Negative Current Pulses Research Articles

Chiral spin textures creation and dynamics in a rectangular nanostructure

Abstract Controlled creation of stable chiral spin textures is required to use them as an energy-efficient information carrier in spintronics. Here we have studied the stable creation of isolated chiral spin texture (skyrmion and antiskyrmion) and its pair through the magnetization reversal of a rectangular nanostructure using spin-polarized currents. An isolated spin texture is created through a negative current pulse. Dynamics of the stable spin texture are explored under external magnetic fields, and the resonant frequencies are calculated. A stable skyrmion pair is created using an asymmetric current pulse, and their interaction is studied using the Thiele equation. The stability of isolated or paired spin texture depends on the Dzyaloshinskii–Moriya interaction strength, spin-polarized current density, and pulse duration. In addition, the stability of the skyrmion pair depends on their initial separation, and a threshold for the separation between skyrmions of 78 nm is observed.

Identification of corona discharges based on wavelet scalogram images with deep convolutional neural networks

This paper presents a new wavelet-based approach to automate the identification of positive and negative DC corona discharge current pulses. Two electrode systems with variable gap spacings formed corona discharges, and two commercial sensors (a high-frequency current transformer (HFCT) and a shunt resistor) captured transient corona discharge currents. The proposed method employs a continuous wavelet transform to generate time-frequency representations of corona discharge pulse currents, called scalogram images. The effects of sampling interval, data acquisition time, data shifting, and external noise components in the signals on the scalogram images were examined. The well-known pre-trained convolutional neural network models, AlexNet, MobileNet, and ShuffleNet, were tailored, and their ensemble structure was generated to discriminate scalogram images of discharge pulses. A framework was constructed to increase the generalization ability of the study. The results demonstrate that the scalogram images are robust candidates for corona discharge identification.

Electrical and optical characterization of multi-hollow surface dielectric barrier discharge in configuration with the air-exposed electrode

In this paper, multi-hollow surface dielectric barrier discharge generated by a perforated ceramic substrate in a configuration with the air-exposed electrode was investigated. The electrical characteristics (discharge power, peak, and average amplitude of current pulses) and optical characteristics (emission intensity) of the discharge were evaluated under various conditions of applied voltage (peak voltage 3–6 kV, frequency 200–2000 Hz), air flow rate (0.5–2.4 L/min), and air relative humidity (0%–80%). Temperature of ceramic substrate was also monitored. Statistical analysis of current pulses was also performed, and histograms of amplitudes of current pulses were calculated. The results showed that discharge characteristics strictly depend on given working conditions. The analysis of current pulses showed opposite trends in average overall number of positive and negative pulses with an increase of discharge power: number of positive current pulses gradually increased, while number of negative current pulses slightly decreased. The highest peak currents were found at 4 kV (1.8 W). With further increase of peak voltage, peak current decreased and beginning of detection of current pulses upon a rising (declining) slope of applied voltage was slightly shifted toward earlier times. At the highest applied peak voltage, pulses appeared even before polarity of applied voltage reversed. Therefore, we suppose that a residual charge accumulated on dielectric surface plays a crucial role in characteristics of the current pulses. Significant influence on current pulses and discharge emission intensity was also found with a change of air relative humidity, while the effect of air flow rate was found weaker.

Characterization of the effects of high-intensity negative current pulses on metal transfer and melting rate in the AC-GMAW process

The use of variants of the gas metal arc welding (GMAW) process has become an affordable option in industry. Alternating current–gas metal arc welding (AC-GMAW) arises as one of them, providing additional degrees of freedom for process controllability and versatility. This study focused on the analysis of a complex waveform of the AC-GMAW process for welding stainless steel, employed in modern synergic programs, which has not been widely disseminated in the technical literature and assessed scientifically. The main objective was to characterize the effects of high-intensity pulses in negative polarity over the process and to discuss the potential of this strategy, since it has not been used in conventional AC synergic programs. In order to bring to light information on the phenomena involved, such as the arc climbing on the wire electrode, advanced techniques of high-speed videography were used, synchronized with the acquisition of electrical welding process signals, as well as infrared thermography, to verify the evolution of the cooling of the piece after welding. The results grounded discussions on different AC-GMAW waveforms. The process’ electrical data, along with images of the arc and analysis of the wire melting and workpiece thermal behavior, showed that there was a significant visible increase in wire melting during the negative pulse. In addition, it evidenced how the negative electrode increment contributed to the increase in wire melting even at lower power and also showed the thermal effects on the workpiece.

