Sinusoidal Discharge Research Articles

Combustion Characteristics of Hydrogen/Air Mixtures in a Plasma-Assisted Micro Combustor

This work performs an analysis of plasma-assisted non-premixed H2-air flames in Y-shaped micro combustors in the presence of field emission dielectric barrier discharge (FE-DBD) plasma actuators. The combustion, flow, and heat transfer characteristics are numerically investigated, and the effect of sinusoidal plasma discharges on combustion performance is examined at various equivalence ratios (φ). A coupled plasma and chemical kinetic model is implemented, using a zero-dimensional model based on the solution of the Boltzmann equation and the ZDPlasKin toolbox to compute net charges and radical generation rates. The estimated body forces, radical production rates, and power densities in the plasma regions are then coupled with hydrogen combustion in the microchannel. Plasma-assisted combustion reveals improvements in flame length and maximum gas temperature. The results demonstrate that FE-DBDs can enhance mixing and complete the combustion of unreacted fuel, preventing flame extinction. It is shown that even in cases of radical and thermal quenching, these plasma actuators are essential for stabilizing the flame.

Mechanism and Reactive Species in a Fountain-Strip DBD Plasma for Degrading Perfluorooctanoic Acid (PFOA)

Perfluorooctanoic acid (PFOA) is an artificially synthesized perfluorinated chemical widely used in industries. It is often released into the environment without treatment, which causes pollution in groundwater. Recently, we have reported a rapid and efficient removal of PFOA in aqueous solution by using a fountain-strip dielectric barrier discharge reactor (SF-DBD). This design allows for the gaseous–liquid interaction to happen in a large space at atmospheric pressure, so it is a promising method to efficiently remove PFOA from water. Recently, we reported the effects of the process parameters, including power mode, pulse time, sinusoidal wave discharge, the discharge gas, initial concentration, pH, conductivity, and positive and negative discharges, on the efficiency of this method for PFOA degradation. Understanding the reaction mechanism is key to further improve the efficiency of the system. In this work, we reported the decomposition mechanism of the SF-DBD for PFOA degradation. The mass spectrum (MS) showed that PFOA was degraded to perfluoroheptanoic acid, perfluorohexanoic acid, perfluoropentanoic acid, perfluorobutanoic acid, perfluoropropionic acid, and trifluoroacetic acid after the plasma treatment. The optical emission spectroscope (OES) and the radical scavenger experiments indicated that the excited argon atoms and hydroxyl radicals played a major role in PFOA degradation, while the contributions from the solvated electrons (e−aq), superoxide anion radical (·O2−), and singlet oxygen (1O2) were negligible in initiating the cleavage reaction.

Influence of millimeter electromagnetic waves on the functional capabilities of the lower limb muscles in athletes - volleyball players

The authors, when observing 22 athletes - volleyball players of different volleyball specialization, assessed the effect of millimeter electromagnetic waves (EMW) on the functional state of the muscular system of the lower extremities. The electromagnetic effect was carried out using the "Complex SP 80" apparatus (frequencies 3900 - 4120 kHz were used). Electrodes were applied to the muscles of the thigh and lower leg, sinusoidal discharges were applied for 10 seconds during the strength training period. The results of observations showed that under the influence of EME, the height of the jump increases by 7%, due to the increase in the energy of the jump and its intensity. The release of the activity of the knee joint is also noted. The authors believe that under the influence of EME, the transmission of regulatory impulses in neuromuscular contact improves, which contributes to the synchronization and strength of contractions of the muscle fiber bundles. Also, under the influence of EMW, blood microcirculation in the muscle improves.

Polymerdimethylsiloxane surface treatment with an atmospheric pressure helium plasma jet driven by unipolar nanosecond pulses

A nanosecond-pulse power source transfers energy to electrons of atmospheric pressure discharges in a nanosecond-scale rising time and shows different plasma chemistry than a slowly varying sinusoidal discharge. We report how the operation parameters, such as applied voltage, pulse duration, and repetition frequency, affect the discharge characteristics and the surface property of polydimethylsiloxane (PDMS). The applied voltage controls the energy delivery per a pulse cycle, and the repetition frequency dominantly affects the plasma density in a long-term operation. The water contact angle, the optical emission spectroscopy, and the atomic force microscope diagnostics on the PDMS are presented. While the polarity of the nano pulse bias changes the emission length of the plasma jet, the hydrophilicity is not affected by it because the chemical reactions by radicals are more dominant than the physical reactions of charged particles on PDMS.

