Strong Transverse Magnetic Field Research Articles

Electromagnetically induced transparency with magnetically induced ΔF=0,mF=0→mF=0 probe transition

Interest in magnetically induced (MI) transitions of alkali metal atoms is caused by the fact that their intensities can exceed the intensities of ‘regular’ atomic transitions in a wide magnetic field range (200–4000 G). The goal of this work was to form and study, for the first time, electromagnetically induced transparency (EIT) resonance in a strong magnetic field using probe radiation tuned to |Fg=F,mF=0⟩→|Fe=F,mF=0⟩ MI transition, which is forbidden in zero magnetic fields. Two narrow-band linearly polarized cw diode lasers were used to form EIT resonance on a Λ-type system of a Cs atomic D2 line in a strong transverse magnetic field (up to 1000 G). The resonance was formed in a Cs atomic vapor nanocell with an atomic vapor column thickness of 850 nm.

Numerical simulation of MHD on sudden expansion duct under strong transverse magnetic field

This research delves into the analysis of quasi-two-dimensional flow dynamics in liquid metal confined within a sudden expansion duct, subjected to a strong magnetic field. Utilizing numerical simulations derived from the SM82 model, the study concentrates on examining the magnetohydrodynamic (MHD) responses across a defined range of parameters. These simulations were conducted maintaining a constant Reynolds number (Re), while systematically varying the Hartmann number (Ha) across a spectrum of values [1000, 2000, 5000, 10000, 15000, 20000] to enable a thorough exploration of the magnetic fields influence on the flow dynamics. The outcomes of this study reveal a marked transition in flow behavior corresponding with the escalation in magnetic field strength. Notably, as the magnetic field intensifies, the flow undergoes a transformation from a state of instability to stability. This shift is predominantly characterized by a diminution, followed by a complete cessation, of shear vortex shedding. Additionally, beyond a Ha of 5000 and at a longitudinal position of x = 6, both the velocity and pressure profiles begin to exhibit near-identical and symmetric characteristics. Post the Ha exceeding 1000, the vortex profile demonstrates symmetry about the y=0 axis. These observations significantly enhance the comprehension of MHD fluid dynamics under quasi-two-dimensional conditions.

Numerical simulations of flow past a backward-facing step under a strong transverse magnetic field

The flow of liquid metal over a backward-facing step (BFS) exhibits unique flow characteristics due to the influence of strong magnetic field. In this study, direct numerical simulation of the BFS flow under a strong magnetic field is conducted based on a quasi-two-dimensional model (with a large interaction number, N≫1, and a large Hartmann number, Ha≫1). The Reynolds number (Re), Hartmann number (Ha), and expansion ratio (ER) are investigated within the ranges of [100−80 000], [100−40 000], and [1.67−5], respectively. Three typical flow regimes are defined based on the evolution of the free shear layer vortices and the separation state of the boundary layer. Furthermore, a comprehensive flow regime map is presented for different ER, revealing a positive correlation between the critical Reynolds number (Rec1) and Ha at the onset of instability. Specifically, Rec1 is proportional to Ha0.5, Ha0.54, and Ha0.56 for ER = 5, 2.5, and 1.67, respectively. Moreover, the maximum relative thickness of the free shear layer at Hac1 appears in the range of approximately 0.7–0.78Lr for ER = 5, while for ER = 2.5, it appears in the range of approximately 0.80–0.85Lr, indicating that the instability position of the free shear layer occurs earlier for large ER. Our numerical investigation also demonstrates that an increase in the transverse magnetic field compresses the free shear layer and delays the process of vortex pairing, thereby suppressing the oscillatory behavior of the shear layer.

