Azimuthal Magnetic Field Research Articles

Cylindrical shock wave propagation in a self-gravitating rotational axisymmetric perfect gas under the influence of azimuthal or axial magnetic field and monochromatic radiation with variable density

Cylindrical shock wave propagation in a self-gravitating rotational axisymmetric perfect gas under the influence of azimuthal or axial magnetic field and monochromatic radiation with variable density

On the Causes of the Slow Solar Wind: 1. The Solar Unipolar Induction Currents

AbstractThe cause of the solar wind is sought on a large‐scale (J × B) force resulting from the solar unipolar induction current, rather than coronal heating and small‐scale processes in the corona. In this paper, we consider the unipolar induction system considered by Alfven (1981, https://doi.org/10.1007/978-94-009-8374-8) the polar current (1.5 × 109 A) flowing out from the polar region of the sun spreads down longitudinally, which produces azimuthal magnetic fields. We considered two models, A and B. In Model A, the current spreads down fairly uniform in five divided regions of the heliosphere (rather than flowing only along the outer surface of the heliosphere). The resulting (J × B) force is mainly directed outward, causing an outward flow of the heliospheric plasmas. However, in this case, the speed at a distance of 1 AU is only 1 km/s, although the acceleration in each divided region is much greater than the solar gravity. In Model B, one third of the dynamo current is assumed to be concentrated in the area between 9.5 and 10.5 (where denotes the solar radius) and B = 10−6 T (103 nT) at 10 . The acceleration is estimated to be 1.4 × 102 m/s2 and the resulting speed at 1 AU is 200 km/s. Therefore, there is a possibility that the solar unipolar induction provides partially a new possibility for the cause of a slow, bulk flow of the solar wind.

Computation of Electromagnetic Field Generated by Lightning Strikes to a Tall Object in Presence of a Vertically Stratified Ground Using the 3D-FDTD Method

In this paper, a study about lightning electromagnetic radiation in a complex geometry is presented. Indeed, it is about examining the effect of a vertically stratified ground presence on the electromagnetic field generated by lightning strikes to a tall object (tower), using the three dimension Finite Difference Time-Domain (3D-FDTD) method. The space-time distribution of the current along the lightning channel and along the tower is modeled and calculated using the Transmission Line (TL) model extended in order to include a tall strike object. The developed computing code is validated by the comparison with the results obtained in the specialized literature. In this comparison, a satisfactory agreement between results is observed. According to the obtained results it is shown that both up-ground and under-ground electromagnetic field components (vertical and horizontal electric field and azimuthal magnetic field) magnitudes are affected by the presence of the vertically stratified ground.

Magnetic field induction and magnetic force distribution profiles in plasma focus discharge device

We report a simple-to-perform technique to investigate the distribution of the azimuthal magnetic field induction, B θ , and the induced magnetic force acting on the plasma current sheath (PCS) in a plasma focus (PF) discharge. This in situ measurement technique can undoubtedly be beneficial when other fast-imaging techniques are not available. techniques are not available. Experimental work was conducted in the low-energy Mather-type EAEA-PF1 device operated in argon. The axial distribution (B θ ) z along the coaxial electrodes system was measured with a four magnetic-probe set technique at different radial distances (r = 2.625 × 10−2 to 4.125 × 10−2 m) within the annular space between the coaxial electrodes during the 1st and 2nd half cycles of the discharge current waveform, where inner electrode of coaxial electrode system has a +ve polarity and −ve polarity, respectively. Axial, radial and total magnetic force distribution profiles were estimated from B θ data. Investigation of PCS shape in terms of its inclination (curvature) angle, θ, along the axial rundown phase and the correlation between the magnetic forces per unit volume acting on the PCS, the inclination angle θ of the PCS, and the formation of a powerful PF action during the 1st and 2nd half cycles is carried out. Dependence of inclination angle, θ, on total magnetic force per unit volume acting on PCS axial motion was studied, separately, during the 1st and 2nd half cycles.

Azimuthal magnetic field distribution in gas-puff Z-pinch implosions with and without external magnetic stabilization.

