Bulletin of the American Physical Society
60th Gaseous Electronics Conference
Volume 52, Number 9
Tuesday–Friday, October 2–5, 2007; Arlington, Virginia
Session LW2: Plasma Propulsion |
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Chair: Walter Lempert, The Ohio State University Room: Doubletree Crystal City Crystal Ballroom B |
Wednesday, October 3, 2007 1:30PM - 2:00PM |
LW2.00001: Ion Acceleration by Beating Electrostatic Waves: Theory, Experiments and Relevance to Spacecraft Propulsion Invited Speaker: After a brief overview of electrodeless plasma propulsion concepts, we will focus on a recently discovered ion acceleration mechanism, which appears to occur naturally in Earth's ionosphere, holds promise as an effective means to energize ions for applications in thermonuclear fusion and electrodeless space plasma propulsion. Unlike previously known mechanisms for energizing plasmas with electrostatic (ES) waves, and which accelerate only ions whose initial velocities are above a certain threshold (close to the wave's phase velocity), the new acceleration mechanism, involving pairs of beating ES waves, is non-resonant and can accelerate ions with arbitrarily small initial velocities, thus offering a more effective way to couple energy to plasmas. We will discuss the fundamentals of the nonlinear dynamics of a single magnetized ion interacting with a pair of beating ES waves and show that there exist necessary and sufficient conditions for the phenomenon to occur. We will see how these fundamental conditions are derived by analyzing the motion's Hamiltonian using a second-order perturbation technique in conjunction with Lie transformations. The analysis shows that when the Hamiltonian lies outside the energy barrier defined by the location of the elliptic and hyperbolic critical points of the motion, the electric field of the beating waves can accelerate ions regularly from low initial velocities, then stochastically, to high energies. We will then illustrate real plasma effects using Monte Carlo numerical simulation and discuss the recent results from a dedicated experiment in my lab in which laser-induced fluorescence (LIF) measurements of ion energies have provided the first laboratory observation of this acceleration mechanism. The talk will conclude with a few ideas on how the fundamental insight can be applied to develop novel plasma propulsion concepts. [Preview Abstract] |
Wednesday, October 3, 2007 2:00PM - 2:15PM |
LW2.00002: Passive optical diagnostic of electric propulsion Xe plasmas: the role of metastable atoms Rainer A. Dressler, Yu-hui Chiu, Lalita Sharma, Rajesh Srivastava, George F. Karabadzhak Metastable Xe atoms play an important role in the radiation of xenon propelled electric thrusters. Experimental and theoretical cross sections for electron-excitation from the 5$p^{5}$6$s \quad J$=2 metastable level (1$s_{5}$ state in Paschen notation) to the lowest six 5$p^{5}$6$p$ (2p) levels have recently become available, thereby providing important rate coefficients for the depopulation of the 1$s_{5 }$state. Application of a collisional radiative model to near-infrared spectral intensities observed in the plume of a Hall thruster, however, demonstrates that additional depopulation paths are important. Present calculations show that the electron-induced excitation to 5$p^{5}$6$s$ J=1 (1$s_{4})$ and other 5$p^{5}$6$s$ levels, for which newly calculated cross sections are presented, can account for the additional de-excitation mechanisms in plasma regions with low electron temperatures. [Preview Abstract] |
Wednesday, October 3, 2007 2:15PM - 2:30PM |
LW2.00003: Experimental studies of a Microdischarge Plasma Thruster in a Tri-Electrode Configuration. Utsav KC, John Bingaman, Philip Varghese, Laxminarayan Raja We present results from investigation of a direct-current microdischarge based miniaturized plasma thruster called Micro Plasma Thruster (MPT). The MPT consists of three molybdenum electrodes separated by interlayer dielectrics, and uses argon at $\sim $1 sccm as propellant. The discharge is generated in the hollow fabricated to run through the MPT. The hollow in the upstream part comprising the first two electrodes is sufficiently small (about 100 $\mu $m dia.) that a pilot microdischarge can be generated. The hollow from the second to third electrode is larger (about 300 $\mu $m dia.) to allow for expansion of the gas to lower pressure so that an intense secondary discharge, which is stabilized by the pilot discharge, is created in this region. Thrust is generated by the expulsion of ions and neutral species. The MPT is operated with modest voltage ($<$ 1 kV) and low power ($\sim $ 1 W). We demonstrate conditions under which a stable microdischarge can be sustained. The voltage-current characteristics from the MPT provide insights into discharge operations. Optical imaging, and spatially resolved optical emission spectroscopy in the plume region are used to characterize the composition of the plume. We also perform electrical probe measurements in the plume to characterize its ion distribution. [Preview Abstract] |
Wednesday, October 3, 2007 2:30PM - 2:45PM |
