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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.

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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS2009

NEXT Long-Duration Test Plume and Wear Characteristics after 16,550 h of Operation and 337 kg of Xenon Processed

The NASA s Evolutionary Xenon Thruster (NEXT) program is developing the next-generation ion propulsion system with significant enhancements beyond the state-of-the-art. The NEXT ion propulsion system provides improved mission capabilities for future NASA science missions to enhance and enable Discovery, New Frontiers, and Flagship-type NASA missions. As part of a comprehensive thruster service life assessment utilizing both testing and analyses, a Long-Duration Test (LDT) was initiated to validate and qualify the NEXT propellant throughput capability to a qualification-level of 450 kg, 1.5 times the mission-derived throughput requirement of 300 kg. This wear test is being conducted with a modified, flight-representative NEXT engineering model ion thruster, designated EM3. As of June 25, 2008, the thruster has accumulated 16,550 h of operation: the first 13,042 h at the thruster full-input-power of 6.9 kW with 3.52 A beam current and 1800 V beam power supply voltage. Operation since 13,042 h, i.e., the most recent 3,508 h, has been at an input power of 4.7 kW with 3.52 A beam current and 1180 V beam power supply voltage. The thruster has processed 337 kg of xenon (Xe) surpassing the NSTAR propellant throughput demonstrated during the extended life testing of the Deep Space 1 flight spare. The NEXT LDT has demonstrated a total impulse of 13.3 106 N s; the highest total impulse ever demonstrated by an ion thruster. Thruster plume diagnostics and erosion measurements are obtained periodically over the entire NEXT throttle table with input power ranging 0.5 to 6.9 kW. Observed thruster component erosion rates are consistent with predictions and the thruster service life assessment. There have not been any observed anomalous erosion and all erosion estimates indicate a thruster throughput capability that exceeds ~750 kg of Xe, an equivalent of 36,500 h of continuous operation at the full-power operating condition. This paper presents the erosion measurements and plume diagnostic results for the NEXT LDT to date with emphasis on the change in thruster operating condition and resulting impact on wear characteristics. Ion optics grid-gap data, both cold and operating, are presented. Performance and wear predictions for the LDT throttle profile are presented.

Herman, Daniel A.↗
DOE OSTI2024

Analytical model and dynamical phase-field simulation of terahertz transmission across ferroelectrics

Here, we theoretically investigate the steady-state transmission of continuous terahertz (THz) wave across a freestanding ferroelectric slab. Based on the Landau-Ginzburg-Devonshire theory of ferroelectrics and the coupled equations of motion for polarization and electromagnetic (EM) waves, we derive the analytical expressions of the frequency- and thickness-dependent dielectric susceptibility and transmission coefficient at the thin slab limit in the harmonic excitation regime. When the slab thickness is much smaller than the THz wavelength in the ferroelectric, the analytical predictions agree well with the numerical simulations from a dynamical phase-field model that incorporates the coupled dynamics of strain, polarization, and EM wave in multiphase systems. At larger thicknesses, the transmission is mainly determined by the frequency-dependent attenuation of THz waves in the ferroelectric and the formation of a standing polarization/THz wave. Our results advance the understanding of the interaction between THz wave and ferroelectrics and suggest the potential of exploiting ferroelectrics to achieve low-heat-dissipation, nonvolatile voltage modulation of THz transmission for high-data-rate wireless communication.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Significant Improvements to Si Calendar Lifetime Using Rapid Electrolyte Screening via Potentiostatic Holds

Silicon-based lithium-ion batteries exhibit severe time-based degradation resulting in poor calendar lives. This has been identified as the major impediment towards commercialization with cycle life considered a solved issue through nanosizing and protective coatings allowing over 1000 cycles of life to be achieved. In this work, rapid screening of sixteen electrolytes for calendar life extension of Si-rich systems (70 wt% Si) is performed using the voltage hold (V-hold) protocol. V-hold significantly shortens the testing duration over the traditional open circuit voltage reference performance test allowing us to screen electrolytes within a span of two months. We find a novel ethylene carbonate (EC) free electrolyte formulation containing lithium hexafluorophosphate (LiPF 6 ) salt, and binary solvent mix of fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC) that extends calendar life of Si cells as compared to conventional EC based electrolyte. Our coupled experimental-theoretical analysis framework provides a decoupling of the parasitic currents during V-hold, allowing us to extrapolate the capacity loss to predict semiquantitative calendar lifetimes. Subsequently, cycle aging and oxidative stability tests of the EC free system also show enhanced performance over baseline electrolyte.

