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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 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Design and Analysis of High Heat Flux Plasma-Facing Components for NSTX Upgrade

The National Spherical Tokamak Experiment (NSTX) upgrade (NSTX-U) requirements lead to enhanced heat loads on plasma-facing components (PFCs) especially in the divertor regions, where normal heat flux density can reach up to 8 MW/m 2 . For these high heat flux (HHF) regions, the PFCs were redesigned, to use castellations which relieved the thermal stresses associated with high incident heat flux. Another design feature of HHF PFCs is the absence of front face mounting holes which create localized areas of high temperature and thermal stress concentrations. Optimized shaping of the front face of the HHF PFCs eliminates regions where the front face is perpendicular to the heat flux direction during normal helicity operation and spreads the heat load. A unique mechanism was designed to connect PFC tiles to the NSTX-U center stack casing using locking features accessible from the low heat flux regions. Isotropic graphite was selected as the HHF PFC tile material. Initial tile design parameters were accessed using analytical expressions for pulsed heat flux loading. A working prototype of the locking mechanism was created during the initial stages of the design to prove the concept performance. This article presents an overview of the divertor HHF PFC design and the results of the thermal and structural analyses performed using ANSYS software. The results of the analyses cover normal operating conditions and disruptions which impose electromagnetic (EM) loads from eddy and halo currents. The 3-D, transient, nonlinear analyses took into account the temperature-dependent properties of the materials, friction interfaces between the parts, and variable electric properties of the parts and interfaces. The results confirm that the HHF PFC tiles remain within the allowable limits for the loads defined by the NSTX-U Recovery Project. In addition, tolerance stack up analyses were performed to ensure tile performance in the worst possible assembly configuration. Finally, the design process was completed successfully, and the NSTX HHF PFC tiles are currently in the production phase.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Interpreting Mass and Radius Measurements of Neutron Stars with Dark Matter Halos

Abstract The high densities of neutron stars (NSs) could provide astrophysical locations for dark matter (DM) to accumulate. Depending on the DM model, these DM admixed NSs (DANSs) could have significantly different properties than pure baryonic NSs, accessible through X-ray observations of rotation-powered pulsars. We adopt the two-fluid formalism in general relativity to numerically simulate stable configurations of DANSs, assuming a fermionic equation of state (EOS) for the DM with repulsive self-interaction. The distribution of DM in the DANS as a halo affects the path of X-rays emitted from hot spots on the visible baryonic surface, causing notable changes in the pulse profile observed by telescopes such as NICER, compared to pure baryonic NSs. We explore how various DM models affect the DM mass distribution, leading to different types of dark halos. We quantify the deviation in observed X-ray flux from stars with each of these halos. We identify the pitfalls in interpreting mass and radius measurements of NSs inferred from electromagnetic radiation and constraining the baryonic matter EOS if these dark halos exist.

Shawqi, Shafayat (ORCID:0000000210956183)↗
NASA NTRS1977

Interaction of electromagnetic and acoustic waves in a stochastic atmosphere

This paper considers the interaction of electromagnetic and acoustic waves where a Radio Acoustic Sounding System (RASS) is operated in a stochastic environment characterized by turbulence, winds and mean-temperature gradients. It has been shown that for a RASS operating at acoustic frequencies below a few kilohertz propagating under typical atmospheric conditions, turbulence has little effect on the strength of the received radio signal scattered from the pulse at heights up to a few kilometers. This result implies that the received RF signal level (power) is primarily a function of sound intensity which decreases as x exp minus 2 where x is the altitude.

Bhatnagar, N.↗
DOE OSTI2021

Neutron Stars and the Nuclear Matter Equation of State

Neutron stars provide a window into the properties of dense nuclear matter. Several recent observational and theoretical developments provide powerful constraints on their structure and internal composition. Among these are the first observed binary neutron star merger, GW170817, whose gravitational radiation was accompanied by electromagnetic radiation from a short γ-ray burst and an optical afterglow believed to be due to the radioactive decay of newly minted heavy r-process nuclei. These observations give important constraints on the radii of typical neutron stars and on the upper limit to the neutron star maximum mass and complement recent pulsar observations that established a lower limit. Pulse-profile observations by the Neutron Star Interior Composition Explorer (NICER) X-ray telescope provide an independent, consistent measure of the neutron star radius. Theoretical many-body studies of neutron matter reinforce these estimates of neutron star radii. Studies using parameterized dense matter equations of state (EOSs) reveal several EOS-independent relations connecting global neutron star properties.