Braiding Operations for a Topological Josephson Junction Array using SFQ Current Pulses

Majorana bound states (MBSs) can occur in topological Josephson junction (JJ) arrays with the presence of a fractional vortex with 2π-phase winding. It has been theoretically shown that the braiding operation can be achieved by using current pulses, compatible with single flux quantum (SFQ) technology. Therefore, we designed an SFQ logic circuit for the braiding operations of the topological JJ array using single flux quanta in a conventional JJ array. Braiding operations could be realized by an SFQ logic circuit with double flux quantum driver. To obtain positive and negative current pulses using the SFQ logic circuit, we used SFQ logic circuits with ac biasing for simulation. Finally, we confirmed the CNOT operation using an array-type SFQ circuit by means of simulation and estimated the CNOT operation speed.

Dynamics of negative coronas in airflow

Recent numerical studies captured the effects of airflow on positive streamers, when subjected to a lateral wind. The positive streamers initiate from the trailing side of the anode and propagate with a clear tilting in the direction of the airflow. In this paper, we present the results of a simulation of two successive negative corona pulses and investigate their behaviour when exposed to a lateral wind. We use a three-dimensional numerical model that couples the electrical discharge dynamics with the airflow and allows the study of the discharge on electrons and ions timescales. The results show that negative coronas are not easily influenced by the airflow and tilt just slightly in the flow direction. Our simulation explains the physical mechanism that governs the formation and termination of negative corona pulses (Trichel pulses) and describes for the first time the proposed cathode-directed streamer mechanism for negative corona current pulses.

Development of a Wideband Current Amplifier dedicated to Fission Chamber Measurement

Fission chambers are widely used in nuclear reactors, either occasionally to probe the neutron flux maps in nuclear power plants or as part of the nuclear instrumentation used in research reactors to characterize neutron flux levels in irradiation locations. Wide dynamic range acquisition systems are very limited in the nuclear instrumentation market. Thus, since 2012, CEA is developing the MONACO system, which allows measurement in pulse, fluctuation, and current mode running simultaneously on the same channel. The simultaneous use of three measurement modes places high requirements on the amplification stage. Indeed, the current mode exploits a bandwidth between 0 and a few kHz, while the fluctuation mode is based on the frequency range of 100 kHz 1MHz. Finally, for the pulse mode, it is necessary to identify current pulses of a few uA in amplitude and with a duration of about ten nanoseconds, which implies a bandwidth that extends up to 10 or 20 MHz. In the frame of the industrialization of the MONACO system, a new preamplifier was designed to meet those requirements. With a first prototype, LDCI and I-TECH performed very promising bench tests in October 2020. Tests with synthetic signals corresponding to pulse and fluctuation mode showed very good performance of the electronics. The positive and negative current pulses are correctly amplified and the measurement noise was estimated at 0.1 µApp thanks to proper electronic shielding. The DC measurement is also satisfactory in the tested range with an accuracy of less than nA and a bandwidth of 1kHz. Preamplifier qualifications are planned within realistic experiments using a fission chamber placed in a neutron field.

Rapid Open-Circuit Voltage Measurement Method for Lithium-Ion Batteries Using One-Cycle Bipolar-Current Pulse

Accurate estimation of state-of-charge (SOC) of battery is important for battery storage systems. A lookup table between the battery open-circuit voltage (OCV) and SOC has been widely adopted for online SOC estimation. However, it is time-consuming to obtain an accurate SOC-OCV correlation since the battery requires several hours to reach an inner-equilibrium state. Some acceleration methods utilized the measured terminal voltage to predict the final OCV, but they have accumulated errors. Therefore, instead of predicting the OCV, a directly fast OCV measurement method for lithium-ion batteries based on one-cycle bipolar-current pulse, namely, a positive current pulse followed by a negative current pulse with the same duration and amplitude is proposed in this article. Explicitly, a second-order relaxation model, which shows a good balance between accuracy and simplicity, is established for analyzing the relationship between current and polarization voltage. Furthermore, considering the safe operation of the battery and hysteresis voltage issue, a 1 C bipolar-current pulse with 6-min duration is chosen for implementation. Experimental results on LiNiMnCoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and LiNiCoAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> batteries have proven the effectiveness of the proposed method, which can reduce up to 90% (depending on SOC level) of the time as compared with the conventional method.

