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A computational model for the interaction of a high-pressure microplasma with an electromagnetic wave is presented. A one-dimensional particle-in-cell Monte Carlo collision model is used to investigate the plasma non-ideality effects in a second-stage laser-heated xenon plasma with a comprehensive chemistry mechanism, including excited species. A xenon microplasma at a temperature of 300 K and pressure of 10 bar becomes non-ideal after the laser heating stage with lower ionization and electronic excitation barriers, which makes the presence of excited species important to the plasma generation process. For these conditions, two-step ionization via excited species becomes a major contributor to plasma ionization. We find that full ionization of the plasma is obtained in ∼2 ps when excited species are included in the chemistry model, as opposed to ∼2.5 ps for a chemistry mechanism that does not consider their effect. With excited species, the ionization mode transitions from direct ionization via electron-neutral collisions to direct and stepwise ionization as the plasma generation progresses. [ABSTRACT FROM AUTHOR]

Abstract: Flow actuation by a continuous/pulsed, direct-current (DC) surface glow discharge is explored. The discharge comprises an array of pin electrode pairs flush mounted on a dielectric actuator surface that lies adjacent to stagnant air. Strong electrostatic fields produced in the cathode sheath region of the discharge provides a motive force on the ions which in turn drag the background gas resulting in directed air flow from the anode to the cathode. The induced flow velocity is estimated by particle image velocimetry (PIV) at 10 Hz with TiO2 seeding. For a pulsed DC discharge with peak power of 5 W per electrode pair, the induced flow velocity reaches peak values of about 1.7 m/s which is comparable to dielectric-barrier discharge (DBD) or corona discharge actuators. The actuation effect quantified by the magnitude of induced velocity increases as the pulse frequency increases from 0 to 1 kHz. The actuation effect decreases for further increase in frequency above 1 kHz. Decreased actuation effect at high frequency is accompanied by structural change in the discharge. At fixed frequency of 1 kHz, flow actuation effect is highest for a square wave pulse with a duty cycle of 50% indicating that pulsed DC discharges produces better actuation than continuous DC with a corresponding reduction in energy consumption. [ABSTRACT FROM AUTHOR]

An experimental study is conducted to characterize the performance of a pulsed-plasma jet (called a "spark jet" by other researchers) for potential use in supersonic flow control applications. A pulsed-plasma jet is a high-speed synthetic jet that is generated by striking an electrical discharge in a small cavity. The gas in the cavity pressurizes owing to the heating and is allowed to escape through a small orifice. To obtain an estimate of the relative strength of the pulsed-plasma jet, the jet is injected normally into a Mach 3 crossflow and the penetration distance is measured by using schlieren imaging. These measurements show that the jet penetrates 1.5 boundary-layer thicknesses into the crossflow and the jet-to-crossflow momentum flux ratio is estimated to be 0.6. A series of experiments was conducted to determine the characteristics of the pulsed-plasma jet issuing into stagnant air at a pressure of 35 torr. These results show that typical jet velocities of about 250 m /s can be induced with discharge energies of about 30 mj per jet. Furthermore, the maximum pulsing frequency was found to be about S kHz, because above this frequency the jet begins to misfire. The misfiring appears to be due to the finite time it takes for the cavity to be recharged with ambient air between discharge pulses. The velocity at the exit of the jet is found to be primarily dependent on the discharge current and independent of other discharge parameters such as cavity volume and orifice diameter. Temperature measurements are made using optical emission spectroscopy and reveal the presence of considerable nonequilibrium between rotational and vibrational modes. The gas heating efficiency was found to be 10% and this parameter is shown to have a direct effect on the plasma jet velocity. These results indicate that the pulsed-plasma jet creates a sufficiently strong flow perturbation that holds great promise as a supersonic flow actuator. [ABSTRACT FROM AUTHOR]

In an effort to understand the opaque nature of high-voltage nanosecond microdischarges and their ability to block 532 nm nanosecond laser pulses, as demonstrated by Bataller et al. [Appl. Phys. Lett. 105, 223501 (2014)], Levko and Raja have published a paper [Phys. Plasmas 22, 123518 (2015)] which simulates spark discharges in 1 bar of xenon gas. At this ambient pressure, Levko and Raja simulate final electron densities much too low to explain the observed opacity and conclude the probing laser generates the requisite ionization for self-blocking. However, the experimental findings of Bataller et al. showed opacity being reached at 10 bar, an order of magnitude larger than the pressure simulated by Levko and Raja. Furthermore, Bataller et al. showed the spark remained opaque for very low laser intensities, insufficient to cause any significant ionization. Although the simulation performed by Levko and Raja could have merit at 1 bar, it is not an appropriate comparison to the regime studied by Bataller et al. [ABSTRACT FROM AUTHOR]

