Discharge Mode Research Articles

Study on hollow cathode discharge mode with high flow rate

Abstract Hall and ion propulsion systems at power levels of ten kilowatts or higher are in development or application stages in recent years, yet research on the operational characteristics of corresponding hollow cathodes remains incomplete. This study conducts experimental research using a hollow cathode with a rated condition of 15 sccm of krypton gas and 10 A of current. By supplying a larger flow rate, the study expands the range of discharge currents to investigate changes in the discharge modes. The plume plasma characteristics and spatial distributions under various conditions were measured using a Langmuir single probe mounted on a planar two-dimensional displacement platform. The experimental results indicate that at krypton flow rates of 25 sccm and 30 sccm, as the current increases, the anode voltage and discharge oscillations increase at first but decrease later. The discharge mode transitions from low-current spot mode to plume mode, and then back to spot mode at high current. The increase in anode voltage and oscillations during the first transition phase is gradual and continuous, while the decrease during the second transition phase is abrupt. Conditions of 10 A, 12.5 A, and 20 A were selected to represent these three modes for single-probe plume spatial diagnostics. The results indicate that in the high-current spot mode, the axial potential gradient is significantly reduced compared to the radial gradient, and the cathode plasma plume is more collimated. This study shows that at high flow rates, hollow cathodes may exhibit nonlinear impedance and undergo multiple discharge mode transitions, with each transition phase displaying distinct characteristics.

Deep learning via CNN for identification of blue core phenomenon in helicon plasma discharge

Based on deep learning image recognition techniques, a convolutional neural network model for discharge mode recognition of helicon plasma was trained. The accuracy of the model was evaluated using functions such as F1-scores and the confusion matrix. The final recognition accuracy was more than 98.18% after 30 iterations. Interpretable analysis was done using methods such as gradient-weighted class activation mapping to verify the model's robustness as well as repeatability. The model identification results were compared with Langmuir probe diagnostic results. It was found a good fit between the model and the probe results, corroborating the correctness of the model. The present model can well identify the critical power of entering W mode in the discharge process of helicon plasma. As the discharge database expands, it has great potential for recognizing the higher-order discharge modes based on deep learning.

Effect of field emission on contact spark in the spark test apparatus

Explosion-proof electrical equipment must be tested with the spark test apparatus (STA). This discharge was important for electrical explosion-proof safety. This study aimed to investigate the effect of field emission on the contact spark of the STA. Results show that the primary discharge modes were field emission and electron impact ionization. The gap width was estimated to be 6–8 μm. The distribution of the ions and radicals were revealed under the different field emissions. The impact of radicals on ignition was also discussed.

Modeling the Inception and Stepped Propagation of Upward Positive Lightning Leaders

AbstractPositive lightning leaders are a ubiquitous, yet poorly understood, component of lightning flashes. Upward lightning started by positive leaders may be formed when nearby storm activity induces electrical charges in a tall structure, such as communications towers or wind turbines. Alternatively, upward lightning can be triggered with the rocket‐and‐wire technique. In this paper, we introduce a new self‐consistent model for this important discharge mode, one which solves Maxwell's equations under the quasi‐electrostatic approximation. The model also includes a realistic treatment of the nonlinear plasma conductivity within the leader channel. This new computational tool explains the origin of the positive leader speed, of 10s of km/s, as well as why it displays a steady behavior over time. The model also explains the temporal evolution of current to ground measured during the early stages of rocket‐triggered lightning, where the current exhibits a series of small‐amplitude pulses, which disappear over time. The article also outlines straightforward criteria for leader inception, which may have practical applications for lightning protection.

