Current Pulse Duration Research Articles

Effect of Peak Current and Pulse On Time on the Coating Layer Thickness using Electrical Discharge Coating

The present study focused on the surface modification of aluminum 6061 by using electrical discharge coating (EDC) with powder suspension. The effects of peak current (Ip) and pulse on time (Ton) on the coating layer thickness were investigated. This study used Tungsten powder as an additive and mixed it with the kerosene oil and surfactant Span 83. The results indicated that peak current and pulse on-time significantly affected the coating layer thickness. The thinnest coating layer was observed at 3A, 150 µs, while the thickest coating layer with an average value of 17.239 µm was obtained at parameter 4A and 250 µs. In conclusion, the high value of peak current and longer pulse duration on time increased the thickness of the coating layer.

Measurement of the duration of runaway current pulses using measuring equipment with bandwidths up to 50 GHz

The duration of current pulses of runaway electrons generated during the formation of a nanosecond discharge in air in a sharply inhomogeneous electric field was measured using measuring equipment with a bandwidth of 50 GHz. The influence of the gas pressure and the shape of a cathode on the duration of the RE current pulses is investigated. Current pulses with full width at half maximum of 16–28 ps were recorded, depending on the conditions.

Energy density distribution of a modulated electron beam in a source with a plasma cathode based on a low pressure arc

The article presents the results of studies devoted to the study of the energy density distribution in the amplitude-modulated regime of electron beam generation. It is shown that in the first ≈ 50 μs of the duration of the beam current pulse, its spatial rearrangement occurs, due to the development of the arc discharge current. Thus, the rearrangement of the arc current, which develops from the axis of the system, leads to an axial diving of the emission current density and the beam current density on the target. With the development of the arc current, the energy density on the target on the axis of the system decreases and after ≈ 50 μs takes on a steady-state value, which can change only as a result of a change in the conditions for generating an electron beam or the transition to a modulated regime of electron beam generation. It has been experimentally shown using calorimetric measurements that the shape of the electron beam current pulse with its amplitude modulation with a pulse duration of more than 100 μs has little effect on the distribution of the beam energy density in the target region.

Investigation of Annular Explosive-Emission Cathodes of the Conductor–Insulator Structure

Research is devoted to investigation of properties of pulsed explosive emission cathodes for X-ray tubes. Three types of annular explosive emission cathodes were studied: metal ceramic with slits (of a comb-shaped kind), ring metal ceramic, and carbon ceramic. A pulsed high-voltage generator used in experiments is characterized with the following parameters: voltage pulse full-width at half-maximum is about 20 ns, pulse voltage amplitude is up to 150 kV, and pulse repetition rate is up to 200 Hz. The installation makes it possible to study demountable models of pulsed X-ray tubes of different designs. Current and voltage waveforms corresponding to different operation modes and rates of rise of X-ray tube anode voltage were analyzed. The obtained characteristics of explosive cathodes depend on the cathode’s material, the shape, and the supply voltage of the primary energy storage. The current pulse duration for the ring carbon-ceramic cathode is considerably lower than that for the other cathodes, although it generates a higher radiation dose rate.

Electrodeposition of multilayer NiW alloy coating for improved anticorrosion performance

The attractiveness of electroplating linked to cathodic current density (CD) has tried to exploit here to the development of coatings of high corrosion resistance. Multilayer NiW alloy coatings of better anticorrosion performance were electrodeposited from a tartrate bath by periodic pulsing of CD between two values, during the process of deposition. The multilayer coatings of different configurations, in terms of composition and thickness of individual layers were developed by proper modulation of amplitude and duration of the square current pulse, respectively. The deposition conditions were optimized for best performance of the coatings against corrosion. Our experimental study revealed that under optimal condition, multilayer NiW coating having (NiW)1.0/3.0/120 configuration is almost six times more corrosion resistant than its monolayer coating, deposited from same bath for same duration. The reason for improved corrosion performance in multilayer NiW alloy coating was explained in the light of effect of larger interfaces affected due to layered deposition and confirmed by scanning electron microscopy analysis, energy dispersive spectroscopy and X-ray diffraction study. The mechanism of corrosion responsible for its better performance, in relation to its monolayer coating is given, and results are discussed.

