Magnetic Geometry Research Articles

Measuring magnetic force field distributions in microfluidic devices: Experimental and numerical approaches.

Precisely and accurately determining the magnetic force and its spatial distribution in microfluidic devices is challenging. Typically, magnetic microfluidic devices are designed in a way to both maximize the force within the separation region and to minimize the necessity for knowing such details-such as designing magnetic geometries that create regions of nearly constant magnetic force or that dictate the behavior of the magnetic force to be highly predictable in a specified region. In this work, we present a method to determine the spatial distribution of the magnetic force field in a magnetic microfluidic device by particle tracking magnetophoresis. Polystyrene microparticles were suspended in a paramagnetic fluid, gadolinium, and this suspension was exposed to various magnetic field geometries. Polystyrene particle motion was tracked using a microscope and images processed using Fiji (ImageJ). From a sample with a large spatial distribution of particle tracks, the magnetic force field distribution was calculated. The force field distribution was fitted to nonlinear spatial distribution models. These experimental models are compared to and supported by 3D simulations of the magnetic force field in COMSOL.

Harnessing magnetic fields to accelerate oxygen evolution reaction

The challenge of overcoming the bottleneck in water electrolysis can potentially be addressed by utilizing permanent magnets without extra energy consumption, but the underlying mechanism of magnetic field effects is still puzzling despite increasing efforts in last few years. In this work, by dip-coating a superhydrophilic γ-Fe2O3 layer onto different electrode substrates, their surface wettability and magnetism are modified, so the ever-tangled effects of magnetic field are separated and identified. It is determined that the primary contribution of magnetic fields at the high current density was due to additional Lorentz force and Kelvin force exerted on oxygen gas bubble, with the former being dependent on the external magnetic field's geometry and the latter closely tied to the electrodes’ magnetism. Strategies to maximize effects of magnetic field as well as the overall efficiency of water electrolysis is proposed.

Metal Dipicolylamines and their Biomedical Applications: A Mini Review

Research in synthetic inorganic chemistry demonstrates that metal complexes are widely utilized as therapeutic as well as diagnostic agents. Due to the coordinative saturation, substitutional inertness, and unique redox characteristics, metal polypyridyl complexes have ignited attention and have been exploited in a number of biological and biomedical fields. The polypyridyl ligand, dipicolylamine (DPA) is a symmetrical secondary amine with two pyridyl rings. Delocalization of excited electrons occurs throughout the ligand system due to its conjugated character and the metal-to-ligand charge transfer transitions, resulting in a strong fluorescence signal. The high lipophilic nature of this ligand has proven to improve metal-DPA complex absorption by cell membranes. The N–H amine group in DPA and its analogues have the additional function of allowing hydrogen bonds to form, and deprotonation of this amine has allowed the creation of mononuclear and polynuclear species, with deprotonation of the bridging amine nitrogen also playing a significant role in the coordination sequence. DPA-appended metal complexes have garnered attention in the quest for linkages between magnetic, spectroscopic, structural, and coordination geometries. A number of mononuclear metal-DPA complex crystal structures with four, five, or six coordinated metal centers have been synthesized and explored for their biological properties. This study reviews DPA-derivatized ligand-linked metal complexes as promising cancer, microbial, and fungal inflammatory therapeutics, as well as potential diagnostic agents for fluorescence imaging and radiopharmaceuticals.
 Keywords: Dipicolylamine, metal complexes, coordination geometries, fluorescent agents

A Hale-like Cycle in the Solar Twin 18 Scorpii

Abstract Characterizing the cyclic magnetic activity of stars that are close approximations of our Sun offers our best hope for understanding our Sun’s current and past magnetism, the space weather around solar-type stars, and more generally, the dynamos of other cool stars. The nearest current approximation to the Sun is the solar twin 18 Scorpii, a naked-eye Sun-like star of spectral type G2 Va. However, while 18 Scorpii’s physical parameters closely match those of the Sun, its activity cycle is about 7 yr, and shorter than the solar cycle. We report the measurement of a periodicity of 15 yr that corresponds to a longer activity cycle for 18 Scorpii based on observations extending to the last three decades. The global magnetic geometry of 18 Scorpii changes with this 15 yr cycle and appears to be equivalent to the solar 22 yr magnetic polarity cycle. These results suggest that 18 Scorpii is also a magnetic proxy for a younger Sun, adding an important new datum for testing dynamo theory and magnetic evolution of low-mass stars. The results perturb our understanding of the relationship between cycle and rotation, constrain the Sun’s magnetism and the Sun–Earth connection over the past billion years, and suggest that solar Schwabe and Hale cycle periods have increased over that time span.

