Bulletin of the American Physical Society
2006 59th Annual Gaseous Electronics Conference
Tuesday–Friday, October 10–13, 2006; Columbus, Ohio
Session LW1: Plasma Aerodynamics and Propulsion II |
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Chair: Igor V. Adamovich, Ohio State University Room: Holiday Inn Salon CD |
Wednesday, October 11, 2006 1:30PM - 2:00PM |
LW1.00001: Physics of the after-spark channel decay in dense gas Invited Speaker: Considerable experimental data on the dynamics of cooling of a post-discharge channel formed by high-power spark discharges, pulsed arcs, and laser sparks have been accumulated. Cooling of the hot post-discharge channel is a problem of major practical importance. The cooling rate determines the dielectric strength recovery rate. There is a regime when the turbulent gas motion develops in a decaying post-discharge channel, dramatically enhancing heat transfer compared with molecular heat conduction. Such turbulent motion arising in the after-spark channel can substantially enhance the rate of fuel-gas mixing, which may control the mixing rate in ramjet or scramjet engines. A known experimental results and simple theoretical models for self-consistent calculations of the entire evolution of a spark discharge and the subsequent cooling of the post-discharge channel, taking into account the generation and dissipation of turbulent motion of the gas are presented. Classical cascade and non-cascade mechanisms of a turbulence dissipation are discussed. The stabilizing effect of the continuous residual electric current on the plasma cooling in the channel is analyzed. This effect cannot be explained merely by Joule heating but is largely governed by the fact that the turbulent heat transport is substantially suppressed. The results for computed rate of restoration of dielectric strength are compared with known experiments. [Preview Abstract] |
Wednesday, October 11, 2006 2:00PM - 2:15PM |
LW1.00002: Modeling of Thermionic Devices With Nonequilibrium Inert Gas Plasmas Sergey Macheret, Mikhail Shneider, Richard Miles Large temperature gradients occur between surfaces exposed to high temperatures associated with aircraft engines and external surfaces, and thermionic devices may offer a way of converting a significant portion of the heat flux into electricity. We theoretically study a possibility of operating thermionic devices with self-sustained or auxiliary nonequilibrium ionization in inert gas filled cells, without the conventionally used cesium vapor. Modeling of plasma kinetics shows that under certain conditions (low pressure, relatively high voltage and emitted current) the electric field-induced heating of plasma electrons can result in self-sustained ionization sufficient for the argon-filled device functioning without external ionization. The self-sustained nonequilibrium ionization regime is also characterized by oscillations of electron temperature and density, with the frequency determined by ion motion. At relatively low voltages or emitted currents, the heating of plasma electrons is not sufficient to sustain the ionization, and repetitive short pulses are shown to be capable of sustaining the plasma in an argon-filled device, with only a small fraction of the generated power spent on the auxiliary ionization. [Preview Abstract] |
Wednesday, October 11, 2006 2:15PM - 2:30PM |
LW1.00003: A Microwave-Excited Microplasma Thruster: Plasma Diagnostics, Performance Testing, and Numerical Analysis Yoshinori Takao, Kouichi Ono, Koji Eriguchi Decreasing the scale of propulsion systems is of critical importance on the development of microspacecraft. This paper is concerned with an application of microplasmas to a microthruster, presenting some experimental and numerical results. The microthruster consists of a cylindrical microplasma source 10 mm in length and 1.5 mm in inner diameter and a conical micronozzle fabricated in a 1.0 mm thick quartz plate with a throat diameter of 0.2 mm. The microplasma source produces hot plasmas by 4-GHz microwaves in the pressure range from 5 to 50 kPa, and then the micronozzle converts such high thermal energy into directional kinetic energy as a supersonic jet. Plasma diagnostics and performance testing showed that the electron density, rotational temperature, thrust, and specific impulse obtained were 10$^{19}$ m$^{-3}$, 1000 K, 1.1 mN, and 73 s, respectively, at an Ar/N$_2$ gas flow rate of 50/0.5 sccm and an input power of 9 W. Comparison with a numerical analysis implies that the micronozzle has an adiabatic wall rather than an isothermal one. [Preview Abstract] |
Wednesday, October 11, 2006 2:30PM - 2:45PM |