Influence of Lateral Temperature Gradients on the Failure Modes at Power Cycling

In this article, the influence of the insulated gate bipolar transistor (IGBT) chip-near temperature gradient on the failure modes in the power cycling test is investigated with the finite element (FE) simulation and experiment. Two important aspects influencing the temperature gradient are studied: one is the load current pulse duration t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</sub> from the testing aspect; the other is the area ratio between the chip region and direct copper bonding (DCB) top side copper determined by the device package layout. The IGBT chip-near temperature gradient caused by these two factors is first investigated using the FE thermal simulation. It was found that by varying t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</sub> and the area ratio, a significant influence on the temperature gradient of the chip and the average temperature of the solder layer can be achieved, which could lead to different dominating failure modes under the same power cycling test conditions. Furthermore, experiments considering those two factors were designed and performed to verify the inference derived from the simulation. The results show that the failure mode indeed can be shifted because of the changed temperature gradient.

In-situ post-assembly magnetization of large rare-earth permanent-magnet machines

Auxiliary permanent magnet generator (PMG) represents an essential part of the large steam generator excitation system. It provides energy for main exciter (rated power 1600 kVA) which supplies excitation for steam generator (rated power 300 MW). While auxiliary PMG is out of service, its permanent magnets are demagnetized. In order to put auxiliary PMG into operation, magnetization of permanent magnet poles is needed. This paper presents a method for in-situ post-assembly magnetization (PAM) of rare-earth PMG by applying DC current to all three phases of its stator windings. Magnetization process is performed in the power plant, and all equipment used in experiment is readily accessible to plant maintenance personnel (transformer, rectifier, circuit breaker, cables, etc.). The main advantage of this technique is that magnetization is performed without demounting the PMG off the main rotor shaft, and as a result, generator overhaul duration is significantly reduced, and magnetization costs are decreased. Throughout the procedure, magnetizing currents, voltage on PMG stator terminals and magnetic induction (flux density) are measured. Prior to magnetization, DC currents, current pulse duration and rotor position are calculated. Based on the calculated values, the temperature rise in stator windings has to be checked. The technique is validated through case study in the real power plant at the PMG, rated power 35 kVA, which was successfully magnetized. Subsequently, the simulation is performed, in order to determine the unknown parameters of the equipment used.

High rising speed discharge current pulse for EDM generated by inductive boosting voltage circuit

This paper introduces a newly developed EDM pulse generator whose high open voltage for discharge is generated by induced electromotive force using a power supply of only 5 V. The pulse generator can generate short duration and high discharge current pulses. The rising time of discharge current pulses to 5 A can be made shorter than 50 ns with a pulse duration of 200 ns or shorter. The results proved that such discharge current pulse shapes increase material removal volume per discharge and that the higher boosting open voltage facilitates the machining of high resistivity materials.

Pulsed X-ray source with the pulse duration of 50 ns and the peak power of 70 MW for capturing moving objects.

Traditionally, X-ray systems for capturing moving objects consist of a continuous X-ray source and a detector that operates at a predetermined frame rate. This study investigates the possibility of using pulsed X-ray source with an inductive energy storage device and a semiconductor opening switch for shooting moving objects. The study uses a high-voltage pulse generator that has the following parameters namely, the pulse voltage amplitude up to 320 kV, the pulse current up to 240 A, the current pulse duration of about 50 ns, and the pulse repetition rate up to 2 kHz. The duration and intensity of glow for standard CsI:Tl and Gd2O2S:Tb X-ray phosphors after their irradiation with X-ray flashes of about 50 ns duration are investigated. After X-ray radiation is converted into light, the signal is recorded using semiconductor detectors. We acquired several images of an object moving at a speed of about 20 m/s. A semiconductor detector with phosphor, which operates in the mode of continuous signal accumulation, is used. When using the pulsed X-ray source and phosphors with a short afterglow, the individual frames can be obtained at the pulse repetition rate of several kilohertz, and the detector does not contain the residual luminescence from the previous frame by the arrival of the next frame. The X-ray source shows good pulse-to-pulse reproducibility of X-rays, and can be used to capture objects in motion at a frame rate of several kHz.

