Homogeneous Magnetic Field Research Articles

Mechanical Equilibrium of a Nonmagnetic Body Immersed in a Cylindrical Container with a Magnetic Fluid Magnetized by an External Homogeneous Magnetic Field

Purpose. Analytical and numerical description of the magnetohydrodynamic forces acting on a small nonmagnetic spherical body in a cylindrical container with magnetic fluid (magnetofluid dispenser and separator approximation) that determine the hydrostatic mechanical equilibrium in the system.Methods. The numerical study solves the magnetostatic problem by the finite element method in the FEMM program package using the Lua script language. The system of Maxwell’s equations is solved by the standard method in the vector potential formulation. The analytical solution of the magnetostatic problem is obtained by the mirror image method using a simplifying model representation of the linear law of magnetization of a magnetic fluid. The ponderomotive force acting on a body immersed in a magnetic fluid is calculated using the Rosensweig formula and the energy approach.Results. A refined expression for the magnetic ponderomotive force acting on a nonmagnetic sphere immersed in a cylindrical container with magnetized magnetic fluid is obtained. Direct numerical simulation of the laboratory experiment is performed, which allows us to compare the accuracy of the numerical and analytical solutions with the experimental data. Despite violating the limits of applicability of the analytical theory, the new expression correctly describes the nonmonotone coordinate dependence of the force, and the error in determining the coordinate extremums does not exceed 6 % and 26 % in absolute value. The physical justification for the condition of mechanical equilibrium in the model system under study is given.Conclusion. The competition of two oppositely directed magnetic forces leads to the fact that a nonmagnetic sphere in a cylindrical container with magnetized magnetic fluid has one unstable mechanical equilibrium position in the center of the container, so that the body is pressed against the wall, or (additionally) two stable equilibrium positions that allow the body to levitate near the container wall without touching it.

Thermal equilibrium of collisional non-neutral plasma in a magnetic dipole trap

This paper discusses thermal equilibrium states of single-species plasmas, such as pure electron plasmas and pure positron plasmas, that are confined in a dipole trap. Thermal equilibrium states for such plasmas are routinely realized in the homogeneous magnetic field of Penning–Malmberg traps. We generalize the theory of these states to include inhomogeneous magnetic dipole fields. The approach to thermal equilibrium takes place in two stages with well separated time scales. On the collision time scale, thermal equilibrium is established along each magnetic field line. On the much longer transport time scale, heat conduction and viscosity bring the plasmas on different flux contours into thermal equilibrium, we call this a state of global thermal equilibrium. We present numerical results for local and global thermal equilibria. These results agree with the analytic predictions for charge collections that are large compared with the Debye length. There is, in principle, no limit to the confinement time of a single-species plasma in a global thermal equilibrium state. Experiments with hot electron–ion plasmas performed in the LDX and RT1 devices give us confidence that, in contrast to a Penning–Malmberg trap, a magnetic dipole field can also confine cold quasi-neutral electron–positron pair plasmas on the time scale of the phenomena of interest. Such pair plasmas are assumed to form in the magnetosphere of neutron stars but have so far not been realized in a laboratory. The creation of an electron–positron pair plasma is the main goal of the APEX collaboration.

On equations for ion cyclotron modes in ‘warm’ bounded plasmas

An equation describing eigenmodes in the ion cyclotron frequency range in ‘warm’ bounded plasmas, i.e. eigenmodes which are absent in the two-fluid model but exist in kinetic theory due to finite Larmor radius of the ions, is derived for the first time. It is valid for electrostatic modes but the developed approach is generic. Calculations are carried out for two cases: first, for a homogeneous magnetic field; second, taking into account the effects of toroidicity in tokamaks. It is found that, in general, equations for eigenmodes in warm plasmas do not reduce to second-order differential equations (in contrast to those which are usually used to describe the radial structure of eigenmodes in fusion devices). The study of modes in warm plasmas is of interest, in particular, in connection with the recent observations of superthermal ion cyclotron emission in the NSTX-U spherical torus and DIII-D tokamak, which can be hardly explained by conventional theories employing fast magnetoacoustic modes.

