Strong Magnetic Field Research Articles

A ferrofluid microrobot for manipulation in multiple workspaces

Ferrofluid droplet has wide applications in bioanalysis manipulation. This study presents a ferrofluid microrobot for manipulation in different workspaces. Based on the deformation character of droplet, the ferrofluid microrobot has the capabilities of climbing the 3D (3-dimensional) surface, splitting in the channel, and transporting large particles. To manipulate in multiple workspaces with the capabilities, the size and magnetic force of ferrofluid are studied for suitable scenes. It shows that the diameter of 0.5 μl ferrofluid is around 980 μm. The manipulation force of different ferrofluid microrobots ranges from micronewton to millinewton. Subsequently, we have verified the manipulation of the ferrofluid microrobot on a 3D chip by permanent magnet. The ferrofluid microrobot can climb the stairs only when the height of the magnetic fluid is higher than twice the height of the stairs. Meanwhile, splitting of ferrofluid microrobot in the microfluidic chip has been successfully demonstrated. It indicates that the splitting influenced by the magnetic field and large magnetic force is easier to split the microrobot. Finally, the transportation of large polystyrene microparticles (150 μm) is confirmed by the ferrofluid microrobot. These capabilities show that the ferrofluid microrobot has the potential application advantage in biomedicine's micro-drug testing.

Automatic Detection and Classification of Aurora in THEMIS All‐Sky Images

AbstractWe report a novel machine‐learning algorithm for automatically detecting and classifying aurora in all–sky images (ASI) that is largely trained without requiring ground–truth labels. By including a small number of labeled images, we are able to automatically label all of the approximately 700 million images in the Time History of Events and Macroscale Interactions during Substorms (THEMIS) ASI data set from 2008 to 2022. We use a two–stage approach. In the first stage, we adapt the Simple framework for Contrastive Learning of Representations (SimCLR) algorithm to learn latent representations of THEMIS all–sky images. We then finetune a classifier network on the latent representations our model learns of the manually labeled Oslo aurora THEMIS (OATH) data set. We demonstrate that this two–stage approach achieves excellent classification results on data for which there is no current ML classification benchmark. The outcome of this work will facilitate efficient information retrieval for researchers interested in specific categories of aurora and will enable large scale statistical studies and machine learning analyses of THEMIS all–sky images that have not previously been possible. To demonstrate possible ways to utilize this database, we performed a statistical analysis of the occurrence rates of auroral labels with respect to solar wind parameters, interplanetary magnetic field vector, and geomagnetic indices. We further investigate the occurrence rates of auroral phenomena in the annotated data set and their geoeffectiveness by utilizing the co–located THEMIS ground magnetometer data set.

MHD Modeling of a Geoeffective Interplanetary Coronal Mass Ejection with the Magnetic Topology Informed by In Situ Observations

Variations of the magnetic field within a solar coronal mass ejection (CME) in the heliosphere depend on the CME’s magnetic structure as it leaves the solar corona and its interplanetary evolution. To account for this evolution, we developed a new numerical model of the inner heliosphere that simulates the propagation of a CME through a realistic solar wind background and allows various CME magnetic topologies. To this end, we incorporate the Gibson–Low CME model within our global MHD model of the inner heliosphere, GAMERA-Helio. We apply the model to study the propagation of the geoeffective CME that erupted on 2010 April 3, aiming to reproduce the temporal variations of the magnetic field vector during the CME’s passage by Earth. Parameters of the Gibson–Low CME are informed by STEREO white-light observations near the Sun. The magnetic topology for this CME—the tethered flux rope—is informed by in situ magnetic field observations near Earth. We performed two simulations testing different CME propagation directions. For an in-ecliptic direction, the simulation shows a rotation of all three magnetic field components within the CME, as seen at Earth, similar to that observed. However, the magnitudes of the components, particularly at the back of the CME, are underestimated by the model. With a southward direction, suggested by coronal imaging observations, the B x component lacks the observed change from negative to positive. In both cases, the model favors the east–west orientation of the flux rope, consistent with the orientation previously inferred from the images from STEREO/Heliospheric Imager.

