Compensating for Parasitic Voltage Drops in Resistive Memory Arrays.
Abstract not provided.
Agarwal, Sapan↗
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Low voltage drop tunnel junctions grown monolithically by MOCVD
Tunnel junction devices grown monolithically by metal organic chemical vapor deposition were optimized for minimization of the tunnel junction voltage drop. Here, two device structures were studied: an all-GaN homojunction tunnel junction and a graded InGaN heterojunction-based tunnel junction. This work reports a record-low voltage drop in the graded-InGaN heterojunction based tunnel junction device structure achieving a de-embedded tunnel junction voltage drop of 0.17 V at 100 A/cm 2 . The experimental data were compared with a theoretical model developed through technology computer-aided design (TCAD) simulations that offer a physics-based approach to understanding the key components of the design space, which lead to a more efficient tunnel junction.
42 ENGINEERING↗
Effect of Concentration, Temperature, and Interelectrode Gap on the Voltage Drop in an Electrochemical System of GdCl{sub 3}-LiCl-KCl
One of the most common conversations for those in the nuclear field and the public when discussing nuclear power is the issue of nuclear waste. When used nuclear fuel (UNF) is removed from a reactor, it contains fission products, some of which are long lived isotopes that will continue to irradiate for hundreds of years. One of several solutions to this issue is reprocessing, a process where minor actinides and other fission products are separated from still fissile and fertile materials. In the United States, there is no reprocessing of UNF at an industrial scale; however, one of the methods that universities and national labs are currently researching is known as pyro-processing. Pyro-processing utilizes electrochemistry in a molten salt environment to treat UNF and remove uranium and plutonium. The heart of the pyro-processing system is an electrorefining process, where most of the U in the UNF is selectively collected on a solid cathode in molten lithium-potassium chloride (LiCl-KCl) at high temperatures (723 K - 773 K). To model the behavior of materials in the electro-refiner, small bench-scale electrochemical experiments are being performed at many research universities and national labs to better understand material behavior. Within the electrochemical cell, there is a small resistance to current between the cathode and anode. This results in a voltage drop, which can affect the results of the experiments. This voltage drop varies based upon concentration of the salt, the temperature, the distance between the anode and cathode, and the scan rate. For this study, cyclic voltammetry will be performed on GdCl{sub 3}-LiCl-KCl at various temperatures (723 K - 798 K), various sample concentrations (1, 5, and 10 wt%), various scan rates (50, 100, 200, and 300 mV/s), and two different electrode spacing configurations. The resulting cyclic voltammograms will be compared for both electrode configurations to see the impact of interelectrode gap on the voltage drop.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
III-Nitride p-down green (520 nm) light emitting diodes with near-ideal voltage drop
We demonstrate p-down green emitting LEDs with low turn-on voltage enabled by efficient tunnel junctions. Due to the polarization field alignment in the (In,Ga)N/GaN interface with the p-down orientation, the electrostatic depletion barrier for electron and hole injection is reduced when compared with the conventional p-up LEDs. A single (In,Ga)N/GaN heterostructure quantum well active region with a GaN homojunction tunnel junction exhibited very low forward operating voltage of 2.42 V at 20 A/cm 2 with a peak electroluminescence emission wavelength of 520 nm for current densities above 100 A/cm 2 . Furthermore, the bottom tunnel junction with minimal voltage drop enabled excellent hole injection into the bottom p-GaN layer.
36 MATERIALS SCIENCE↗
1.2 kV, 10 A, 4H-SiC Bi-Directional Field Effect Transistor (BiDFET) with Low On-State Voltage Drop
Bidirectional power switches are used in matrix-or cyclo-converters and in multistage inverter circuits to facilitate high-frequency AC-to-AC conversion. A new 1.2 kV bidirectional MOSFET (BiDFET) with low on-resistance is achieved and demonstrated using two discrete SiC power MOSFET bare die chips, packaged within a four-terminal custom-designed module. Static and dynamic characterization has been carried out to inspect the on-state and switching behaviour of the BiDFET. Here, the BiDFET is shown to have a low forward voltage drop of 0.6 V at a current of 10 A, which is more than 2.5x smaller than previous Si IGBT and SiC MOSFET based bidirectional switch implementations.
