Capacitive Discharge Research Articles

Resonant electron confinement and sheath expansion heating in magnetized capacitive oxygen discharges

In weakly magnetized capacitive radio frequency (RF) plasmas electrons accelerated into the plasma bulk by the expanding RF boundary sheath at one electrode can be returned to this electrode due to their gyromotion around an externally applied magnetic field oriented parallel to the electrodes. If the driving frequency and magnetic field are chosen so that the electron cyclotron frequency, ω ce, equals half of the driving RF, ω rf, such energetic beam electrons will be returned to the sheath during its expansion phase and, thus, will be confined and heated resonantly. This magnetized RF sheath resonance (MRSR) effect is studied based on kinetic particle-in-cell simulations in weakly magnetized capacitively coupled oxygen plasmas. In comparison with electropositive argon plasmas, this resonance mechanism is found to be affected strongly by the electronegativity of oxygen discharges. In the unmagnetized case, low-pressure capacitive oxygen discharges operate in an electropositive mode, where nonlinear high-frequency sheath oscillations play an important role similar to previous observations in electropositive discharges with low electron densities. If the resonance condition is fulfilled (), the discharge efficiency is enhanced due to the MRSR effects, resulting in an increase in plasma density. Our numerical results demonstrate that this resonance effect is particularly efficient at low pressure and low electronegativity. However, in strongly electronegative discharges, the time it takes a typical resonant electron to return to the expanding sheath edge is found to be affected by drift and ambipolar electric fields in the plasma bulk, which cause a deviation from the resonance condition, resulting in a reduction of this type of resonance effect.

Design and performance of a micro-scale detonation train with a built-in pyrotechnic MEMS-based safety and arming device

To improve the equipment miniaturization and reliability of weapons and ammunition systems, this study designs a micro-scale detonation train (MDT) with a built-in pyrotechnic microelectromechanical system (MEMS)-based safety and arming (S&A) device, which consists of an energetic semiconductor bridge (ESCB) detonator, and a S&A device with built-in isolation mechanisms, and a micro-detonation train. Furthermore, this study investigates the effects of the slider thickness, the spring beams’ thickness, and the positioning beam type on the security of the S&A device using the Finite Element Dynamics software and verifies the function of the MDT through experiments of capacitive charge and discharge ignition. As indicated by the results, an encouraging arming function can be achieved under a slider thickness of 1.0 ​mm and a positioning beam type of PB, while the spring beam thickness is less relevant. Additionally, the results show that the arming function of the MDT can be completed in 0.6 ​ms.

Instant EOFF measurement error in cathodically protected pipelines: A parametric assessment study

Buried pipeline systems benefit from mitigation wires (earthing systems) in order to be protected against electric shock hazards. Moreover, cathodic protection (CP) systems are incorporated into pipeline systems to provide protection against corrosion by injecting an impressed DC current. DC decoupling devices are normally installed between the pipeline's metallic wall and the earthing wire, functioning as a filter that blocks the DC component (of the CP system) while allowing the hazardous AC interference current to be dissipated into the earth. However, the internal capacitance of the DC decoupling devices introduces an error in the routine survey measurement of the CP effectiveness, as frequently reported by pipelines’ system operators. In this paper, the factors influencing this measurement error are investigated by modeling the electrical behavior of the CP-pipeline system. This investigation concluded that the capacitive discharge time constant and by extension, the measurement error highly depends on the pipeline resistance to remote earth (coating resistance), as well as on the number and the capacitance C of the capacitive DC decoupling devices. To this extent, methods for minimizing Eoff measurement error are proposed.

Spatial distributions of the ion flux in a capacitive hydrogen RF discharge using a hollow cathode with double toroidal grooves enclosed by magnets

A hydrogen high-density capacitively coupled plasma has been developed using a hollow cathode with double toroidal grooves enclosed by magnets and without an iron yoke disk. It is found that this plasma source allows generating higher plasma densities compared to the conventional RF magnetron plasma sources. Spatial distributions of the ion flux have been measured at various H2 gas pressures, p, of 1–20 Pa. It is found that the hybrid combination of a hollow cathode effect and magnetic confinement of electrons is attained for p ≥ 5 Pa, while for p ≤ 3 Pa, a conventional capacitive discharge is generated. The radial profile of the ion flux becomes uniform with increasing axial distance from the target for the hollow cathode discharge. The characteristic decay length of the roughness of the ion flux profile increases with increasing the gas pressure.

