Discharge Current Waveform Research Articles

Experimental analysis of normal spark discharge voltage and current with a RC-type generator in micro-EDM

This paper focused on the experimental analysis of the discharge voltage and current waveforms in micro-EDM with a RC-type generator. A quasi-maintaining voltage assumption was proposed, and the spark gap discharge voltage was modeled as a voltage source in a first-order liner form. The discharge current and the discharge capacitor voltage under different machining conditions were calculated and compared with the real experimental waveforms of good and bad conductive workpiece, respectively. For the good conductive materials, the discharge voltage looked more like a constant maintaining voltage, and for the bad conductive materials, a low resistive ceramics composite and P-type monocrystalline silicon, the gap discharge voltage featured a relatively high average value and a relatively large variation slope rate. Based on the comparisons, the proposed discharge gap model and its simplification simulated the real discharge waveform and can be used for pulse discrimination and pulse energy prediction in micro-EDM.

Anode position influence on discharge modes of a LaB6 cathode in diode configuration

A laboratory model of a 5 A-class cathode was experimentally studied in diode configuration with a disk anode. The core of the cathode is a flat disk lanthanum hexaboride (LaB6) insert. Electron emission is achieved using a heating element in direct contact with the insert. The paper reports the characterization of the LaB6 cathode operated at xenon mass flow rates between 0.4 and 1.0 mg s−1 with discharge currents ranging from 2 A to 12 A. Apart from the operating envelope and discharge mode (spot versus plume) differentiation, the influence of anode position on cathode discharge mode was studied. For this purpose, the cathode was operated at 4 A and 0.6 mg s−1 and at 10 A and 0.6 mg s−1, while the cathode-anode gap was increased from 20 mm to 70 mm. Both electrical and plasma parameters were collected and analyzed in order to highlight the main changes in cathode discharge when the cathode-anode gap was increased. Particular attention was paid to the identification of the discharge mode and mode transition based on spectral analysis of discharge current waveforms. It was demonstrated that an increase in the cathode-anode gap induces the discharge mode transition from spot mode, corresponding to lower gap values, to plume mode, corresponding to higher gap values. Changes in plasma property were also noticed, the cathode-anode gap increase inducing lower plasma density and higher electron temperature in the cathode plume.

Combined influence of the impurities and radial electric field on dielectric barrier discharges in atmospheric helium

The combined influence of nitrogen impurities and radial electric field on dielectric barrier discharges in atmospheric helium is investigated using a two-dimensional (2D) fluid simulation. Discharge current waveforms, 2D electron densities, distributions of surface charge, and radial and axial components of the electric field at the electrode edge are calculated for different impurity levels varying from 0 to 30 ppm. It is observed that the discharge presents the characteristic of a column in pure helium, and it gradually becomes a relatively uniform glow discharge as the impurity level is increased to 20 ppm; for the higher impurity level of 30 ppm, the discharge adopts a concentric-ring pattern discharge. Our result shows that the radial electric field at the electrode edge is approximately 0.6–1.2 kV/cm during the discharge. This radial electric field has an effect that leads to a non-uniform discharge. After doping a low level of impurities, the Penning ionizations caused by the impurities can inhibit this effect and lead to a uniform discharge. However, for a higher impurity level (30 ppm), the effect of the radial electric field again becomes dominant, which easily leads to a non-uniform discharge. These results provide a new perspective on obtaining a uniform glow discharge when both influences of the impurity and radial electric field are taken into account.

