Search NASA⌕ Search

SEARCH · Search NASA

Results for “Very Low Frequency”

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.

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

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2017

Kinetic Scale Structure of Low-Frequency Waves and Fluctuations

The dissipation of solar wind turbulence at kinetic scales is believed to be important for the heating of the corona and for accelerating the wind. The linear Vlasov kinetic theory is a useful tool for identifying various wave modes, including kinetic Alfven, fast magnetosonic/whistler, and ion-acoustic (or kinetic slow), and their possible roles in the dissipation. However, the kinetic mode structure in the vicinity of ion-cyclotron modes is not clearly understood. The present paper aims to further elucidate the structure of these low-frequency waves by introducing discrete particle effects through hybrid simulations and Klimontovich formalism of spontaneous emission theory. The theory and simulation of spontaneously emitted low-frequency fluctuations are employed to identify and distinguish the detailed mode structures associated with ion-Bernstein modes versus quasi-modes. The spontaneous emission theory and simulation also confirm the findings of the Vlasov theory in that the kinetic Alfven waves can be defined over a wide range of frequencies, including the proton cyclotron frequency and its harmonics, especially for high-beta plasmas. This implies that these low-frequency modes may play predominant roles even in the fully kinetic description of kinetic scale turbulence and dissipation despite the fact that cyclotron harmonic and Bernstein modes may also play important roles in wave-particle interactions.

waves↗
DOE OSTI2024

Regulatory Treatment of Low Frequency External Events under a Risk-Informed Performance-Based Licensing Pathway: Safety Criteria Evaluation

There has been recent progress in the development of risk-informed performance-based (RIPB) design and licensing approaches, which leverage the insights gained from detailed risk assessments and utilize performance-based metrics to permit flexibility and innovation. The RIPB approaches have included the probabilistic treatment of external hazards, including low frequency events that are beyond the design basis. A preceding study conducted in FY21 noted that there are certain challenges to the probabilistic treatment of low frequency external events, which are primarily the result of uncertainty in the hazard curve and the associated plant response to rare, severe events. The current work expands on the previous study by examining the regulatory safety criteria contained within draft 10 CFR Part 53 and associated draft RIPB seismic design guidance. The evaluation identified potential challenges in demonstrating satisfaction of the safety criteria for low frequency external events, with specific difficulties associated with demonstrating compliance with cumulative safety criteria metrics, such as the quantitative health objectives (QHOs). Non-LWRs are expected to utilize the direct calculation of offsite consequence, rather than use surrogates, for comparison to the QHOs, which can be particularly challenging as the previously identified uncertainties are compounded by uncertainties in the response of the neighboring population. The current work details this evaluation and key findings. The central recommendation from this effort is that it is necessary to develop an approach for demonstrating compliance with the safety criteria in draft Part 53 that addresses the key challenges while providing flexibility to applicants.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS2003

Low Frequency High Amplitude Temperature Oscillations in Loop Heat Pipe Operation

This paper presents viewgraphs on the low frequency high amplitude temperature oscillations observed in loop heat pipe operations. The topics include: 1) Proposed Theory; 2) Test Loop and Test Results; and 3) Effects of Various Parameters. The author also presents a short summary on the conditiions that must be met in order to sustain a low frequency high amplitude temperature oscillation.

Ku, Jentung↗
NASA NTRS1994

Low-frequency oscillations of forced barotropic flow

Jin and Ghil demonstrate that for topographically resonant flow, low-frequency finite-amplitude oscillations may arise from wave -- wave interactions and topographic form drag. Their model is extended to include a zonally asymmetric vorticity source, which is shown to interact with the perturbation field to produce zonally rectified wave fluxes that dramatically alter the Hopf bifurcation from stationary solutions to low-frequency oscillations. The frequency, intensity, and general character of these oscillations are shown to depend crucially upon the phasing and relative strength of the forcings.

Nathan, Terrence R.↗
NASA NTRS1975

The solar elogation distribution of low frequency radio bursts

Over 500 days of low frequency (less than 5 MHz) radio observations from the IMP-6 spacecraft were accumulated to produce a two dimensional map (frequency versus elongation) of solar type III burst occurrences. This map indicates that most solar bursts are emitted at the second harmonic of the plasma frequency rather than the fundamental. The map also shows that the solar wind electron density varies.

Kaiser, M. L.↗
NASA NTRS1976

Study of low frequency hydromagnetic waves using ATS-1 data

Low frequency oscillations of the magnetic field at ATS-1 were analyzed for the 25 month data interval, Dec., 1966 through 1968. Irregular oscillations and those associated with magnetic storms were excluded from the analysis. Of the 222 events identified, 170 were found to be oscillating predominantly transverse to the background magnetic field. The oscillations were observed to occur most frequently in the early afternoon hours. They also seemed to occur more frequently during Dec., Jan., and Feb. than at any other time of the year. During a given event, the frequency was fairly constant. The event duration varied between a minimum of 10 min. and a maximum of 14 hrs and 26 min. During a given event the amplitude varied.

