Current Pulse Amplitude Research Articles

Numerical simulation of high-intensity metal ion beam generation

The features and regularities of plasma-immersion formation of high-intensity repetitively pulsed beams of aluminum ions, as well as their transportation and ballistic focusing in an accelerating system with a curvilinear extracting potential grid electrode under application of negative bias with high pulse repetition rate of f = 105 Hz are studied by numerical methods. It is shown that the amplitude and shape of the ion beam current pulse depend significantly on the dynamic conditions of space charge neutralization of the beam. In case of using of bias potential with high duty factor, e.g. conditions of limited time of vacuum-arc plasma preinjection, the process of transportation and ballistic focusing of the ion beam up to densities manifold exceeding the density of the preliminary injected plasma, it is possible to obtain conditions leading to the formation of a virtual anode. It is shown that secondary electrons can be one of the additional mechanisms of compensation of the beam space charge which results in the improvement of transportation of high-intensity beams of aluminum ions.

Analysis of Terahertz Radiation Spectra in Multilayer GaAs/AlGaAs Heterostructures

The results of examination of the terahertz radiation spectra of multilayer GaAs/AlGaAs heterostructures synthesized on GaAs substrates are presented. The dependence of the radiation spectrum on the amplitude of the excitation current pulse and temperature dependences of the threshold lasing current and the radiation power of terahertz quantum cascade lasers with a double metallic waveguide, which were built on the basis of these structures, have been obtained. The maximum amplitude of the total radiation power is estimated at 28 μW in the range 3.25–3.32 THz at a temperature of 15 K. The spectral radiation density of the oscillator is measured. Changes in the mode content of radiation induced by the bias-current variation have been observed.

LTT switch unit for capacitive energy storages

Abstract When the capacitor cell is discharged in the short-circuit mode, the current pulse amplitude and duration are maximal. Therefore, this mode is the most severe for discharge switches of capacitive energy storage. The characteristics of the transient process of the discharge capacitive energy storage and the current loads acting in the facility discharge circuit have been defined for this mode. The test bench for definition of the LTT (Light Triggered Thyristors) loading capacity is described. The limiting characteristics have been experimentally obtained for LTT, at which there emerges the thermo-generation peak. The process of OFF-ON switching of LTTs has been investigated, the necessity is shown to use the speed-up R-C circuits to ensure fast and stable transition of LTT into the conducting state. The design of the switch unit for the capacitive energy storage comprising LTTs and crowbar diodes is described, and the transient processes of current switching in crowbar diodes are considered. The tests carried out during switching of pu1se current up to 100 kA at a voltage of 6 kV have confirmed the workability of the switch unit.

Modeling false alarm rate and related characteristics of laser ranging and LIDAR avalanche photodiode photoreceivers

An analysis is presented of the error introduced into estimates of avalanche photodiode (APD) laser-rangefinder performance by assuming Gaussian distribution of the APD multiplication gain. The amplitude of current pulses emitted by an APD obeys the McIntyre distribution, the tails of which diverge from the Gaussian distribution having the same mean and variance. Because extinction of false alarms requires setting a discrimination threshold far into the tail of an analog photoreceiver’s output distribution, the threshold level required to achieve a specified false alarm rate (FAR) using an APD-based photoreceiver is often not accurately predicted by the standard FAR model of Rice. Characteristics of APD-based photoreceivers are calculated using the McIntyre distribution and are compared with characteristics calculated using the Gaussian approximation.

Engineering Artificial Somatosensation Through Cortical Stimulation in Humans.

Sensory feedback is a critical aspect of motor control rehabilitation following paralysis or amputation. Current human studies have demonstrated the ability to deliver some of this sensory information via brain-machine interfaces, although further testing is needed to understand the stimulation parameters effect on sensation. Here, we report a systematic evaluation of somatosensory restoration in humans, using cortical stimulation with subdural mini-electrocorticography (mini-ECoG) grids. Nine epilepsy patients undergoing implantation of cortical electrodes for seizure localization were also implanted with a subdural 64-channel mini-ECoG grid over the hand area of the primary somatosensory cortex (S1). We mapped the somatotopic location and size of receptive fields evoked by stimulation of individual channels of the mini-ECoG grid. We determined the effects on perception by varying stimulus parameters of pulse width, current amplitude, and frequency. Finally, a target localization task was used to demonstrate the use of artificial sensation in a behavioral task. We found a replicable somatotopic representation of the hand on the mini-ECoG grid across most subjects during electrical stimulation. The stimulus-evoked sensations were usually of artificial quality, but in some cases were more natural and of a cutaneous or proprioceptive nature. Increases in pulse width, current strength and frequency generally produced similar quality sensations at the same somatotopic location, but with a perception of increased intensity. The subjects produced near perfect performance when using the evoked sensory information in target acquisition tasks. These findings indicate that electrical stimulation of somatosensory cortex through mini-ECoG grids has considerable potential for restoring useful sensation to patients with paralysis and amputation.