Biochar from residues of anaerobic digestion and its application as electrocatalyst in Zn–air batteries

BackgroundBiochar, the product obtained by pyrolysis of biomass, is a new eco-friendly material with excellent properties and many promising applications. Among them it can be used as cathode in Zn-air batteries with very satisfactory results MethodsThe residue was obtained by anaerobic digestion of a mixture of corn silage (10%), malt (10%), and cattle manure (80%), aiming to biogas production. It was first freeze–dried and then it was subjected to pyrolysis up to 800oC. Significant findingsThe biochar was physicochemically characterized. It has moderate specific surface area, sufficient sp2/sp3 ratio and metal and non–metal surface chemical species. The biochar demonstrated satisfactory electrocatalytic performance, both as oxygen reduction and oxygen evolution catalyst. When applied as electrocatalyst in Zn–air batteries it reached an open–circuit potential of 1.45 V, a short–circuit current density of 200 mA cm–2 and maximum power density of around 62 mW cm–2. Its energy density was 927 Wh kg–1, (at 20 mA), and 518 Wh kg–1 (at 100 mA). In a charge–discharge mode at 10 mA, the potential varied between 1.35 and 1.90 V. These data, show that the waste biomass can be used as inexpensive material for Zn–air batteries and offers a useful approach to combine waste management with energy storage.

Development of pilot-scale plasma bubble reactors for efficient antibiotics removal in wastewater

Plasma bubble (PB) is a promising technology to control antibiotic wastewater pollution. However, the practical implementation of PB technology at the industrial-scale is still underdeveloped. In addition, the influence of different discharge modes for PB on wastewater treatment is largely unknown. This study designed pilot-scale PB reactors with different discharge modes to investigate the degradation effect of norfloxacin (NOR) and tetracycline (TC) in bulk tap water. Results indicate that the dielectric barrier discharge (DBD) mode with low average discharge power demonstrates superior degradation ability and higher production of O3(g) and .O2−(aq) compared to the spark mode which exhibits the high-intensity spark discharge in the tip area of the tube. After 40 min of treatment in a Double DBD reactor, 97.4% and 100% of NOR and TC are removed from 2 L tap water, attributed to the accumulation of antibiotic molecules by PBs and the in-situ generation of O3(g) and .O2−(aq) produced by plasma. Furthermore, a larger-scale PB reactor is developed by creating an array of four DBD reactors, effectively degrading 8 L mixed antibiotics solution. This study provides valuable insights for PB reactor design and the degradation performance of antibiotic wastewater, which will contribute to the further development of synergistic systems for plasma degradation.

Electrical and optical characteristics of a nanosecond pulsed electrical discharge in air in contact with a water droplet for various electrical conductivities

Abstract Interactions between pulsed electrical discharges and liquid dielectric materials is a growing research field with interests in fundamental discharge physics as well as in applications. Herein, we present an experimental study on the dynamics of nanosecond discharges in air with the presence of a water droplet with various electrical conductivities (EC) and at different applied voltages (Va). The discharges are characterized optically, by employing time-resolved ICCD imaging and optical emission spectroscopy, as well as electrically, by acquiring the current-voltage waveforms for every discharge. The results show that three modes of discharges can be obtained: i) streamer discharge between the cathode and the droplet, ii) streamer discharge between the cathode and the droplet as well as between the anode and the droplet, and iii) spark discharge that connects the two electrodes and propagates over the droplet. We find that the probability to obtain one of the three discharge modes is strongly related to the droplet’s EC as well as to Va. Although the ignition of the streamer is relatively insensitive to EC, its transition to a spark can be finely controlled by the droplet’s EC. The time-resolved ICCD images show that the discharge initiates in the gap between the cathode and the droplet, followed by ignition between the anode/ground electrode and the droplet. Then, an extinction phase is observed before the ignition of a secondary streamer, and depending on the conditions, the discharge may transition to a spark, i.e. a channel with high emission intensity. We find that the duration of each stage of discharge propagation as well as the corresponding emission (path and intensity) are sensitive to droplet’s EC. Finally, emissions from streamers (primary and secondary) as well as from sparks are analyzed using optical spectroscopy. We find that the emission from the streamers is dominated by the second positive system of N2, and that the droplet’s EC does not significantly influence the emission spectra nor the estimated rotational temperature of N2.