Physics↗
NASA NTRS1971

Low power electromagnetic flowmeter providing accurate zero set

A low power, small size electromagnetic flowmeter system is described which produces a zero output signal for zero flow. The system comprises an air core type electromagnetic flow transducer, a field current supply circuit for the transducer coils and a pre-amplifier and demodulation circuit connected to the output of the transducer. To prevent spurious signals at zero flow, separate, isolated power supplies are provided for the two circuits. The demodulator includes a pair of synchronous rectifiers which are controlled by signals from the field current supply circuit. Pulse transformer connected in front of the synchronous rectifiers provide isolation between the two circuits.

Fryer, T. B.↗
NASA NTRS1981

Noise and interference study for satellite lightning sensor

The use of radio frequency techniques for the detection and monitoring of terrestrial thunderstorms from space are discussed. Three major points are assessed: (1) lightning and noise source characteristics; (2) propagation effects imposed by the atmosphere and ionosphere; and (3) the electromagnetic environment in near space within which lightning RF signatures must be detected. A composite frequency spectrum of the peak of amplitude from lightning flashes is developed. Propagation effects (ionospheric cutoff, refraction, absorption, dispersion and scintillation) are considered to modify the lightning spectrum to the geosynchronous case. It is suggested that in comparing the modified spectrum with interfering noise source spectra RF lightning pulses on frequencies up to a few GHz are detectable above the natural noise environment in near space.

Herman, J. R.↗
NASA NTRS1985

Application of photodiodes to the detection of electromagnetic bursts

A new type of photodiode + scintillator (1 m2 x 1 cm) detector is developed to detect the large electro-magnetic burst under an EX-chamber. The threshold burst size is found to be 4.3 x 10 the 5 particles at the center of the scintillator. Therefore a gamma-ray family of 10 TeV is detectable by it, when it is set under 14 r.1. of iron. In addition, a very fast (2.4 nsec width) and very bright (correspond to 10 to the 6 particles) scintillation pulse has become avarable for this study.

Fukushima, Y.↗
NASA NTRS1974

Multi-kw dc power distribution system study program

The first phase of the Multi-kw dc Power Distribution Technology Program is reported and involves the test and evaluation of a technology breadboard in a specifically designed test facility according to design concepts developed in a previous study on space vehicle electrical power processing, distribution, and control. The static and dynamic performance, fault isolation, reliability, electromagnetic interference characterisitics, and operability factors of high distribution systems were studied in order to gain a technology base for the use of high voltage dc systems in future aerospace vehicles. Detailed technical descriptions are presented and include data for the following: (1) dynamic interactions due to operation of solid state and electromechanical switchgear; (2) multiplexed and computer controlled supervision and checkout methods; (3) pulse width modulator design; and (4) cable design factors.

Berkery, E. A.↗
NASA NTRS1972

Propellant sidefeed-short pulse discharge thruster studies

The technique of feeding a solid propellant into the discharge from the sides of the discharge was evaluated. The thrust/power ratio could be significantly effected by the included angle of V-shaped propellants and by the electrode length. This result implies that when results are compared at the same specific impulse it is possible to obtain higher thrust efficiencies. In particular, it was found that for a given discharge energy the thrust/power ratio correlated with propellant mass. Increasing the integral simultaneously increases both the gas dynamic and electromagnetic thrust. An analytic expression was formulated for ablated mass which comprehensively describes experimental data in terms of geometry and electrical parameters. The correlation of the product impulse x specific impulse with discharge energy was also described. It is suggested that the reliability of dry energy storage capacitors does not equal the reliability of liquid impregnated units when the comparison is made at the same joules/Kg rating.

Palumbo, D. J.↗
DOE OSTI2017

On the correlation between ‘non-local’ effects and intrinsic rotation reversals in Alcator C-Mod

Contemporary predictive models for heat and particle transport in tokamak plasmas are based on the assumption that local fluxes can be described in terms of local plasma parameters, where electromagnetic drift-wave-type turbulence is driven by local gradients and results in cross-field transport. The question of whether or not transport could be dominated by non-local terms in certain circumstances is essential for our understanding of transport in magnetically confined plasmas, and critical for developing predictive models for future tokamaks, such as ITER. Perturbative transport experiments using cold-pulse injections at low density seem to challenge the local closure of anomalous transport: a rapid temperature increase in the core of the plasma following a sharp edge cooling is widely observed in tokamaks and helical devices. Past work in Ohmic plasmas in Alcator C-Mod and in ECH plasmas in KSTAR found that the temperature inversions disappear at higher densities, above the intrinsic toroidal rotation reversal density. These observations suggested that the so-called 'non-local' heat transport effects were related to the intrinsic rotation reversal, and therefore to changes in momentum transport. In this work, new experiments and analysis at Alcator C-Mod show that intrinsic rotation reversals and disappearance of temperature inversions are not concomitant in Ohmic plasmas at high plasma current and in ICRH L-modes. This new data set shows that the correlation between transient temperature inversions and intrinsic rotation reversals is not universal, suggesting that 'non-local' heat transport and momentum transport effects may be affected by different physical mechanisms.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

