Bulletin of the American Physical Society
61st Annual Gaseous Electronics Conference
Volume 53, Number 10
Monday–Friday, October 13–17, 2008; Dallas, Texas
Session GW1: Plasma Aerodynamics and Propulsion II |
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Chair: W. Lempert, The Ohio State University Room: Salon E |
Wednesday, October 15, 2008 8:00AM - 8:30AM |
GW1.00001: Electron and Ion Transport in Hall Effect Thrusters Invited Speaker: Hall Effect Thrusters (HETs) are gridless ion sources that can provide thrust on the order of 80 mN per kW of electrical power, with propellant velocity in the 20-30 km/s range. HETs are well suited for tasks such as satellite station keeping and are also considered for interplanetary missions. For these missions, where a small thrust is needed over a long period of time, their large propellant velocity makes them much more efficient than chemical thrusters and allows important cost reduction. The plasma in HETs is generated in the channel between two concentric dielectric cylinders. The anode is located at one end of the channel and the cathode is outside the channel. Gas (xenon) is injected through the anode and is ionized by electrons flowing to the anode. Xenon ions are accelerated by the electric field resulting from a drop of electron conductivity induced by the presence of a magnetic field barrier perpendicular to the electron path from cathode to anode. After a general introduction on space propulsion, the lecture will focus on basic physics questions related to electron and ion transport in a HET. Since most of the neutral flow is ionized, the neutral gas density in the exhaust region of a HET is not large enough to allow collisional electron transport across the magnetic field and to explain experimental measurements. We will describe recent efforts$^{1}$ aimed at understanding the observed anomalous transport, and present a synthesis of results from Particle-In-Cell (PIC) models, Hybrid Models, Laser Induced Fluorescence measurements and Collective Scattering (CS) experiments. PIC simulations predict and CS experiments seem to confirm that electron transport perpendicular to the magnetic field is due to the development of an azimuthal drift instability. [Preview Abstract] |
Wednesday, October 15, 2008 8:30AM - 8:45AM |
GW1.00002: Plasma-assisted ignition at high temperatures Ilya Kosarev, Nickolay Aleksandrov, Svetlana Kindusheva, Svetlana Starikovskaya, Andrei Starikovskii Non-equilibrium plasma of a pulsed nanosecond discharge can be used as an initiator of combustion process in gaseous mixtures. It was shown that, at the temperatures close to the ignition threshold, the time between the start of the experiment and a sharp increase in gas temperature and radical concentrations in combustible mixture (the autoignition delay time) decreases significantly when a short pulsed high-voltage discharge is applied to the system in the beginning of the experiment. Based on a detailed description of the gas discharge and combustion kinetics the kinetic mechanism of the plasma effect on ignition delay has been proposed. The production of electrons, ions, atoms, radicals and excited particles in the discharge and its near afterglow was calculated using the experimental data on $E/N(t)$ and $I(t)$ in the discharge. The analysis showed that by the beginning of the ignition process all active particles have been transported into atoms and radicals. The combustion kinetics was calculated using the standard mechanisms with additions of these species. A good correlation has been obtained between the experiments and calculations for the decrease in the ignition delay time. [Preview Abstract] |
Wednesday, October 15, 2008 8:45AM - 9:00AM |
GW1.00003: PEGASES - plasma propulsion with electronegative gases Ane Aanesland, Pascal Chabert, Gary Leray, Albert Meige, Jean-Luc Raimbault A new concept of plasma propulsion is proposed, where the thrust is provided by both positive and negative ions resulting in a globally neutral beam downstream (in space). The basic idea is to create an ion-ion plasma (electron free region) at the periphery of a highly ionised plasma core such that positive and negative ions can be extracted either simultaneously or alternately by dc biased extractor grids. As the extracted beam is globally neutral there is no need for a neutralizer downstream. The recombination of positive and negative ions is very efficient compared to ion electron recombination. Hence, a fast recombination downstream of the thruster is expected, suppressing the common problems of a downstream plasma behind the thrusters. The ion-ion plasma region is formed in the periphery of a moderately magnetized plasma where the electrons are confined along the magnetic field lines while the ions are not: The applied magnetic field therefore acts as an electron filterer resulting in a stratified plasma with an electro-positive core (electrons and ions) and an ion-ion plasma (electron free) at the periphery. The propellant has to be a strongly electronegative gas in order to effectively create negative ions. The best candidate seems to be iodine, I2, which has a high electron affinity, has a low ionisation threshold, is inexpensive, and does not require heavy and large gas tanks since it is in solid state with a high vapour pressure at room temperature. [Preview Abstract] |
Wednesday, October 15, 2008 9:00AM - 9:15AM |
GW1.00004: Multiprocessor Modeling of Dielectric Barrier Discharge Plasma Actuator Alexandre Likhanskii, Vladimir Semak, Dmitry Opaits, Mikhail Shneider, Sergey Macheret The dielectric barrier discharge (DBD) plasma actuators have been studied both experimentally and numerically for the last decade. The single processor numerical simulations were able to qualitatively describe physics of DBD using some simplifications, such as modeling smaller time and geometrical scales [1] or neglecting some physical processes. For the quantitative description of DBD all physical phenomena of plasma generation, dynamics and decay should be comprehensively described at the experimental conditions. The present work describes the successful development of the multiprocessor numerical model and characterizes the physics of the DBD. The applicability of the currently used approaches for the further optimization of the model, such as modeling small scale DBDs or omitting physical processes, will also be discussed 1. A.V. Likhanskii, M.N. Shneider, S.O. Macheret and R.B. Miles, J. Appl. Phys. \textbf{103}, 053305 (2008) [Preview Abstract] |
Wednesday, October 15, 2008 9:15AM - 9:30AM |
GW1.00005: Experimental Study of the Microdischarge Plasma Thruster (MDPT) Utsav KC, Philip Varghese, Laxminarayan Raja Small satellite propulsion requirements dictate the need for a scaled down propulsion device capable of providing low thrust with small impulse bits. We have designed and studied a simple miniaturized thruster called Microdischarge Plasma Thruster (MDPT). It comprises a tri-layer sandwich structure with a dielectric layer sandwiched between two electrode layers, and a contoured through hollow drilled into the structure. Each layer is 100's microns in thickness and the hole diameter of the same order. Argon is used as the propellant gas with flow rates of $\sim $ 1 SCCM. The pressure is adequate to produce a stable microdischarge between the electrodes even with modest voltages ($\sim $1000 V). The microdischarge adds heat to the supersonic portion of the flowing gas which is shown to produce additional thrust over the baseline cold gas flow. The studies have also demonstrated that the MDPT exhaust plume is composed of ions albeit at low concentrations, suggesting possibility of MDPT to be operated in a mixed electrothermal/electrostatic mode. We present discussion of multiple discharge operating modes and electrical characteristics of the MDPT. Spectral measurements of the plume are used to determine its composition and calculate its temperature. The momentum thrust of the MDPT is measured with a torsion balance. [Preview Abstract] |
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