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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Modulation of centimetric waves by long gravity waves - Progress report on field and laboratory results

Results are presented from laboratory and field experiments on the modulation of short waves by long waves. The field study employed a wave follower capable of tracking ocean waves with frequencies less than 1.0 Hz and heights less than 2.0 m. A high-response laser-optical system was used to detect upwind-downwind and cross-wind slopes of short waves. The laboratory study was conducted with wind over periodic long waves. The laboratory findings are discussed and compared with laboratory radar measurements and also short wave measurements obtained in the field. It is found that long waves significantly modulate the short wave dispersion by their orbital velocity, and that demodulation is necessary if the data collected by remote sensors are to be compared to surface penetrating devices. The modulation level is weak for wavelengths in the range 2.76-3.30 cm. Other relevant results are also presented.

Shemdin, O. H.↗
NASA NTRS1983

Generation of Alfven-ion cyclotron waves on auroral field lines in the presence of heavy ions

Observation of electromagnetic waves in the low-altitude auroral zone at frequencies between the proton and helium gyrofrequencies suggests that Alfven-ion cyclotron waves modified by the presence of helium ions are being excited. Estimates of the growth rates for this mode indicate that the auroral electron beam can provide the free energy for the instability. The effect of the heavy ions is to decrease the group velocity of the waves, leading to larger convective growth. Theoretical wave spectra are computed in the local approximation, which assumes that the gradient scale lengths in density and magnetic field are constant over the ray paths. Narrow banded spectral peaks similar to observations may be produced when the thickness of the electron beam is small (200 m at 3000 km altitude). Narrow beams also limit growth of whistler mode waves, which compete for the free energy of the electron beam.

Lysak, R. L.↗
DOE OSTI2020

Study of laser-driven magnetic fields with a continuous wave Faraday rotation diagnostic

Magnetic fields driven by a laser in coil targets were studied for laser energies of ~25 J and two pulse durations of 2.8 ns and 70 ps. Axial magnetic fields in the coils were measured by continuous wave Faraday rotation diagnostics. The diagnostics indicated magnetic fields of 6–14 T in the coil and currents of 10–20 kA. Magnetic fields were compared for similar laser targets, focusing conditions, and laser energies. A 30-times increase in the intensity of the laser beam by reducing the pulse duration resulted in an increase in the magnetic field and current by a factor of 2. The relaxation time of the magnetic pulse was on the sub-microsecond scale.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Measurement of the properties of the dust acoustic wave in a magnetic field

We present the first experimental observations of the dust acoustic wave where the wave was observed to propagate in the directions of gravity and magnetic field when these directions were not aligned. The experiments were conducted in the Magnetized Dusty Plasma eXperiment facility using a novel electrode system that allows for the angle between gravity and the magnetic field to be varied in a controlled way. This letter reports on measurements in an rf glow discharge argon plasma environment where the angle between direction of gravity and the magnetic field is 45 $^{\circ }$ . When there was no applied magnetic field, the wave was observed to propagate in the direction of gravity. However, as the magnetic field increased and the ions transitioned from flowing in the direction of gravity to the direction of the magnetic field, a second wave emerged and two distinct waves were observed to simultaneously propagate, one in the direction of gravity and one in the direction of the magnetic field. As the magnetic field was further increased, the wave that propagated in the direction of gravity was suppressed and the wave was only observed to propagate in the direction of the applied magnetic field. We also observe that the speed and the kinetic temperature of the dust for the mode that propagated in the direction of gravity decreased with increasing magnetic field while the speed and the kinetic temperature of the dust for the mode that propagated in the direction of the magnetic field increased with increasing magnetic field. These measurements suggest that an ion-dust streaming instability is at least partially responsible for the high temperatures that have previously been observed in dusty plasmas when the dust acoustic wave is present.

Williams, J. D. (ORCID:000000025199707X)↗
NASA NTRS1972

Description of a computer program to calculate reacting supersonic internal flow fields with shock waves using viscous characteristics: Program manual and sample calculations

A computer program for calculating internal supersonic flow fields with chemical reactions and shock waves typical of supersonic combustion chambers with either wall or mid-stream injectors is described. The usefulness and limitations of the program are indicated. The program manual and listing are presented along with a sample calculation.