Stabilization of the Alfvén-ion cyclotron instability through short plasmas: Fully kinetic simulations in a high-beta regime

The Alfvén-ion cyclotron (AIC) mode is an instability that can be driven in magnetized plasmas with anisotropic pressure. Its chief deleterious effect is the driving of enhanced pitch-angle scattering of ions. Although the AIC mode has been observed in several mirror devices, it has not yet been observed in FRC devices developed by TAE Technologies [H. Gota et al., Nucl. Fusion 61, 106039 (2021)]. Previous theoretical work [T. Tajima et al., Phys. Rev. Lett. 39, 201 (1977)] has suggested that sufficient axial inhomogeneity, quantified by a critical axial plasma length, can stabilize this mode. This stabilization mechanism is examined in fully kinetic particle-in-cell simulations with one spatial dimension modeling a simplified magnetic mirror geometry for a plasma with β∼1. A fast-ion population provides the driving anisotropy for the AIC mode, and the resulting effect on the fast-ion pitch angle distribution is examined. The severity of mode activity is recorded for a scan of plasma lengths for multiple fast-ion injection angles. This scan yields critical lengths that show good qualitative agreement with those from the past theoretical work.

A flexible gyro-fluid system of equations

Gyro-fluid equations are velocity space moments of the gyrokinetic equations. Special gyro-Landau-fluid closures have been developed that include the damping due to kinetic resonances by fitting to the collisionless local plasma response functions. This damping allows for accurate linear eigenmodes to be computed with a relatively low number of velocity space moments compared to the number of velocity quadrature points in gyrokinetic codes. However, none of the published gyro-Landau-fluid closure schemes considers the Onsager symmetries of the resulting quasi-linear fluxes as a constraint. Onsager symmetry guarantees that the matrix of diffusivities is positive definite, an important property for the numerical stability of a transport solver. A two parameter real closure for improving the accuracy of low resolution gyro-fluid equations, which preserves the Onsager symmetry and allows higher velocity space moments, is presented in this paper. The new linear gyro-fluid system (GFS) is used to extend the TGLF quasi-linear transport model so that it can compute the energy and momentum fluxes due to parallel magnetic fluctuations, completing the transport matrix. The GFS equations do not use a bounce average approximation. The GFS equations are fully electromagnetic with general flux surface magnetic geometry, pitch angle scattering for electron collisions, and subsonic equilibrium toroidal rotation. Using GFS eigenmodes in the quasi-linear TGLF model will be shown to yield a more accurate match to fluxes computed by CGYRO turbulence simulations. Prospects for future applications of a quasi-linear theory to new plasma transport regimes and magnetic confinement devices in addition to tokamaks are opened by the flexibility of the GFS eigensolver.

Effect of Magnetic Shunts on Shell-Type Transformers Characteristics

A three-dimensional analysis of the leakage magnetic field in a transformer with beveled edges in a magnetic shunt is described. This paper contains a mathematical description of the finite element method used in performing numerical calculations. Formulas allowing to determine the differential and integral parameters of the magnetic field were presented. Magnetic flux density distributions and the points with high values were determined in the shell-type core and movable shunt sub-areas. For different positions of the magnetic shunt, the short-circuit transformer reactance was calculated as the integral parameter of the above-mentioned magnetic field analysis. Their amounts for the extreme positions of the shunt were given, as well. The movable magnetic shunt geometry impact on the short-circuit current value is given. In order to validate the calculation results, the research included some point measurements of magnetic flux density vectors and the winding reactances as well, and good compliance with the simulation data has been obtained. Thus, this analysis can also be applied to other objects with movable shunts in their magnetic systems.

