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NASA NTRS1995

On the injection of fine dust from the Jovian magnetosphere

Using a simple aligned dipole model of the Jovian magnetic field, and exploiting integrals of the gravito-electrodynamic equation of motion of charged dust, we obtain an analytic result which characterizes the nature of the orbits of grains of different (fixed) charge-to-mass ratios launched at different velocities from different radial distances from Jupiter. This enables us to consider various possible sources of the dust-streams emanating from Jupiter which have been observed by the Ulysses spacecraft. We conclude that Jupiter's volcanically active satellite Io is the likely source, in agreement with the earlier calculations and simulations of Horanyi et al. using a detailed three-dimensional model of the Jovian magnetosphere. Our estimates of the size range and the velocity range of these dust grains are also in good agreement with those of the above authors and are within the error bars of the observations.

Maravilla, D.↗

NASA NTRS1995

Bounce-averaged Hamiltonian for charged particles in an axisymmetric but nondipolar model magnetosphere

In order to facilitate bounce-averaged guiding center simulations of geomagnetically trapped particles, we express the kinetic energy of a particle with magnetic coordinates (L,phi) as an analytic function of the first two adiabatic invariants (M,J) and the L value of the field line. The magnetic field model is axisymmetric, consisting of a dipolar vector-B field plus a uniform southward magnetic field parallel to the dipole moment mu(sub E). This model magnetosphere is surrounded by a circular equatorial neutral line whose radius b is an adjustable parameter. Our formulation provides a computationally efficient method for tracing the bounce-averaged adiabatic motion (conserving all three invariants) and nonadiabatic transport (violating the third invariant while conserving the first two invariants) of geomagnetically trapped particles in the model magnetosphere.

Schulz, Michael↗

NASA NTRS2003

Automated Coronal Loop Identification Using Digital Image Processing Techniques

The results of a master thesis project on a study of computer algorithms for automatic identification of optical-thin, 3-dimensional solar coronal loop centers from extreme ultraviolet and X-ray 2-dimensional images will be presented. These center splines are proxies of associated magnetic field lines. The project is pattern recognition problems in which there are no unique shapes or edges and in which photon and detector noise heavily influence the images. The study explores extraction techniques using: (1) linear feature recognition of local patterns (related to the inertia-tensor concept), (2) parametric space via the Hough transform, and (3) topological adaptive contours (snakes) that constrains curvature and continuity as possible candidates for digital loop detection schemes. We have developed synthesized images for the coronal loops to test the various loop identification algorithms. Since the topology of these solar features is dominated by the magnetic field structure, a first-order magnetic field approximation using multiple dipoles provides a priori information in the identification process. Results from both synthesized and solar images will be presented.

Lee, Jong K.↗

NASA NTRS2020

A Mercury Lander Mission Concept Study for the Next Decadal Survey

Mariner 10 provided our first closeup reconnaissance of Mercury during its three flybys in 1974 and 1975. MESSENGER’s 2011–2015 orbital investigation enabled numerous discoveries, several of which led to substantial or complete changes in our fundamental understanding of the planet. Among these were the unanticipated, widespread presence of volatile elements (e.g., Na, K, S); a surface with extremely low Fe abundance whose darkening agent is likely C; a previously unknown landform—hollows— that may form by volatile sublimation from within rocks exposed to the harsh conditions on the surface; a history of expansive effusive and explosive volcanism; substantial radial contraction of the planet from interior cooling; offset of the dipole moment of the internal magnetic field northward from the geographic equator by ~20% of the planet’s radius; crustal magnetization, attributed at least in part to an ancient field; unexpected seasonal variability and relationships among exospheric species and processes; and the presence in permanently shadowed polar terrain of water ice and other volatile materials, likely to include complex organic compounds. Mercury’s highly chemically reduced and unexpectedly volatile-rich composition is unique among the terrestrial planets and was not predicted by earlier hypotheses for the planet’s origin. As an end-member of terrestrial planet formation, Mercury holds unique clues about the original distribution of elements in the earliest stages of the Solar System and how planets (and exoplanets) form and evolve in close proximity to their host stars. The BepiColombo mission promises to expand our knowledge of this planet and to shed light on some of the mysteries revealed by the MESSENGER mission. However, several fundamental science questions raised by MESSENGER’s pioneering exploration of Mercury can only be answered with in situ measurements from the planet’s surface.

