SEARCH · Engineering Papers

Results for “CURRENTS”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 649 records · Page 36

All sources NASA NTRS DOE OSTI

NASA NTRS2014

An Intrinsic Fiber-Optic Sensor for Structure Lightning Current Measurement

An intrinsic optical-fiber sensor based on Faraday Effect is developed that is highly suitable for measuring lightning current on aircraft, towers and complex structures. Originally developed specifically for aircraft installations, it is light-weight, non-conducting, structure conforming, and is immune to electromagnetic interference, hysteresis and saturation. It can measure total current down to DC. When used on lightning towers, the sensor can help validate other sensors and lightning detection network measurements. Faraday Effect causes light polarization to rotate when the fiber is exposed to a magnetic field in the direction of light propagation. Thus, the magnetic field strength can be determined from the light polarization change. By forming closed fiber loops and applying Ampere's law, measuring the total light rotation yields the total current enclosed. A broadband, dual-detector, reflective polarimetric scheme allows measurement of both DC component and AC waveforms with a 60 dB dynamic range. Two systems were built that are similar in design but with slightly different sensitivities. The 1310nm laser system can measure 300 A - 300 kA, and has a 15m long sensing fiber. It was used in laboratory testing, including measuring current on an aluminum structure simulating an aircraft fuselage or a lightning tower. High current capabilities were demonstrated up to 200 kA at a lightning test facility. The 1550nm laser system can measure 400 A - 400 kA and has a 25m fiber length. Used in field measurements, excellent results were achieved in the summer of 2012 measuring rocket-triggered lightning at the International Center for Lightning Research and Testing (ICLRT), Camp Blanding, Florida. In both systems increased sensitivity can be achieved with multiple fiber loops. The fiber optic sensor provides many unique capabilities not currently possible with traditional sensors. It represents an important new tool for lightning current measurement where low weight, complex shapes, large structure dimension, large current, and low frequency capabilities are important considerations.

Nguyen, Truong X.↗

NASA NTRS2017

Current Source Logic Gate

A current source logic gate with depletion mode field effect transistor ("FET") transistors and resistors may include a current source, a current steering switch input stage, and a resistor divider level shifting output stage. The current source may include a transistor and a current source resistor. The current steering switch input stage may include a transistor to steer current to set an output stage bias point depending on an input logic signal state. The resistor divider level shifting output stage may include a first resistor and a second resistor to set the output stage point and produce valid output logic signal states. The transistor of the current steering switch input stage may function as a switch to provide at least two operating points.

Krasowski, Michael J.↗

NASA NTRS2017

Understanding Breaks in Flare X-Ray Spectra: Evaluation of a Cospatial Collisional Return-Current Model

Hard X-ray (HXR) spectral breaks are explained in terms of a one-dimensional model with a cospatial return current. We study 19 flares observed by the Ramaty High Energy Solar Spectroscopic Imager with strong spectral breaks at energies around a few deka-keV, which cannot be explained by isotropic albedo or non-uniform ionization alone. We identify these breaks at the HXR peak time, but we obtain 8 s cadence spectra of the entire impulsive phase. Electrons with an initially power-law distribution and a sharp low-energy cutoff lose energy through return-current losses until they reach the thick target, where they lose their remaining energy through collisions. Our main results are as follows. (1) The return-current collisional thick-target model provides acceptable fits for spectra with strong breaks. (2) Limits on the plasma resistivity are derived from the fitted potential drop and deduced electron-beam flux density, assuming the return current is a drift current in the ambient plasma. These resistivities are typically 2-3 orders of magnitude higher than the Spitzer resistivity at the fitted temperature, and provide a test for the adequacy of classical resistivity and the stability of the return current. (3) Using the upper limit of the low-energy cutoff, the return current is always stable to the generation of ion-acoustic and electrostatic ion-cyclotron instabilities when the electron temperature is nine times lower than the ion temperature. (4) In most cases, the return current is most likely primarily carried by runaway electrons from the tail of the thermal distribution rather than by the bulk drifting thermal electrons. For these cases, anomalous resistivity is not required.

