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Driving rapid atomic order in MnAl via low-magnitude magnetic field annealing
Application of a mild (60 mT), uniform magnetic field during short-term thermal treatment of kinetically retained, atomically disordered (paramagnetic) ε-MnAl was found to deliver a significant ~50 % increase in the formation of L1 0 atomically ordered (ferromagnetic) τ-MnAl product phase, compared to that produced by conventional (i.e., zero-field) annealing under identical thermal conditions. The magnetic field, applied in a passive closed-circuit configuration during annealing, induced significant changes in the structural, magnetic, and phase evolution of the material. Computational results based on electronic structure calculations demonstrate that the effective magnetic susceptibility of τ-MnAl is sensitive to the orientation, rather than the magnitude, of an applied magnetic field in the vicinity of the Curie temperature. The uniaxial magnetocrystalline anisotropy of the L1 0 structure is proposed to act as a filter for selective propagation of the population of τ-MnAl variants that are favorably aligned with the applied field. In this manner, crystallographic “gridlock” is alleviated that would otherwise arise from the coexistence of multiple, energetically equivalent τ-phase variants within the parent ε-phase matrix. These results confirm that static, low-magnitude magnetic field annealing is able to accelerate L1 0 atomic ordering in the MnAl system and likely can exert similar influences in relevant magnetic systems, facilitating efficient tailoring of structure-sensitive magnetic properties for the manufacture of magnetic materials.
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.
Core magnetic field enhancement in single X line, multiple X line and patchy reconnection
Magnetic flux transfer events often show a significant increase of the magnetic field strength at the center of the events. Similar magnetic field observations have been reported for structures in or near the plasma sheet of the magnetotail at about 20 R(sub E). We have carried out two-dimensional (2D) and three-dimensional (3D) and simulations of single X line reconnection (SXR), multiple X line reconnection (MXR), and patchy reconnection to determine and compare the amplification of the magnetic field in the center of the developing flux tubes. The various processes are achieved by appropriate choices of 2D or 3D resistivity models. The simulations show that the increase in magnetic field strength depends on both the property of the initial configuration and the particular reconnection geometry. For the chosen initial conditions the MXR process leads to a larger increase in the core magnetic field than the patchy reconnection and SXR caused by larger magnetic tensions in the MXR process. The 3D processes always lead to a larger amplification than the corresponding 2D processes. In the 3D cases, force imbalance in the y direction will accelerate plasma out of the flux tube. This process reduces the thermal pressure and leads to a further compression of the flux rope, which yields an additional increase in the interior magnetic field strength.
Design and Control of Three-Dimensional Topological Magnetic Fields Using Interwoven Helical Nanostructures
Three-dimensional (3D) magnetic nanostructures are an emerging platform capable of creating complex topological magnetic fields. The control of localized nanoscale magnetic fields is seen to be of importance for diverse areas from bioapplications such as drug delivery, to particle trapping and controlling Majorana Fermions for quantum computing. Three-dimensional geometric confinement and proximity can create tailor-made spin textures not possible in two dimensions. The control of magnetization afforded here can allow the formation of unique stray field textures. Here, we report the creation of reconfigurable 3D topological magnetic field textures induced by an interwoven 3D nanostructure and applied field protocol. These field textures emerge due to distinct DWs formed in this structure and lead to the creation of an antivortex field, a hexapole cusp and a 3D skyrmion field tube of mixed chirality. In conclusion, our results therefore show a key step toward the design and control of topological magnetic fields on the nanoscale.
What we have learned about the magnetic field of Mars
Sufficient and unambiguous evidences of the intrinsic martian magnetic field are: (1) the independence of the field polarity in Maritan magnetic tail from interplanetary magnetic fields (IMF) polarity inversion, established with the help of Mars-5 data; and (2) the incongruity between the sign of the radial component of the field measured in Martian tail (Mars-2) and that of the draped model with IMF data measured simultaneously (Mars-3) on February 23-24, 1972. Mar's dipole magnetic moment is within the limits (1.5 to 2.2) x 10 to e 22 G cc. The dipole axis is deflected from that of rotation on the angle I 15 deg. The North magnetic pole is located in the South Hemisphere. In the frame of the precession-dinamo model the magnetic fields of the planets Mars and Earth are similar. The Martian magnetic field is the real obstacle for the solar wind near the planet.