Examination of a 5 A-class cathode with a LaB6 flat disk emitter in the 2 A–20 A current range

Cathodes are electron sources used for gas ionization and ion beam neutralization in Hall thrusters. A laboratory model of a 5 A-class cathode has been experimentally studied in the so-called diode configuration with a flat metal anode. The cathode design is based on the direct heating of a flat disk lanthanum hexaboride (LaB6) insert to emit electrons. The paper presents the characterization of the LaB6 cathode operated at xenon mass flow rates between 0.2 and 0.6 mg.s-1 with discharge currents ranging from 2 A to 19 A. Electrical parameters and temperature of several parts, including the LaB6 insert, were collected and analyzed in order to investigate the possibility of operating the cathode in an extended range of discharge current with respect to its nominal condition (5 A at 0.4 mg.s-1). Particular attention was paid to the identification of the discharge mode (spot versus plume) through spectral analysis of discharge current waveforms. Temperature measurements performed with thermocouples reveal that the LaB6 insert is moderately heated during the cathode operation (about 1600 °C at 19 A), except for the lowest mass flow rate.

A Method of Generating Timing for a Given Target Current Waveform in Electromagnetic Launch Technology

Under the condition of given charging voltage, by adjusting the timing of the power supply trigger, the electromagnetic emission can produce different discharge current waveforms, and then produce different initial velocity. This paper mainly uses the characteristics of the discharge current in a single power module in electromagnetic launch, by specifying the rising time and the maximum value of the total discharge current; a multipopulation genetic algorithm is used to obtain the optimal trigger timing, and the speed control of electromagnetic launch can be achieved. The specific implementation process of algorithm are as follows: the rising time and the peak value of the expected current are set as the objective function, the timing is set as a variable, and the multiple time series are binary coded to get multiple individuals, and then calculate the degree of survival by crossover, mutation, and heredity among individuals, that is, to judge whether the rising time and the maximum value of the discharge current can reach the expected goal, and to keep the survival of the genes to the next generation and screen repeatedly, and then to select the optimal control timing. The optimal control strategy can be obtained by adjusting the parameters such as genetic algebra and mutation rate. The experimental results show that this method produces the optimal power supply timing, and through the application of digital signal processing control system, the expected discharge current waveform can be obtained in the experiment of electromagnetic launch, which also lay a good foundation for the rate control of electromagnetic launch.

Effect of piecewise linear current waveforms on surge arrester residual voltage

The object of research is the magnitude and shape of the residual voltage that arises between the terminals of the surge arrester models when they are subjected to current and voltage pulses of a piecewise linear waveform. One of the most problematic places in this problem is the approximation of current switching pulses with a short duration and also steep front current pulses. With the help of the well-known double-exponential pulse, it is impossible to describe a pulse whose time-to-half duration is twice bigger the time-to-crest duration . At the same time, current pulses in the manufacturer catalogs of the surge arresters have exactly this ratio (1/2, 30/60 or 45/90 ). With the help of piecewise linear approximation, it is possible, bypassing complex calculations, to describe pulses of almost any shape, including switching current pulses and steep front current pulses. By means of evaluation version of Micro-Cap 11 circuit simulator the residual voltage on the surge arrester terminals is computed during a passage of the current pulses with different amplitude and wave shape. Current sources used in this research represent sources of simplified triangular (piecewise linear) current pulses. It is considered that the current wave rises linearly to its maximum value, and then also decays linearly to half its amplitude value. Comparison of the results suggests that proposed simplification of discharge current waveform has no significant effect on relative calculation error of residual voltage on surge arrester. If it is necessary to estimate only maximum value of residual voltage on surge arrester, it is possible to use piecewise linear approximation of switching and lightning currents with any amplitude and shape without loss of accuracy.

Measurement and modeling of plasma parameters in reactive high-power impulse magnetron sputtering of Ti in Ar/O2 mixtures