Alaoui, Meriem↗

NASA NTRS2018

Current Source Logic Gate

Krasowski, Michael J.↗

NASA NTRS2017

High Current Lanthanum Hexaboride Hollow Cathode for 20-200 kW Hall Thrusters

The demand for higher power Hall and ion thrusters continues for providing high thrust and long life for deep space mission. The X3 nested Hall thruster is capable of power levels in the 20 to 200-kW range, and is being developed by the University of Michigan and Aerojet for future cargo and manned-missions. The cathode for this thruster is required to produce discharge currents of 50 to 350 A with lifetimes in excess of 10 khrs. A high-current lanthanum hexaboride (LaB6) hollow cathode was previously developed at JPL for these applications, and was successfully operated at over 250 A of discharge current. An updated version of this cathode has been designed, built and tested at JPL, and then used to run the X3 nested Hall thruster at currents of up to 250 A. The new version is designed to reduced orifice plate overheating at high currents, and is capable of injecting auxiliary gas directly into the near-cathode plume from two locations to minimize energetic ion generation at high current. The cathode is predicted to be capable of producing over 350 A of discharge current, and has been tested to date at JPL at steady-state discharge currents from 25 A to 300 A.

Goebel, Dan M.↗

DOE OSTI2020

Matrix converter operation in current control mode with regulation of output voltage vector

A matrix converter system having a current control mode operation is provided. The matrix converter system includes a matrix converter that includes a plurality of switches. A unity current reference vector having an amplitude of one is determined that defines an angle and frequency of an output current vector as a function of a reference phase angle, which is a function of the output current vector and an output voltage vector representing feedback signals of a multiphase signal output to a load. The unity current reference vector is used to control the matrix converter, to cause the output current vector to be aligned with the unity current reference vector. A unity voltage reference vector having an amplitude of one is provided that defines a reference angle and frequency as a function of a zero phase angle. The output voltage vector and the unity voltage reference vector are aligned to determine the reference phase angle as an angle between the aligned output voltage vector and the output current vector.

42 ENGINEERING↗

DOE OSTI2021

DC input current ripple reduction in SRM drive for high volumetric power density applications

A control system for a switched reluctance machine includes a capacitor and an inverter connected to the capacitor, wherein the inverter generates current signals and a ripple current returned to the capacitor. A switched reluctance machine (SRM) receives the current signals and generates a position signal. A controller receives the ripple current, current signal values of the current signals, and the position signal and generates desired reference current waveforms received by the inverter to adjust the current signals received by the SRM.

Sozer, Yilmaz↗

DOE OSTI2016

Theoretical Calculation and Simulation Studies of Axisymmetric Plasma and Halo Current Analysis in EAST

A new technology for developing fusion energy is to use hydrogen isotopes i.e., deuterium (D) and tritium (T) which is a combine effort for building up of International Thermonuclear Reactor (ITER) named as Tokamak, which will come into operation in 2020. Handsome amount of work has already been done by many researchers contingent with plasma shape, halo current and plasma equilibrium properties by numerical techniques. Halo current calculation is the most important work in fusion reactors. In this paper, we have calculated halo current and plasma cross-section energy. The research covers calculation of plasma energy and determines the force on the vessel by magnetic field transformation method, which is the essential part of calculating halo current. Further, we have developed VDE up/down halo current models. These models give total magnetic field, asymmetric forces, conducting points and poloidal halo current. Confined plasma by magnetic field is considered to be an abundant and durable source of energy for future aspects. In this paper, plasma magnetic field of each cross section was calculated by using energy integral. Transformation method has been successfully applied which provides the connection between major sideways forces acting on the plasma. Theoretical investigation and analyses of halo current have successfully been done. Two observations were analyzed, large ratio of halo current during VDE down and cancellation of specific forces at conducting point. The results obtained will be useful for equalizing the simulation and experimental results. The research will be extended to developed new models for future fusion research. (authors)

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2015

A fresh look at electron cyclotron current drive power requirements for stabilization of tearing modes in ITER

