Ampere Research Articles

Bunching enhancement for coherent harmonic generation by using phase merging effects

In this paper, promising but simple schemes are investigated to enhance the micro-bunching of relativistic electron beams for coherent harmonic generation (CHG) by using phase merging effects. In contrast to the standard CHG scheme, two specially designed dispersion sections (DSs) are adopted with the DS-modulator–DS configuration. The phase space of the e beam is appropriately coupled in the first DS, and the electrons within one seed wavelength can merge to the same phase with a matched second DS. Micro-bunching of the e beam can thus be enhanced by a large margin with much higher-harmonic components. Taking e beams from laser wakefield accelerators (LWFAs) as an example, start-to-end simulations are performed to show the effectiveness and robustness of the proposed schemes with several configurations. The beam current can be optimized to several tens to hundreds of kiloamperes, and the radiation power reaches hundreds of megawatts in the extreme ultraviolet regime within a 3.5 m-long beamline. The proposed schemes offer new opportunities for future compact free-electron lasers driven by LWFAs and provides prospects for truly compact and widely applicable systems.

Instrumentation for Sub-Ampere Lightning Current Measurement on a Tall Meteorological Tower in Complex Electromagnetic Environment

Measurement of lightning current plays a critical role in the field of atmospheric electricity. Traditionally, Rogowski coils or low-resistance shunts were employed for measuring lightning currents in the range from several amperes up to several hundreds of kilo-amperes, and high-value resistors were utilized for measuring corona discharge currents at sub-ampere levels. However, these approaches were not suitable for continuously recording the vast range of lightning currents. For this sake, we have developed a lightning current measurement system equipped with a shock-tolerant low-noise amplifier module. With the system installed on a tall tower, sub-ampere level currents just before the lightning initiation were observed for the first time. To confirm the authenticity of the recorded currents, the background noise of the measurement system and surrounding environment were identified, and a digital multi-frequency notch filter was proposed for de-noising. Results show that the system can achieve a current identification level of 50 mA even in complex electromagnetic environments, while having a measurement capability of 220 kA.

Experimental Demonstration of High-Sensitivity Nano capacitors via Advanced Nanofabrication Techniques for Nano Electronic Implementations

Nano gap capacitors have recently received significant interest as a key component in a wide range of implementations including photonics, Nanoelectronics, and sensing applications. Many exploratory research projects are being conducted to investigate the electrical characteristics of these nano capacitors. One essential issue that this paper addresses is the need for highly sensitive nano gap capacitors which can be adopted for ultra-low power sensing implementations. In this paper, gold is utilized as the electrode material owing to its superb chemical stability, electrical conductivity, and biocompatibility. The fabrication process is started by designing the mask namely nano gap pad electrodes using AutoCAD software. Subsequently, the designs are finally transferred and fabricated onto a chrome glass surface. In this work, after a combination of conventional photolithography and size reduction approach used to fabricate the device, conventional photolithography is applied to transfer the nano gap pattern onto the gold surface. In order to achieve the desired dimension of the nano gap, a size reduction technique is employed. Describe the most important thing in 2-3 sentences only). Visual inspection using a High Power Microscope (HPM), 3D nano profiler, X-Ray diffractions (XRD), and Field Emission Scanning Electron Microscope (FESEM) have been employed to observe and validate the fabricated structures. Results show that a 2.5 nano Ampere is measured as the applied voltage increases to 10 mV. This firmly demonstrates the ultra-low power consumption, several Pico watts, of these nano gap capacitors. Further, our findings show that the fabricated 4nm gap structure can achieve an approximately 300 nano farad capacitor at low frequencies, which is advantageous for adoption in highly sensitive biosensors.