Numerical Investigation of the Effect of the Wall Properties on Downward Mercury Flow and Temperature Fluctuations in a Vertical Heated Pipe under a Transverse Magnetic Field

The work is motivated by the need to study the effect of abnormal quasi-periodic high-amplitude temperature fluctuations in a liquid metal flow in pipes and channels, which arise under conditions close to those specific for liquid metal (PbLi alloy, etc.) hydrodynamics and heat transfer in blankets of tokamak fusion reactors. Such temperature fluctuations in the cooling channels of the fusion reactor blanket pose a threat to the strength of the channel walls. The influence of the physical properties of the channel walls and potential fouling of their inner surface on the generation of these fluctuations has not been studied as yet. Therefore, this problem has been numerically investigated for a MHD mixed convection of a liquid metal in a round tube for a downward flow of mercury with the one-side heating condition under a strong transverse magnetic field using conjugate problem statement by the LES (Large Eddy Simulation) method. Numerical simulation was performed for four cases: (i) the effect of thermophysical and electrophysical properties of the steel pipe wall is neglected, (ii) the effect of wall material properties is included, (iii) the effect of the moderate contact electrical resistance caused by a layer of fouling deposits or oxides on the inner surface of the pipe is accounted for, and (iv) the resistance of the thin fouling layer is assumed to be very high. The predictions for the cases (i) and (iv) are in good agreement with the experimental data and the results of the direct numerical simulation. They demonstrate the existence of quasi-periodic abnormal high-amplitude temperature fluctuations in the fluid with a frequency of approximately 0.14 Hz. With a relatively low electrical resistance of the fouling film (case iii), the frequency of high-amplitude temperature fluctuations was considerably lower (0.07 Hz). In the absence of electrical contact resistance on the inner surface of the steel pipe (case ii), high-amplitude velocity and temperature fluctuations were not revealed in the fluid. Thus, it was shown for the first time that the physical properties of a wall and the electrical resistance between the fluid and the electrically conducting wall were responsible for the development of abnormal temperature fluctuations in the liquid and the wall and control of their amplitude and frequency. The causes of the revealed effects are discussed.

Double diffusion and Hall effects on MHD sinusoidal natural convection flow of silver water-based nanofluid from a porous vertical plate

This paper scrutinizes Hall current, Soret and Dufour impacts on natural convective flow of nanofluid attributable to variation in sinusoidal surface temperature over a vertical plate through a porous medium with strong transverse magnetic field applied normally to the flow. In this regard, the silver metal is considered as nanoparticles with water as base fluid. The overlapping multi-domain bivariate spectral local linearization method (OMD-BSLLM) has been utilized to solve the dimensionless governing equations which are attained by means of appropriate transformations. The obtained results are portrayed via graphical and tabular formations to inspect flow fields, shear stresses, heat and mass transmission characteristics for varying thermo-physical parameters. We found that there is an enhancement in the flow fields, shear stresses and heat transportation with the use of silver nanoparticles. Thermal and concentration boundary layer thickness enhance by using porous material, whereas diminish with improvement in Hall effect and ratio of buoyancy forces. The flow characteristics decline with the inclusion of porous medium while elevates with increment in Hall parameter. Moreover, an upgrade in thermal-diffusion correspond to a substantial growth in concentration field along with mass transfer rate. Current analysis can be useful in MHD energy generators, and industrial applications such as heating and cooling procedures owing to the involvement of nanoparticles having superior thermal conductivity features.

Magnetohydrodynamics effect of Marangoni nano boundary layer flow and heat transfer with CNT and radiation