ITER is an international project to design and build an experimental fusion reactor based on the “tokamak” concept. ITER relies upon localized electron cyclotron current drive (ECCD) at the rational safety factor q=2 to suppress or stabilize the expected poloidal mode m=2, toroidal mode n=1 neoclassical tearing mode (NTM) islands. Such islands if unmitigated degrade energy confinement, lock to the resistive wall (stop rotating), cause loss of “H-mode” and induce disruption. The International Tokamak Physics Activity (ITPA) on MHD, Disruptions and Magnetic Control joint experiment group MDC-8 on Current Drive Prevention/Stabilization of Neoclassical Tearing Modes started in 2005, after which assessments were made for the requirements for ECCD needed in ITER, particularly that of rf power and alignment on q=2 [1]. Narrow well-aligned rf current parallel to and of order of one percent of the total plasma current is needed to replace the “missing” current in the island O-points and heal or preempt (avoid destabilization by applying ECCD on q=2 in absence of the mode) the island [2-4]. This paper updates the advances in ECCD stabilization on NTMs learned in DIII-D experiments and modeling during the last 5 to 10 years as applies to stabilization by localized ECCD of tearing modes in ITER. This includes the ECCD (inside the q=1 radius) stabilization of the NTM “seeding” instability known as sawteeth (m/n=1/1) [5]. Recent measurements in DIII-D show that the ITER-similar current profile is classically unstable, curvature stabilization must not be neglected, and the small island width stabilization effect from helical ion polarization currents is stronger than was previously thought [6]. The consequences of updated assumptions in ITER modeling of the minimum well-aligned ECCD power needed are all-in-all favorable (and well-within the ITER 24 gyrotron capability) when all effects are included. However, a “wild card” may be broadening of the localized ECCD by the presence of the island; various theories predict broadening could occur and there is experimental evidence for broadening in DIII-D. Wider than now expected ECCD in ITER would make alignment easier to do but weaken the stabilization and thus require more rf power. In addition to updated modeling for ITER, advances in the ITER-relevant DIII-D ECCD gyrotron launch mirror control system hardware and real-time plasma control system have been made [7] and there are plans for application in DIII-D ITER demonstration discharges.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2016

A superconducting direct-current limiter with a power of up to 8 MVA

A resistive switching superconducting fault current limiter (SFCL) for DC networks with a nominal voltage of 3.5 kV and a nominal current of 2 kA was developed, produced, and tested. The SFCL has two main units—an assembly of superconducting modules and a high-speed vacuum circuit breaker. The assembly of superconducting modules consists of nine (3 × 3) parallel–series connected modules. Each module contains four parallel-connected 2G high-temperature superconducting (HTS) tapes. The results of SFCL tests in the short-circuit emulation mode with a maximum current rise rate of 1300 A/ms are presented. The SFCL is capable of limiting the current at a level of 7 kA and break it 8 ms after the current-limiting mode begins. The average temperature of HTS tapes during the current-limiting mode increases to 210 K. After the current is interrupted, the superconductivity recovery time does not exceed 1 s.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2016

Ring current pressure estimation with RAM-SCB using data assimilation and Van Allen Probe flux data

Capturing and subsequently modeling the influence of tail plasma injections on the inner magnetosphere is important for understanding the formation and evolution of the ring current. In this study, the ring current distribution is estimated with the Ring Current–Atmosphere Interactions Model with Self–Consistent Magnetic field (RAM–SCB) using, for the first time, data assimilation techniques and particle flux data from the Van Allen Probes. The state of the ring current within the RAM–SCB model is corrected via an ensemble based data assimilation technique by using proton flux from one of the Van Allen Probes, to capture the enhancement of the ring current following an isolated substorm event on 18 July 2013. The results show significant improvement in the estimation of the ring current particle distributions in the RAM–SCB model, leading to better agreement with observations. Furthermore, this newly implemented data assimilation technique in the global modeling of the ring current thus provides a promising tool to improve the characterization of particle distribution in the near–Earth regions.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2023

Characteristics of upward-connecting-leader current leading to attachment in downward negative cloud-to-ground lightning strokes

