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The dayside near-surface lunar plasma environment is electrostatically complex, due to the interaction between solar UV-induced photoemission, the collection of ambient ions and electrons, and the presence of micron and sub-micron sized dust grains. Further complicating this environment, although less well understood in effect, is the presence of surface relief, typically in the form of craters and/or boulders. It has been suggested that such non-trivial surface topography can lead to complex electrostatic potentials and fields, including “mini-wakes” behind small obstacles to the solar wind flow and “supercharging” near sunlit-shadowed boundaries (Criswell, D.R., De, B.R. [1977]. J. Geophys. Res. 82 (7); De, B.R., Criswell, D.R. [1977]. J. Geophys. Res. 82 (7); Farrell, W.M., Stubbs, T.J., Vondrak, R.R., Delory, G.T., Halekas, J.S. [2007]. Geophys. Res. Lett. 34; Wang, X., Horanyi, M., Sternovsky, Z., Robertson, S., Morfill, G.E. [2007]. Geophys. Res. Lett. 34, L16104). In this paper, we present results from a three-dimensional, self-consistent, electrostatic particle-in-cell code used to model the dayside near-surface lunar plasma environment over a variety of local times with the presence of a crater. Additionally, we use the particle-in-cell model output to study the effect of surface topography on the dynamics of electrostatic dust transport, with the goal of understanding previous observations of dust dynamics on the Moon and dust ponding on various asteroids.

Chemically reactive plasmas operating in the 1 mTorr–10 Torr pressure range are widely used for thin film processing in the semiconductor industry. Plasma modeling has come to play an important role in the design of these plasma processing systems. A number of 3-dimensional (3D) fluid and hybrid plasma modeling examples are used to illustrate the role of computational investigations in design of plasma processing hardware for applications such as ion implantation, deposition, and etching. A model for a rectangular inductively coupled plasma (ICP) source is described, which is employed as an ion source for ion implantation. It is shown that gas pressure strongly influences ion flux uniformity, which is determined by the balance between the location of plasma production and diffusion. The effect of chamber dimensions on plasma uniformity in a rectangular capacitively coupled plasma (CCP) is examined using an electromagnetic plasma model. Due to high pressure and small gap in this system, plasma uniformity is found to be primarily determined by the electric field profile in the sheath/pre-sheath region. A 3D model is utilized to investigate the confinement properties of a mesh in a cylindrical CCP. Results highlight the role of hole topology and size on the formation of localized hot-spots. A 3D electromagnetic plasma model for a cylindrical ICP is used to study inductive versus capacitive power coupling and how placement of ground return wires influences it. Finally, a 3D hybrid plasma model for an electron beam generated magnetized plasma is used to understand the role of reactor geometry on plasma uniformity in the presence of E × B drift.

Summary form only given. Over past decades, microplasma devices (MPDs) became popular research subject for their unique properties and wide range of applications, such as optical emitters, transistors, electron/ion sources, etc. However, MPD integration into electric circuits for consequent transition into industrial applications requires both reduction of MPD sizes and more detailed understanding of the physics behind its operation. In the presentation, we will demonstrate results of kinetic simulation of the state-of-the-art aluminum/aluminum oxide MPD, developed at UIUC [1], using Tech-X's code VORPAL. We will investigate the dependences of ignition voltage and relevant plasma parameters (such as EEDF, charge carrier density, etc.) during quasi steady-state MPD operation on the gas composition, gas pressure as well as scaling with reduction of geometrical sizes. Figure.1 shows our preliminary results on plasma generation for He/Ne mixture at 600 torr pressure.

The paper presents study of one of the examples of nonequilibrium plasmas—dielectric barrier discharge in atmospheric air—using kinetic particle‐in‐cell code VORPAL. It has been demonstrated that the use of state‐of‐the‐art methods for solution of the electrostatic problems and the concept of variable‐weight particles for reduction number of particles in dense plasma regions made simulations numerically efficient. Using the developed model the propagation of the cathode‐directed streamer driven by 4ns positive pulse has been analyzed in both 2D and 3D. The model reproduced all essential physical phenomena of the streamer propagation. The model has been validated via grid resolution study and study of the concept of variable‐weight particles.

