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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

The spin down of the radio pulsars: Braking index

Presently, the value of the retardation dP/dt is well known for most radio pulsars. It is negative for all cases except one and is of the order of 10(exp -15). That single case is when the pulsar, which is located in the star globular system, can have a considerable acceleration leading to the opposite sign of P'= dP/dt due to the Doppler effect. Careful measurements of the period, P, also allow one to determine the variation of this retardation with the course of time- P'' = d(exp 2)P/dt(exp 2). The results of these measurements are usually represented in the form of the dimensionless retardation index n = omega'' omega/omega(exp 2)= 2 - P''P/P(exp 2) (omega is the angular velocity). The data for 21 pulsars are given. The parameter, n, is strongly undetermined both in value and sign in all cases except for four pulsars. Changes of the rotation period, P, and the inclination angle, chi, the angle between the axes of rotation and the magnetic moment are caused by two processes: the regular retardation and nutation due to deviation from the strict spherical shape of the neutron star. Losses which are caused by the currents flowing in the magnetosphere of the neutron star and by being closed on the star surface are considered. Such losses are critical for the neutron star magnetosphere which is full of dense plasma. Since the radio emission is generated in the dense plasma of the polar magnetosphere, then practically all radio pulsars are retarded by the current mechanism. The formula for the braking index is presented along with other aspects of the investigation.

Beskin, V. S.↗
NASA NTRS1991

A YBCO RF-squid variable temperature susceptometer and its applications

The Superconducting QUantum Interference Device (SQUID) susceptibility using a high-temperature radio-frequency (rf) SQUID and a normal metal pick-up coil is employed in testing weak magnetization of the sample. The magnetic moment resolution of the device is 1 x 10(exp -6) emu, and that of the susceptibility is 5 x 10(exp -6) emu/cu cm.

Zhou, Luwei↗
NASA NTRS1992

Distribution in magnetotail of O(+) ions from cusp/cleft ionosphere - A possible substorm trigger

The transport of O(+) ions from the cusp/cleft ionosphere to the magnetotail during highly disturbed times was determined by computing the guiding-center trajectories of the ions to a distance of 6 R(E) from the ionosphere and the full-motion trajectories at later times. Case histories were tallied in six planes perpendicular to the X(GSM) axis, three planes perpendicular to the Y(GSM) axis, and in the center plane of the tail. At various times relative to the enhancement of the convection electric field, the following ion properties were constructed from the case histories: number density, mean energy, energy and pitch angle distributions of the flux, and ion pressure components parallel and perpendicular to the magnetic field. It was found that, after about 1.7 hours, the ion flux in the near-earth magnetotail increased dramatically and the spectrum hardened, much as observed during periods just preceding substorms. This increase is attributed to (1) the increase in the O(+) outflux from the ionosphere, (2) the increased energization of the ions by the convection electric field, and (3) ion trapping, which generally occurs because the ion magnetic moments generally increase after the ions first cross the geomagnetotail center plane.

Cladis, J. B.↗
NASA NTRS1992

Precipitation of ions induced by magnetotail collapse

The precipitation of ions triggered by dipolarization of magnetospheric field lines during substorm expansion phase is examined by means of single-particle codes. As large but short-lived electric fields develop and particles experience transient nonadiabatic motions, it is demonstrated that 'de-trapping' of inner plasma sheet populations can be achieved either via damping of magnetic moment or impulsive accelerations in the parallel direction. It is shown that the former precipitation mechanism results from phasing between gyromotion and the surging electric field. It preferentially affects heavy and low-charge state ions which can display large de-energization rates within a cyclotron period. The latter mechanism rather favors the loss of lighter and/or higher-charge state ions which are less sensitive to temporal nonadiabaticity. In this case, injection into the loss cone may result from enhanced curvature related acceleration. As this latter acceleration occurs on the dipolarization time scale, it affects a limited amount of plasma sheet populations, namely those intercepting the region of maximum curvature at the time of peak induced electric field.

