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At least 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

The problem of solar induced currents

The production of surface electric fields by geomagnetic variations is discussed with reference to magnetotelluric theory; and evidence is presented to show that the severity of solar-induced currents (SIC) at Cornerbrook, Newfoundland is due to channeling of currents induced in the sea through a region adjacent to the power line. An 'isolated loop' approximation is proposed for calculating the quasi-dc currents produced in the power system by the surface electric fields. Identification of the processes causing the geomagnetic perturbations responsible for SIC would be aided by investigation of the local time dependence of SIC occurrence. Such knowledge could potentially be used to provide several hours warning of SIC.

Boteler, D. H.↗
NASA NTRS1980

IMF changes and polar-cap electric fields and currents

The polar cap, defined as the region of the auroral oval, is magnetically connected to the solar wind; currents may flow easily between the two regions, and polar cap electric fields and currents respond sensitively to variations in the interplanetary magnetic field (IMF). In the present paper, the response of polar cap electric field and currents to variations in IMF x, y, and z components is discussed.

Burch, J. L.↗
NASA NTRS1980

Uncertainty in ring current parameters due to the quiet magnetic field variability at mid-latitudes

At midlatitudes the presence of Sq variation is a problem, as variability of Sq currents may produce magnetic perturbations comparable to the magnetic effects of the partial ring current on comparable time scales. The paper reports the results of an empirical determination of the quiet magnetic field, which includes the Sq variation and secular variation at 27 midlatitude magnetic observatories for the 1967-1968 period. The main concern is with the consequences of the quiet field uncertainty in terms of using midlatitude magnetic data to quantify the size and location of the magnetic disturbances caused by substorms and the ring current. Attention is given to investigating the error associated with the empirical model used. It is shown how the uncertainty can be reduced by examining the changes occurring in some interval of time.

Clauer, C. R.↗
NASA NTRS1980

Field-aligned currents and large scale magnetospheric electric fields

D'Angelo's model of polar cap electric fields (1977) was used to visualize how high-latitude field-aligned currents are driven by the solar wind generator. The region 1 and region 2 currents of Iijima and Potemra (1976) and the cusp field-aligned currents of Wilhjelm et al. (1978) and McDiarmid et al. (1978) are apparently driven by different generators, although in both cases the solar wind is their ultimate source.

Dangelo, N.↗
NASA NTRS1980

Origin of the warped heliospheric current sheet

The warped heliospheric current sheet for early 1976 is calculated from the observed photospheric magnetic field by a potential field method. Comparisons with measurements of the interplanetary magnetic field polarity for early 1976 obtained at several locations in the heliosphere by Helios 1, Helios 2, Pioneer 11, and at the earth show a rather detailed agreement between the computed current sheet and the observations. It appears that the large-scale structure of the warped heliospheric current sheet is determined by the structure of the photospheric magnetic field and that 'ballerina skirt' effects may add small scale ripples.

Wilcox, J. M.↗
NASA NTRS1980

Gigahertz analog modulation and differential delay of GaAlAs lasers - Temperature and current behavior

Gigahertz analog modulation characteristics of broad-area commercially available GaAlAs lasers have been investigated as a function of temperature and current in the vicinity of the upper frequency limit, where the resonance phenomena occur. The optimum temperature for small-signal amplitude modulation was found to be around -15 C for our particular broad-stripe geometry double-heterostructure laser. The Q was found to increase by a factor of 2 and the bandwidth by about 2%; the external quantum efficiency was maximized in this range. The optimum dc current bias was about 2% above the threshold current. Differential delays have also been measured down to a few picosecond accuracy by a unique phase-angle measurement method using a vector voltmeter. Some of the temperature effects observed may be related to mode changes and multimode and superradiance behavior.

Eng, S. T.↗
NASA NTRS1980

The origin of the warped heliospheric current sheet

The warped heliospheric current sheet in early 1976 was calculated from the observed photospheric magnetic field using a potential field method. Comparisons with measurements of the interplanetary magnetic field polarity in early 1976 obtained at several locations in the heliosphere at Helios 1, Helios 2, Pioneer 11 and Earth show a rather detailed agreement between the computed current sheet and the observations. It appears that the large scale structure of the warped heliospheric current sheet is determined by the structure of the photospheric magnetic field, and that "ballerina skirt" effects may add small scale ripples.