25 ENERGY STORAGE↗
NASA NTRS1988

Experimental observation of electrochemical rate limitations affecting sodium ion-electron recombination at electrodes of the alkali metal thermoelectric converter at T about 1200 K

This paper considers a model of the internal impedances of thin porous Mo and W alkali metal thermoelectric converter (AMTEC), in which the kinetic parameters associated with the reaction of the beta-double-prime alumina solid electrolite (BASE)/porous metal/gas three-phase boundary can be evaluated. Impedance data in the frequency range 0.01-100,000 Hz were collected over a range of AMTEC cell operating voltages for small-area thin porous Mo and W electrodes, yielding apparent charge transfer resistances at a series of cell potentials/currents. The ohmic resistance in the AMTEC cell could be broken down and characterized with three parameters: the BASE ionic resistance, the electrode film sheet resistance, and the contact/lead resistance, all of which could be calculated or measured independently and used to calculate power curves in good agreement with observed power curves. It is shown that these calculations can be used to predict the properties of electrodes with optimized parameters or to detect enhanced transport modes.

Williams, R. M.↗
NASA NTRS1984

The influence of ground conductivity on the structure of RF radiation from return strokes

The combination of the finite conductivity of the Earth plus the propagation of the return stroke current up the channel which results in an apparent time delay between the fast field changes and RF radiation for distant observers is shown. The time delay predicted from model return strokes is on the order of 20 micro and the received signal has the characteristics of the data observed in Virginia and Florida. A piecewise linear model for the return stroke channel and a transmission line model for current propagation on each segment was used. Radiation from each segment is calculated over a flat Earth with finite conductivity using asymptotics approximations for the Sommerfeld integrals. The radiation at the observer is processed by a model AM radio receiver. The output voltage was calculated for several frequencies between HF-UHF assuming a system bandwidth (300 kHz) characteristic of the system used to collect data in Florida and Virginia. Comparison with the theoretical fast field changes indicates a time delay of 20 microns.

Levine, D. M.↗
NASA NTRS1992

Modelling and design for PM/EM magnetic bearings

A mathematical model of a permanent magnet/electromagnet (PM/EM) radially active bearing is presented. The bearing is represented by both a reluctance model and a stiffness model. The reluctance model analyzes the magnetic circuit of the PM/EM bearings. By combining the two models, the performance of the bearing can be predicted given geometric dimensions, permanent magnet strength, and the parameters of the EM coils. The overall bearing design including the PM and EM design is subject to the performance requirement and physical constraints. A study of these requirements and constraints is discussed. The PM design is based on the required magnetic flux for proper geometric dimensions and magnet strength. The EM design is based on the stability and force slew rate consideration, and dictates the number of turns for the EM coils and the voltage and current of the power amplifier. An overall PM/EM bearing design methodology is proposed and a case study is also demonstrated.

Pang, D.↗
NASA NTRS1995

Method for characterizing the upset response of CMOS circuits using alpha-particle sensitive test circuits

A method for predicting the SEU susceptibility of a standard-cell D-latch using an alpha-particle sensitive SRAM, SPICE critical charge simulation results, and alpha-particle interaction physics. A technique utilizing test structures to quickly and inexpensively characterize the SEU sensitivity of standard cell latches intended for use in a space environment. This bench-level approach utilizes alpha particles to induce upsets in a low LET sensitive 4-k bit test SRAM. This SRAM consists of cells that employ an offset voltage to adjust their upset sensitivity and an enlarged sensitive drain junction to enhance the cell's upset rate.

Buehler, Martin G.↗
NASA NTRS2018

Effects of Normal Metal Features on Superconducting Transition-Edge Sensors

In transition-edge sensors (TESs), the addition of normal metal stripes on top of the superconducting bilayer, perpendicular to the current direction, is known to globally alter the sensitivity of the resistance R to changes in temperature T and current I. Here, we describe measurements of the dependence of the TES current on magnetic field B, bath temperature and voltage bias in devices with various numbers of stripes. We show that the normal metal features have a profound effect on the appearance of localized regions of very large (T/R) dR/dT. We associate this with changes in the current distribution and corresponding changes in the oscillatory pattern of I (B). 140 μm TESs with no stripes are found to have a relatively smooth resistive transition and sufficiently low noise that the measured energy resolution is 1.6 eV for X-rays of 1.5 keV. The predicted energy resolution at 6 keV is better than 2 eV, once the heat capacity is optimized for these higher energies..