Ernst, C. M.↗

DOE OSTI2026

Modeling the Effect of the Heliospheric Magnetic Field on Cosmic Ray Muon Shadows

Shadows cast in the cosmic ray (CR) muon sky by the Sun were located using muon data from the MINOS far detector in Northern Minnesota. The shadows were observed independently across three time periods; near solar minimum, near solar maximum, and over the entire 13 year span of the data. A distribution of muon positions for each shadow was then sampled to simulate CR motions near the Sun using the Parker spiral model of the Heliospheric Magnetic Field (HMF) and a dipole model of the Geomagnetic Field (GMF). The resulting particle distributions were then compared to their position with respect to the Sun. Results show that the Parker spiral model is most consistent with the solar minimum shadow and least consistent with the solar maximum shadow, as expected. The simple Parker spiral is more consistent with the data for a harder CR spectrum than is actually present, indicating the need for a more detailed HMF model. Plausible modifications to the Parker spiral model which would affect the overall shift of the Sun's CR shadow are discussed.

Adamson, P. [Fermilab]↗

DOE OSTI2018

Conceptual Design of a Large Aperture Dipole for Testing of Cables and Insert Coils at High Field

© 2017 IEEE. Advances in the performance of low- and high-temperature superconductors enable the development of advanced magnets for a range of applications, including tokamaks for fusion energy, dipoles, and quadrupoles for hadron colliders, and solenoids for nuclear magnetic resonance studies. The capability of testing prototype cables and insert coils at high field is critical to these developments. We present here the conceptual design of a test facility dipole with features suitable to support the advanced magnet development efforts of both Fusion and HEP communities. In particular, a background field of 15 T is provided over a minimum homogeneous length of 1000 mm, and the magnet clear bore of approximately 144 × 94 mm can accommodate large fusion conductors as well as prototype coils for high field dipoles, along with flexible cryogenic and mechanical provisions for sample characterization. Two technical solutions are considered. The first uses a forced flow cable-in-conduit conductor and follows the design developed by EFDA for the EDIPO magnet. The second uses a bath cooled Rutherford cable and follows a block-coil design similar to the CERN FRESCA2 dipole, and the LBNL HD and LD1 dipoles. Following a comparison between the two approaches, we present two designs for the Rutherford cable approach including performance objectives, key parameters, and preliminary magnetic, mechanical and quench protection analysis.

Bruzzone, Pierluigi↗

NASA NTRS1979

The magnetic fields of Mercury, Mars, and moon

Mariner observations have shown a significant global magnetic field at Mercury with a dipole moment at a tilt of 14 + or - 5 deg relative to the normal of the orbit plane. A presently active dynamo is the most likely origin for the planet's magnetic field. Limited evidence for an intrinsic magnetic field on Mars was obtained by USSR spacecraft in 1971 and 1974. The Martian magnetic field, if it exists, may result from either remanent magnetism or an active dynamo. On the moon, local magnetic fields have been detected by the Apollo and Lunokhod missions, but no global correlation of the steady state values has been noted.

Ness, N. F.↗

DOE OSTI2017

SIMULATION STUDY OF HEMISPHERIC PHASE-ASYMMETRY IN THE SOLAR CYCLE

Observations of the Sun suggest that solar activities systematically create north–south hemispheric asymmetries. For instance, the hemisphere in which sunspot activity is more active tends to switch after the early half of each solar cycle. Svalgaard and Kamide recently pointed out that the time gaps of polar field reversal between the northern and southern hemispheres are simply consequences of the asymmetry of sunspot activity. However, the mechanism underlying the asymmetric feature in solar cycle activity is not yet well understood. In this paper, in order to explain the cause of the asymmetry from the theoretical point of view, we investigate the relationship between the dipole- and quadrupole-type components of the magnetic field in the solar cycle using the mean-field theory based on the flux transport dynamo model. As a result, we found that there are two different attractors of the solar cycle, in which either the north or the south polar field is first reversed, and that the flux transport dynamo model explains well the phase-asymmetry of sunspot activity and the polar field reversal without any ad hoc source of asymmetry.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1982

