E Foster In a discharge involving plasma-liquid interactions, many complex dynamics including thermal transfer, fluid mechanics, chemical reactions, and plasma physics are all coupled at the plasma-liquid interface. One of the more remarkable phenomena that occurs at the interface is the formation of the observed self-organized pattern that forms on a liquid anode of the air pressure DC glow discharge. The pattern apparently is coupled to prevailing interfacial processes and responds to discharge conditions by changing its shape and size. In an open system such as this nonequilibrium thermodynamics plays an important role in governing the heat and mass transport at the interface. The ohmic heating of discharge cause substantial water evaporation at interface and drive species transport and interactions through the pattern region. In the liquid phase, temperature gradients induce density variations and lead to the substantial convective flow and movement of the pattern. A highly localized hot spot may also give rise to the Marangoni effect which in turn may also effect the pattern shape. |
Thursday, October 20, 2022 4:12PM - 4:24PM |
UO08.00012: Correlating Plasma Properties to Liquid Chemistry in a Nanosecond Pulsed Helium Gas-Liquid Water Discharge Bruce R Locke, Radha Krishna Murthy Bulusu, Robert J Wandell, Shurik Yatom To develop nonthermal plasma gas-liquid chemical reactors it is important to understand how the plasma properties such as electron density and electron temperature affect the chemical reactions. Therefore, we determine electron density and energy as functions of pulse width and pulse frequency with nanosecond pulsed discharges in a continuous flow gas-liquid film reactor with helium and deionized liquid water. The electron density was determined by the Stark broadening of Hα and Hβ. The excitation temperature was found from the intensity ratio of the H-Balmer lines. The pulse frequency was varied between 1 – 10 kHz and the pulse width from 40 – 200 ns using a commercial power supply (Eagle Harbor Technologies, NSP-120-20, Seattle, WA). A custom-made power supply (Airity Technologies, Palo Alto, CA) was used to vary the pulse frequency from 5 – 100 kHz. The temporal variation of electron density for a single pulse is compared with our previous work with argon where the electron densities were found to reach maximums at specific resonant frequencies. With argon, the results correlated with chemical reactions of perfluorinated organic compounds but not hydrogen peroxide formation. |
Thursday, October 20, 2022 4:24PM - 4:36PM |
UO08.00013: Regime transitions in liquid metal response to pulsed Lorentz forces Daniel P Weber, Colin S Adams, William Brown, Stefano Brizzolara, Bhuvana Srinivasan The Liquid Electrode eXperiment (LEX) at Virginia Tech is configured to pulse current through a solid wire intersecting the surface of a liquid metal (LM). This design was chosen as a surrogate scenario to study the effect of large current densities present in the liquid first wall of future fusion reactor concepts. The self-generated magnetic fields and resulting Lorentz forces produce an annular jet of LM originating at the free surface and rising to significant heights; in some cases reaching the top of the containing vessel (≈0.25 m). Along with this feature, a void is created below the wire which appears to expand before obscuration by the upwards-traveling jet. As the LM is subjected to a range of driving current amplitudes from 50–200 kA and wire radii from 1.59 mm to 2.38 mm, transitions are observed in the qualitative behavior of the LM wave as the Lorentz force increases. Hydrodynamic simulations of the LM response to electromagnetic forces and Ohmic heating are employed to interpret experimental results. Evidence also indicates that the vertical velocity of the jet is proportional to the Lorentz force, and that other parameters such as void formation and initial phase velocity may be similarly proportional. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700