A reactive high-power impulse magnetron sputtering (HiPIMS) process using a titanium target in a mixture of Ar/O2 has been investigated for different modes of operation including pure argon, metallic, transition, and compound mode. The trends and changes in the plasma density ne and the effective electron temperature Teff, have been measured by the time-resolved Langmuir probe technique. The same experimental process conditions have also been studied using a recently developed reactive ionization region model (R-IRM), making it possible to compare the acquired experimental results with the model results. It was found that trends in the plasma density and mean electron energy as measured by the Langmuir probe are in good agreement with the results obtained from the R-IRM model for different pulse discharge current densities. The effective electron temperature generally increases with an increasing oxygen flow rate. It is likely due to a reduction of sputtered Ti, due to compound formation on the target, which forces the discharge to increase the electron energy to increase the ionization rate of the process gas (Ar/O2) to maintain a high HiPIMS discharge current. Small variations in the plasma density were detected between the middle part of the plasma pulse as compared to the end of the plasma pulse, when transitioning from the metal mode to the poisoned mode. It is found that the time-evolution of the electron density is rather well correlated with the discharge current waveform. On the other hand, the mean electron energy did not change significantly between the middle and the end of the plasma pulse. For the lower pulse discharge current, both the model and experimental data have shown a slight increase in the plasma density with increasing O2 mass flow rate.

Comparison between the 1st and 3rd order mode temporal characteristics of two-sided multipactor discharge in cavity

For investigating the influence of high order two-sided multipactor discharge on the accelerator field-building process, the temporal characteristics of the 3rd order two-sided multipactor discharge in oxygenfree copper cavity are studied numerically. The particle-in-cell and Monte-Carlo methods are used in the simulation and the characteristics of the 1st order mode are also studied for comparison. The numerical results can be concluded as follows. In the multipactor discharge evolution, the electron number, discharge current, deposited and discharge power increase exponentially and tend to be saturated. At the saturation stage of the 3rd order mode, the values of electron number, discharge current, deposited and discharge power are lower than at the saturation stage of the 1st order mode. Meanwhile, the rising time of waveform in the 3rd order mode is longer than in the 1st order mode. There is a time-delay phenomenon in the waveform of discharge current, which results in a partial charging process in multipactor discharge. The average value of the discharge power is equal to the average deposited power. The value of discharge power in the 3rd order mode is about 1% of that in the 1st order mode. Therefore, the 3rd order mode is not significant in accelerator field-building process compared with the 1st order mode. The characteristic of the 1st order two-sided multipactor discharge is the accelerated motion of single electron beam, while that of the 3rd order is the complex accelerated-decelerated-accelerated motion of multi-electron beams. When the multipactor discharge enters into the saturation stage, the space charge effect of the 3rd order mode is not stronger than that of 1st order mode.

反応性大電力パルススパッタリング（R-HiPIMS）における遷移領域制御技術

This is to review a novel approach stabilizing reactive mode at transition regime in reactive high-power impulse magnetron sputtering (R-HiPIMS). The proposed method is based on a real-time monitoring of peak discharge current. To stabilize the process conditions at a given set point, a feedback control system, which automatically regulates the pulse frequency, and thereby the average sputtering power, was implemented to maintain a constant maximum discharge current. As a representative result, the variation of the pulse current waveforms over a wide range of reactive gas flows and pulse frequencies during a R-HiPIMS of Hf in an Ar-N2 atmosphere illustrates that the discharge current waveform is an excellent indicator of the process conditions. Applicability of the proposed method was successfully demonstrated.

Discharge On Solar Array Coupon By Debris Impact

Recently, a risk of impact between spacecraft and debris is increasing. An impact on solar arrays can cause electrical damage such as sustained arc as well as mechanical damage. If sustained arc occurs, electricity does not flow to the payload and the power generation capacity is reduced. In this study, discharge due to debris impact is reproduced by hypervelocity impact test, and plasma and discharge currents are measured. As a result, high density plasma and discharge due to impact were confirmed. Moreover, it became clear that some difference appears in the discharge current waveform depending on the impact point.

