Uniform Ambient Magnetic Field Research Articles

Axisymmetric MHD viscous flow about a highly-slipping sphere translating parallel with a uniform ambient magnetic field

The slow translation of a highly-slipping sphere with radius a in an unbounded viscous conducting Newtonian liquid with constant viscosity μ and conductivity σ is investigated. The liquid is subject to a steady uniform magnetic field B parallel to the sphere velocity, flows about the sphere and exerts on its a drag force. The resulting axisymmetric MHD flow is expanded as a serie of fundamental flows earlier gained elsewhere for a different Oseen flow problem. The coefficients entering in the serie are determined by enforcing the impermeability and zero tangent stress conditions on the sphere surface, As a result, the highly-slipping sphere drag coefficient Cd is numerically obtained and its sensitivity to the problem Hartmann number Ha=a|B|/(μ/σ)1/2 is examined. Moreover, a polynomial handy formula for Cd is proposed for Ha ≤ O(1) and the computed velocity patterns are presented and discussed for Ha=1,10. Tables 2, Figs 4, Refs 12.

Impact of partially thermal electrons on the propagation characteristics of extraordinary mode in relativistic regime

Abstract On employing linearized Vlasov–Maxwell equations the solution of relativistic electromagnetic extraordinary mode is investigated for the wave propagating perpendicular to a uniform ambient magnetic field (in the presence of arbitrary magnetic field limit i.e., ω > Ω > k.v) in partially degenerate (i.e., for T F ≥ T and T ≠ 0) electron plasma under long wavelength limit (ω ≫ k.v). Due to the inclusion of weak quantum degeneracy the relativistic Fermi–Dirac distribution function is expanded under the relativistic limit ( m 0 2 c 2 2 p 2 < 1 $\frac{{m}_{0}^{2}{c}^{2}}{2{p}^{2}}< 1$ ) to perform momentum integrations which generate the Polylog functions. The propagation characteristics and shifting of cutoff points of the extraordinary mode are examined in different relativistic density and magnetic field ranges. The novel graphical results of extraordinary mode in relativistic quantum partially degenerate (for μ T = 0 $\frac{\mu }{T}=0$ ), nondegenerate (for μ T ≈ − 1 $\frac{\mu }{T}\approx -1$ ) and fully/completely degenerate (for μ T ≈ $\frac{\mu }{T}\approx $ 1) environments are obtained and the previously reported results are retraced as well.

Numerical modeling on hybrid nanofluid (Fe3O4+MWCNT/H2O) migration considering MHD effect over a porous cylinder.

The free convective hybrid nanofluid (Fe3O4+MWCNT/H2O) magnetized non-Darcy flow over a porous cylinder is examined by considering the effects constant heat source and uniform ambient magnetic field. The developed coupled PDEs (partial differential equations) are numerically solved using the innovative computational technique of control volume finite element method (CVFEM). The impact of increasing strength of medium porousness and Lorentz forces on the hybrid nanofluid flow are presented through contour plots. The variation of the average Nusselt number (Nuave) with the growing medium porosity, buoyancy forces, radiation parameter, and the magnetic field strength is presented through 3-D plots. It is concluded that the enhancing medium porosity, buoyancy forces and radiation parameter augmented the free convective thermal energy flow. The rising magnetic field rises the temperature of the inner wall more drastically at a smaller Darcy number. An analytical expression for Nusselt number (Nuave) is obtained which shows its functional dependence on the pertinent physical parameters. The augmenting Lorentz forces due to the higher estimations of Hartmann retard the hybrid nanoliquid flow and hence enhance the conduction.

Euler Potentials for the Earth Magnetic Field With Field‐Aligned Currents

AbstractEuler potentials of the Earth's dipole magnetic field with field‐aligned currents are found. The results generalize ones obtained earlier for systems of plane currents parallel to an ambient uniform magnetic field. A real current system corresponding to an observed increase of the magnetic field measured by a low‐altitude spacecraft is used in this modeling. Parameters of charged particle trajectories, such as length and period, are determined for typical and strongly disturbed conditions. A particle distribution function is calculated.