Thermodynamic properties of substrate-induced graphene superlattice in homogeneous magnetic field

In this article we study the thermodynamic properties of a substrate-induced graphene superlattice in the presence of uniform magnetic field B. We derive an expression for the partition function of the system with uniform magnetic field B using the zeta function approach and find all related thermodynamic functions such as Helmholtz free energy, total energy, specific heat capacity and entropy for three cases related to the sublattice potential. We also show that the Dulong-Petit law is verified for all cases in the high-temperature limit. These results may shed light on the study of graphene superlattices in the developement of thermo-electric devices.

Design of 3D printed stage for in situ magnetic field application in magnetic force microscopy

We propose a design of 3D printed magnetic stage that allows application of static magnetic fields during magnetic force microscopy measurements. The stage utilizes permanent magnets providing spatial homogeneous magnetic fields. The design, assembly, and installation are described. Numerical calculations of the field distribution are used to optimize the size of magnets and the spatial homogeneity of the field. The stage offers a compact and scalable design, which can be adapted as an accessory onto several commercially available magnetic force microscopy platforms. The stage’s utility for in situ magnetic field application during magnetic force microscopy measurements is demonstrated on a sample of thin ferromagnetic strips.

Efficient prediction of MRI gradient-induced heating for guiding safety testing of conductive implants.

To propose an efficient numerical method to predict the temperature increase of an implantable medical device induced by any linearly polarized homogeneous magnetic field, according to the ISO 10974 methodology for testing of gradient-induced device heating. The concepts of device-specific power and temperature tensors are introduced to mathematically describe the electromagnetic and thermal anisotropic behavior of the device, from which the device heating for an arbitrary exposure direction can be predicted. The proposed method is compared to a brute-force approach based on simulations, and validated by applying it to four reference orthopedic implants with a commercial simulation software. The proposed method requires about 5 of the time required by the brute-force approach, and 30 of the memory occupancy. The temperature increase predicted by the proposed method over a range of incident magnetic field exposures deviated from brute-force direct simulations by less than 0.3 . The proposed method allows efficient prediction of the heating of an implantable medical device induced by any linearly polarized homogeneous magnetic field using a small fraction of the simulations required by the brute-force approach. The results can be used to predict the worst-case orientation of the gradient field, for subsequent experimental characterization according to the ISO 10974 standard.

Magnetic Relaxation Switching Assay Using IFNα-2b-Conjugated Superparamagnetic Nanoparticles for Anti-Interferon Antibody Detection

Type I interferons, particularly IFNα-2b, play essential roles in eliciting adaptive and innate immune responses, being implicated in the pathogenesis of various diseases, including cancer, and autoimmune and infectious diseases. Therefore, the development of a highly sensitive platform for analysis of either IFNα-2b or anti-IFNα-2b antibodies is of high importance to improve the diagnosis of various pathologies associated with the IFNα-2b disbalance. For evaluation of the anti-IFNα-2b antibody level, we have synthesized superparamagnetic iron oxide nanoparticles (SPIONs) coupled with the recombinant human IFNα-2b protein (SPIONs@IFNα-2b). Employing a magnetic relaxation switching assay (MRSw)-based nanosensor, we detected picomolar concentrations (0.36 pg/mL) of anti-INFα-2b antibodies. The high sensitivity of the real-time antibodies’ detection was ensured by the specificity of immune responses and the maintenance of resonance conditions for water spins by choosing a high-frequency filling of short radio-frequency pulses of the generator. The formation of a complex of the SPIONs@IFNα-2b nanoparticles with the anti-INFα-2b antibodies led to a cascade process of the formation of nanoparticle clusters, which was further enhanced by exposure to a strong (7.1 T) homogenous magnetic field. Obtained magnetic conjugates exhibited high negative MR contrast-enhancing properties (as shown by NMR studies) that were also preserved when particles were administered in vivo. Thus, we observed a 1.2-fold decrease of the T2 relaxation time in the liver following administration of magnetic conjugates as compared to the control. In conclusion, the developed MRSw assay based on SPIONs@IFNα-2b nanoparticles represents an alternative immunological probe for the estimation of anti-IFNα-2b antibodies that could be further employed in clinical studies.

