Coaxial Magnetic Field Research Articles

In-situ X-ray imaging of the breakup dynamics of current-carrying molten metal jets during arc discharge

The flow dynamics of current-carrying molten metal jet breakup during arc discharge serves as mass and heat sources in wire-arc-based metal deposition processes, thereby optimizing the resultant product quality. However, the spatiotemporal flow interaction between the molten metal jet and the surrounding arc plasma remains unclear. Here, using in-situ synchrotron X-ray imaging, we simultaneously track surface deformation and internal flow in molten aluminum jets during argon arc discharge. We reveal that modulating the magnitude and path of the arc discharge current can accelerate the jet velocity by 200–300% beyond its initial injection speed, thereby facilitating significant jet elongation. Our results provide consistent evidence that the jet flow dynamics are predominantly governed by the interaction between the arc discharge current and its coaxial self-induced magnetic field. This study establishes a framework at the intersection of fluid dynamics and electromagnetism, contributing to optimized control and precision in wire-arc-based applications.

Spatiotemporal characteristics of magneto-acousto-electric fields generated by Bessel beams

The magneto-acousto-electric (MAE) effect shows great significance in neural modulation, whereas the high-precision stimulation cannot be realized by the unidirectional electric distribution perpendicular to the orthogonal acoustic and magnetic fields. A new MAE model is established based on helical wave fronts of Bessel beams in a coaxial magnetic field. Numerical and experimental studies are conducted for quasi-Bessel beams constructed by the saw-tooth phase modulation for a sectorial planar transducer array in a coaxial toroidal magnet. The MAE field induced by the Bessel beam of lth order is determined by those of (l-1)th and (l + 1)th orders. The rotary MAE field with a constant peak-intensity center can only be constructed by the Bessel beam of 1st order, which is effective for neural stimulation. Assisted by therapeutic effects of center-captured drug particles by acoustic-vortex tweezers, the center-converging MAE field may advance a new collaborative stimulation strategy with improved accuracy and reduced acoustic energy.

Magneto-acousto-electric effects based on focused acoustic-vortex beams in a coaxial magnetic field

Magneto-acousto-electric effects based on focused acoustic-vortex beams in a coaxial magnetic field

Development of parametric window and optimization of process parameters to predict bead profile in magnetically controlled gas tungsten arc welding

A novel methodology has been proposed to tame the arc shape by adopting an external magnetic field, resulting weld profile as required. The co-axial magnetic field developed by specially designed electromagnets is superimposed on the welding arc. It was found that 0-0-S-N configuration provided more penetration than conventional gas tungsten arc welding. A parametric window has been developed for the selected configuration to obtain the desired bead geometry. The experiments were performed using process parameters as suggested by the design matrix, developed using response surface method technique. Mathematical models were evolved from experimental data for penetration and bead width. The evolved model for penetration is adequate up to 99.72% confidence level and for bead width is 99.98% confidence level. The effects of process parameters have been presented in a graphical manner for better understanding. The penetration achieved with the magnetically controlled GTAW process is 3.92 mm, which is 30% more than that achieved with conventional GTAW. The bead width increases initially, up to a certain limit, and then reduces with an increase in excitation current. Further, the experiments have been conducted on the optimized parameters for the validation of models. The refined grains were obtained due to magnetic stirring of the molten pool, which is desirable for improvement in mechanical properties of welds. The average grain size was reduced from 42.55 to 31.03 µm. The improved microstructure containing more amount of acicular ferrite was obtained with magnetically controlled arc.

Multiplex nanozymatic biosensing of Salmonella on a finger-actuated microfluidic chip.