Формирование двух импульсов тока пучка убегающих электронов

The conditions for the formation of two current pulses of runaway electron beams during the breakdown of a point-to-plane and tube-to-plane gaps in high-pressure air, nitrogen, and helium are studied. It has been shown experimentally that, depending on a pressure and kind of gas, a rise time of voltage pulse with an amplitude of tens of kilovolts, three modes of generation of runaway electron beams are observed. In the first mode, a single current pulse of runaway electron beam is observed at the maximum voltage across the gap, when a streamer appears in the vicinity of the pointed electrode (cathode). Its duration is ≈100 ps. In the second mode, two current pulses of runaway electron beams are observed at a lower pressure. The first pulse is generated as in the first mode. The second pulse is generated after the gap is bridged by the streamer (the first ionization wave). The electron energy in the second pulse is significantly less than in the first one, but the duration and amplitude of second current pulse under optimal conditions are greater. The third mode is implemented at lower pressures than in the second one. The generation of runaway electrons continues after the first pulse without a pause in the quasi-stationary stage. The total current pulse duration is hundreds of picoseconds.

Simulation of Magnetic Electron Cut-off in a Vacuum Switch with an Anode in the Form of an Inductor

The simulation of the process of magnetic cut-off of electrons in a vacuum switch (VC) with an anode in the form of an inductor was performed. Calculations were performed according to the physico-topological model of physical processes in the vacuum switch, which took into account current distribution along electrodes, the trajectory of electrons emitted by the cathode and the conditions of current interruption in VC. Determination of current distribution along the anode, as well as configurations of electric and magnetic fields were performed according to a mathematical model based on Maxwell's equations for vacuum and conductive medium of the anode and boundary conditions adapted to the shape of the elements of the VC. Material equations were also used for certainty. The initial kinetic energy of electrons emitted from the cathode was set equal to zero. Their direction of departure from the cathode surface was determined by the direction of the lines of force of the electric field near the surface. Electron emission was given by the uniform distribution of emission points on the surface of the cathode tip. The calculation of the structure of the magnetic field was performed taking into account the secondary magnetic fields and the current distribution over the cross section of the anode inductor, which is caused by the skin effect.It is established that a decrease in the step of the inductor turns and an increase in the amplitude of the current pulse in it lead to an increase in the magnetic field strength in the cathode region, which improves the focusing of electrons. At anode-cathode voltage of 10 kV, the step of the inductor of 6 mm and the amplitude of the anode inductor current pulse of 900 A, all the electrons emitted from the cathode are focused outside the anode.The influence of design parameters on the electron cut-off efficiency is determined. For the investigated design, the optimal cathode-anode distance was 12 mm with a step between the turns of the inductor of 6 mm. The results of calculations showed that reducing the distance between the turns of the inductor increases the efficiency of electron cut-off, which confirms the physical adequacy of the mathematical model and the correctness of the calculations. Calculations also showed that at a cathode-anode distance below 12 mm, the focusing of electrons deteriorates.In the proposed design of the VC with the anode inductor in the form of three turns, the complete cut-off of electrons, i.e. the time of flight of electrons through the electrode system, at anode-cathode voltage of 10 kV, occurred by less than 1 ns at an inductor current pulse of 900 A. The inductor current pulse duration was 5 μs had the form of the half-sinusoid arc. The used method of modeling allows to establish in what part of the inductor pulse the full cut-off of electrons is provided.The obtained results can be used in the development of the VC with interruption of the current of vacuum-arc discharge.

Hybrid electronically addressable random fiber laser.

We report here a novel architecture for a random fiber laser exploiting the combination of a semiconductor optical amplifier (SOA) and an erbium doped fiber (EDF). The EDF was optically biased by a continuous wave pump laser, whereas the SOA was arranged in a fiber loop-mirror and driven by nanosecond duration current pulses. Laser pulses were obtained by synchronizing the SOA driver to the returning amplified Rayleigh back-scattered light from a selected short section of the EDF. By tuning the SOA pulse rate, random lasing was achieved by addressing selected meter-long sections of the 81-m long EDF, which was open-ended. Laser oscillation can be potentially obtained with SOA modulation frequencies from several kHz to the MHz regime. We discuss the mechanism leading to the hybrid random laser emission, connecting with phase sensitive optical time domain reflectometry and envision potential applications of this electronically addressable random laser.