This paper provides a comprehensive analysis of the viscous effects for the DBD operation. Maximum DBD induced flow velocity is estimated based on the conservation laws without the viscous effects. It is demonstrate d that inclusion of the viscosity leads to the twice smaller maximum DBD induced flow velocity. The possibility to increase maximum induced flow velocity by use of a series of DBDs is considered. The significant dependence of the DBD induced flow on the spatial distribution of the DBD body force is shown. Based on the study of the boundary layer profile , it is demonstrated that the DBD force should not only be maximized, but also generated at the optimum location for optimum DBD performance. The possibility of using DBD as a de-icing device is also analyzed.

In this paper, we study the surface plasma induced jets using analytical self-similar solution for the viscous wall jet problem. It is shown that the entire induced flow field outside the plasma can be found from the velocity profile measured in a single streamwise location. Analytical expressions for key plasma induced flow characteristics are found. The analytical model’s applicability to the dielectric barrier discharge (DBD) plasma actuators is validated experimentally.

Surface charge buildup and its effect on performance of DBD plasma actuators driven by repetitive voltage pulses added to dc bias were studied. A simplified numerical model showed a good agreement with the experimental data. This confirms that the surface charge is deposited by the ions which drift from the plasma region to the dielectric surface in the applied bias field . Based on the results of surface charge studies, a new configuration of the DBD plasma actuators was proposed – an asymmetric DBD plasma actuator with a slightly conductive dielectric that would deplete the surface charge between the pulses. Two materials that have been considered as slightly conductive dielectrics – zinc oxide and linen based phenolic, showed some promise, but one was too conductive, and the other too resistive. Further search for suitable materials could potentially improve performance of plasma actuators.

An effective parallel comprehensive, physically based numerical model of an asymmetric dielectric barrier discharge (DBD) plasma actuator in air, which takes into account the photoionization mechanism, has been developed for multiprocessor computations. Using the developed model the propagation of the cathodedirected streamer driven by 4ns positive pulse has been analyzed. The streamer parameters have been compared to ones computed using the concept of artificial plasma generation. It has been shown that the streamer, computed based on the photoionization model, is several times thicker than one computed based on the artificial plasma. The maximum electric field at the streamer head is lower for the case of photoionization.

Based on the early developed single-processor numerical model for the dielectric barrier discharge simulation we have developed a multi-processor model. The time required for the DBD simulation is shown to be significantly less for the multiprocessor model than for the single-processor one. Based on the understanding of the physics of the DBD, operated with nanosecond pulses and bias voltage, we have implemented a modified time step for the plasma kinetic calculation between the breakdowns. This approach has provided a 3-orders of magnitude increase in the speed of computations between pulses. Using the multi-processor model with modified time step a 4kV, 4ns positive pulse with 1kV DC bias has been simulated on 32 processors. The qualitative results are in agreement with previously obtained results for lower voltages, however the speed of computation has significantly increased.

A parallel comprehensive, physically based numerical model of an asymmetric dielectric barrier discharge (DBD) plasma actuator in air has been developed for multi-processor computations. Based on the numerical model for DBD simulations, a model has been also developed which allows the computation of the charge distribution on the dielectric surface of DBD using the experimentally obtained electric potential distribution. The surface charge motion has been analyzed, and a theory of charge motion on the dielectric surface has been developed. It is concluded that the main negative charge carriers on the surface are negative ions.

DBD plasma actuators driven by repetitive nanosecond pulses added to low frequency bias voltage are studied, and parametric results of plasma-induced thrust versus voltage profile parameters are presented. The results of the thrust measurements agree with schlieren visualization results obtained earlier and indicate that dielectric surface charge plays a major role in the thrust. Direct measurements of the dielectric surface potential and its dynamics show that charge builds up at the dielectric surface and extends far downstream of the plasma. For a sinusoidal voltage waveform, the dielectric surface charges positively. With the voltage waveform consisting of nanosecond pulses superimposed on a dc bias, the sign of the dielectric surface charge is the same as the sign (polarity) of the bias voltage. Based on the surface charge measurements, a modified configuration of DBD plasma actuator is proposed. Preliminary experiments show its effectiveness at relatively low voltages. Variations of the permittivity of dielectric with temperature and frequency were also considered in relation to their role in DBD actuator performance.