Electrostatic solitary pulses in magnetized relativistic spin-polarized quantum plasma

A Magnetized Relativistic Quantum Hydrodynamics model is used to study the behavior of low fRequency electrostatic solitons in relativistic magnetized spin-polarized quantum plasma. The constituents of the plasma are inertia-less relativistic quantum electrons having concentration of both spin-up and spin-down species, and relativistic classical ions. We have used two-dimensional geometry in which a uniform ambient magnetic field is applied in the z-direction i.e. . The linear analysis shows the presence of two types of modes; slow (acoustic) mode and a fast Langmuir-like mode. A nonlinear Zakharov–Kuznetsov (ZK) type equation is derived for the electrostatic potential by using reductive perturbation technique. The dependence of the spin density polarization ratio κ on the properties of solitary wave profile is being investigated. It has been demonstrated that amplitude as well as width of the soliton depend significantly on the spin density polarization ratio, obliqueness and relativistic effects. We have also observed that the soliton solution of the ZK equation is unstable to the oblique perturbations. The instability growth rate varies appreciably with the density polarization and relativistic effects.

Design of Magnetic Shielding and Field Coils for a TES X-ray Microcalorimeter Test Platform

The performance of transition-edge sensors (TES) and their SQUID multiplexed readouts is very sensitive to ambient magnetic field and its fluctuations. In order to run ground experiments on thousands of X-ray TES microcalorimeters with a small uniform ambient magnetic field (< 1 μT, with a uniformity < 0.1 μT), we need a very low ambient field to be trapped into the superconducting magnetic shields. We have designed a sub-Kelvin test platform to reach these specifications. For this purpose, we modeled a new design for the shielding consisting of a series of different mu-metal and superconducting shields, including a niobium shield at 50 mK, a cryoperm (A4K) shield at 3 K, and a mu-metal shield at 300 K. A magnetic field coil is used to vary the local perpendicular magnetic field over the TES array. To optimize this field, we have studied a number of different field-coil designs and the impact of the different shield geometries, in order to reach the required field uniformity.

Axisymmetric MHD viscous flows bounded by a solid plane normal to a uniform ambient magnetic field: fundamental flows and application to a solid sphere translating normal to the wall

This work first determines two axisymmetric fundamental Magneto Hydrodynamic (MHD) flows induced, in a conducting Newtonian liquid domain bounded by a plane wall, by distributing either radial or a...

Fokker-Planck coefficients for a magnetized ion-electron plasma

The Fokker-Planck coefficients are developed for an ion-electron plasma in an ambient uniform magnetic field. The calculation is based on the binary collision model where a single encounter between an ion and an electron is first considered. The collision is taken as a perturbation to the free helical motion of the two particles involved, and the terms are kept up to the second order. The collision process is reformulated in terms of the changes of the perpendicular and parallel speeds and gyrophase shift. This new approach allows us to properly take into account the persisting helical motion in the magnetic field when the collisional interaction ceases.

Creeping axisymmetric MHD flow about a sphere translating parallel with a uniform ambient magnetic field

Creeping axisymmetric MHD flow about a sphere translating parallel with a uniform ambient magnetic field

