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  • 1
    Electronic Resource
    Electronic Resource
    Effect of a magnetic field on the plasma plume from Hall thrusters (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 4786-4791 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An axial profile of the quasineutral plasma jet exhaust from a Hall thruster is studied. The plasma jet expansion is modeled using the sourceless steady-state hydrodynamic equations. It is considered that the plasma jet has a conical shape with a half angle of about 40°. The magnetic field surrounding the Hall thruster exit is included in the calculation. It is found that a magnetic field may significantly affect the axial profile of the plasma potential. For instance, in the case of zero magnetic field, the plasma potential is about −10 V at 1 m from the thruster exit, while in the case of a 0.1 T magnetic field, the plasma has a potential of about +25 V. Results predicted by the model are found to be in good agreement with experimental data for three different Hall thruster designs. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371444
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  • 2
    Electronic Resource
    Electronic Resource
    Vibrational–translational energy exchange models for the direct simulation Monte Carlo method (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 11 (1999), S. 2117-2126 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The model which controls the distribution of energy among the different molecular modes is a crucial component of accurate simulation of nonequilibrium rarefied flows. Two new models for the direct simulation Monte Carlo method that govern energy redistribution between the translational and vibrational modes are presented here. The first model is a modified form of the phenomenological Borgnakke–Larsen model. The probability of inelastic collision is evaluated using the relative velocity of collision. The second energy exchange model considered in this study is the multiple quantum-step transition model. The process of vibrational relaxation occurs through transitions between the different energy levels, allowing jumps of more than one level. Probabilities of activation and deactivation which depend on the relative velocity are used here. The new models are compared with existing schemes for several conditions. Significant differences are found for the vibrational energy distribution function computed in a hypersonic bow-shock wave. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870074
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  • 3
    Electronic Resource
    Electronic Resource
    Vaporization of heated materials into discharge plasmas (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 3095-3098 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The vaporization of condensed materials in contact with high-current discharge plasmas is considered. A kinetic numerical method named direct simulation Monte Carlo (DSMC) and analytical kinetic approaches based on the bimodal distribution function approximation are employed. The solution of the kinetic layer problem depends upon the velocity at the outer boundary of the kinetic layer which varies from very small, corresponding to the high-density plasma near the evaporated surface, up to the sound speed, corresponding to evaporation into vacuum. The heavy particles density and temperature at the kinetic and hydrodynamic layer interface were obtained by the analytical method while DSMC calculation makes it possible to obtain the evolution of the particle distribution function within the kinetic layer and the layer thickness. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1345860
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  • 4
    Electronic Resource
    Electronic Resource
    Far field modeling of the plasma plume of a Hall thruster (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 92 (2002), S. 1764-1774 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hall thrusters are an attractive form of electric propulsion that are being developed and implemented to replace chemical systems for many in orbit propulsion tasks on communications satellites. One concern in the use of these devices is the possible damage their plumes may cause to the host spacecraft. Computer models of Hall thruster plumes play an important role in integration of these devices onto spacecraft as the space environment is not easily reproduced in ground testing facilities. In this article, a hybrid particle-fluid model of a Hall thruster plume is applied to model the SPT-100 thrusters used on the Russian Express satellites. The emphasis of the article is on making assessment of the model through direct comparison with measurements of ion current density and ion energy distributions taken on board Express spacecraft. A model for simulating atom–ion collisions is described. The sensitivity of the plume simulation results to various aspects of the physical modeling is investigated. The plume model is able to predict many of the most important characteristics of the measured data. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1492014
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  • 5
    Electronic Resource
    Electronic Resource
    Relaxation of discrete rotational energy distributions using a Monte Carlo method (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2278-2286 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new model is presented for simulating rotational energy relaxation in the direct simulation Monte Carlo method (DSMC) using discrete distributions. The method extends the phenomenological approach generally employed that simulates the distribution as a continuum. The discrete approach simulates the mechanics of relaxation for the rigid rotor model. The theory is developed and combined for use with an existing model for simulating the rate of rotational relaxation. A number of test problems are then considered. Each set of flow conditions is chosen because of the availability of experimental data. Some of the experimental measurements provide rotational energy distributions thus allowing detailed comparison with the numerical simulations. Generally, the comparisons are quite favorable, although it is indicated that more sophisticated models are required to simulate some of the detailed structure of the energy distributions observed experimentally.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858531
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  • 6
    Electronic Resource
    Electronic Resource