Correlation between audible noise and corona current generated by AC corona discharge in time and frequency domains

Corona-generated audible noise is induced by the collisions between space charges and air molecules. It has been proven that there is a close correlation between audible noise and corona current from DC corona discharge. Analysis on the correlation between audible noise and corona current can promote the cognition of the generation mechanism of corona discharge. In this paper, time-domain waveforms of AC corona-generated audible noise and corona current are measured simultaneously. The one-to-one relationship between sound pressure pulses and corona current pulses can be found and is used to remove the interferences from background noise. After the interferences are removed, the linear correlated relationships between sound pressure pulse amplitude and corona current pulse amplitude are obtained through statistical analysis. Besides, frequency components at the harmonics of power frequency (50 Hz) can be found both in the frequency spectrums of audible noise and corona current through frequency analysis. Furthermore, the self-correlation relationships between harmonic components below 400 Hz with the 50 Hz component are analyzed for audible noise and corona current and corresponding empirical formulas are proposed to calculate the harmonic components based on the 50 Hz component. Finally, based on the AC corona discharge process and generation mechanism of audible noise and corona current, the correlation between audible noise and corona current in time domain and frequency domain are interpreted qualitatively. Besides, with the aid of analytical expressions of periodic square waves, sound pressure pulses, and corona current pulses, the modulation effects from the AC voltage on the pulse trains are used to interpret the generation of the harmonic components of audible noise and corona current.

The Dynamics of Prosthetically Elicited Vestibulo-Ocular Reflex Function Across Frequency and Context in the Rhesus Monkey.

Electrical vestibular neurostimulation may be a viable tool for modulating vestibular afferent input to restore vestibular function following injury or disease. To do this, such stimulators must provide afferent input that can be readily interpreted by the central nervous system to accurately represent head motion to drive reflexive behavior. Since vestibular afferents have different galvanic sensitivity, and different natural sensitivities to head rotational velocity and acceleration, and electrical stimulation produces aphysiological synchronous activation of multiple afferents, it is difficult to assign a priori an appropriate transformation between head velocity and acceleration and the properties of the electrical stimulus used to drive vestibular reflex function, i.e., biphasic pulse rate or pulse current amplitude. In order to empirically explore the nature of the transformation between vestibular prosthetic stimulation and vestibular reflex behavior, in Rhesus macaque monkeys we parametrically varied the pulse rate and current amplitude of constant rate and current amplitude pulse trains, and the modulation frequency of sinusoidally modulated pulse trains that were pulse frequency modulated (FM) or current amplitude modulated (AM). In addition, we examined the effects of differential eye position and head position on the observed eye movement responses. We conclude that there is a strong and idiosyncratic, from canal to canal, effect of modulation frequency on the observed eye velocities that are elicited by stimulation. In addition, there is a strong effect of initial eye position and initial head position on the observed responses. These are superimposed on the relationships between pulse frequency or current amplitude and eye velocity that have been shown previously.

The effect of photoemission on nanosecond helium microdischarges at atmospheric pressure

Atmospheric-pressure microdischarges excited by nanosecond high-voltage pulses are investigated in helium-nitrogen mixtures by first-principles particle-based simulations, which include VUV resonance radiation transport via the tracing of photon trajectories. The VUV photons, of which the frequency redistribution in the emission processes is included in some detail, are found to modify the computed discharge characteristics remarkably, due to their ability to induce electron emission from the cathode surface. Electrons created this way enhance the plasma density, and a significant increase of the transient current pulse amplitude is observed. The simulations allow the computation of the density of helium atoms in the 21P resonant state, as well as the density of photons in the plasma and the line shape of the resonant VUV radiation reaching the electrodes. These indicate the presence of significant radiation trapping in the plasma and photon escape times longer than the duration of the excitation pulses are found.