Cavalleri, R. J.↗
NASA NTRS1990

Millimeter wave near-field study

The possibility is evaluated of current technology measuring large aperture millimeter wave antennas. Included are a mathematical modeling of system errors, experimental data supporting error model, predictions of system accuracy at millimeter wavelengths, advantage of near-field measurements, and a cost estimate for a facility upgrade. The use is emphasized of software compensation and other inexpensive alternatives to develop a near optimum solution to near-field measurement problems at millimeter wavelengths.

Kefauver, Neill↗
NASA NTRS1984

Kinetic Alfven waves on auroral field lines

It is suggested on the basis of several observations of Alfven waves near auroral arcs that kinetic Alfven waves play a significant role in the process of particle acceleration. The characteristic properties of kinetic Alfven waves are summarized according to the theoretical classifications provided by Hasegawa and Mima (1979). The resonant coupling of large-scale surface waves to kinetic Alfven waves is also discussed. It is shown that kinetic Alfven waves can explain observations of what have previously been known as 'electrostatic' shocks.

Goertz, C. K.↗
NASA NTRS2010

Initial Results of DC Electric Fields, Associated Plasma Drifts, Magnetic Fields, and Plasma Waves Observed on the C/NOFS Satellite

Initial results are presented from the Vector Electric Field Investigation (VEFI) on the Air Force Communication/Navigation Outage Forecasting System (C/NOFS) satellite, a mission designed to understand, model, and forecast the presence of equatorial ionospheric irregularities. The VEFI instrument includes a vector DC electric field detector, a fixed-bias Langmuir probe operating in the ion saturation regime, a flux gate magnetometer, an optical lightning detector, and associated electronics including a burst memory. Compared to data obtained during more active solar conditions, the ambient DC electric fields and their associated E x B drifts are variable and somewhat weak, typically < 1 mV/m. Although average drift directions show similarities to those previously reported, eastward/outward during day and westward/downward at night, this pattern varies significantly with longitude and is not always present. Daytime vertical drifts near the magnetic equator are largest after sunrise, with smaller average velocities after noon. Little or no pre-reversal enhancement in the vertical drift near sunset is observed, attributable to the solar minimum conditions creating a much reduced neutral dynamo at the satellite altitude. The nighttime ionosphere is characterized by larger amplitude, structured electric fields, even where the plasma density appears nearly quiescent. Data from successive orbits reveal that the vertical drifts and plasma density are both clearly organized with longitude. The spread-F density depletions and corresponding electric fields that have been detected thus far have displayed a preponderance to appear between midnight and dawn. Associated with the narrow plasma depletions that are detected are broad spectra of electric field and plasma density irregularities for which a full vector set of measurements is available for detailed study. Finally, the data set includes a wide range of ELF/VLF/HF oscillations corresponding to a variety of plasma waves, in particular banded ELF hiss, whistlers, and lower hybrid wave turbulence triggered by lightning-induced sferics. The VEFI data represents a new set of measurements that are germane to numerous fundamental aspects of the electrodynamics and irregularities inherent to the Earth's low latitude ionosphere.

Pfaff, R.↗
NASA NTRS1989

Picture of the global field of quasi-monochromatic gravity waves observed by stratospheric balloons and MST radars

In MAP observations, it was found that: (1) gravity waves in selected or filtered portions of data are fit for monochromatic structures, whereas (2) those in fully continuous and resolved observations take universal continuous spectra. It is possible to explain (2) by dispersion of quasi-monochromatic (or slowly varying) wave packets observed locally as (1), since the medium atmosphere is unsteady and nonuniform. Complete verification of the wave-mean flow interactions by tracking individual wave packets seems hopeless, because the wave induced flow cannot be distinguished from the basic flow independent of the waves. Instead, the primitive picture is looked at before MAP, that is, the atmosphere is just like an entertainment stage illuminated by cocktail lights of quasi-monochromatic gravity waves. The wave parameters are regarded as functions of time and spatial coordinates. The observational evidences (1) and (2) suggest that the wave parameter field is rather homogeneous, which can be explained by interference of quasi-monochromatic wave packets.