For this work, we analyzed currents associated with upward connecting leaders (UCLs) initiated from the Kennedy Space Center Industrial Area Tower in two negative cloud-to-ground strokes that struck the tower. One stroke was also recorded using a high-speed video camera located 760 m from the KSC IAT. The NLDN-reported peak currents for the two strokes were – 31.7 and – 98.5 kA. During the UCL development phase the current waveforms exhibited a monotonically (quasi-exponentially) increasing “background” current overlaid with 10-μs scale pulses with a median amplitude of 51.1 A. The UCL current durations for the two strokes were 1039 and 449 μs, respectively. During the pre-attachment processes (UCL and slow front) the total negative charge effectively transferred to ground were 70.2 and 55 mC, respectively. For the stroke captured on high-speed video, the average line-charge-density for the 109-m long UCL was found to be 0.5 mC/m. The average UCL 2-D speed was 2.4 × 10 5 m/s, and it was observed to accelerate toward the downward leader prior to attachment. We observed that UCL-pulse amplitudes are larger, background currents are higher, and interpulse intervals are shorter at later times during UCLs, which can be attributed to the intensification of the local electric field due to the approaching downward negative leader. The median positive charge injected into the UCL by a pulse was 297 μC. The UCL associated with the higher peak-current stroke produced the highest injected pulse-charge values about three times sooner during its development, likely due to the 2–2.7 times faster average downward leader vertical speeds.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2023

A lightweight and metal-free current collector for battery anode applications

The requirement for high energy density batteries is driving the development of high-capacity electrode materials while reducing the amount of inactive battery components such as separators, binders, and current collectors. Though current collectors are an inactive component, they are still required for successful working of a battery cell. Conventional current collectors include aluminum foil for cathode and copper foil for anode. Copper foil is quite heavy (8.7 mg/cm 2 ) for 10μm thickness. Therefore, there is a need for a lightweight current collector for anode applications. In this work, a metal-free current collector comprised of aligned carbon fiber (CFs) layer filled with carbon nanotubes (CNTs) mixed in polymer (P) is developed to be used as a current collector for anodes. Further, anodes coated on the CF-CNT-P showed lower charge transfer resistance and improved rate capability compared with the anodes fabricated on conventional copper foil-based current collectors. The CF-CNT-P are lighter (≈1.5 mg/cm 2 ) than the commonly used copper foil (8.7 mg/cm 2 ), which will increase the gravimetric energy density.

25 ENERGY STORAGE↗

DOE OSTI2023

Aligned carbon fibers-carbon nanotube-polymer-based composite as lithium-ion battery current collector

High energy density demand is pushing the development of high-voltage cathode materials, which necessitates improved electrochemical stability of other battery components such as binders, electrolytes, and current collectors. Current collectors are considered to be an inactive component but still play an essential role. In this study, a metal-free composite film containing directionally aligned carbon fiber (CF), carbon nanotube (CNT), and polymer (P) was developed to replace aluminum foil as a cathode current collector, which relies on forming an Al 2 O 3 layer to ensure electrochemical stability at high voltage. Here, each component in the new cathode current collector played a functional role. The CNTs provided uniform current densities, and CFs improved the electronic conductivity and mechanical strength of the composite material. The polymer enhanced the adhesion of the cathode coating with the current collector and provided an impervious support to the cathode materials. The CF-CNT-P composite demonstrated excellent electrochemical and thermal stability. Cathodes coated on the CF-CNT-P composite exhibited lower charge transfer resistance, improved rate capability, and improved cyclic stability compared with the cathodes deposited on conventional aluminum foil. Additionally, the composite current collector was lighter (1.81 mg/cm 2 and 15 µm thick) than the commonly used aluminum foil (4.35 mg/cm2 and 15 µm thick), which can increase the cell energy density. Additionally, the CF-CNT-P did not need to be separated from the cathode coating during recycling and can be burnt out with binder, simplifying the recycling process.