Propagation Mechanism of Branched Downward Positive Leader Resulting in a Negative Cloud‐To‐Ground Flash

AbstractOur basic knowledge of downward positive lightning leaders is incomplete due to their rarity and limited ability of VHF mapping systems to image positive streamers. Here, using high‐speed optical records and wideband electric field and magnetic field derivative signatures, we examine in detail the development of a descending positive leader, which extended intermittently via alternating branching at altitudes of 4.2 to 1.9 km and involved luminosity transients separated by millisecond‐scale quiet intervals. We show that the transients (a) are mostly initiated in previously created but already decayed branches, at a distance of the order of 100 m above the branch lower extremity, (b) extend bidirectionally with negative charge moving up, (c) establish a temporary (1 ms or so) steady‐current connection to the negative part of the overall bidirectional leader tree, and (d) exhibit brightening accompanied by new breakdowns at the positive leader end. One of the transients unexpectedly resulted in a negative cloud‐to‐ground discharge. Both positive and negative ends of the transients extended at speeds of 106–107 m/s, while the overall positive leader extension speed was as low as 103–104 m/s. Wideband electric field signatures of the transients were similar to K‐changes, with their millisecond‐ and microsecond‐scale features being associated with the steady current and new breakdowns, respectively. For transients with both ends visible in our optical records, charge transfers and average currents were estimated to be typically a few hundreds of millicoulombs and some hundreds of amperes, respectively.

Shock-Tolerated Multi-Range Low-Noise Analog Front End for Lightning Current Measurements From Milliamperes to Hundreds of Kiloamperes

Shock-Tolerated Multi-Range Low-Noise Analog Front End for Lightning Current Measurements From Milliamperes to Hundreds of Kiloamperes

Biopolymer and its nanoparticles for surface coating enhancement of epoxy primer on zinc: electrochemical and surface studies

ABSTRACT The purpose of the current work is to develop an eco-friendly formulation which can be successfully utilised to mitigate zinc corrosion in marine environments. Biopolymer amylopectin and its nanoparticles were used to improve the coating characteristics of epoxy primer on zinc. Amylopectin nanoparticles (AMP-Np) were prepared by the microwave-assisted nanoprecipitation method and characterised using XRD, ATR-FTIR, and TEM studies. Inhibition studies were performed to achieve the optimum inhibitor concentration required for corrosion inhibition of zinc in 3.5% NaCl. Detailed surface morphology was studied using scanning electron microscopy and atomic force microscopic techniques. The overall efficiency of the coating after incorporating AMP (0.02 gL−1) was found to be 99.5%. With the addition of AMP-Np (0.005 gL−1), 99.9% coating efficiency was attained by reducing the concentration to 1/4th of AMP. The epoxy-coated metal coupons, along with micro and nano AMP, were dipped in 3.5% NaCl for 15 days to mitigate corrosion of zinc.

Rogowski and D-Dot Sensors for Nanosecond High-Voltage and High-Current Pulse Measurements in Impedance-Matched Pulse Generators

To measure the output voltage and current in our impedance-matched solid-state Marx generator we developed a voltage and current sensor integrated with the IMG structure. One of the advantages of our IMG structure is the coaxial inner transmission line (TL). The end of this TL is the output connection, which consists of a grounded ring and a smaller high-voltage (HV) inner conductor (coaxial). This structure is ideal for fitting D-dot and Rogowski-coil sensors, as these sensors can benefit from the strictly defined electric and magnetic fields in this waveguide. We developed D-dot and Rogowski-coil sensors on printed circuit boards (PCB) and show their usability in our application for measuring HV pulses. The sensors have a bandwidth of about 200 MHz, measure voltages up to 20 kV, and currents up to hundreds of amperes. Their simple PCB design makes them easily reproducible and cheap compared to commercial sensors. Although designed for our IMG, they can be fit on any coaxial line. Next, we made passive integrators to partly integrate the differentiated sensor signal, which improves the signal quality when measured with an oscilloscope. Finally, after software signal postprocessing, we achieve far better voltage measurements and similar current measurements compared to commercial probes.