The investigation focuses on 2-dimensional MHD steady incompressible flow and heat transfer. To improve the thermal efficiency, nanoparticles are added to the water base fluid and a strong transverse magnetic field is applied. After performing the appropriate similarity transformations, the governing equations for the prescribed flow form a system of PDEs, which are then converted to a system of ODEs. After solving the resulting system analytically, the velocity profile and temperature distribution are expressed in terms of exponential and Gamma functions. The existence of physical threats and the flow field are influenced by factors such as magnetic field, viscoelasticity, and suction/injection. However, the temperature field is influenced by factors including thermal radiation, Prandtl number, and others. The result shows that the axial velocity is influenced by the viscoelastic constraint, magnetic field, and suction/injection parameters. Graphical representations of the effects of mass transpiration on velocity profiles and temperature distribution are provided. It was discovered that Marangoni convection improved the rate of heat transfer. In contrast, it decreases as a result of the applied magnetic energy. Additionally, SWCNT nano liquid is hotter than nano liquid. Numerous commercial and scientific applications of the issue under discussion can be found in fields like aviation and medicine. Under the influence of radiation, the effects of MHD and suction/injection on the fluid's flow and heat transfer properties are investigated. The results of each profile's solution and the results of the interface velocity and rate of surface heat transfer are shown in the form of figures.

A first-principles study of magnetic switching and hysteresis effect in the ferromagnetic Fe metal

The first-principles calculation method used in this study has an extended Hamiltonian, which contains both spin states, so that the spin magnetic moment per unit cell, m , and magnetization vector, M , can be obtained via the spinors of atomic orbitals. Both spin- and orbital- B -field couplings are considered. The magnetic field, B , induces not only components of m and M along their directions, which vanish when the field is cut off, but also bi-stable spontaneous z components, m z and M z . This study reveals that the spin- B -field coupling is energetically too weak to reverse m z / M z directly. The B field is found to reverse the spin polarization of itinerant s p electrons first when B reaches a threshold, which then triggers the reversal of m z / M z via nonlocal exchange interactions with localized d electrons. The hysteresis effect is found to be due to the existence of bi-stable m z / M z and that without a reversed B the spin-polarization of itinerant s p electrons won’t be reversed to trigger magnetic switching. • The first use of spinors to obtain the 3-D magnetization vector in Fe. • The conventional magnetic field is energetically too weak to cause magnetic switching directly. • The magnetic field reverses spin polarization of sp electrons first, which then triggers reversal of magnetization through nonlocal exchange couplings. • The relationship between the calculated magnetization and the magnetic field is hysteresis-loop-like. • The magnetic switching can be assisted by an accompanying strong transverse magnetic field.

Scrutiny of convective MHD second‐grade fluid flow within two alternatively conducting vertical surfaces with Hall current and induced magnetic field

AbstractThe focus of this paper is to examine the heat and mass transport behavior of transient magnetohydrodynamics second‐grade fluid (elastico‐viscous fluid) flow within a vertical channel bounding the porous regime with the Hall phenomenon and induced magnetic field (IMF). The flow system consists of a strong transverse magnetic field that gives rise to the Hall phenomenon and IMF. The right vertical surface of the channel is conducting and oscillations in its plane in the vertical direction while the left vertical surface of the channel is nonconducting and stationary. The suitable dimensionless setup transforms the flow model into a simplified comparable model which is solved analytically with the assistance of the method of separation of variables. Numerical computation is performed with the aid of MATHEMATICA software to explore the results from the analytical solutions. The results of the investigation are helpful in analyzing the nature of the elastic‐viscous fluids. A noteworthy result noted from the investigation is that there appears a reverse flow in the direction of normal flow when the magnetic interaction parameter is large. For the small magnetic interaction parameter, such a flow is not seen. Hall current reduces the strength of the principal IMF and induces the strength of the secondary generated magnetic field. Furthermore, it is explored that the elastico‐viscous nature of the second‐grade fluid has a tendency of enhancing the principal flow and principal‐produced magnetic field.