Capacitive discharge in flash experiments: A discussion of the charged species

AbstractWe report on the discharge of the capacitance formed at the electrodes in flash experiments with yttria stabilized zirconia. The experiments were carried out by disconnecting the current, and, instead, short circuiting the electrodes through a resistor. The time dependent voltage across the resistor was measured; the ratio yielded the discharge current. The current decayed exponentially with time, as expected in an RC circuit, which allowed the measurement of the capacitance. Experiments were carried out in two ways. In one case the specimens were flashed within a glove box filled with Ar (< 1 ppm O2): these yielded electronic conductors. In the other case the specimens were flashed in ambient air: while electronically conducting in‐flash these specimens recover their prior insulating behavior as soon as the current is turned off. The stored charge was two orders of magnitude greater in the Ar experiments. Rather unexpectedly, the sign of the voltage expressed at the electrodes was opposite in experiments carried out in air and in Ar. The capacitance measured in the discharge experiments is attributed to the formation of space charge adjacent to the electrodes. In the case of Ar experiments, the capacitance is very large, approaching 1 F; in this case the space charge is expected to be constituted from ions. In the air experiments the specimen becomes insulating, trapping the electrons as a space charge. Hall effect measurements of the carrier density and X‐ray photoelectron spectroscopy characterization of electronically conducting single crystal specimen of cubic zirconia are reported.

On the importance of excited state species in low pressure capacitively coupled plasma argon discharges

In the past three decades, first principles-based fully kinetic particle-in-cell Monte Carlo collision (PIC/MCC) simulations have been proven to be an important tool for the understanding of the physics of low pressure capacitive discharges. However, there is a long-standing issue that the plasma density determined by PIC/MCC simulations shows quantitative deviations from experimental measurements, even in argon discharges, indicating that certain physics may be missing in previous modeling of the low pressure radio frequency (rf) driven capacitive discharges. In this work, we report that the energetic electron-induced secondary electron emission (SEE) and excited state atoms play an important role in low pressure rf capacitive argon plasma discharges. The ion-induced secondary electrons are accelerated by the high sheath field to strike the opposite electrode and produce a considerable number of secondary electrons that lead to additional ionizing impacts and further increase of the plasma density. Importantly, the presence of excited state species even further enhances the plasma density via excited state neutral and resonant state photon-induced SEE on the electrode surface. The PIC/MCC simulation results show good agreement with the recent experimental measurements in the low pressure range (1–10 Pa) that is commonly used for etching in the semiconductor industry. At the highest pressure (20 Pa) and driving voltage amplitudes 250 and 350 V explored here, the plasma densities from PIC/MCC simulations considering excited state neutrals and resonant photon-induced SEE are quantitatively higher than observed in the experiments, requiring further investigation on high pressure discharges.

Streamers Initiated by a Capacitive Discharge at Air Pressure 0.2–6 Torr

Streamers Initiated by a Capacitive Discharge at Air Pressure 0.2–6 Torr

A new J.E probe for measurement of spatial profiles of power absorption in RF produced plasma.

This paper reports an indigenously developed probe for the measurement of spatial profiles of the absorbed/generated RF power density Pabs (W/m3) in RF discharges. The technique utilizes a calibrated current (J) probe based on the Rogowski coil principle and an electric field (E) probe based on capacitive coupling, both integrated into a single probe called the J.E probe. Various aspects of the probe, such as its design, fabrication, calibration, and limitations, were resolved before it was used for obtaining axial profiles of RF power absorption/generation. Also presented are the first experimental results for the absorbed power density profiles at the fundamental (13.56MHz) and harmonic (27.12MHz) along the length of a capacitively coupled discharge. The axial scans between the powered and grounded electrode were taken at different argon gas pressures (10-800mTorr) at a fixed RF power of 10W. Detailed analysis of the results shows that even for systems with large electrode gaps, i.e., plasmas with long bulk plasma regions, practically all the fundamental power is absorbed in a narrow edge region near the powered electrode, irrespective of the pressure. Absorption is high near the RF electrode since the RF fields peak in this region. Another important conclusion is that stochastic absorption of the fundamental and harmonic generation proceeds fairly efficiently in the vicinity of the powered electrode even at high pressures. It may be mentioned that the probe technique introduced here is the first of its kind, and although there is considerable scope for miniaturization, it has, nonetheless, provided some key insights into the nature of RF power absorption in capacitive discharges.