Controllability and Robustness of Quantum Correlation in XXZ Heisenberg Model With Dzyaloshinskii –Moriya Interaction and Homogeneous Magnetic Field

Controllability and Robustness of Quantum Correlation in XXZ Heisenberg Model With Dzyaloshinskii –Moriya Interaction and Homogeneous Magnetic Field

Exploring quantum correlations of two-qubit Heisenberg chain model influenced by magnetic dipole–dipole, magnetic field, and a symmetric cross interaction

The concepts of concurrence, 3-steerability, and Clauser–Horne–Shimony–Holt (CHSH) inequality are employed to investigate the environmental impacts on the quantum correlations of the two-spin-1/2 Heisenberg XYZ chain model. In particular, the effects of a homogeneous magnetic field, symmetric cross interaction, and dipole–dipole interaction on the entanglement, degree of steerability, and non-locality are discussed. Results show that the entanglement and steering phenomena are bounded by the non-locality for both positive and negative values of dipole–dipole coupling. It has also been observed that higher symmetric cross-interaction strengthens the quantum correlations, whereas the homogeneous magnetic field weakens the quantumness of the system. The findings indicate that a magnetic field normal to the magnetic dipole yields better quantum correlations than when they are parallel.

A Magnetically-Actuated Coiling Soft Robot With Variable Stiffness

Soft and flexible magnetic robots have gained significant attention in the past decade. These robots are fabricated using magnetically-active elastomers, are capable of large deformations, and are actuated remotely thus allowing for small robot size. This combination of properties is appealing to the minimally invasive surgical community, potentially allowing navigation to regions of the anatomy previously deemed inaccessible. Due to the low forces involved, one particular challenge is functionalizing such magnetic devices. To address this limitation we introduce a proof-of-concept variable stiffness robot controlled by remote magnetic actuation, capable of grasping objects of varying sizes. We demonstrate a controlled and reversible high deformation coiling action induced via a transient homogeneous magnetic field and a synchronized sliding nitinol backbone. Our soft magnetic coiling grasper is visually tracked and controlled during three experimental demonstrations. We exhibit a maximum coiling deformation angle of 400 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> .

Fluid-chemical modeling of the near-cathode sheath formation process in a high current broken in DC air circuit breaker

When the contacts of a medium-voltage DC air circuit breaker (DCCB) are separated, the energy distribution of the arc is determined by the formation process of the near-electrode sheath. Therefore, the voltage drop through the near-electrode sheath is an important means to build up the arc voltage, which directly determines the current-limiting performance of the DCCB. A numerical model to describe the near-electrode sheath formation process can provide insight into the physical mechanism of the arc formation, and thus provide a method for arc energy regulation. In this work, we establish a two-dimensional axisymmetric time-varying model of a medium-voltage DCCB arc when interrupted by high current based on a fluid-chemical model involving 16 kinds of species and 46 collision reactions. The transient distributions of electron number density, positive and negative ion number density, net space charge density, axial electric field, axial potential between electrodes, and near-cathode sheath are obtained from the numerical model. The computational results show that the electron density in the arc column increases, then decreases, and then stabilizes during the near-cathode sheath formation process, and the arc column’s diameter gradually becomes wider. The 11.14 V–12.33 V drops along the 17 μm space charge layer away from the cathode (65.5 kV/m–72.5 kV/m) when the current varies from 20 kA–80 kA. The homogeneous external magnetic field has little effect on the distribution of particles in the near-cathode sheath core, but the electron number density at the near-cathode sheath periphery can increase as the magnetic field increases and the homogeneous external magnetic field will lead to arc diffusion. The validity of the numerical model can be proven by comparison with the experiment.

