Search NASA⌕ Search

SEARCH · Search NASA

Results for “DC magnetics”

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 NTRS2024

EMIC Wave Energy Dissipation as a Source of O + Conics and Warm Plasma Cloak in the Earth's Inner Magnetosphere

This study focuses on a specific source of the O + conics and warm plasma cloak in the Earth's inner magnetosphere due to electromagnetic ion cyclotron (EMIC) wave energy dissipation. We analyze the EMIC wave event observed by Van Allen Probe-A in the early afternoon off equatorial magnetosphere on 18 November 2015, where the two dominant EMIC wave bands, He + -band and H + -band, were observed for ∼4 min. All the wave and plasma parameters, the DC magnetic field, and ion distributions needed for our analysis are taken from the Van Allen Probe-A observations during the event. The major results of our analysis are as follows. (a) The H + and He + heating by EMIC waves is negligible. (b) A strong heating of O + by the wave energy dissipation around the third, fifth, and sixth harmonics of the O + gyrofrequency is revealed, where the majority of energy dissipated goes into heating of O + with the energies ≲100 eV and pitch angles ∼20°–90°. The estimated energy deposition rate is ∼0.1–3.4 eV/s per O + , totaling to the deposition of ∼20–800 eV per O + during the event. (c) EMIC waves substantially contribute to the formation of O + conics and warm plasma cloak by heating the upgoing low-energy ionospheric O + because waves heat ions with the energies and pitch angles that are characteristic of conics and warm plasma cloak, and the energy deposition per O + is comparable to those characteristic energies.

Konstantin V. Gamayunov↗
NASA NTRS1987

Dynamics of runaway tails with time-dependent sub-Dreicer dc fields in magnetized plasmas

The evolution of runaway tails driven by sub-Dreicer time-dependent dc fields in a magnetized plasma are studied numerically using a quasi-linear code based on the Ritz-Galerkin method and finite elements. It is found that the runaway tail maintained a negative slope during the dc field increase. Depending on the values of the dc electric field at t = 0 and the electron gyrofrequency to the plasma frequency ratio the runaway tail became unstable to the anomalous Doppler resonance or remained stable before the saturation of the dc field at some maximum value. The systems that remained stable during this stage became unstable to the anomalous Doppler or the Cerenkov resonances when the dc field was kept at the saturation level or decreased. Once the instability is triggered, the runaway tail is isotropized.

Moghaddam-Taaheri, E.↗
NASA NTRS1992

Study Of Dc Modulation Noise In Magnetic Recording Disks

Report discusses dc modulation noise in thin-film magnetic medium on magnetic recording disk. Presents study of statistical and spectral characteristics of noise and describes study of dependence of noise upon applied magnetic field, thickness of magnetic layer, and roughness of surface of layer. DC modulation noise attributed to nucleation of isolated regions of reversal of magnetization in recording medium, and to growth and coalescence of regions with increasing reverse applied magnetic field. Inhomogeneities in magnetic recording media, not roughnesses of surfaces, are dominant sources of noise.

Katti, Romney R.↗
NASA NTRS1988

Dovetail Rotor Construction For Permanent-Magnet Motors

New way of mounting magnets in permanent-magnet, electronically commutated, brushless dc motors. Magnets wedge shaped, tapering toward center of rotor. Oppositely tapered pole pieces, electron-beam welded to rotor hub, retain magnets against centrifugal force generated by spinning rotor. To avoid excessively long electron-beam welds, pole pieces assembled in segments rather than single long bars.

Kintz, Lawrence J., Jr.↗
NASA NTRS2005

EM Properties of Magnetic Minerals at RADAR Frequencies

Previous missions to Mars have revealed that Mars surface is magnetic at DC frequency. Does this highly magnetic surface layer attenuate RADAR energy as it does in certain locations on Earth? It has been suggested that the active magnetic mineral on Mars is titanomaghemite and/or titanomagnetite. When titanium is incorporated into a maghemite or magnetite crystal, the Curie temperature can be significantly reduced. Mars has a wide range of daily temperature fluctuations (303K - 143K), which could allow for daily passes through the Curie temperature. Hence, the global dust layer on Mars could experience widely varying magnetic properties as a function of temperature, more specifically being ferromagnetic at night and paramagnetic during the day. Measurements of EM properties of magnetic minerals were made versus frequency and temperature (300K- 180K). Magnetic minerals and Martian analog samples were gathered from a number of different locations on Earth.

Stillman, D. E.↗
NASA NTRS1990

dc modulation noise in thin film magnetic recording disk media

A study of dc modulation noise as a function of magnetic layer thickness has been conducted for plated longitudinal low-noise Co-alloy disk media with a range of 900 to 1100 Oe. The noise, produced by the application of a reverse longitudinal dc field to a uniformly magnetized disk, supplies data regarding the uniformity of the disk. A spectrum analyzer measures the noise by means of electronic detection, and noise spectra and autocorrelation functions calculated with a model are compared to the experimental results. The model correlates with experimental data to more than 0.99. The maximum distance between effective transitions diminishes from 2.8 microns to 1 micron when the thickness of the magnetic layer is increased from 25 nm to 60 nm. The maximum average transition amplitude is found to be independent of thickness, and is bounded by 0.001 of the saturation magnetization.