$\Delta V-\Delta I$ Plane-Based Line Faults Detection and Classification in DC Microgrid

The high fault current rise due to instantaneous capacitor discharge necessitates quick line fault detection in DC microgrids. Hence, this paper proposes a communication-less <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Delta V-\Delta I$</tex-math></inline-formula> plane-based line faults detection and classification scheme in a Low-Voltage (LV) DC microgrid using local parameters. Simultaneous threshold violations of difference of successive line current and bus voltage samples, with sum of squared currents and disagreement of instantaneous line current to its average echo, aid the scheme to identify forward and backward faults and categorize Pole-to-Ground (PG) and Pole-to-Pole (PP) faults. The proposed scheme is time-efficient as it quickly detects and classifies the worst possible close-in and line-end PG and PP High Resistance Faults (HRFs) within 0.72 ms. The proposed method's feasibility is validated in Real-Time Digital Simulator (RTDS), Numerical Relay Development Environment (NRDE), and microcontroller-based hardware in loop setup. Comparison with previous techniques and tests on two LV DC microgrids indicate that the thresholds in the proposed scheme can aid in quick fault (even line-end HRFs) detection. Also, the proposed scheme is robust to grid-connected and islanded modes of operation, ring and radial configurations, noise, and non-fault events, like load switching, varying power output of sources, and AC side and internal converter faults.

Fault identification scheme for protection and adaptive reclosing in a hybrid multi-terminal HVDC system

A fault identification scheme for protection and adaptive reclosing is proposed for a hybrid multi-terminal HVDC system to increase the reliability of fault isolation and reclosing. By analyzing the "zero passing" characteristic of current at the local end during the converter capacitor discharge stage, the fault identification scheme is proposed. The distributed parameter-based fault location equation, which incorporates fault distance and fault impedance, is developed with the injection signal and the distributed parameter model during the adaptive reclosing stage. The fault distance is determined using a trust region reflection algorithm to identify the permanent fault, and a fault identification scheme for adaptive reclosing is developed. Simulation results show that the proposed scheme is suitable for long-distance transmission lines with strong anti-fault impedance and anti-interference performance. Also, it is less affected by communication delay and DC boundary strength than existing methods.

Electrical Shock During Phone Assisted Troubleshooting of Laboratory Equipment

Researchers have the potential to be exposed to a wide variety of hazards inherent to the equipment they use and maintain. When equipment does not function as expected, researchers sometimes reach out to their vendors for assistance. Early diagnostic or troubleshooting interactions between researcher and vendor are often conducted over the telephone and can lead to researchers performing work outside of their area of expertise and exposure to unknown hazards. This type of interaction significantly contributed to an incident where during diagnostic activities a researcher accidentally contacted, and discharged, a capacitor in an X-ray diffraction instrument. While this incident did not produce a serious injury, if the capacitor discharge path had occurred hand-to-hand across the heart, a serious injury may have been possible.

A novel integrated monitoring method for MPPF capacitor and IGBT junction temperature of half‐bridge modules

AbstractCapacitance and Insulated gate bipolar transistor (IGBT) junction temperature are two critical healthy parameters for modular multilevel converters (MMC) sub‐modules (SMs) condition monitoring. This paper proposes an integrated monitoring method for capacitance degradation and IGBT junction temperature variation. By measuring multiple characteristics of the same port voltage, the capacitance and the junction temperature can be obtained simultaneously, which greatly simplifies the measurement unit required for condition evaluation and realizes the submodule‐level condition monitoring at a lower cost. The capacitance is characterized by voltage changes during capacitor discharging and the junction temperature is monitored by capacitor voltage overshoot (peak value) during IGBT turn‐off. Theoretical analysis and experimental results verify the effectiveness of the proposed method and articulated the influence of load current, SM capacitor pre‐discharge voltage, and junction temperature. Moreover, an online data‐acquisition circuit for time‐specific capacitor voltage characterization is devised.