The OES Diagnosis in Removal of HCHO by the Uniform Bipolar Nanosecond-Pulsed DBD Using Wire-Cylinder Electrode Configuration in Atmospheric N2

In this paper, the uniform bipolar nanosecondpulsed dielectric barrier discharge (NPDBD) with 15-ns rising time generating in a wire-cylinder reactor is employed to remove the gaseous formaldehyde in atmospheric pressure N 2 . The image, the waveforms of pulse voltage and discharge current, the optical emission spectra of the discharges, and the removal rate of formaldehyde are recorded and calculated, respectively. It is found that the emission intensity of OH (A 2 Σ → X 2 Π, 0-0) rises when increasing the input power density (PD). Furthermore, with the increase of input PD and the emission intensity of OH (A 2 Σ → X 2 Π, 0-0), the removal rate of formaldehyde rises correspondingly. The results also indicate that when the O 2 concentration rises within 0%-5%, the removal rate of formaldehyde increases, however, when the O 2 concentration rises within 5%-20%, the formaldehyde removal rate decreases correspondingly. In addition, at the same conditions, the DBD synergistically removing formaldehyde with Al 2 O 3 and TiO 2 could increase the removal rate by 10%-30% compared with the discharge only.

An ionization region model of the reactive Ar/O2 high power impulse magnetron sputtering discharge

A new reactive ionization region model (R-IRM) is developed to describe the reactive Ar/O2 high power impulse magnetron sputtering (HiPIMS) discharge with a titanium target. It is then applied to study the temporal behavior of the discharge plasma parameters such as electron density, the neutral and ion composition, the ionization fraction of the sputtered vapor, the oxygen dissociation fraction, and the composition of the discharge current. We study and compare the discharge properties when the discharge is operated in the two well established operating modes, the metal mode and the poisoned mode. Experimentally, it is found that in the metal mode the discharge current waveform displays a typical non-reactive evolution, while in the poisoned mode the discharge current waveform becomes distinctly triangular and the current increases significantly. Using the R-IRM we explore the current increase and find that when the discharge is operated in the metal mode Ar+ and Ti+ -ions contribute most significantly (roughly equal amounts) to the discharge current while in the poisoned mode the Ar+ -ions contribute most significantly to the discharge current and the contribution of O+ -ions, Ti+ -ions, and secondary electron emission is much smaller. Furthermore, we find that recycling of atoms coming from the target, that are subsequently ionized, is required for the current generation in both modes of operation. From the R-IRM results it is found that in the metal mode self-sputter recycling dominates and in the poisoned mode working gas recycling dominates. We also show that working gas recycling can lead to very high discharge currents but never to a runaway. It is concluded that the dominating type of recycling determines the discharge current waveform.

Investigation of electromagnetic interference effects by ESD simulator on test parameters of tunneling magnetic recording heads

Electrostatic discharge (ESD) has been an important issue in the manufacturing processes of hard disk drive. It can also generate electromagnetic interference (EMI) which could possibly damage magnetic recording heads. The aims of this work are to measure the EMI from ESD events and to examine the effects of EMI on the heads. The discharge current and the EMI generated by an ESD simulator were experimentally measured. Also, the EMI was applied to the heads to determine if this can cause changes of head parameters. Our results show that the discharge current waveform is consistent with the theoretical waveform of the IEC ESD standard. Additionally, we found that the EMI applied due to ESD at distances greater than 2cm does not have any significant effect on the head parameters. Hence, further detailed experiments are proposed to evaluate the EMI effects on recording head parameters in order to improve the measurement methodologies to prevent the degradation of the heads performance and to increase the robustness of the heads.