A colorimetric biosensor was elaboratively designed for fast, sensitive and multiplex bacterial detection on a single microfluidic chip using immune magnetic nanobeads for specific bacterial separation, immune gold@platinum palladium nanoparticles for specific bacterial labeling, a finger-actuated mixer for efficient immunoreaction and two coaxial rotatable magnetic fields for magnetic nanobead capture (outer one) and magnet-actuated valve control (inner one). First, preloaded bacteria, nanobeads and nanozymes were mixed through a finger actuator to form nanobead-bacteria-nanozyme conjugates, which were captured by the outer magnetic field. After the inner magnetic field was rotated to successively wash the conjugates and push the H2O2-TMB substrate for resuspending these conjugates, colorless TMB was catalyzed into blue TMBox products, followed by color analysis using ImageJ software for bacterial determination. This simple biosensor enabled multiplex Salmonella detection as low as 9 CFU per sample in 45 min.

Gate-Controlled Quantum Interference Effects in a Clean Single-Wall Carbon Nanotube p-n Junction.

The precise control and deep understanding of quantum interference in carbon nanotube (CNT) devices are particularly crucial not only for exploring quantum coherent phenomena in clean one-dimensional electronic systems, but also for developing carbon-based nanoelectronics or quantum devices. Here, we construct a double split-gate structure to explore the Aharonov-Bohm (AB) interference effect in individual single-wall CNT p-n junction devices. For the first time, we achieve the AB modulation of conductance with coaxial magnetic fields as low as 3T, where the flux through the tube is much smaller than the flux quantum. We further demonstrate direct electric-field control of the nonmonotonic magnetoconductance through a gate-tunable built-in electric field, which can be quantitatively understood in combination with the AB phase effect and Landau-Zener tunneling in a CNT p-n junction. Moreover, the nonmonotonic magnetoconductance behavior can be strongly enhanced in the presence of Fabry-Pérot resonances. Our Letter paves the way for exploring and manipulating quantum interference effects with combining magnetic and electric field controls.

Quantum dispersion properties of eigenmodes in semiconductor nanotubes with dielectric filling in dc magnetic field

Dispersion properties of electromagnetic eigenmodes in a semiconductor nanotube (with quadratic electron dispersion law) filled by a nonmagnetic dielectric and placed in a coaxial dc magnetic field are studied theoretically. A new quantum electrodynamical phenomenon is predicted. Namely, it is shown that increase in the electron density n02D in the nanotube results in the appearance of new branches in the eigenmodes spectrum. These branches arise in a bifurcation manner at some critical values of n02D, when a new electron energy subzone starts to fill in. The number of branches monotonously increases with growth n02D and oscillates with increase in the number of magnetic flux quanta through the nanotube (i.e., a peculiar Aharonov–Bohm effect takes place). We also found that the dispersion curves have parts with anomalous dispersion. The analytical expression for electron energy loss due to the excitation of eigenmodes under the Cherenkov resonance condition is derived and numerically analyzed.

Viscometer for investigating the viscosity of magnetic fluid media

The rational application of magnetic fluids in various technical systems requires their stability analysis, hydrodynamic particle size, dissipative processes in the colloid control. The existing viscometers do not fully meet all requirements, in particular, they do not allow research in a magnetic field of given magnitude and certain topography. It is proposed to determine rheological properties of magnetic fluids using rotary viscometer, in which two measuring gaps are structurally designed and filled with studied fluid, which is important for calculating characteristics of low viscosity magnetic media. The device design implements practically homogeneous magnetic field, varying within wide range and directed perpendicular to liquid shear stress. The device allows to steadily maintain shear rate in medium under study, and to determine viscosity with a sufficiently large change. A small magnetic fluid volume is required to estimate rheological characteristics. The accuracy of measurements of the internal friction force, device heating temperature, coaxial cylinders rotation speed and magnetic field inside investigated medium meet the requirements of international standards. Laminar fluid flow process in the device gap is described mathematically. This made it possible to justify the construction geometrical dimensions in order to increase the measurements and determine rheological properties of low-viscosity magnetic materials. The formulas for calculation of Newtonian fluid viscosity coefficient, shear stress and shear rate based on experimental data were obtained.