Comprehensive Analysis and Experiment of Extreme Faults in MMC Based on IGCT

High voltage direct current voltage source converter (HVDC-VSC) technology is one of most important solutions for transmission of large-scale renewable sources. Modular multilevel converter (MMC) is one of the most popular topologies for HVDC-VSC system. The extreme faults affect the safety and reliability of MMC greatly. This paper gives comprehensive analysis and experiment of extreme faults in MMC based on integrated gate commutated thyristor (IGCT). Causes and characterization of the extreme faults are analyzed in detail. A new protection solution based on IGCT with controlled punch-through design (CP-IGCT) and fast recovery diode with high surge current capability (HS-FRD) is proposed. The surge current capability of HS-FRD is validated via experiment successfully. Theoretical calculation shows that the protection solution based on CP-IGCT and HS-FRD can help reduce the maximum fault current below 50% when the anode inductor is 0.8 μH in the extreme shoot-through fault. Test results show that the protection solution can realize the discharge of the DC capacitor below 4.5 kV in the extreme shoot-through fault. The maximum fault current in MMC based on IGCT is only about 600 kA while the maximum fault current in MMC based on insulated gate bipolar transistor (IGBT) is over 1100 kA. Explosion proof of CP-IGCT is validated during the tests, which is similar to that of the protection thyristor. However, IGBT can't guarantee the stability of the package and may cause severe safety problem. The failed CP-IGCT has the short circuit failure mode (SCFM) and can be used for bypass of the faulty MMC sub-module (MMC-SM). Via comparison, the proposed protection solution has lowest cost and complexity, as well as the highest safety.

Influence of magnetic field gradient on the capacitive argon discharge at 8 MHz and 40 MHz

A one-dimensional implicit particle-in-cell/Monte Carlo collision model is used to study the effects of magnetic field gradients on the capacitively coupled argon plasma at 8 MHz and 40 MHz. The magnetic field strength at the powered electrode is fixed at 10 G, while varies from 30 to 100 G at the grounded electrode. The simulations show that the magnetic field with variable gradient can produce controllable asymmetry in the plasma density and ion flux profiles to each electrode. Increasing the magnetic field gradient will generate a significant dc self-bias, which results in a large ion bombardment energy at the powered electrode. The magnetic field gradients have been demonstrated to be an approach to create the dc self-bias and also effectively improve the plasma density. It is also found that at a higher frequency of 40 MHz, the dc self-bias voltage decreases, due to the fact that high collision rate of electrons with background gas will disturb the cyclotron motion of electrons, so the effect of the magnetic field is weakened. As a result, the ability to independently control ion energy and flux is weakened.

Semiconductor Bridge Temperature Change Study under Different Excitation Methods and Sizes

The temperature of the semiconductor bridge increases due to the Joule heat effect in the way of capacitive discharge voltage excitation and current excitation, but the temperature distribution and the effect of different excitation methods and different sizes on the temperature change are not very clear; aiming at this problem, the temperature distribution of the semiconductor bridge after electrical energy excitation is simulated by finite element simulation. The effects of excitation mode and bridge area size on the temperature rise process of the bridge were studied by the control variable method; finally, the high-temperature area of the bridge body is only distributed in the bridge area, the temperature of the bridge body is positively correlated with electrical energy but negatively correlated with the area of the bridge area, and the current excitation method is better than the effect of voltage excitation. In addition, the conclusion is that the appropriate increase in excitation energy and the reduction of bridge size can help the temperature rise to improve the efficiency of the semiconductor bridge in practical applications.

New cascaded multilevel inverter with series connection of novel capacitor based basic units

AbstractThis research proposes a novel multilevel inverter based on a new capacitor basic unit. Four capacitors are deployed in this unit to provide both even and odd voltage levels. Two‐cell proposed cascaded multilevel inverters and developed cascaded multilevel inverters are evaluated in order to improve the number of output levels generated. Calculations are made for all associated equations after determining the value of the necessary DC voltage source. Additionally, both inverters' switching tables and capacitor charge and discharge modes are fully explained. The merits and disadvantages of the proposed topology are then assessed by contrasting the cascaded multilevel inverter under consideration with a number of widely used multilevel inverters. The key benefit of the suggested architecture is the increase in the number of output levels produced while using fewer power electronic devices and DC voltage sources overall. The proposed one‐cell cascaded inverter is then utilized to evaluate the performance of the proposed topology using the relevant equations, simulations, and experimental data. The simulation is carried out using the EMTDC/PSCAD software, and a lab prototype yields the experimental data.

A Case Study about Innovative Electromagnetic Engineering Education based on Capacitor Charging and Discharging

Capacitor charging and discharging is basic knowledge in electromagnetic education. This work proposes an innovative course teaching method of “self-learning as the mainstay, supplemented by circuit examples”, which can improve the student’s knowledge absorption and enthusiasm in the class. The simulation tool Multisim is used as an auxiliary software to strengthen the connection between theory and practice, which reviews the knowledge they have learned and helps students to develop the habit of using simulation software to assist their learning. This innovative course teaching method improves the role of students in the classroom and cultivates the ability of students to learn independently and practice automatically, lays a foundation for the design of electromagnetic theories in the future.

