Discharge Current Flow Research Articles

On the Energy Cost for Nitrogen Fixation in DC Glow Discharges in Atmospheric‐Pressure Air

ABSTRACTModeling of the production of nitrogen oxide molecules in DC discharges in laminar longitudinal flows of atmospheric‐pressure air is performed. Two‐dimensional nonequilibrium discharge model includes the system of gas dynamic equations and balance equations for various plasma components. Simulations are performed for the discharge currents 50–600 mA and gas flow velocities 1–10 m/s. In considered conditions, the gas temperature in the discharge core varies in the range of 3000–6000 K. Spatial profiles of the densities and fluxes of produced species are obtained, both inside the discharge and in the afterglow region. The energy cost for the production of nitrogen oxides is calculated, depending on the discharge current, gap length, and gas flow velocity. The results of the simulation are compared with available experimental data.

Жоғары вольтты электр желілерінің аспалы оқшаулағышының конструкциясы

The article substantiates the relevance of theoretical studies of partial discharge currents. Electromagnetic processes occurring on the surface of a suspended insulator are considered. The design of a poppet suspension insulator is given. The physical process of the pulse current occurrence is described. A replacement scheme of partial discharge current flow on the surface of a suspended insulator has been developed

Hollow cathode discharge instability onset in electric thrusters

Hollow cathodes are an integral part of ion, and Hall thrusters are used for electric propulsion in deep space missions and in commercial communications satellites. Hollow cathodes are known to operate in a quiescent “spot mode” and in a noisy “plume mode” in which plasma instabilities generate erosive energetic ions. The onset of the plume mode in hollow cathodes has been defined historically as when the keeper voltage oscillation values exceed 5 Vpp (peak-to-peak). Using a LaB6 hollow cathode in a vacuum chamber setup that simulates operation in ion and Hall thrusters, a set of emissive and Langmuir probes have been used to investigate the plasma properties associated with plume mode onset as a function of discharge current and gas flow rate. We find that the plume mode onset occurs at even less than 2 Vpp of the keeper voltage for the 5–75 A hollow cathode investigated here and starts at higher gas flow rates than expected from the traditional 5 Vpp metric used by those in the field. Mode competition and coupling between three different instabilities observed in the near-cathode plume affect the overall plasma oscillation levels that are correlated to energetic ion production. We find that the plasma oscillation levels measured by in situ plasma diagnostics are more indicative of the presence of oscillations and the generation of energetic ions than indirect keeper voltage measurements.

A global model for evaluating discharge characteristics and performance of hollow cathodes

Hollow cathode, with the highest plasma density, current density, and temperature, becomes one of the most important components in the electro-thruster system. As the electric-propulsion thruster performance is directly related to the ionization rate, reliability, and lifetime of the hollow cathode, this paper develops a global model to study the effects of discharge current, gas flow rate, and gas species on the discharge characteristics in the insert and orifice regions of the hollow cathode. The emitter wall temperatures of hollow cathodes predicted by the global model are compared with experimental results from NSTAR thruster neutralization cathodes, confirming the model's validity. The influence of hollow cathode emitter material and structure sizes on the plasma parameters in the internal regions was also evaluated. The simulation results show that there is an optimal matching relationship between the discharge current and gas flow rate to guarantee the maximum ionization rate. The optimal working region for the hollow cathode has been determined under different energetic, regime and structural parameters. The global model established in this paper can quickly determine the key structure and operating parameters of hollow cathode at the design stage, and provide the theoretical basis for hollow cathode design and development.

Chemical constitution of coatings deposited remotely by activation of hexamethyldisiloxane in positive column plasma of glow discharge in argon flow

The present work deals with the chemical constitution of coatings deposited by plasma activation of hexamethyldisiloxane in positive column plasma of a low-pressure DC glow discharge in an argon flow (mass flow rate 230 mg/min). X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) are used to analyze deposit chemistry. The substance is complex and consists of many constitutional units forming branched and cross-linked irregular macromolecules. Chemical constitution depends on both discharge current (10–60 mA) and monomer flow rate (1–10 mg/min). Using the specific energy (SE) and Arrhenius-like approach, the threshold energy for the plasma polymerization of HMDSO has been estimated to be 12 ± 1 eV. Two regimes of the plasma chemical system have been identified. At SE near the threshold energy (from 5 to 40 eV/molecule), polymethylsiloxane-like coatings are deposited and variation of SE practically does not lead to changes in chemical constitution, but significantly affects the mass yield of deposit. At specific energies much higher than threshold energy, polymethylhydroxysiloxane-like coatings are formed; the coating structure is strongly SE-dependent, while the mass yield of the deposit does not change.