Experimental investigation to analyze the electromagnetic radiation exposure from wireless communication devices

Recent advancements in wireless communication technologies have led to the existence of a higher amount of electromagnetic radiation (EMR) in the atmosphere. The intensity of these exposed radiation depends upon the frequency of operation from these communication devices. The paper presents a scientific study on assessing the intensity of electromagnetic waves emitted by different wireless communication devices with human beings based on analyzing the electric field, magnetic field and power density generated from various electronic gadgets and wireless communication devices like smartwatch, laptop, mobile phone, nano-station, headset and mobile towers using an electro-smog meter (Electromagnetic Field (EMF) Meter - PCE-EM 29). The interaction is being studied by placing different wireless communication equipment near to human body. Based on the study, it is identified that a portion of the EMR is absorbed by nearby human beings and is identified by differentiating the field characteristics with and without its presence and is tested in near or far away from the devices. From the test results, it is identified that a portion of the EMR is absorbed by the body parts of the human beings near to the wireless device. This result could act as scientific evidence providing the effects of EMR interactions like electromagnetic hypersensitivity symptoms on humans. Similarly, most of the field exposures from the radiating devices are highly influenced by all the biotic community including human beings based on its interaction. All these field exposures to radiation from various wireless communication devices are direct indications of the Specific Absorption Rate (SAR).

X-Ray Hardening Preceding the Onset of SGR 1935+2154's Radio Pulsar Phase

Magnetars are neutron stars with extremely strong magnetic fields, frequently powering high-energy activity in X-rays. Pulsed radio emission following some X-ray outbursts has been detected, albeit its physical origin is unclear. It has long been speculated that the origin of magnetars’ radio signals is different from those from canonical pulsars, although convincing evidence is still lacking. Five months after magnetar SGR 1935+2154's X-ray outburst and its associated fast radio burst 20200428, a radio pulsar phase was discovered. Here we report the discovery of X-ray spectral hardening associated with the emergence of periodic radio pulsations from SGR 1935+2154 and a detailed analysis of the properties of the radio pulses. The observations suggest that radio emission originates from the outer magnetosphere of the magnetar, and the surface heating due to the bombardment of inward-going particles from the radio emission region is responsible for the observed X-ray spectral hardening.

Numerical simulation of YSO jet collimated by toroidal magnetic fields and radiative cooling effect

Abstract The mechanism of generation and collimation of YSO jets remains an unsolved problem and is a research hotspot in contemporary astrophysics. Here, we conducted a two-dimensional (2D) cylindrical coordinates simulation experiment using radiative magnetic-hydro-dynamic FLASH code and systematically analyzed the effects of toroidal magnetic fields generated by Biermann Battery term and radiative cooling effect on jet evolution. In the simulation, strong toroidal magnetic fields are generated at the boundary of the plasma flow. A comparison of jets generated in different cases indicates that the magnetic fields play a significant role in hydrocarbon (CH) plasma jet collimation, surpassing the impact of radiative cooling effects. Additionally, it is observed that the magnetic fields can alter knots velocities. This platform provides a way to investigate the role of toroidal magnetic fields in jet evolution without external devices and provides a better understanding of the evolution of protostellar jets.

QCD phase transition with nonextensive NJL model in the strong magnetic field

In this work we make use of the Nambu–Jona-Lasinio model to investigate thermodynamic properties of magnetized three-flavor quark matter. The nonequilibrium Tsallis distribution is characterized by a dimensionless nonextensive parameter q. We find that the system always undergoes a crossover transition for all given q values and the pseudocritical temperature decreases with the increasing nonextensive parameter. We show the variation of the pressure and its anisotropy in parallel and perpendicular directions. However, the diamagnetic nature appears within a certain temperature range at zero chemical potential. Moreover, strong magnetic fields can affect the property of a nonextensive system by changing the magnetization significantly. At high temperatures, the paramagnetic nature always occurs no matter how strong the magnetic field is. Finally, we study the effects of nonextensive parameter q on the trace anomaly and the speed of sound of the system. Published by the American Physical Society 2024

Strong-field magnetohydrodynamics for neutron stars

We present a formulation of magnetohydrodynamics which can be used to describe the evolution of strong magnetic fields in neutron star interiors. Our approach is based on viewing magnetohydrodynamics as a theory with a one-form global symmetry and developing an effective field theory for the hydrodynamic modes associated with this symmetry. In the regime where the local velocity and temperature variations can be neglected, we derive the most general constitutive relation consistent with symmetry constraints for the electric field in the presence of a strong magnetic field. This constitutive relation not only reproduces the phenomena of Ohmic decay, ambipolar diffusion, and Hall drift derived in a phenomenological model by Goldreich and Reisenegger, but also reveals terms in the evolution of the magnetic field which cannot easily be seen from such microscopic models. This formulation gives predictions for diffusion behaviors of small perturbations around a constant background magnetic field, and for the two-point correlation functions among various components of the electric and magnetic fields. Published by the American Physical Society 2024