Soft Switching Bidirectional Converter for Reflex Charger With Minimum Switches

In this article, a new soft switching bidirectional dc–dc converter for battery charger application based on reflex charge technique is proposed. The proposed bidirectional dc–dc converter applies flyback converter to provide negative current pulses for reflex charge method while providing zero-voltage switching (ZVS) for the buck converter switch which is used to control charging current. The flyback converter switch is also soft switched. Flyback converter switch operates under zero-current switching (ZCS) turn- on and ZVS turn- off conditions. The proposed bidirectional converter applies only two switches to implement a fully soft switched pulsewidth modulation (PWM) bidirectional converter. Hence, the proposed topology provides a fully soft switched bidirectional converter with minimum number of switches using PWM control method. The proposed converter is implemented, analyzed, and experimental results are presented. The experimental results verify the theoretical analysis presented in the article. Efficiency comparison performed shows proper efficiency of proposed converter while applying minimum number of switches.

A Spin–Orbit‐Torque Memristive Device

AbstractMemristors, demonstrated by solid‐state devices with continuously tunable resistance, have emerged as a new paradigm for self‐adaptive networks that require synapse‐like functions (artificial synapse, for example). Spin‐based memristors offer advantages over other types of memristors because of their significant endurance and high energy efficiency. Yet it remains a challenge to build dense and functional spintronic memristors with structures and materials that are compatible with existing ferromagnetic devices. Here, a memristive device based upon Ta/CoFeB/MgO heterostructures is demonstrated, which are commonly used in out‐of‐plane magnetized magnetic tunnel junctions (MTJ). To achieve the memristive function, a domain wall (DW) is driven back and forth in a continuous manner in the CoFeB layer by applying in‐plane positive or negative current pulses along the Ta layer, utilizing the spin–orbit torque (SOT) that the current exerts on the CoFeB magnetization. Hence, the magnetization and consequently the anomalous Hall effect (AHE) resistance are modulated in an analog manner, being controlled by the pulsed current characteristics including amplitude, duration, and repetition number. The quasi‐continuous AHE resistance variation is explained by the SOT‐induced DW creep motion. These results pave the way for developing SOT‐based energy‐efficient neuromorphic systems.

Improved sensing of vertical velocity for vertical position control using loop voltage signals on EAST

Vertical position control of shaped plasma is essential for all elongated tokamaks to achieve safe and stable plasma discharge. In EAST, the in-vessel coil (IC) is employed for fast control of plasma vertical motion which power supply capabilities limits the controllability of vertical instability. Besides, adequate signal-to-noise ratio of vertical position measurement can also realize an improvement in vertical control. In EAST, plasma vertical position Zp is produced nearly by all integrated magnetics, fast Z error signal is obtained by filtering from Zp. Then this fast Z error and its derivative term (dz/dt) are controlled by IC with a separate PD controller. However, it has a low signal-to-noise ratio which limits the gains that can be used successfully in the PD control loops. To provide less noisy dz/dt signal, the successful use of multiple up/down loop voltage pairs instead of derivative of z derived from magnetic probe signals will be discussed. Experiment show that even a single pair of loop voltage signal has better signal-to-noise ratio than differentiation of Zp. In addition, flux loop pickup signals from the IC current are also measured with series of positive and negative IC current pulses.

Cyproheptadine Regulates Pyramidal Neuron Excitability in Mouse Medial Prefrontal Cortex.