Cummings, W. D.↗
NASA NTRS1978

Compton interaction of free electrons with intense low frequency radiation

Electron behavior in an intense low frequency radiation field, with induced Compton scattering as the primary mechanism of interaction, is investigated. Evolution of the electron energy spectrum is studied, and the equilibrium spectrum of relativistic electrons in a radiation field with high brightness temperature is found. The induced radiation pressure and heating rate of an electron gas are calculated. The direction of the induced pressure depends on the radiation spectrum. The form of spectrum, under the induced force can accelerate electrons to superrelativistic energies is found.

Illarionov, A. F.↗
NASA NTRS1982

Laboratory observation of a very low frequency instability in an argon plasma

Very low frequency (50 to 500 Hz) self-excited electrostatic waves are detected in a cylindrical argon plasma column with a weak axial magnetic field (10 to 100 G). The waves propagate azimuthally with a phase velocity in the electron diamagnetic drift direction, but with a speed at least an order of magnitude less than the ion acoustic speed. A number of known plasma instabilities are considered as possible explanations, though most of them do not seem to account for the observed characteristics of the waves.

Reinleitner, L.↗
NASA NTRS1984

Three dimensional ray tracing of the Jovian magnetosphere in the low frequency range

Ray tracing studies of Jovian low frequency emissions were studied. A comprehensive three-dimensional ray tracing computer code for examination of model Jovian decametric (DAM) emission was developed. The improvements to the computer code are outlined and described. The results of the ray tracings of Jovian emissions will be presented in summary form.

Menietti, J. D.↗
NASA NTRS1992

Funnel-shaped, low-frequency equatorial waves

Funnel-shaped, low-frequency radiation, as observed in frequency time spectrograms, is frequently found at the earth's magnetic equator which extends from the proton-cyclotron frequency up to the lower hybrid frequency. Ray-tracing calculations can qualitatively reproduce the observed frequency-time characteristics of these emissions if the waves are propagating in the fast magnetosonic mode starting with wave normal angles of about 88 deg at the magnetic equator. The funnel-shaped emissions are consistent with generation by protons with a ring-type velocity space distribution. A ring-shaped region of positive slope in the velocity space density distribution of protons is observed near the Alfven velocity, indicating that the ring protons strongly interact with the waves. Ray-tracing calculations show that for similar equatorial wave normal angles lower-frequency fast magnetosonic waves are more closely confined to the magnetic equator than higher-frequency fast magnetosonic waves. For waves refracted back toward the equator at similar magnetic latitudes, the lower-frequency waves experience stronger damping in the vicinity of the equator than higher-frequency waves. Also, wave growth is restricted to higher frequencies at larger magnetic latitudes. Wave damping at the equator and wave growth off the equator favors equatorial wave normal angle distributions which lead to the funnel-shaped frequency time characteristic.

Boardsen, S. A.↗
NASA NTRS2016

Low-Frequency Radio Bursts and Space Weather

Low-frequency radio phenomena are due to the presence of nonthermal electrons in the interplanetary (IP) medium. Understanding these phenomena is important in characterizing the space environment near Earth and other destinations in the solar system. Substantial progress has been made in the past two decades, because of the continuous and uniform data sets available from space-based radio and white-light instrumentation. This paper highlights some recent results obtained on IP radio phenomena. In particular, the source of type IV radio bursts, the behavior of type III storms, shock propagation in the IP medium, and the solar-cycle variation of type II radio bursts are considered. All these phenomena are closely related to solar eruptions and active region evolution. The results presented were obtained by combining data from the Wind and SOHO missions.

coronal mass ejection↗
NASA NTRS1983

Observations of upstream ions and low-frequency waves on ISEE 3

Three examples are presented of observations of upstream ions and low-frequency waves made at ISEE 3 at distances of up to 200 earth radii upstream from the earth's bow shock. The observations demonstrate that even at 200 earth radii, weak scattering plays an important role in the transport of upstream ions. At ISEE 3, during long-lasting events, a correlation is observed between the growth of the waves and the intensity of the upstream ions. An increase in the number of pitch-angle-scattered ions, frequently with a moderate amount of ions having pitch angles greater than 90 deg, is observed, and this is correlated with the growth of the waves. It is concluded that during long-lasting events an equilibrium is reached where the region between the spacecraft and the bow shock contains a significant amount of low-frequency wave activity, together with significant pitch angle scattering.

Sanderson, T. R.↗
NASA NTRS1983

Modification of the photoionization of hydrogen by a low-frequency laser

The modification of the photoionization cross section due to the presence of an intense low-frequency laser is obtained for the hydrogen-atom target. Previous calculations of this effect have neglected the effects of the Coulomb potential in the final state. A sum rule was obtained which indicates that the photoelectric current is unaffected by the presence of the low-frequency laser to lowest order in the laser frequency. It is found that the Coulomb potential changes this result and that the photoelectric current is changed by a factor which depends upon the laser parameters and the electron momentum. A simple experiment is suggested to confirm this prediction.

Fiordilino, E.↗