TSVDシミング計算とMRI磁石を用いた超良好一様（±0.1 ppm）磁場実現のシミング試験

Two muon experiments, which require extremely homogeneous magnetic fields, are under preparations in J-PARC. One of the experiments is the MuSEUM（Muonium Spectroscopy Experiment Using Microwave）experiment that requires＋/-0.1 ppm homogeneity in a spheroidal volume of 20 cm in diameter and 30 cm in length. To confirm that such an extremely homogeneous magnetic field can be obtained in a whole-body MRI magnet, intensive shimming tests were conducted using a shimming calculation based on TSVD of linear algebra with a passive shimming structure. In the first shimming test, we found that small shim-piece unit is necessary, and in the second test an extremely homogeneous magnetic field was realized with Ni shim plates, the magnetic moment of which is 1/6 of the ordinal Fe shim plates of MRI magnetic field. This result confirms that an extremely homogeneous magnetic field can be realized for the experiment.

Nontrivial effect of dephasing: Enhancement of rectification of spin current in graded XX chains.

In order to reveal mechanisms to control and manipulate spin currents, we perform a detailed investigation of the dephasing effects in the open XX model with a Lindblad dynamics involving global dissipators and thermal baths. Specifically, we consider dephasing noise modeled by current-preserving Lindblad dissipators acting on graded versions of these spin systems, that is, systems in which the magnetic field and/or the spin interaction are growing (decreasing) along the chain. In our analysis, we study the nonequilibrium steady state via the covariance matrix using the Jordan-Wigner approach to compute the spin currents. We find that the interplay between dephasing and graded systems gives rise to a nontrivial behavior: When we have homogeneous magnetic field and graded interactions we have rectification enhancement mechanisms, and when we have fully graded systems we can control the spin current in order to keep the direction of the particle and/or spin flow even with inverted baths. We describe our result in detailed numerical analysis and we see that rectification in this simple model indicates that the phenomenon may generally occur in quantum spin systems.

Transient dynamics of the field induced force in the isotropic magnetorheological elastomer

The transition dynamics in silicon rubber based isotropic magnetorheological (MR) elastomers in terms of the normal force induced by an external homogeneous magnetic field is experimentally addressed. The primary goal was to evaluate dynamic performances of the MR elastic isotropic composite using a transparently presented measuring system with known characteristics in contrast to few previous studies on the topic. It was found that an increase in the magnetic field leads to an increase in the induced force and a decrease in the response time of the MR elastomer. At the same time, both the use of coarse particles as magnetic filler and a significant reduction in the stiffness of the polymer matrix reduce the response time of the MR elastomer under study. The analysis carried out takes into account the dynamics of the electromagnetic coil and the eddy currents induced in the magnet circuit. The shortest response times obtained for various MR elastomer samples are in the range of 27–72 ms for the maximal used magnetic field with an induction of 230 mT. These times correspond to the fastest previously reported ones for MR elastomers and MR elastomer based systems. In addition, the obtained results indicate the presence of different mechanisms responsible for the measured magnetodeformational effect observed in MR elastomers.

Increasing the accuracy of measuring the physicochemical parameters of wastewater samples when implementing a new informative method

Increasing the accuracy of measuring the physicochemical parameters of wastewater samples when implementing a new informative method

Synthetic spin dynamics with Bessel-Gaussian optical skyrmions.

Skyrmions are topologically stable fields that cannot be smoothly deformed into any other field configuration that differs topologically, that is, one that possesses a different integer topological invariant called the Skyrme number. They have been studied as 3-dimensional and 2-dimensional skyrmions in both magnetic and, more recently, optical systems. Here, we introduce an optical analogy to magnetic skyrmions and demonstrate their dynamics within a magnetic field. Our optical skyrmions and synthetic magnetic field are both engineered using superpositions of Bessel-Gaussian beams, with time dynamics observed over the propagation distance. We show that the skyrmionic form changes during propagation, exhibiting controllable periodic precession over a well defined range, analogous to time varying spin precession in homogeneous magnetic fields. This local precession manifests as the global beating between skyrmion types, while still maintaining the invariance of the Skyrme number, which we monitor through a full Stokes analysis of the optical field. Finally, we outline, through numerical simulation, how this approach could be extended to create time varying magnetic fields, offering free-space optical control as a powerful analogue to solid state systems.

