Current Pulse Amplitude Research Articles

Design and Simulation of HTS Coils With a New Structure for an Inductive Pulsed Power Generator

Inductive pulsed power supplies (PPS) attract attention from several research institutions and scholars since the energy density of inductors is approximately one order of magnitude higher than that of capacitors. To effectively improve the output current of high-temperature superconductor (HTS) PPS and lower requirements for the switch, research studies have been done on STRETCH meat grinder circuit with HTS coils as an inductive module of XRAM. This paper mainly discusses the possibility of HTS coils applying to the STRETCH meat grinder as one of the fundamental research for PPS. With the characteristics of strong mechanical properties, high Ic, and low loss, HTS wire has become sufficiently available to build prototypes and practical instruments. This paper proposes a new coil winding structure that makes HTS coils applicable to the STRETCH meat grinder. Simulation results show that the transposition method can obtain a relative even current distribution in HTS parallel coils. By using the HTS magnet in the STRETCH meat grinder, maximum pulse current amplitude of 625 A can be obtained with a current multiplication factor of 5.2. Compared with the simulation results, experiments will be taken in the near future to verify the feasibility of the proposed coil structure and will be described in detail in further research work.

Pre-Chirped Pulse Excitation EnhancedTerahertz Radiation

The enhanced broadband THz radiation excited by pre-chirping the femtosecond pumping laser pulse is explored from a photoconductive antenna made by the low-temperature molecular-beam-epitaxy (LT-MBE) grown Gallium Arsenide (GaAs). Nearly 3-dB enlargement on peak amplitude of THz radiation accompanied with broadened bandwidth is achieved with positively chirped pulse excitation. The laser with short pulsewidth assists the broadening of THz bandwidth, whereas the peak intensity of THz relies strictly on lengthened carrier lifetime. The enhancement of high-frequency radiation components at low pumping intensity also indicates the nature of power dependence in such a coherently controlled process. When photocurrent saturation occurs in the LT-MBE-grown GaAs under high-power pumping condition, the clipping effect on peak amplitude of current pulse lengthens the duration of current surge effect. Both the peak intensity and the frequency spectrum of the generated THz pulse concurrently declines. The physical mechanism related to pre-chirped pulse excitation dependent carrier dynamics is proposed to elucidate the spectral response as well as the power dependence in such a coherently controlled THz radiation process.

A new method of charged particle identification based on frequency spectrum analysis**Supported by National Natural Science Foundation of China (11175254, 11375264)

abstractA new frequency domain method for charged particle identification, called Frequency Ratio Analysis (FRA), is proposed by analyzing the frequency spectra of proton pulses and alpha pulses acquired from a totally depleted Si detector. Identification performance of the FRA method is evaluated and compared with two time domain methods, the current pulse amplitude method and the second moment method. The results show that the FRA method is not only feasible and effective but also superior to the two time domain methods, as it achieves an obvious increase in value of the figure-of-merit (FOM).

Application of generalized switching laws for increasing current pulse value

To obtain the current pulses applied to the active load, the circuit breaking effect has been used in the primary winding of the pulse transformer. When the direct current voltage source is disconnected, the current of primary winding is reduced to zero, so that a current pulse is formed in the secondary winding of the pulse transformer that is transmitted into the load. A circuit of the inductive pulse generator operating on the basis of generalized switching laws was developed so as to increase the amplitude of current pulses in the active load and the corresponding power. The circuit contains a pulse transformer, the secondary winding of the pulse transformer is connected to the load, and an additional inductor is connected parallel to the primary winding of the pulse transformer. When the direct current voltage source is disconnected, the current of primary winding passes through zero and decreases to a negative value, which leads to a significant increase in the current pulse in the load. In accordance with the generalized law of commutation, the relationships for the calculation of the current jump of pulse transformer primary winding and a jump in the load current have been obtained. Using the state-space technique, mathematical models of the circuits mentioned above with linear active load have been developed. Theoretical and experimental studies have shown a significant increase in the current pulse value and its capacity in the active linear load when the inductive pulse generator has been used. The values of currents in inductive coils detected experimentally were practically the same as the calculated values.

Design and Analysis of a Variable-Flux Pole-Changing Permanent Magnet Memory Machine

This paper proposes a new topology of a variable-flux pole-changing permanent magnet (PM) memory machine. The fractional-slot concentrated windings are employed in the stator side, which can increase the utilization ratio of winding under different pole modes. The neodymium–iron–boron PM poles and aluminum–nickel–cobalt (AlNiCo) PM poles are hybridized in the rotor side. The proposed machine features the capability of its pole number to switch back and forth between six poles and two poles through changing the magnetization directions of AlNiCo PMs via the stator winding. Besides, the air gap flux can be flexibly adjusted by varying the amplitudes of magnetization current pulses. The topology and design principle of the machine are described in detail, and the electromagnetic characteristics, including magnetic field distributions, air-gap flux density, as well as back electromotive force (EMF), in different operation modes are computed using a finite-element method. Due to the existence of the fifth harmonic component of back EMF, the torque quality is improved through injecting the fifth harmonic current under different magnetized levels of AlNiCo PMs. Besides, the field regulation capabilities in both the pole modes are analyzed.