Broadband Spectral Modeling of the M87 Nucleus

We study spectra produced by weakly accreting black hole (BH) systems using the semianalytic advection-dominated accretion flow (ADAF) model and the general-relativistic magnetohydrodynamic (GRMHD) simulation. We find significant differences between these two approaches related to a wider spread of the flow parameters as well as a much steeper radial distribution of the magnetic field in the latter. We apply these spectral models to the broadband spectral energy distribution (SED) of the nucleus of the M87 galaxy. The standard (in particular, 1D) formulation of the ADAF model does not allow us to explain it; previous claims that this model reproduces the observed SED suffer from an inaccurate treatment of the Compton process. The spectra based on GRMHD simulation are in a much better agreement with the observed data. In our GRMHD model, in which we assumed the BH spin a = 0.9, the bulk of radiation observed between the millimeter and the X-ray range is produced in the disk area within 4 gravitational radii from the BH. In this solution, the synchrotron component easily reproduces the spectral data between the millimeter and the UV range, and the Compton component does not violate the X-rays constraints, for Ṁ≲0.01M⊙ yr−1 and a relatively strong magnetic field, with the plasma β ∼ 1 in the region where radiation is produced. However, the Compton component cannot explain the observed X-ray spectrum. Instead, the X-ray spectrum can be reproduced by a high-energy tail of the synchrotron spectrum if electrons have a hybrid energy distribution with a ∼5% nonthermal component.

Experimental study on the effect of wall proximity on the flow around a cylinder under an axial magnetic field

Investigations are conducted on the effect of wall proximity on the flow around a cylinder under an axial magnetic field, using the electrical potential probe technology to measure the velocity of liquid metal flow. The study focused on the impact of the inlet velocity of the fluid, the magnetic field and wall proximity on the characteristics of velocity fields, particularly on the vortex-shedding mode. Based on different magnitudes of the magnetic field and the distance from the cylinder to the duct wall, three types of vortex-shedding modes are identified, (I) shear layer oscillation state, (II) quasi-two-dimensional vortex-shedding states and (III) transition of the magnetohydrodynamic to hydrodynamic Kármán street. The transitions between these modes are analysed in detail. The experimental results show that the weak wall-proximity effect leads to the formation of the Kármán vortex street, while a reverse Kármán vortex street and secondary vortices emerge under a strong wall-proximity effect. It is noticed that the Kelvin–Helmholtz instability drives vortex shedding under regime I, leading to an increase in the Strouhal number (St) with stronger magnetic fields. Additionally, under a strong axial magnetic field, the wall-proximity effect (‘Shercliff layer effect’) promotes the instability of shear layers on both sides of the cylinder. These unique coupling effects are validated by variations in modal coefficients and energy proportions under different vortex-shedding regimes using the proper orthogonal decomposition method.

Microwave field vector detector based on the off-resonant spin rectification effect

Normal microwave (MW) electromagnetic field detectors convert microwave power into voltages, which results in loss of the vector characteristics of the microwave field. In this work, we developed a MW magnetic field (h-field) vector detector based on the off-resonant spin rectification effect. By measuring and analyzing the angle dependence of the rectification voltages under off-resonant conditions, we can extract the three components of the h-field. As an initial test of this method, we obtained the h-field distributions at 5.4 GHz generated by a coplanar waveguide with sub-wavelength resolution. Compared to methods using ferromagnetic resonance, this technique offers a faster and more convenient way to determine the spatial distribution of the h-field, which can be used for MW integrated circuit optimization and fault diagnosis.

Slope of Magnetic Field–Density Relation as an Indicator of Magnetic Dominance

The electromagnetic field is a fundamental force in nature that regulates the formation of stars in the Universe. Despite decades of efforts, a reliable assessment of the importance of the magnetic fields in star formation relations remains missing. In star formation research, our acknowledgment of the importance of magnetic fields is best summarized by the R. M. Crutcher et al. B–ρ relation, logB(ρ)/Gauss=−5,ifρ≲10−20gcm−323·logρ+logρ0,ifρ≳10−20gcm−3, whose interpretation remains controversial. The relation is either interpreted as proof of the importance of a magnetic field in gravitational collapse or as the result of self-similar collapse where the role of the magnetic field is secondary to gravity. Using simulations, we find a fundamental relation, MA –k B−ρ (the slope of the B–ρ relation): MAMA,c=kB−ρK≈MA7.5≈kB−ρ1.7±0.15. This fundamental B–ρ slope relation enables one to measure the Alfvénic Mach number, a direct indicator of the importance of the magnetic field, using the distribution of data in the B–ρ plane. It allows us to apply the following empirical B–ρ relation: BBc=expγK−1ρρcγK≈B10−6.3G≈exp9ρ10−16.1gcm−30.11, which offers an excellent fit to the Crutcher et al. data, where we assume an MA−ρ relation ( MAMA,c=ρρcγ≈MA/7.5≈ρ/10−16.1gcm−30.19 ). The foundational MA-kB−ρ relation provides an independent way to measure the importance of the magnetic field against the kinematic motion using multiple magnetic-field measurements. Our approach offers a new interpretation of the classical B–ρ relation, where a gradual decrease in the importance of B at higher densities is implied.