Pulse power supply of diode-pumped solid-state lasers

Recently, solid-state pumped semiconductor lasers have become increasingly widespread. Lasers of this type have several advantages over solid-state lasers with lamp pumping. First of all, this is high efficiency, long service life, small dimensions and weight. The use of semiconductor laser diodes for pumping solid-state active media imposes a number of rather stringent requirements on the power sources of laser diodes. The power source should provide rectangular current pulses with a flat top, a steep leading edge of the pulses and the absence of reverse current surges at the trailing edge.A pulsed power source for a diode pump system of a ytterbium-erbium laser was developed, manufactured and studied. In this source, the control unit provides functions for protecting the load in emergency conditions, controlling the charge of the storage capacitors to the required voltage and generating current pulses to power the laser diode line. The current is regulated by a field effect transistor operating in a linear mode. The load is included in the source circuit of the field-effect transistor, and the reference signal is generated by the DAC of the microcontroller. Such an approach made it possible to create a relatively simple, reliable and small-sized laser power source with a wide range of adjustment of the duration and amplitude of current pulses. This makes it possible to select the optimal operating mode depending on the characteristics of the active medium of the laser. Particular attention is paid to solving the problems of protecting expensive rulers of laser diodes from failure. The developed source can be used to pump other solid-state lasers with shorter lifetimes of the upper laser level than erbium.

Effects of Voltage and Current Waveforms on Pulse Discharge Energy Transfer to Underwater Shock Waves for Medical Applications

The effects of voltage and current pulse durations of underwater discharge on shock wave generation are reported. In this article, underwater discharges were generated by using a magnetic pulse compression (MPC) circuit. The compression number of the MPC circuit was varied from two compressions to one and no compression; also the capacitance of an output peaking capacitor connected in parallel to discharge electrodes (load) was varied from 10 to 6 and 2 nF. As a result, electric pulses with different rise time/duration and variable peak voltages and currents were obtained and applied to generate shock waves. The shock waves were quantitatively measured with optical principles using a fiber optic probe hydrophone (FOPH) pressure transducer. By reflecting the generated shock waves from a reflector, uniform shock waves were produced, which made it possible to accurately measure the shock waves. The maximum pressure of the generated shock wave after the reflection was in the range of 40 MPa. The energies of the output shock waves were calculated from the pressure histories and the electrical to shock wave energy conversion efficiency was calculated from the electrical energy used to generate the shock waves. The results indicated that the rise time of voltage and current significantly affects the electrical energy that can be delivered to generate the shock waves. For the range of the electric pulse durations of 100 to 500 ns of this article, the shock waves pressures were independent of the pulse duration for the same input energy consumed during the rise and full width at half maximum times of the current. The method presented here gives possibility to select the shock wave profile, which would be crucial for successful medial applications.

Thermal and Structural Analysis of Outboard Divertor Row 1&amp;2 Tiles for NSTX-U

The National Spherical Torus eXperiment (NSTX) has recently undergone a major upgrade and recovery to NSTX-U at Princeton Plasma Physics Laboratory (PPPL). With the double toroidal field, plasma current, and longer pulse duration, the original outboard divertor row 1&2 (OBD12) tiles could not meet the higher thermal requirements of NSTX-U project. The OBD tiles are used to protect the OBDs from the plasma and also protect the plasma from impurities generated by that surface. The transient thermal models with different faceted fishscaling factors and static structural models with halo and eddy loads have been analyzed to check the design qualification of new OBD12 tiles. The simplified rod and key submodels have been developed to optimize design elements and to resolve the over-stress issues with the rod and key contact areas. The redesign of OBD12 tiles can meet the system requirements on the high-flux plasma-facing components (PFCs).

Electromechanical installation based on a powerful current pulse generator for materials treatment

The electromechanical device containing an electromagnetic solenoid with a piston operating in the reciprocating motion mode was developed. Technologies with similar operating modes are widely used in various industries. Economical generator of powerful unipolar current pulses with unique systems is used in the electromechanical device. It allows its main parameters to be regulated in a wide range and with high speed: pulse reproduction frequency and amplitude. The principle of generator operation is based on the periodic discharge of pre-charged capacitors to a low-resistance active-inductive load. The parameters of the mechanical and electrical parts of the electromechanical device are calculated: the initial coordinate of the piston, the magnetomotive force resulting from a change in the inductance L(x), the spring elasticity, the resistance force of the piston proportional to its speed, amplitude, duration and frequency of current pulses. A simulation model of the device in the environment of Matlab-Simulink was developed. Plots of transients during the device idling and under load were constructed. The analysis of the device operating modes was performed. The developed electromechanical installation allows the process parameters to be adjusted.

