Magnetic Gap Research Articles

Magnetic field evolution around a fast-moving pore emerging from the quiet Sun

Context. Solar pores are intense concentrations of magnetic fields on the solar surface and plasma flows have always played a key role in spurring the evolution of the pores. Aims. In this study, we present the evolution of the magnetic field and plasma velocity around a fast-moving pore. The target pore expands into the quiet Sun area with a sufficiently fast speed after its emergence, while the background magnetic fields around the pore are simple. These characteristics provide us with an excellent opportunity to study the interaction between plasma motions and ambient magnetic fields. Methods. We analyzed the Helioseismic and Magnetic Imager (HMI) vector magnetograms with a pixel size of 0.5″ and a temporal cadence of 12 min across a duration of 11 h. We also adopted he HMI dopplergrams present the line-of-sight velocities. The horizontal flow fields were obtained using the Differential Affine Velocity Estimator for Vector Magnetograms method. Results. Pure horizontal magnetic fields are generated in the moving frontwards when the pore is subject to fast movement. The generated magnetic fields occur outside the emerging site and thus can be ruled out as the emerging flux from the interior. Instead, they are highly correlated with the broader downflows and expanding horizontal plasma motions in front of the pore. A magnetic gap can be observed between the magnetic fields inside and outside the pore. The temporal evolution of the generated magnetic fields is related to the speed of the pore, which is also distinguished from the original fields within the pore. Conclusions. The observations suggest that the plasma flows driven by the fast proper motion of the pore compress and stretch the local magnetic field to a horizontal non-radial direction, ultimately leading to the magnetic field amplification in the front part of the moving pore.

Investigation of end effect in integrated permanent magnetic damper for cylinder block–valve plate pair in axial piston pump

The present work develops an integrated permanent magnetic damper (IPMD) to apply magnetic torque on a cylinder block, which makes it possible to suppress eccentric wear of the cylinder block–valve plate pair in an axial piston pump. Then, the structure and working principle of the IPMD are described. According to the relationship between the axial and the radial magnetic pole gap, the corresponding end flux tube models are established. Based on the principle of micro-displacement, the axial magnetic force and torque output by IPMD are derived. After separating from the relevant structures inside the pump, to ensure the effectiveness of the results, the test method of IPMD independent of the axial piston pump is provided. To make a more comprehensive analysis of the magnetic bearing characteristics, the prototype of IPMD is manufactured and tested. The influence of the end effect of IPMD on the residual hydraulic torque under different discharge pressures is studied. The results verified the correctness of the theoretical analysis, which have important guiding significance to improve the reliability of the cylinder block–valve plate pair in the axial piston pump.

Continuous wave desktop coherent superheterodyne X-band EPR spectrometer

This article describes a desktop X-band superheterodyne spectrometer designed to measure EPR spectra in the vicinity of g = 2. The spectrometer operates in the vicinity of the 9.2 GHz frequency in the power range of about 40 mW–1 nW. The device uses Time Locking concept with digital quadrature detection of intermediate frequency (100 MHz) and the synthesis of all signals used in the device from a single driving oscillator. To register CW spectra, a TE102 rectangular cavity with the capability of matching and frequency tuning is used. The microwave part of the spectrometer is implemented in the form of two non-tunable modules based on microstrip technology and commercially available microwave MMICs. Two modes of operation are provided – both with PLL of microwave sources with a highly stable driving oscillator as a reference and an AFC system without frequency modulation. All signal processing after digitization of the intermediate frequency is performed digitally using FPGA resources. It is possible to record EPR spectra both with magnetic field modulation at various frequencies and without modulation. The bandwidth of the receiving path can be selected from the widest 46 MHz to about 1.5 kHz, which allows the spectrometer to be used both for recording weak signals and for recording fast-flowing processes. The spectrometer uses a magnetic system on permanent magnets Sm-Co with magnetic field uniformity of about 3 * 10−5. Changing the magnetic field in permanent magnets is done using scanning coils which provides a field change of >800 G (p-p). The control of the magnetic field induction in the magnet gap is performed by a specially designed precision Hall effect magnetometer, which provides a resolution of 1 mG with an absolute error of no more than 0.2 G. A personal computer for spectrometer control is connected via Ethernet. The spectrometer is stable and easy to use. The high performance of the spectrometer is confirmed by the recorded spectra.