Research on soft x-rays in high-current plasma-focus discharges and estimation of plasma electron temperature

The paper presents results of experimental studies of dense and high-temperature plasmas, which were produced by pulsed high-current discharges within a modernised PF-1000U facility operated at different initial gas conditions, and supplied from a condenser bank which delivered energy of about 350 kJ. The investigated discharges were performed at the initial deuterium filling under pressure of 1.6–2.0 hPa, with or without an additional puffing of pure deuterium (1 cm3, under pressure 0.15 MPa, at instants 1.5–2 ms before the main discharge initiation). For a comparison discharges were also performed at the initial neon filling under pressure of 1.1–1.3 hPa, with or without the addition of deuterium puffing. The recorded discharge current waveforms, laser interferometric images, signals of hard x-rays and fusion neutrons, as well as time-integrated x-ray pinhole images and time-resolved x-ray signals were compared. From a ratio of the x-ray signals recorded behind beryllium filters of different thickness there were estimated values of a plasma electron temperature (Te) in a region at the electrode outlets. For pure deuterium discharges an averaged Te value amounted to 150–170 eV, while for neon discharges with the deuterium puffing it reached 330–880 eV (with accuracy of ±20%).

Direct synthesis of AlN nano powder by dielectric barrier discharge plasma assisted high-energy ball milling

In this paper, a method of direct synthesis of aluminum nitride nano powder by dielectric barrier discharge assisted mechanical ball milling is presented. The mixtures of Al and LiOH·H2O powders, as samples, treated by dielectric barrier discharge assisted mechanical ball milling are characterized by X-ray diffraction and scanning electron microscope. It is shown that AlN nano powders are generated in 1 h milling time and the powders present a loose lamellar structure in the irregular distribution. For a long milling time (6 h), the crystallite size decreases with the milling time increasing and reduces to about 40 nm. Also, to study the mechanism of direct synthesis of aluminum nitride assisted by plasma, the waveforms of discharge voltage and current, and optical emission spectra of active species are recorded. The main physiochemical processes of production of active species in DBD are discussed.

Amplitude−temporal characteristics of a supershort avalanche electron beam generated during subnanosecond breakdown in air and nitrogen

The amplitude−temporal characteristics of a supershort avalanche electron beam (SAEB) with an amplitude of up to 100 A, as well as of the breakdown voltage and discharge current, are studied experimentally with a picosecond time resolution. The waveforms of discharge and SAEB currents are synchronized with those of the voltage pulses. It is shown that the amplitude−temporal characteristics of the SAEB depend on the gap length and the designs of the gas diode and cathode. The mechanism for the generation of runaway electron beams in atmospheric-pressure gases is analyzed on the basis of the obtained experimental data.

Spectroscopic and electrical characters of SBD plasma excited by bipolar nanosecond pulse in atmospheric air

In this paper, an atmospheric surface barrier discharge (SBD) generated by annular electrodes in quartz tube is presented through employing bipolar nanosecond pulse voltage in air. The discharge images, waveforms of pulse voltage and discharge current, and optical emission spectra emitted from the discharges are recorded and calculated. A spectra simulation method is developed to separate the overlap of the secondary diffraction spectra which are produced by grating in monochromator, and N2 (B3Πg→A3Σu+) and O (3p5P→3s5S2o) are extracted. The effects of pulse voltage and discharge power on the emission intensities of OH (A2Σ+→X2Пi), N2+ (B2Σu+→X2Σg+), N2 (C3Πu→B3Πg), N2 (B3Πg→A3Σu+), and O (3p5P→3s5S2o) are investigated. It is found that increasing the pulse peak voltage can lead to an easier formation of N2+ (B2Σu+) than that of N2 (C3Πu). Additionally, vibrational and rotational temperatures of the plasma are determined by comparing the experimental and simulated spectra of N2+ (B2Σu+→X2Σg+), and the results show that the vibrational and rotational temperatures are 3250±20K and 350±5K under the pulse peak voltage of 28kV, respectively.

