Radial Magnetic Field Research Articles

Dynamo action of the zonal winds in Jupiter

The new data delivered by NASA’s Juno spacecraft significantly increase our understanding of the internal dynamics of Jupiter. The gravity data constrain the depth of the zonal flows observed at cloud level and suggest that they slow down considerably at a depth of about 0.96 rJ, where rJ is the mean radius at the one bar level. The magnetometer onboard Juno reveals the internal magnetic field of the planet. We combine the new zonal flow and magnetic field models with an updated electrical conductivity profile to assess the zonal-wind-induced dynamo action, concentrating on the outer part of the molecular hydrogen region of Jupiter where the conductivity increases very rapidly with depth. Dynamo action remains quasi-stationary and can therefore reasonably be estimated where the magnetic Reynolds number remains smaller than one, which is roughly the region above 0.96 rJ. We calculate that the locally induced radial magnetic field reaches rms values of about 10−6 T in this region and may just be detectable by the Juno mission. Very localized dynamo action and a distinct pattern that reflects the zonal wind system increases the chance to disentangle this locally induced field from the background field. The estimates of the locally induced currents also allow calculation of the zonal-flow-related Ohmic heating and associated entropy production. The respective quantities remain below new revised predictions for the total dissipative heating and total entropy production in Jupiter for any of the explored model combinations. Thus, neither Ohmic heating nor entropy production offer additional constraints on the depth of the zonal winds.

Design of high shielding effectiveness magnetic shield for fiber optic gyroscope

A new type of magnetic shield with annular cavity structure is designed based on the study of the factors affecting the shielding effectiveness for fiber optic gyroscope (FOG). In order to prove the feasibility of using the finite element method (FEM) to research the magnetic shielding effectiveness problem, we design a simulation and experimental comparison verification test for the currently used magnetic shield. The optimized design parameters are obtained by discussing the effects of the number of layers, the layer spacing, the via holes and the gap width on the shielding effectiveness. The shielding effectiveness of the annular cavity structure magnetic shield under radial magnetic field is about 55 dB, which is 20 dB higher than that of the current magnetic shield. The shielding effectiveness under axial magnetic field is about 80 dB which improved by 45 dB. Meanwhile, this annular cavity structure reduces the weight of the FOG.

Analysis of entropy generation in peristalsis of Williamson fluid in curved channel under radial magnetic field

The objective of present study is to analyze the peristaltic activity of Williamson fluid in curved configuration. Flow formulation is made by employing radial magnetic field and Soret and Dufour effects. Slip conditions for velocity, temperature and concentration are applied. Entropy analysis is also carried out. Modeling is given using lubrication approach. Stream function, velocity, temperature and concentration solutions have been derived. Effects of different parameters are analyzed on flow quantities of interest. Moreover streamlines are examined for different embedded parameters. Result reveals that Lorentz force tends to slow down the fluid velocity. The slip parameters for velocity and temperature lead to enhancement in corresponding profile whereas opposite behavior is noticed for concentration. Soret and Dufour effects lead to increase the temperature as well as entropy of the system. Complaint nature walls increase the fluid velocity for elastance parameters whereas damping nature reduces the fluid velocity.

The Modulation of Solar Wind Hydrogen Deposition in the Martian Atmosphere by Foreshock Phenomena

AbstractThe neutral exosphere of Mars extends far upstream beyond the bow shock, and as a result, solar wind protons can charge exchange with this neutral exosphere to produce energetic neutral atoms. Energetic neutral atoms produced directly upstream of Mars will precipitate into the Martian dayside atmosphere, where some fraction can undergo a charge stripping reaction and can be observed as “penetrating protons.” Clear, quasiperiodic modulations in penetrating proton densities are observed during certain Mars Atmosphere and Volatile EvolutioN (MAVEN) periapsis passes, and we show that these modulations occur during radial interplanetary magnetic field conditions. During such times, the region sunward of Mars is defined by quasi‐parallel shock conditions, generating foreshock structures characterized by enhancements in magnetic field strength, enhancements in proton density, and deceleration and deflection of the solar wind flow. These structures are observed at time cadences equal to the modulation of penetrating proton densities at periapsis. Particle tracing simulations show that the convection of these structures with the solar wind leads to localized enhancements in the rate of charge exchange upstream of the shock, producing the observed temporal variations in penetrating proton densities at periapsis. The observation of modulated penetrating proton densities at periapsis can thus be used to infer the existence of radial interplanetary magnetic field conditions upstream of the bow shock at Mars at times when MAVEN does not sample the upstream solar wind.