Magnetic Field Projector for Deep Brain Stimulation

Deep brain stimulation (DBS) is an established surgical therapy for treatment of a number of neurological and neuropsychiatric disorders based on the modulation of neuronal firing deep in the brain. However, the delicate surgical operation and extremely expensive cost of the current DBS technology impede its wide applications. For non-invasive brain stimulation, transcranial magnetic stimulation and transcranial direct current stimulation have been tried in various therapeutic applications with little success due to two major imitations with their applied electromagnetic field: 1) the field does not focus on targeted brain functional sites, and 2) the field penetration depth is too shallow to be effective in stimulating targeted brain functional sites. In this paper, a novel magnetic field projector (MFP) capable of magnetically inducing deep brain modulation of neuronal firing is presented. The MFP projects a focused magnetic field to deep brain regions while suppressing the field on the scalp. The field penetration depth can be adjusted by configuring the structure parameters of the device as well as the excitation pulse current amplitude. An MFP prototype has been developed and tested on rats to modulate upward the neuronal firing frequency at the brain functional site ventrolateral preoptic nucleus for sleep induction, with the brain responses measured by EEG. The results showed that EEG sleep spindles were induced by a train of 9 Hz magnetic stimulation pulses for 10 s.

Experience of Pseudospark Switch Operation in Pulse Power Applications

The paper demonstrates the results of TDIl-200k/25SN-P pseudospark switch (PSS) developed by Russian company "Pulsed Technologies Ltd" application. PSS was used in pulsed power unit intended for electric-discharge fracture of rocks and concrete blocks and splitting off from monolith. The pulsed power unit has a pulse current generator with the capacity of 560 μF, stored energy of up to 63 kJ, operating voltage of up to15 kV, current pulse amplitude of up to 200 kA and pulse duration more than 200 μsec. The study also shows the current waveforms determined in the short-circuit experiment of the pulse current generator and in the experiments of the electric-discharge fragmentation of concrete at the charging voltage of 13 kV. PSS was operated in ringing single-pulse mode with the exceedance of more than two maximum permissible parameters: current pulse amplitude, current pulse duration and maximum pulse energy. Internal electrode erosion of PSS is shown and possible reasons of asymmetric current feed are discussed.

Enhancing the Linear Dynamic Range in Multi-Channel Single Photon Detector beyond 7OD.

We present design, implementation, and characterization of a single photon detector based on 32-channel PMT sensor [model H7260-20, Hamamatsu]. The developed high speed electronics enables the photon counting with linear dynamic range (LDR) up to 108count/s per detector's channel. The experimental characterization and Monte-Carlo simulations showed that in the single photon counting mode the LDR of the PMT sensor is limited by (i) "photon" pulse width (current pulse) of 900ps and (ii) substantial decrease of amplitudes of current pulses for count rates exceeding 108 count/s. The multi-channel architecture of the detector and the developed firm/software allow further expansion of the dynamic range of the device by 32-fold by using appropriate beam shaping. The developed single photon counting detector was tested for the detection of fluorescence labeled microbeads in capillary flow.

The cerebral blood flow response dependency on stimulus pulse width is affected by stimulus current amplitude - a study of activation flow coupling.

The coupling of cerebral blood flow (CBF) to neuronal activation, referred to as activation flow coupling (AFC), has been a fundamental brain physiology property. The stimulus-evoked CBF response was usually considered as a surrogate marker for neuronal activity in AFC studies. The selection of appropriate stimulation parameters, e.g., current amplitude and pulse width, is of great importance yet the effect of pulse width changes remained contradictory in previous studies. In this work, we use laser speckle contrast imaging (LSCI) to study the spatiotemporal CBF response to hindpaw somatosensory stimulation of different pulse widths (0.3 ms vs 1 ms) and current amplitudes (3 mA vs 6 mA) in a rodent experiment. The results showed that the change of pulse width significantly affected the CBF peak value at a lower current level (p<;0.05). In addition, the duration for observing significantly different average CBF response, denoted as td, at various pulse widths, was dependent on stimulus current amplitude. At a lower amplitude (3 mA), td was 6.5 s; While at a higher amplitude (6 mA), td was 2.5 s. It was indicated that the changes of pulse width had longer influence on the average CBF response at a lower current amplitude. Our findings may help to understand and explain the inconsistent AFC with different stimulation parameters in fundamental brain physiology.