Diatomic-py: A Python module for calculating the rotational and hyperfine structure of 1Σ molecules

We present a computer program to calculate the quantised rotational and hyperfine energy levels of Σ1 diatomic molecules in the presence of dc electric, dc magnetic, and off-resonant optical fields. Our program is applicable to the bialkali molecules used in ongoing state-of-the-art experiments with ultracold molecular gases. We include functions for the calculation of space-fixed electric dipole moments, magnetic moments and transition dipole moments. Program summaryProgram Title: Diatomic-PyCPC Library link to program files:https://doi.org/10.17632/3yfxnh5bn5.1Developer's repository link:https://doi.org/10.5281/zenodo.6632148Licensing provisions: BSD 3-clauseProgramming language: Python ≥ 3.7Nature of problem: Calculation of the rotational and hyperfine structure of Σ1 molecules in the presence of dc magnetic, dc electric, and off-resonant laser fields.Solution method: A matrix representation of the Hamiltonian is constructed in the uncoupled basis set. Eigenstates and eigenenergies are calculated by numerical diagonalization of the Hamiltonian.Additional comments including restrictions and unusual features: Restricted to calculating the Stark and Zeeman shifts with co-axial electric and magnetic fields.

Dynamical electromagnetic actuation system for microscale manipulation

AbstractElectromagnetic actuation systems (EMA) have excelled themselves in microscale manipulation. Yet, the fastened structure of the current systems tethers the controlled workspace. In this paper, a new electromagnetic actuation principle is investigated. The actuator structure consists of a pair of coaxially movable electromagnets integrated to a robotic manipulator. The pair induces a coaxial homogeneous magnetic field or gradient to control the magnitude of the magnetic torque or force by changing the distance between the electromagnets asymmetrically. The robotic manipulator, on the other hand, transports the pair at five degrees of freedom to manipulate a microrobot in 3D space by closed-loop control with integrated vision feedback system. Numerical analyses are performed to investigate the induced electromagnetic field at the symmetrical/asymmetrical configuration of the coaxial pair. Accordingly, a correlation between the magnitude of the magnetic force and the asymmetric distance is obtained for flexible force control. A proof of concept prototype is constructed to validate the proposed actuation principle and evaluate its performance experimentally. The experimental results verify the numerical analysis and show the system applicability of inducing controlled forces on a micro-object in 2D and 3D workspaces at a velocity range of 65 to 157 $\mu$ m/s. Moreover, micromanipulation on a helical route is also demonstrated with an absolute error mean from the reference path of 191 $\mu$ m.

Self-Rotational Dynamics of Dust Grains in a Magnetic Field

The self-rotation of dust particles in a magnetic field up to 0.02 T is researched. The stratified glow discharge and a coaxial magneticfield are used. The dust particles are hollow glass microspheres, whose horizontal deflection is observed. The dependences of the rotation frequency and the direction of dust grains on the magnitude and the direction of a superimposed magnetic field are studied. The hysteresis effect of a particle self-rotation direction at the variation of the magnetic field intensity is examined.

Waves of a Magnetoplasma Solid-State Cylinder Under Quasi-Stationary Conditions

The theory of electromagnetic eigenwaves of a cylindrical plasma waveguide located in a constant coaxial magnetic field is developed. The dispersion equation for a waveguide with high electronic conductivity is obtained. It is shown that the waveguide supports the propagation of bulk and bulk-surface hybrid waves of helicon origin. The nonreciprocity effect of waveguide eigenwaves with the identical field distributions, but differing in the direction of propagation along the azimuthal coordinate and also when the direction of the external magnetic field is reversed, is discovered.