Development and characteristics study of compact Penning ion source

A compact-size Penning ion source with a small discharge volume (1.24 cm3) is developed. It consists of two concentric cylinders of different heights that act as cathodes and one hollow cylindrical anode. A homogeneous magnetic field is achieved within the discharge volume with geometrical optimization of the ion source. As a result, dense plasma is generated at low discharge power. The dynamics of the pulse mode discharge at low pulse width and frequency of anode voltage are studied. A high discharge (hundreds of amperes) current pulse with low delay time and fast rise time is recorded. The ion source is equally efficient to operate in continuous as well as pulse modes of ionization for various gases. It is operated in a wide range of low pressure at low anode voltage. An extraction system is designed to extract ions efficiently in the axial direction at a variable extraction voltage. The beam current of 200 µA in continuous mode and 6 A fast pulse in the pulsed mode of discharge have been measured. Variable beam current can be extracted with variable extraction voltage for any potential application.

Blending or Bonding? Mechanochromism of an Aggregachromic Mechanophore in a Thermoplastic Elastomer

A straightforward way for the preparation of mechanochromic polymers consists of incorporating a suitable content of a mechanophore in the polymeric matrix either by physical dispersion or via covalent functionalization. Although covalent incorporation may require demanding chemical efforts, this approach can offer significant advantages over physical dispersion. In this work, a common thermoplastic elastomer, styrene-b-(ethylene-co-butylene)-b-styrene triblock copolymer grafted with maleic anhydride (SEBS-MAH), was covalently functionalized with 1-aminomethylpyrene (AMP). MAH functional groups are covalently linked to the ethylene-co-butylene blocks, thus allowing a precise and selective confinement of the chromogenic AMP units in the soft block. Flat, fully conjugated pyrene units undergo the reversible formation of π–π aggregates, readily distinguishable by their red-shifted emission. These aggregates were heavily affected by the application of mechanical stimuli. Despite the low degree of mechanophore functionalization (about 1 wt %), uniaxial deformation of the polymer was reliably monitored via fluorescence and a clear drop in the excimer to monomer emission ratio (IE/IM) was observed starting from 50% of strain. The marked mechanochromism was confirmed by emission lifetime measurements and also by near-field investigations. In addition, the mechanoresponse showed good reversibility after repeated stress–relaxation cycles. Control experiments performed on formulations comprising a physical dispersion of pyrene in unfunctionalized SEBS showed faint excimer emission and a negligible mechanochromic response up to 5 wt % of doping, in substantial agreement with the scanning near-field optical microscopy analysis. An evident drop of the IE/IM ratio occurred for 10 wt % of pyrene, albeit the excimer emission remained predominant even at the highest deformation, being a smaller fraction of pyrene moieties involved. Overall, the covalent approach appeared as an elegant procedure to confine the chromogenic unit in the soft phase of block copolymers and thus to provide an elastomeric film showing a detectable and reversible mechanochromic response with a modest (i.e., ∼1 wt %) amount of pyrene molecules, i.e., 10 times smaller compared to the dispersed system.

IMPACT OF LIGHTNING ON OPTICAL FIBERS

The study of trigger lightning is of great practical importance, since the action of protective structures and lightning rods, as well as the development of lightning discharges in high-rise buildings and in the mountains, begins as in trigger lightning with the development of a positive leader to the cloud, and flashes of γ-rays possibly occur during lightning discharges with high structures, which is confirmed by practice, since the occurrence of X-ray and γ-rays was observed inside or close to clouds and on mountain tops. If an optical cable contains metal elements in its design, then they are exposed to current, the value of which can reach several tens of kiloamperes. It is the magnitude of the current during lightning strikes and the consequences of its impact on objects that have always attracted the attention of researchers, while the other characteristics of lightning have received less attention. Meanwhile, the return stroke phase of the lightning strike process, during which a current of hundreds of kiloamperes can flow, is a relatively short-lived part of the lightning strike. Recent research into lightning has revealed surprising new phenomena that are not yet fully understood and require further study to determine the dangers they pose to fiber optic communication lines and the need for possible protective measures.

