Bulletin of the American Physical Society
67th Annual Gaseous Electronics Conference
Volume 59, Number 16
Sunday–Friday, November 2–7, 2014; Raleigh, North Carolina
Session CT2: Propulsion and Aerodynamics |
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Room: State C |
Tuesday, November 4, 2014 8:00AM - 8:15AM |
CT2.00001: Using the DC self-bias effect for simultaneous ion-electron beam generation in space thruster applications Dmytro Rafalskyi, Ane Aanesland In this work we discuss ways to use the self-bias effect for broad ion-electron beam generation and present recent experimental results. In asymmetrical systems the self-bias effect leads to rectification of the applied RF voltage to a DC voltage dropped across the space charge sheath near to the electrode having smaller area. Thus, continuous ion acceleration is possible towards the smaller electrode with periodical electron extraction due to the RF plasma potential oscillations. We propose a new concept of neutralizer-free gridded space thruster called NEPTUNE. In this concept, the RF electrodes in contact with the plasma are replaced by a two-grid system such that ``the smaller electrode'' is now the external grid. The grids are biased with RF power across a capacitor. This allows to locate RF space charge sheath between the acceleration grids while still keeping the possibility of a DC self-bias generation. Here we present first proof-of-concept of the NEPTUNE thruster prototype and give basic parameters spacing for such thruster. Comparison of the main parameters of the beam generated using RF and a classical ``DC with neutralizer'' acceleration method shows several advantages of the NEPTUNE concept. [Preview Abstract] |
Tuesday, November 4, 2014 8:15AM - 8:30AM |
CT2.00002: Experimental Study of RailPAc Plasma Actuator for High-Authority Aerodynamic Flow Control in One Atmosphere 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 study of the RailPAc will include a description of the transient arc discharge structure through high-speed imaging and a description of the arc composition and temperature through time-resolved emission spectroscopy. Time-resolved force measurements quantify momentum transfer from the arc to the surrounding air and provides a direct measure of the actuator control authority. [Preview Abstract] |
Tuesday, November 4, 2014 8:30AM - 9:00AM |
CT2.00003: Enhanced momentum delivery by electric force to an ion flux due to collisions of ions with neutrals Invited Speaker: Amnon Fruchtman A major figure of merit in propulsion in general and in electric propulsion in particular is the thrust per unit of deposited power, the ratio of thrust over power. We have recently demonstrated experimentally and theoretically [1-4] that for a fixed deposited power in the ions, the momentum delivered by the electric force is larger if the accelerated ions collide with neutrals during the acceleration. The higher thrust for given power is achieved for a collisional plasma at the expense of a lower thrust per unit mass flow rate, reflecting what is true in general, that the lower the flow velocity is, the higher the thrust for a given power. This is the usual trade-off between having a large specific impulse and a large thrust. Broadening the range of jet velocities and thrust levels is desirable since there are different propulsion requirements for different space missions. The mechanism of thrust enhancement by ion-neutral collisions has been investigated in the past in the case of electric pressure, what is called ionic wind [5]. I will describe in the talk experimental results for an enhanced thrust due to ion-neutral collisions in a configuration where the thrust is a result of magnetic pressure [1, 3]. The plasma is accelerated by $\overrightarrow J \times \overrightarrow B $ force, in a configuration similar to that of Hall thrusters. Our measurements for three different gases and for various gas flow rates and magnetic field intensities, confirmed that the thrust increase is proportional to the square-root of the number of ion-neutral collisions [3]. Additional measurements of local discharge parameters will be shown to be consistent with the force measurements. Issues that are crucial for the use of this mechanism in an electric thruster will also be discussed. These are the possible increase of the electron transport across magnetic field lines by electron-neutral collisions, and the possible effect on various sources of inefficiency. \\[4pt] [1] G. Makrinich and A. Fruchtman, Phys. Plasmas \textbf{16}, 043507 (2009); Appl. Phys. Lett. \textbf{95}, 181504 (2009).\\[0pt] [2] A. Fruchtman, IEEE Trans. Plasma Sci. \textbf{39}, 530 (2011).\\[0pt] [3] G. Makrinich and A. Fruchtman, Phys. Plasmas \textbf{20}, 043509 (2013).\\[0pt] [4] A. Fruchtman, Plasma Chem. Plasma Process. \textbf{34}, 647 (2014).\\[0pt] [5] R. S. Sigmond, J. Appl. Phys. \textbf{53}, 891 (1982). [Preview Abstract] |
Tuesday, November 4, 2014 9:00AM - 9:15AM |