Pulsed Electron Source with Grid Plasma Cathode and Longitudinal Magnetic Field for Modification of Material and Product Surfaces

The description and the main characteristics of the pulsed electron source “SOLO” developed on the basis of the plasma cathode with grid stabilization of the emission plasma boundary are presented. Тhe emission plasma is generated by a low-pressure arc discharge, and that allows to form the dense low-energy electron beam with a wide range of independently adjustable parameters of beam current pulses (pulse duration of 20–250 μs, pulse repetition rate of 1–10 s–1, amplitude of beam current pulses of 20–300 A, and energy of beam electrons of 5–25 keV). Тhe special features of generation of emission plasma by constricted low-pressure arc discharge in the grid plasma cathode partially dipped into a non-uniform magnetic field and of formation and transportation of the electron beam in a longitudinal magnetic field are considered. The application area of the electron source and technologies realized with its help are specified.

Modeling and Simulation of Railgun System Driven by Multiple HTSPPT Modules

In the rail-type electromagnetic launching system, the equivalent load of pulsed-power supplies (PSs) varies with the launching process, while it has a certain influence on the discharge of pulsed PS. However, in the analysis and design of pulsed PS, researchers usually use the fixed resistance and inductance to simulate the load, which is impossible to accurately study the characteristics of the pulsed PS. The electromagnetic launching needs high-amplitude current pulse. Therefore, in this paper, a mathematical model of electromagnetic launching system driven by multiple superconducting inductive pulsed PS modules is established. In this model, the fixed resistance and inductance load are replaced by the dynamic load model of the railgun; the effects of dynamic load and fixed load on the discharge characteristics are analyzed; the parallel discharge characteristics of multiple high-temperature superconducting pulsed-power transformer (HTSPPT) modules are studied; and the characteristics of the simple rail-type electromagnetic launching driven by multiple HTSPPT modules are analyzed. The simulation results show that a high amplitude of current pulse can be produced using synchronous parallel discharge of multiple HTSPPT modules. The simulation results show that when the resistance and inductance of load are fixed at 2 $\text{m}\Omega$ and 0.5 $\mu \text{H}$ , respectively, the current amplification factor is 15.666, and the maximum voltage of the auxiliary capacitor is 1079 V. In the dynamic load model, the current amplification factor is 17.174, and the error is 9.6%. The maximum voltage of the auxiliary capacitor is 983 V, and the error is 8.9%. Therefore, the discharge characteristics of pulsed PS can be more accurately studied using dynamic models.

Investigation of the I – V characteristics asymmetry in semiconducting Y–Ba–Cu–O diodes

Thin films of YBa2Cu3O7–x (YBCO) oxygen-deficient superconductor were used to manufacture asymmetric microdiodes and investigate their asymmetric non-linear current–voltage (I –V) dependences at temperatures T > Tc, where Tc is the temperature of the onset of superconductivity in the material. The diodes are based on being asymmetrically narrowed down to a 10-μm-wide–neck mesa exhibit voltage asymmetry depending on the current bias conditions, the mesa's temperature, and a residual oxygen content in its neck region. The intrinsic electric field in the biased diode causes free-carrier drift velocity saturation, initiated in the mesa's neck and following its asymmetric enlarging towards the mesa's electrodes depending on the biasing pulsed current amplitude, polarity, and rise time/fall time of the pulse's leading/trailing edges. The variation of the I –V characteristics asymmetry has been associated with change in the mesa's electric resistivity, affected by the electric field's asymmetric distribution in the YBCO mesa. It has been also demonstrated that our asymmetric diodes with the reduced oxygen content are sensitive detectors of microwave radiation.

Electrical stimulation of microengineered skeletal muscle tissue: Effect of stimulus parameters on myotube contractility and maturation.