25 ENERGY STORAGE↗

DOE OSTI2018

Mathematical modeling of a proton-conducting solid oxide fuel cell with current leakage

Here, a framework of charge transports in proton-conducting solid oxide fuel cells (H-SOFCs) with considering current leakage is developed by assuming four electrode reactions. Current leakage happens when electron holes pass through the electrolyte and combine with electrons at the anode side. An analytical solution of leakage currents is proposed depending on the Nernst-Planck equation. On the basis of the analysis expression, a mathematical model of H-SOFCs is proposed, which can provide the information about current-voltage characteristics, leakage current density, Faraday and energy efficiencies. Moreover, H-SOFCs with the BaZr 0.8 Y 0.2 O 3 electrolyte are fabricated and tested, and the proposed model well reproduces the experimental data. The simulation results indicate that current leakage primarily affects the H-SOFC performance when the output voltage is close to the OCV. Both Faraday efficiencies and energy efficiencies decrease with increasing operating temperatures due to the existence of current leakage.

25 ENERGY STORAGE↗

DOE OSTI2016

Evolution of mechanical properties of ultrafine grained 1050 alloy annealing with electric current

The tensile properties and microstructures of 1050 aluminum alloy prepared by equal channel angular pressing at cryogenic temperature (cryoECAP) after electric current annealing at 90–210 °C for 3 h were investigated by tensile test, electron back scattering diffraction (EBSD) and transmission electron microscopy (TEM). An unexpected annealing-induced strengthening phenomenon occurs at 90–210 °C, due to a significant decrease in the density of mobile dislocations after annealing, and thus a higher yield stress is required to nucleate alternative dislocation sources during tensile test. The electric current can enhance the motion of dislocations, lead to a lower dislocation density at 90–150 °C, and thus shift the peak annealing temperature from 150 °C to 120 °C. Moreover, the electric current can promote the migration of grain boundaries at 150–210 °C, result in a larger grain size at 150 °C and 210 °C, and thus causes a lower yield stress. The sample annealed with electric current has a lower uniform elongation at 90–120 °C, and the deviation in the uniform elongation between samples annealed without and with electric current becomes smaller at 150–210 °C. - Highlights: • An unexpected annealing-induced strengthening phenomenon occurs at 90–210 °C. • The d. c. current can enhance the motion of dislocations at 90–150 °C, and thus shift the peak annealing temperature from 150 °C to 120 °C. • The d. c. current can promote the grain growth at 150–210 °C, and thus cause a lower yield stress. • The DC annealed sample has a lower uniform elongation at 90–120 °C.

36 MATERIALS SCIENCE↗

DOE OSTI2013

Current disruption and its spreading in collisionless magnetic reconnection

Recent magnetic reconnection experiments (MRX) [Dorfman et al., Geophys. Res. Lett. 40, 233 (2013)] have disclosed current disruption in the absence of an externally imposed guide field. During current disruption in MRX, both the current density and the total observed out-of-reconnection-plane current drop simultaneous with a rise in out-of-reconnection-plane electric field. Here, we show that current disruption is an intrinsic property of the dynamic formation of an X-point configuration of magnetic field in magnetic reconnection, independent of the model used for plasma description and of the dimensionality (2D or 3D) of reconnection. An analytic expression for the current drop is derived from Ampere's Law. Its predictions are verified by 2D and 3D electron-magnetohydrodynamic (EMHD) simulations. Three dimensional EMHD simulations show that the current disruption due to localized magnetic reconnection spreads along the direction of the electron drift velocity with a speed which depends on the wave number of the perturbation. The implications of these results for MRX are discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2013

Field-dependent critical state of high-Tc superconducting strip simultaneously exposed to transport current and perpendicular magnetic field

We present an exact analytical approach for arbitrary field-dependent critical state of high-T{sub c} superconducting strip with transport current. The sheet current and flux-density profiles are derived by solving the integral equations, which agree with experiments quite well. For small transport current, the approximate explicit expressions of sheet current, flux-density and penetration depth for the Kim model are derived based on the mean value theorem for integration. We also extend the results to the field-dependent critical state of superconducting strip in the simultaneous presence of applied field and transport current. The sheet current distributions calculated by the Kim model agree with experiments better than that by the Bean model. Moreover, the lines in the I{sub a}-B{sub a} plane for the Kim model are not monotonic, which is quite different from that the Bean model. The results reveal that the maximum transport current in thin superconducting strip will decrease with increasing applied field which vanishes for the Bean model. The results of this paper are useful to calculate ac susceptibility and ac loss.

36 MATERIALS SCIENCE↗