Spectral Studies of Super‐Eddington Accreting Neutron Stars in the Magellanic Clouds

ABSTRACTMajor outbursts of BeXRBs offer a unique laboratory for studying accretion onto magnetized neutron stars (NSs) over a large dynamic range. The accreting material is entrained from the accretion disk by the strong magnetic field, and then channeled onto the NS, forming a so‐called accretion column (AC). Physical simulation of the AC requires consideration of various physical processes occurring in strongly magnetized plasma, including complex multi‐dimensional radiative transfer and the presence of a radiation‐dominated shock. Analytical models based on the Becker and Wolff (2007) model have proven successful at reproducing the observed AC spectra in super‐critical sources in which radiation pressure plays the dominant role in controlling the dynamics of the accreting material. In this study, we will apply the model to obtain spectra observed during super‐Eddington outbursts of BeXRBs in the Magellanic Clouds.

Macau Scientific Satellite‐1 Initial Magnetic Field Model

AbstractEight months of vector magnetic field measurements from the Macau Scientific Satellite‐1 (MSS‐1), supplemented by higher latitude field intensity measurements from the Swarm satellites, are used to derive an MSS‐1 Initial Field Model (MIFM). Robust root‐mean‐square misfits between MIFM and the three components of the MSS‐1 vector field data are found to be below 3.3 nT. MIFM agrees well with the CHAOS‐7 field model and we find even better agreement with an identically parameterized model derived only from Swarm data. MSS‐1 and Swarm vector data can moreover be fit simultaneously with only a small increase in misfit (by less than 0.2 nT). We show that both lithospheric anomalies and core surface field changes can be studied using MSS‐1 data. With its fast coverage of local times MSS‐1 is a valuable addition to the global geomagnetic observing system.

Highly sensitive fiber vector magnetic field sensor based on an open-cavity Mach-Zehnder interferometer filled with magnetic fluid

In this paper, we proposed and demonstrated a highly sensitive fiber vector magnetic field sensor utilizing an open-cavity Mach-Zehnder interferometer (MZI) filled with magnetic fluid. The MZI sensor was fabricated using large-offset splicing technique to form an open cavity, facilitating the easy introduction of magnetic fluid samples into the open cavity. The MZI sensor was then encapsulated in a glass capillary containing diluted magnetic fluid. As the applied magnetic field varies, the refractive index of the magnetic fluid undergoes a corresponding change, subsequently inducing a shift in the transmission spectrum of the MZI. By monitoring the wavelength shift of the transmission spectrum, we can accurately detect the intensity of the magnetic field. The proposed sensor can achieve vector magnetic field measurement because of the axially asymmetric open-cavity MZI. The maximum sensitivity to magnetic field direction is 0.260 nm/°. Notably, the proposed sensor achieves an ultrahigh sensitivity, reaching an value of −17.306 nm/mT within the range of 4 mT to 7 mT. In addition, a temperature sensitivity of 2.236 nm/℃ is obtained within the temperature range of 30 ℃ to 65 ℃. Given its advantages, including high sensitivity, compact size and low cost, our MZI sensor holds immense potential for diverse applications in magnetic field measurement.

Performance of ITER pressure gauges during deuterium operation in the large helical device

Abstract During deuterium campaigns on the heliotron large helical device (LHD), ITER pressure gauges with different cathode materials were used to measure the neutral pressure in the sub-divertor region. Throughout these campaigns, it was observed that the performance of the LaB6 cathodes was unsatisfactory, credited to the generation of neutrons impacting the gauges. Conversely, measurements taken with pressure gauges with a ZrC cathode performed well throughout the deuterium pulses. The ITER pressure gauge with the ZrC cathode could be operated with a very high electron current of 800 µA, thus improving the lower detection limit of the neutral pressure in LHD. With this design it was also possible to avoid jumps in the ion current within strong magnetic fields, improving the accuracy of the measurement from 15% uncertainty to 5%. These features allowed very precise neutral pressure measurements to be made in a fusion device with magnetic confinement. The total running time in the magnetic field was around 60 hours, less than the cathode life time of 350 hours.