An equivalent layer magnetization model for the United States derived from satellite altitude magnetic anomalies

Long wavelength magnetic anomalies measured by the Pogo series satellites at altitudes 400-700 km over the United States and adjacent areas are inverted to an equivalent layer magnetization model based on an equal area dipole source array at the earth's surface. Minimum source spacing giving a stable solution and a physically meaningful magnetization distribution is 300 km, and a scheme is presented for effectively sampling the distribution on a grid twice as fine. The model expresses lateral variation in the vertical integral of magnetization and is a starting point for models of lateral variation in the form of the magnetization-depth curve in the magnetic crust. The magnetization model contours correlate with large-scale tectonic features, and in the western part of the country, probably reflect Curie isotherm undulations.

Mayhew, M. A.↗

NASA NTRS2001

The UAH Spinning Terrella Experiment: A Laboratory Analog for the Earth's Magnetosphere

The UAH Spinning Terrella Experiment has been modified to include the effect of a second magnet. This is a simple laboratory demonstration of the well-known double-dipole approximation to the Earth's magnetosphere. In addition, the magnet has been biassed $\sim$-400V which generates a DC glow discharge and traps it in a ring current around the magnet. This ring current is easily imaged with a digital camera and illustrates several significant topological properties of a dipole field. In particular, when the two dipoles are aligned, and therefore repel, they emulate a northward IMF Bz magnetosphere. Such a geometry traps plasma in the high latitude cusps as can be clearly seen in the movies. Likewise, when the two magnets are anti-aligned, they emulate a southward IMF Bz magnetosphere with direct feeding of plasma through the x-line. We present evidence for trapping and heating of the plasma, comparing the dipole-trapped ring current to the cusp-trapped population. We also present a peculiar asymmetric ring current produced in by the plasma at low plasma densities. We discuss the similarities and dissimilarities of the laboratory analog to the collisionless Earth plasma, and implications for the interpretation of IMAGE data.

Sheldon, R. B.↗

DOE OSTI2025

Advanced Design for the WIQ Magnet With Steering Corrector Function

The Facility for Rare Isotopes Beams (FRIB) delivers heavy-ion primary beams at energies of up to 300 MeV/u at 10 kW of beam power to generate rare isotope beams for experiments and will eventually operate at beam power of 400 kW. The preseprator of the Advanced Rare Isotope Separator (ARIS) is equipped with six warm-iron quadrupole (WIQ) singlets and two dipoles integrated right after the production target. They have a compact structure and operate in a high radiation vacuum environment within a hot cell having remote handling capabilities for installation and maintenance. Due to asymmetry with respect to the quadrupole poles, nested sextupole excitations in WIQs induce vertical dipoles that offset the centroid trajectory; Magnet misalignments also result in trajectory offsets. Such offsets degrade separator performance but can be minimized by changing the current distribution on sextupole and octupole coils. In this work, we show how modifications to the WIQ coil design can allow superimposed dipole fields to be included to the octupole and sextupole windings, as well as addition of dipole components by splitting coil currents over groups with separator power supplies. Adjusting the group currents can cancel the sextupole-induced vertical dipole component which can be as high as 0.012 Tm. Octupole coil changes may superimpose a horizontal dipole integrated strength as high as 0.0332 Tm. Unwanted higher harmonics induced as a side effect of the new design are kept to a minimum such that separator performance is preserved as much as possible.

Accelerator magnets↗

NASA NTRS1980

A model of the heliospheric magnetic field configuration

A three-dimensional model of the magnetic field configuration in the heliosphere is constructed by assuming that the interplanetary magnetic field consists of four components, (1) the solar dipole, (2) a large number of small spherical dipoles located along an equatorial circle just inside the sun (representing the magnetic field line arcade), (3) the field of the poloidal current system generated by the solar unipolar induction, and (4) the field of an extensive current disc around the sun lying in the ecliptic plane. The magnetic field intensity at a distance of 1 AU (about 20 solar radii above the ecliptic plane) is normalized to fit the observed spiral configuration.