Plume Divergence and Discharge Oscillations of an Accessible Low-Power Hall Effect Thruster

Hall effect thrusters (HETs) are an increasingly utilized proportion of electric propulsion devices due to their high thrust-to-power ratio. To enable an accessible research thruster, our team used inexpensive materials and simplified structures to fabricate the 44-mm-diameter Western Hall Thruster (WHT44). Anode flow, discharge voltage, magnet current, and cathode flow fraction (CFF) were independently swept while keeping all other parameters constant. Simultaneously, a Faraday probe was used to test plume properties at a variety of polar coordinate distances, and an oscilloscope was used to capture discharge oscillation behavior. Plasma plume divergence angle at a fixed probe distance of 4.5 thruster diameters increased with increasing anode flow, varying from 36.7° to 37.4°. Moreover, divergence angle decreased with increasing discharge voltage, magnet current, and CFF, by 0.3°, 0.2°, and 8°, respectively, over the span of the swept parameters. Generally, the thruster exhibited a strong oscillation near 90 kHz, which is higher than a similarly sized HET (20–60 kHz). The WHT44 noise frequency spectra became more broadband and the amplitude increased at a CFF of less than 1.5% and greater than 26%. Only the low flow and low voltage operating conditions showed a quiescent sinusoidal discharge current; otherwise, the discharge current probability distribution was Gaussian. This work demonstrates that the WHT44 thruster, designed for simplicity of fabrication, is a viable tool for research and academic purposes.

Optimization of the Active Neutralization of Polypropylene Film Using Response Surface Methodology

In roll-to-roll manufacturing of products, such as thin films, fibers, textiles, or membranes, the generation and accumulation of electric charges by the triboelectric effect represents a major source of electrostatic hazards. The best solution to this problem is to eliminate these charges. The aim of this article is to pave the way to the use of a triode-type corona electrode system at an industrial frequency (50 Hz) for active neutralization of electrically charged insulating films. The experimental study was carried out on dc corona charged polypropylene films that were neutralized by a sinusoidal corona discharge. The neutralization efficiency was evaluated by noncontact measurement of the electric potential at the surface of charged and neutralized polypropylene film samples. The response surface methodology was used for quantifying the effects of the various influential factors (i.e., voltage amplitude, duration of exposure to the discharge, and relative position of the neutralizer with respect to the sample) and optimizing the neutralization process.

Experimental study of controlled active neutralization of polypropylene films

AC corona discharge is widely employed for neutralizing the electric charges at the surface of insulating bodies: films, plates, granules, etc. If uncontrolled, this active neutralization process is accompanied by the persistence of a residual charge at the surface of the treated bodies. The aim of this present work is to demonstrate experimentally the efficiency of the controlled active neutralization using AC corona generated in a triode-type electrode configuration, with the grid connected to the ground. The experimental study was carried out on DC corona charged polypropylene films that were neutralized by a sinusoidal corona discharge at industrial frequency (50 Hz). The distribution of the electric potential at the surface of the charged and neutralized samples were measured by a non-contact electrostatic voltmeter. The factors under study were: the amplitude of the AC voltage applied to the corona electrode of the triode system, the duration of exposure to the corona discharge, the scanning speed, and the spacing between the grid and sample. The experimental results obtained show that the neutralization rate is close to 100%, i.e. the electric potential profiles obtained at the surface exposed to AC corona discharge show the absence of the residual charge. The results show that the efficiency of the controlled active neutralization depends on the energy that the AC corona discharge imparts to the charged samples, and that affects the trapped bulk charge.