Skeletal muscle tissues engineered in vitro are aneural, are short in the number of fibres required to function properly and degenerate rapidly. Electrical stimulation has been widely used to compensate for such a lack of neural activity, yet the relationship between the stimulation parameters and the tissue response is subject to debate. Here we studied the effect of overnight electrical stimulation (training) on the contractility and maturity of aligned C2C12 myotubes developed on micropatterned gelatin methacryloyl (GelMA) substrates. Bipolar rectangular pulse (BRP) trains with frequency, half-duration and applied pulse train amplitudes of f=1Hz, ton =0.5ms and Vapp ={3V, 4V, 4.5V}, respectively, were applied for 12h to the myotubes formed on the microgrooved substrates. Aligned myotubes were contracting throughout the training period for Vapp ≥4V. Immediately after training, the samples were subjected to series of BRPs with 2≤Vapp ≤5V and 0.2≤ton ≤0.9ms, during which myotube contraction dynamics were recorded. Analysis of post-training contraction revealed that only the myotubes trained at Vapp =4V displayed consistent and repeatable contraction profiles, showing the dynamics of myotube contractility as a function of triggering pulse voltage and current amplitudes, duration and imposed electrical energy. In addition, myotubes trained at Vapp =4V displayed amplified expression levels of genes pertinent to sarcomere development correlated with myotube maturation. Our findings are imperative for a better understanding of the influence of electrical pulses on the maturation of microengineered myotubes.

An Experimental Analysis on the Impacts of Current Pulsing with Varying Current Amplitudes on Lithium-Ion Cells

Lithium-ion cells can be charged using different techniques. CCCV (constant current, constant voltage) charging is the standard method that is typically employed for charging the lithium ion batteries/cells. A theoretical analysis of pulse charging using varying current amplitudes with the relaxation periods has shown reduction in the charging time without reaching lithium saturation over the period [1]. It is based on the concept of increasing surface concentration of lithium at initial stages and maintaining the concentration value close to the saturation, resulting in enhanced performance. The objective of this work is to experimentally analyze the impacts of varying current pulse amplitudes on the lithium ion battery materials. This method comprises constant width charging, a rest period and decrease in applied current as the charging progress. Implementing the pulsed currents of different amplitudes on cathodic (Lithium Iron Phosphate, Lithium Manganese Dioxide) and anodic (Graphite and Li 4Ti5O12) half cells separately will impact the electrode materials in various ways. The results of charging time and effects on the electrode materials are compared with conventional charging method. Figures 1 and 2 show the constant current and a portion of pulsed current profile that are used in the analysis. In this experiment, pulsed current profile is controlled by varying the duty cycle and relaxation periods between pulses while the current amplitudes are reduced as the charging progress. SEM and equivalent circuit modelling based on EIS data are used in analyzing the impacts of both the charging protocols on the lithium-ion cells.

Electric Field-Assisted Pressureless Sintering of Ceramic Protonic Conductors

Gadolinium, yttrium and samarium-doped barium cerate (BCGd, BCY and BCSm, respectively) polycrystalline green pellets were submitted to electric field-assisted pressureless sintering experiments isothermally in the temperature range 800-1200oC under 100-200 V cm-1 electric fields, limiting to 1-5 A the electric current pulse amplitude. The sintering experiments were carried out in ambient atmosphere with the pellets positioned inside a vertical dilatometer furnace with Pt-Ir electrodes connected either to a power supply for applying the electric field or to an impedance analyzer for collecting [-Z''(ω) x Z'(ω)] data to evaluate the bulk and the grain boundary contributions to the electrical resistivity. Near full density was achieved in the sintered samples. The combined results of dilatometry and impedance spectroscopy measurements before and after flash sintering show substantial improvement of the electrical conductivity of flash sintered specimens. Joule heating is assumed to be the primary effect of the electric current pulse through the specimens. Improved grain-to-grain contact and the removal of depleted chemical species due to Joule heating at the space charge region are proposed, respectively, as the reasons for the almost total disappearance of the grain boundary component in the impedance diagrams and the improvement of the bulk electrical conductivity.

Generation of Boron-Rich Plasma by a Pulsed Vacuum Arc With Lanthanum Hexaboride Cathode

We report on the generation of boron-rich plasma by a pulsed vacuum arc with lanthanum hexaboride cathode. Two different ranges of arc current pulse duration and amplitude were investigated: the first one has pulse duration of 5–20 $\mu \text{s}$ and arc current of 100–700 A and the second one has pulse duration of 300 $\mu \text{s}$ and arc current of 140 A. The ion mass-to-charge spectrum of the plasma was investigated by both time-of-flight spectrometry and magnetic analysis. The results of measurements of the plasma ion composition for different arc parameters are presented and discussed. For all arc parameters considered, the fractional composition of boron and lanthanum ions agrees well with the stoichiometric composition of these elements into the lanthanum hexaboride cathode.