    Rotational–translational energy transfer in rarefied nonequilibrium flows (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 447-452 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new model for simulating the transfer of energy between the translational and rotational modes is derived for a homogeneous gas of diatomic molecules. The model has been developed specifically for use in discrete particle simulation methods where molecular motion and intermolecular collisions are treated at the molecular level. In such methods it is normal to assume a constant rotational collision number for the entire flow field. The new model differs in that a temperature dependence is introduced, which has been predicted by theory and observed in experiment. The new model is applied to the relaxation of rotational temperature, and is found to produce significant differences in comparison with the model normally employed at both high and low temperatures. Calculations have also been performed for a Mach 7 normal shock wave. Large differences in the solutions are again observed, with the new model offering an improved correspondence to the available experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.857740
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  • 7
    Electronic Resource
    Electronic Resource
    Analysis of vibration-dissociation-recombination processes behind strong shock waves of nitrogen (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 178-185 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Computations are presented for the relaxation zone behind strong, one-dimensional shock waves of nitrogen. The numerical results are compared with existing experimental data. It is indicated that the derivation of chemical rate coefficients must account for the degree of vibrational nonequilibrium in the flow. A nonequilibrium chemistry model is employed together with equilibrium rate data to compute successfully the flow in several different nitrogen shock waves. The analysis is performed with the direct simulation Monte Carlo method (DSMC). The DSMC code is vectorized for efficient use on a supercomputer. The code simulates translational, rotational, and vibrational energy exchange, and dissociative and recombinative chemical reactions. A new model is proposed for the treatment of three-body recombinative collisions in the DSMC technique, which usually simulates binary collision events. The new formulation represents improvement over previous models in that it can be employed with a wide range of chemical rate data, does not introduce into the flow field troublesome pairs of atoms that may recombine upon further collision (pseudoparticles), and is compatible with the vectorized code.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858495
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  • 8
    Electronic Resource
    Electronic Resource
    Monte Carlo simulation of nonequilibrium flow in a low-power hydrogen arcjet (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 9 (1997), S. 3086-3095 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A particle-based Monte Carlo numerical method is developed for computation of flow in a low-thrust hydrogen arcjet. The method employs the direct simulation Monte Carlo technique to compute the nonequilibrium fluid mechanics and thermochemical relaxation. Simulation of plasma effects is included at a simple level that ensures charge neutrality. A new model is developed to include Ohmic heating in the simulation. Results are presented for a flow condition that has been studied experimentally with a number of different diagnostic techniques. A strong degree of thermal nonequilibrium is found in the flow. It is demonstrated that Ohmic heating is important, and that the Monte Carlo model captures the important physics very well. The predicted results are in very good agreement with most of the experimental data. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869474
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  • 9
    Electronic Resource
    Electronic Resource
    Models for direct Monte Carlo simulation of coupled vibration–dissociation (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 478-489 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Models are developed to permit direct Monte Carlo techniques to simulate coupled vibration–dissociation (CVD) behavior prevalent in high-temperature gases. This transient thermochemical phenomenon leads to dissociation incubation, reduced quasisteady dissociation rates, and non-Boltzmann distributions of vibrational energy during both dissociation and recombination. Essential for simulation of rarefied gas dynamics, Monte Carlo methods employ discrete particles to simulate molecular interactions directly, but have traditionally incorporated simplistic reaction models which failed to capture CVD behavior. To identify thermochemical collisions within the gas, a new dissociation selection probability is developed as a function of the extent by which the collision energy exceeds the gap between the dissociation threshold and the molecular vibrational energy of bounded anharmonic oscillators. A free parameter φ in the probability function controls the extent of vibrational favoring in dissociation selection. The new model is modified for application to the unbounded simple harmonic oscillator. Simulation of dissociation- and recombination-dominated thermochemical relaxation of O2 reservoirs, as well as the dissociation incubation behavior of N2 behind strong shock waves, demonstrates the ability of the new models to capture CVD behavior. Parameter φ is assessed empirically for O2 and N2 dissociation by comparison to experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858870
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  • 10
    Electronic Resource
    Electronic Resource
    Resolution of differences between collision number definitions in particle and continuum simulations (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2282-2284 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The use of the same symbol, Z, representing a "collision number'' for thermal relaxation, has lead to confusion regarding its definition in the context of both continuum and particle simulations. Examination of the relaxation mechanics employed in particle simulations demonstrates that these definitions differ by a numerical factor that depends upon the intermolecular potential. Particle and continuum simulations employing appropriate definitions of Z lead to identical results during isothermal and adiabatic stationary relaxation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.857964
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