36 MATERIALS SCIENCE↗
Low voltage drop, cross-field, gas switch and method of operation
A gas switch includes an anode and a cathode spaced apart from the anode, wherein the cathode includes a conduction surface. The gas switch also includes a plurality of magnets arranged to generate a magnetic field that defines an annular path over a portion of the conduction surface at a radial distance from a switch axis, and a control grid positioned between the anode and the cathode. In operation, the control grid is arranged to establish a conducting plasma between the anode and the cathode, wherein, in the presence of the conducting plasma, a voltage drop between the anode and the cathode is less than 150 volts, and wherein the conducting plasma forms a cathode spot that circles the annular path.
42 ENGINEERING↗
Compensating for parasitic voltage drops in circuit arrays
Various technologies for improving uniformity of operation of elements in an array circuit are described herein. In an exemplary embodiment, a plurality of resistive elements are incorporated into an array circuit such that voltages developed across any two elements is substantially the same when an equal voltage is applied to energize the elements. In a crossbar array circuit that comprises a plurality of elements arranged in rows and columns, the resistance of each of the resistive elements is based upon a row or column to which the resistive element is connected.
42 ENGINEERING↗
Dissociate Lattice Oxygen Redox Reactions from Capacity and Voltage Drops of Battery Electrodes
The oxygen redox (OR) reaction is a promising concept for improving battery energy density, however oxygen activities are generally considered detrimental to the stability and kinetics of batteries. Studies of OR activities often mix the lattice OR with other oxygen-involved reactions, such as gas release, radical oxygen evolution and surface reactions, further shadowing the true property of the practically meaningful lattice OR activities. Here, based on high-efficiency mapping of resonant inelastic X-ray scattering (mRIXS) of both the transition-metals and oxygen, we distinguish and quantify the lattice OR activities Na 0.6 [Li 0.2 Mn 0.8 ]O 2 .
25 ENERGY STORAGE↗
Mechanically induced thermal runaway severity analysis for Li-ion batteries
Thermal runaway is one of the most important safety concerns in the deployment of Li-ion batteries. For this study, we developed a standardized single-side indentation test protocol to induce an internal short-circuit. Cell voltage, temperature, and applied compressive force are monitored as a function of time. Each cell is given an observed hazard severity (OHS in five categories) modified from the EUCAR table. Meanwhile a calculated hazard severity (CHS) is obtained solely based on temperature and voltage curves. The calculation formula considers the cell temperature, rate of temperature increase, cell capacity, state of charge (SOC), voltage drop, and voltage drop rate. Each term is assigned with an appropriate weight to scale the calculated score from 0 to100. This method was applied to >100 Li-ion batteries with various SOCs and chemistries, and their OHS and CHS were displayed against SOC. The purpose is to provide battery designers, manufacturers, and end-users a clear comparison of thermal runaway severity of different batteries.