Cyproheptadine (CPH), a first-generation antihistamine, enhances the delayed rectifier outward K+ current (IK) in mouse cortical neurons through a sigma-1 receptor-mediated protein kinase A pathway. In this study, we aimed to determine the effects of CPH on neuronal excitability in current-clamped pyramidal neurons in mouse medial prefrontal cortex slices. CPH (10 µmol/L) significantly reduced the current density required to generate action potentials (APs) and increased the instantaneous frequency evoked by a depolarizing current. CPH also depolarized the resting membrane potential (RMP), decreased the delay time to elicit an AP, and reduced the spike threshold potential. This effect of CPH was mimicked by a sigma-1 receptor agonist and eliminated by an antagonist. Application of tetraethylammonium (TEA) to block IK channels hyperpolarized the RMP and reduced the instantaneous frequency of APs. TEA eliminated the effects of CPH on AP frequency and delay time, but had no effect on spike threshold or RMP. The current-voltage relationship showed that CPH increased the membrane depolarization in response to positive current pulses and hyperpolarization in response to negative current pulses, suggesting that other types of membrane ion channels might also be affected by CPH. These results suggest that CPH increases the excitability of medial prefrontal cortex neurons by regulating TEA-sensitive IK channels as well as other TEA-insensitive K+ channels, probably ID and inward-rectifier Kir channels. This effect of CPH may explain its apparent clinical efficacy as an antidepressant and antipsychotic.

A variable-mode stator consequent pole memory machine

In this paper, a variable-mode concept is proposed for the speed range extension of a stator-consequent-pole memory machine (SCPMM). An integrated permanent magnet (PM) and electrically excited control scheme is utilized to simplify the flux-weakening control instead of relatively complicated continuous PM magnetization control. Due to the nature of memory machine, the magnetization state of low coercive force (LCF) magnets can be easily changed by applying either a positive or negative current pulse. Therefore, the number of PM poles may be changed to satisfy the specific performance requirement under different speed ranges, i.e. the machine with all PM poles can offer high torque output while that with half PM poles provides wide constant power range. In addition, the SCPMM with non-magnetized PMs can be considered as a dual-three phase electrically excited reluctance machine, which can be fed by an open-winding based dual inverters that provide direct current (DC) bias excitation to further extend the speed range. The effectiveness of the proposed variable-mode operation for extending its operating region and improving the system reliability is verified by both finite element analysis (FEA) and experiments.

Study of the Relationship Between Maximum Specific Energy and Wire Diameter During Electrical Explosion of Tungsten Wires

Driven by a pulsed current of 1–3 kA in amplitude and 15–30 ns in risetime, electrical explosions of tungsten wires of different diameters (25/18/15/12.5/10 $\mu \text{m}$ ) were carried out. Shadowgraphs as well as interferograms of exploding tungsten wires were obtained with a YAG Laser. The experimental results showed that with the decrease in wire diameter, the maximum specific energy $E_{\mathrm {sm}}$ (the maximum deposition energy per atom), as well as the wire expansion speed has an increase-decrease tendency under both negative and positive current pulses. In order to understand this phenomenon, the specific power $P_{v}$ at the start moment of vaporization was simulated, and the changing tendency of $P_{v}$ versus diameter was found to be similar to that of $E_{\mathbf {sm}}$ versus diameter. Based on the experiments and simulations, we propose that the specific power $P_{v}$ at the evaporating point must also be regarded as an important factor leading to the change in the maximum specific energy $E_{\mathrm {sm}}$ .

Modulation effect produced by adjacent AC voltage on the characteristics of negative corona current pulses in a wire-cylinder electrode configuration

In this paper, a wire-cylinder electrode system was designed to study the negative DC corona pulses due to the influence of AC voltage applied to an adjacent conductor. The corona onset voltage and distribution pattern and the parameters of the corona current pulses such as the rise time, pulse duration and the average pulse amplitude are systematically analyzed. The AC voltage is found to have an interesting modulation effect on the time interval of the current pulses. At last, based on a simplified ion cloud model, a full explanation is given to reveal the mechanism behind the influence of the AC voltage on negative DC corona.

Fully vaporized electrical explosion of bare tungsten wire in vacuum

A flashover switch inserted between the cathode and wire end was used to enhance the deposition energy into an exploding wire in vacuum. It was found that this flashover switch can play two roles. The first one is to reduce the rise time of the current pulse, the second and more important one to greatly improve the surface radial electric field and suppress the electronic emission that is responsible for triggering the surface breakdown of the exploding wire. Only when the flashover switch is on the cathode, the second one can take effect and result in a much higher deposition energy. In this case, the deposition energy could increase by ∼three times (3.4 eV/atom–12 eV/atom) under the negative current pulse and by ∼two times (5.7 eV/atom–13 eV/atom) under the positive one, and fully vaporized wire core was observed with laser interferometry.