RECONNECTION-DRIVEN CORONAL-HOLE JETS WITH GRAVITY AND SOLAR WIND

ABSTRACT Coronal-hole jets occur ubiquitously in the Sun's coronal holes, at EUV and X-ray bright points associated with intrusions of minority magnetic polarity. The embedded-bipole model for these jets posits that they are driven by explosive, fast reconnection between the stressed closed field of the embedded bipole and the open field of the surrounding coronal hole. Previous numerical studies in Cartesian geometry, assuming uniform ambient magnetic field and plasma while neglecting gravity and solar wind, demonstrated that the model is robust and can produce jet-like events in simple configurations. We have extended these investigations by including spherical geometry, gravity, and solar wind in a nonuniform, coronal hole-like ambient atmosphere. Our simulations confirm that the jet is initiated by the onset of a kink-like instability of the internal closed field, which induces a burst of reconnection between the closed and external open field, launching a helical jet. Our new results demonstrate that the jet propagation is sustained through the outer corona, in the form of a traveling nonlinear Alfvén wave front trailed by slower-moving plasma density enhancements that are compressed and accelerated by the wave. This finding agrees well with observations of white-light coronal-hole jets, and can explain microstreams and torsional Alfvén waves detected in situ in the solar wind. We also use our numerical results to deduce scaling relationships between properties of the coronal source region and the characteristics of the resulting jet, which can be tested against observations.

Comparison of electric dipole and magnetic loop antennas for exciting whistler modes

The excitation of low frequency whistler modes from different antennas has been investigated experimentally in a large laboratory plasma. One antenna consists of a linear electric dipole oriented across the uniform ambient magnetic field B0. The other antenna is an elongated loop with dipole moment parallel to B0. Both antennas are driven by the same rf generator which produces a rf burst well below the electron cyclotron frequency. The antenna currents as well as the wave magnetic fields from each antenna are measured. Both the antenna currents and the wave fields of the loop antenna exceed that of the electric dipole by two orders of magnitude. The conclusion is that loop antennas are far superior to dipole antennas for exciting large amplitude whistler modes, a result important for active wave experiments in space plasmas.

Traveling Wave Solutions of the Incompressible Ideal Hall Magnetohydrodynamics**Supported by the National Natural Science Foundation of China under Grant No 11375190.

The solutions of incompressible ideal Hall magnetohydrodynamics are obtained by using the traveling wave method. It is shown that the velocity and magnetic field parallel to the wave vector can be arbitrary constants. The velocity and magnetic field perpendicular to the wave vector are both helical waves. Moreover, the amplitude of the velocity perpendicular to the wave vector is related to the wave number and the circular frequency. In addition, further studies indicate that, no matter whether the uniform ambient magnetic field exists or not, the forms of the traveling wave solutions do not change.

Motion of an insulating solid particle near a plane boundary under the action of uniform ambient electric and magnetic fields

Motion of an insulating solid particle near a plane boundary under the action of uniform ambient electric and magnetic fields

Free-Space Fundamental Solution of a 2D Steady Slow Viscous MHD Flow

The fundamental free-space 2D steady creeping MHD flow produced by a concentrated point force of strength g located at a so-called source point x0 in an unbounded conducting Newtonian liquid with uniform viscosity μ and conductivity σ>0 subject to a prescribed uniform ambient magnetic field B=Be1 is analytically obtained. More precisely, not only the produced flow pressure p and velocity u but also the resulting stress tensor field σ are expressed at any observation point x≠x0 in terms of usual modified Bessel functions, the vectors g,x−x0 and the so-called Hartmann layer thickness d=(μ/σ−−−√)/B (see Hartmann (1937)). The resulting basic flows obtained for g either parallel with or normal to the magnetic field B are examined and found to exhibit quite different properties.

