Bulletin of the American Physical Society
2005 58th Gaseous Electronics Conference
Sunday–Thursday, October 16–20, 2005; San Jose, California
Session GT2: Plasma Propulsion and Combustion II |
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Chair: Toza Popovic, Old Dominion University Room: Doubletree Hotel Cedar |
Tuesday, October 18, 2005 8:00AM - 8:15AM |
GT2.00001: Simulation of microdischarge gas heating in electrothermal class of small satellite propulsion devices Prashanth Kothnur, Laxminarayan Raja Microdischarges have unique features such as high power density (kW/cm$^{3})$ and high gas temperatures (1000-2000K) that enable use in electrothermal plasma devices with highly controllable thrust levels in the mN range. Two-dimensional modelling is used to simulate a flow-through microhollow electrode geometry with helium as the operating gas. Bulk fluid conservation equations are solved using the semi-implicit pressure linked equations (SIMPLE) approach and coupled to a nonequilibrium self-consistent plasma model [1]. Results indicate that plasma parameters are relatively insensitive to the flow rate. Electron temperatures as high as 20eV near the cathode fall and gas temperatures of 1000-2000K depending on the pressure and current are observed. Low Reynolds numbers and large surface-to-volume ratios result in strong sensitivity of gas temperatures to wall conditions. It is shown that wall losses must be minimized for any significant heating of the flow downstream of the electrodes, emphasizing the need for new refractory and insulating materials.\newline [1] P.S. Kothnur, and L.L. Raja, J. App. Phys. 97(2005), 043305. [Preview Abstract] |
Tuesday, October 18, 2005 8:15AM - 8:30AM |
GT2.00002: Electron Kinetics in Helicon Discharge Guangye Chen, Laxminarayan Raja, Alexey Arefiev, Boris Breizman The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) project employs helicon discharge as a plasma source [1]. A self-consistent description of the helicon discharge requires a power balance analysis, which involves electron kinetics. A steady-state electron distribution establishes when electron Ohmic heating becomes balanced by electron energy losses on atom excitation. RF-electric field and plasma density are the key parameters that determine features of the steady-state electron energy distribution function. The electron distribution has been studied in four different heating regimes using the Direct Simulation Monte Carlo method. We have found that the electron distribution is significantly non-Maxwellian in the dense gas regime, when elastic electron-atom collisions dominate. The non-Maxwellian feature of the electron distribution function has a strong impact on the cost of ionization in the discharge. \newline \newline [1] F.R. Chang-Diaz, Sci. Am. \textbf{283}, 90 2000. [Preview Abstract] |
Tuesday, October 18, 2005 8:30AM - 9:00AM |
GT2.00003: Efficiency of Nanosecond High--Voltage Discharge in Ignition and Combustion Enhancement Invited Speaker: The problem of a fast homogeneous ignition of a combustible mixture is topical. High electric field in a front of nanosecond discharge and behind it results in effective ionization, dissociation and excitation. Two topics will be discussed: the efficiency of nanosecond discharges as active particles generator for ignition and study of nanosecond barrier discharge influence on a flame. Experimental results of a shift of ignition delays under the discharge are obtained for a set of combustible mixtures with H2 or hydrocarbons (up to C5H12) in a temperature range of 700-- 2300 K and pressure range of 0.1-1.5 atm, numerical modeling was performed for the same conditions. Comparative study of laser flash-photolysis and nanosecond discharge allowed us to make a conclusion about a role of excited atomic oxygen in the process of ignition. Experiments on plasma-- assisted combustion with a nanosecond barrier discharge at atmospheric pressure have demonstrated that with energy input negligible in comparison with burner's chemical power, it is possible to obtain double flame blow-off velocity increase. The role of addition of different radicals and excited species by the discharge is discussed. The lecture will be based on works carried out at the Laboratory of Physics of Nonequilibrium Systems of MIPT. In collaboration with Ilya Kosarev, Eugene Mintoussov, Andrei Nikipelov, and Andrei Starikovskii of the Moscow Institute Physics and Technology. [Preview Abstract] |
Tuesday, October 18, 2005 9:00AM - 9:30AM |
GT2.00004: Air plasmas sustained by repetitive high-voltage nanosecond pulses: fundamental kinetics and aerodynamic applications Invited Speaker: The paper reviews the recent studies of highly efficient generation of weakly ionized plasmas and their applications to supersonic/hypersonic flight. Plasmas can be used simply as means of delivering energy (heating) to the flow, and also for electromagnetic flow control and magnetohydrodynamic (MHD) power generation. Plasma and MHD control can be especially effective in transient off-design flight regimes. In cold air, nonequilibrium plasmas must be created, and the ionization power budget determines the design and performance envelope of plasma/MHD devices. The minimum power budget is provided by electron beams or repetitive high-voltage nanosecond pulses, and the paper describes theoretical modeling of those plasmas. The models include coupled equations for non-local and unsteady electron energy distribution function (modeled in forward-back approximation), plasma kinetics, and electric field. The modeling is in good agreement with experimental studies of quiescent air plasmas sustained by 2-nanosecond, 5 kV/cm, high (100 kHz) repetition rate pulses, where the average energy cost per electron was found to be about 100 eV, two orders of magnitude lower than in quasineutral DC and RF plasmas. Detailed investigations of the plasma dynamics revealed a critical role of the cathode sheath that was found to take up most of the peak voltage applied to the electrodes. The extremely high E/N, much higher than the Stoletov's field at the Paschen minimum point, results in a very high ionization cost in the sheath. In contrast, the E/N in the quasineutral plasma is closer to that associated with the Stoletov's point, resulting in a near-optimal electron generation. The positive space charge in the sheath and its relatively slow relaxation due to the low ion mobility was also found to result in reversal of electric field direction in the plasma at the tail of the high-voltage pulse. Experimental studies at Princeton University have also successfully demonstrated stable diffuse plasmas sustained by repetitive nanosecond pulses in supersonic air flow, and for the first time have demonstrated the existence of MHD effects in such plasmas. As one potential application, cold-air hypersonic MHD devices are shown to permit optimization of scramjet inlets at off-design Mach numbers while operating in self-powered regime. [Preview Abstract] |
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