High precision real-time insertion device and monochromator synchronization at NSLS-II

Insertion devices have become the dominant photon source at synchrotron and free electron laser light source facilities the world over. Undulators, characterized by their small deflection parameter, exhibit a high degree of constructive interference in photon production from high energy charged particle beams leading to very high photon rates at specific harmonics of the fundamental frequency with relatively narrow spectral widths. Spectroscopic measurements of interest typically span several of these harmonic widths, which requires precision adjustment of an undulator’s magnetic gap to maintain peak flux within the much narrower bandwidth of a beamline monochromator at the desired energy. High precision insertion device controls are developed at NSLS-II including real-time linked control of monochromator hardware allowing for fast, high precision, hardware triggered, spectroscopic measurements. This fast fly scan method is described, compared statistically for self consistency, and shown to be far superior in both efficiency and accuracy as compared to standard step scan measurements.

Modeling and Analysis of Dual-Winding Bearingless Flux-Switching Permanent Magnet Motor Considering Magnetic Saturation Based on Subdomain Model

Dual-winding bearingless flux-switching permanent magnet machine (BFSPMM) is composed of power winding and suspension winding. The permanent magnet and the power winding provide a biased air gap magnetic field, and the suspension winding generates an air gap modulation magnetic field. The structure of stator and rotor are double salient poles. This paper proposes a subdomain model for the on-load field prediction in dual-winding BFSPMM. In the developed model, the field domain is divided into seven types of subdomains, viz. rotor slot, internal air gap, stator slot, permanent magnet slot upper layer, permanent magnet slot lower layer, permanent magnet, and external air gap. The electromagnetic parameters of the motor are analyzed, including air gap flux density, flux linkage, back-EMF, suspension forces, and electromagnetic torque. Based on the principle of conservation of magnetomotive force, a distributed equivalent magnetic circuit model is proposed to compensate for the magnetic saturation. Finally, the analytical predictions are verified by finite-element analysis and prototype experiments.

Research on the Flow and Transmission Performance of Magnetorheological Fluid between Two Discs

The viscoplastic flow of magnetorheological fluid in a disc was analyzed based on the Navier–Stokes Momentum Equation, and the yielded and unyielded decomposition surfaces were obtained. For the shear-thinning phenomenon of magnetorheological fluid, the magnetorheological properties of the magnetorheological fluid were described based on the Herschel–Bulkley model. Then, the relationship between torque, magnetic field, material, size and motion was established, and the magnetic field and working gap were optimized and analyzed. The results show that in the unyielding region, the magnetorheological fluid flows rigidly. In the yielding region, it flows as a viscous fluid. The degree of error of the proposed torque equation decreased gradually with the increase to current, as observed by experimental comparison.

Magnetic field reconstruction using the pulsed wire method: An accuracy analysis

Learning how to reconstruct the magnetic field profile from the pulsed wire method (PWM) is of fundamental importance to characterize undulators with limited magnetic gap accessibility. This paper presents a new data processing approach to reconstruct undulator magnetic field profiles from the PWM. We study via numerical simulations the accuracy and precision of the novel approach to recover the local undulator parameter and the root-mean-square (RMS) phase error. Due to the wire parameters uncertainties, the PWM can, in the best case, reach an accuracy of approximately 10−3 to reconstruct the local undulator parameter, and a precision (needed to determine the magnetic field quality) of about 10−5. Furthermore, our results show that the RMS phase error can be determined with a precision better than 0.2°. This contribution opens the possibility to apply the PWM to perform magnetic field reconstruction in small-gap short-period long undulators for advanced light sources.

Superconducting multipole wiggler with large magnetic gap for HEPS-TF

Superconducting multipole wiggler with large magnetic gap for HEPS-TF

Enhancement of anomalous Hall effect in epitaxial thin films of intrinsic magnetic topological insulator MnBi2Te4 with Fermi-level tuning

The recently discovered intrinsic magnetic topological insulator MnBi2Te4 has attracted keen interest for exotic quantum states such as a quantum anomalous Hall insulator and an axion insulator. Such quantum states of MnBi2Te4 have been intensively studied mainly in atomically thin exfoliated samples, yet thin film samples with critically tuned Fermi level would be indispensable for further pursuit of topological functionality in MnBi2Te4 and related heterointerfaces. Here, we report on fabrication of an Sb-doped MnBi2Te4 thin film by molecular beam epitaxy and their transport properties. The Sb-substitution induces the change in the carrier type and the subsequent increase in resistivity, demonstrating the tuning of the Fermi level (EF) across the bulk bandgap and the phase change to the topologically nontrivial phase. The EF is further finely controlled in a field-effect transistor device. We observe the enhancement of the anomalous Hall conductivity at the charge neutral point, confirming the opening of the magnetic exchange gap in surface Dirac states. The precise control of the band structure and the Fermi level in the thin-film form will lead to exploring exotic phenomena based on intrinsic magnetic topological insulators.