25 ENERGY STORAGE↗
Massive, long-lived electrostatic potentials in a rotating mirror plasma
Abstract Hot plasma is highly conductive in the direction parallel to a magnetic field. This often means that the electrical potential will be nearly constant along any given field line. When this is the case, the cross-field voltage drops in open-field-line magnetic confinement devices are limited by the tolerances of the solid materials wherever the field lines impinge on the plasma-facing components. To circumvent this voltage limitation, it is proposed to arrange large voltage drops in the interior of a device, but coexist with much smaller drops on the boundaries. To avoid prohibitively large dissipation requires both preventing substantial drift-flow shear within flux surfaces and preventing large parallel electric fields from driving large parallel currents. It is demonstrated here that both requirements can be met simultaneously, which opens up the possibility for magnetized plasma tolerating steady-state voltage drops far larger than what might be tolerated in material media.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DC electric field generation and distribution in magnetized plasmas
Very large DC and AC electric fields cannot be sustained between conducting electrodes because of volume gas breakdown and/or surface field emission. However, very large potential fields are now routinely generated in plasma structures, such as laser generated wake in unmagnetized plasmas. In magnetized plasmas, large DC fields can also be sustained and controlled perpendicular to the magnetic field, but the metallic end plates limiting the plasma, terminating the magnetic field lines, and usually providing the voltage drop feed between the field lines impose severe restrictions on the maximum field. However, it is shown that very large radial DC voltage drops can be sustained by injecting waves of predetermined frequencies and wave vectors, traveling along the azimuthal direction of an axially magnetized plasma cylinder, or by injecting fast neutral particles beams along this azimuthal direction. The large conductivity along the magnetic field lines and the small conductivity between the field lines then distribute this voltage drop. Furthermore, the global power balance and control parameters of wave and beam generated large DC electric fields in magnetized plasmas are identified, described, and analyzed.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Hybrid Ag 2 VO 2 PO 4 /CF x as a High Capacity and Energy Cathode for Primary Batteries
In this report, we describe the electrochemistry of hybrid dual silver vanadium phosphorus oxide/carbon fluoride (Ag 2 VO 2 PO 4 /CF x ) cathodes with various weight ratios. Through modification of the Ag 2 VO 2 PO 4 /CF x ratio, we can control the gravimetric and volumetric capacity, as well as mitigate the voltage drop during high current pulses. The increase in impedance caused by irreversible LiF formation in CFx was reduced by the silver reduction-displacement during electrochemical discharge of the Ag 2 VO 2 PO 4 . Moreover, the addition of graphite was shown to reduce initial voltage delay. When Ag 2 VO 2 PO 4 dominates the electrode mass (i.e. 75/25 Ag 2 VO 2 PO 4 /CF x ) in the hybrid cathode, pulse testing shows less voltage drop and delay, but at the expense of capacity and energy density. As the amount of CFx in the composite increases (i.e. Ag 2 VO 2 PO 4 /CF x ratio of to 50/50 or 25/75), charge capacity and energy density increases, but at the expense of larger voltage drops and delays early in the discharge process. Thus, controlling the Ag 2 VO 2 PO 4 /CF x ratio can be used to tune the electrochemical properties of the dual cathode, allowing for optimization of capacity and power depending on the application.
25 ENERGY STORAGE↗
Initial Argonne Sodium Draining Tests: Analysis of Test Results and Comparison with Water Draining Behavior
Three initial sodium draining experiments have been carried out in which sodium was drained from a 0.46 m high 4.6 mm inner diameter vertical stainless steel tube wetted by the sodium representative of a sodium channel in a compact diffusion-bonded sodium-to-CO 2 heat exchanger. Prior to the startup of sodium testing, shakedown tests were conducted with water. In all three sodium experiments, the sodium drained efficiently from the channel. Sodium and water both drain efficiently from a 4.6 mm inner diameter vertical stainless steel tube. This is an important and good result for the design of compact diffusion-bonded heat exchanger sodium channels. Sodium drains more efficiently than water. This is also an important and good result for the design of compact diffusion-bonded heat exchanger sodium channels. The draining phenomena observed with sodium and water are significantly different. The draining of water involves an initial rapid slug draining phase followed by a linear rate draining phase followed by a slow draining phase involving draining of rivulets and drops. This behavior has previously been reported in the literature for viscous fluids. The draining of sodium involves an initial rapid slug draining phase but no discernable linear rate draining phase. There is a subsequent slow draining phase. However, unlike the slow draining phase with water that involves a number of rivulets and drops, the slow draining phase with sodium in two out of three sodium tests mainly involves a single discrete event in which a mass of sodium drains from the tube. This single discrete draining event encompasses most of the sodium mass remaining inside of the tube following the rapid slug draining phase. The existence of a single discrete draining event during the slow draining phase with sodium versus several rivulet and drop draining events with water is thought to simply reflect the fact that significantly lower mass fractions of liquid are left behind inside of the tube following the rapid slug draining phase with sodium relative to water. For the sodium tests, the progress of wetting of the stainless steel by sodium was monitored by means of the voltage drop across the tube outer diameter measured by pairs of opposing electrodes welded to the tube outer surface at three different elevations. The electrode data remarkably reveals phenomena during the sodium draining. The downward passage of the sodium slug trailing edge past each electrode was observed from which a mean slug trailing edge velocity could be determined. The subsequent slower increase in voltage drop suggests draining and thinning of a sodium film left behind upon the tube inner surface; wiggles in the voltage drop data are suggestive of the descent of waves on the film. It is thought that the draining sodium film collects as a mass likely near the lower end of the tube and detaches corresponding to the single discrete draining event observed in the load cell data. The minimum circular channel inner diameter for the draining of water and sodium without the formation of lenses that bridge the channel and may remain inside of the tube without draining is predicted with a correlation to be 2.2 mm. The highest priority for future sodium draining testing is to investigate other channel geometries such as a rectilinear channel or a semicircular channel.