Spatial variation of compound muscle action potentials across human gastrocnemius medialis.

The massed action potential (M wave) elicited through nerve stimulation underpins a wide range of physiological and mechanical understanding of skeletal muscle structure and function. Although systematic approaches have evaluated the effect of different factors on M waves, the effect of the location and distribution of activated fibers within the muscle remains unknown. By detecting M waves from the medial gastrocnemius (MG) of 12 participants with a grid of 128 electrodes, we investigated whether different populations of muscle units have different spatial organization within MG. If populations of muscle units occupy discrete MG regions, current pulses of progressively greater intensities applied to the MG nerve branch would be expected to lead to local changes in M-wave amplitudes. Electrical pulses were therefore delivered at 2 pps, with the current pulse amplitude increased every 10 stimuli to elicit different degrees of muscle activation. The localization of MG response to increases in current intensity was determined from the spatial distribution of M-wave amplitude. Key results revealed that increases in M-wave amplitude were detected somewhat locally, by 10-50% of the 128 electrodes. Most importantly, the electrodes detecting greatest increases in M-wave amplitude were localized at different regions in the grid, with a tendency for greater stimulation intensities to elicit M waves in the more distal MG region. The presented results indicate that M waves recorded locally may not provide a representative MG response, with major implications for the estimation of, e.g., the maximal stimulation levels, the number of motor units, and the onset and normalization in H-reflex studies.

Avalanche mode of high-voltage overloaded p+–i–n+ diode switching to the conductive state by pulsed illumination

A simple analytical theory of high-voltage overvolting p+-i-n+-structures picosecond switching into conducting state by pulsed lighting has been developed. Relationship between parameters of structure, light pulse, external circuit and the main characteristics of the process (pulse current amplitude, delay time and duration of switching process) have been obtained and confirmed by numerical simulation. It was shown that the energy of picosecond light pulse that is needed for effective switching can be reduced by 6-7 orders of magnitude due to the intensive avalanche multiplication of electrons and holes.

Nanopore detection of double stranded DNA using a track-etched polycarbonate membrane

We investigate the resistive-pulse sensing of 50-bp DNA using track-etched polycarbonate (PC) nanopores and show the translocation dynamics originating from the electrophoretic transport of DNAs. Conically shaped PC nanopore membranes have been prepared with asymmetric chemical etching technique. We show the potential and concentration dependence of DNA translocation through a PC nanopore. We find that the translocation of DNA scales linearly with both potential and concentration. Additionally, the threshold potential is determined to complete the translocation. Finally, by investigating the current-pulse amplitudes of nanopores with different tip sizes, we show that the nanopore size can be successfully used to distinguish the DNA molecules. These results suggest great promise for the sensing of short DNAs and understanding the dynamics of the translocation process using chemically-etched PC nanopores.

Luminescence characteristics of the Kr2F* excimer molecules in (Kr-SF6) gas mixtures with a Low SF6 content upon pumping by a pulsed beam of fast electrons

Emission spectra of dense Kr + SF6 gas mixtures with different composition excited by a pulsed beam of fast electrons are measured. The electron energy is 150 keV, and the amplitude and duration of a beam current pulse are 5 A and 5 ns. The composition of gas mixtures was Kr (190–1900) Torr and SF6 (0.1–1.0) Torr. The efficiency of formation of excimer Kr2F* molecules was found to be high in dense (∼1 atm) Kr-SF6 mixtures with a low SF6 donor content. The luminescence times and quenching constants of broadband emission of the Kr2F* molecule (λmax = 404.7 nm) by components of a gas mixture are measured.

The correlation between audible noise and corona current in time domain caused by single positive corona source on the conductor

Audible noise and corona current are two main DC corona effects, and they may both highly depend on the characteristics of space charges generated during corona discharge. However, relatively little investigation has previously been done on the correlation between them especially in time-domain. In the present work, the timedomain waveforms of audible noise and corona current generated by single positive corona source were recorded simultaneously. Their characteristics were carefully analyzed and found to be closely related. It was found that both the audible noise and the corona current consisted of repetitive pulses, and one-to-one relationship in time could be observed and confirmed between them. Furthermore, a linear correlation between the peak-to-peak values of audible noise pulses and the amplitude of corona current pulses was obtained. Empirical formulas with the same forms for them were derived to further prove the linear correlation. The close correlation between the audible noise and the corona current was interpreted qualitatively in the presented work and found to be highly related to the generated space charges.