Comparison of Arc Motion in Different Lifetime Sealed Vacuum Interrupters With RMF Contacts

Vacuum circuit breakers are well established in the distribution levels of the electrical power grids. To maximize the short-circuit interruption performance, an radial magnetic field (RMF)-contact design forces the arc from a fault current to rotate. The performance of the RMF-contact designs is usually evaluated in a model vacuum chamber with viewing ports that allows observing arc rotation with the help of high-speed cameras. These setups differ significantly from lifetime sealed vacuum bottles in geometry (and thus volume) and due to the fact that the main metallic vapor shield cannot be present. This, in turn, can affect the arc rotation behavior. In order to overcome these shortcomings, a new diagnostic tool has been developed to analyze the arcing behavior in standard lifetime sealed vacuum interrupters. Optical methods are not possible here, since the view is blocked by the opaque ceramics and the metallic vapor shield. For this reason, a Hall-sensor-based measuring system is applied, in which the variation in the magnetic field from the arc position is observed by multiple sensors. This paper presents the comparison of arc motion in lifetime sealed vacuum interrupters with different bottle geometries. For this purpose, investigations with identical spiral-shaped RMF contacts inside different vacuum bottle designs with differing vacuum volumes are performed. Also, for comparison, an interrupter with contrate cup contacts was investigated. Similarities and differences between the corresponding arc motion behaviors are discussed.

Effects of uniform radial electric field on the MHD and heat transfer due to a shrinking stretching rotating disk

Flow and heat transfer of an incompressible electrically conducting fluid on radially shrinking/stretching rotating disk in presence of uniform magnetic field are studied in the present paper. The problem is an extension of the well-known von Karman viscous pump problem to the configuration with a shrinkable/stretchable disk with or without rotation. Navier-Stokes equations, Maxwell equation and energy equation have been modied in presence of uniform radial electric field and magnetic field. The governing partial differential equations have been transformed into ordinary differential form by using similarity transformations. The system of equations generated by Navier-Stokes, Maxwell and energy equations has been solved by using Chebyshev collocation technique for varying values of radial electric, magnetic interaction parameters, Eckert and rotation numbers. Accuracy of the method is verified through comparing results in the literature. Effects of parameters in the governing equations are depicted graphically and are analyzed.

Research Progress of Model of Vacuum Arc and Anode Activity Under Axial Magnetic Fields

Modeling and numerical simulation is an important tool for the research of the physical mechanisms of the vacuum arc (VA). Compared with the experiments of the VA, numerical simulation is more efficient and economical. Axial magnetic fields (AMFs) are also the most popular control technology in vacuum interrupters and other application fields. First, the model of VA was reviewed from a relatively simple zero-order one to 2-D one, and then a 3-D one, which gives us a more comprehensive understanding of VA. Second, the influence of spatial distribution of magnetic fields on VA behavior is also studied. VA behavior under different commercial AMF contacts was simulated and compared based on 3-D magnetohydro-dynamic model. Influence of the radial slots and magnetic field generated by adjacent phase and bus bar on arc characteristics has been reviewed. Third, the VA modeling with active anode is reviewed and discussed. Anode vapor can cool arc plasma, and leads to changed distribution of current density and plasma parameters. Model and simulation technology of anode activity have also been reviewed in this paper, from 1-D, 2-D, to 3-D, and then the deformation of anode melting pool is considered. Deformation of anode melting pool will make anode temperature more reasonable. Finally, the challenge and research direction of VA modeling is also given and discussed.

Boundary effects on the magnetic Hamiltonian dynamics in two dimensions

We study the Hamiltonian dynamics of a charged particle submitted to a pure magnetic field in a two-dimensional domain. We provide conditions on the magnetic field in a neighbourhood of the boundary to ensure the confinement of the particle. We also prove a formula for the scattering angle in the case of radial magnetic fields.

Corrugated Features in Coronal-mass-ejection-driven Shocks: A Discussion on the Predisposition to Particle Acceleration

The study of the acceleration of particles is an essential element of research in the heliospheric science. Here, we discuss the predisposition to the particle acceleration around coronal mass ejections (CMEs)-driven shocks with corrugated wave-like features. We adopt these attributes on shocks formed from disturbances due to the bimodal solar wind, CME deflection, irregular CME expansion, and the ubiquitous fluctuations in the solar corona. In order to understand the role of a wavy shock in particle acceleration, we define three initial smooth shock morphologies each one associated with a fast CME. Using polar Gaussian profiles we model these shocks in the low corona. We establish the corrugated appearance on smooth shock by using combinations of wave-like functions that represent the disturbances from medium and CME piston. For both shock types, smooth and corrugated, we calculate the shock normal angles between the shock normal and the radial upstream coronal magnetic field in order to classify the quasi-parallel and quasi-perpendicular regions. We consider that corrugated shocks are predisposed to different process of particle acceleration due to irregular distributions of shock normal angles around of the shock. We suggest that disturbances due to CME irregular expansion may be a decisive factor in origin of particle acceleration. Finally, we regard that accepting these features on shocks may be the start point for investigating some questions in the sheath and shock, like downstream-jets, instabilities, shock thermalization, shock stability, and injection particle process.