Study of the Metal Sphere Explosion Driven by Pulsed Discharge for Separating Adherends

A metal sphere’s state by pulsed discharge in air was characterized for the application of an explosion of a metal sphere inserted in the bonding adhesive caused by the pulsed discharge to separate bonded structures. Although the adhesive is widely used in composite materials for automobiles and aircraft, dismantling bonded structures has been challenging. Therefore, facile and selective separation of bonded structures is required for easy disassembly. In this study, a metal sphere set in the adhesive in place of an alumina sphere that adjusted the thickness of the adhesive layer was exploded by the Joule heating caused by the discharge current flow to fracture the adhesive and separate the adherend. High-speed images of the metal sphere’s state in air, as the behavior in the adhesive is not observable, showed that an explosion occurred at the contact point between the metal sphere and the electrode. An electrothermal simulation using the measured current flow to consider the contact conditions indicated that the Joule heating at the contact point increased the sphere’s temperature above the boiling point of iron at the time of the explosion observed in the experiment. A test model of the bonded structure containing the adhesive with the sphere also showed that the sphere allowed control of the discharge path in the adhesive, separating 25-mm2 adhesive surfaces with a charging energy of 30 J. These results indicated that adding a metal sphere to adhesive is effective for selectively separating the adherend from the bonded structure using pulsed discharge to generate the explosion of the sphere at the contact point.

An equivalent model of discharge instability in the discharge chamber of Kaufman ion thruster

The industrial application of the Kaufman ion thruster in its arc stage is limited owing to the instability of the discharge pulse. Presently, a complete prediction model that can predict the discharge pulse in the high-current stage does not exist. In this study, a complete prediction model for the pulse in the ion thruster is established using the zero-dimensional plasma discharge model and equivalent circuit model. The zero-dimensional plasma discharge model is used to obtain the corresponding plasma parameters by calculating the beam current, discharge current, voltage, and gas flow under actual working conditions. The input parameters of the equivalent circuit model are calculated using empirical formulae to acquire the estimated discharge waveforms. The pulse waveforms obtained using the model are found to be consistent with the experimental results. The model is used to evaluate the process of rapid changes in plasma density. Additionally, this model is employed to predict changes in the pulse waveforms when the volume of the discharge chamber and grid plate transmittance are changed.

Physics of thermionic, orificed hollow cathodes: I. Theory and experimental validation

A model aimed at illuminating the physics of thermionic, orificed hollow cathodes is developed and validated with experimental data. The model is intended to describe the variation of total (neutrals, ions, and electrons) static pressure with controllable parameters. That pressure must be properly evaluated because it influences important plasma parameters in the cathode such as the attachment length and the electron temperature, which directly impact the lifetime of thermionic inserts. The model, which combines a zero-dimensional approach to the conservation of energy and momentum for the combined plasma-neutral fluid and a charge-exchange-limited ambipolar diffusion model, allows for the computation of all plasma quantities, including the total fluid pressure. The model depends on the operating conditions (discharge current and mass flow rate), cathode geometry, and the gas species, along with two non-controllable parameters: the neutral gas temperature and the sheath potential. Total pressure data at up to 307 A of cathode discharge current were obtained experimentally and were used, along with data from the literature, to validate the model. Good agreement is obtained for all quantities. The model is used in a companion paper to clarify the role of magnetic and gasdynamic pressure in the scaling of total pressure, to derive scaling laws applicable to thermionic, orificed hollow cathodes, and to propose novel cathode design rules.