Akasofu, S.-I.↗

DOE OSTI2018

Reasonable Beam Deviation Envelope for Ray-tracing

At NSLS-II the unused dipole radiation is intercepted by the photon absorbers installed inside the vacuum chamber. The water-cooled absorbers are designed to take away the heat therefore the temperature is kept within the safety limit. However, if the beam orbit is severely perturbed, the radiation fan could pass through the geometry and strikes on the vacuum chamber components. This ray-leakage is a possible reason of the accelerator component temperature rise observed during the high-current operations. The goal of this work is to find the maximum beam deviation at the dipole hence ray-tracing can be re-examined under the operational constraints. The beam is confined to the orbit by the bending and focusing magnets. At NSLS-II the orbit is further controlled by a real time orbit feedback loop. Beam could be lost in any unpredictable direction if the magnet malfunctions. Consequently reasonable assumptions must be made to define the deviation envelope. It was determined that the dipole radiation is not powerful enough to cause damage within 10 ms, for example, if the rf power is shut off and the beam deviates from the orbit. Therefore we consider the radiation produced by the stored beam only; temporarily processes, such as unstable oscillating beam, should not be a concern. The orbit of the stored beam can be altered during magnet failures. The dipole current is interlocked to a small range of ±2% from the nominal value. If the dipole current changes slowly the beam energy automatically adjusts and the orbit remains the same. If the dipole current changes rapidly the beam will not be stable. Therefore dipole variation need not to be considered. For the other magnets we consider one magnet failure at a time because it is unlikely that two fail at the same time. It was found that the beam lifetime drops dramatically if one quadrupole power supply is turned off; therefore this scenario does not meet the stable beam condition. The current of one quadrupole could drop but will not result in orbit change with the feedback on. Beam could survive if one sextupole power supply is turned off, but the orbit will not be changed. Magnet could partially fail, for example, one or part of the coil shorts due to break-down. This is a low probability event and will not be considered. During daily operations the orbit is changed by the correctors and the rf frequency. In this work the correctors and the rf frequency are varied to explore the deviation envelope.

36 MATERIALS SCIENCE↗

NASA NTRS1983

MAGSAT investigation of crustal magnetic anomalies in the eastern Indian Ocean

Crustal magnetic anomalies in a region of the eastern Indian Ocean were studied using data from NASA's MAGSAT mission. The investigation region (0 deg to 50 deg South, 75 to 125 deg East) contains several important tectonic features, including the Broken Ridge, Java Trench, Ninetyeast Ridge, and Southeast Indian Ridge. A large positive magnetic anomaly is associated with the Broken Ridge and smaller positive anomalies correlate with the Ninetyeast Ridge and western Australia. Individual profiles of scalar data (computed from vector components) were considered to determine the overall data quality and resolution capability. A set of MAGSAT ""Quiet-Time'' data was used to compute an equivalent source crustal magnetic anomaly map of the study region. Maps of crustal magnetization and magnetic susceptibility were computed from the equivalent source dipoles. Gravity data were used to help interpretation, and a map of the ratio of magnetization to density contrasts was computed using Poisson's relation. The results are consistent with the hypothesis of induced magnetization of a crustal layer having varying thickness and composition.

Sailor, R. V.↗

NASA NTRS2011

Gamma-Ray Pulsar Light Curves in Offset Polar Cap Geometry

Recent studies have shown that gamma-ray pulsar light curves are very sensitive to the geometry of the pulsar magnetic field. Pulsar magnetic field geometries, such as the retarded vacuum dipole and force-free magnetospheres, used to model high-energy light curves have distorted polar caps that are offset from the magnetic axis in the direction opposite to rotation. Since this effect is due to the sweepback of field lines near the light cylinder, offset polar caps are a generic property of pulsar magnetospheres and their effects should be included in gamma-ray pulsar light curve modeling. In slot gap models (having two-pole caustic geometry), the offset polar caps cause a strong azimuthal asymmetry of the particle acceleration around the magnetic axis. We have studied the effect of the offset polar caps in both retarded vacuum dipole and force-free geometry on the model high-energy pulse profile~. We find that. corn pared to the profile:-; derived from :-;ymmetric caps, the flux in the pulse peaks, which are caustics formed along the trailing magnetic field lines. increases significantly relative to the off-peak emission. formed along leading field lines. The enhanced contrast produces greatly improved slot gap model fits to Fermi pulsar light curves like Vela, which show very little off-peak emIssIon.