Design of Piezoelectric Energy Harvester Generating Power over a Range of Excitation Frequencies Using

Today, there is a real desire to develop the piezoelectric ‎power harvester to enhance the performance of Wi-Fi sensors ‎and low-power devices to use them in heavy weather for longer times. In this study, the harvester model built from piezoelectric bimorphs called; “Piezo Bending ‎Actuators 427.0085.11Z” from Johnson Matthey, N42 ‎magnets, and some electrical parts such as; accelerometer, ‎shaker, HP 54601B oscilloscope used ‎in the ‏experimental setup‎. ‎
 The results show, that the system frequency has ‎an inverse relationship with a gap between magnets, where the ‎frequency increases 100% as the distance decreases from 4.6mm ‎to 0.7 mm‏.‏‎ In addition, the amplitude of increases by 104% as ‎the gap decreases from 4.6mm to 0.7 mm. Also, the ‎production power and amplitude have an inverse relation ‎with the magnet distance. ‎Keywords: power harvester, magnetic gap, tuned magnetic force, piezoelectric, resonances.

Low-frequency sound insulation performance of novel membrane acoustic metamaterial with dynamic negative stiffness

For improving the low-frequency sound insulation properties of membrane/plate structures, a new quasi-zero stiffness membrane acoustic metamaterial with dynamic magnetic negative stiffness is proposed. When the equivalent magnetic charge theory is used to investigate the dynamic magnetic negative stiffness, a theoretical model of proposed metamaterial with finite dimension is established based on the Galerkin method. Through a combination of theoretical analysis, numerical simulation and experimental measurement, the low-frequency (1–1000 Hz) sound insulation performance of the metamaterial is investigated from several perspectives, including structural modality, vibration mode, average velocity, phase curve, equivalent mass density, and equivalent spring-mass dynamics model. The results show that at a certain initial membrane tension, the decreasing of the magnetic gap or the increasing of the residual flux density can increase the dynamic magnetic negative stiffness. This in turn leads the peak frequency to decrease and the bandwidth of sound insulation to increase, thus achieving effective low-frequency sound insulation over a wide frequency band. Further, when the magnetic gap is larger than the second critical magnetic gap and smaller than the first critical magnetic gap, the first-order modal resonance of the metamaterial disappears, and the corresponding value of sound insulation valley increases significantly, thus demonstrating superior sound insulation effect in a wide frequency band. The proposed method of using dynamic magnetic negative stiffness to improve low-frequency sound insulation valleys due to modal resonance provides useful theoretical guidance for designing membrane/plate type low-frequency sound insulation metamaterials.

Low-frequency sound insulation performance of novel membrane acoustic metamaterial with dynamic negative stiffness

For improving the low-frequency sound insulation properties of membrane/plate structures, a new quasi-zero stiffness membrane acoustic metamaterial with dynamic magnetic negative stiffness is proposed. Upon applying the equivalent magnetic charge theory to derive the dynamic magnetic negative stiffness, a theoretical model of proposed metamaterial with finite dimensions is established based on the Galerkin method. Through a combination of theoretical analysis, numerical simulation and experimental measurement, the low-frequency (1—1000 Hz) sound insulation performance of the metamaterial is investigated from several perspectives, including structural modality, vibration mode, average velocity, phase curve, equivalent mass density, and equivalent spring-mass dynamics model. Results show that, at a certain initial membrane tension, decreasing the magnetic gap or increasing the residual flux density can increase the dynamic magnetic negative stiffness. This in turn leads to decreased peak frequency and enlarged bandwidth of sound insulation, thus achieving effective low-frequency sound insulation over a wide frequency band. Further, when the magnetic gap is larger than the second critical magnetic gap and smaller than the first critical magnetic gap, the first-order modal resonance of the metamaterial disappears, and the corresponding value of sound insulation valley increases significantly, thus demonstrating superior sound insulation effect with wide frequency band. The proposed method of using dynamic magnetic negative stiffness to improve low-frequency sound insulation valleys due to modal resonance provides useful theoretical guidance for designing membrane/plate type low-frequency sound insulation metamaterials.