Yamanaka, M. D.↗
NASA NTRS1996

Effects of low frequency waves and spiky electric fields in the magnetotail

Intense low frequency waves and large amplitude spiky electric fields are commonly observed in the active magnetotail. These fields are of dynamic significance for substorms because the amplitude of the waves is large enough to provide the dissipation necessary for reconnection. The waves modify the trajectories of ions in the magnetotail, resulting in enhanced energization and pitch angle scattering in comparison with the trajectories obtained without waves. The spikes may represent the nonlinear evolution of the waves. Observations are presented of low frequency waves and spiky electric fields measured in the plasma sheet. The relationship between the waves and the spikes is compared to wave evolution theories. The Lundquist number is evaluated for the magnetotail based on the wave observations and previously published studies of the current sheet scale sizes. The effects of the waves on the ion trajectories are discussed using the results from a particle tracing code.

Cattell, C.↗
DOE OSTI2021

Relic cosmological vector fields and inflationary gravitational waves

Here we show that relic vector fields can significantly impact a spectrum of primordial gravitational waves in the postinflationary era. We consider a triplet of U(1) fields in a homogeneous, isotropic configuration. The interaction between the gravitational waves and the vector fields, from the end of reheating to the present day, yields novel spectral features. The amplitude, tilt, shape, and net chirality of the gravitational wave spectrum are shown to depend on the abundance of the electric- and magneticlike vector fields. Our results show that even a modest abundance can have strong implications for efforts to detect the imprint of gravitational waves on the cosmic microwave background polarization. We find that a vector field comprising less than 2% of the energy density during the radiation-dominated era can have a greater than order unity effect on the predicted inflationary gravitational wave spectrum.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Ab initio electronic density in solids by many-body plane-wave auxiliary-field quantum Monte Carlo calculations

We present accurate many-body results of the electronic densities in several solid materials, including Si, NaCl, and Cu. These results are obtained using the ab initio auxiliary-field quantum Monte Carlo (AFQMC) method working in a plane-wave basis with norm-conserving, multiple-projector pseudopotentials. AFQMC has been shown to be an excellent many-body total energy method. Computation of observables and correlation functions other than the ground-state energy requires back-propagation, whose adaption and implementation in the plane-wave basis AFQMC framework are discussed in the present paper. This development allows us to compute correlation functions, electronic densities, and interatomic forces, paving the way for geometry optimizations and calculations of thermodynamic properties in solids. Finite supercell size effects are considerably more subtle in the many-body framework than in independent-electron calculations. We analyze the convergence of the electronic density, and obtain best estimates for the thermodynamic limit. The densities from several typical density functionals are benchmarked against our near-exact results. The electronic densities we obtained can also be used to help construct improved density functionals.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Field Induced Density Wave in a Kagome Superconductor

On the kagome lattice, electrons benefit from the simultaneous presence of band topology, flat electronic bands, and Van Hove singularities, forming competing or cooperating orders. Understanding the interrelation between these distinct order parameters remains a significant challenge, leaving much of the associated physics unexplored. In the kagome superconductor KV 3 Sb 5 , which exhibits a charge density wave (CDW) state below T ≃ 78 K, we uncover an unpredicted field-induced phase transition below 6 K. The observed transition is marked by a hysteretic anomaly in the resistivity, nonlinear electrical transport, and a change in the symmetry of the electronic response as probed via the angular dependence of the magnetoresistivity. These observations surprisingly suggest the emergence of an unanticipated broken symmetry state coexisting with the original CDW. To understand this experimental observation, we developed a theoretical minimal model for the normal state inside the high-temperature parent CDW phase, where an incommensurate CDW order emerges as an instability subleading to superconductivity. Here, the incommensurate CDW emerges when superconducting fluctuations become fully suppressed by large magnetic fields. Our results suggest that, in kagome superconductors, quantum states can either coexist or are nearly degenerate in energy, indicating that these are rich platforms to expose new correlated phenomena.

Charge density waves↗
NASA NTRS1985

High time resolution plasma wave and magnetic field observations of the Jovian bow shock

High time resolution (60 ms) Voyager magnetometer and plasma wave measurements of a strong (fast Mach number 16), quasi-perpendicular Jovian bow shock reveal an abrupt change in the plasma wave spectrum at the leading edge of the shock foot. Upstream electron plasma waves terminate at the leading edge, and are replaced by a lower-frequency broadband spectrum of ion-acoustic-like waves, which terminates at the main shock ramp. The clear association with the foot region of the lower frequency component suggests that it is generated by reflected ions. If the upstream plasma waves are generated by an escaping electron heat flux, their termination at the leading edge suggests that electrons are heated by the low-frequency waves in the shock foot.

Moses, S. L.↗