The development and application of a cold atmospheric plasma generator for treatment of skin and soft-tissue injuries in animals

We describe a device for obtaining cold plasma in air at atmospheric pressure using a system of positive high-voltage pin electrodes, which is intended for the treatment of skin and soft-tissue injuries in animals. Plasma is generated due to the development of periodic pulsed discharge of nanosecond duration at current pulse amplitudes 10–20 mA, characteristic frequencies 10–20 kHz, and applied voltages within 8–10 kV. The high efficacy of the proposed device and method is confirmed by the good clinical results of treating large domestic animals with traumatic injuries.

Simulation and experimental investigation of a high-Temperature superconducting inductive pulsed power supply with time delay effect of the secondary side

In this paper, to obtain a higher amplitude, higher energy transfer efficiency and better waveform quality of pulse current, a pulsed power supply that has time delay effect of the secondary side and the structure of inductive and capacitive hybrid energy storage is presented. The discharge circuit of power supply is improved and its principles and working processes are firstly analyzed. Besides, simulations and experiments are conducted for verification of the principles. It is found that, under the same experimental conditions, when delay time is 1 ms, the amplitude of pulse current is increased from 2769A to 3185A; and the energy transfer efficiency from the primary to secondary side is improved from 57.75% to 58.2%; the quality of pulse waveform is improved clearly compared with that of traditional discharge circuit. The aforementioned three aspects are compared comprehensively, which proves the feasibility and advantages of the improved discharge circuit. In Addition, the analysis of experimental results reveals the controllability of the proposed pulsed power supply, with which the continuous variation of the amplitude of pulsed current within limits can be realized.

Influence of electrode spacing and gas pressure on parameters of a runaway electron beam generating during the nanosecond breakdown in SF 6 and nitrogen

This study deals with experimental and theoretical simulation data showing the influence of electrode spacing and gas pressure on parameters of a supershort avalanche electron beam (SAEB) formed in SF6 and nitrogen at different rise times and amplitudes of a voltage pulse. Using GIN-55-01, VPG-30-200, and SLEP-150M pulsers, tubular cathodes with a diameter of 6 mm, as well as gaps of 3, 5, and 8 mm, it was shown that the SAEB current amplitude can both increase and decrease depending on an electrode spacing, a waveform and a rise time of the voltage pulse, as well as the pressure of SF6 and nitrogen. It was established as a result of simulation that maximal voltage across the gap during the process of generation of runaway electrons and the thickness of an anode foil have a major effect on the SAEB current pulse amplitude.

Effects of hippocampal low-frequency stimulation in idiopathic non-human primate epilepsy assessed via a remote-sensing-enabled neurostimulator

Individuals with pharmacoresistant epilepsy remain a large and under-treated patient population. Continued technologic advancements in implantable neurostimulators have spurred considerable research efforts directed towards the development of novel antiepileptic stimulation therapies. However, the lack of adequate preclinical experimental platforms has precluded a detailed understanding of the differential effects of stimulation parameters on neuronal activity within seizure networks. In order to chronically monitor seizures and the effects of stimulation in a freely-behaving non-human primate with idiopathic epilepsy, we employed a novel simultaneous video-intracranial EEG recording platform using a state-of-the-art sensing-enabled, rechargeable clinical neurostimulator with real-time seizure detection and wireless data streaming capabilities. Using this platform, we were able to characterize the electrographic and semiologic features of the focal-onset, secondarily generalizing tonic-clonic seizures stably expressed in this animal. A series of acute experiments exploring low-frequency (2Hz) hippocampal stimulation identified a pulse width (150μs) and current amplitude (4mA) combination which maximally suppressed local hippocampal activity. These optimized stimulation parameters were then delivered to the seizure onset-side hippocampus in a series of chronic experiments. This long-term testing revealed that the suppressive effects of low-frequency hippocampal stimulation 1) diminish when delivered continuously but are maintained when stimulation is cycled on and off, 2) are dependent on circadian rhythms, and 3) do not necessarily confer seizure protective effects.

Magnetization reversal by superconducting current in φ Josephson junctions

We study magnetization reversal in a φ0 Josephson junction with direct coupling between magnetic moment and Josephson current. Our simulations of magnetic moment dynamics show that by applying an electric current pulse, we can realize the full magnetization reversal. We propose different protocols of full magnetization reversal based on the variation of the Josephson junction and pulse parameters, particularly, electric current pulse amplitude, damping of magnetization, and spin-orbit interaction. We discuss experiments that can probe the magnetization reversal in φ0-junctions.