Wilcox, J. M.↗
NASA NTRS1980

Design of energy-storage reactors for single-winding constant-frequency dc-to-dc converters operating in the discontinuous-reactor-current mode

This paper presents an algorithm and equations for designing the energy-storage reactor for dc-to-dc converters which are constrained to operate in the discontinuous-reactor-current mode. This design procedure applied to the three widely used single-winding configurations: the voltage step-up, the current step-up, and the voltage-or-current step-up converters. A numerical design example is given to illustrate the use of the design algorithm and design equations.

Chen, D. Y.↗
NASA NTRS1981

Explorer 34 magnetic field measurements near the tail current sheet and auroral activity

Explorer 34 (Imp 4) 2.56 s magnetic data obtained during 131 traversals of the tail current sheet are presented, along with the simultaneous 2.5 min auroral electrojet indices AE and AL. The normal magnetic field satellite crossing times and positions are tabulated for these 131 crossings. Normal magnetic field is defined in the center of the sheet: it is the vector magnetic field at the time of field minimum during the crossing. It is remarkable that the only normal components too large in magnitude to be classified as fine structure occur near the time of onset of an AE event. Cases are discussed where the normal component, defined near the plasma sheet edges, has the opposite sign compared to the normal component defined at the sheet center. For quiet times, the current sheet may be only about 1000 km thick within a 3 earth-radii plasma sheet, and may carry some 10-15% of the total tail current.

Speiser, T. W.↗
NASA NTRS1981

What causes the warp in the heliospheric current sheet

A comparative discussion of the warp in the heliospheric current sheet is presented. Pioneer 10 and 11 data of the interplanetary magnetic field compared with earlier data (Helios 1 and 2) show a good agreement on the phenomenon of the warp; however, the interpretations differ. One theory (Thomas and Smith, 1980) proposes that fast solar wind streams associated with interaction regions may move the current sheet higher to heliospheric latitudes, thus causing the warp; while the earlier theory (1976) adequately explained the phenomenon by using the observed photospheric magnetic field and the Zeeman effect but omitted the solar wind dynamical considerations as part of the computations. It is shown that the Helios data of the polarity of the interplanetary magnetic field are in good agreement with the computed location of the current sheet, confirming the earlier theory.

Wilcox, J. M.↗
NASA NTRS1981

Saturn's ring current and inner magnetosphere

The Voyager 1 magnetic field observations at Saturn are shown in a graph. The departure of the oberved magnetic field from the field of a dipole is considered. The observed field magnitude is appreciable less than that of the model dipole at small radial distances and greater than the model dipole in the more distant magnetosphere. These characteristics can be understood by introducing a model current system similar to a system originally applied to observations of the Jovian magnetic disk. Saturn's ring current has important implications for charged-particle motion in Saturn's magnetosphere, particularly the absorption of trapped radiation by its many satellites and rings. The absorption signature observed by the Voyager 1 cosmic ray experiment near the orbital position of Rhea illustrates well the effects of Saturn's ring current on charged particle trajectories.

Connerney, J. E. P.↗
NASA NTRS1982

A determination of the current density in electron beams

Current gathering rotating probe techniques were used to examine the envelope shape and power density profile of electron beams used in electron beam welding devices. The electron power density contours which determine the shape of the weld vapor cavity, penetration, and local heat distribution were considered. A mathematical analysis consistent with a rotating probe technique necessary to determine the current density distribution (assumed symmetrically radial) in a cross-section of the beam is provided. An explanation of the experimental technique for obtaining data, a BASIC language computer program to determine the current density from the data, and a study indicating the level of confidence to be associated with results obtained are also provided. An example of the application of the analysis to some experimental electron beam data is included.