Runaway dynamics in reactor-scale spherical tokamak disruptions

Understanding generation and mitigation of runaway electrons in disruptions is important for the safe operation of future tokamaks. In this paper we investigate the runaway dynamics in reactor-scale spherical tokamaks, focusing on a compact nominal design with a plasma current of 21 megaamperes (MA), 1.8 T magnetic field on axis and major radius of approximately 3 m. We study both the severity of runaway generation during unmitigated disruptions, and the effect that typical mitigation schemes based on massive material injection have on runaway production. The study is conducted using the numerical framework dream (Disruption Runaway Electron Analysis Model). We find that, in many cases, mitigation strategies are necessary to prevent the runaway current from reaching multi-MA levels. Our results indicate that, with a suitably chosen deuterium–neon mixture for mitigation, it is possible to achieve a tolerable runaway current and ohmic current evolution. However, this does not account for the runaway source due to wall activation, which has been found to severely limit successful mitigation at conventional aspect ratios, but whose definition requires a more complete wall specification. Furthermore, the majority of the thermal energy loss is found to happen through radial transport rather than radiation, which poses a risk of unacceptable localised heat loads.

3D stretchable and self-encapsulated multimaterial triboelectric fibers.

A robust power device for wearable technologies and soft electronics must feature good encapsulation, high deformability, and reliable electrical outputs. Despite substantial progress in materials and architectures for two-dimensional (2D) planar power configurations, fiber-based systems remain limited to relatively simple configurations and low performance due to challenges in processing methods. Here, we extend complex 2D triboelectric nanogenerator configurations to 3D fiber formats based on scalable thermal processing of water-resistant thermoplastic elastomers and composites. We perform mechanical analysis using finite element modeling to understand the fiber's deformation and the level of control and engineering on its mechanical behavior and thus to guide its dimensional designs for enhanced electrical performance. With microtexture patterned functional surfaces, the resulting fibers can reliably produce state-of-the-art electrical outputs from various mechanical deformations, even under harsh conditions. These mechanical and electrical attributes allow their integration with large and stretchable surfaces for electricity generation of hundreds of microamperes.

Gliding arc/glow discharge for CO2 conversion: Comparing the performance of different discharge configurations

We studied the use of low current (hundreds of milliamperes) gliding arc/glow discharges for CO2 dissociation, at atmospheric pressure, in three different configurations. All of these are based on the gliding arc design with flat diverging electrodes. The discharge is mainly in the normal glow regime with contracted positive column. The CO2 gas is injected from a nozzle, at the closest separation between the electrodes. A pair of quartz glasses is placed on both sides of the electrodes, so that the gas flow is restricted to the active plasma area, between the electrodes. For two of the tested configurations, an external magnetic field was applied, to create a magnetic force, both in the direction of the gas flow, and opposite to the gas flow. In the first case, the arc is accelerated, shortening the period between ignition and extinction, while in the second case, it is stabilized (magnetically-stabilized). We studied two quantities, namely the CO2 conversion and the energy efficiency of the conversion. Generally, the CO2 conversion decreases with increasing flow rate and increases with power. The energy efficiency increases with the flow rate, for all configurations. The magnetically-stabilized configuration is more stable and efficient at low gas flow rates, but has poor performance at high flow rates, while the non-stabilized configurations exhibit good conversion for a larger range of flow rates, but they are generally more unstable and less efficient.

Bidirectional field–circuit coupling analysis of converter transformer inter‐tap short‐circuit faults in on‐load tap changers

Converter transformer inter-tap short-circuit faults in on-load tap changers have occurred successively in recent years, resulting in severe accidents and enormous losses. Due to the lack of an effective model and credible arc-in-oil conductance parameters, related fault analysis has remained a challenge. This paper develops a bidirectional field–circuit coupling method for modelling inter-tap faults, in which the electromagnetic field and electric circuit are directly coupled and simultaneously solved. After verification based on on-site arcing tests, the Schavemaker model is applied to calculate the non-linear arc conductance. Taking a ±800 kV UHVDC system as a study case, inter-tap faults in a 415 MVA/500 kV converter transformer are simulated and analysed. Under an inter-tap fault, the flux distribution is significantly distorted, with large radial leakage fluxes near the shorted turns, and the circulating current can reach tens or even hundreds of kiloamperes. Further calculation results for faults between various taps indicate that leakage flux distortion and the change in the transformation ratio are the main factors influencing the short-circuit current. These representative findings effectively reveal the variation characteristics of the leakage flux and the short-circuit current as well as the non-linear relationship between fault severity and tap position under inter-tap faults.