Conversion of CO2 in a pulsed arc discharge

We present a study of CO2 gas conversion into a mixture of CO2, CO and O2 by means of a pulsed arc discharge at atmospheric pressure. The CO2 molecule is dissociated as a result of the interaction with the highly energetic electrons and excited species produced in the plasma domain. The plasma conversion of CO2 provides a relatively simple approach to CO2 conversion without the need of special materials required by chemical reactors. In this study, the discharge operates at atmospheric pressure, which leads to a reduced efficiency compared to the low pressure operation due to the additional electron losses via elastic collisions. The operation at atmospheric pressure, however, provides simplicity, robustness and low cost of the discharge system, which makes it very attractive from an industrial point of view. Further, we use a pulsed discharge, which, in comparison to the DC discharges, provides additional possibilities for optimizing the dissociation process by controlling precisely the energy input into the plasma. This is achieved by controlling the pulse repetition rate and duty ratio in addition to the discharge current and gas flow characteristics. We present results for the CO2 dissociation rate and energy efficiency for a wide range of different discharge parameters.

Investigation of the plasma composition of a discharge with a self-heating hollow cathode and an active anode in a gas mixture with titanium and hexamethyldisilazane vapors

The analysis of composition of low-pressure (~0.1-1 mTorr) hollow cathode arc plasma in Ar+N2 gas mixture with Ti+hexamethyldisilazane vapors was carried out by optical emission spectroscopy. The influence of HMDS flow rate (1-10 g/h), discharge current (10-50 A) and Ti-vapors flow on hexamethyldisilazane decomposition degree and plasma composition and was investigated. The proposed plasma activation method provides both an intense flow and a high activation degree of metal vapors, and a sufficient decomposition degree of precursor vapors for the formation of solid TiSiCN coatings at a high deposition rate. Test coatings with a thickness of 6 microns and a hardness of 31 GPa were obtained in 1 hour at 400ºC.

Comparison of the performance of atmospheric pressure glow discharges operated between a flowing liquid cathode and either a pin-type anode or a helium jet anode for the Ga and In determination by the optical emission spectrometry

Novel atmospheric pressure glow discharge (APGD) microplasma systems, sustained between a miniaturized flowing liquid cathode (FLC) and either a pin-type anode or a He nozzle jet were investigated for the determination of Ga and In by the optical emission spectrometry (OES). The most influential working parameters, i.e., solution flow rate, acid concentration, discharge current, and He flow rate, were optimized for both studied systems. Furthermore, the effect of the addition of low molecular weight organic compounds (LMWOCs) into the FLC solution on the signals intensity of Ga and In was investigated. Subsequently, the impact of concomitant ions on the signals intensity of Ga and In was thoroughly studied and it was established that both studied methods are relatively resistant to matrix effects. Under the optimized conditions, the detection limits (DLs, assessed on the basis of the 3σ criterion) of the studied elements were similar for both discharges and ranged between 1.8 and 2.3 μg L−1 for Ga and 0.37–0.40 μg L−1 for In. The received DLs were therefore better than those obtained for other spectrometric methods being premised upon microplasma systems and comparable with those obtained by currently employed large-scale instrumentation. The system with the pin-type anode was successfully applied for the Ga and In determination in four leachates of solders and electronic scrap as well as river water, using external calibration with simple standard solutions. The received results were compared to those obtained from ICP-OES or ICP-MS measurements and their recoveries were fallen within the range of 98–114%, confirming the excellent accuracy and reliability of the developed FLC-APGD-OES method.

Spectroscopic analysis of gold nanoparticle synthesis using plasma liquid interaction technique

Surfactant free AuNPs were prepared via Plasma-Liquid Interaction (PLI) technique, using -plasma, as a function of time, discharge current and gas flow rate. Atomic oxygen [O] and nitrogen [N] densities were determined to study their effect on the intensities of UV radiation and OH radical, which in turns controls the synthesis of AuNPs. UV radiation, OH radical and atomic densities of [O] and [N] were determined through optical emission spectroscopy from gas phase plasma. The increase in UV radiation intensities and OH radicals with time was observed and results were verified by observing increasing trend in the [O] and [N] atomic densities. We report the role of versatile discharge species generated in PLI, like [O] and [N] atomic densities, in the control synthesis of surfactant free AuNPs.