A novel carbon nanotubefet based bulk built-in current sensor for single event upset detection

The continuous scaling down of circuits has resulted in the development of carbon nanotubes (CNT) which provides a better alternative of silicon. High device packing densities is one of the advantageous factors of CNTFET compared to CMOS technology. This paper describes the new bulk current based built-in current sensor (BBICS) for the detection of single event upset (SEU) in CNTFET SRAM with less number of transistors compared to previous designs. The advantage of it is that its ability to detect low ranges of micro-current. The complete circuit, both SRAM and Sensor are built with CNTFET. This also possesses the advantage of being used in the detection of negative current pulses with the addition of an inverter circuit. This circuit operates best for two different technology nodes. This built-in current sensor is connected to the bulk terminal of the CNTFET SRAM. PVT analysis and power dissipation analysis were done for the proposed circuit.

Key factors determining the development of two morphologies of plasma electrolytic coatings on an Al–Cu–Li alloy in aluminate electrolytes

Abstract The porosity within plasma electrolytic oxidation (PEO) coatings strongly affects their properties, such as the wear resistance. Two typical types of coatings, i.e. bi-layered coatings with large internal pores, which show low wear resistance, and single-layered coatings with excellent wear performance, have been found following PEO of aluminium alloys under pulsed current regimes with an aluminate electrolyte. In this paper, the mechanisms of formation of the different coatings are investigated and discussed based on a thorough investigation of PEO of an Al–Cu–Li alloy using systematic variations of 1000 Hz pulsed current waveforms and electrolyte concentration. Both parameters have important roles in determining the structure of the resultant coatings. The coatings formed in a dilute electrolyte, containing 5 g l− 1 NaAlO2, were bi-layered and contained both large pores and pancake structures irrespective of the application of a negative pulse. In contrast, the application of negative current pulse favored the formation of single-layered coatings that contained fewer pancake structures in an electrolyte 32 g l− 1 NaAlO2. A more concentrated electrolyte, containing 56 g l− 1 NaAlO2, resulted in relatively compact, single-layered coatings independently of a negative current pulse. Similar observations for the coating morphologies were made if the alloy was replaced by high purity aluminium and also for the alloy when the frequency was reduced to 100 Hz. Two different models for the growth of single- and bi-layered coatings are proposed.

A generator of aperiodic current pulses of artificial lightning with a rationed temporal form of 10 μs/350 μs with an amplitude of ±(100–200) kA

A high-power high-voltage generator that forms aperiodic current pulses of artificial lightning of a temporal form of 10 μs/350 μs and an amplitude of ±(100–200) kA with tolerances, which are normalized according to the IEC 62305-1–2010 International Standard, is described. The circuit and design solutions are described that make it possible, using a generator that is developed on the basis of capacitive energy storages, to provide the generation of aperiodic positive (negative) current pulses of a simulated lightning across an electric load with an ohmic resistance of 0.1 Ω and an inductance of 1.5 μH. The time in which the magnitude of the pulse amplitude Im reaches 106 kА is tm ≈ 24 μs, the pulse duration at a level of 0.5Im is τp ≈ 340 μs, and the pulse-front duration is τf ≈ 15 μs. The action integral of a current pulse of the first short stroke of artificial lightning with an amplitude of Im ≈ 106 kА, which was obtained according to the IEC 62305-1–2010 standard, was Ja ≈ 3.03 × 106 А2 s, and the electric charge that passed through the aforementioned load was ql ≈ 52.2 C.

Dynamic Evolution of Helium Atmospheric Pressure Plasma Jet With ITO-PET Electrodes

A helium atmospheric pressure plasma jet configured with transparent double ring electrodes is driven by an ac high voltage power, and its dynamic evolution in a whole cycle is carefully investigated with ns scale intensified-charge coupled device images. During the positive current pulse, a plasma bullet appears at downstream of active electrode and donut shape plasma presents inside ground electrode, respectively, and wavepacket-like behavior emerges in Dielectric Barrier Discharge (DBD) zone. However, for negative current pulse, the phenomena with double plasma bullets occur beneath active electrode, and plasma inside ground electrode is formed via overflow of diffuse plasma in DBD zone.