An experimental study of the magnetic field distribution in gas-puff Z pinches with and without a preembedded axial magnetic field (B_{z0}) is presented. Spatially resolved, time-gated spectroscopic measurements were made at the Weizmann Institute of Science on a 300 kA, 1.6 μs rise time pulsed-power driver. The radial distribution of the azimuthal magnetic field, B_{θ}, during the implosion, with and without a preembedded axial magnetic field of B_{z0}=0.26T, was measured using Zeeman polarization spectroscopy. The spectroscopic measurements of B_{θ} were consistent with the corresponding values of B_{θ} inferred from current measurements made with a B-dot probe. One-dimensional magnetohydrodynamic simulations, performed with the code trac-ii, showed agreement with the experimentally measured implosion trajectory, and qualitatively reproduced the experimentally measured radial B_{θ} profiles during the implosion when B_{z0}=0.26T was applied. Simulation results of the radial profile of B_{θ} without a preembedded axial magnetic field did not qualitatively match experimental results due to magneto-Rayleigh-Taylor (MRT) instabilities. Our analysis emphasizes the importance of MRT instability mitigation when studying the magnetic field and current distributions in Z pinches. Discrepancies of the simulation results with experiment are discussed.

The effect of the inclined lightning channel on electromagnetic fields and the induced voltages on overhead lines

In this study, the effect of lightning channel inclination on above-ground lightning electromagnetic (LEM) fields and their induced voltages on the overhead lines at different distances from stroke location (SL) in the presence of lossy soil ground is investigated. To this end, the finite element method is used to solve the full-wave Maxwell’s equations. The results show that channel inclinations affect LEM fields significantly at all distances from the SL. At an equal distance from SL, the observation point position relative to the lightning channel is important, and LEM fields of the points located on the horizontal axis of the lightning channel are affected more than other points. If the ground is more conductive, increasing channel inclination affects the radial component of the electric field at a close distance to the SL more; if the ground is more resistive, increasing channel inclination angle affects the radial component of the electric field at a far distance to SL more significantly. The vertical electric fields and azimuthal magnetic fields are slightly affected by ground conductivity but significantly affected by the position and channel inclination angle. Seven different states are considered for the channel position relative to the overhead line, and the lightning-induced voltage along the line is calculated at three points. The obtained results show that position and soil electrical parameters significantly affect the peak and wave shape of the induced voltage. If the lightning channel passes above the overhead line, the induced voltage peak will increase at points near the SL. If the horizontal axis of the lightning channel is parallel to the overhead line, the induced voltage peak will increase for the ground with lower conductivity by increasing the channel inclination angle. In this case, at distances farther from the SL, the effect of increasing the channel angle is negligible for high-conductivity grounds, but the induced voltage peak for less conductive grounds will increase. If the lightning channel's horizontal axis is perpendicular to the overhead line and the lightning channel does not pass above the overhead line, close to the SL, the induced voltage peak will decrease by increasing channel angle. At points far from the SL, increasing the channel angle in the low-conductivity ground will increase the voltage peak, and grounds with larger conductivity will decrease the voltage peak.

A self-similar solution for unsteady adiabatic and isothermal flows behind the shock wave in a non-ideal gas using Lie group analysis method with azimuthal or axial magnetic field in rotating medium

The similarity solutions using Lie group analysis for shock wave propagation in a rotational axisymmetric non-ideal gas with azimuthal or axial magnetic field in the case of isothermal and adiabatic flows are obtained. All possible cases of similarity solutions are discussed using the Lie group analysis for the isothermal and adiabatic flows. The arbitrary constants involved in the generators of local Lie groups bring various possible cases of solutions with exponential law and power law shock paths. Similarity solution for isothermal and adiabatic flows with power law shock path is discussed in detail. The density of ambient medium is taken to be constant. The axial and azimuthal fluid velocities and magnetic field in the ambient medium are assumed to be varying according to power law. The effect on shock wave strength and that on the flow variables due to variation of the Alfven Mach number, adiabatic index of the gas, non-idealness parameter, rotational parameter and initial magnetic field variation exponent are investigated. It is found that these parameters have decaying effects on shock wave. The obtained results in the case of isothermal and adiabatic flows are also compared with each other.