Delcourt, D. C.↗
NASA NTRS1992

Characterization of YBa2Cu3O7, including critical current density Jc, by trapped magnetic field

Spatial distributions of persistent magnetic field trapped by sintered and melt-textured ceramic-type high-temperature superconductor (HTS) samples have been studied. The trapped field can be reproduced by a model of the current consisting of two components: (1) a surface current Js and (2) a uniform volume current Jv. This Js + Jv model gives a satisfactory account of the spatial distribution of the magnetic field trapped by different types of HTS samples. The magnetic moment can be calculated, based on the Js + Jv model, and the result agrees well with that measured by standard vibrating sample magnetometer (VSM). As a consequence, Jc predicted by VSM methods agrees with Jc predicted from the Js + Jv model. The field mapping method described is also useful to reveal the granular structure of large HTS samples and regions of weak links.

Chen, In-Gann↗
NASA NTRS1992

Nonadiabatic transport features in the outer cusp region

The dayside to nightside circulation of plasma along the magnetopause inside the magnetosphere is examined by means of three-dimensional single-particle codes. It is demonstrated that particles incident upon the outer cusp region experience transient non-adiabatic motions, owing to a localized minimum in the field magnitude. Here, possibly large magnetic moment changes yield injection into the loss cone of fractions of the incoming population or, alternatively, enhanced bouncing motions at high altitudes. It is shown that particles gaining access to the magnetotail over the polar cap are progressively extracted from the weak field region by the large-scale convection electric field. In this latter case, the trajectory simulations suggest an implicit 'entry boundary' into the nightside magnetosphere, which corresponds to the sunward edge of field lines featuring monotonic decrease of the field magnitude along their length.

Delcourt, D. C.↗
NASA NTRS1994

Probing the antiferromagnetic long-range order with Glauber spin states

It is well known that the ground state of low-dimensional antiferromagnets deviates from Neel states due to strong quantum fluctuations. Even in the presence of long-range order, those fluctuations produce a substantial reduction of the magnetic moment from its saturation value. Numerical simulations in anisotropic antiferromagnetic chains suggest that quantum fluctuations over Neel order appear in the form of localized reversal of pairs of neighboring spins. In this paper, we propose a coherent state representation for the ground state to describe the above situation. In the one-dimensional case, our wave function corresponds to a two-mode Glauber state, when the Neel state is used as a reference, while the boson fields are associated to coherent flip of spin pairs. The coherence manifests itself through the antiferromagnetic long-range order that survives the action of quantum fluctuations. The present representation is different from the standard zero-point spin wave state, and is asymptotically exact in the limit of strong anisotropy. The fermionic version of the theory, obtained through the Jordan-Wigner transformation, is also investigated.

Cabrera, Guillermo G.↗
NASA NTRS1995

Observational magnetometer calibration with the Hubble Space Telescope's new magnetometers

The two magnetometers recently replaced on the Hubble Space Telescope during the STS-61 Servicing Mission are now being used successfully for Coarse Attitude Determination during spacecraft vehicle safemode recovery operation. The magnetometer alignments relative to the spacecraft's vehicle's reference frame and the magnetic coupling of the sensors to the four magnetic torquer bars were determined. Coarse Attitude determination errors are now reduced to an average of 0.6 deg. Magnetometer Sensing System calibration and Coarse Attitude determination testing with the new calibration parameters is a geometrical problem. Telemetered earth magnetic field data was collected at twenty-six different vehicle attitudes. The spacecraft attitudes selected were distributed as widely apart as possible throughout the Geocentric Inertial Coordinate reference frame. It is also desirable to sample the Earth's magnetic field over as many different locations of the spacecraft's passage over the Earth as possible, within the limitation of the +/- 28.5 deg orbital inclination. A full range of magnetic moment outputs from the torquer bars needs to be sampled, +/- 3600 ampmeters squared, as well as data when the torquer bars have zero current. Graphic utilities were also developed to visually aid in optimizing the data collection process. Finally, a brief discussion of a method for collecting data for future calibrations is suggested.

Broude, Sidney M.↗
NASA NTRS1994

The kinetic response of a stochastic plasma to low frequency perturbations

Following suggestion that substorm breakup might be caused by an interchange or ballooning instability, several magnetohydrodynamic (MHD) and gyro-kinetic stability analysis have been performed for plasma sheet magnetic field geometries. However, the stochastic ion dynamics in the highly stressed, thin high-beta near earth plasma sheet violate the locality requirements of MHD and the invarience of the magnetic moment, mu, required by gyro-kinetic theories. In this paper we develop a new linear Vlasov kinetic theory (for low frequency modes omega less than omega(sub b), omega(sub b) being the bounce frequency) which includes the dynamics of stochastic ions.