Magnetic Field Sensing via Acoustic Sensing Fiber with Metglas® 2605SC Cladding Wires
Magnetic field sensing has the potential to become necessary as a critical tool for long-term subsurface geophysical monitoring. The success of distributed fiber optic sensing for geophysical characterization provides a template for the development of next generation downhole magnetic sensors. In this study, Sentek Instrument’s picoDAS is coupled with a multi-material single mode optical fiber with Metglas® 2605SC cladding wire inclusions for magnetic field detection. The response of acoustic sensing fibers with one and two Metglas® 2605SC cladding wires was evaluated upon exposure to lateral AC magnetic fields. An improved response was demonstrated for a sensing fiber with in-cladding wire following thermal magnetic annealing (~400 °C) under a constant static transverse magnetic field (~200 μT). A minimal detectable magnetic field of ~500 nT was confirmed for a sensing fiber with two 10 μm cladding wires. The successful demonstration of a magnetic field sensing fiber with Metglas® cladding wires fabricated via traditional draw processes sets the stage for distributed measurements and joint inversion as a compliment to distributed fiber optic acoustic sensors.
The B-dot Earth Average Magnetic Field
The average Earth's magnetic field is solved with complex mathematical models based on mean square integral. Depending on the selection of the Earth magnetic model, the average Earth's magnetic field can have different solutions. This paper presents a simple technique that takes advantage of the damping effects of the b-dot controller and is not dependent of the Earth magnetic model; but it is dependent on the magnetic torquers of the satellite which is not taken into consideration in the known mathematical models. Also the solution of this new technique can be implemented so easily that the flight software can be updated during flight, and the control system can have current gains for the magnetic torquers. Finally, this technique is verified and validated using flight data from a satellite that it has been in orbit for three years.
Properties of a large-scale interplanetary loop structure as deduced from low-energy proton anisotropy and magnetic field measurements
Correlated particle and magnetic field measurements by the ISEE 3 spacecraft are presented for the loop structure behind the interplanetary traveling shock event of Nov. 12, 1978. Following the passage of the turbulent shock region, strong bidirectional streaming of low-energy protons is observed for approximately 6 hours, corresponding to a loop thickness of about 0.07 AU. This region is also characterized by a low relative variance of the magnetic field, a depressed proton intensity, and a reduction in the magnetic power spectral density. Using quasi-linear theory applied to a slab model, a value of 3 AU is derived for the mean free path during the passage of the closed loop. It is inferred from this observation that the proton regime associated with the loop structure is experiencing scatter-free transport and that either the length of the loop is approximately 3 AU between the sun and the earth or else the protons are being reflected at both ends of a smaller loop.
A large-scale pattern in the solar magnetic field.
Large scale pattern in solar magnetic field correlated with interplanetary magnetic field
Standard Practices for Usage of Inductive Magnetic Field Probes with Application to Electric Propulsion Testing
Inductive magnetic field probes (also known as B-dot probes and sometimes as B-probes or magnetic probes) are often employed to perform field measurements in electric propulsion applications where there are time-varying fields. Magnetic field probes provide the means to measure these magnetic fields and can even be used to measure the plasma current density indirectly through the application of Ampere's law. Measurements of this type can yield either global information related to a thruster and its performance or detailed, local data related to the specific physical processes occurring in the plasma. Results of the development of a standard for B-dot probe measurements are presented, condensing the available literature on the subject into an accessible set of rules, guidelines, and techniques to standardize the performance and presentation of future measurements.