Effects of magnet shapes on total harmonic distortion and cogging torque in a permanent magnet synchronous generator for wind turbines

Abstract This paper explores and theoretically reports the effects of different magnet structures on the cogging torque and the total harmonic distortion of the output waveforms from a permanent magnet generator. The generator is a radial flux machine and four different structures are considered for the magnet arrangement in the rotor component and modelled in the Ansys/Maxwell electromagnetic simulation program. This three-phase machine exhibits different behaviours towards various magnet structures, i.e. rectangular, inclined slotted rectangular, skewed double rectangular and inclined slotted skewed double rectangular, respectively. It has been proven by finite element analysis and Fourier analysis that both the cogging and total harmonic distortion values vary significantly for all models. The cogging torque values change in the range of 89.95 to 436.75 mNm and the lowest cogging torque is measured for the inclined slotted skewed double rectangular magnet geometry, while the conventional rectangular magnet geometry yields the worst value with 436.75 mNm. Furthermore, the total harmonic distortion values varies between 1.63 and 3.55 for different magnetic orientations. While the worst total harmonic distortion value is obtained from the inclined slotted rectangular magnet, the best total harmonic distortion is acquired from the skewed double rectangular magnet. All these results will provide scientists and engineers with important information in order to obtain more efficient machines.

Predictive SOLPS-ITER simulations to study the role of divertor magnetic geometry in detachment control in the MAST-U Super-X configuration

The SOLPS-ITER code has been utilised to study the movement of the detachment front location from target towards the X-point for MAST-U Super-X plasmas. Two sets of detached steady state solutions are obtained by either varying the deuterium (D 2) fuelling rate or the nitrogen (N) seeding rate to scan the corresponding ‘control’ parameters of outboard midplane density, , and the divertor impurity concentration, . At seeding and fuelling rates ∼10× and ∼5× that required to start detachment at the divertor target, the detachment front only reaches ∼50% of the poloidal distance to the X-point, , corresponding to a region of strong parallel gradients in the total magnetic field B. The region of strong total field gradients correlates with where the detachment front location becomes less sensitive to control parameter variation. This result is qualitatively consistent with the predictions of a simple, analytic detachment location sensitivity (DLS) model (Lipschultz et al 2016 Nucl. Fusion 56 056007) which is based in a scaled parallel-to-B space, z. While the DLS model predictions are in agreement with SOLPS-ITER results in terms of where the front location becomes less sensitive to controls (i.e. in the region of strong parallel gradients in B), the DLS model predicts a higher sensitivity in the region of weak parallel gradients in B downstream as compared to the simulation results. Potential sources of differences between the SOLPS-ITER and DLS model predictions were explored: The DLS model does not include energy sinks beyond radiation from a single impurity nor cross-field energy transport. Momentum and particle balance are also not included in the DLS model. The tight opening into the divertor for flux surfaces could lead to variations in plasma-neutral pressure balance as the detachment front reaches that region, exactly how this affects the front movement needs further investigation.

Dynamics of Non-Magnetic Droplets and Bubbles in Magnetic Fluids in Microfluidic Channels under the Influence of a Magnetic Field

The microfluidics of magnetic fluids is gaining popularity due to the possibility of the non-contact control of liquid composite systems using a magnetic field. The dynamics of non-magnetic droplets and gas bubbles in magnetic fluids were investigated for various configurations of magnetic fields, coatings, and channel geometries, as well as the rate of component supply and their physical properties. Optimal regimes for forming droplet and bubble flows were determined. The mechanism for non-contact control of the size of droplets and bubbles using a magnetic field is proposed in this article. The dependences of the sizes of non-magnetic inclusions in magnetic liquids on the continuous phase flow rate and the displacement of magnets were obtained. The obtained dependences of the volume of non-magnetic inclusions on the flow rate of the continuous phase follow the classic dependences. Changing the size of air bubbles can be achieved by shifting the magnet from −5 mm to +2 mm. The ratio of the maximum and minimum breakaway inclusion varies from 5 to 2 depending on the flow rates of the continuous phase. The range of changing the size of oil droplets with the displacement of magnets is from 1.1 to 1.51. These studies show how, with the help of various mechanisms of influence on microfluidic flows, it is possible to control the size of bubbles and droplets forming in microchannels. The obtained data can be applied for controlled microfluidic dosing and counting devices.