Role of Suction/Injection on Natural Convection Flow of Magnetite $$ ({\text{Fe}}_{ 3} {\text{O}}_{ 4} ) $$ Nanoparticles in Vertical Porous Micro-annulus Between Two Concentric Tubes: A Purely Analytical Approach

Natural convection heat transfer analysis was carried out to examine the flow of magnetite–water ferrofluid in an annular zone between a pair of vertical micro-cylindrical tubes under conditions of slip velocity and thermal jump at the porous wall of cylinders. The effects of radial magnetic field and thermal radiation are also considered along with suction/injection at the walls. Linear Rosseland approximation was employed to obtain the expression for thermal radiation. Similarity variables and non-dimensional parameters are introduced to express the resultant flow equations in term of continuity, momentum and energy in a dimensionless fashion. A closed-form solution of the problem was constructed in the form of modified Bessel functions of the first and second kind. The numerical values of the obtained expressions for fluid velocity, temperature profiles, volume flow rate, surface friction and Nusselt number were plotted to examine the significance of different flow parameters. It was found that the fluid velocity was reduced when injection parameter was increased, while it was augmented when the suction parameter was increased. In contrast to this, opposite effects were observed in the temperature distribution. Further, the suction parameter enhances the rate of heat transfer at the inner surface of outer porous cylinder, while the injection parameter has a decreasing effect on the same.

A reduced stochastic model of core surface dynamics based on geodynamo simulations

SUMMARYWe make use of recent geodynamo simulations to propose a reduced stochastic model of the dynamics at the surface of Earth’s core. On decadal and longer periods, this model replicates the most energetic eigen directions of the geodynamo computation. Towards shorter timescales, it proposes a compensation for weaknesses of these simulations. This model furthermore accounts for the signature, in the geomagnetic secular variation, of errors of representativeness associated with unresolved processes. We incorporate the reduced stochastic model into a geomagnetic data assimilation algorithm—an augmented state ensemble Kalman filter—and apply it to re-analyse magnetic field changes over the period 1880–2015. Errors of representativeness appear to be responsible for an important fraction of the observed changes in the secular variation, as it is the case in the dynamo simulation.Recovered core surface motions are primarily symmetric with respect to the equator. We observe the persistence of the eccentric westward gyre over the whole studied era and vortices that partly follow isocontours of the radial magnetic field at the core surface. Our flow models provide a good fit to decadal changes in the length-of-day and predict its interannual variations over the period 1940–2005. The largest core flow acceleration patterns are found in an equatorial belt below 10° in latitude and are associated with non-axisymmetric features. No systematic longitudinal drift of acceleration patterns is found, even over the past decades where satellite data are available. The acceleration of the high-latitude westward jet in the Pacific hemisphere is, during the satellite era, a factor 5 smaller than previously reported and its structure shows some evidence for equatorial asymmetry. The era of continuous satellite records provides enhanced contrast on the rapid core flow variations. The proposed assimilation algorithm offers the prospect of evaluating Earth-likeness of geodynamo simulations.

Mixed Convection Flow of Viscous Reactive Fluids with Thermal Diffusion and Radial Magnetic Field in a Vertical Porous Annulus

This paper investigates the influence of the Frank–Kamenetskii, mixed convection, buoyancy force parameter, Soret effect, and radial magnetic field on steady-state fully developed free convection flow of viscous reactive fluids in the annular region between concentric cylinder r = 1 and r = b in the presence of thermal diffusion and radial magnetic field. The nonlinear ordinary differential equation governing the flow are solved using the semi-analytical method (perturbation series method). The solution obtained is graphically represented and the effect of various controlling pertinent parameters such as λ, Gre, N, Sr, and M on the flow formation is discussed. The physical quantities such as skin friction, Nusselt number and Sherwood number are also computed. It is interesting to observe that increasing the values of Frank–Kamenetskii (λ), mixed convection (Gre), and Soret (Sr) increases the velocity while increase in the radial magnetic field (M) decreases the velocity.