Angular momentum transport by magnetoconvection and the magnetic modulation of the solar differential rotation

In order to explain the variance of the solar rotation law during the activity minima and maxima, the angular momentum transport by rotating magnetoconvection is simulated in a convective box penetrated by an inclined azimuthal magnetic field. Turbulence-induced kinetic and magnetic stresses and the Lorentz force of the large-scale magnetic background field are the basic transporters of angular momentum. Without rotation, the sign of the magnetic stresses naturally depends on the signs of the field components as positive (negative) BθBϕ transport the angular momentum poleward (equatorward). For fast enough rotation, however, the turbulence-originated Reynolds stresses start to dominate the transport of the angular momentum flux. The simulations show that positive ratios of the two meridional magnetic field components to the azimuthal field reduce the inward radial as well as the equatorward latitudinal transport, which result from hydrodynamic calculations. Only for BθBϕ > 0 (generated by solar-type rotation laws with an accelerated equator) does the magnetic-influenced rotation at the solar surface prove to be flatter than the nonmagnetic profile together with the observed slight spin-down of the equator. The latter phenomenon does not appear for antisolar rotation with polar vortex as well as for rotation laws with prevailing radial shear.

Shock wave propagation in perfectly conducting rotational axisymmetric two-phase medium with increasing energy under the action of heat conduction and radiation heat flux

The distribution of divergent cylindrical shock waves, under the effect of the variable azimuthal or axial magnetic field in space, in a perfectly conducting rotational axisymmetric dusty gas is studied. The profiles of the fluid variables were determined using numerical estimation. The effects of changing the piston velocity index, rotational parameter, and Shock Cowling number are studied. The result is that pressure and density disappear in the piston, and then the vacuum is produced at the axis of symmetry, which is perfectly in conformity with the conditions for producing a shock wave in the laboratory when the azimuthal magnetic field is present.

Destabilization of super-rotating Taylor–Couette flows by current-free helical magnetic fields

In an earlier paper we showed that the combination of azimuthal magnetic fields and super-rotation in Taylor–Couette flows of conducting fluids can be unstable against non-axisymmetric perturbations if the magnetic Prandtl number of the fluid is $\textrm {Pm}\neq 1$ . Here we demonstrate that the addition of a weak axial field component allows axisymmetric perturbation patterns for $\textrm {Pm}$ of order unity depending on the boundary conditions. The axisymmetric modes only occur for magnetic Mach numbers (of the azimuthal field) of order unity, while higher values are necessary for the non-axisymmetric modes. The typical growth time of the instability and the characteristic time scale of the axial migration of the axisymmetric mode are long compared with the rotation period, but short compared with the magnetic diffusion time. The modes travel in the positive or negative $z$ direction along the rotation axis depending on the sign of $B_\phi B_z$ . We also demonstrate that the azimuthal components of flow and field perturbations travel in phase if $|B_\phi |\gg |B_z|$ , independent of the form of the rotation law. Within a short-wave approximation for thin gaps it is also shown (in an appendix) that for ideal fluids the considered helical magnetorotational instability only exists for rotation laws with negative shear.

Analysis of magnetogasdynamic spherical shock wave in dusty real gas with gravitational field and monochromatic radiation

For the unsteady, self-similar flow-field from spherical shock to a moving piston behind it in a dusty gas, solutions are obtained. The dust consists of tiny solid particles continually scattered in a non-ideal gas. The medium is subjected to gravitational and magnetic fields with monochromatic radiation. The Roche model is appropriate here, i.e., because of a central mass of its origin the gravitational field exists. The flow of radiation is thought to pass into a non-ideal electrical gas with static intensity and energy is only captured by shocks in the opposite direction of radiation. The outcomes of having an impact of the gravitational or magnetic fields and the absence of these fields are compared. It is exciting to be aware that on the piston, the pressure and density disappear in the presence of an azimuthal magnetic field, and consequently at the middle of symmetry a vacuum is formed, which is in high-quality agreement to generate a shock wave in the laboratory.

