Magnetic Field Configuration Research Articles

Effect of Magnetic Field Configuration on Stray-Crystal Formation with Different Platform Sizes during Directional Solidification of Single-Crystal Superalloy

Effect of Magnetic Field Configuration on Stray-Crystal Formation with Different Platform Sizes during Directional Solidification of Single-Crystal Superalloy

Multi-scale magnetic field investigation of the M-dwarf eclipsing binary CU Cancri

We aim to characterise the magnetic field of the eclipsing binary CU Cancri, which consists of two M-dwarf components. The determination of the magnetic field parameters of this target enables comparisons with both observations of similar stars and theoretical predictions of the magnetic field strength in CU Cnc. The target therefore provides an excellent opportunity to test our understanding of the generation of magnetic fields in low-mass stars and its impact on stellar structure. We used spectropolarimetric observations obtained with ESPaDOnS at the CFHT to investigate the magnetic properties of CU Cnc. To improve the signal, we used least-squares deconvolution (LSD) to create average line profiles. From these LSD profiles, we extracted information about the radial velocities of the components, significantly expanding the number of radial velocity measurements available and allowing for a determination of the orbital parameters. Stokes $V$ LSD profiles were used with Zeeman Doppler imaging to obtain the large-scale magnetic field structures of the two components. We also used detailed polarised radiative transfer modelling to investigate the small-scale fields, by Zeeman-splitting magnetically sensitive Ti I lines in non-polarised spectra. We obtain both the small- and large-scale magnetic field properties of the two components. The large-scale fields are dominantly poloidal, and both components have an average strength of approximately 100\,G. This analysis of the large-scale fields likely suffers from some amount of hemisphere degeneracy due to the high inclination of the target, which would cause the large-scale field strength of the components to be underestimated. Both components also show unusual magnetic field configurations compared to stars with similar parameters: the primary is weakly axisymmetric (sim \,10\,<!PCT!>), and the secondary has a strong toroidal contribution (sim \,20\,<!PCT!>). The small-scale fields are significantly stronger, 3.1 and 3.6\,kG for the primary and secondary, respectively. This measurement is in excellent agreement with surface field strength predictions for CU Cnc from magneto-convective stellar evolution models. These results indicate that magnetic fields could play a significant role in the radius inflation due to convective inhibition.

Investigating Isogyres in Ferrofluids and Horocycles from Parlaseric Circle in a Ferrocell

This study explored the complex relationship between magnetic fields and light polarization in thin films of ferrofluid. Utilizing techniques such as polarized light imaging, multipolar expansion, and Mueller matrix formalism, this work investigated the formation of isogyres, which are distinct patterns observed when polarized light passes through the ferrofluid under various magnetic field configurations. The analysis revealed that the alignment of nanoparticles in response to the magnetic field resulted in the formation of a diffraction grating, influencing light polarization. Through the application of Stokes vectors and Mueller matrices, we gained insights into the complex interplay between magnetic fields and optical properties. The experiment presents the evolution of isogyres from straight lines to parabolas under the influence of a hexapolar magnetic field. The Mueller matrix effectively represented the magnetic field's impact on polarized light, highlighting dark regions corresponding to isogyres. We also report the formation of some patterns related to atmospheric optics and their analogy with the formation of patterns of the parlaseric circle and the luminous horocycle.

Synthetic Mirnov diagnostic for the validation of experimental observations.

A synthetic Mirnov diagnostic has been developed to investigate the capabilities and limitations of an arrangement of Mirnov coils in terms of a mode analysis. Eight test cases have been developed, with different coil arrangements and magnetic field configurations. Three of those cases are experimental configurations of the stellarator Wendelstein 7-X. It is observed that, for a high triangularity of the flux surfaces, the arrangement of the coils plays a significant role in the exact determination of the poloidal mode number. For the mode analysis, torus and magnetic coordinates have been used. In most cases, the reconstruction of the poloidal mode number of a prescribed mode was found to be more accurate in magnetic coordinates. As an application, the signal of an Alfvén eigenmode, which has been calculated with a three-dimensional magnetohydrodynamics code, is compared to experimental observations at Wendelstein 7-X. For the chosen example, the calculated and measured mode spectra agree very well and additional information on the toroidal mode number and localization of the mode has been inferred.