Potential development and electron energy confinement in an expanding magnetic field divertor geometry

The formation of electrostatic potential in an expanding magnetic field divertor is numerically simulated using a kinetic model. As theoretically expected, the electrostatic potential is formed in the expanding magnetic field, which, in combination with the Debye potential near target walls, repels electrons back and balances electron and ion currents. Going beyond the existing theoretical description of the pre-sheath potential formation limited to the asymptotically low electron flow (ue≪vTe), we demonstrate the limit of applicability of asymptotic theory and study pre-sheath potential in practically important range of electron flow [0<Ie<2Isat, where Isat=en(Te+Ti)/mi is the ion saturation current]. Results of the asymptotic theory are fully reproduced at the low side of this range (Ie≪Isat), whereas at high electron current range Ie∼Isat, the pre-sheath potential substantially decreases. The formation of the pre-sheath potential minimizes the interaction of plasma electrons with the material walls and reduces the Debye sheath potential. Reducing the Debye potential forms favorable conditions for eliminating arcing and cold electron emission from the walls. In these favorable conditions, electron thermal losses at the wall could be reduced to minimal theoretical limit of ∼5−8Te per lost ion.

Effect of Pole Head Profile on Torque Performance of a Disc-Type Multipole Magnetorheological Brake

A magnetorheological brake (MRB) works on the shearing effect of MR fluid in the magnetic field to develop resistance between the stator and the rotor, which are relative moving surfaces. Researchers achieved high torque volume ratios in magnetorheological fluid braking systems by adding multiple layers and using multipole approaches. Even though several designs already exist, there is a need for innovative ideas and advanced structures of MRBs for practical engineering applications. The number of magnetic poles, pole geometry and placement have a significant effect on the performance of multipole MR brakes. This research focused on the effect of the pole head geometry in a multipole dual disc compact MR brake to understand the relationship between the geometry and its magnetic flux flow. The magnetic field generated by the electromagnetic coil’s orthogonal travel through pole heads, rotor and MR fluid layers results in friction to fulfill the action of braking that achieves maximum brake torque. This flow depends on the magnetic pole head area and corresponding core dimensions. This study considered polygon, square, hexagon, trapezoid and ellipse pole head profiles in place of the conventional circular pole and the best possible core dimensions were used for each geometry. To study the brake’s performance, COMSOL Multiphysics software (version 5.5) commonly used for 3D electromagnetic modeling was used to simulate and examine the magnetic flux intensity for various pole head configurations. Results indicate an improvement compared to previous works, considering the same dimensional limitations and the flux leakage between the adjacent poles being much less. The hexagonal and elliptical pole heads had better magnetic field area, magnetic intensity distribution and higher magnetic flux lines piercing through the MR fluid perpendicularly than the circular and square pole heads. An increment of 3.88% for braking torque performance was obtained, and the braking torque was significantly enhanced.

The radio shut-off, glitch, and X-ray burst in 1E 1547.0−5408 interpreted through magnetic reconfiguration

ABSTRACT A short X-ray burst was observed from the radio-loud magnetar 1E 1547.0–5408 in 2022 April. Unusually however, the source stopped showing radio pulsations $\gtrsim 3\,$ weeks prior to the burst. After recovery, radio timing revealed that the object had also undergone a modest glitch. A model for the overall event is constructed where an initially mild perturbation adjusts the magnetic geometry near the polar caps, leading to shallow fractures. Crustal ejecta or particles leaking from a pair-plasma fireball pollute the magnetospheric gaps, shutting off the pulsar mechanism, but the energy release is not yet large enough to noticeably enhance the X-ray flux. This perturbation gradually ramps, eventuating in a large-scale energy redistribution which fuels the burst. The star’s mass quadrupole moment changes in tandem, issuing a glitch. Some quantitative estimates for the magnetic reconfiguration under this interpretation are provided, based on a quasi-static model where the fluid evolves through a sequence of hydromagnetic equilibria.

How well can VMEC predict the initial saturation of external kink modes in near circular tokamaks and l = 2 stellarators?