Measurements of Stray Magnetic Fields of Fe-Rich Amorphous Microwires Using a Scanning GMI Magnetometer

A scanning magnetometer based on a magnetoimpedance sensor with a 1 mm spatial resolution and 10 nT sensitivity was used to study stray magnetic fields of Fe74B13Si11C2 amorphous ferromagnetic microwires. Spatial magnetic images and vertical component profiles of stray magnetic fields of the studied microwires were obtained in a longitudinal homogeneous magnetic field of Helmholtz coils with a strength in the range of ±600 A/m. A magnetic calculation method is suggested that allows for using the measured magnetic fields to determine the magnitude and pattern of magnetization for the microwire. Characteristic values of the microwires’ average magnetization and width of closure domains for various values of bias fields were found.

Comparison of PCB Based Actuator Coils for Untethered Actuation

Recently magnetic actuation has become a versatile tool for manipulation on both the micro and macro scale. Due to the problems arising from scale, conventional electromagnet production methods are insufficient to produce the desired electromagnets to be used for this purpose. To solve the problems arising from this situation, researchers have been forced to work in alternative electromagnet production and application areas and paved the way for PCB-based electromagnetic actuators. For this reason, this article will explain the design principles of PCB planar coils for electromagnetic actuator applications and will provide the basis for later studies to create a coil matrix using this coil design and an actuator that can move ferromagnetic particles or magnets in the plane with this 2D coil matrix. The presented project design steps can be listed as follows; First of all, to be able to design a coil that consists of copper paths on the PCB and can meet expectations (homogeneous magnetic field, high magnetic force/current ratio). PCB coils consisting of square, circular and hexagonal coils are manufactured and various measurements are made. The measured results are consistent with the simulated results proving the accuracy and applicability of PCB coil actuators, and they are highly suitable for a new actuator version. In the tests carried out, coils energized with 1A can provide a maximum field strength of 1400 (A/m) and an average of 900 (A/m) and due to the lack of magnetic core, the created magnetic field has the shape of a bell. In order to overcome this situation, it is foreseen that making studies to increase the working current and, as a more important development, switching from the planar single-layer structure to the structure of two or more layers can increase the magnetic field produced by this type of coils, but this layer increase should take into account the cost and PCB production and application capabilities. should be made available.

INVESTIGATION OF THE PROPERTIES OF MICROPARTICLES IN THE GLOW DISCHARGE STRATUM IN A CROSSED ELECTRIC AND MAGNETIC FIELD

In this work, the behavior of charged micron-sized particles in the DC glow discharge stratum at low pressure in a crossed magnetic and electric field was experimentally studied. The experiment was conducted in a vertically oriented gas-discharge glass tube. A homogeneous magnetic field was created using a two-section Helmholtz coil. The results showed that the micron-sized dust particles move in the opposite direction to the ExB drift as the magnetic field induction increases. Once the induction reaches a specific threshold (B&gt;10 mT), the dust particles start rotating and forming counter-rotating vortex pairs on the horizontal plane. Moreover, it was observed that the shape of the dust structures changes from a disk to an ellipsoid. The PIV (particle image velocimetry) method was employed to analyze the dust vortices' dynamic behavior, and the generation of the co-vortex rotation was explained through the dust particles' charge gradient, which was orthogonal to the ion drag force.

Development and characteristics study of compact Penning ion source

A compact-size Penning ion source with a small discharge volume (1.24 cm3) is developed. It consists of two concentric cylinders of different heights that act as cathodes and one hollow cylindrical anode. A homogeneous magnetic field is achieved within the discharge volume with geometrical optimization of the ion source. As a result, dense plasma is generated at low discharge power. The dynamics of the pulse mode discharge at low pulse width and frequency of anode voltage are studied. A high discharge (hundreds of amperes) current pulse with low delay time and fast rise time is recorded. The ion source is equally efficient to operate in continuous as well as pulse modes of ionization for various gases. It is operated in a wide range of low pressure at low anode voltage. An extraction system is designed to extract ions efficiently in the axial direction at a variable extraction voltage. The beam current of 200 µA in continuous mode and 6 A fast pulse in the pulsed mode of discharge have been measured. Variable beam current can be extracted with variable extraction voltage for any potential application.