Effects of pulse rise time and pulse width on discharge mode transition of SDBD plasma under repetitive pulses

Abstract Affected by environmental states and power supply parameters, the discharge mode of surface dielectric barrier discharge (SDBD) plasma may gradually transfer from O3 mode to NO x mode, resulting in various gas-phase species for different applications. Despite the intensive study of attempts to control this discharge mode transition by changing discharge conditions and power excitations in recent years, the effects of the pulse rise time and the pulse width on the discharge mode transition have not been discussed. In the present study, a SDBD was excited by repetitive pulses with different pulse rise times or pulse widths, and the time-varying concentrations of key long-lived species (O3 and NO2) were quantified. The results demonstrated that it was possible to modulate the discharge mode by adjusting pulse rise time/pulse width. The quenching of O3 was observed to occur at a faster rate and the mode transition was noted to occur at an earlier point in time as the pulse rise time decreased from 225 ns to 125 ns and the pulse width increased from 0.5 μs to 4 μs. The employment of a zero-dimensional model for the analysis of plasma chemical kinetics revealed that the reduction in pulse rise time and the prolongation of pulse width resulted in an increase in the mean vibrational energy of N2(v) and a more rapid electrode temperature rise caused by plasma heating. The former enhanced the generation of NO, while the latter accelerated the thermal decomposition of O3, thereby promoting the speed of mode transition.

Semiconductor WO3 thin films deposited by pulsed reactive magnetron sputtering

A pulsed reactive magnetron sputtering system with a tungsten target and a gas mixture of argon and oxygen was investigated as a source for the deposition of semiconductor WO3 thin films on soda lime glass substrates and on the glass with transparent conductive SnO2:F (FTO) electrode. The reactive sputtering process was performed in HiPIMS mode with low pulse repetition frequency fp ≈ 50–100 Hz and short pulse duration in HiPIMS discharge Ton = 100 μs. The second mode investigated was the mid-frequency (MF) magnetron discharge with pulse frequency fp = 40 kHz and pulse length Ton = 15 μs. The plasma parameters were investigated for both HiPIMS and MF modes using the planar RF probe operating at the frequency fprobe = 350 kHz and the grid QCM with biased collector electrode. Ion density ni and tail electron temperature (Te) were determined in both pulsed reactive magnetron sputtering discharge modes with time resolution. The maximum value ni ≈ 5 · 1017 m−3 was found in the reactive HiPIMS mode, and the maximum value ni ≈ 7 · 1016 m−3 was found in the reactive MF (40 kHz) mode. The degree of ionization of sputtered particles in reactive HiPIMS was determined for different values of (QO2) and was found to be in the range of ri ≈ 0.1–0.3. The deposition rate determined by QCM in reactive HiPIMS was practically independent on (QO2), but in the case of reactive MF, the measured deposition rate decreased significantly with increasing (QO2). The WO3 films deposited in both modes have a predominantly monoclinic crystal structure. The light and dark conductivity and the light/dark conductivity ratio (Ld) were measured under dark conditions and UV light illumination. At higher (QO2), the maximum value of Ld ≈ 300 was found for MF deposited WO3 and the maximum value of Ld ≈ 30 was found for HiPIMS deposited WO3. The photoelectrochemical measurement of WO3 deposited on FTO electrodes confirmed the n-type conductivity, and these films functioned as photoanodes in photoelectrochemical cells. MF deposited WO3 films systematically exhibited slightly higher photocurrents than HiPIMS deposited WO3. It was shown that these optimum photocurrents for HiPIMS and MF were found at QO2 ≈ 80 sccm and could not be improved by further increasing of (QO2).

A collisional-radiative model for atmospheric-pressure low-temperature air discharges

Plasma-assisted combustion technology has been a hot spot in aero-engines and scramjet-engines. The electron density is a key discharge parameter related to the active-particle density. The latter has been considered playing an important role in the above applications by the kinetic effect. In this work, an atmospheric pressure air plasma collisional-radiative model considering the excited states of atomic nitrogen and oxygen is built based on previous widely kinetic investigations of molecules and radicals, as well as their excited states. The excited states, especially the atomic nitrogen and oxygen states were less investigated in previous works. The emission intensity distributions from the model have a good agreement with those measured in the glide arc plasma with two discharge modes, as well as the microwave plasma. Based on the kinetics of molecular and atomic emitting states, the line-ratio method is presented to determine the electron density. The N2(337 nm)/O(844 nm) and N2(337 nm)/NO(γ) line ratios are used for the glide arc plasma and microwave plasma torch, respectively. Besides, the kinetics of the excited states involved with two line-ratios are also investigated in the two types of discharges. Combined with the atmospheric pressure actinometry method, the kinetic effect of the plasma-assisted combustion can be revealed quantitatively in the future.