MHD modelling of coronal loops: injection of high-speed chromospheric flows

Observations reveal a correspondence between chromospheric type II spicules and bright upwardly moving fronts in the corona observed in the EUV band. However, theoretical considerations suggest that these flows are unlikely to be the main source of heating in coronal magnetic loops. We investigate the propagation of high-speed chromospheric flows into coronal magnetic flux tubes, and the possible production of emission in the EUV band. We simulate the propagation of a dense $10^4$ K chromospheric jet upwards along a coronal loop, by means of a 2-D cylindrical MHD model, including gravity, radiative losses, thermal conduction and magnetic induction. The jet propagates in a complete atmosphere including the chromosphere and a tenuous cool ($\sim 0.8$ MK) corona, linked through a steep transition region. In our reference model, the jet's initial speed is 70 km/s, its initial density is $10^{11}$ cm$^{-3}$, and the ambient uniform magnetic field is 10 G. We explore also other values of jet speed and density in 1-D, and of magnetic field in 2-D, and the jet propagation in a hotter ($\sim 1.5$ MK) background loop. While the initial speed of the jet does not allow it to reach the loop apex, a hot shock front develops ahead of it and travels to the other extreme of the loop. The shock front compresses the coronal plasma and heats it to about $10^6$ K. As a result, a bright moving front becomes visible in the 171 \AA\ channel of the SDO/AIA mission. This result generally applies to all the other explored cases, except for the propagation in the hotter loop. For a cool, low-density initial coronal loop, the post-shock plasma ahead of upward chromospheric flows might explain at least part of the observed correspondence between type II spicules and EUV emission excess.

Euler potentials for two current sheets of nonzero thickness along ambient uniform magnetic field

Euler potentials of two current sheets of nonzero thickness parallel or antiparallel to each other and aligned with a uniform ambient magnetic field are constructed analytically. The results generalize ones obtained earlier for systems of two line currents and of two current sheets with zero thickness. Conditions for particle mirroring in this field structure are investigated. The results can be applied to Birkeland currents.

Resistive magnetohydrodynamic model for cylindrical plasma expansion in a magnetic field

The study of hot plasma expansion in a magnetic field is of interest for many laboratory and astrophysical applications. In this paper, an exactly solvable analytical model is proposed for an expanding resistive plasma in an external magnetic field in the regime in which the magnetic field does not perturb the plasma motion. The model is based on a class of exact solutions for the purely radial expansion of the plasma in the absence of a magnetic field. This approximation permits the reduction of the electromagnetic problem to consideration of a diffusion equation for the magnetic field. Explicit solutions are derived for a resistive cylindrical plasma expanding into a uniform ambient magnetic field. Some numerical examples related to the laser-produced plasma experiments are presented.

Euler potentials for two current sheets along ambient uniform magnetic field

Euler potentials of two current sheets of finite width parallel or antiparallel to each other and aligned with a uniform ambient magnetic field are constructed analytically. It is shown how analytic treatment can be simplified using complex number analysis. Our approach generalizes results obtained earlier for a system of two line currents (wires). In the present solution the latter system represents a limiting case, and differences between results from configurations with sheets/wires are discussed. The solution is applied for study of bouncing motion of particles trapped between mirror points of this field structure. The result can be applied to Birkeland currents and to laboratory plasma experiments.

Motion of arbitrary 2-bubble clusters immersed in a conducting liquid when subject to uniform ambient electric and magnetic fields

This work examines the slow viscous migration of two insulting spherical bubbles freely suspended in a conducting Newtonian liquid when subject to superposed uniform and steady electric and magnetic fields. Assuming vanishing Reynolds and Hartmann numbers makes it possible to end up with decoupled problems for the disturbed electric field and the Stokes flow about the 2-bubble cluster. Such problems are efficiently addressed by resorting to a boundary approach, which finally reduces the determination of each bubble velocity to the calculation of a very few and carefully selected surface quantities at the cluster boundary. Relevant boundary-integral equations governing these required surface quantities are derived and the associated numerical implementation is tested against the analytical solution and the asymptotic predictions derived in a previous paper for a single bubble and two widely-separated bubbles, respectively. Numerical results for close bubbles reveal strong bubble-bubble interactions deeply depending upon the applied electric and magnetic fields.

Euler potentials for two line currents aligned with an ambient uniform magnetic field

[1] Euler potentials of two line currents parallel or antiparallel to each other and aligned with a uniform ambient magnetic field are constructed. Explicit expressions for magnetic field lines are found. The solution is applied for study of bouncing motion of particles trapped between mirror points of this field structure. The result can be applied to Birkeland currents and also to laboratory plasma experiments.