Thermal instabilities in micropinches under turbulent heating conditions

Anomalous thermal (AT) instabilities occurring in micropinches are analyzed based on the theory of small perturbations. Instabilities of this type develop in a high-temperature plasma under turbulent heating conditions in the presence of an anomalous resistance resulting from the scattering of electrons by lower hybrid drift oscillations. When turbulent heating occurs in the plasma of a micropinch, its resistivity increases with decreasing density; this may lead to the formation of plasma layers normal to the current flow (stratification). For the AT instability, a dispersion relation taking into account the effect of the plasma self-radiation has been derived, and the characteristic instability growth rates and wavelengths have been determined. A comparison of the development pattern has been performed between AT and sausage-type magnetohydrodynamic instabilities. It has been shown that for any pinch material, there is a threshold current below which AT instabilities prevail over magnetohydrodynamic instabilities. For the metals considered (aluminum, titanium, copper, molybdenum, and tungsten), the threshold currents are hundreds of kiloamperes. The threshold current increases with atomic number: for tungsten, it is approximately 3.5 times higher than for aluminum. The conclusions drawn from the analysis based on the linear small perturbation theory are compared with the results of experiments in which the parameters of ‘hot spots’ formed in X pinches were determined.

(Digital Presentation) Review on Electronic Interfaces for Electrochemical Sensor – Enabling Research from the Lab to Market

The recent development in the material sciences and facility to synthesis different types of materials made way for advances in electrochemical sensors. A lot of research articles being published on electrochemical sensors on different applications such as human health (metabolites, nutrients, biomarkers of diseases, or development pathologies), potential hazards (environmental pollutants, food contaminants, genotoxic chemicals, etc.), structural monitoring, animal health diagnosing, corrosion detection, Lab-on-chip solutions, etc. Most of the sensors are characterized in any of the detection principle measurement of current (amperometric), charge accumulation or a measurable potential (potentiometric) or change in the conductive properties of medium (conductometric), change in the impedance due to the change in the properties of the material due to species/analyte to be detected (impedimetric) and field-effect which exploits transistor principle to change in current a result of a potentiometric effect at a gate electrode. Most of the reported results are conducted by sophisticated expensive instruments. Researchers are unable to accentuate their research from their lab to market due to a lack of awareness of the instrumentation being used in the instrument. The prominent results of the lab need to be converted into any of the devices like point-of-care (POC), point-of-care testing (POCT), point-of-test (POT), point-of-interest/point-of-incidence (POI), or portable field device. The present review focuses on low-level measurements like quantifying microampere in resolution with nano ampere, mV changes as well as a few ohms to a few kilo-ohms. The current paper also explains to choose suitable components to design analog frontend to acquire signals from different types of electrochemical sensors. Current work also aims to create awareness on available Application-specific integrated circuits (IC) to design suitable instrumentation for the electrochemical sensor. Different power sources and Packaging techniques are also discussed to make the device portable, wearable, implantable, etc. Recent advancements in ultra-low power with more computational power capability microcontroller with various communication technologies appropriate to make device also elucidated in the paper. Thus, the paper imparts the required knowledge to do translation research on electrochemical biosensors.

