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 WF1: Plasma Thrusters and Flow Control |
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Chair: John Foster, University of Michigan Room: 301 B |
Friday, October 16, 2015 3:30PM - 3:45PM |
WF1.00001: Effects of Secondary Electron Emissions from a Plasma Immersed Graphite Substrate Adrian Lopez Secondary electron emissions (SEE) from surfaces immersed in plasma has the potential to affect not only the sheath potential distribution and overall sheath voltage, but also influ-ence the near plasma properties. In order to better understand how SEE can bring about changes in the bulk plasma, electron energy distribution measurements are made outside the sheath using a Langmuir probe. Rather than numerically differentiating the I-V characteristic, an AC superimposed signal is used to obtain the electron energy distribution function (EEDF). This approach allows for better resolution of the distribution function, in particular, the distri-bution tail. In this manner, numerical noise and artificial structure that arises due to numerical differentiation can be avoided. EEDF changes will be correlated with observed changes in the sheath potential of a graphite substrate irradiated with a monoenergetic electron beam. The implications of these observations for Hall engine operation are discussed. [Preview Abstract] |
Friday, October 16, 2015 3:45PM - 4:00PM |
WF1.00002: Ion Acceleration Modes in a Miniature Helicon Thruster Timothy A. Collard, Frans H. Ebersohn, J.P. Sheehan Operation and characterization of the CubeSat Ambipolar Thruster (CAT), a miniature helicon electric propulsion device, is presented. Its small plasma volume ($\sim$ 10 cm$^{3})$ and low power requirements (\textless 100 W) make it ideal for propelling nanosatellites (\textless 10 kg). Permanent magnets generated a magnetic nozzle with a maximum field strength of 800 G. This field decreased to 0.5 G, the strength of earth's magnetic field, within 50 cm allowing the entire exhaust plume to develop in the vacuum chamber without being affected by the chamber walls. A parametric study of the thruster operational parameters was performed to determine its capabilities as both a thruster and as a plasma source for magnetic nozzle experiments. Operating with xenon and argon, separately, the plasma density, electron temperature, and plasma potential in the plume were measured with Langmuir probes, double probes, and emissive probes. Two modes of operation were observed. At low flow rates ($\sim$ 5 sccm) the plasma was well collimated along the magnetic nozzle and produced beam ions in excess of 50 eV. At high flow rates ($\sim$ 25 sccm) charge exchange collisions disrupted the magnetic nozzle and no ion beam was observed. [Preview Abstract] |
Friday, October 16, 2015 4:00PM - 4:15PM |
WF1.00003: A fully 2D electron fluid model for Hall thrusters Horatiu Dragnea, Kentaro Hara, Iain Boyd A Hall thruster is a cross-field device used for spacecraft propulsion. Recent Hall thruster developments, such as magnetic shielding and nested channels, have prompted the need to improve simulation capabilities. State-of-the-art hybrid methods such as HPHall [Fife, PhD MIT, 1998] employ a quasi-1D fluid electron model, which decouples the electron transport along and across the magnetic field lines. However, this approach cannot be used for complex magnetic field topologies, or extended computational domains. In this study, we present a fully 2D fluid electron model that directly captures the multidimensional electron transport in complex magnetic field configurations. More specifically, the plasma potential is calculated by solving a 2$^{nd}$ order partial differential equation obtained from the generalized Ohm's law for electrons in conjunction with the charge conservation equation, and assuming a quasineutral plasma. A 9-point Cartesian stencil is used to capture the effects introduced by the cross-terms and a thruster channel test case is constructed assuming dielectric channel walls as well as an anode and cathode. We present test cases under several magnetic field configurations in comparison with previous modeling results [Geng et al, JAP, 2013], and a quasi-1D model. [Preview Abstract] |
Friday, October 16, 2015 4:15PM - 4:30PM |
WF1.00004: Water-based Electric Propulsion for Small Spacecraft John Slough, Justin Little, Anthony Pancotti, Jordan Neuhoff In-space micropropulsion systems must strike a balance between simplicity, performance and mass/volume requirements, while having the flexibility of working with high-density propellants, and compatibility with the onboard power source. The Inductive Coupled Electromagnetic (ICE) thruster has the potential to achieve the highest level performance in all of these criteria, making it ideal for small satellite station-keeping and de-orbit maneuvers. The plasma generation is achieved with a small ($\sim$4 cm diameter), spiral cut, porous stainless steel antenna with an integrated RF oscillator. The ICE thruster positions the coil driver, as well as all other circuit elements, immersed in the liquid propellant providing for a PPU energy transfer efficiency of near unity. The use of a porous material as the interface between the driver coil and plasma generation zone at the thruster exit eliminates the need for a complex, miniature high pressure gas feed and valve system. A number of ICE developmental milestones have been achieved. Preliminary work has characterized the influence of the coil injector porosity on the mass flow rate of liquid water into the plasma generation zone. The device has been operated on a thrust stand, and preliminary results will be discussed. Work is now underway to transform the present form of the ICE to a proto-flight thruster. [Preview Abstract] |
Friday, October 16, 2015 4:30PM - 4:45PM |