We present a self-consistent 2-D multispecies multi-temperature model of dc nonequilibrium surface plasma discharge phenomena in the presence of a low-pressure imposed high-speed convective flow. For pressures of a few torr and voltages of a few kilovolts, a nonequilibrium glow discharge is generated between the electrodes. Peak charge densities in the discharge on the order of 1014 - 1016 m-3, electron temperatures on the order of 1 eV, and gas temperatures on the order of 2000 K are observed. Increasing voltages are found to increase the charge density in the discharge and also cause a constriction of the discharge volume. The same trend is also observed with an increase in the discharge pressure. The discharge is highly asymmetric owing to the high-speed convective flow, with the discharge activity restricted to the flow downstream edge of the cathode surface. The convective flow also causes a quasi-neutral plasma-tail-like feature that provides a major loss mechanism for charged and neutral species in the discharge. Despite sufficient cathode surface area, the discharge operates in an abnormal glow mode, with a positive differential resistivity, owing to a flow-induced constricted cathode attachment. Relatively large cathode sheath dimensions on the order of 1 cm are observed with a net electrostatic forcing restricted to this region. The net electrostatic forcing is largely vertical toward the cathode surface, but also has a component in the direction against the flow. [ABSTRACT FROM AUTHOR]

Helicon discharges produce plasmas with a density gradient across the confining magnetic field. Such plasmas can create a radial potential well for nonaxisymmetric whistlers, allowing radially localized helicon (RLH) waves. This work presents new evidence that RLH waves play a significant role in helicon plasma sources. An experimentally measured plasma density profile in an argon helicon discharge is used to calculate the rf field structure. The calculations are performed using a two–dimensional field solver under the assumption that the density profile is axisymmetric. It is found that RLH waves with an azimuthal wave number m=1 form a standing wave structure in the axial direction and that the frequency of the RLH eigenmode is close to the driving frequency of the rf antenna. The calculated resonant power absorption, associated with the RLH eigenmode, accounts for most of the rf power deposited into the plasma in the experiment. [ABSTRACT FROM AUTHOR]

Presents information on a study that investigated the structure of a capacitively coupled high-pressure glow discharge in high-purity helium using a one-dimensional modeling approach. Methodology of the study; Results and discussion on the study.

Describes a model to study the electrogun (ignitor) plasma flow fluid. Background of modeling ignitor; Description of electrothermal ignitor operation; Analysis of the electro-thermal ignitor (electrogun); Results and discussion of the analysis; Conclusions.

Plasmas respond nonlinearly to GHz electromagnetic waves, owing to nonlinear interactions described by the electron momentum equation. These nonlinearities are especially important in high field regions of the plasma as is common in resonant structures that generate plasma discharges with intense localized amplification of the incident field. Most models treat the plasma as a linear Drude material that does not capture the nonlinear polarization terms of a plasma. In this work, we couple the nonlinear electron momentum equation to electromagnetic wave simulation in order to explore the nonlinear behavior. We develop a theoretical foundation via perturbation analysis to guide our expectations from numerical simulation. Through numerical simulation of 2D TE-polarized waves incident on a cylindrical plasma, we show that in the presence of electrical field strengths of ∼MV/m and higher, dense microplasmas have second harmonic power conversion efficiency approaching 10 − 6 at low pressures. The generated harmonic power is shown to arise mostly from the inertial term in the electron momentum equation. Therefore, a significant portion of the harmonic current density is generated at the surfaces of critical electron density for the fundamental frequency. [ABSTRACT FROM AUTHOR]

The aim of the present paper is to examine the influence of assumption on the electron energy distribution function on the relation between the plasma potential and the electron temperature for both electropositive (argon) and electronegative (chlorine) plasmas. A one-dimensional fluid model is used for simplicity although similar results were obtained using a self-consistent two-dimensional fluid model coupled with the Maxwell's equations for inductively coupled plasmas. We find that for electropositive plasma only a bi-Maxwellian electron energy distribution function provides reasonable results compared to measurements in low-pressure inductively coupled plasmas, namely, the increasing plasma potential for increasing electron temperature. For electronegative plasma, the plasma potential is an increasing function of the electron temperature for all electron distributions considered in the model. However, the scaling factors do not agree with the conventional plasma theory. We explain these results by the deviation of electrons from a Boltzmann distribution, which is due to non-equilibrium and non-local nature of plasma at the low-pressure conditions. [ABSTRACT FROM AUTHOR]

The dynamics of a subnormal mode of direct-current micro-discharge in pressurized nitrogen is studied using a self-consistent one-dimensional plasma fluid model coupled with the compressible Navier–Stokes equations. To clarify different time scales, we use a hierarchy of plasma reaction mechanisms. The simplest mechanism considers the two-species plasma without any excited species. The excitation of electronic and vibrational levels of nitrogen is only considered in the electron energy balance. The second mechanism considers multiple ions and electronically excited species. The most comprehensive third mechanism expands the second mechanism by tracking the vibrationally excited species as well as the reactions of vibrational-translational and vibrational-vibrational relaxation. By using this third mechanism, we analyze the dynamics associated with the relaxation of the vibrational distribution function of nitrogen. [ABSTRACT FROM AUTHOR]