The equilibrium code, VMEC, is used to study external kinks in low β tokamaks and l = 2 stellarators. The applicability of the code when modeling nonlinear MHD effects is explored in an attempt to understand and predict how the initial saturation of the MHD mode depends on the external rotational transform. It is shown that helicity preserving, free boundary VMEC computations do not converge to a single perturbed solution with increasing spectral resolution. Additional constraints are applied to narrow down the numerical resolution parameters appropriate for physical scans. The dependence of the modeled (4, 1) kink mode on the external rotational transform and field periodicity is then studied. While saturated states can be identified which decrease in amplitude with increasing external rotational transform, alternative bifurcated states are found, which contradict this trend. As a result, it was not possible to use VMEC alone to identify the physical dependency of the nonlinear mode amplitude on the magnetic geometry. Nevertheless, the accuracy of VMEC solutions is demonstrated by showing that the expected toroidal mode coupling is captured in the magnetic energy spectrum for stellarator cases. Comparing with the initial value code, JOREK, the predicted redistribution of poloidal magnetic energy from the vacuum to plasma region in VMEC is shown to be physical. This work is a first step toward using VMEC to study MHD modes in stellarator geometry.

P24: Mechanical Circulatory Support Device Technologies Incorporating Mechanical Pressure Regulation

Study: Mechanical circulatory support (MCS) devices perform in variable hemodynamic environments and must enable changes in speed, flow, and pressure based on performance requirements dictated by specific clinical states. In order to perform as intended, sensing of hemodynamic environment, and having a mechanism of pressure regulation, are necessary when experiencing differential pressures during operation inside a circulatory system. Herein, we report MCS devices with this pressure regulation feature. Methods and Results: By creating a passive rotor assembly through magnetic scheme and physical geometry of the housing’s interior, minimal pressure differentials upstream and downstream are able to influence the rotor’s position. In Figures 1 A and B, our universal ventricular assist device (UVAD) is depicted in open and closed positions, respectively. The rotor (shown in tan) spins about the (black) motor coils, but is also able to move axially (up and down in these figures), depending on the pressures acting on it. In Figure 1 C, flow shut off occurs when the rotor shoulder (located at the base of impeller blades) is near the corresponding internal shoulder of the (blue) housing, reducing the aperture between these features. Thus, limiting blood flow through the UVAD. Similarly, this passive rotor movement is designed into our family of continuous-flow total artificial hearts (CFTAH). Pressure differences generated by the left and right sides of the heart influence and affect the rotor’s axial position, regulating pressure and flow. Our pediatric CFTAH (P-CFTAH) is shown in Figure 1 D. Conclusion: Due to the environment, in which these devices operate, we can take advantage of the inherent differential pressures experienced, and simplify operation and control of our MCS devices. We have successfully implemented passive rotors in several developmental iterations of the UVAD, and three versions of our CFTAH (adult, pediatric, infant).

Analysis of locally-aligned and non-aligned discretisation schemes for reactor-scale tokamak edge turbulence simulations

Edge turbulence codes will play a key role in the interpretation of ITER data and for reliable predictions of EU-DEMO. At present, such codes are not yet capable of routine simulations at reactor scale, and instead focus on smaller experiments like TCV or ASDEX Upgrade. Numerical methods have to be identified that scale to reactor size, and are able to cope with the highly anisotropic turbulent structures and simultaneously with the complex magnetic geometry in the edge with X-point(s), the vessel wall and divertor targets present. Particularly for such conditions two main approaches, non-aligned discretisation schemes and a locally-aligned discretisation scheme (commonly referred to as Flux-Coordinate Independent approach (FCI)), have emerged. We analyse both schemes concerning their applicability and scalability to next generation fusion reactors. We find that the ratio of the computational cost of a non-aligned scheme compared to aligned scheme scales as ∝(R0qρs)2 for shear Alfvén dynamics, and as (R0qρs)3 for electron heat conduction, where R0 is the major radius of a tokamak, q an estimate for the safety factor at the edge and ρs is the drift scale representing the typical size of turbulent structures to be resolved. Locally-aligned schemes can therefore be considered strongly favourable for reactor scale tokamaks concerning computational performance. On the other hand, locally-aligned schemes suffer from a more complex treatment of boundary conditions, for which an immersed boundary approach (IBA) was recently proposed. We demonstrate numerically the validity of this method in combination with the FCI approach. Finally, we present a first attempt of an ITER edge turbulence simulation with the FCI code GRILLIX at realistic parameters and in realistic geometry.