Array hollow-anode microsecond-pulsed plasma jets at atmospheric pressure: mode transition and influencing factors

Abstract Hollow cathode plasma jets are commonly utilized across various fields, yet there is limited research on hollow anode discharge, particularly on array hollow anode plasma jets. This letter presents the novel design of a array hollow anode discharge device excited by microsecond pulse. Systematical investigations about the discharge characteristics and mode transition process of the device are examined from the perspectives of electricity and space-time distribution to get insights into the formation mechanisms of array hollow anode plasma jets. Results show that three distinct discharge modes when the array hollow anode plasma jets interacting with ITO plate are identified based on the number and location of the discharged hollow anodes: Mode A involves all 16 hollow anodes discharging, Mode B entails 12 hollow anodes discharging, and Mode C comprises 4 hollow anodes discharging at the four vertices of the device. It is observed that experimental outcomes are influenced by the distance from the hollow anode tube port to the plate. The formation mechanism is determined by an increase in distance impacting spatial electric field distribution and facilitating mode transition. Furthermore, the impacts of pulse voltage, pulse frequency, and flow rate on the variation of interval length under different modes are investigated. The results indicate that voltage has the most significant effect on interval length, followed by frequency, while flow rate has a minimal effect. These findings hold significant implications for enhancing understanding of mode transition and influencing factors of array hollow anode plasma jets.

Discharge modes evolution characteristics of metal particle on the spacer surface in AC gas insulated switchgear

Abstract Flashover faults on gas insulated switchgear (GIS) insulators induced by metal particles occur frequently. Previous studies have obtained the characteristics of partial discharges (PDs) induced by metal particles on spacer surfaces, but these characteristics cannot explain the detection failure of ultra-high frequency (UHF) online monitoring. To enable further study of the PD characteristics induced by surface metal particles, the space electric field and a very-high-sensitivity pulse current (PC) measurement system were established. The electric field and PC characteristics of a PD induced by metal particle on the spacer surface of a 126 kV GIS were obtained. Two PD modes were found to be induced by surface metal particles. In addition to the typical pulse discharge (TP), there is a micro-discharge group (MG) mode with low apparent charge and long duration. The average apparent charge of the MG mode is approximately one-tenth of that of the TP at 0.4 pC. Its duration may extend to the millisecond level, causing significant distortion of the spatial electric field while hardly producing UHF signals. Moreover, increasing the applied voltage will increase the proportion of the MG within the total discharge, where this proportion can reach more than 90% before flashover, and the proportion of the discharge pulses that generates UHF signals is as low as 1%. The MG generation mechanism is analysed, the ion group stranded on the spacer surface by the TP changes the local electric field at the tip of the metal particle, which reduces the development length and apparent charge of the MG. Low apparent charge is cleared easily by the background electric field and thus the discharge interval is very short. This paper can provide an important basis for revealing the mechanism of GIS spacer surface discharge induced by metal particles and solving the effectiveness of PD monitoring devices.

Enhancing energy control for a hybrid system comprising a wind turbine, diesel generator, and storage systems

The increase in demand for electrical energy has made renewable energy sources, such as wind power, increasingly attractive. However, intermittency and variability represent the major problems of these types of energies. The hybridization of several energy sources allows to have a reliable and efficient supply system. This paper was interested in the control of a hybrid energy system, which includes a wind turbine, storage systems (batteries and super-capacitors) and a conventional diesel generator, with the aim of generating constant power. A control strategy is developed taking into account the various constraints of the hybrid system. Both of storage systems as well as the diesel generator operate according to the modes presented in the supervision algorithm to absorb and compensate the fluctuation of the wind energy and reach to a constant energy flow. The super-capacitor operates before the battery to absorb the power peaks in both charge and discharge modes. The hybrid system is simulated using MATLAB/Simulink software, and the results are provided in order to show the effectiveness of this control strategy.