LW2.00004: Simulation Studies of Direct-Current Microdischarges for Electrostatic Mode Microelectric Propulsion Thomas Deconinck, Shankar Mahadevan, Laxminarayan Raja We are currently developing an electrostatic plasma thruster device based on a direct-current microdischarges. The design uses a dual-stage tri-electrode microdischarge configuration. The pilot stage ($\sim $100 $\mu$m dia.) provides sufficient constriction to enable low propellant (argon) flow rates $\sim$ 1 sccm, while keeping the pressures high enough ($\sim $ 100 Torr) to sustain a pilot microdischarge. A second stage ($\sim $300 $\mu$m dia.) downstream of the pilot microdischarge expands the flow to near vacuum conditions. In this work we simulate the tri-electrode microdischarge using a coupled plasma-bulk flow computational model. The plasma model provides a self-consistent, multi-species, multi-temperature description of the microdischarge phenomena while the gas dynamics model provides a description of the high-speed low Reynolds viscous compressible flow. A detailed description of the plasma dynamics in the microdischarge including power deposition, ionization, coupling of the plasma phenomena with high-speed flow, and propulsion system performance will be reported. The computational results will be compared to experimental results based on work being done in our group. [Preview Abstract] |
Wednesday, October 3, 2007 2:45PM - 3:00PM |
LW2.00005: Experimental study of plasma induced flow actuation by direct current discharge. Jichul Shin, Noel Clemens, Laxminarayan Raja Plasma induced flow actuation using direct-current discharge is conducted at high pressure. The actuator is made of ceramic dielectric plate on which pin-like electrodes (dia. 1/16 inches) are flush mounted. The experiment is conducted in stagnant air at 1 atm.. The velocity field of induced flow is acquired at 10 Hz rep. rate using PIV technique with TiO$_{2}$ seeding. Under low current DC discharge conditions ($\sim$ 10's mA), a flow is induced by electrohydrodynamic (EHD) forces in the direction from the anode to the cathode. The induced velocity with a continuous 26 mA DC is about 1 m/s with one pair of electrode being turned on. When the DC is pulsed, the flow actuation is improved for pulse frequencies upto about 1 kHz and diminishes for higher frequencies. Also the average discharge power is reduced with pulsed DC. The decrease of pulse duration also improves the actuation down to 50{\%} duty cycle but lower duty cycles reduces the actuation. For larger area actuation such as in airfoils, a linear array of discharges is required to produce an actuation over a finite span-wise length. With an array of discharges, it is expected to reduce the viscous effect of individual actuator pair and hence to improve the actuation performance. The effect of an array of discharges will be presented at various conditions. The performance will be compared with dielectric-barrier discharge (DBD) actuator. [Preview Abstract] |
Wednesday, October 3, 2007 3:00PM - 3:15PM |
LW2.00006: Simulation of Direct-Current Air Glow Discharge Phenomena Shankar Mahadevan, Laxminarayan Raja Surface plasma discharges are of increasing interest as actuators for flow control. Non-equilibrium glow discharges are particularly attractive for flow actuation since they have significantly lower power requirements compared to other discharges such as thermal arcs. While volumetric heating and electrostatic forcing can be important for flow actuation, the relative importance of each of these mechanisms needs to be understood. In this work develop a 2D computational model of air glow discharges in parallel-plate DC discharge under conditions similar to plasma flow actuator applications. The model is validated against experimental data and provides a good starting point for plasma flow actuator studies. All important positive and negative ions, radicals, and electrons are included with a finite-rate air chemistry mechanism. Results of model and comparison with experimental data are presented. Characteristics of the air glow discharge in the abnormal and normal glow discharge regime are represented well by the model. Voltage-current characteristics and charged species density profiles in the discharge are compared directly with experimental results and are shown to be in reasonably good agreement. [Preview Abstract] |
Wednesday, October 3, 2007 3:15PM - 3:30PM |
LW2.00007: Investigation of asymmetric dielectric barrier discharge plasma actuator, driven by repetitive nanosecond pulses. Alexandre Likhanskii, Dmitry Opaits, Mikhail Shneider, Sergey Macheret, Richard Miles DBD plasma actuators are known to be effective for low speed flow control. A comprehensive physically-based numerical model has been developed for explanation of DBD operation. The modeling showed the advantages of using repetitive nanosecond pulses with bias over the sine voltage. If the sine voltage is applied, it carries two functions -- plasma generation and producing the body force on the gas. In the pulse case these processes are separated. The plasma is generated using repetitive nanosecond pulses, and the driving of charge particles, which produces the force on the gas, is between the pulses. In pulse configuration the variation of pulse amplitude, sign and the voltage between pulses can produce different force and heating effects on the flow. The verification of the modeling has been done in the experimental investigation of DBD. A new experimental approach for non-intrusive diagnostic of DBD induced flows in quiescent gas was proposed. The schlieren technique, burst mode of plasma actuator operation, and 2D Navier-Stokes numerical model coupled together allowed restoring the entire 2D induced flow and characteristics of the plasma induced force. [Preview Abstract] |
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