Hall Current’s Impact on Ionized Ethylene Glycol Containing Metal Nanoparticles Flowing Through Vertical Permeable Channel

From engineering and industrial perspectives, the transportation of non-Newtonian nanofluids in a magnetic environment has become an emergent research area. Motivated by its incessant boosting applications in advanced industries and technologies, a mathematical model is proposed to address the consequences of Hall currents on an unsteady magnetohydrodynamic flow of a partially ionized ethylene glycol (EG) transporting silver nanoparticles (Ag-NPs) through a vertical permeable channel subject to a strong transverse magnetic field, Darcy’s resistance, and thermal radiation. Ethylene glycol (EG) is considered as the base fluid. A uniform suction or injection is imposed at the channel walls. The thermal radiation effect is embraced in the energy equation. Closed-form solutions of the leading dimensionless equations are determined. The impacts of emerging parameters upon the flow profiles are examined and physically argued via profile graphs. The wall shear stresses and the rate of heat transfer are computed numerically, and numerical data on varying thermo-physical parameters are documented in tables. After a detailed analysis, it is documented that an augmentation in Hall parameter gives rise to the profiles of velocity components and shear stresses. Enlarging Casson parameter and Darcy number both urge the magnitude of the velocity components. A graphical comparison is provided for EG and Ag-EG nanofluid. The relatively lowest temperature is noted for Ag-EG nanofluid in comparison with EG. The current model may be featured in industrial processes, food processing, intelligent lubrication technology, high-energy cooling systems, auto cooling machines, etc. This study is very prolific to the analysts to understand the dynamics and heat transfer characteristics of non-Newtonian nanofluids through a straight channel subject to a strong magnetic field.

Searching strong ‘spin’-orbit coupled one-dimensional hole gas in strong magnetic fields

We show that a strong ‘spin’-orbit coupled one-dimensional hole gas is achievable via applying a strong magnetic field to the original two-fold degenerate (spin degeneracy) hole gas confined in a cylindrical Ge nanowire. Both strong longitudinal and strong transverse magnetic fields are feasible to achieve this goal. Based on quasi-degenerate perturbation calculations, we show the induced low-energy subband dispersion of the hole gas can be written as , a form exactly the same as that of the electron gas in the conduction band. Here the Pauli matrices σ z,x represent a pseudo spin (or ‘spin’), because the real spin degree of freedom has been split off from the subband dispersions by the strong magnetic field. Also, for a moderate nanowire radius R = 10 nm, the induced effective hole mass and the ‘spin’-orbit coupling α (0.35 ∼ 0.8 eV Å) have a small magnetic field dependence in the studied magnetic field interval 1 < B < 15 T, while the effective g-factor of the hole ‘spin’ only has a small magnetic field dependence in the large field region.

Numerical simulations of MHD flows around a 180-degree sharp bend under a strong transverse magnetic field

The quasi-two-dimensional flow of a liquid metal subjected to a strong transverse magnetic field around a 180-degree sharp bend is investigated by means of parametric numerical simulations where the Reynolds number Re, Hartmann number Ha and the gap ratio β (defined as the ratio of the gap thickness to the inlet width) vary in the respective ranges [100–50 000], [100–2000] and [0.04–1]. Both steady-state flow solutions and the evolution of unsteady flow regimes can be captured within this parameter space. The critical Reynolds number for transition from steady to unsteady flow increases as Ha increases for all β. It is shown, for 0.04 ⩽ β ⩽ 0.25, the critical Reynolds number remains almost linear relationship with the parameter Re/Ha0.9, whereas for β = 1, the key parameter is dominated by Re/Ha0.6. The present simulations aim to investigate the physical mechanism of this phenomenon and characterizing the position where the vortices are shed from the free shear layer. We discover that the vortices shedding is originated in the outlet region for 0.04 ⩽ β ⩽ 0.25 other than the turning part in bend region for β = 1. Additionally, the free shear layer separates the recirculation bubble from mainstream and its instability is proposed to interpret the transition, commonly known as Kelvin–Helmholtz instability. The effect of a strong transverse magnetic field on flow characteristics is considered such as the length of recirculation bubbles and the pressure drop between inlet and outlet. A further frequency analysis reveals that at the end of vortices shedding, the oblique waves resonance exists, or a new vortex street consisting of the vortices detached from the boundary layer and upstream fluctuations appears. Finally, according to the influence of β on the transition, we present a modified map of fluid regimes for prediction, which provides useful information for improved mixing and heat transport.