Development of a data acquisition system using LabVIEW and Arduino microcontroller for a centrifugal pump test bench connected in series and parallel

A data acquisition system using LabVIEW software and the Arduino microcontroller for a test bench of centrifugal pumps connected in series and parallel has been developed. The acquisition system allows real-time display of centrifugal pump discharge pressure values, voltage, current and volumetric flow of the test bench. A description of the system operation (front panel and block diagram) as well as the elements (actuators, instruments, controller and software) used in the system is given. From the front panel it became possible to operate the test bench for three modes of operation (Individual, Series and Parallel). Pressure, voltage, current and volumetric flow values were recorded over time and stored in a text file generated by the acquisition system.

Temporal Evolution and Spatial Distribution of the Plume Plasma from an MPD Arc Generator

We used a triple Langmuir probe to measure the temporal evolution and spatial distribution of the plasma parameters of a newly designed steady-state applied-field magnetoplasmadynamic arc generator. Varying the discharge current, mass flow rate, and applied magnetic field strength during a 170-s steady discharge, we investigated the corresponding instantaneous variations of electron temperature and density. The temporal profiles show that both the discharge current increase and mass flow rate decrease result in a reduction of electron temperature and density. On the contrary, the application of the external magnetic field, confining the plume expansion, can raise the electron temperature and density by 10 times. The centerline electron temperature and density show a linear decrease from 20- to 34-cm downstream along the thruster axis. The radial distribution exhibits an adiabatic expansion behavior with the ratio of specific heat $\gamma $ in the range of 1.1–1.5.

Synthesis and spectroscopic characterization of gold nanoparticles via plasma-liquid interaction technique

Fabrication of non-functionalized gold nanoparticles is interesting owing to their potential applications in sensing and biomedicine. We report on the synthesis of surfactant-free gold nanoparticles (AuNPs) by Plasma-Liquid Interaction (PLI) technique, using micro-atmospheric pressure D.C. plasma. The effects of discharge parameters, such as discharge current, precursor concentration and gas flow rates on the structure and morphology of AuNPs have been investigated. Optical Emission Spectroscopy (OES) was employed to estimate the UV radiation intensity and OH radical density. Scanning electron microscopy (SEM) and ultraviolet-visible (UV-Vis) optical spectroscopy were employed to study the morphology and structure of AuNPs. The normalized intensities of UV radiation and OH radical density found to increase with increase in discharge current. We observed that the particle size can be tuned by controlling any of the following parameters: intensity of the UV radiation, OH radical density, and concentration of the Au precursor. Interestingly, we found that addition of 1% Ar in the feedstock gas results in formation of relatively uniform size distribution of nanoparticles. The surfactant-free AuNPs, due to their bare-surface, exhibit excellent surface-enhanced Raman scattering (SERS) properties. The SERS study of Rhodamine 6G using AuNPs as substrates, shows significant Raman enhancement and fluorescence quenching, which makes our technique a potentially powerful route to detection of trace amounts of dangerous explosives and other materials.

Life Evaluation of a Lanthanum Hexaboride Hollow Cathode for High-Power Hall Thruster

Lanthanum hexaboride () hollow cathodes have been in development in the United States for electric thruster applications for nearly 15 years. The life of the lanthanum-hexaboride insert in these hollow cathodes is projected to range from 10 kh to over 100 kh based on insert evaporation calculations. A detailed investigation of the life of a 1.5 cm outside-diameter lanthanum-hexaboride hollow cathode has been made. This cathode can provide discharge currents between 5 and 100 A and has an estimated lifetime in excess of 50 kh depending on discharge current and mass flow rate. The insert evaporation rate is determined from a 4000 h discharge wear test of a laboratory model cathode, where insert weight-loss measurements were made at the start, middle, and end of the test. Detailed insert temperature and plasma measurements are used in a one-dimensional disk evaporation model that accommodates the insert temperature profiles found with different discharge currents, flow rates, and cathode orifice diameters, to predict the insert life. The results suggest that insert outgassing is significant early in life, and lanthanum redeposition reduces the net evaporation rate and extends the cathode life.