Relation of electric conditions between a source of Ar plasma jet and a substrate with a configuration of a plasma sheet on a target

The paper presents the experimental results relevant to the external electrical influence on the structure of a thin plasma sheet formed atop a substrate surface by Ar plasma jet that is being generated by a coaxial sinusoidal barrier discharge (BD) in an argon flow. The electrical influence on the target is being created due to connecting of a high-voltage or grounded electrode of the BD to the metal plate on which the dielectric or metallic substrate to be treated is located. Such an approach ensures a synchronism of the interaction of the external auxiliary electric field with the own electric field of the ionization wave (plasma bullet) propagating along the argon plasma jet toward the substrate during each period of the BD alternating voltage. An image of the structure of the plasma sheet on the substrate surface averaged over many periods of sinusoidal voltage was recorded in the experiments.

Research on the Compensation Matching Design and Output Performance for Two-Axis-Compensated Compulsators

Compulsators are popular choices for various high-power electromagnetic launch applications, especially for the electromagnetic railgun. A two-axis-compensated compulsator with lower internal impedance and higher power density was proposed in the authors’ previous paper. The field windings and compensating windings are allocated electrical orthogonally, providing the opportunity to design the direct-axis and quadrature-axis compensations independently. Due to the excitation function of the field windings, as well as field windings and compensating windings at the same rotor periphery, the ratio between $d$ -axis and $q$ -axis compensation is determined not only by the waveform of the air-gap flux density but also by the occupied space of windings, electromagnetic force during discharge and temperature rise and cooling condition. All these aspects mentioned above were analyzed in this paper. Furthermore, the output performance for single pulse discharge of a 2-m railgun with 100-g armature and multiple pulses discharge of a 5-m railgun with 300-g armature was simulated and compared. The results indicated that the two-axis compensation could obtain benefits by introducing more sinusoidal discharge currents for single pulse mission comparing to traditional compensation structure, whereas no obvious advantages for a flat-topped current waveform for multiple pulses mission.

Chapter 2 - Focal epilepsies and focal disorders

Electroencephalographic (EEG) investigations are crucial in the diagnosis and management of patients with focal epilepsies. EEG may reveal different interictal epileptiform discharges (IEDs: abnormal spikes, sharp waves). The EEG visibility of a spike depends on the surface area of cortex involved (>10cm2) and the brain localization of cortical generators. Regions generating IEDs (defining the "irritative zone") are not necessarily equivalent to the seizure onset zone. Focal seizures are dynamic processes originating from one or several brain regions (that generate fast oscillations and are called the epileptogenic zone) before spreading to other structures (that generate lower frequency oscillations and are called the propagation zone). Several factors limit the expression of seizures on scalp EEG, such as the area involved, degree of synchronization, and depth of the cortical generators. Different scalp EEG seizure onset patterns may be observed: fast discharge, background flattening, rhythmic spikes, sinusoidal discharge, or sharp activity. However, to a large extent EEG changes are linked to seizure propagation. Finally, in the context of presurgical evaluation, the combination of interictal and ictal EEG features is crucial to provide an optimal hypothesis concerning the epileptogenic zone.

Disparity between current and voltage driven capacitively coupled radio frequency discharges

In simulation as well as analytical modeling studies of low-pressure capacitively coupled radio frequency (CCRF) discharges, the assumption of both a driving voltage source or a driving current source is commonly used. It is unclear, however, how and to what extent the choice of the mode of driving, that prescribes either a sinusoidal discharge voltage or a sinusoidal discharge current, itself defines the discharge dynamics that results from these studies. To address this issue, 1d3v cylindrical particle-in-cell/Monte Carlo collisions simulations of asymmetric CCRF discharges are performed in the low pressure regime (p < 2 Pa). We study the nonlocal and nonlinear dynamics of these discharges on a nanosecond timescale. We find that the excitation of the plasma series resonance in the voltage driven case strongly enhances the nonlinear electron power dissipation. However, this resonance is suppressed when a current source is used, because the excitation of harmonics in the RF current is not allowed. Consequently, significant differences between both driving sources are observed in the plasma density as well as in the electron and the power coupling dynamics. We conclude that caution is advised in comparisons between simulations and experiments, as in the former the discharge dynamics is partly defined by the method of driving of the plasma source, while in the latter the addressed resonance phenomena are inherently present at low pressures, since experiments are typically voltage driven.