Wakeham, N. A.↗
DOE OSTI2020

Parametric study of operating conditions of an SO 2 -depolarized electrolyzer

Large-scale hydrogen generation is needed to satisfy both existing commercial demands and the realization of a hydrogen economy. The hybrid sulfur cycle has the potential to meet this goal without the use of fossil fuels. The ability to model and predict how the electrolyzer step of the cycle is affected by independent and interdependent variables is vital to maximizing the efficiency of the overall cycle. Herein, we report that our parametric study of the SO 2 -depolarized electrolyzer, representing one half of the overall reaction cycle, has identified desirable conditions and will help guide further development for operation that will achieve the benchmarks for economic feasibility. We discuss the interactions among the inlet flow rates, applied current, and cell temperature and pressure, on the resulting cell voltage and acid concentration in the liquid product stream. For example, we find that using a sulfonated polybenzimidazole (s-PBI) membrane and a platinum catalyst, a constant current density of either 0.5 A cm -2 , 0.75 A cm -2 , or 1 A cm -2 with an acid concentration of 65 wt% H 2 SO 4 can be produced at a cell voltage of 0.59 V, 0.63 V, and 0.67 V, respectively, by maintaining a cell temperature of 130 °C, a pressure of 2 bar, and a water-to-SO 2 stoichiometry of 2.77. Finally, we discuss directions for future research based on the findings in this manuscript.

08 HYDROGEN↗
NASA NTRS1978

Noise as a tool for evaluating the activation of cathodes

Measurements, at low frequencies, of the shot noise current from space charge limited cathodes always produced results substantially in excess of theoretical predictions. Measuring the ratio (I sub eq)/S yielded a relation (I sub eq)/S = 1.288 V sub k = 1.288 k(T sub k)/e, independent of the operating point of the diode (triode) as long as all parts of the cathode had a full space charge controlled emission. This method was so sensitive as to permit detection of cathode temperature changes by 1 K, thus it allowed a powerful screening method between well and poorly activated cathodes, superior to dip tests and other current-voltage methods.

Kosmahl, H.↗
DOE OSTI2022

Nanoscale Control of Polar Surface Phases in Layered van der Waals CuInP 2 S 6

Antiferroelectric (AFE) materials, in which alternating dipole moments cancel out to a zero net macroscopic polarization, can be used for high-density energy storage and memory applications. The AFE phase can exist in bulk CuInP 2 Se 6 , CuBiP 2 S 6 , and a few other transition-metal thiophosphates below 200 K. The required low temperature poses challenges for practical applications. In this work, we report the coexistence of ferrielectric (FE) states and a stable surface phase that does not show piezoelectric response (“zero-response phase”) in bulk CuInP 2 S 6 at room temperature. Using piezoresponse force microscopy (PFM) tomographic imaging together with density functional theory, we find that direct and alternating voltages can locally and stably convert FE to zero-response phases and vice versa. While PFM loops show pinched hystereses reminiscent of antiferroelectricity, PFM tomography reveals that the zero-response areas form only on top of the FE phase in which the polarization vector is pointing up. Theoretical calculations suggest that the zero-response phase may correspond to AFE ordering where stacked CuInP 2 S 6 layers have alternating polarization orientations thereby leading to a net-zero polarization. Consistent with experimental findings, theory predicts that the FE polarization pointing down is robust up to the top surface, whereas FE polarization pointing up energetically favors the formation of an AFE surface layer, whose thickness is likely to be sensitive to local strains. AFE order is likely to be more robust against detrimental size effects than polar order, therefore providing additional opportunities to create multifunctional heterostructures with 2D electronic materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1982

Power availability at terrestrial receptor sites for laser-power transmission from the satellite power system

A statistical model was developed for relating the temporal transmission parameters of a laser beam from a solar power satellite to observable meteorological data to determine the influence of weather on power reception at the earth-based receiver. Sites within 100 miles of existing high voltage transmission lines were examined and the model was developed for clear-sky and clouded conditions. The cases of total transmission through clouds at certain wavelengths, no transmission, and partial transmission were calculated for the cloud portion of the model. The study covered cirriform, stratiform, cumiliform, and mixed type clouds and the possibility of boring holes through the clouds with the beam. Utilization of weapons-quality beams for hole boring, was found to yield power availability increases of 9-33%, although no beneficial effects could be predicted in regions of persistent cloud cover. An efficiency of 80% was determined as possible if several receptor sites were available within 200-300 miles of each other, thereby allowing changes of reception point in cases of unacceptable meteorological conditions.

Beverly, R. E., III↗
NASA NTRS2004

Ferroelectric Field Effect Transistor Model Using Partitioned Ferroelectric Layer and Partial Polarization

A model of an n-channel ferroelectric field effect transistor has been developed based on both theoretical and empirical data. The model is based on an existing model that incorporates partitioning of the ferroelectric layer to calculate the polarization within the ferroelectric material. The model incorporates several new aspects that are useful to the user. It takes into account the effect of a non-saturating gate voltage only partially polarizing the ferroelectric material based on the existing remnant polarization. The model also incorporates the decay of the remnant polarization based on the time history of the FFET. A gate pulse of a specific voltage; will not put the ferroelectric material into a single amount of polarization for that voltage, but instead vary with previous state of the material and the time since the last change to the gate voltage. The model also utilizes data from FFETs made from different types of ferroelectric materials to allow the user just to input the material being used and not recreate the entire model. The model also allows the user to input the quality of the ferroelectric material being used. The ferroelectric material quality can go from a theoretical perfect material with little loss and no decay to a less than perfect material with remnant losses and decay. This model is designed to be used by people who need to predict the external characteristics of a FFET before the time and expense of design and fabrication. It also allows the parametric evaluation of quality of the ferroelectric film on the overall performance of the transistor.