Hurricane, Omar A.↗
NASA NTRS1994

Solar wind contribution to the average population of energetic He(+) and He(++) ions in the Earth's magnetosphere

Measurements with the ion charge-energy-mass spectrometer CHEM on the AMPTE/CCE spacecraft were used to investigate the origin of energetic He(+) and He(++) ions observed in the equatorial plane at 3 less than or equal to L less than or equal to 9. Special emphasis was laid on the dependence of long-term average distributions on magnetic local time (MLT) and the geomagnetic activity index K(sup p). The observations are described in terms of the phase space densities f(sub 1) (for He(+)) and f(sub 2) (for He(++)). They confirm preliminary results from a previous study f(sub 1) is independent of MLT, whereas f(sub 2) is much larger on the nightside than on the dayside. They show, furthermore, that f(sub 1) increases slightly with K(sub p) on intermediate drift shells, but decreases on high drift shells (L greater than or equal to 7). f(sub 2) increases with K(sub p) on all drift shells outside the premidnight sector. Within this sector a decrease is observed on high drift shells. A simple ion tracing code was developed to determine how and from where the ions move into the region of observations. It provides ion trajectories as a function of the ion charge, the magnetic moment and K(sub p). The ion tracing enables a distinction between regions of closed drift orbits (ring current) and open convection trajectories (plasma sheet). It also indicates how the outer part of the observation region is connected to different parts of the more distant plasma sheet. Observations and tracing show that He(++) ions are effectively transported from the plasma sheet on convection trajectories. Their distribution in the observation region corresponds to the distribution of solar wind ions in the plasma sheet. Thus, energetic He(++) ions most likely originate in the solar wind. On the other hand, the plasma sheet is not an important source of energetic He(+) ions. Convection trajectories more likely constitute a sink for He(+) ions, which may diffuse onto them from closed drift orbits and then get lost through the magnetopause. An ionospheric origin of energetic He(+) ions is unlikely as well, since the source mechanism should be almost independent of K(sub p). There is considerable doubt, however, that a plausible mechanism also exists during quiet periods that can accelerate ions to ring current energies, while extracting them from the ionosphere. It is concluded, therefore, that energetic He(+) ions are mainly produced by charge exchange processes from He(++) ions. This means that most of the energetic He(+) ions constituting the average distributions also very likely originate in the solar wind. Additional ionospheric contributions are possible during disturbed periods.

Kremser, G.↗
NASA NTRS1993

Electron distributions in the inner Jovian magnetosphere: Voyager 1 observations

Using several improvements in the analysis of the observations of the Low Energy Charged Particle (LECP) experiment on Voyager 1, electron phase space densities in the inner Jovian magnetosphere (5 - 10 R(sub J) were first calculated at constant first and second invariants (represented by mu and K, respectively), based on the LECP measurements. The calculated electron phase space density profiles show that in the inner Jovian magnetosphere there exist evident time and longitude variations, energetic electron injections, and present radial transport and distributed losses. To study the radial and pitch angle diffusions of Jovian electrons, we have calculated the phase space densities in the K-L space. It is found that the electron population in the inner Jovian magnetosphere seems to consist of two components: electrons radially diffusing from a main external source and electrons generated from local sources. The radially diffusing electrons have a relatively time stationary and isotropic distribution, while the locally created electrons mainly concentrate around the equatorial plane and have relatively lower energies, in comparison with the inward diffusing electrons. Consequently, the sources of precipitation losses to the ionosphere must be primarily electrons transported from outer sources, and the major precipitations occur in the inner magnetosphere (L less than 7.5 R(sub J). In the inner Jovian magnetosphere (L = 5 to approximately 10 R(sub J)) it is estimated that for electrons with magnetic moment mu = 300 MeV/G, the diffusion coefficient D is roughly 10(exp -8) to approximately 10(exp -6) R(exp 2)(sub J)/s, and the lifetime against the diffusion losses is of the order of 10(exp 4) to approximately 10(exp 6) s.