Linear stability analysis of a Newtonian ferrofluid cylinder under a magnetic field

Abstract

Simultaneous Observation of an Auroral Dawn Storm With the Hubble Space Telescope and Juno

AbstractOn July 13, 2016, the Hubble Space Telescope observed the onset of a dawn storm in Jupiter's northern ultraviolet aurora, while the NASA Juno spacecraft simultaneously traversed the dawnside outer magnetosphere. This represents the first concurrent auroral and in situ magnetospheric observations of the onset of a dawn storm at Jupiter. Mapping the auroral emission to the magnetosphere reveals the dawn storm corresponds to a source region at ∼60 Jupiter radii, and the eastward edge propagates toward local noon at speeds exceeding corotation. Particle observations from Jovian Auroral Distributions Experiment (JADE) and Jupiter Energetic particle Detector Instrument (JEDI) reveal the presence of enhanced hot plasma density in the outer magnetosphere during this interval, and pitch angle distributions measured with JEDI reveal pronounced field‐aligned proton and heavy ion motion. Juno magnetometer (MAG) signatures reveal a reversal in the azimuthal magnetic field at the time of storm onset, suggesting acceleration of the hot plasma population above typical sub‐corotational speeds. JEDI also detects a region of energetic particles which persists throughout the day following the storm, a feature which is not observed during subsequent perijoves. We interpret this dawn storm as the result of reconnection at earlier local times, possibly associated with a disruption of the azimuthal magnetodisk current.

Magnetic inhibition of the recollimation instability in relativistic jets

ABSTRACT In this paper, we describe the results of three-dimensional relativistic magnetohydrodynamic simulations aimed at probing the role of regular magnetic field on the development of the instability that accompanies recollimation of relativistic jets. In particular, we studied the recollimation driven by the reconfinement of jets from active galactic nuclei (AGN) by the thermal pressure of galactic coronas. We find that a relatively weak azimuthal magnetic field can completely suppress the recollimation instability in such jets, with the critical magnetization parameter σcr < 0.01. We argue that the recollimation instability is a variant of the centrifugal instability (CFI) and show that our results are consistent with the predictions based on the study of magnetic CFI in rotating fluids. The results are discussed in the context of AGN jets in general and the nature of the Fanaroff–Riley morphological division of extragalactic radio sources in particular.

Modeling and analysis of a magnetoelastic annular membrane placed in an azimuthal magnetic field

This work presents the development of a 2D nonlinear magnetoelastic framework for a thin membrane undergoing large deformations. An asymptotic theory is obtained, starting from the 3D variational magnetostatic and force balance equations for a weakly magnetizable material. The model is subsequently specialized to axisymmetry and applied to a pre-stretched annular membrane deforming under azimuthal magnetic field and transverse pressure loading. Parametric studies are performed by varying the pre-stretch, magnetic field, and transverse pressure inputs.

Helical Magnetic Cavities: Kinetic Model and Comparison With MMS Observations

AbstractMagnetic cavities are sudden depressions of magnetic field strength widely observed in the space plasma environments, which are often accompanied by plasma density and pressure enhancement. To describe these cavities, self‐consistent kinetic models have been proposed as equilibrium solutions to the Vlasov‐Maxwell equations. However, observations from the Magnetospheric Multi‐Scale (MMS) constellation have shown the existence of helical magnetic cavities characterized by the presence of azimuthal magnetic field, which could not be reconstructed by the aforementioned models. Here, we take into account another invariant of motion, the canonical axial momentum, to construct the particle distributions and accordingly modify the equilibrium model. The reconstructed magnetic cavity shows excellent agreement with the MMS1 observations not only in the electromagnetic field and plasma moment profiles but also in electron pitch‐angle distributions. With the same set of parameters, the model also predicts signatures of the neighboring MMS3 spacecraft, matching its observations satisfactorily.