MacLeod, Todd C.↗
DOE OSTI2022

Electric field distribution in a non-self-sustained RF discharge with ionization generated by Ns discharge pulses

Abstract Electric field in a capacitively coupled, non-self-sustained RF discharge nitrogen plasma with external ionization generated by high-voltage ns pulses has been measured by ps Electric field induced second harmonic generation (EFISH). The measurements are made both in the bulk of the plasma and in the sheaths, using the absolute calibration by the Laplacian field between two plane electrodes. The results are compared with the kinetic modeling calculations. The RF electric field in the sheaths is significantly higher compared to that in the plasma, due to the displacement of the electrons by the drift oscillations and the resultant plasma self-shielding. However, the kinetic modeling predictions indicate that the electron impact ionization in the sheaths is largely ineffective, due to the low electron density. The reduction of the electric field in the plasma by the self-shielding in the sheaths is moderate, such that the energy is coupled to the plasma by the below-breakdown RF field. The peak RF field in the plasma is in the range of 15–25 Td, indicating the efficient vibrational excitation of N 2 by electron impact. The modeling predictions suggest that the targeted vibrational excitation of molecular species in a non-self-sustained RF discharge with external ionization is scalable to high pressures, electron densities, and discharge powers. The present approach can be extended to the vibrational excitation of other molecular species where the vibrational relaxation is relatively slow, such as CO, CO 2 , and H 2 .

Physics↗
NASA NTRS1988

Space plasma contactor research, 1987

A simple model describing the process of electron collection from a low pressure ambient plasma in the absence of magnetic field and contactor velocity effects is presented. Experimental measurments of the plasma surrounding the contactor are used to demonstrate that a double-sheath generally develops and separates the ambient plasma from a higher density, anode plasma located adjacent to the contactor. Agreement between the predictions of the model and experimental measurements obtained at the electron collection current levels ranging to 1 A suggests the surface area at the ambient plasma boundary of the double-sheath is equal to the electron current being collected divided by the ambient plasma random electron current density; the surface area of the higher density anode plasma boundary of the double-sheath is equal to the ion current being emitted across this boundary divided by the ion current density required to sustain a stable sheath; and the voltage drop across the sheath is determined by the requirement that the ion and electron currents counterflowing across the boundaries be at space-charge limited levels. The efficiency of contactor operation is shown to improve when significant ionization and excitation is induced by electrons that stream from the ambient plasma through the double-sheath and collide with neutral atoms being supplied through the hollow cathode.

Wilbur, Paul J.↗
DOE OSTI2022

Current distribution monitoring enables quench and damage detection in superconducting fusion magnets

Abstract Fusion magnets made from high temperature superconducting ReBCO CORC ® cables are typically protected with quench detection systems that use voltage or temperature measurements to trigger current extraction processes. Although small coils with low inductances have been demonstrated, magnet protection remains a challenge and magnets are typically operated with little knowledge of the intrinsic performance parameters. We propose a protection framework based on current distribution monitoring in fusion cables with limited inter-cable current sharing. By employing inverse Biot-Savart techniques to distributed Hall probe arrays around CORC ® Cable-In-Conduit-Conductor (CICC) terminations, individual cable currents are recreated and used to extract the parameters of a predictive model. These parameters are shown to be of value for detecting conductor damage and defining safe magnet operating limits. The trained model is then used to predict cable current distributions in real-time, and departures between predictions and inverse Biot-Savart recreated current distributions are used to generate quench triggers. The methodology shows promise for quality control, operational planning and real-time quench detection in bundled CORC ® cables for compact fusion reactors.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Effect of fluorination and Li-excess on the Li migration barrier in Mn-based cathode materials

Disordered rocksalt (DRX) Li-rich transition metal (TM) oxides, especially those based on Mn, are prospective high-energy-density cathode materials for the next generation of Li-ion batteries that use earth abundant metals. Fluorine substitution on the oxygen sublattice has been shown to reduce oxygen redox by lowering the average anion valence and increasing the amount of redox-active TM, and simultaneously improve energy density, average voltage and capacity retention. While these benefits of fluorination are well established, it is not well understood how F affects Li transport and therefore the rate performance of Mn-based DRX cathodes. Herein, we investigate the effects of both F substitution and the accompanying Li-excess on Li migration barriers using first-principles calculations. Finally, we demonstrate that F has a small negative effect on Li migration barriers while Li-excess decreases Li migration barriers. Because fluorination enables more Li-excess, these results do not predict any detrimental impact on Li transport.

25 ENERGY STORAGE↗