High field hybrid photoinjector electron source for advanced light source applications

The production of high spectral brilliance radiation from electron beam sources depends critically on the electron beam qualities. One must obtain very high electron beam brightness, implying simultaneous high peak current and low emittance. These attributes are enabled through the use of very high field acceleration in a radio-frequency (rf) photoinjector source. Despite the high fields currently utilized, there is a limit on the achievable peak current in high brightness operation, in the range of tens of Ampere. This limitation can be overcome by the use of a hybrid standing wave/traveling wave structure; the standing wave portion provides acceleration at a high field from the photocathode, while the traveling wave part yields strong velocity bunching. This approach is explored here in a C-band scenario, at field strengths ($>100\text{ }\text{ }\mathrm{MV}/\mathrm{m}$) at the current state-of-the-art. It is found that one may arrive at an electron beam with many hundreds of Amperes with well-sub-micron normalized emittance. This extremely compact injector system also possesses attractive simplification of the rf distribution system by eliminating the need for an rf circulator. We explore the use of this device in a compact 400 MeV-class source, driving both inverse Compton scattering and free-electron laser radiation sources with unique, attractive properties.

Electromechanical Analysis of Core- and Shell-Type Inductive Superconducting Fault Current Limiters Under General Fault Conditions

In transmission and distribution grids, electrical currents in rated conditions can reach hundreds of amps. Under fault conditions, these currents can reach ten times or more their rated value. In power devices, particularly in superconducting fault current limiters (SFCLs), this current rise leads to the development of electromechanical forces that can damage the superconducting tape, so should be properly analyzed, for the sake of equipment integrity. Additionally, when asymmetric faults occur in the grid, the desired circumstance is that a fault in one phase does not affect the other ones, to minimize damages and disturbances in the grid and protection devices. In this article, core- and a shell-type inductive SFCLs are tested under several fault conditions. The main objectives are to measure and analyze the electromechanical forces developed in each superconducting winding, to evaluate their integrity after faults, and to compare the performance of both types of limiters under the same fault conditions. Electromechanical forces measurements in the three phases are made simultaneously, using a device based on strain gauges, calibrated to operate at 77 K. This article contributes to evaluating the robustness and best geometry of this inductive limiter of transformer type.

Ignition conditions for a self-pulsing discharge with the microhollow cathode in air

This work is devoted to the study of the electrical characteristics of a discharge with a microhollow cathode in air at atmospheric pressure. It was experimentally found that the discharge with a microhollow cathode developed in a self-pulsing mode with an average current of hundreds of microamperes. According to the experimental data it was concluded that the self-pulsing frequency linearly depended on the consumed current. The values of the ignition voltage of the self-pulsing discharge with a microhollow cathode at different hole diameters were obtained.

A High-Efficiency High-Power-Density On-Board Low-Voltage DC–DC Converter for Electric Vehicles Application

The on-board low-voltage dc-dc converter (LDC) in electric vehicles (EVs) is used to connect the high-voltage battery with the low-voltage auxiliary system. With the advancement of auxiliary equipment in EVs, the output current of the LDC can be hundreds of amperes, which will cause high-conduction loss and severe thermal concern. In this article, a high-efficiency high-power-density on-board LDC is presented. To reduce current stress and improve efficiency, three-phase interleaved LLC dc-dc converters are paralleled to provide 270 A load current. Synchronous rectifier is used to reduce secondary conduction loss. zero-voltage-switching (ZVS) turn-on of primary switches and ZCS turn-off of secondary switches are achieved, thus switching loss can be reduced significantly. Moreover, phase-shedding technology is used to improve light load efficiency. Switch-controlled capacitor (SCC) technology is used to achieve accurate load current sharing among the three phases, which protects the devices against high-current stress, reduces the conduction loss, and improves the reliability of the system. As SCC switches achieve ZVS turn-on and turn-off by its nature, the loss of the SCC circuit is of less concern with regard to the rated output power. In addition, GaN HEMTs are used in the primary side to improve the power density and eventually help achieving light weight. A 3.8-kW (14 V/270 A) LDC prototype is developed and tested. Experimental results show good current balancing among the three phases. A peak efficiency of 96.7% at 140 A load and a full load efficiency of 95.8% are achieved with 3 kW/L power density and 1.5 kg weight.