Characterization of Magnetic Flux Contents for Two Flux Transfer Events From Both In Situ and Ionospheric Observations

AbstractFlux transfer events (FTEs) are a type of magnetospheric phenomena that exhibit distinctive observational signatures from the in situ spacecraft measurements. They are generally believed to possess a magnetic field configuration of a magnetic flux rope and formed through magnetic reconnection at the dayside magnetopause, sometimes accompanied with enhanced plasma convection in the ionosphere. We examine two FTE intervals under the condition of southward interplanetary magnetic field (IMF) with a dawn‐dusk component. We apply the Grad‐Shafranov (GS) reconstruction method to the in situ measurements by the Magnetospheric Multiscale (MMS) spacecraft to derive the magnetic flux contents associated with the FTE flux ropes. In particular, given a cylindrical magnetic flux rope configuration derived from the GS reconstruction, the magnetic flux content can be characterized by both the toroidal (axial) and poloidal fluxes. We then estimate the amount of magnetic flux (i.e., the reconnection flux) encompassed by the area “opened” in the ionosphere, based on the ground‐based Super Dual Auroral Radar Network (SuperDARN) observations. We find that for event 1, the FTE flux rope is oriented in the approximate dawn‐dusk direction, and the amount of its total poloidal magnetic flux falls within the range of the corresponding reconnection flux. For event 2, the FTE flux rope is oriented in the north‐south direction. Both the FTE flux and the reconnection flux have greater uncertainty. We provide a detailed description about a formation scenario of sequential magnetic reconnection between adjacent field lines based on the FTE flux rope configurations from our results.

Effect of Large-Angle Scattering on Particle Transport and Heat Flux in Advanced Divertor Magnetic Field Configurations

Effect of Large-Angle Scattering on Particle Transport and Heat Flux in Advanced Divertor Magnetic Field Configurations

Influence of cusp magnetic field configuration on plasma parameters of radio frequency driven negative ion source for CRAFT NNBI

Radio Frequency (RF) driven negative ion source is the preferred ion source for negative ion based Neutral Beam Injection system (NNBI). The plasma generator, which consists of RF driver(s) and an expansion chamber, is one of the key parts for NNBI. The distribution of cusp magnetic field which is generated by permanent magnets installed at the lateral wall of the expansion chamber is a common issue, due to the great influence on electron density, electron temperature and spatial uniformity of plasma density in the extraction area. Two kinds of configuration of cusp magnetic field (checkerboard type and symmetric type) and three types of arrangement of permanent magnets (with three, four and five rows of magnets) have been carried out with the approach of finite element and the experimental performance. On the RF negative ion source testbed, a moveable Langmuir probe has been adopted to investigate the characteristic of electron density and temperature near the extraction area. Since the symmetric type with three rows of permanent magnets generates the distribution of cusp magnetic field that contribute to extract the plasma from RF driver and improve the probability of particle collision easily, the higher electron density and the lower electron temperature was obtained via simulation. The experimental conclusion is that the symmetric type with three rows of permanent magnets leads to a higher electron density and lower electron temperature, showing a great agreement with simulation results. The results are helpful to optimize the structure and performance of high power ion source, and provide support for the development of large area RF negative ion sources with multi-driver.

Equation of state and anisotropy of pressure of magnetars

AbstractMagnetars are the neutron stars with the highest magnetic fields up to 1015–1016 G. It has been proposed that they are also responsible for a variety of extra‐galactic phenomena, ranging from giant flares in nearby galaxies to fast radio bursts. Utilizing a relativistic mean field model and a variable magnetic field configuration, we investigate the effects of strong magnetic fields on the equation of state and anisotropy of pressure of magnetars. It is found that the mass and radius of low‐mass magnetars are weakly enhanced under the action of the strong magnetic field, and the anisotropy of pressure can be ignored. Unlike other previous investigations, the magnetic field is unable to violate the mass limit of the neutron stars.

Constraints on axion-like particles from the observation of GRB 221009A by LHAASO

The LHAASO collaboration recently reported the measurement of the gamma-ray spectra of GRB 221009A, which is the brightest burst ever, covering an energy range from 0.3 TeV to about 10 TeV. Based on the observation, we investigate the ALP-photon oscillation effect in the host galaxy of GRB 221009A and the Milky Way. The CLs method is applied to set constraints on the ALP parameters in this study. Given the uncertain magnetic field configuration in the host galaxy, we use three different models: a homogeneous magnetic field model, a magnetic field model identical to that of the Milky Way, and a model constructed from the HST observations of the host galaxy. We find that the constraints derived using these three host galaxy magnetic field models are comparable. Our results are complementary in the small ALP mass regions compared with other experiments.