Characterization of a dielectric barrier discharge in contact with liquid and producing a plasma activated water

In this work a low-temperature plasma source for the generation of plasma activated water (PAW) is developed and characterized. The plasma reactor was operated by means of an atmospheric-pressure air dielectric barrier discharge (DBD). The plasma generated is in contact with the water surface and is able to chemically activate the liquid medium. Electrodes were supplied by both sinusoidal and nanosecond-pulsed voltage waveforms. Treatment times were varied from 2 to 12 min to increase the energy dose released to the water by the DBD plasma. The physics of the discharge was studied by means of electrical, spectroscopic and imaging diagnostics. The interaction between the plasma and the liquid was investigated as well. Temperature and composition of the treated water were detected. Images of the discharges showed a filamentary behaviour in the sinusoidal case and a more homogeneous behaviour in the nanosecond-pulsed one. The images and the electrical measurements allowed to evaluate an average electron number density of about 4 × 1019 and 6 × 1017 m−3 for the sinusoidal and nanosecond-pulsed discharges respectively. Electron temperatures in the range of 2.1÷2.6 eV were measured by using spectroscopic diagnostics. Rotational temperatures in the range of 318–475 K were estimated by fitting synthetic spectra with the measured ones. Water temperature and pH level did not change significantly after the exposure to the DBD plasma. The production of ozone and hydrogen peroxide within the water was enhanced by increasing the plasma treatment time and the energy dose. Numerical simulations of the nanosecond-pulsed discharge were performed by using a self-consistent coupling of state-to-state kinetics of the air mixture with the Boltzmann equation of free electron kinetics. Temporal evolution of the electron energy distribution function shows departure from the Maxwellian distribution especially during the afterglow phase of the discharge. When limited deviations from Maxwellian distribution were observed, calculated electron temperature is in good agreement with the one measured by means of spectroscopic diagnostics. Computed temporal evolution of the energy delivered to the discharge is comparable with the one obtained from electrical measurements. The electrical discharges supplied by both voltage waveforms produce plasma activated water with negligible thermal effects and pH variations.

Determination of Thermal Energy Storage (TES) characteristics by Fourier analysis of heat load profiles

Heat demand and generation can be decoupled by the use of thermal energy storages, resulting in improved energy efficiencies and enhanced possibilities for integration of renewable energy resources. The design and sizing of TES systems need to satisfy the requirements of the building regarding the thermal power as well as the capacity of the storage. The ratio of those two parameters can be expressed as the specific storage thermal power q̇s. If this ratio of a selected storage technology does not match the requirements of the given application, then the storage has to be oversized either in terms of the thermal power or storage capacity, probably resulting in higher investment costs.In this research, the required values of q̇s for different kinds of buildings (residential, governmental, business) were determined by a frequency analysis of heat load profiles. Therefore, these profiles were resolved into single cosine oscillations, allowing the identification of dominant frequencies with high heat load amplitudes. The main idea was to use different, well adapted TES for elimination of these dominant cosine oscillations, resulting in a smoothed residual load profile for the heat generator. An analytical solution for q̇s in the case of a sinusoidal charge and discharge cycle is presented, showing a decrease of q̇s in proportion to the reciprocal of the charging/discharging period T with typical values for q̇s between 400W/kWh to below 1W/kWh for short-term (daily) and long-term (seasonal) applications, respectively.Latent heat and thermochemical storages often use packed bed reactors for heat and mass transfer. Optimizations regarding thermal power usually have an inverse effect on the storage density. This leads to the conclusion that unique TES designs should be used for different storage periods. To match the requirements of the building, multiple TES should be linked together.