On the correlation between ‘non-local’ effects and intrinsic rotation reversals in Alcator C-Mod

Contemporary predictive models for heat and particle transport in tokamak plasmas are based on the assumption that local fluxes can be described in terms of local plasma parameters, where electromagnetic drift-wave-type turbulence is driven by local gradients and results in cross-field transport. The question of whether or not transport could be dominated by non-local terms in certain circumstances is essential for our understanding of transport in magnetically confined plasmas, and critical for developing predictive models for future tokamaks, such as ITER. Perturbative transport experiments using cold-pulse injections at low density seem to challenge the local closure of anomalous transport: a rapid temperature increase in the core of the plasma following a sharp edge cooling is widely observed in tokamaks and helical devices. Past work in Ohmic plasmas in Alcator C-Mod and in ECH plasmas in KSTAR found that the temperature inversions disappear at higher densities, above the intrinsic toroidal rotation reversal density. These observations suggested that the so-called 'non-local' heat transport effects were related to the intrinsic rotation reversal, and therefore to changes in momentum transport. In this work, new experiments and analysis at Alcator C-Mod show that intrinsic rotation reversals and disappearance of temperature inversions are not concomitant in Ohmic plasmas at high plasma current and in ICRH L-modes. This new data set shows that the correlation between transient temperature inversions and intrinsic rotation reversals is not universal, suggesting that 'non-local' heat transport and momentum transport effects may be affected by different physical mechanisms.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Plasma physics in strong-field regimes: Theories and simulations

In strong electromagnetic fields, unique plasma phenomena and applications emerge whose description requires recently developed theories and simulations [Y. Shi, Ph.D. thesis, Princeton University (2018)]. In the classical regime, to quantify effects of strong magnetic fields on three-wave interactions, a convenient formula is derived by solving the fluid model to the second order in general geometry. As an application, magnetic resonances are exploited to mediate laser pulse compression, whereby higher intensity pulses can be produced in wider frequency ranges, as confirmed by particle-in-cell simulations. In even stronger fields, relativistic-quantum effects become important, and a plasma model based on scalar quantum electrodynamics (QED) is developed which unveils observable corrections to Faraday rotation and cyclotron absorption in strongly magnetized plasmas. Beyond the perturbative regime, lattice QED is extended as a numerical tool for plasma physics, using which the transition from wakefield acceleration to electron-positron pair production is captured when laser intensity exceeds the Schwinger threshold.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2001

Experimental Results of Schlicher's Thrusting Antenna

Experiments were conducted to test the claims by Rex L. Schlicher, et al., (Patent 5,142,86 1) that a certain antenna geometry produces thrust greatly exceeding radiation reaction, when driven by repetitive, fast rise, and relatively slower decay current pulses. In order to test this hypothesis, the antenna was suspended by strings as a 3 in pendulum. Current pulses were fed to the antenna along the suspension path by a very flexible coaxial line constructed from loudspeaker cable and copper braid sheath. When driving the antenna via this cabling, our pulser was capable of sustaining 1200 A pulses at a rate of 30 per second up to a minute. In this way, bursts of pulses could be delivered in synch with the pendulum period in order to build up any motion. However, when using a laser beam passing through a lens attached to the antenna to amplify linear displacement by a factor of at least 25, no correlated motion of the beam spot could be detected on a distant wall. We conclude, in agreement with the momentum theorem of classical electromagnetic theory, that any thrust produced is far below practically useful levels. Hence, within classical electrodynamics, there is little hope of detecting any low level motion that cannot be explained by interactions with surrounding structural steel and the Earth's magnetic field.

Fralick, Gustave C.↗
NASA NTRS1990

A novel sample-positioning system for microgravity application

This paper proposes a novel method for sample positioning in containerless processing at microgravity, using a system based on pulsed lasers. The method has two attributes. First, by generating beams that cancel out vectorially, the suspended material can be heated without being accelerated, a feature that can be used in melting and heat-treatment applications. Second, the specimen can be positioned within a fairly large work space. It is emphasized that this method can service a regime unfulfilled by the other levitation methods, such as electromagnetic levitation, active magnetic suspension, acoustic levitation, of electrostatic suspension.