A Study of Flow and Heat Transfer of a Nanofluid Over a Vertical Cone With Heat Generation Using Legendre-Galerkin Method

An efficient Legendre-Galerkin method was applied to describe the nanofluid flow along an upward cone and how the heat transfers under the impacts of heat generation and thermal radiation. A strong uniform transverse magnetic field subjects to the flow and perpendicular to the cone surface. Suitable transformations with appropriate variables are presented to put the administering equations and the boundary conditions in a helpful structure for calculation. The arising sets of nonlinear system are settled using a Galerkin method with the Legendre function as a base. The study on the impacts of magnetic, Eckert number, heat source, and Hall parameters on fluid temperature, velocity profiles, local skin-friction coefficient, and Nusselt number are analyzed and introduced in tables and graphs forms. The volume fraction parameter of nanoparticles and their type assumed a significant part to fundamentally decide the stream behavior. Upon validation of the proposed study with special cases from other previous studies in the literature, an excellent agreement is obtained.

Effect of magnetic field on the steady nanofluid flow past obstacle

The fluid flow and heat transfer of a nanofluid past a circular cylinder in a rectangular duct under a strong transverse magnetic field is studied numerically using a quasitwo-dimensional model. Transition from laminar flow with separation to creeping laminar flow is determined as a function of Hartmann number and the volume fraction of nanoparticle, as are critical Hartmann number, and the heat transfer from the heated wall to the fluid. Downstream cross-stream mixing induced by the cylinder wake was found to increase heat transfer. The successive changes in the flow pattern are studied as a function of the Hartmann number. Suppression of vortex shedding occurs as the Hartmann number increases.

Linear global stability of a downward flow of liquid metal in a vertical duct under strong wall heating and transverse magnetic field

A three-dimensional unstable oscillatory instability is found for a downward flow of liquid metal in a vertical duct under strong wall heating and a transverse magnetic field. The unstable oscillatory mode first occurs at the specific flow structure which has an upward reverse flow near the heating wall and a downward flow near the opposite wall. The existence of an inflection point is the key instability mechanism of the three-dimensional oscillatory mode which may be regarded as an alternative physical explanation of the high-amplitude, low-frequency pulsations of temperature in experiments and related numerical simulations.

Enhanced X-ray emission arising from laser-plasma confinement by a strong transverse magnetic field

We analyze, using experiments and 3D MHD numerical simulations, the dynamic and radiative properties of a plasma ablated by a laser (1 ns, 10^{12}–10^{13} W/cm^2) from a solid target as it expands into a homogeneous, strong magnetic field (up to 30 T) that is transverse to its main expansion axis. We find that as early as 2 ns after the start of the expansion, the plasma becomes constrained by the magnetic field. As the magnetic field strength is increased, more plasma is confined close to the target and is heated by magnetic compression. We also observe that after sim 8 ns, the plasma is being overall shaped in a slab, with the plasma being compressed perpendicularly to the magnetic field, and being extended along the magnetic field direction. This dense slab rapidly expands into vacuum; however, it contains only sim 2% of the total plasma. As a result of the higher density and increased heating of the plasma confined against the laser-irradiated solid target, there is a net enhancement of the total X-ray emissivity induced by the magnetization.

Transformation of a submerged flat jet under strong transverse magnetic field

A duct flow generated by a planar jet at the inlet and affected by a magnetic field perpendicular to the jet's plane is analyzed in high-resolution numerical simulations. The case of very high Reynolds and Hartmann numbers is considered. It is found that the flow structure is drastically modified in the inlet area. It becomes determined by three new planar jets oriented along the magnetic field lines: two near the walls and one in the middle of the duct. The downstream evolution of the flow includes the Kelvin-Helmholtz instability of the jets and slow decay of the resulting quasi-two-dimensional turbulence.