Magnetogasdynamic shock wave propagation using the method of group invariance in rotating medium with the flux of monochromatic radiation and azimuthal magnetic field

Abstract The propagation of a cylindrical shock wave in rotating medium with azimuthal magnetic field under the action of monochromatic radiation using a method of group invariance is investigated. To derive similarity solutions as well as exact solutions, the group invariance technique is used. All classes of the solutions depending on the absorption coefficient are discussed by considering absorption coefficient to be variable or constant. A similarity solution is obtained, when the absorption coefficient is assumed to be variable. Two cases of solutions with a power law shock path are obtained by the different choices of arbitrary constants involving in the infinitesimal generators of the Lie group of transformations. To obtain the similarity solution in the case of the power law shock path, the density, magnetic field, axial and azimuthal velocity components are assumed to be varying and obeying power laws in the undisturbed medium. It is observed that with increase in the values of Alfven Mach number, adiabatic exponent and rotational parameter, shock strength decreases. The effects of variation of magnetic field strength, adiabatic exponent, rotational parameter and initial magnetic field variation index on the flow variables and on shock waves are analyzed graphically. Also, all classes of exact solutions are obtained by considering a constant absorption coefficient.

Nonlinear hydromagnetic instability of oscillatory rotating rigid-fluid columns

The current paper is concerned with the nonlinear stability analysis of rotating magnetic fluid columns. The rotation sources are a mixture of both uniform and oscillating behavior. The motivation behind tackling this topic is the increasing interest in atmospheric and oceanic motions. The system consists of two magnetic phase fluid that fills two infinite vertical cylinders. An azimuthal uniform magnetic field is penetrated on the system. The governing equations of motion, in terms of the Coriolis force and reduced pressure, along with Maxwell’s equation in the quasi-static approximations are considered. Consequently, the disturbance of the interface has an azimuthal behavior. The fluids are fully saturated in porous media. In light of the implication of the nonlinear boundary conditions, the solutions of the linearized equations of motion resulted in a nonlinear characteristic dispersion equation. Utilizing the homotopy perturbation technique, this equation is analyzed. A modification of the latter equation is made to seem like a nonlinear Klein–Gordon equation. The stability criteria are realized in linear as well as nonlinear approaches. A set of diagrams is graphed to illustrate the effects of several non-dimensional numbers on the stability profile in resonance as well as non-resonance cases.

Mesh Dependency on a Partial Element Equivalent Circuit Model for an NI HTS Coil

In general, when evaluating a performance of a high-temperature superconductor (HTS) no-insulation (NI) magnet, current, voltage, and center magnetic field are considered as main parameters. To achieve detailed results of the main parameters of NI HTS magnet, distributed circuits which can analyze internal physical phenomena of the magnet are required. Among distributed circuits, a circuit that divides inside of each turn into several cells in azimuthal direction is called a Partial Element Equivalent Circuit (PEEC). In this paper, we compared the main parameters of simple NI HTS magnet according to different numbers of cells in PEEC. When the number of cells per turn is different, average azimuthal current and center magnetic field of each turn coincide with each other, but voltage does not. The result suggests that PEECs with different number of cells per turn may be different circuits for each others, and the main reason for this seems to be that an accurate discussion of the characteristic resistance according to the length was not made.

Performance limitations of active plasmonic devices based on magnetic field detuning of the surface plasmon-polariton resonance in subwavelength semiconductor wires

Subwavelength plasmonic wires provide a very simple, ultracompact, and efficient platform for active plasmonics. We theoretically investigate magnetically switched transparency in subwavelength semiconductor wires. The main difficulty limiting the performance of magnetoplasmonic devices and subwavelength optical isolators is the need to use a strong magnetic field. We reveal that the required magnetic field intensity in subwavelength semiconductor wires is twice higher than that in planar semiconductor interfaces and is determined by the carrier mobility of the constituent semiconductor and does not directly depend on other material parameters such as the coating dielectric permittivity, the semiconductor carrier density, and the electron's effective mass. The azimuthal magnetic field can be excited by a direct electric current or by an optical pump through the semiconductor wires. Our finding points to the important limitations on the performance of active plasmonic devices based on magneto-optical transparency in the plasmonic wires.