The use of discharge perturbations to understand in situ vegetation resistance in wetlands

AbstractThe ability to better quantify resistance to water flow exerted by vegetation is receiving increased attention due to ongoing worldwide efforts to restore natural vegetation communities in the wetlands and use of vegetation for environmental benefits in streams and wetlands. In south Florida, vegetation resistance affects discharge through shallow wetlands of the Everglades and projects under way in the system to restore remaining natural systems. A more detailed knowledge of the flow dynamics in these wetlands is required to improve modeling of these systems that supports restoration and management efforts. The goal of this investigation is to understand the flow dynamics and the vegetation resistance within a 3 km by 7 km area in the Everglades referred to as STA‐3/4 Cell 3A. Methods are developed to demonstrate the use of analytical solutions of partial differential equations (PDEs) and inverse methods to obtain bulk and spatially varying resistance parameters. To achieve this goal, a field test was conducted using sinusoidal discharge disturbances capable of creating water waves in the storm water treatment area (STAs). The discharges, wave speeds, and the wave attenuation rates from the test are used to develop graphical and empirical functions expressing discharge in terms of water depth and energy slope. The empirical functions developed are power law type, and different functions are developed for different depths. The results show that the Manning's equation is not applicable for wetlands with thick emergent vegetation, as well as the difficulty of applying a single power law‐type expression for vegetation resistance over a wide range of depths and energy slopes without errors. This is partly due to the existence of multiple flow regimes and different power exponents over depth and energy slopes in these regimes. Results show that the flow regime at low depths is similar to porous media flow, and the flow regime at higher depths is more turbulent.

Capacitively coupled radio-frequency plasmas excited by tailored voltage waveforms

By applying certain types of ‘tailored’ voltage waveforms (TVWs) to capacitively coupled plasmas, a dc self-bias and an asymmetric plasma response can be produced, even in geometrically symmetric reactors. Furthermore, these arbitrary applied waveforms can produce a number of interesting phenomena that are not present in typical single-frequency sinusoidal discharges. This electrical asymmetry effect presents emerging possibilities for the improved control of the ion energy and ion flux in these systems; parameters of vital importance to both etching and deposition applications for materials processing. With a combined research approach utilizing both experimental measurements, and particle-in-cell simulations, we review and extend recent investigations that study a particular class of TVW. The waveforms used have a pulse-type shape and are composed of a varying number of harmonic frequencies. This allows a strong self-bias to be produced, and causes most of the applied voltage to be dropped across a single sheath. Additionally, decreasing the pulse width (by increasing the number of harmonics), allows the plasma density and ion flux to be increased. Simulation and experimental results both demonstrate that this type of waveform can be used to separately control the ion flux and ion energy, while still producing a uniform plasma over large area (50 cm diameter) rf electrodes.

Manifestation of Constrained Dynamics in a Low-Pressure Spark

Some features of neutron emission from dense plasma focus suggest that the participating deuterons have energy in the range of 105 eV and have a directionality of toroidal motion. Theoretical models of these devices assume that the plasma evolves through a purely irrotational flow and thus fail to predict such solenoidal flow on the scale of the plasma dimensions. Predictions of a relaxation theory are consistent with experimental data [S K H Auluck, Physics of Plasmas,18, 032508 (2011)], but the assumptions upon which it is based are not compatible with known features of these devices. There is thus no satisfactory theoretical construct which provides the necessity for solenoidal flow in these devices. This paper proposes such theoretical construct, namely, the principle of constrained dynamics, and describes an experiment which provides support for this idea. The experiment consisted of low inductance, self-breaking spark discharge in helium at a pressure ~100 hPa between two pointed electrodes separated by 30-50 mm distance kept inside a vacuum chamber mounted on a low inductance high voltage capacitor. The current derivative signal showed reproducible sharp dips at all the extrema of the damped sinusoidal discharge. A planar diamagnetic loop centered with and perpendicular to the discharge axis consistently showed a signal representing rate of change of axial magnetic flux. A qualitative explanation of observed phenomena is obtained using a simple model using the proposed principle.