Impacts of Chemical Reaction, Diffusion-Thermo and Radiation on Unsteady Natural Convective Flow past an Inclined Vertical Plate under Aligned Magnetic Field

In this article, diffusion-thermo, thermal radiation, and first-order chemical reaction effects are studied analytically when the aligned magnetic field set to the fluid/ the plate on the unsteady, free convective fluid passing through an inclined vertical plate by flexible surface conditions, concentration diffusion under the action of a coaxial magnetic field. The governing PDE's are derived from the physical model and transformed into dimensionless form. Then a closed-form solution is obtained using the Laplace transform method. The effects of controlling parametric quantities like M, R, Sc, Pr, Du, Gr, Gm are analyzed through graphs for fluid properties. A comparative study has been made with published results in the absence of some non-dimensional parameters for a particular case (aligned magnetic field set to the fluid) found in good agreement.

Fast electron transport dynamics and energy deposition in magnetized, imploded cylindrical plasma.

Inertial confinement fusion approaches involve the creation of high-energy-density states through compression. High gain scenarios may be enabled by the beneficial heating from fast electrons produced with an intense laser and by energy containment with a high-strength magnetic field. Here, we report experimental measurements from a configuration integrating a magnetized, imploded cylindrical plasma and intense laser-driven electrons as well as multi-stage simulations that show fast electrons transport pathways at different times during the implosion and quantify their energy deposition contribution. The experiment consisted of a CH foam cylinder, inside an external coaxial magnetic field of 5 T, that was imploded using 36 OMEGA laser beams. Two-dimensional (2D) hydrodynamic modelling predicts the CH density reaches , the temperature reaches 920 eV and the external B-field is amplified at maximum compression to 580 T. At pre-determined times during the compression, the intense OMEGA EP laser irradiated one end of the cylinder to accelerate relativistic electrons into the dense imploded plasma providing additional heating. The relativistic electron beam generation was simulated using a 2D particle-in-cell (PIC) code. Finally, three-dimensional hybrid-PIC simulations calculated the electron propagation and energy deposition inside the target and revealed the roles the compressed and self-generated B-fields play in transport. During a time window before the maximum compression time, the self-generated B-field on the compression front confines the injected electrons inside the target, increasing the temperature through Joule heating. For a stronger B-field seed of 20 T, the electrons are predicted to be guided into the compressed target and provide additional collisional heating.This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 2)’.

Theory of magnetotransport in shaped topological insulator nanowires

We show that shaped topological insulator (TI) nanowires, i.e. such that their cross-section radius varies along the wire length, can be tuned into a number of different transport regimes when immersed in a homogeneous coaxial magnetic field. This is in contrast with widely studied tubular nanowires with constant cross-section, and is due to magnetic confinement of Dirac surface carriers. In flat 2D systems such a confinement requires non-homogeneous magnetic fields, while for shaped nanowires of standard size homogeneous fields of the order of $B\sim\,1$T are sufficient. We put recent work [Kozlovsky et al., Phys. Rev. Lett. 124, 126804 (2020)] into broader context and extend it to deal with axially symmetric wire geometries with arbitrary radial profile. A dumbbell-shaped TI nanowire is used as a paradigmatic example for transport through a constriction and shown to be tunable into five different transport regimes: (i) conductance steps, (ii) resonant transmission, (iii) current suppression, (iv) Coulomb blockade, and (v) transport through a triple quantum dot. Switching between regimes is achieved by modulating the strength of a coaxial magnetic field and does not require strict axial symmetry of the wire cross-section. As such, it should be observable in TI nanowires fabricated with available experimental techniques.

Verdet constant determination of dielectric media using a new versatile, portable and low-cost magneto-optical rotator

The full details of a newly developed versatile, portable and low-cost magneto-optical device for the accurate determination of Verdet constant over the wavelength range of 400–480 nm in undergraduate physics and chemistry labs are presented. The elevated sensitivity of the device is achieved by using a semiconducting photodiode detector coupled with an electronic circuit board, which is configured to autonomously record the finest rotation angle in the polarization direction of the transmitted light relative to a reference polarizer. Two different mechanisms to generate a strong coaxial magnetic field of ∼1.34 T are presented, using either a ring neodymium permanent magnet or a solenoid fed by a lithium-ion battery cell. Due to its versatility, portability and low-cost, the presented device is expected to replace most currently existing bulky and expensive setups.