22 GENERAL STUDIES OF NUCLEAR REACTORS↗
Impact of lithium wall conditioning and wave-frequency on high density lower hybrid current drive experiment on EAST
A series of dedicated lower hybrid current drive (LHCD) experiments on EAST shows that lithium wall conditioning extends LH current drive and heating up to the line-averaged density of n ̅_e≈ 4x1019 m-3 for both 2.45 and 4.6 GHz. Current drive at such a high density is crucial for the development of long-pulse non-inductive scenarios on EAST. With lithiation, the LH power injection of 1.5 MW at 2.45 GHz resulted in a drop of loop voltage of ~ 0.3 V, which is a comparable loop voltage drop observed with 1.1 MW at 4.6 GHz. The observed decrease in loop voltage is attributed mostly to the RF heating effect. Another LHCD experiment suggests that lithium wall coating has a more significant impact on the scrape-off-layer (SOL) properties than changes in the Greenwald fraction. LHCD at 2.45 GHz still suffers from a loss of efficiency. Enhanced power ionization in front of the launcher may cause the onset of density-dependent wave instabilities. The rise in the midplane SOL density may also accelerate a transition in the divertor regime, leading to additional ionization and collisional losses in the X-point divertor plasma. Ray-tracing modeling supports that a lower wave frequency is more prone to collisional power loss. The experiments confirm that lithiation is a useful tool to control the SOL plasma, and suggest that density control in front of the launcher may be critical to mitigating power loss mechanisms in the plasma boundary.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Robust PCA-Deep Belief Network Surrogate Model for Distribution System Topology Identification with DERs
With the expansion of distribution networks and increased penetration of distributed energy resources (DERs), it is becoming increasingly important to obtain accurate distribution network topology in real-time. In this paper, a robust principal component analysis coupled deep belief network (PCA-DBN) surrogate model is proposed for distribution system topology identification. It integrates the benefits of robust feature extraction from PCA to deal with data quality issues and filter out noise, and the strength of DBN in capturing the nonlinear relationship between voltage amplitudes and the binary states of switchable connections. This also significantly reduces the DBN training complexity without loss of accuracy. It is shown that the widely used standard deviation of voltage drop and the voltage covariance matrix features yield less accuracy as compared to that of the voltage amplitudes in presence of high penetration of DERs and ZIP loads. Comparison results with other alternatives, such as the random forest (RF), multi-output regression (MOR) and the traditional DBN methods demonstrate that the proposed method can achieve a much higher topology identification accuracy while maintaining robustness to missing data and measurement noise under various penetration levels of DERs.
deep belief network↗
Ripple-Type Voltage Control for Extreme-Event Contingencies: Preprint
Frequent and intense extreme events make grid operation unprecedentedly challenging. Disruptive events could lead to dangerous voltage drops and even voltage collapse if corrective actions are not quickly taken. In this paper, we present a real-time algorithm for voltage control suitable for mitigating electric grid damage scenarios. In our strategy, when agents (generators, substations) experience a dangerous undervoltage, they first respond locally. When the local control resources are depleted, agents seek assistance from peer nodes over a communication network. The algorithm is simulated on a realistic test transmission system. Using fragility curve methodology, we simulate hurricane damages to the components of the synthetic 2000-bus grid representing the ERCOT system. Although being tested over a damaged grid after a hurricane event, our algorithm can be equally successfully applied to any other emergency low-voltage situation.