Blandford-Znajek jets in MOdified Gravity

General relativity (GR) will be imminently challenged by upcoming experiments in the strong gravity regime, including those testing the energy extraction mechanisms for black holes. Motivated by this, we explore magnetospheric models and black hole jet emissions in Modified Gravity (MOG) scenarios. Specifically, we construct new power emitting magnetospheres in a Kerr-MOG background which are found to depend non-trivially on the MOG deformation parameter. This may allow for high-precision tests of GR. In addition, a complete set of analytic solutions for vacuum magnetic field configurations around static MOG black holes are explicitly derived, and found to comprise exclusively Heun's polynomials.

Effect of a permanent-magnet-induced cusp field on a magnetic nozzle radio frequency plasma thruster

A cusp magnetic field is formed upstream of a radio frequency antenna by using a permanent magnet (PM) array in a radio frequency plasma source attached to a diffusion chamber, while an expanding magnetic field configuration downstream of the source is maintained by placing a solenoid near the source tube’s exit, resembling a magnetic nozzle plasma thruster. The PM array is composed of 16 neodymium magnets and is designed to be movable axially, providing a movable axial location of the cusp field. The source is operated at a frequency of 13.56 MHz and an rf power of up to 2.6 kW in low-pressure argon. A force exerted on a target plate located downstream of the source is assessed by a pendulum target technique, showing that the force is increased if the cusp field is closer to the radio frequency antenna. The result is consistent with the previously reported result for the cusp field configuration applied by two sets of solenoids, while the present configuration can reduce the consumed electricity for the upstream solenoid.

Helium pool boiling critical heat flux under various magnetically controlled gravity levels

The characterization of Critical Heat Flux (CHF) under magnetic compensation of gravity in liquid helium (LHe) is particularly important for the design of the future very high magnetic field superconducting magnets. Through a series of experimental sessions, the critical heat flux in LHe pool boiling has been determined under various gravity conditions ranging from 0.03g to 2.2g using magnetic forces. It is the largest range of gravity variation, from reduced to hyper-gravity, ever studied in a single facility so far. The study was conducted in a very high magnetic field up to 30 T. The magnetic compensation of gravity does not allow for perfect resulting gravity homogeneity. Nevertheless, for the first time, the magnetic field configuration is considered in the experimental results analysis. The relative resulting gravity inclination with respect to the heat exchange surface is also taken into account. The experimental results are compared with the well-known CHF correlation in LHe pool-boiling and show a very good behavior agreement. For our experimental gravity level, the CHF is ranging from 3000 W/m2 to 12000 W/m2.

The Hemispheric Difference in Electric Potential and Electron Precipitation Observed by DMSP in the Auroral Zone

AbstractIn this case study, we focus on how hemispheric differences in the electric potential distribution in the auroral zones are related to hemispheric differences in the energetic particle precipitation that indicate the presence of field‐aligned potential drops. Utilizing data during the spring and fall equinox in 2013 and 2014 from the Defense Meteorological Satellite Program (DMSP) F16 and F17 satellites, we systematically examine simultaneous measurements of plasma drift velocity and particle precipitation in magnetically conjugate regions across the auroral zone in both hemispheres. This allows us to establish the degree to which the interhemispheric differences in ionospheric electric potential may be accounted for by field‐aligned potential drops. Thirty‐seven eligible cases examined show accelerated electron energy spectra at conjugate locations in the northern and/or southern hemispheres. Of these 37 cases, 23 show conjugate differences in electric potential that agree qualitatively with the observed electron acceleration and average energy of precipitating electrons in each hemisphere. This result suggests that the hemispheric differences in ionospheric electric potential in the auroral zone may be most frequently accounted for by field‐aligned potential drops along the magnetic flux tubes connecting conjugate points to the equatorial plane. The spatial and temporal variability of the potential distribution, electron precipitation, and magnetic field configuration could account for deviations from the normally observed situation in the remaining cases. More magnetically conjugate observations at various altitudes in both hemispheres are needed to investigate this hemispheric coupling in more detail.