Fixed-time sliding mode attitude control of a flexible spacecraft with rotating appendages connected by magnetic bearing.

This study focuses on the attitude control of a flexible spacecraft comprising rotating appendages, magnetic bearings, and a satellite platform capable of carrying flexible solar panels. The kinematic and dynamic models of the spacecraft were established using Lagrange methods to describe the translation and rotation of the spacecraft system and its connected components. A simplified model of the dynamics of a five-degrees-of-freedom (DOF) active magnetic bearing was developed using the equivalent stiffness and damping methods based on the magnetic gap variations in the magnetic bearing. Next, a fixed-time sliding mode control method was proposed for each component of the spacecraft to adjust the magnetic gap of the active magnetic bearing, realize a stable rotation of the flexible solar panels, obtain a high inertia for the appendage of the spacecraft, and accurately control the attitude. Finally, the numerical simulation results of the proposed fixed-time control method were compared with those of the proportional-derivative control method to demonstrate the superiority and effectiveness of the proposed control law.

Non-monotonic variation of the Kramers point band gap with increasing magnetic doping in BiTeI

Polar Rashba-type semiconductor BiTeI doped with magnetic elements constitutes one of the most promising platforms for the future development of spintronics and quantum computing thanks to the combination of strong spin-orbit coupling and internal ferromagnetic ordering. The latter originates from magnetic impurities and is able to open an energy gap at the Kramers point (KP gap) of the Rashba bands. In the current work using angle-resolved photoemission spectroscopy (ARPES) we show that the KP gap depends non-monotonically on the doping level in case of V-doped BiTeI. We observe that the gap increases with V concentration until it reaches 3% and then starts to mitigate. Moreover, we find that the saturation magnetisation of samples under applied magnetic field studied by superconducting quantum interference device (SQUID) magnetometer has a similar behaviour with the doping level. Theoretical analysis shows that the non-monotonic behavior can be explained by the increase of antiferromagnetic coupled atoms of magnetic impurity above a certain doping level. This leads to the reduction of the total magnetic moment in the domains and thus to the mitigation of the KP gap as observed in the experiment. These findings provide further insight in the creation of internal magnetic ordering and consequent KP gap opening in magnetically-doped Rashba-type semiconductors.

Band gap of silicon photonic crystal with square-lattice and windmill-shaped defects

A new type of 2D square-lattice photonic crystal with different windmill-shaped defects is proposed. Based on the plane wave expansion method and super cell theory, the band gaps of defect models are numerically analyzed according to the symmetry. We aim at further reducing the defect symmetry of photonic crystals compared to previous studies and researching the effect of translation and rotation of different windmill-shaped defect structures on the transverse magnetic (TM) band gap. The results reveal that the translation distance of defects brings great impacts on the band gap of 2D square-lattice photonic crystals and the width of the TM band gap can be further expanded after rotating on the basis of translation. In addition, we discovery that the band gap of the model with even-numbered fan-shaped defects is wider than that of the model with odd-numbered fan-shaped defects. Among the five different defect models (three-wings, four-wings, five-wings, six-wings, rotating-cross), the four-wing windmill defect model produces the largest band gap, which reaches 5.307 × 10−2 (ɷa/2πc). This research is helpful to understand the band gap characteristics of photonic crystals, which will contribute to the design of photonic crystal devices.

A General Origin for Multiplanetary Systems With Significantly Misaligned USP Planets

Abstract Ultra-short-period (USP) planets are exoplanets that have orbital periods of less than one day and are unique because they orbit inside the nominal magnetic truncation gap of their host stars. In some cases, USP planets have also been observed to exhibit unique dynamical parameters such as significant misalignments in inclination angle with respect to nearby planets. In this paper, we explore how the geometry of a multiplanet system hosting a USP planet can be expected to evolve as a star ages. In particular, we explore the relationship between the mutual inclination of the USP planet and the quadrupole moment (J 2) of the host star. We use secular perturbation theory to predict the past evolution of the example TOI-125 system, and then confirm the validity of our results using long-term N-body simulations. Through investigating how the misalignment between the candidate USP planet and the three other short-period planets in the TOI-125 system arose, we intend to derive a better understanding of the population of systems with misaligned USP planets and how their observed parameters can be explained in the context of their dynamical histories.

