Browsing by Subject "plasma"
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Item Gas Kinetic Study of Magnetic Field Effects on Plasma Plumes(2012-12-07) Ebersohn, Frans 1987-Plasma flow physics in magnetic nozzles must be clearly understood for optimal design of plasma propulsion devices. Toward that end, in this thesis we: i) perform an extensive literature survey of magnetic nozzle physics, ii) assess the validity of magnetohydrodynamics for studying magnetic nozzle physics, and iii) illustrate the effects of the Hall term in simple flows as well as in magnetic nozzle configurations through numerical experiments with the Magneto-Gas Kinetic Method (MGKM). The crucial steps necessary for thrust generation in magnetic nozzles are energy conversion, plasma detachment, and momentum transfer. These three physical phenomena must be understood to optimize magnetic nozzle design. The operating dimensionless parameter ranges of six prominent experiments are considered and the corresponding mechanisms are discussed. An order of magnitude analysis of the governing equations reveal: i) most magnetic nozzles under consideration operate at the edge of the continuum regime rendering continuum-based description and computation valid; ii) in the context of MHD framework, the generalized Ohm?s law must be used to capture all of the relevant physics. This work also continues the development of the Magneto Gas Kinetic Method (MGKM) computational tool. Validation of the solver is performed in shock-tube and Hartmann channel flows in the Hall physics regime. Comparison with theory and available data is made whenever possible. Novel numerical experiments of magnetic nozzle plasma jets in the Hall regime are performed, confirming the theoretically predicted azimuthal rotation of the plasma jet due to Hall physics. The primary conclusion from this work is that the addition of the Hall effect generates helical structures in magnetic nozzle plasma flows. Preliminary results are encouraging for future magnetic nozzle studies and further challenges are identified.Item Plasmachemical Synthesis of Carbon Suboxide(2012-12-11) Geiger, RobertA nonthermal carbon monoxide plasma is known to produce a solid deposition which is thought to be a polymer of carbon suboxide (C3O2); however there are very few investigations of this deposition in the literature. This thesis contains an analysis of the theoretical thermodynamics and kinetics of carbon suboxide formation as well as experimental results. The theoretical analysis suggests that carbon suboxide may be an equilibrium product even at ambient conditions but favors lower temperatures; furthermore if solid carbon is considered to be kinetically limited, and therefore not a product, then carbon suboxide is more likely to be a product under these pseudo-equilibrium conditions. Experimentally, solid films were produced in a dielectric barrier discharge (DBD) containing pure carbon monoxide. Optical emission spectroscopy was used to analyze the plasma and models of the emission spectra were created to determine the plasma temperatures. Deposition rates were determined to be on the order of 0.2 mg/min at a power of about 10W; it is expected however that these conditions are not optimized. The overall kinetics of carbon suboxide was analyzed and optimal conditions for operation can be estimated. Characterization of the solid depositions were carried out using Solid State Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared Spectroscopy (FTIR), Electrospray Ionization Mass Spectroscopy (ESI-MS), and Matrix-assisted Laser Desorption Ionization Mass Spectroscopy (MALDI-MS). The characteristics of the film are very comparable to hydrolyzed carbon suboxide polymer suggesting that carbon suboxide polymer were in fact created in the carbon monoxide plasma at atmospheric conditions.Item Prediction of Damage to Structure resulting from Recirculation of Particles from a Magnetoplasma Spacecraft Engine(2014-12-17) Martin, Michael WilliamA magnetoplasma spacecraft engine, such as the Variable Area Specific Inpulse Magnetoplasma Rocket (VASIMR?), uses magnetic fields and a magnetic nozzle to constrict and accelerate plasma to produce thrust. Most of the ejected plasma particles are expected to detach from the magnetic field lines and escape to provide thrust but some particles may not and could impact the spacecraft structure resulting in surface erosion and electrical charging. The plasma plume for a magnetoplasma engine was modeled computationally and scaled to determine what percentage of particles remained in the magnetic field and the kinetic energy of all impacting particles. Factors such as average particle velocity at the engine exit, magnetic field strength, and plume density distribution (i.e. width) were varied in a full factorial experiment to ascertain the effects of each factor and the important inter-relationships. The results are presented for a generic magnetoplasma engine and for the specific VASIMR? case. Detachment was found to be occurring with 99.42% of particles escaping under the worst conditions and only 0.0172% of particles impacting structure. It was determined that three things led to an increase in the number of impacting particles on spacecraft structure: a stronger magnetic field, a lower exit velocity of particles into the plume, and a wider plume. In addition, there was an ?erosion zone? where an increasing particle exit velocity led to more erosion until the number of impacting particles was negligible and erosion dropped significantly. For the specific case under nominal conditions, the erosion rate was 1.386 nm/month of engine operating time on aluminum and 0.611 nm/month on silicon. The electrical charging on spacecraft surfaces was found to be -27.85 V DC, which can be mitigated with current plasma contactor technology or some variant. Therefore, magnetoplasma spacecraft engines can be shown to cause minimal erosion and electrical charging and should be capable of operating safely with current technology by varying the three parameters previously mentioned.