An earlier developed detailed physical model of an asymmetric dielectric barrier discharge (DBD) plasma actuator in air driven by repetitive nanosecond voltage pulses and ac/dc bias is used to model realistic experimental conditions, such as nonideal pulses with multiple reflections. The force and heating rate calculated by the plasma model is used as an input to two-dimensional viscous flow solver to predict the time-dependent DBD-induced flowfield. The calculations reproduce the wall jet and vortices observed in experiments and enable determination of the induced flow velocity at the plasma edge and the body force magnitude from the schlieren imaging. A three-electrodes DBD system is theoretically explored, and its advantages are shown to only exist during a very short time following the voltage pulse.

A theoretical and experimental investigation of the Rayleigh-Taylor instability stabilization in the multi-layer liquid system using high frequency oscillations was carried out. The stabilization criterion for a layer of deep liquid, confined by air, was derived to coincide with stabilization criterion for the deep liquid above air. For a narrow layer of liquid the stabilization parameters depend only on the layer depth, but not on a wave vector. The possibility of the Saffman-Taylor instability stabilization in the Hele-Show cell using an alternating pressure was shown. The theoretical dependence of the alternating pressure amplitude on its frequency to stabilize the Saffman-Taylor instability was derived. These results may be useful for stabilization of instabilities in plasma and during mineral oil production. The problems of the Rayleigh-Taylor instability (RTI) come across in different physics fields, such as hydrodynamics, plasma physics and astrophysics. The theory of the hydrodynamic RTI is described in [1-3] for liquids in the systems of plane, cylindrical and spherical geometries under external forces and pressure gradients. The effects of liquid viscosity and spatial inhomogeneity were taken into account. The stability conditions for different cases are obtained and the nonlinear dynamics of the RTI on liquid boundaries are analyzed. The asymptotic behavior for the nonlinear stage of the RTI was investigated using the Fourier-series expansion [4,5]. A number of the experimental researches of the nonlinear and chaotic RTI dynamics [6-9] and the RTI dynamics in inertial confinement fusion [10-12] were carried out. Another example of the hydrodynamic instability is the Saffman-Taylor instability (STI). It arises on the boundary between two viscous liquids, when the less viscous one pushes the more viscous one in porous media, and consists in the development of transverse perturbations of the displacement front. The nonlinear stage of these perturbations results in the formation of so called “viscous fingers”. The problem of appearance of the viscous fingers in the Hele-Show cell is associated with the STI in porous media. The similarity between these phenomena was noticed by Paterson in [13]. The extensive theoretical, experimental and numerical investigations of the STI for different liquid systems, such as multi-layer systems or systems with mixed layer, were carried out [14-18]. In many practical problems the RTI and the STI development should be suppressed. For example, one way of the increase of mineral oil production from depleted oil field is an injection of water under the oil region and oil extrusion by the water. Since the water viscosity is less than the oil one, the STI arises on the displacement front between the water and the oil. This instability leads to the water outbreak through the oil and oil production stops. Therefore the question of its stabilization arises. There are different ways to stabilize the RTI and the STI. It is possible to use a magnetic field to suppress the RTI in plasma [19] or an oscillating magnetic field to stabilize conductive heavy liquid supported against gravity [20]. The RTI of the boundary between two liquids of different densities can be stabilized using high-frequency oscillations [21]. In that paper the theoretical model of the RTI stabilization for two “infinitely deep” ideal liquids using the Kapitza method [22] was developed as well as the number of experiments on stabilization of the RTI in the cylindrical geometry were carried out. A theory of the stabilization of the RTI is also developed using the Floquet method [2,23]. A goal of the present paper is a theoretical investigation of the stabilization of the RTI in the system of three layers of liquids in plane geometry, theoretical investigation of the stabilization of the STI in the Hele-Show cell and carrying out the experiment on stabilization the inverted vessel with liquid and layer of liquid, confined within the air. In contrast to the earlier researches on the hydrodynamic instabilities stabilizations, in which the systems with only single boundary between liquids were taken into consideration, the present paper demonstrates theoretical and experimental possibilities of the stabilization of the coupled waves systems.