Faithful guiding-center orbits in an axisymmetric magnetic field

The problem of the charged-particle motion in an axisymmetric magnetic geometry is used to assess the validity of higher-order Hamiltonian guiding-center theory, which includes higher-order corrections associated with gyrogauge invariance as well as guiding-center polarization induced by magnetic-field non-uniformity. Two axisymmetric magnetic geometries are considered: a magnetic mirror geometry and a simple tokamak geometry. When a magnetically confined charged-particle orbit is regular (i.e., its guiding-center magnetic moment is adiabatically invariant), the guiding-center approximation, which conserves both energy and azimuthal canonical angular momentum, is shown to be faithful to the particle orbit when higher-order corrections are taken into account.

Optimal Design of a Matrix Planar Transformer in an LLC Resonant Converter for Data Center Applications

The 48-V bus converter has been gradually adopted in intermediate bus architecture. The ever-growing development of data centers consumes significant power, thereby pushing power converters to be more efficient. This article focuses on the optimization of the transformer for an LLC resonant converter used in data centers, which is the second stage operating as a dc transformer to realize the isolation and a fixed voltage step-down ratio. The front stage is a multiphase buck converter. The magnetic core geometry reported in this article for the LLC enables a single turn for both primary and secondary windings. Compared with the previous research, the improved interleaving winding scheme benefits from reduced conduction path, lower ac resistance, and smaller core volume. Ansys 3D simulation performs the design and optimization of the magnetic core. The proposed magnetic core, winding layout, and design optimization are verified in the 30-/5-V 660-W LLC resonant converter. It has higher current stress but achieves a higher efficiency of 97.7%, better thermal performance, and lower components count than the state of the art.

A C0-HSDT free vibration of magneto-electro-elastic functionally graded porous plates using a moving Kriging meshfree method

This research examines the natural vibration analysis of magneto-electro-elastic functionally graded porous (MEE-FGP) plates. The study employs a moving Kriging (MK) meshfree method to analyze the MEE-FGP plates composed of piezoelectric and piezomagnetic materials with both even and uneven distributions of porosity. The electric and magnetic potentials in the three-dimension are assumed to follow a combination of cosine and linear variations in the thickness direction to satisfy the Maxwell equations in the two-dimension. The displacement field, electric potential and magnetic potential are approximated by the MK interpolation shape function, which satisfies the Kronecker's delta property. This property allows to impose directly essential boundary conditions as those in the finite element method. The governing equilibrium equations are derived using a C0-type higher-order shear deformation plate theory (C0-HSDT) in conjunction with the virtual work principle and then solved using the MK meshfree method. Various geometries are performed to determine the natural frequency of MEE-FGP plates. The impact of the porosity distribution, porosity volume fraction, volume fraction index, initial external electric voltage, initial magnetic potential and geometry on the natural frequency of the MEE-FGP plates is fully investigated. Numerical results provide an effective approach to analyze and calculate the natural vibration of MEE-FGP plates.

Simplified Optimization of the Magnetic Configuration of HEMP-Thrusters

One type of ion thruster that has gained attention in recent years is the High Efficiency Multistage Plasma (HEMP) thruster. Optimizing the performance of these thrusters can be challenging due to the complexity of the underlying physics. Since the construction of new designs is expensive, cheaper methods for optimization, e.g., numerical optimization, are being sought. This paper presents a fast, analytical approach to finding realistic starting points for the magnetic geometry design of HEMP thrusters. First, a ratio of length to radius is presented, where the magnetic field is especially parallel at the center of the magnetic ring. This result is confirmed with the open-source library magpylib. Its speed and accuracy qualify this tool for further optimization processes. Here, we present some simple performance indicators, which may be beneficial to characterize the magnetic field structure for further optimization.