extreme weather events↗
Diffusion and Flow of CO{sub 2} in Carbon Anode for Aluminium Smelting
Using a well-made carbon anode with the right porosity characteristics is essential to the successful operation of a Hall–Héroult cell. Bubble generation at this carbon anode and its contribution to the overall voltage drop in aluminum production holds significant potential for reducing overpotential and improving energy savings. This voltage drop is believed to be greatly influenced by the gas diffusion in the anode carbon, for which there are a limited number of measurements to correlate with the carbon anode properties. In the present study, the CO{sub 2} gas diffusion characteristics were first investigated via measuring anode porosity using mercury intrusion porosimetry (MIP) for different samples with different permeability. Second, diffusion experiments were conducted by flowing CO{sub 2} gas into the anode sample at elevated temperatures (up to 960 °C). The impact of temperature, average pore size, and permeability on the diffusion coefficient was investigated. The diffusion coefficient was consequently calculated by curve fitting using diffusion theories. The value obtained varied from 1.38 × 10{sup −6} to 7.89 × 10{sup −6} m{sup 2}/s. A high diffusion coefficient was measured in the carbon sample with larger average pore size and higher permeability. It was found that anomalous diffusion behavior in the temperature range 600 °C to 960 °C was caused by convective flow effects, different diffusion mechanisms, and the Boudouard reaction for these carbon anode samples. Furthermore, by plotting the measured diffusion coefficient against average pore size and permeability, an increasing trend of diffusivity with an increase in pore size and permeability was observed.
36 MATERIALS SCIENCE↗
Hydrodynamic model of a dielectric-barrier discharge in pure chlorine
A one-dimensional hydrodynamic model of a dielectric-barrier discharge (DBD) in pure chlorine is developed, and the properties of the discharge are modeled. The discharge is excited in an 8-mm-long discharge gap between 2-mm-thick dielectric quartz layers covering metal electrodes. The DBD spatiotemporal characteristics at gas pressures of 15–100 Torr are modeled for the case in which a 100-kHz harmonic voltage with an amplitude of 8 kV is applied to the electrodes. The average power density deposited in the discharge over one voltage period is 2.5–5.8 W/cm{sup 3}. It is shown that ions and electrons absorb about 95 and 5% of the discharge power, respectively. In this case, from 67 to 97% of the power absorbed by electrons is spent on the dissociation and ionization of Cl{sub 2} molecules. Two phases can be distinguished in the discharge dynamics: the active (multispike) phase, which follows the breakdown of the discharge gap, and the passive phase. The active phase is characterized by the presence of multiple current spikes, a relatively high current, small surface charge density on the dielectrics, and large voltage drop across the discharge gap. The passive phase (with no current spikes) is characterized by a low current, large surface charge density on the dielectrics, and small voltage drop across the discharge gap. The peak current density in the spikes at all pressures is about 4 mA/cm{sup 2}. In the multispike phase, there are distinct space charge sheaths with thicknesses of 1.5–1.8 mm and a mean electron energy of 4.3–7 eV and the central region of quasineutral plasma with a weak electric field and a mean electron energy of 0.8–3 eV. The degree of ionization of chlorine molecules in the discharge is ~0.02% at a pressure of 15 Torr and ~0.01% at 100 Torr. The DBD plasma is electronegative due to the fast attachment of electrons to chlorine atoms: e + Cl{sub 2} → Cl + Cl{sup –}. The most abundant charged particles are Cl{sub 2}{sup +} and Cl{sup −} ions, and the degree of ionization during current spikes in the active phase is (4.1–5.5) × 10{sup –7}. The mechanism of discharge sustainment is analyzed. The appearance of a series of current spikes in the active phase of the discharge is explained.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