Beil, R. J.↗
NASA NTRS1982

Preliminary analytical results using surface current integration for predicting effects of surface pillows on RF performance

An overview of the fast integral RF evaluation (FIRE) program is presented. This program uses surface current integration to evaluate RF performance of antenna systems. It requires modeling of surfaces in X, Y, Z coordinates along equally spaced X and Y grids with Z in the focal directon. The far field contribution of each surface point includes the effects of the Z-component of surface current which is not included in the aperture integration technique. Because of this, surface current integration is the most effective and inclusive technique for predicting RF performance on non-ideal reflectors. Results obtained from use of the FIRE program and an aperture integration program to predict RF performance of a LSS antenna concept are presented.

Farrell, C. E.↗
NASA NTRS1982

NASA Redox cell stack shunt current, pumping power, and cell performance tradeoffs

The NASA Redox energy storage system is under active technology development. The hardware undergoing laboratory testing is either 310 sq. cm. or 929 sq. cm. (0.33 sq. ft. or 1.0 sq. ft. per cell active area with up to 40 individual cells connected to make up a modular cell stack. This size of hardware allows rather accurate projections to be made of the shunt power/pump power tradeoffs. The modeling studies that were completed on the system concept are reviewed along with the approach of mapping the performance of Redox cells over a wide range of flow rates and depths of discharge of the Redox solutions. Methods are outlined for estimating the pumping and shunt current losses for any type of cell and stack combination. These methods are applicable to a variety of pumping options that are present with Redox systems. The results show that a fully developed Redox system has acceptable parasitic losses when using a fixed flow rate adequate to meet the worst conditions of current density and depth of discharge. These losses are reduced by about 65 percent if variable flow schedules are used. The exact value of the overall parasitics will depend on the specific system requirements of current density, voltage limits, charge, discharge time, etc.

Hagedorn, N.↗
NASA NTRS1982

The 1981 current research on aviation weather (bibliography)

Current and ongoing research programs related to various areas of aviation meteorology are presented. Literature searches of major abstract publications, were conducted. Research project managers of various government agencies involved in aviation meteorology research provided a list of current research project titles and managers, supporting organizations, performing organizations, the principal investigators, and the objectives. These are tabulated under the headings of advanced meteorological instruments, forecasting, icing, lightning and atmospheric electricity; fog, visibility, and ceilings; low level wind shear, storm hazards/severe storms, turbulence, winds, and ozone and other meteorological parameters. This information was reviewed and assembled into a bibliography providing a current readily useable source of information in the area of aviation meteorology.

Daniel, J.↗
NASA NTRS1981

Investigation of the effects of external current systems on the MAGSAT data utilizing grid cell modeling techniques

Efforts devoted to reading MAGSAT data tapes in preparation for further analysis of the MAGSAT data are discussed. A modeling procedure developed to compute the magnetic fields at satellite orbit due to hypothesized current distributions in the ionosphere and magnetosphere is described. This technique utilizes a linear current element representation of the large-scale space-current system. Several examples of the model field perturbations computed along hypothetical satellite orbits are shown.

Klumpar, D. M.↗
NASA NTRS1981

Computer simulation of current collection in a plasma environment

The pattern of current collection by a biased strip of stainless steel placed in the plasma environment produced by a 30 cm Kaufman ion thruster is studied. Two positions of the collector relative to the ion source were used. Edge on, in which case currents were measured on both sides of the collector, and face on, in which case currents were again measured on both sides of the collector. In the latter case, the surface of the collector that faces the ion thruster is referred to as the front face, the other side as the back face. A qualitative summary of the experimental results is presented.

Zei, D.↗
NASA NTRS1982

Investigation of the effects of external current systems on the MAGSAT data utilizing grid cell modeling techniques

Efforts in support of the development of a model of the magnetic fields due to ionospheric and magnetospheric electrical currents are discussed. Specifically, progress made in reading MAGSAT tapes and plotting the deviation of the measured magnetic field components with respect to a spherical harmonic model of the main geomagnetic field is reported. Initial tests of the modeling procedure developed to compute the ionosphere/magnetosphere-induced fields at satellite orbit are also described. The modeling technique utilizes a liner current element representation of the large scale current system.

Klumpar, D. M.↗