Principles of Charge Estimation Methods Using High-Frequency Current Transformer Sensors in Partial Discharge Measurements.

This paper describes a simplified model and a generic model of high-frequency current transformer (HFCT) sensors. By analyzing the models, a universal charge estimation method based on the double time integral of the measured voltage is inferred. The method is demonstrated to be valid irrespective of HFCT sensor, assuming that its transfer function can be modelled as a combination of real zeros and poles. This paper describes the mathematical foundation of the method and its particularities when applied to measure nanosecond current pulses. In practice, the applicability of the method is subjected to the characteristics and frequency response of the sensor and the current pulse duration. Therefore, a proposal to use the double time integral or the simple time integral of the measured voltage is described depending upon the sensor response. The procedures used to obtain the respective calibration constants based on the frequency response of the HFCT sensors are explained. Two examples, one using a HFCT sensor with a broadband flat frequency response and another using a HFCT sensor with a non-flat frequency response, are presented.

Liquid-Fed Pulsed Plasma Thruster with Low-Energy Surface Flashover Igniter for Propelling Nanosatellites

This paper presents the initial development and characterization of a novel micropropulsion system for nanosatellite applications: a liquid-fed pulsed plasma thruster (LF-PPT) comprising a Lorentz-force pulsed plasma accelerator (PPA) and a low-energy surface flashover (LESF) igniter. In this work, LESF was demonstrated as a sufficient means of igniting the primary discharge in a PPA operating with a pentaphenyl trimethyl trisiloxane () dielectric liquid propellant, and initial characterization of the propulsion system parameters was performed. PPA current pulse durations of about with peaks of were observed, and plasma jet exhaust velocity was measured at using a time-of-flight technique via a set of double probes located along the jet’s path. Intensified charge-coupled device (ICCD) photography was concurrently leveraged to visualize plasma dynamics and confirm successful operation in the LESF ignition regime. A peak thrust and impulse bit of and , respectively, were estimated using large-area Langmuir probe measurements of total ion flux produced by the thruster. This paper additionally exhibits successful operation of the LF-PPT with the hydroxylammonium-nitrate-based propellant AF-M315e. The results of this paper suggest the befitting of LESF igniters in LF-PPTs, and the compatibility of LF-PPTs with the green propellant AF-M315e.

Limited Stochastic Current for Energy-Optimized Switching of Spin-Transfer-Torque Magnetic Random-Access Memory

Reducing the write-error rate (WER) is one of the main concerns for commercialization of spin-transfer-torque magnetic random-access memory (STT-MRAM). While most studies have been focused on finding proper material, this work discusses the use of limited stochastic (LS) current, for which WER is controlled. By solving the Fokker-Planck equation, an analytical expression for the LS current for a given WER is obtained. Most importantly, by using the LS current and optimizing it together with the related pulse duration, the authors find the optimum combination of current amplitude and pulse duration, which can reduce the energy consumption of STT-MRAM by up to 75%.

Effect of electropulsing on the fatigue resistance of aluminium alloy 2014-T6

The effects of electropulsing on the fatigue resistance of aluminium alloy 2014-T6 were studied in relation to electric current amplitude, pulse duration, and number of repetitions. Utilising the Taguchi method, the present study identified the current amplitude and the duration of the electropulsing as the two critical treatment parameters for improved fatigue resistance. A 97% fatigue life improvement was achieved under the electropulsing conditions that were applied. An increase in microhardness and a decrease in electrical conductivity due to electropulsing were correlated with enhanced fatigue resistance in the alloy. Mechanisms related to the effects of the electropulsing treatment were elucidated based on observations from scanning electron microscopy (SEM) and transmission electron microscopy (TEM) as well as numerical simulation results. The mechanisms identified by observation included dislocation movement and the secondary precipitation of GP-zones. Further explication of these mechanisms was provided by the application of a “magnetic field’’ model.