Using multi‐component carbon composite as current collector in ultra‐battery

AbstractThis study introduces a multi‐component composite as a substitute for lead grids in ultra‐battery structures. The presented composite decreases the weight and simultaneously extends the cycle life of the traditional lead‐acid battery. Overall, UBZCP (the sample containing metal oxides and polyaniline), as the best sample, increases the cyclic stability by 3.3 and 1.4 times under high rate partial state of charge (HRPSoC) mode, compared to Native and UB450 samples. Metal oxides predominantly enhance the electrical conductivity of carbon‐based composites due to catalytic effects in the reduction of graphene oxide during heat treatment. Poly aniline shows considerably positive effect of electrochemical performance due to the high pseudo‐capacitive properties, high interaction of lead ions and the nitrogen in the polymer chains and accordingly hydrogen evolution reaction (HER) inhibition. The synergistic effect of polyaniline and metal oxides makes the best performance in the UBZCP sample achieve. Also, the UBZCP sample represented an enhancement of about 1.21 and 1.39 times in battery life and specific capacity under deep discharge mode compared to the Native sample. As a result, the introduced multi‐component composite making a 3D conductive network, facilitates Pb/PbSO4 reaction reversibility, and reduces the lead sulfate crystal size.

Firing patterns transitions and resonance effects of the extended Hindmarsh-Rose neural model with Gaussian noise and transcranial magneto-acousto-electrical stimulation

Considering the fact that the typical three-variable Hindmarsh-Rose(HR) neural model has limitations in describing the complex non-linear features and precise behavior patterns of neuron, the influences of transcranial magneto-acousto-electrical stimulation(TMAES) on firing patterns and resonance effects are analyzed based on an extended HR neural model in this paper. Obtained results show that TMAES can induce transitions in the firing patterns of extended HR neuron, such as spiking and multi-periodic bursting state, etc If appropriate parameters are selected, the multimodal discharge modes can also be observed. Coefficient of variation is calculated to further investigate the effect of TMAES and Gaussian white noise on the firing rhythm of extended HR neuron, and relevant results indicate that TMAES can induce coherent resonance phenomena in HR neuronal systems similar to the effects of Gaussian white noise, which reveals a new mechanism of coherent resonance induced by TMAES. Further more, TMAES can also regulate coefficient of variation to exhibit anti-coherent resonance and multiple anti-coherent resonance structures, exhibiting richer regulatory functions than Gaussian white noise in regulating neuronal firing rhythm. This study seeks to enhance the understanding of the processes that influence the firing patterns and coherence degree of neuron under TMAES in neuroses or psychoses.

Enhancing degradation of PLA-made rigid biodegradable plastics with non-thermal plasma treatment

This study evaluated the efficacy of Dielectric Barrier Discharge Non-Thermal Plasma (DDBD-NTP) as a pretreatment method to enhance the degradation of rigid biodegradable plastics (RBP) during composting, specifically focusing on polylactic acid (PLA) products such as drinking cups (CS) and spoon handles (SH). Using a Single-Factor-At-A-Time (SFAT) design, the impact of NTP parameters, including input voltage and treatment duration, on the physicochemical properties was evaluated, and the subsequent degradation rate of RBP was assessed by measuring the degree of disintegration in a home-scale composter. The filamentary discharge mode of the DDBD plasma system selectively altered the surface characteristics of RBP without significantly affecting their bulk properties. High-voltage treatments significantly increased surface roughness and accelerated degradation rates, while low-voltage and short-duration treatments enhanced oxidation, as indicated by the increased O/C ratio (85.5% for SH and 66.1% for CS), showing a non-linear response to plasma intensity. Furthermore, NTP treatment reduced water contact angles (up to a 39.79% reduction for SH and 82.65% for CS), indicating enhanced hydrophilicity. All NTP-treated samples demonstrated significantly higher degradation rates compared to both untreated and thermally treated counterparts. Notably, ‘high-voltage for short-duration’ treatments, such as CS-3 and SH-3, exhibited the highest degradation rates among the samples. CS-3 achieved complete disintegration (100%) within 20 days, markedly exceeding the 2% observed in untreated CS samples. Similarly, SH-3 reached 36% disintegration after 35 days, considerably surpassing the 9% seen in untreated SH samples. The findings indicate that NTP treatment is a viable and sustainable method to enhance the biodegradation of plastic waste.