Experimental studies were conducted of a flow induced in an initially quiescent room air by a single asymmetric dielectric barrier discharge driven by voltage waveforms consisting of repetitive nanosecond high-voltage pulses superimposed on dc or alternating sinusoidal or square-wave bias voltage. To characterize the pulses and to optimize their matching to the plasma, a numerical code for short pulse calculations with an arbitrary impedance load was developed. A new approach for nonintrusive diagnostics of plasma actuator induced flows in quiescent gas was proposed, consisting of three elements coupled together: the schlieren technique, burst mode of plasma actuator operation, and two-dimensional numerical fluid modeling. The force and heating rate calculated by a plasma model was used as an input to two-dimensional viscous flow solver to predict the time-dependent dielectric barrier discharge induced flow field. This approach allowed us to restore the entire two-dimensional unsteady plasma induced flow pattern as well as characteristics of the plasma induced force. Both the experiments and computations showed the same vortex flow structures induced by the actuator. Parametric studies of the vortices at different bias voltages, pulse polarities, peak pulse voltages, and pulse repetition rates were conducted experimentally. The significance of charge buildup on the dielectric surface was demonstrated. The charge buildup decreases the effective electric field in the plasma and reduces the plasma actuator performance. The accumulated surface charge can be removed by switching the bias polarity, which leads to a newly proposed voltage waveform consisting of high-voltage nanosecond repetitive pulses superimposed on a high-voltage low frequency sinusoidal voltage. Advantages of the new voltage waveform were demonstrated experimentally.

Direct measurements of the dielectric surface potential and its dynamics in asymmetric dielectric barrier discharge (DBD) plasma actuators show that the charge builds up at the dielectric surface and extends far downstream of the plasma. The surface charge persists for a long time (tens of minutes) after the driving voltage has been turned off. For a sinusoidal voltage waveform, the dielectric surface charges positively. With the voltage waveform consisting of nanosecond pulses superimposed on a dc bias, the sign of the dielectric surface charge is the same as the sign (polarity) of the bias voltage. The surface charging significantly affects DBD plasma actuator performance.

A detailed physical model for asymmetric dielectric barrier discharge (DBD) in air at low voltages (1.5–2 kV) is developed. Modeling of DBD with an applied sinusoidal voltage is carried out in two dimensions. The leading role of charging the dielectric surface by electrons in the cathode phase is shown to be critical, acting as a harpoon that pulls positive ions forward and accelerates the gas in the anode phase. The positive ion motion back toward the exposed electrode is shown to be a major source of inefficiency in the sinusoidal or near-sinusoidal voltage cases. Based on understanding of the DBD physics, an optimal voltage waveform is proposed, consisting of high repetition rate, short (a few nanoseconds in duration), negative pulses combined with a positive dc bias applied to the exposed electrode.

A detailed physical model for an asymmetric dielectric barrier discharge (DBD) in air driven by repetitive nanosecond voltage pulses is developed. In particular, modeling of DBD with high voltage repetitive negative and positive nanosecond pulses combined with positive dc bias is carried out. Operation at high voltage is compared with operation at low voltage, highlighting the advantage of high voltages, however the effect of backward-directed breakdown in the case of negative pulses results in a decrease of the integral momentum transferred to the gas. The use of positive repetitive pulses with dc bias is demonstrated to be promising for DBD performance improvement. The effects of the voltage waveform not only on force magnitude, but also on the spatial profile of the force, are shown. The crucial role of background photoionization in numerical modeling of ionization waves (streamers) in DBD plasmas is demonstrated.

Experimental studies were conducted of a flow induced in an initially quiescent room air by a single asymmetric dielectric barrier discharge driven by voltage waveforms consisting of repetitive nanosecond high-voltage pulses superimposed on DC or alternating sinusoidal or square-wave bias voltage. To characterize the pulses and to optimize their matching to the plasma, a numerical code for short pulse calculations with an arbitrary impedance load was developed. A new approach for non-intrusive diagnostics of plasma actuator induced flows in quiescent gas was proposed, consisting of three elements coupled together: the schlieren technique, burst mode of plasma actuator operation, and 2-D numerical fluid modeling. This approach allowed us to restore the entire two-dimensional unsteady plasma induced flow pattern as well as characteristics of the plasma induced force. The experiments and computations showed vortex flow structures induced by the actuator. Parametric studies of the vortices at different bias voltages, pulse polarities, peak pulse voltages, and pulse repetition rates were conducted. The significance of charge build-up on the dielectric surface was demonstrated. Based on the observations, a new voltage waveform, consisting of high-voltage nanosecond repetitive pulses superimposed on a highvoltage low-frequency sinusoidal voltage, was proposed. Advantages of the new voltage waveform were demonstrated experimentally.