Prompt GRB polarization from non-axisymmetric jets

ABSTRACT Time-resolved linear polarization (Π) measurements of the prompt gamma-ray burst emission can reveal its dominant radiation mechanism. A widely considered mechanism is synchrotron radiation, for which linear polarization can be used to probe the jet’s magnetic-field structure, and in turn its composition. In axisymmetric jet models, the polarization angle (PA) can only change by 90°, as Π temporarily vanishes. However, some time-resolved measurements find a continuously changing PA, which requires the flow to be non-axisymmetric in at least one out of its emissivity, bulk Lorentz factor, or magnetic field. Here, we consider synchrotron emission in non-axisymmetric jets, from an ultrarelativistic thin shell, comprising multiple radially expanding mini-jets (MJs) or emissivity patches within the global jet, that yield a continuously changing PA. We explore a wide variety of possibilities with emission consisting of a single pulse or multiple overlapping pulses, presenting time-resolved and integrated polarization from different magnetic field configurations and jet angular structures. We find that emission from multiple incoherent MJs/patches reduces the net polarization due to partial cancellation in the Stokes plane. When these contain a large-scale ordered field in the plane transverse to the radial direction, Π always starts near maximal and then declines over the single pulse or shows multiple highly polarized peaks due to multiple pulses. Observing $\Pi \lesssim 40~{{\ \rm per\ cent}}$ (15 per cent) integrated over one (several) pulse(s) will instead favour a shock-produced small-scale field either ordered in the radial direction or tangled in the plane transverse to it.

Magnetic Field Intervention Enhances Cellular Migration Rates in Biological Scaffolds.

The impact of magnetic fields on cellular function is diverse but can be described at least in part by the radical pair mechanism (RPM), where magnetic field intervention alters reactive oxygen species (ROS) populations and downstream cellular signaling. Here, cellular migration within three-dimensional scaffolds was monitored in an applied oscillating 1.4 MHz radiofrequency (RF) magnetic field with an amplitude of 10 µT and a static 50 µT magnetic field. Given that cellular bioenergetics can be altered based on applied RF magnetic fields, this study focused on a magnetic field configuration that increased cellular respiration. Results suggest that RF accelerated cell clustering and elongation after 1 day, with increased levels of clustering and cellular linkage after 7 days. Cell distribution analysis within the scaffolds revealed that the clustering rate during the first day was increased nearly five times in the RF environment. Electron microscopy provided additional topological information and verified the development of fibrous networks, with a cell-derived matrix (CDM) visualized after 7 days in samples maintained in RF. This work demonstrates time-dependent cellular migration that may be influenced by quantum biology (QB) processes and downstream oxidative signaling, enhancing cellular migration behavior.

Constraints on the internal physics of neutron stars from the observational data of several young pulsars: The role of a power-law decaying dipole magnetic field

The observational data (e.g., the timing data and magnetic tilt angles χ) of young pulsars can be used to probe some critical issues about the internal physics of neutron stars (NSs), for instance, the number of precession cycles ξ and the internal magnetic field configuration (IMFC) of NSs. Evolution of the dipole magnetic field Bd of NSs may play an important role in determining the final results. In this work, a power-law form is adopted to describe the decay of Bd. In such a scenario, the IMFC and ξ of young pulsars with an ordinary Bd∼1012−1013 G and a steady braking index n are investigated. Since the tilt angle change rates χ˙ of pulsars with n<3 can be theoretically predicted, a test on the power-law decay model can thus be made by comparing the theoretical values to that obtained from observations. However, such a comparison can only be made on the Crab pulsar currently, and the results show that the power-law decay model is inconsistent with the Crab's observations. We suggest that rather than decay, the Crab's Bd should increase with time at a rate ∼12−14 G/s. A definite conclusion on the validity of the power-law decay model for pulsars with ordinary Bd may be given if χ˙ of other pulsars could be measured.

A Semi-Empirical Model of Cathodic Arc Spot Motion under the Influence of External Magnetic Fields

Plasma generation by cathodic arc spots plays a crucial role for coating processes that make use of the Arc-PVD technology. Usually, the arc spot motion over the cathode is steered by a magnetic field of a particular distribution and magnitude to ensure a continuous plasma generation, the avoidance of liquid droplets, and a proper utilization of cathode material by homogeneous erosion. This study presents a semi-empirical model that allows for an examination and characterization of the arc spot motion with regard to direction and speed as a function of an imposed magnetic field. This model considers the different components of random walk, retrograde, and Robson drift motion. Introduced empirical coefficients were determined by corresponding experimental investigations. The calibrated model describes the arc spot motion in good agreement to the recorded spot tracks and can therefore be applied for an evaluation of different magnetic field configurations.