Non-Hermitian band topology from momentum-dependent relaxation in two-dimensional metals with spiral magnetism

We study the emergence of non-Hermitian band topology in a two-dimensional metal with planar spiral magnetism due to a momentum-dependent relaxation rate. A sufficiently strong momentum dependence of the relaxation rate leads to exceptional points in the Brillouin zone, where the Hamiltonian is nondiagonalizable. The exceptional points appear in pairs with opposite topological charges and are connected by arc-shaped branch cuts. We show that exceptional points inside hole and electron pockets, which are generally present in a spiral magnetic state with a small magnetic gap, can cause a drastic change of the Fermi surface topology by merging those pockets at isolated points in the Brillouin zone. We derive simple rules for the evolution of the eigenstates under semiclassical motion through these crossing points, which yield geometric phases depending only on the Fermi surface topology. The spectral function observed in photoemission exhibits Fermi arcs. Its momentum dependence is smooth -- despite of the nonanalyticities in the complex quasiparticle band structure.

Remote acquisition of insulator icing flashover signal based on frequency optimization of ring-shaped intelligent current sensor

In order to improve the safety of power grid operation and avoid the hidden danger in the process of power supply, a remote acquisition method of insulator ice-covered flashover signal based on the frequency optimization of ring intelligent current sensor was proposed. According to principle of take electricity by capacitance, transmission line, current sensor, current sensor B and double rectifier circuit composed of parallel resonant magnetic circuit for electric model. By monitoring the current sensor and current sensor B the secondary side of induction electromotive force, magnetic core KaiQi gap equivalent permeability values, such as through the calculation of current sensor parameters of iron core and coil number of turns. In this paper, the current sensor is optimized to improve the power monitoring effect, and the remote acquisition of the flashover signal of insulator icing is realized. The experimental results show that. This monitoring method can effectively monitor the maximum load power, load resistance and load voltage of the model when the current value is different. In the face of impedance branch resonant, resonant and open air gap and other circumstances, can effectively monitor the power taking situation, a wide range of applications.

Effect of Alternating Magnetic Field on Arc Plasma Characteristics and Droplet Transfer during Narrow Gap Laser-MIG Hybrid Welding

In this paper, the morphological characteristics of arc plasma and droplet transfer during the alternating magnetic field-assisted narrow gap groove laser-MIG (metal inert gas) hybrid welding process were investigated. The characteristics of arc plasma and droplet transfer, electron temperature, and density were analyzed using a high-speed camera and spectrum diagnosis. Our results revealed that the arc maintained a relatively stable state and rotated at a high speed to enhance the arc stiffness, and further improved the stability of the arc under the alternating magnetic field. The optimum magnetic field parameters in this experiment were B = 16 mT and f = 20 Hz, the electron temperature was 9893.6 K and the electron density was 0.99 × 1017 cm−3 near the bottom of the groove, which improved the temperature distribution inside the narrow gap groove and eliminated the lack of sidewall fusion defect. Compared to those without a magnetic field, the magnetic field could promote droplet transfer, the droplet diameter decreased by 17.6%, and the transition frequency increased by 23.5% (owing to the centrifugal force during droplet spinning and electromagnetic contraction force). The width of the weld bead was increased by 12.4% and the pores were also significantly reduced due to the stirring of the magnetic field on the molten pool.

Field-angle anisotropy of proximate Kitaev systems under an in-plane magnetic field

We have investigated the field-angle behaviors of magnetic excitations under an in-plane magnetic field for proximate Kitaev systems. By employing the exact diagonalization method in conjunction with the linear spin wave theory, we have demonstrated that the magnetic excitation gap in the polarized phase is determined by the magnon excitation at $M$ points and has a strong anisotropy with respect to the field direction in the vicinity of the critical field limit. The specific heat from this magnon excitation bears qualitatively the same anisotropic behaviors as expected one for the non-Abelian spin liquid phase in the Kitaev model and experimentally observed one of the intermediate phases in $\alpha$-RuCl$_3$.