Harding, Alice K.↗

NASA NTRS1991

On the influence of the magnetization of a modal solar wind on a laboratory magnetosphere

The interaction of a magnetized plasma beam with a stationary dipole field, analogous to the interaction of the solar wind with the earth's magnetosphere, is explored in a laboratory experiment. Experimental parameters are chosen to scale qualitatively similar to the parameters in the earth's magnetosphere. It is found that the magnetization of the laboratory 'solar wind', generated by injecting a plasma across a preexisting magnetic field, requires a certain minimum magnetic field strength. Differences between the resulting magnetospheres for northward and southward 'solar wind' or 'interplanetary' magnetic fields (IMF) are demonstrated by global pictures and by magnetic field measurements above the north polar region. These measurements show patterns of the variation of the transverse field component which are similar to those found by satellite measurements above the earth. This indicates the presence of similar field-aligned current systems. Particularly, the presence (for northward IMF) and absence (for southward IMF) of the pattern attributed to the 'NBZ' (northward Bz) current system are demonstrated.

Rahman, H. U.↗

NASA NTRS2001

Magnetohydrodynamic Simulations of the Effects of the Solar Wind on the Jovian Magnetosphere

We have used a three-dimensional magnetohydrodynamic simulation of the interaction between the solar wind and a rapidly rotating magnetosphere to study the effects of the solar wind dynamic pressure and the interplanetary magnetic field IMF on the configuration of the Jovian magnetosphere. Both the solar wind dynamic pressure and the IMF can cause substantial changes in the magnetosphere. On the dayside when the pressure increases the bow shock and magnetopause move toward Jupiter and the equatorial magnetic field in the middle magnetosphere becomes more dipole-like. When the pressure decreases the boundaries move farther from Jupiter and the dayside magnetic field becomes stretched out into a more tail-like configuration. For northward IMF the boundaries move toward Jupiter but the field becomes more tail-like. Finally, for southward IMF the boundaries move away and the field becomes more dipole-like. These changes are qualitatively consistent with those observed on spacecraft passing through the dayside magnetosphere. However, we were not always able to get quantitative agreement. In particular the model does not reproduce the extremely tail-like magnetic field observed during the Pioneer 10 and Ulysses inbound passes. The solar wind and IMF also influence the configuration of the middle magnetosphere in the magnetotail. Tailward flows were found in the nightside equatorial plasma sheet for most IMF orientations. Both inertial effects and the IMF influence reconnection in the tail. The only time the tailward flow in the magnetotail stopped was during prolonged intervals with southward IMF. Then reconnection in the polar cusp caused the flow to move out of the equatorial plane.

Walker, Raymond J.↗

DOE OSTI2022

On the synthesis of heavy nuclei in protomagnetar outflows and implications for ultra-high energy cosmic rays

ABSTRACT It has been suggested that strongly magnetized and rapidly rotating protoneutron stars (PNSs) may produce long duration gamma-ray bursts (GRBs) originating from stellar core collapse. We explore the steady-state properties and heavy element nucleosynthesis in neutrino-driven winds from such PNSs whose magnetic axis is generally misaligned with the axis of rotation. We consider a wide variety of central engine properties such as surface dipole field strength, initial rotation period, and magnetic obliquity to show that heavy element nuclei can be synthesized in the radially expanding wind. This process is facilitated provided the outflow is Poynting-flux dominated such that its low entropy and fast expansion time-scale enables heavy nuclei to form in a more efficient manner as compared to the equivalent thermal GRB outflows. We also examine the acceleration and survival of these heavy nuclei and show that they can reach sufficiently high energies ≳ 1020 eV within the same physical regions that are also responsible for powering gamma-ray emission, primarily through magnetic dissipation processes. Although these magnetized outflows generally fail to achieve the production of elements heavier than lanthanides for our explored electron fraction range 0.4–0.6, we show that they are more than capable of synthesizing nuclei near and beyond iron peak elements.

79 ASTRONOMY AND ASTROPHYSICS↗