LW1.00004: Experimental Studies of a Direct-Current Microdischarge Plasma Thruster Stephen A. Yeldell, Laxminarayan L. Raja, Philip L. Varghese Recently we proposed a novel Microdischarge Plasma Thruster (MPT) using direct-current microdischarges. The MPT uses a dc-microdischarge to provide intense and controllable heating of a propellant gas stream, before it is expanded into vacuum through a sub-millimeter nozzle. This paper reports experimental results for an MPT operated with inert gas (He and Ar) propellants. Characteristic dimensions of the discharge and the nozzle are about 300 $\mu $m. We report electrical characteristics of the MPT under different geometric and operating conditions. We have also performed optical imaging and emission spectroscopy of the MPT plume expanding into a vacuum. Results indicate that a stable microdischarge can be established in the MPT configuration, with bulk gas flow, at breakdown voltages as low as 150 V for upstream reservoir (stagnation) pressures ranging from 100 to 500 Torr. Optical images show a well collimated luminous plume that extends a few centimeters from the nozzle exit plane. Emission spectroscopy was used to make line-integrated relative intensity measurements of several transitions in helium between 380 and 590nm immediately downstream of the nozzle exit plane in the plume. Boltzmann plots based on emission intensity suggest electronic excitation temperatures of $\sim $0.3 eV. [Preview Abstract] |
Wednesday, October 11, 2006 2:45PM - 3:00PM |
LW1.00005: ECR Discharge Ion Engines and Their Space Experiences Hitoshi Kuninaka, Tatsuya Nakai, Kazutaka Nishiyama Ion engine $\mu $10 has a long life and high reliability because of electrodeless ECR plasma generation in both the ion generator and the neutralizer using 4GHz microwave. Measurements on the electron energy distribution in the ion generator revealed the discharge mechanism to heat gradually a part of the thermal electron along magnetic track. The high-energy electrons generate ions in collision process and return to the thermal electrons. The recycling process of electrons results in the effective plasma generation in comparison with the DC discharge ion generator, in which the high-energy electrons are expendable. Four $\mu $10, each generating a thrust of 8 mN, specific impulse of 3,200 seconds, and consuming 350 W of electric power, propel the ``HAYABUSA'' asteroid explorer launched on May 2003. After vacuum exposure and several runs of baking to reduce residual gas, the ion engine system established continuous acceleration. In 2005, HAYABUSA, using solar electric propulsion, managed to successfully cover the distance between 0.86 AU and 1.7 AU in the solar system, as well as rendezvous with, land on, and lift off from the asteroid. During the 3-year flight, the ion engine system generated a delta-V of 1,400 m/s while consuming 22 kg of xenon propellant and operating for 25,900 hours. [Preview Abstract] |
Wednesday, October 11, 2006 3:00PM - 3:15PM |
LW1.00006: Experimental and spectroscopic study of flow actuation phenomena using DC discharge at a Mach 3 flow. J. Shin, V. Narayanaswamy, L. Raja, N. Clemens A study of flow actuation phenomena of DC discharge will be presented. An array of pin-like electrodes is flush mounted on a co-planar ceramic actuator that is inserted in the test section. The different discharge structures -- diffuse, constricted, and mixed mode -- are observed in the presence of a flow. A discernable actuation, as visualized by schlieren imaging, is achieved by diffuse discharge, whereas the constricted discharge does not show detectable flow perturbation at the same current. The flow actuation in the form of an induced oblique shock occurs within one frame of laser schlieren imaging at 4.5 kHz. Rotational (gas) and vibrational temperatures are measured by fitting spectra of N2 and N2+ bands near 365-395 nm. Electronic temperatures are measured using Boltzmann plot of Fe (I) lines. Gas temperatures of diffuse discharges drop from $\sim $1500 K to $\sim $500 K in the presence of a flow while vibrational and electronic temperatures remain almost the same at $\sim $3000 K and $\sim $1.25 eV, respectively. Gas temperatures of constricted discharge are found to be similar with diffuse discharge whereas only diffuse discharge shows an actuation. An examination of spatial extent of the plasma reveals that the diffuse discharge occupies a larger region of the flow than the constricted discharge. This indicates that the flow actuation is dependent on flow dilatation which is governed by temperature rise as well as the spatial extent over which the temperature rise is observed. [Preview Abstract] |
Wednesday, October 11, 2006 3:15PM - 3:30PM |
LW1.00007: Electron-Beam Produced Air Plasma: Optical Measurement of Beam Current Robert Vidmar, Kenneth Stalder, Megan Seeley Experiments to quantify the electron beam current and distribution of beam current in air plasma are discussed. The air plasma is produced by a 100-keV 10-mA electron beam source that traverses a transmission window into a chamber with air as a target gas. Air pressure is between 1 mTorr and 760 Torr. Strong optical emissions due to electron impact ionization are observed for the N$_{2}$ 2$^{nd}$ positive line at 337.1 nm and the N$_{2}^{+}$ 1$^{st}$ negative line at 391.4 nm. Calibration of optical emissions using signals from the isolated transmission window and a Faraday plate are discussed. The calibrated optical system is then used to quantify the electron distribution in the air plasma. [Preview Abstract] |
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