Sridharan, G.↗
NASA NTRS1994

Coupling of ELF/ULF energy from lightning and MeV particles to the middle atmosphere, inosphere, and global circuit

In an attempt to explain numerous atmospheric electrical phenomena, the elements of the global electrical circuit are reexamined. In addition to being a 'quasi-static 'DC' generator' and source of radiated energy at VLF and higher, the thunderstorm is found to be a pulse generator, with most of the external energy contained in ELF and ULF pulse currents to the ionosphere (and Earth). The pulse energy is found to deposit largely in the middle atmosphere above the thunderstorm. The VLF and above components are well understood, as are the ULF components due to the conductivity gradient. However, a previously poorly understood ELF component on the millsecond timescale, or 'slow tail,' contains a large fraction of the electrical energy. This component couples strongly to the ionosphere and also launches a unipolar transverse electromagnetic (TEM) wavelet in the radial Earth-ionosphere transmission line. The increase in charge with distance associated with such wavelets, and their ensemble sum at a point, may explain some large mesospheric 'DC' fields but there are still difficulties explaining other than rare occurrences, except for antipodal reconvergence. These millisecond duration unipolar wavelets also coupled to the ionosphere and may trigger other lightning at a distance. A schema is elucidated by which the charge of MeV particles deposited in the middle atmosphere persists for much longer than the local relaxation time. This also gives rise to unipolar waves of global extent which may explain lower-latitude field perturbations associated with solar/geomagnetic events.

Hale, Leslie C.↗
DOE OSTI2023

Ultrafast Laser Pulse Generation by Mode Locking: MATLAB-Based Demonstrations

Ultrafast laser spectroscopy is a valuable and increasingly accessible technique for studies of rapid chemical reactions. Critical to ultrafast spectroscopy is the concept of mode locking, a technique that enables a fixed phase relationship between laser modes, resulting in laser pulses with very short duration (in the fs or ps range). Despite the increasing importance of ultrafast lasers in chemistry, the introduction of key concepts behind their operation into the undergraduate and graduate chemistry coursework has been limited. To help the incorporation of these topics into chemistry courses, we report here a hands-on activity that helps students develop an intuitive understanding of the factors that impact electromagnetic wave evolution in optical cavities and the process of mode locking. We first provide the theoretical background by introducing cavity modes and contrasting them with well-known propagating electromagnetic waves. We then explore what happens when modes are added and how the relative phase between the modes affects their behavior. In the second section of this report, three teaching modules are provided, along with associated MATLAB codes and animated images, that can be used in the classroom to introduce concepts of cavity modes and mode locking. These teaching modules start by contrasting propagating electromagnetic waves with cavity modes and then illustrate what happens when multiple modes are present in the cavity and how the relative phase between the modes affects the overall electromagnetic field in the cavity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2000

Energetic Combustion Devices for Aerospace Propulsion and Power

Chemical reactions have long been the mainstay thermal energy source for aerospace propulsion and power. Although it is widely recognized that the intrinsic energy density limitations of chemical bonds place severe constraints on maximum realizable performance, it will likely be several years before systems based on high energy density nuclear fuels can be placed into routine service. In the mean time, efforts to develop high energy density chemicals and advanced combustion devices which can utilize such energetic fuels may yield worthwhile returns in overall system performance and cost. Current efforts in this vein are being carried out at NASA MSFC under the direction of the author in the areas of pulse detonation engine technology development and light metals combustion devices. Pulse detonation engines are touted as a low cost alternative to gas turbine engines and to conventional rocket engines, but actual performance and cost benefits have yet to be convincingly demonstrated. Light metal fueled engines also offer potential benefits in certain niche applications such as aluminum/CO2 fueled engines for endo-atmospheric Martian propulsion. Light metal fueled MHD generators also present promising opportunities with respect to electric power generation for electromagnetic launch assist. This presentation will discuss the applications potential of these concepts with respect to aero ace propulsion and power and will review the current status of the development efforts.

Litchford, Ron J.↗
NASA NTRS2008

Preliminary Development and Testing of a Self-Injecting Gallium MPD Thruster

Discharge current and terminal voltage measurements were performed on a gallium electromagnetic thruster at discharge currents in the range of 20-54 kA. It was found that the arc impedance has a value of 6-7 m(Omega) at peak current. The absence of high-frequency oscillations in the terminal voltage trace indicates lack of the "onset" condition often seen in MPD arcs, suggesting that a sufficient number of charge carriers are present for current conduction. The mass ablated per pulse was not measured experimentally; however the mass flow rate was calculated using an ion current assumption and an anode power balance. Measurement of arc impedance predicts a temperature of 3.5 eV which from Saha equilibrium corresponds to Z = 2.0 - 3.5, and assuming Z = 2 yields an Isp of 3000 s and thrust efficiency of 50%.

Thomas, Robert E.↗