Temporal response of silicon EUV and soft X-ray detectors

A small-sized generator of picosecond electron beams is used to measure the temporal resolution of EUV and soft X-ray silicon detectors produced by the Ioffe Physical Technical Institute, Russian Academy of Sciences. The temporal resolution of the EUV and soft X-ray detectors based on silicon photodiodes is shown to be ∼1 ns. Preliminary experiments have been performed using these detectors with the aim of investigating the radiation characteristics of a soft X-ray source based on an X-pinch driven by a small-sized highcurrent generator with a current pulse amplitude of 250 kA. This source is used at the Institute of High Current Electronics for soft X-ray backlighting diagnostics of various plasmas.

Role of Hydrogen in Cavitation Degradation of Iron in Water Solutions

Hydrogen ingress into a metal has been observed at cavitation in distilled water and in 3% NaCl solution at open circuit potential. The measurements of hydrogen permeation rate have been made using an ultrasonic cavitation facility with an attached Devanathan-Stachurski double cell. Increase in vibration amplitude has been associated with the increase in amplitude of electrochemical voltage and current pulses and with the modification of hydrogen permeation rate. Hydrogen behavior within the metal has been affected by the cavitation induced dynamic stresses and metal deformation hardening, ascertained on the basis of the appearance of hydrogen permeation transients at cavitation in comparison with those recorded for the unstressed state. Metal damage has been a resultof associated effects of cavitation and hydrogen.

Picosecond switching of high-voltage reverse-biased p +-n-n + structures to the conductive state by pulsed light

An analytical theory of high voltage reverse-biased p+-n-n+-structures picosecond switching into conducting state by pulsed lighting has been developed and a numerical simulation of this process has been performed. Combining the results of theory and simulation allowed us to obtain a simple relation between the parameters of structure, light pulse, external circuit and main characteristics of the process - the load current pulse amplitude and duration of switching process.

Linear synchronous electromagnetic machines for low-frequency impact technologies

The trend is considered toward development and application of various linear electromagnetic impact machine designs wherein the reciprocal motion of the plunger (armature) is timed with the frequency of the voltage pulses fed to the motor winding (coil) or a system of such coils from a mains-frequency power source. Based on the differences found between the methods of regulating the forced mechanical vibration regimes of the plunger, an analysis is made of the advantages and shortcomings of the operating cycles of synchronous machines built mainly around single- and double-coil designs. Novel electromagnetic synchronous machine designs are presented, along with their operating cycle control methods providing for a necessary sequence of alternation of the voltage half-waves applied to the coils, which make it possible to reduce the current pulse amplitude and the effect of the operation of the impact-type electric drive on the supply circuit. New technical solutions are suggested for improvement of the adjustment accuracy and stability of the forced vibration regime, which improves the performance characteristics and operating conditions of machines.

Wave mode high voltage consolidation of powder materials

The densification of electrically conductive powders by high voltage consolidation is studied. High voltage consolidation method (HVC) includes the simultaneous exposure of a powder sample to mechanical pressure (50–500MPa) and to a short (less than 300ms) high voltage (above 1kV) electric discharge with the pulse current amplitude of a few hundred kA/cm2. The densification kinetics of industrial iron powder is analyzed by ultra-rapid video-recording. The integral temperature of the sample has a maximum value at the beginning of the densification process. The compaction process lasts less than 16ms for all the values of the parameters studied. The shortness of the densification process in comparison with the cooling of the sample provides a constant temperature throughout the entire compaction process. Based on the analysis of the obtained experimental results a mathematical model of high rate wave mode compaction of a powder material under conditions of HVC is formulated. The constitutive equation of the mechanical behavior of the consolidated material accounts for the plastic flow of powder particles and for the collapse of the inter-particle pores. The numerical simulation results reveal optimal values of the dimensionless parameters controlling the HVC process.

Statistical modelling of discharge behavior of atmospheric pressure dielectric barrier discharge

In this work, stochastic behavior of atmospheric pressure dielectric barrier discharge (DBD) has been investigated. The experiment is performed in a DBD reactor consisting of a pair of stainless steel parallel plate electrodes powered by a 50 Hz ac high voltage source. Current pulse amplitude distributions for different space gaps and the time separation between consecutive current pulses are studied. A probability distribution function is proposed to predict the experimental distribution function for the current pulse amplitudes and the occurrence of the transition regime of the pulse distribution. Breakdown voltage at different positions on the dielectric surface is suggested to be stochastic in nature. The simulated results based on the proposed distribution function agreed well with the experimental results and able to predict the regime of transition voltage. This model would be useful for the understanding of stochastic behaviors of DBD and the design of DBD device for effective operation and applications.