The analysis of high amplitude of potential oscillations near the hollow cathode of ion thruster

The influence of gas flow, current level, and different shapes of anode on the oscillation amplitude and the characteristics of the hollow cathode discharge were investigated. The average plasma potential, temporal measurements of plasma potential, ion density, the electron temperature, as well as waveforms of plasma potential for test conditions were measured. At the same time, the time-resolved images of the plasma plume were also recorded. The results show that the potential oscillations appear at high discharge current or low flow rate. The potential oscillation boundaries, the position of maximum amplitude of plasma potential, and the position where the highest ion density was observed, were found. Both of the positions are affected by different shapes of anode configurations. This high amplitude of potential oscillations is ionization-like instabilities. The xenon ions ionized in space was analyzed for the fast potential rise and spatial dissipation of the space xenon ions was the reason for the gradual potential delay.

Electrical Characteristics of Nonthermal Gliding Arc Discharge Reactor in Argon and Nitrogen Gases

Gliding arc discharge (GAD) has the properties of both thermal and nonthermal plasma conditions. GAD plasma in the atmospheric pressure with argon/nitrogen and its characteristics are described. Some experimental results about alternating current gliding arc plasma generator have been obtained. It seems that the current density strongly depends on the gas type, and increased with increasing discharge current and gas flow rate. In addition, the discharge current of GAD in nitrogen gas (N2) is greater than one in argon gas (Ar) because of N2 needs more breakdown voltage than Ar. The intensity of GAD increased with increasing the gas flow rate. The oscillograms of discharge current in each case of Ar and N2 were obtained. The electron temperatures of Ar and N2 plasma were calculated to be 22 800 and 8400 K, respectively. The characteristics of both Ar and N2 gases in atmospheric pressure, such as current density, electron density with flow rates (5, 10, 20, and 40) standard cubic foot per hour, were investigated and all experimental results were classified. An experimental study was carried out through using of GAD device for medical treatment by exposing three human blood samples of leukemia to the nonthermal GAD plasma for different periods.

Water droplet initiated discharges on epoxy nanocomposites under DC voltages

Epoxy nanocomposites with different percentages of nano clay filler are prepared using a shear mixer technique. Corona inception voltage (CIV) due to water droplets on the epoxy nanocomposite is high under negative direct voltage compared with positive polarity voltage. It was found that an increase in droplet volume and number of droplets within the gap reduces the CIV. The magnitude of discharge current flow is high under negative polarity. Surface charge accumulation studies indicate nonlinear variation in distribution of charges on the surface of the epoxy nanocomposite with water droplets. Optical Emission Spectroscopy (OES) results confirm high temperature plasma during water droplet initiated electrical discharges on the surface of epoxy resin. Laser Induced Breakdown Spectroscopy (LIBS) results indicate the presence of carbon on the degraded surface of the sample. The absorbed energy on the sample surface during arcing is measured through leakage current, and is observed to be higher for negative polarity. UHF signals were radiated due to corona discharges from water droplets on the epoxy nanocomposites under direct voltages and their bandwidth is in the range of 1–2 GHz.

Optimization of Multiple Response Characteristics of EDM Process Using Taguchi-Based Grey Relational Analysis and Modified PSO

Electrical discharge machining is an alternative process for machining complex and intricate shapes. In this paper, an inter-relationship of various electrical discharge machining parameters, namely discharge current, pulse on and off time and dielectric flow rate on material removal rate (MRR), tool wear rate (TWR), surface finish ( SR a) and dimensional tolerance using a Taguchi–Grey relational analysis. The response surface methodology is used to develop a second order model for MRR, TWR and SR a in terms of process parameters. Finally, a multi-objective optimization problem is formulated by using MRR, TWR and SR a. The multi-objective problem is then optimized through a modified particle swarm optimization (PSO) algorithm to find the optimum level of parameters. In this research, the results of the proposed method are validated through confirmation experiment. The work piece material used for experimentation is stainless steel of S304 grade.