Electron dynamics in planar radio frequency magnetron plasmas: III. Comparison of experimental investigations of power absorption dynamics to simulation results

In magnetized capacitively coupled radio-frequency (RF) discharges operated at low pressure the influence of the magnetic flux density on discharge properties has been studied recently both by experimental investigations and in simulations. It was found that the magnetic asymmetry effect allows for a control of the DC self-bias and the ion energy distribution by tuning the magnetic field strength. In this study, we focus on experimental investigations of the electron power absorption dynamics in the presence of a magnetron-like magnetic field configuration in a low pressure capacitive RF discharge operated in argon. Phase resolved optical emission spectroscopy measurements provide insights into the electron dynamics on a nanosecond-timescale. The magnetic flux density and the neutral gas pressure are found to strongly alter these dynamics. For specific conditions energetic electrons are efficiently trapped by the magnetic field in a region close to the powered electrode, serving as the target surface. Depending on the magnetic field strength an electric field reversal is observed that leads to a further acceleration of electrons during the sheath collapse. These findings are supported by two-dimensional particle in cell simulations that yield deeper insights into the discharge dynamics.

Effects of a radial variation of surface coefficients on plasma uniformity in capacitive RF discharges

With the increasing demands toward large area plasma etching and deposition, the radial uniformity of capacitively coupled plasmas (CCPs) becomes one of the key factors that determine process performance in industrial applications. However, there is a variety of parasitic effects, e.g. electromagnetic and electrostatic edge effects, that typically lead to the formation of nonuniform radial plasma density profiles at various discharge conditions with a density peak appearing either at the center or near the edges of the electrodes. Moreover, in commercial CCPs different surface materials are in contact with the plasma at various positions as parts of boundary surfaces such as focus rings, masks, showerhead electrodes, wall and/or target materials. Via complex material specific plasma-surface interactions, the presence of such different surface materials affects plasma uniformity in a way that is typically not understood and, thus, not controlled. In this work, aided by 2d3v graphics processing unit accelerated particle-in-cell/Monte Carlo collision simulations, we study the effects of radial variations of electrode materials on the plasma via their different ion and electron induced secondary electron emission as well as electron reflection coefficients on the discharge characteristics. Based on such fundamental understanding we tailor the radial variation of boundary surface materials to improve plasma uniformity in low pressure CCPs. Such investigations are performed at different neutral gas pressures, where both center and edge high radial plasma density profiles form in the presence of radially uniform surface coefficients that resemble the presence of a single electrode material. It is demonstrated that by radially varying the surface coefficients at the grounded electrode, the radial plasma density profile can be finely adjusted and the plasma uniformity above the wafer placed at the powered electrode can be improved in both cases.

GRAIN SIZE OF ELECTROCORUNDUM SINTERED FROM DISPERSED WASTE ALUMINUM GRADE AD0E

To develop technologies for obtaining electrocorundum by spark plasma sintering of aluminum waste dispersed by electroerosion and to evaluate the effectiveness of their practical application, comprehensive the oretical and experimental studies are required. The purpose of this work was the grain size of electrocorundum sintered from dispersed aluminum waste of the AD0E brand. Electrodispersion of aluminum waste of the AD0E brand was carried out in distilled water at the original installation with a capacity of 65.5 UF discharge capacitors, a voltage at the electrodes of 200 V, a pulse repetition frequency of 200 Hz. As a result of exposure to short-term electrical discharges, particles of electroerosive powder of various sizes were formed in the water. Further, the fusion of the electroerosion charge was carried out in the spark plasma fusion system SPS 25-10 "Thermal Technology" (USA) at a pressure of 30 MPa, a temperature of 560 °C and a holding time of 3 minutes. Analysis of the microstructure of sintered electrocorundum showed that it has a fine-grained structure, without inclusions, uniform phase distribution and the absence of significant pores, cracks and discontinuities. The grain size of the studied alloys, determined using the SIMAGIS Photolab automated image analysis system and the OLYMPUS GX51 optical inverted microscope, was about 0.45 microns. The small grain size of the resulting electrocorundum is associated with the high dispersion of the initial electroerosion charge and the effect of "grain growth suppression" during spark plasma fusion due to the short working cycle time, high pressure and uniform heat distribution over the sample when exposed to pulsed electric current and the so-called "spark discharge plasma effect". The conducted studies will allow to perform resource conservation and import substitution in the production of electrocorundum from aluminum waste of the AD0E brand.