Ye, G.↗
NASA NTRS1993

Counterstreaming suprathermal electron events upstream of corotating shocks in the solar wind beyond approximately 2 AU: Ulysses

Enhanced fluxes of suprathermal electrons are commonly observed upstream of corotating forward and reverse shocks in the solar wind at heliocentric distances beyond approximately 2 AU by the Los Alamos plasma experiment on Ulysses. The average duration of these events, which are most intense immediately upstream from the shocks and which fade with increasing distance from them, is approximately 2.4 days near 5 AU. These events are caused by the leakage of shock-heated electrons into the upstream region. The upstream regions of these shocks face back toward the Sun along the interplanetary magnetic field, so these leaked electrons commonly counterstream relative to the normal solar wind electron heat flux. The observations suggest that conservation of magnetic moment and scattering typically limit the sunward propagation of these electrons as beams to field-aligned distances of approximately 15 AU. Although it seems unlikely that these shock-associated events are an important source of counterstreaming events near 1 AU, remnants of the backstreaming beams may contribute importantly to the diffuse solar wind halo electron population there.

Gosling, J. T.↗
NASA NTRS1995

A simple test of the induced nature of the Martian tail

The cross flow direction of the interplanetary magnetic field is strongly correlated with the cross flow direction several hours earlier and later. This correlation allows a simple test of the nature of the magnetic field in the Martian magnetotail. If the magnetotail is entirely induced, then the cross tail direction of the magnetic field should be along the direction of the cross flow component just upstream of the bow shock. We find that these directions of the tail field and the implementary magnetic field are so highly correlated that any intrinsic magnetic field of Mars must make at most a small contribution to the magnetotail. We estimate an upper limit to the magnetic moment of Mars to be about 4 x 10(exp 11) T(cu m).

Russell, C. T.↗
NASA NTRS1995

Processing and property evaluation of metal matrix superconducting materials

Metal - superconductor (YBCO) systems have been prepared and characterized by resistivity, ac susceptibility and dc SQUID magnetic moment measurements. The silver composites showed superconducting transition for all the composites processed and the superconducting transition temperature tends to depend upon the concentration of the silver in the composite. Aluminum composites showed an unusual resistivity results with two transitions around 90 K and 120 K. The superconducting property of silver composites can be explained qualitatively in terms of the proximity theory that has been suggested for the low temperature superconductors.

Rao, Appajosula S.↗
NASA NTRS1995

Test-particle simulations in increasingly strong turbulence

Quasi-linear theory supposes that the energy in resonant fluctuations is small compared to that in the mean magnetic field. This is evident in the fact that the zeroth-order particle trajectories are helices about a mean field B(sub o) that is spatially uniform over many correlation lengths. However, in the solar wind it is often the case that the fluctuating part of the field is comparable in magnitude to the mean part. It is generally expected that quasi-linear theory remains viable for particles that are in resonance with a region of the fluctuation spectrum having only small energy density, but even so, care must be taken when comparing simulations to theoretical predictions. We have performed a series of test-particle simulations to explore the evolution of ion distributions in turbulent situations with varying levels of magnetic fluctuations. As delta-B/B(sub o) is increased the distinctions among absolute pitch angle (defined relative to B(sub o)), local pitch angle (defined relative to B(x)), and magnetic moment become important, some of them exhibiting periodic sloshing unrelated to the nonadiabatic processes of interest. Comparing and contrasting the various runs illustrates the phenomena that must be considered when the premise underlying quasi-linear theory are relaxed.

Pontius, D. H., Jr.↗
NASA NTRS1961

Satellite Attitude Control Utilizing the Earth's Magnetic Field

A study was conducted to determine the feasibility of a satellite attitude fine-control system using the interaction of the earth's magnetic field with current-carrying coils to produce torque. The approximate intensity of the earth's magnetic field was determined as a function of the satellite coordinates. Components of the magnetic field were found to vary essentially sinusoidally at approximately twice orbital frequency. Amplitude and distortion of the sinusoidal components were a function of satellite orbit. Two systems for two-axis attitude control evolved from this study, one using three coils and the other using two coils. The torques developed by the two systems differ only when the component of magnetic field along the tracking line is zero. For this case the two-coil system develops no torque whereas the three-coil system develops some effective torque which allows partial control. The equations which describe the three-coil system are complex in comparison to those of the two-coil system and require the measurement of all three components of the magnetic field as compared with only one for the two-coil case. Intermittent three-axis torquing can also be achieved. This torquing can be used for coarse attitude control, or for dumping the stored momentum of inertia reaction wheels. Such a system has the advantage of requiring no fuel aboard the satellite. For any of these magnetic torquing schemes the power required to produce the magnetic moment and the weight of the coil seem reasonable.