Characterization of a radiofrequency linear plasma device in uniform and convergent magnetic fields

A linear radiofrequency plasma device is constructed, where a source operating at a frequency of 13.56 MHz and a maximum power of several kW is attached to a cylindrical vacuum chamber about 1 m in length. Seven solenoids are located around the source and the chamber, providing various magnetic field configurations by changing the solenoid currents. The plasma density of the radiofrequency linear plasma device is initially characterized in uniform and convergent magnetic field configurations. A blue mode argon plasma, being inherent to the helicon or high-density discharge, is observed in the chamber downstream of the source for both configurations, while the density near the antenna is lower than that in the chamber. Furthermore, the density for the convergent magnetic field configuration is found to be larger than that for the uniform case, providing a maximum density of about . Spatiotemporal measurements of the ion saturation current reveal that the density peak is formed near the rf antenna at the initial time of the discharge and the peripheral high-density region subsequently appears downstream of the antenna, implying that the rf power is efficiently coupled with the electrons downstream of the antenna once the initial plasma is created. A few ms after turning on the rf power, the density over the whole region reduces, which seems to be due to a neutral depletion.

Geomagnetic Storm Effects on the LEO Proton Flux During Solar Energetic Particle Events

AbstractDuring a few solar energetic particle (SEP) events, solar protons were trapped within the geomagnetic field and reached the outer edge of the inner radiation belt. We reproduced this phenomenon by modeling the proton flux distribution at the Low‐Earth Orbit (LEO) for different geomagnetic conditions during solar particle events. We developed a three‐dimensional relativistic test particle simulation code to compute the 70–180 MeV solar proton Lorentz trajectories in low L‐shell range from 1 to 3. The Tsyganenko model (T01) generated the background static magnetic field with the IGRF (v12) model. We have selected three Dst index values: −7, −150, and −210 nT, to define quiet time, strong, and severe geomagnetic storms and to generate the corresponding inner magnetic field configurations. Our results showed that the simulated solar proton flux was more enhanced in the high‐latitude regions and more expanded toward the lower latitude range as long as the geomagnetic storm was intensified. Satellite observations and geomagnetic cutoff rigidities confirmed the numerical results. Furthermore, the LEO proton flux distribution was deformed, so the structure of the proton flux inside the South Atlantic Anomaly (SAA) became longitudinally extended as the Dst index decreased. Moreover, we have assessed the corresponding radiation environment of the LEO mission. We realized that, for a higher inclined LEO mission during an intense geomagnetic storm (Dst = −210 nT), the probability of the occurrence of the Single Event Upset (SEU) rates increased by 19% and the estimated accumulated absorbed radiation doses increased by 17% in comparison with quiet conditions.

Mode Changing in PSR B0844-35 and PSR B1758-29 with Enhanced Emission at the Profile Centers

We have studied the single pulse emission from two pulsars, PSR B0844-35 and PSR B1758-29, over a wide frequency range of 300–750 MHz using the upgraded Giant Metrewave Radio Telescope. The two pulsars have relatively wide profiles with multiple components, which are a result of the line of sight traversing near the center of the emission beam. In both pulsars, the single pulse sequences show the presence of two distinct emission states, where the profiles become much brighter at the center, with prominent core components during one of the modes, while in the other mode the single pulses show odd–even subpulse drifting with a periodicity of around 2P, P being the rotation period of the pulsar. The centrally bright mode was seen for 10% of the observing duration in PSR B0844-35, which usually lasted for short durations of around 10 pulses, but had two longer sequences of around 100 pulses. On the contrary, the centrally bright mode was dominant in PSR B1758-29 and was seen for around 60% of the observing duration. PSR B1758-29 also showed period amplitude modulations of 60P–70P in both modes. The mode changing in these two pulsars facilitates investigation of the sparking process in the inner acceleration region, dominated by nondipolar magnetic fields. The change in the surface magnetic field configurations likely results in the emission mode change.