Theoretical research on the annular intensive relativistic electron motion focused by coaxial cusped periodic permanent magnetic field

This paper theoretically investigates the motion characteristics of an annular intensive relativistic electron beam (IREB) in a coaxial, smooth waveguide under a cusped periodic permanent magnetic (CPPM) field. The motion of the electron beam clearly exhibits a periodic oscillation in a CPPM. For the effective transmission of an IREB, the structural parameters of the CPPM must be chosen carefully. Based on theoretical analysis, stability conditions are suggested. The influence of the magnetic field phase, strength, and period on the oscillation amplitude of the beam envelope is analyzed, and the criteria for minimal oscillation amplitude are proposed accordingly. Notably, the theoretical formula, used to predict the oscillation period of the beam envelope, is proposed and verified by single-particle and particle-in-cell simulation results.

Magnetoconductance, Quantum Hall Effect, and Coulomb Blockade in Topological Insulator Nanocones.

Magnetotransport through cylindrical topological insulator (TI) nanowires is governed by the interplay between quantum confinement and geometric (Aharonov-Bohm and Berry) phases. Here, we argue that the much broader class of TI nanowires with varying radius-for which a homogeneous coaxial magnetic field induces a varying Aharonov-Bohm flux that gives rise to a nontrivial masslike potential along the wire-is accessible by studying its simplest member, a TI nanocone. Such nanocones allow us to observe intriguing mesoscopic transport phenomena: While the conductance in a perpendicular magnetic field is quantized due to higher-order topological hinge states, it shows resonant transmission through Dirac Landau levels in a coaxial magnetic field. Furthermore, it may act as a quantum magnetic bottle, confining surface Dirac electrons and leading to a largely interaction-dominated regime of Coulomb blockade type. We show numerically that the above-mentioned effects occur for experimentally accessible values of system size and magnetic field, suggesting that TI nanocone junctions may serve as building blocks for Dirac electron optics setups.

The Influence of an External Coaxial Magnetic Field on the Characteristics of a High-Current ARC in a Vacuum Switch

The influence of an external synchronous axial magnetic field on the characteristics of a vacuum-arc discharge is investigated within the range of discharge currents from 6 to 14 kA. The magnetic field amplitude is regulated in a wide range (from 0 to 190 mT) irrespective of the discharge current, while the specific magnetic field induction (in mT/kA) remains constant during the arc burning time. A critical specific magnetic field induction is determined, which prevents the discharge channel from constriction in the gap. It is shown that an application of an external magnetic field does not give rise to the formation of an anode spot, while the cathode is covered with a large number of microspots evenly distributed across its surface. An analysis of the probe currents demonstrates that the density of the post-arc plasma under these conditions decreases, and its decay is accelerated.

Effect of coaxial electromagnetic field on separation density of dense-medium cyclone

To decrease the separation density of a dense-medium cyclone by using an online control method, a coaxial coil was placed outside the lower cone position of the dense-medium cyclone, and a separation test of coal with a size of 0–3 mm was performed in a coaxial magnetic field. Subsequently, the density composition of the separation products was determined through a float-and-sink analysis. Further, the magnetic force of the dense-medium particles in a magnetic field generated by the coil was analyzed through the Ansoft software. The results showed that dense-medium particles were attracted into the underflow by the downward axial magnetic field force. Therefore, the separation density of the dense-medium cyclone can be decreased in the magnetic field created by the coil with large passing currents (i.e. 12.5–20 A). Hence, this study may provide a new method to control the separation density of dense-medium cyclones, which has a considerable significance to improve the automation of coal preparation plants.