Force detection of high-frequency electron spin resonance near room temperature using high-power millimeter-wave source gyrotron

We report the measurement of force-detected electron spin resonance (FDESR) at 154 GHz using a gyrotron. The high output power allows the use of a strong transverse magnetic field larger than 10−4 T, which is sufficient to cause ESR saturation. We obtained the FDESR signal with a high spin sensitivity on the order of 1012 spins/G at 280 K. Our system has promising applications in high-frequency ESR studies of low-spin concentration samples, such as metalloprotein solutions.

MHD mixed convection on an inclined stretching plate in Darcy porous medium with Soret effect and variable surface conditions

AbstractThis work is concerned with a steady 2D laminar MHD mixed convective flow of an electrically conducting Newtonian fluid with low electrical conductivity along with heat and mass transfer on an isothermal stretching semi-infinite inclined plate embedded in a Darcy porous medium. Along with a strong uniform transverse external magnetic field, the Soret effect is considered. The temperature and concentration at the wall are varying with distance from the edge along the plate, but it is uniform at far away from the plate. The governing equations with necessary flow conditions are formulated under boundary layer approximations. Then a continuous group of symmetry transformations are employed to the governing equations and boundary conditions which determine a set of self-similar equations with necessary scaling laws. These equations are solved numerically and similar velocity, concentration, and temperature for various values of involved parameters are obtained and presented through graphs. The momentum boundary layer thickness becomes larger with increasing thermal and concentration buoyancy forces. The flow boundary layer thickness decreases with the angle of inclination of the stretching plate. The concentration increases considerably for larger values of the Soret number and it decreases with Lewis number. The skin friction coefficient increases for increasing angle of inclination of the plate, magnetic and porosity parameters, however it decreases for rise of thermal and solutal buoyancy parameters. In this double diffusive boundary layer flow, Nusselt and Sherweed numbers increase for rise of thermal and solutal buoyancy parameters, Prandtl number, but they behave opposite nature in case of angle of inclination of the plate, magnetic and porosity parameters. The Sherwood number increases for increasing Lewis number but it decreases for increasing Soret number.

Recent Progress in Birdcage RF Coil Technology for MRI System.

The radio frequency (RF) coil is one of the key components of the magnetic resonance imaging (MRI) system. It has a significant impact on the performance of the nuclear magnetic resonance (NMR) detection. Among numerous practical designs of RF coils for NMR imaging, the birdcage RF coil is the most popular choice from low field to ultra-high field MRI systems. In the transmission mode, it can establish a strong and homogeneous transverse magnetic field B1 for any element at its Larmor frequency. Similarly, in the reception mode, it exhibits extremely high sensitivity for the detection of even faint NMR signals from the volume of interest. Despite the sophisticated 3D structure of the birdcage coil, the developments in the design, analysis, and implementation technologies during the past decade have rendered the development of the birdcage coils quite reasonable. This article provides a detailed review of the recent progress in the birdcage RF coil technology for the MRI system.

Understanding asymmetry in electromagnetically induced transparency for 87Rb in strong transverse magnetic field

We present the results of our experimental investigation performed for D2 line of 87Rb. In this work, we have studied the phenomenon of electromagnetically induced transparency of 87Rb in presence of a transverse magnetic field and it is interesting to find the EIT spectrum shows signature of the closely lying hyperfine excited states in particular F′ = 1. We choose two different configurations for our study namely, Λ1 and Λ2 realised by locking probe beam at two different transition i.e. |F = 1〉 → |F′ = 2〉 and |F = 2〉 → |F′ = 2〉 respectively. We observe asymmetric features in both configurations at high magnetic field and for Λ1 configuration we find complete conversion from transmission to absorption. We explain the observations by quantitative assessment of the impurities in the dark states which arises because of the influence of the neighbouring states. We substantiate our experimental findings with density based numerical calculations.