3-D Mapping of the Magnetic Field in the Active Region by the CLASP2.1 Rocket Experiment
Comprehensive magnetic field measurements of the solar atmosphere are crucial for understanding energy transport from the photosphere to the corona and its dissipation. However, observations of the magnetic field in the chromosphere and the upper atmospheric layers above the chromosphere, where the gas pressure dominance changes from (β>1) to magnetic pressure dominance (β<1), are overwhelmingly lacking. Therefore, we have focused on the polarization of ultraviolet radiation emitted from the upper chromosphere and transition layer and have conducted the Japan-U.S.-EU observation rocket experiment CLASP in order to demonstrate its usefulness. In CLASP2.1 conducted on October 8, 2021, scan observations were made at 16 locations in the active region, and Stokes (intensity $I$, linearly polarized $Q$, $U$, circularly polarized $V$) spectra in the 280~nm wavelength range were obtained. Looking at the observed region with AIA 171~{¥AA} on board the SDO satellite, we see that it consists of a region where a structure corresponding to the foot of a high-temperature loop called moss (moss) is seen, and a region where a low-temperature loop spreading from a sunspot is seen. We focused on the ionized magnesium $h$ & $k$ lines (emitted from the middle and uppermost of the chromosphere) and the manganese lines (emitted from the low part of the chromosphere), which show particularly prominent circular polarization, and derived the line-of-sight magnetic fields in the low, middle and uppermost parts of the chromosphere by applying weak field approximation to them. Furthermore, by combining the results with observations by the Solar Optical Telescope onboard the solar observing satellite HINODE, we obtained three-dimensional information on the magnetic field in the active region from the photosphere to the uppermost part of the chromosphere. In general, the magnetic field in the active region becomes weaker and smoother as one goes up in the sky, as reported by the CLASP2 observation (Ishikawa et al. 2021). However, in some regions, polarity reversal was observed only in the uppermost part of the chromosphere, and comparison with high spatial resolution transition layer and coronal images recorded by SDO/AIA revealed the connection between the magnetic field structure in the chromosphere and coronal loops.
The magnetic field investigation on Cluster
The magnetic field investigation of the Cluster four-spacecraft mission is designed to provide intercalibrated measurements of the B magnetic field vector. The instrumentation and data processing of the mission are discussed. The instrumentation is identical on the four spacecraft. It consists of two triaxial fluxgate sensors and of a failure tolerant data processing unit. The combined analysis of the four spacecraft data will yield such parameters as the current density vector, wave vectors, and the geometry and structure of discontinuities.
Radiation from Relativistic Shocks with Turbulent Magnetic Fields
Recent PIC simulations of relativistic electron-positron (electron-ion) jets injected into a stationary medium show that particle acceleration occurs at shocked region. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the shock. The "jitter" radiation from deflected electrons in turbulent magnetic fields has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants. New recent calculation of spectra with various different Lorentz factors of jets (two electrons) and initial magnetic fields. New spectra based on small simulations will be presented.
The magnetic field of Mercury
The paper examines the magnetic field observations and their analyses relating to the determination of the Mercury magnetic field. Methods of analyzing data included: (1) comparison of bow shock and magnetopause relative positions at Mercury to the earth, (2) direct spherical harmonic analysis, (3) magnetosphere modeling by an image dipole, and (4) scaling of a mathematical model for the terrestrial magnetosphere. Dipole moments were determined using partial quadrupole and octupole terms to improve the least-square fit of models to observations; analyses by method (2) yield a convergent series of dipole moments values considered to best represent the intrinsic planetary field. Finally, it is suggested that the origin of the magnetic field of Mercury cannot be uniquely determined, but the sources of convective energy may be radiogenic decay and heat release, gravitational settling, and differentiation of processional torques.
Interstellar Magnetic Fields and Polarimetry of Dust Emission
Magnetic fields are an important ingredient in the stormy cosmos. Magnetic fields: (1) are intimately involved with winds from Active Galactic Nuclei (AGN) and stars (2) create at least some of the structures observed in the ISM (3) modulate the formation of clouds, cores, and stars within a turbulent medium (4) may be dynamically important in protostellar accretion disks (5) smooth weak shocks (C-shocks).
Comments on the reconnexion rate of magnetic fields.
The reconnection rate of magnetic fields is crucial in understanding the fields found in turbulent flows in the solar photosphere and in the galaxy, and in flare phenomena. The behavior of magnetic fields in the neighborhood of an X-type neutral point is examined. The treatment is kinematic specifying the velocity field v and constructing solutions to the hydromagnetic equation for B. The calculations demonstrate that the reconnection rate is controlled by the diffusion in the near neighborhood of the neutral point, and is not arbitrarily large, as has been suggested by similarity solutions of the complete field and fluid equations for vanishing diffusion.
Studies of solar magnetic fields during the solar maximum year
Observations and studies of solar magnetic fields that were carried out during the period of the solar maximum year (SMY) January 1980 to June 1981, are reviewed with the goal of providing a summary of what was learned about solar magnetic fields during the SMY. Such subjects as the relationship between solar magnetic fields and flares, the role of magnetic fields in the sunspot phenomenon, the magnetic-canopy structure overlying the supergranular network as well as the turbulent magnetic fields within the network, the fields within the polar crown prominences, and the solar magnetic cycle are addressed.