Energy balance in nanosecond pulse discharges in nitrogen and air

Kinetic modeling is used to analyze energy partition and energy transfer in nanosecond pulse discharges sustained between two spherical electrodes in nitrogen and air. The modeling predictions are compared with previous time-resolved temperature and vibrational population measurements by picosecond broadband coherent anti-Stokes Raman spectroscopy (CARS) and phase-locked Schlieren imaging. The model shows good agreement with experimental data, reproducing experimental discharge current pulse waveforms, as well as dominant processes of energy transfer in the discharge and the afterglow. Specifically, the results demonstrate that the temperature rise in the plasma occurs in two stages, (i) ‘rapid’ heating on sub-acoustic time scale, dominated by energy pooling processes, N2(B3Πg) and N(2P,2D) quenching (in nitrogen), and by quenching of excited electronic states of N2 molecules by O2 (in air), and (ii) ‘slow’ heating due to N2 vibrational relaxation by O atoms (in air), nearly completely missing in nitrogen. Comparison of the model predictions with N2 vibrational level populations confirms that the N2 vibrational temperature rises after the discharge pulse is caused by the ‘downward’ vibrational–vibrational exchange depopulating higher vibrational levels and populating vibrational level v = 1. The model reproduces temporal dynamics of vibrational level populations and temperature in the discharge and the afterglow, indicating that energy partition among different modes (vibrational, electronic, dissociation, and ionization) is predicted accurately. At the present conditions, energy fraction coupled to the positive column of the discharge filament in air is approximately 50%, with the rest coupled to the cathode layer. Nearly 10% of the total pulse energy is spent on O atom generation, and about 10% is thermalized on a sub-acoustic time scale, producing a strong compression wave in the radial direction. The experimental wave speed is considerably higher compared to the model predictions, by approximately 30%. The reason for this difference may be due to interaction between the cylindrical and spherical compression waves generated in the discharge filament and in the cathode layer, respectively.

Process stabilization by peak current regulation in reactive high-power impulse magnetron sputtering of hafnium nitride

A simple and cost effective approach to stabilize the sputtering process in the transition zone during reactive high-power impulse magnetron sputtering (HiPIMS) is proposed. The method is based on real-time monitoring and control of the discharge current waveforms. To stabilize the process conditions at a given set point, a feedback control system was implemented that automatically regulates the pulse frequency, and thereby the average sputtering power, to maintain a constant maximum discharge current. In the present study, the variation of the pulse current waveforms over a wide range of reactive gas flows and pulse frequencies during a reactive HiPIMS process of Hf-N in an Ar–N2 atmosphere illustrates that the discharge current waveform is a an excellent indicator of the process conditions. Activating the reactive HiPIMS peak current regulation, stable process conditions were maintained when varying the N2 flow from 2.1 to 3.5 sccm by an automatic adjustment of the pulse frequency from 600 Hz to 1150 Hz and consequently an increase of the average power from 110 to 270 W. Hf–N films deposited using peak current regulation exhibited a stable stoichiometry, a nearly constant power-normalized deposition rate, and a polycrystalline cubic phase Hf-N with (1 1 1)-preferred orientation over the entire reactive gas flow range investigated. The physical reasons for the change in the current pulse waveform for different process conditions are discussed in some detail.

Development of a Pulse Generator for Rough Cutting of Oil-based Micro Wire-EDM

This paper aims to develop a specific pulse generator for rough cutting of oil-based micro wire electrical discharge machining (wire-EDM). A two-stage current-limiting resistance power supply was presented to suppress thermal damage on the machined surface of polycrystalline diamond (PCD) while achieving stable machining by supplying high open voltage and low discharge current pulse waveforms. Tests revealed that the two-stage resistance power supply could achieve lower thermal damaged layer, better surface quality and surface finish than a conventional pulsed power supply since the former could provide smaller peak current and shorter discharge duration than the later. Experimental results demonstrate that boron-doped polycrystalline composite diamond (BD-PCD) is superior to polycrystalline diamond in the smoothness of cutting edge, surface quality and surface roughness since the former has lower specific resistance and thermal conductivity than the later. This study has indicated that the proposed power supply could enable a prototype micro wire-EDM machine to achieve a surface finish as low as 0.45μm Ra and a thermal damaged layer as small as 6μm on the machined surface of BD-PCD after one rough machining operation.