Research and application of chromatic effect in laser-driven proton therapy

Based on the rapid development of ultra high-power laser technology and due to the urgent need for miniaturized particle radiotherapy accelerator construction, compact laser accelerators have been studied as a research focus. The collection of the beam with large divergence angle and the selection of beam energy spread from initial generated beam are core issues in the design of laser accelerator. Chromatic effect is an effective method of energy selection while collecting beam. However, it is found that the nonlinear effect introduced by the actual edge field of a strong magnetic field and the special beam distribution produced by laser acceleration directly affect the energy selection. Based on the design of CLAPA-II, we analyze chromatic effect of energy selection by combining the 3-D strong magnetic field of particle collecting solenoid and the initial particle library of laser acceleration generated by PIC. We further propose a more compact laser-driven proton therapy design using the chromatic effect and energy reducer. And we research a broad-spectrum treatment planning system corresponding to it. It can effectively reduce proportion of low energy particles and complete energy selection after considering nonlinear effect of high 3-D magnetic field and special initial distribution. This can be applied in the design of gantry, which can be lighter than the traditional gantry. And for head, neck, and lung tumor models, dose delivery can be completed in 10 min and 20 min.

Magnetotransport in a graphite cylinder under quantizing fields

We analyze the transport properties of curved, three-dimensional graphite samples in strong magnetic fields. Focusing on a millimeter-scale graphite cylinder as a prototypical curved object, we perform longitudinal and Hall voltage measurements while applying quantizing magnetic fields. These measurements are investigated as a function of field strength and angles. Most importantly, we find that angle-dependent Shubnikov-de Hass oscillations are superimposed with angle-independent features. Reproducing the experimental observations, we introduce a network model that accounts for the cylindrical geometry effect by conceptualizing the cylinder as composed of strips of planar graphite in an effectively inhomogeneous magnetic field. Our work highlights how the interplay between geometric curvature and quantizing magnetic fields can be leveraged to engineer tunable spatial current densities within solid-state systems, and paves the way for understanding transport properties of curved and bent three-dimensional samples more generally. Published by the American Physical Society 2024

Kilogauss magnetic field and jet dynamics in the quasar NRAO 530

The advancement of the Event Horizon Telescope has enabled the study of relativistic jets in active galactic nuclei down to sub-parsec linear scales even at high redshift. Quasi-simultaneous multifrequency observations provide insights into the physical conditions in compact regions and allow accretion theories to be tested. Initially, we aimed to measure the magnetic field strength close to the central supermassive black hole in by studying the frequency-dependent opacity of the jet matter, Faraday rotation, and the spectral index in the millimeter-radio bands. was observed quasi-simultaneously at 15, 22, 43, 86, and 227\,GHz at four different very long baseline interferometer (VLBI) networks. By means of imaging and model-fitting, we aligned the images, taken at different frequencies. We explored opacity along the jet and the distribution of the linearly polarized emission in it. Our findings reveal that the jet of at 86 and 227\,GHz is transparent down to its origin, with 70\,mJy emission detected at 227\,GHz potentially originating from the accretion disk. The magnetic field strength near the black hole, estimated at $5r_ g $, is $3 (depending on the central black hole mass). These values represent some of the highest magnetic field strengths reported for active galaxies. We also report the first ever VLBI measurement of the Faraday rotation at 43--227\,GHz, which reveals rotation measure values as high as -48000 rad/m2, consistent with higher particle density and stronger magnetic fields at the jet's outset. The complex shape of the jet in is in line with the expected behavior of a precessing jet, with a period estimated to be around $6 years.

Anisotropic charge transport in strongly magnetized relativistic matter

We investigate electrical charge transport in hot magnetized plasma using first-principles quantum field theoretical methods. By employing Kubo’s linear response theory, we express the electrical conductivity tensor in terms of the fermion damping rate in the Landau-level representation. Utilizing leading-order results for the damping rates from a recent study within a gauge theory, we derive the transverse and longitudinal conductivities for a strongly magnetized plasma. The analytical expressions reveal drastically different mechanisms that explain the high anisotropy of charge transport in a magnetized plasma. Specifically, the transverse conductivity is suppressed, while the longitudinal conductivity is enhanced by a strong magnetic field. As in the case of zero magnetic field, longitudinal conduction is determined by the probability of charge carriers to remain in their quantum states without damping. In contrast, transverse conduction critically relies on quantum transitions between Landau levels, effectively lifting charge trapping in localized Landau orbits. We examine the temperature and magnetic field dependence of the transverse and longitudinal electrical conductivities over a wide range of parameters and investigate the effects of a nonzero chemical potential. Additionally, we extend our analysis to strongly coupled quark-gluon plasma and study the impact of the coupling constant on the anisotropy of electrical charge transport.