Comparison of sinusoidal and pulsed-operated dielectric barrier discharges in an O2/N2 mixture at atmospheric pressure

Experiments on the spatial and temporal structure of the breakdown process of sinusoidal- and pulsed-operated dielectric barrier microdischarges (MDs) are compared. Three different waveforms are considered: a sinusoidal waveform at 20 kHz and pulsed-bipolar and unipolar-voltage profiles at 10 kHz with varying duty cycles (asymmetric pulse). Electrical data and simultaneous streak and iCCD images of individual MDs in dielectric barrier discharges (DBDs) with 1 mm gap in a gas mixture of 0.1 vol% O2 in N2 at atmospheric pressure are recorded. For sinusoidal-operated DBDs there are no significant differences between the MDs at positive and negative half-periods. Sinusoidal operation corresponds to pulsed-bipolar operation with symmetrical pulses, but with lower streamer velocities and different spatio-temporal emission distribution. The development of pulsed-driven MDs is determined by the voltage between both electrodes and not by the polarity of the driven electrode, resulting in nearly the same behavior of bipolar- and unipolar-pulsed-driven MDs. DBDs operated with asymmetric pulses show a significant difference in the spatial structure and in the temporal behavior between the rising and falling slopes of the high voltage pulse.

Control of the ion flux and ion energy in CCP discharges using non-sinusoidal voltage waveforms

Using particle-in-cell simulations we perform a characterization of the ion flux and ion energy in a capacitively coupled rf plasma reactor excited with non-sinusoidal voltage waveforms. The waveforms used are positive Gaussian type pulses (with a repetition frequency of 13.56 MHz), and as the pulse width is decreased, three main effects are identified that are not present in typical symmetric sinusoidal discharges: (1) the ion flux (and plasma density) rapidly increases, (2) as the pressure increases a significant asymmetry in the ion fluxes to the powered and grounded electrodes develops and (3) the average ion energy on the grounded electrode cannot be made arbitrarily small, but in fact remains essentially constant (together with the bias voltage) for the pressures investigated (20–500 mTorr). Effects (1) and (3) potentially offer a new form of control in these types of rf discharges, where the ion flux can be increased while keeping the average ion energy on the grounded electrode constant. This is in contrast with the opposite control mechanism recently identified in Donkó et al (2009 J. Phys. D: Appl. Phys. 42 025205), where by changing the phase angle between applied voltage harmonics the ion flux can be kept constant while the ion energy (and bias voltage) varies.

Sinusoidal pumping of groundwater near cylindrical inhomogeneities

A new analytic-element solution is presented for a well with a sinusoidal discharge pumping near cylindrical inhomogeneities. Both the transmissivity and the storage coefficient may be different inside each cylinder. The solution consists of separate series solutions inside and outside each cylinder; asymptotic expansions are presented for cases where the sinusoidal period is small and the radius and transmissivity of the cylinder are large. The complex coefficients in the series solutions are determined by requiring continuity of head and normal flow across the boundary of each cylinder resulting in a linear system of complex equations that may be solved with standard methods. The solution represents one of the few analytic solutions for two-dimensional transient groundwater flow in an aquifer with inhomogeneities. Computer implementation requires truncation of the series; machine accuracy may be reached when enough terms are used in the series solutions. The effect of cylindrical inhomogeneities on the amplitude and phase of the head are investigated. The complex behavior suggests it may be difficult to determine location and properties of cylindrical inhomogeneities from pump tests, which confirms reported difficulties of interpreting pump test results from heterogeneous aquifers.

High brightness extreme ultraviolet (at 13.5 nm) emission from time-of-flight controlled discharges with coaxial fuel injection

Extreme ultraviolet (EUV) emission from discharge produced plasma with the coaxial injection of fuel vapor (tin and lithium) produced by laser ablation is experimentally studied. Multiple plasma pinches preceding a strong and long recombination radiation of EUV are observed in the first half cycle of a sinusoidal discharge current. Due to the time-of-flight control type of the discharge, the shape of pinch radiation pulses is almost identical. With the coaxial injection of time-of-flight controlled discharges, the highest brightness of EUV emission (maximum extracted energy of 244.3 mJ/2π sr per pulse with the emitter size of ∼1×0.3 mm2 in full width at half maximum) is provided with efficiency exceeding 2% of deposited energy into the plasma (or 1% of dissipated energy in the discharge) due to a much better matching with the optimal plasma parameters in the recombination regime and a decrease in the off-duty factor. Stability of emitting plasma of the repetitive pinches is essentially improved with use of a second laser pulse.