Katti, R. R.↗
NASA NTRS1983

Improved transistor-controlled and commutated brushless DC motors for electric vehicle propulsion

The development, design, construction, and testing processes of two electronically (transistor) controlled and commutated permanent magnet brushless dc machine systems, for propulsion of electric vehicles are detailed. One machine system was designed and constructed using samarium cobalt for permanent magnets, which supply the rotor (field) excitation. Meanwhile, the other machine system was designed and constructed with strontium ferrite permanent magnets as the source of rotor (field) excitation. These machine systems were designed for continuous rated power output of 15 hp (11.2 kw), and a peak one minute rated power output of 35 hp (26.1 kw). Both power ratings are for a rated voltage of 115 volts dc, assuming a voltage drop in the source (battery) of about 5 volts. That is, an internal source voltage of 120 volts dc. Machine-power conditioner system computer-aided simulations were used extensively in the design process. These simulations relied heavily on the magnetic field analysis in these machines using the method of finite elements, as well as methods of modeling of the machine power conditioner system dynamic interaction. These simulation processes are detailed. Testing revealed that typical machine system efficiencies at 15 hp (11.2 kw) were about 88% and 84% for the samarium cobalt and strontium ferrite based machine systems, respectively. Both systems met the peak one minute rating of 35 hp.

Demerdash, N. A.↗
NASA NTRS1980

Dynamic modeling of brushless dc motors for aerospace actuation

A discrete time model for simulation of the dynamics of samarium cobalt-type permanent magnet brushless dc machines is presented. The simulation model includes modeling of the interaction between these machines and their attached power conditioners. These are transistorized conditioner units. This model is part of an overall discrete-time analysis of the dynamic performance of electromechanical actuators, which was conducted as part of prototype development of such actuators studied and built for NASA-Johnson Space Center as a prospective alternative to hydraulic actuators presently used in shuttle orbiter applications. The resulting numerical simulations of the various machine and power conditioner current and voltage waveforms gave excellent correlation to the actual waveforms collected from actual hardware experimental testing. These results, numerical and experimental, are presented here for machine motoring, regeneration and dynamic braking modes. Application of the resulting model to the determination of machine current and torque profiles during closed-loop actuator operation were also analyzed and the results are given here. These results are given in light of an overall view of the actuator system components. The applicability of this method of analysis to design optimization and trouble-shooting in such prototype development is also discussed in light of the results at hand.

Demerdash, N. A.↗
NASA NTRS2013

External Magnetic Field Reduction Techniques for the Advanced Stirling Radioisotope Generator

Linear alternators coupled to high efficiency Stirling engines are strong candidates for thermal-to-electric power conversion in space. However, the magnetic field emissions, both AC and DC, of these permanent magnet excited alternators can interfere with sensitive instrumentation onboard a spacecraft. Effective methods to mitigate the AC and DC electromagnetic interference (EMI) from solenoidal type linear alternators (like that used in the Advanced Stirling Convertor) have been developed for potential use in the Advanced Stirling Radioisotope Generator. The methods developed avoid the complexity and extra mass inherent in data extraction from multiple sensors or the use of shielding. This paper discusses these methods, and also provides experimental data obtained during breadboard testing of both AC and DC external magnetic field devices.

Thermoelectric Power Generation↗
NASA NTRS1979

Dynamic modeling of brushless dc motor-power conditioner unit for electromechanical actuator application

A comprehensive digital model for the analysis of the dynamic-instantaneous performance of a power conditioner fed samarium-cobalt permanent magnet brushless DC motor is presented. The particular power conditioner-machine system at hand, for which this model was developed, is a component of an actual prototype electromechanical actuator built for NASA-JSC as a possible alternative to hydraulic actuators as part of feasibility studies for the shuttle orbiter applications. Excellent correlation between digital simulated and experimentally obtained performance data was achieved for this specific prototype. This is reported on in this paper. Details of one component of the model, its applications and the corresponding results are given in this paper.

Demerdash, N. A.↗
NASA NTRS2016

Parametric Characterization of TES Detectors Under DC Bias

The X-ray integrated field unit (X-IFU) in European Space Agency's (ESA's) Athena mission will be the first high-resolution X-ray spectrometer in space using a large-format transition-edge sensor microcalorimeter array. Motivated by optimization of detector performance for X-IFU, we have conducted an extensive campaign of parametric characterization on transition-edge sensor (TES) detectors with nominal geometries and physical properties in order to establish sensitivity trends relative to magnetic field, dc bias on detectors, operating temperature, and to improve our understanding of detector behavior relative to its fundamental properties such as thermal conductivity, heat capacity, and transition temperature. These results were used for validation of a simple linear detector model in which a small perturbation can be introduced to one or multiple parameters to estimate the error budget for X-IFU. We will show here results of our parametric characterization of TES detectors and briefly discuss the comparison with the TES model.

X-ray Integral Field↗