CT2.00004: Optical Diagnostics of Air Flows Induced in Surface Dielectric Barrier Discharge Plasma Actuator Takuya Kobatake, Masanori Deguchi, Junya Suzuki, Koji Eriguchi, Kouichi Ono A surface dielectric barrier discharge (SDBD) plasma actuator has recently been intensively studied for the flow control over airfoils and turbine blades in the fields of aerospace and aeromechanics. It consists of two electrodes placed on both sides of the dielectric, where one is a top powered electrode exposed to the air, and the other is a bottom grounded electrode encapsulated with an insulator. The unidirectional gas flow along the dielectric surfaces is induced by the electrohydrodynamic (EHD) body force. It is known that the thinner the exposed electrode, the greater the momentum transfer to the air is [1], indicating that the thickness of the plasma is important. To analyze plasma profiles and air flows induced in the SDBD plasma actuator, we performed time-resolved and -integrated optical emission and schlieren imaging of the side view of the SDBD plasma actuator in atmospheric air. We applied a high voltage bipolar pulse (4--8 kV, 1--10 kHz) between electrodes. Experimental results indicated that the spatial extent of the plasma is much smaller than that of the induced flows. Experimental results further indicated that in the positive-going phase, a thin and long plasma is generated, where the optical emission is weak and uniform; on the other hand, in the negative-going phase, a thick and short plasma is generated, where a strong optical emission is observed near the top electrode.\\[4pt] [1] C. L. Enloe \textit{et al}., AIAA Journal, Vol. 42, 2004, pp. 595--604. [Preview Abstract] |
Tuesday, November 4, 2014 9:15AM - 9:30AM |
CT2.00005: Time-Resolved Laser-Induced Fluorescence Measurements of Ion Velocity Distribution in the Plume of a 6 kW Hall Thruster with Unperturbed Discharge Oscillations Christopher Durot, Alec Gallimore We present laser-induced fluorescence (LIF) measurements of the time-resolved ion velocity distribution in the plume of a 6 kW laboratory Hall thruster. To our knowledge, these are the first measurements of time-resolved ion velocity distribution on completely unperturbed Hall thruster operating conditions. To date, time-resolved LIF measurements have been made on Hall thrusters with oscillations driven or perturbed to be amenable to averaging techniques that assume a periodic oscillation. Natural Hall thruster breathing and spoke oscillations, however, are not periodic due to chaotic variations in amplitude and frequency. Although the system averages over many periods of nonperiodic oscillation, it recovers the time-resolved signal in part by assuming that a constant transfer function exists relating discharge current and LIF signal and averaging over the transfer function itself (http://dx.doi.org/10.1063/1.4856635). The assumption of a constant transfer function has been validated for a Hall thruster and the technique is now applied to a Hall thruster for the first time. [Preview Abstract] |
Tuesday, November 4, 2014 9:30AM - 10:00AM |
CT2.00006: The physics, performance and predictions of the PEGASES ion-ion thruster Invited Speaker: Ane Aanesland Electric propulsion (EP) is now used systematically in space applications (due to the fuel and lifetime economy) to the extent that EP is now recognized as the next generation space technology. The uses of EP systems have though been limited to attitude control of GEO-stationary satellites and scientific missions. Now, the community envisages the use of EP for a variety of other applications as well; such as orbit transfer maneuvers, satellites in low altitudes, space debris removal, cube-sat control, challenging scientific missions close to and far from earth etc. For this we need a platform of EP systems providing much more variety in performance than what classical Hall and Gridded thrusters can provide alone. PEGASES is a gridded thruster that can be an alternative for some new applications in space, in particular for space debris removal. Unlike classical ion thrusters, here positive and negative ions are alternately accelerated to produce thrust. In this presentation we will look at the fundamental aspects of PEGASES. The emphasis will be put on our current understanding, obtained via analytical models, PIC simulations and experimental measurements, of the alternate extraction and acceleration process. We show that at low grid bias frequencies (10s of kHz), the system can be described as a sequence of negative and positive ions accelerated as packets within a classical DC mode. Here secondary electrons created in the downstream chamber play an important role in the beam space charge compensation. At higher frequencies (100s of kHz) the transit time of the ions in the grid gap becomes comparable to the bias period, leading to an ``AC acceleration mode.'' Here the beam is fully space charge compensated and the ion energy and current are functions of the applied frequency and waveform. A generalization of the Child-Langmuir space charge limited law is developed for pulsed voltages and allows evaluating the optimal parameter space and performance of PEGASES. [Preview Abstract] |
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