WF1.00005: Flow separation control over a NACA0015 airfoil by nanosecond-pulse-driven plasma actuator Atsushi Komuro, Keisuke Takashima, Naoki Tanaka, Takahiro Senzaki, Daiju Numata, Toshiro Kaneko, Akira Ando, Keisuke Asai Separation flow control using a nanosecond-pulse-driven plasma actuator was studied experimentally. Wind tunnel experiments on a 10-cm chord NACA0015 airfoil were carried out at various post-stall angles of attack for free stream velocity up to 40 m/s. The pressure distribution on an airfoil surface was measured and the results showed that the nanosecond-pulse-driven plasma actuator caused flow attachment to the airfoil surface at post-stall angles. We use the custom-made pulse power source which can be operated in various operation mode such as continuous frequency mode and burst pulse mode. The effects of the pulse repetition rate, amplitude of the voltage, and rise rate of the voltage on the flow were measured. The results show that the most effective frequency of the voltage changes depending on the angle of attack and the velocity of the free stream. Additionally, the flow around the airfoil was visualized by the smoke-wire method. It is clearly shown that the normally separated flow is reattached to the suction surface of the airfoil by an on-off control of the plasma actuator. [Preview Abstract] |
Friday, October 16, 2015 4:45PM - 5:00PM |
WF1.00006: Optimizations of the RailPAc Plasma Actuator for Atmospheric Aerodynamic Flow Control Miles Gray, Young-Joon Choi, Laxminarayan Raja, Jayant Sirohi Dielectric barrier discharge (DBD) actuators, a type of electrohydrodynamic (EHD) plasma actuator, have generated considerable interest in recent years. However, theoretical performance limitations hinder their application for high speed flows.\footnote{D. F. Opaits et al., \textbf{J. Appl. Phys.} 104, 043304} Magnetohydrodynamic (MHD) plasma actuators with higher control authority circumvent these limitations, offering an excellent alternative. The rail plasma actuator (RailPAc) is an MHD actuator which uses Lorentz force to impart momentum to the surrounding air.\footnote{B. Pafford et al., \textbf{J. Appl. Phys. D.} 46, 485208} RailPAc functions by generating a fast propagating arc column between two rail electrodes that accelerate the arc through $J\times B$ forces in a self-induced B-field. The arc column drags the surrounding air to induce aerodynamic flow motion. Our current work on the RailPAc focuses on a novel arc ignition method allowing for repeatable RailPAc firing necessary for any real world application as well as the effects of temperature, rail material, size, and external magnetic fields on induced velocities. [Preview Abstract] |
Friday, October 16, 2015 5:00PM - 5:15PM |
WF1.00007: Theoretical Modeling of Pulse Discharge Cycle in DBD Plasma Actuator Shintaro Sato, Naofumi Ohnishi In order to reveal a detailed mechanism of discharge cycle in dielectric barrier discharge (DBD) plasma actuator, we have conducted two-dimensional simulations of the DBD plasma actuator with a drift-diffusion model and theoretical analysis based on them. There are two distinct phases in the discharge process when a positive ramp voltage is applied to the exposed electrode. In the first phase, an ion cloud is formed at the edge of the exposed electrode due to electron avalanche. A simple theoretical model is proposed that considers time evolution of electron number density at the edge of the exposed electrode using the first Townsend ionization coefficient and provides a good agreement with the result of the numerical simulation. In the second phase, the cloud expands along the dielectric surface, followed by the streamer propagation at a high velocity. The period of streamer discharge cycle becomes shorter as the voltage slope increases. The simulation result shows that the period of the first phase is inversely proportional to the voltage slope, while that of the second phase is inversely proportional to the square of the voltage slope. [Preview Abstract] |
Friday, October 16, 2015 5:15PM - 5:30PM |
WF1.00008: Piezoelectric transformers for the production of low-voltage atmospheric-pressure gas discharges and electrohydrodynamic flows Michael Johnson, Mark McDonald, David Go Typically, atmospheric-pressure gas discharges are formed by the application of very high voltages, $\sim$ kV, to metal electrodes. However, for some applications, including hand-held devices, such voltages can be prohibitive from a design perspective. In this work, we explore using a piezoelectric transformer to amplify a relatively small voltage input ($\sim$ 10 V) to a sufficiently high potential to breakdown air. Analogous to classical magnetic transformers which convert between magnetic and electrical energy to produce a gain in voltage, piezoelectric transformers use the electromechanical coupling present within the piezoelectric to produce a similar voltage gain. As such, a high potential can be formed on the surface of a piezoelectric crystal that is sufficient to form a corona-like discharge. In this work, we demonstrate the generation of atmospheric air discharges off of the surface of piezoelectric transformers with input voltages as low as 7 Vamp. We use two different configurations, one with the piezoelectric surface acting as an electrode in a traditional two-electrode corona discharge configuration and the second using no second electrode to form a surface discharge. One potential application of these piezoelectric-driven discharges is as electrohydrodynamic flow sources, also called ionic wind generators. Using a combination of infrared thermography and anemometry, we measure the induced flows by piezoelectric-driven discharges, and explore how the external system and resonant frequency affect flow generation. [Preview Abstract] |
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