Emerging lessons from experiences at transitions in care among hospitalised patients with cancer with postdischarge frequent emergency department use: a qualitative study using linked clinical and patient-reported interview data from Quebec, Canada

BackgroundWhile teamwork is essential to providing high-quality patient-centred care, challenges in interprofessional collaboration and decision-making in hospital settings are common, especially for patients with cancer. The purpose of this qualitative...

Gas flows generated by pulse-periodic optical breakdown and quiet optical discharge

Quiet optical discharge in high-pressure xenon is visually stable pre-breakdown stage of optical discharge supported by pulse-periodic short-wavelength infrared laser radiation with intensity of the order of 109 W/cm2. Increasing the laser intensity leads to the transition of the quiet discharge into a pulse-periodic optical breakdown. In this study, quasi-stationary directional flows generated by both the quiet discharge and the optical breakdown are observed. The flows and their initial stages under limited number of discharge pulses are visualized by shadow imaging method using a point-like laser-plasma radiation source. It is shown that the gas streams outflow points in a quiet discharge correspond to the positions of the laser radiation intensity local maxima in the focal beam waist with astigmatism complicated by defocusing effect of thermal lens arising in the discharge zone. The pulse-periodic optical breakdown emits a turbulent gas flow toward the laser beam. The beam refraction on density gradients in the turbulent flow causes the breakdown instability from pulse to pulse. It was found that time-average absorption of laser radiation in a quiet discharge is about 3% (also in a pulse), while that in optical breakdown is 15% and higher (from 70% to 100% in a pulse). Laser beam intensity for quiet discharge at pulse repetition rate νp = 20 kHz ranges from 1.3 × 109 to 1.5 × 109 W/cm2. At intensities above 4 × 109 W/cm2 and repetition rates νp > 50–55 kHz, laser breakdowns are observed in each laser pulse with the focal ratio f/d ≤ 7. At f/d = 10.6 and νp > 28 kHz, the quiet discharge does not transit to laser breakdown due to defocusing by the thermal lens induced.

Plasma electron density profile tomography for EAST based on integrated data analysis

Abstract Plasma electron density is a crucial parameter in plasma studies. Accurately inverting the plasma electron density profile is vital for plasma control experiments and the investigation of plasma physical mechanisms. This paper proposes an integrated data analysis (IDA) method based on Bayesian inference, which integrates polarimetric interferometry (POINT), hydrogen cyanide (HCN) laser
interferometer, and microwave reflectometer (RFL) diagnostics for inverting the plasma electron density profile. To enhance inversion accuracy, a Gaussian prior probability of the non-stationary hyperparameter is used. This prior probability effectively simulates
situations where there is a large plasma electron density gradient in the pedestal, especially under the condition of high-confinement mode discharge. Compared to the use of Gaussian prior probability for the stationary hyperparameter, the proposed IDA
method based on the non-stationary hyperparameter prior probability achieves higher inversion accuracy.

Simulation of mode transitions in capacitively coupled Ar/O2 plasmas

In this work, the effects of the frequency, pressure, gas composition, and secondary-electron emission coefficient on the discharge mode in capacitively coupled Ar/O2 plasmas were carefully studied through simulations. Three discharge modes, i.e., α, γ, and drift-ambipolar (DA), were considered in this study. The results show that a mode transition from the γ-DA hybrid mode dominated by the γ mode to the DA-α hybrid mode dominated by the DA mode is induced by increasing the frequency from 100 kHz to 40 MHz. Furthermore, the electron temperature decreases with increasing frequency, while the plasma density first decreases and then increases. It was found that the electronegativity increases slightly with increasing pressure in the low-frequency region, and it increases notably with increasing pressure in the high-frequency region. It was also observed that the frequency corresponding to the mode transition from γ to DA decreased when the secondary-electron emission coefficient was decreased. Finally, it was found that increasing the oxygen content weakens the γ mode and enhances the DA mode. More importantly, the density of oxygen atoms and ozone will increase greatly with increasing oxygen content, which is of great significance for industrial applications.