White, John S.↗
NASA NTRS2001

Solar Dynamo Driven by Periodic Flow Oscillation

We have proposed that the periodicity of the solar magnetic cycle is determined by wave mean flow interactions analogous to those driving the Quasi Biennial Oscillation in the Earth's atmosphere. Upward propagating gravity waves would produce oscillating flows near the top of the radiation zone that in turn would drive a kinematic dynamo to generate the 22-year solar magnetic cycle. The dynamo we propose is built on a given time independent magnetic field B, which allows us to estimate the time dependent, oscillating components of the magnetic field, (Delta)B. The toroidal magnetic field (Delta)B(sub phi) is directly driven by zonal flow and is relatively large in the source region, (Delta)(sub phi)/B(sub Theta) much greater than 1. Consistent with observations, this field peaks at low latitudes and has opposite polarities in both hemispheres. The oscillating poloidal magnetic field component, (Delta)B(sub Theta), is driven by the meridional circulation, which is difficult to assess without a numerical model that properly accounts for the solar atmosphere dynamics. Scale-analysis suggests that (Delta)B(sub Theta) is small compared to B(sub Theta) in the dynamo region. Relative to B(sub Theta), however, the oscillating magnetic field perturbations are expected to be transported more rapidly upwards in the convection zone to the solar surface. As a result, (Delta)B(sub Theta) (and (Delta)B(sub phi)) should grow relative to B(sub Theta), so that the magnetic fields reverse at the surface as observed. Since the meridional and zonai flow oscillations are out of phase, the poloidal magnetic field peaks during times when the toroidal field reverses direction, which is observed. With the proposed wave driven flow oscillation, the magnitude of the oscillating poloidal magnetic field increases with the mean rotation rate of the fluid. This is consistent with the Bode-Blackett empirical scaling law, which reveals that in massive astrophysical bodies the magnetic moment tends to increase with the angular momentum of the fluid.

Mayr, Hans G.↗
NASA NTRS2007

Predicting the Starquakes in PSR J0537-6910

We report the results of more than seven years of monitoring of PSR J0537-6910, the 16 ms pulsar in the Large Magellanic Cloud, using data acquired with the Rossi X-ray Timing Explorer. During this campaign the pulsar experienced 22 sudden increases in frequency ("glitches" - 21 with increases of at least eight microHz) amounting to a total gain of over six parts per million of rotation frequency superposed on its gradual spindown of nu-dot = -2 x 10(exp -l0) Hz /s. The time interval from one glitch to the next obeys a strong linear correlation to the amplitude of the first glitch, with a mean slope of about 400 days per part per million (6.5 days per micro Hz), such that these intervals can be predicted to within a few days, an accuracy which has never before been seen in any other pulsar. There appears to be an upper limit of approximately 40 micro Hz for the size of glitches in all pulsars, with the 1999 April glitch of PSR J0537-6910 as the largest so far. The change of its spindown across the glitches, delta (nu-dot), appears to have the same hard lower limit of -1.5 x 10 (exp -13) Hz/s, as, again, that observed in all other pulsars. The spindown continues to increase in the long term, nu-dot = -10(exp -21) Hz / s(exp 2), and thus the timing age of PSR 505374910 (-0.5 nu nu-dot (exp -1) continues to decrease at a rate of nearly one year every year, consistent with movement of its magnetic moment away from its rotational axis by one radian every 10,000 years, or about one meter per year. PSR J0537-6910 was likely to have been born as a nearly-aligned rotator spinning at 75-80 Hz, with a absolute value of nu considerably smaller than its current value of 2x 10(exp -10) Hz per second. Its pulse profile consists of a single pulse which is found to be flat at its peak for at least 0.02 cycles. Glitch activity may grow exponentially with a timescale of 170 years nu nu-dot ((nu nu-dot)(sub crab))exp -l in all young pulsars.

Middleditch, J.↗