Simulations on the transient heat fluxes for the low-hybrid wave heating H-mode on EAST

In the previous simulations on the divertor heat fluxes of C-Mod and EAST, the inverse proportional to the plasma current or poloidal magnetic field trend of Eich’s Scaling is well reproduced by the BOUT+ + simulations. However, the simulated SOL width is only half of the value realized in EAST measurements. The reason is believed to be the lack of RF heating scheme in the simulations. The RF heating on EAST, especially lower hybrid wave (LHW), is considered to change the boundary topology and increase the flux expansion. To prove the topology change effects of LHW in the scraped-off layer (SOL), a modeled helical current filament (HCF) due to LHW in SOL, which has the same amplitude of 13 kA to the experiments, is added as the force-free form into the 6-field 2-fluid module of BOUT++. The radial magnetic field induced by this HCF could be much smaller than the perturbed field induced by the edge tubulence or ELM, but it is able to force the perturbations of the turbulence or ELM with the same toroidal mode number to grow up at the start of the linear phase during the simulations. This forced mode is effective to compete with the spontaneous fluctuations and change their linear properties, which leads to the suppression of the divertor heat flux and the broadening of SOL width. The modeling results imply that the HCF with the toroidal mode number is able to increase the SOL width by ∼, and the peak parallel heat flux towards divertor target is decreased by ∼. The scan of the toroidal mode number of HCF indicates that the smaller could generate the broader SOL width and lower peak heat flux. The modeled broadening of the particle flux by HCF clearly shows the secondary striate filaments on divertor target, which is similar to the splitting of the strike point observed in the measurements by the divertor probes.

Localized Ionization Hypothesis for Transient Ionospheric Layers

AbstractThe persistent two‐peaked vertical structure of the Martian ionosphere is created by extreme and far ultraviolet radiation whose energies, respectively, determine their ionization altitude. A third low‐altitude transient layer (previously referred to as M3 or Mm) has been observed by radio occultation techniques and attributed to meteor ablation. However, recent remote sensing and in situ observations disfavor a meteoric origin. Here we propose an alternative hypothesis for these apparent layers associated with impact ionization from penetrating solar wind ions, previously observed as proton aurora. Localized ionization, occurring nonglobally at a given altitude range, breaks the symmetry assumed by the radio occultation technique, and creates electron layers apparently lower in the ionosphere than their true altitude. This may occur when the upstream bow shock is altered by a radial interplanetary magnetic field configuration, which allows the solar wind to penetrate directly into the thermosphere. This localized ionization hypothesis provides an explanation for apparent layers' wide variation in heights and their transient behavior. Moreover, this hypothesis is testable with new observations by the Mars Atmospheric and Volatile EvolutioN Radio Occultation Science Experiment in future Mars years. This hypothesis has implications for the ionospheres of Venus and Titan, where similar transient layers have been observed.

Numerical studies of the ExB electron drift instability in Hall thrusters

The properties of the ExB drift mode in Hall thrusters were investigated through particle-based simulations. Two different two-dimensional models coupling the ExB drift azimuthal direction with the axial accelerating field and radial magnetic field directions, respectively, were implemented assuming Cartesian slab geometry. While the azimuthal-axial model is self-sustaining through the closure of the anode-cathode circuit, the radial-azimuthal one is equipped with an injection system that preserves the number of ions and with a secondary electron emission module for electron-wall interaction. Results identify the linear growth and nonlinear saturation mechanisms consisting of electron heating along azimuthal and radial directions and of ion wave trapping. The latter leads to the ion rotation along the azimuthal direction giving the ion distribution a long tail. The discrete band structure of ExB electron drift instability evolves by an inverse cascade process toward small wavenumbers characterized by broader resonances giving to the spectrum an ion-acoustic-like nature. The larger lobes are due to electron heating and to the presence of a radial component by a modified two-stream instability. Important correlations at macroscopic level between the azimuthal modulation of the azimuthal electric field and the axial modulation of the accelerating field are proof of the complexity of the electron transport in Hall thrusters.

Well-posedness of axisymmetric nonlinear surface waves on a ferrofluid jet

We consider free surface waves propagating on a ferrofluid jet under a radial magnetic field. The waves investigated are axisymmetric solutions of the Euler equations, formulated in cylindrical coordinates, for an incompressible and inviscid ferrofluid flowing irrotationally, which satisfy the generalized Young-Laplace equation with magnetic stresses included and the kinematic condition on the free surface. The main objective of the present study is to solve a basic question on the theoretical side, i.e. the local well-posedness issue. We establish local existence and uniqueness of solutions for the initial value problem in Sobolev spaces, which are achieved based on analyses of the radially symmetric Dirichlet-Neumann operator and energy method.

Equatorially trapped waves in Earth’s core

Author(s): Buffett, B; Matsui, H | Abstract: Short-period fluctuations in geomagnetic acceleration are detected in recent satellite observations. A major component of this signal is confined to the equatorial region, suggesting the presence of equatorial waves, but the precise nature of these waves is not known. We explore the possibility that these waves arise from an interplay of magnetic, Archimedes and Coriolis forces in a stratified layer at the top of the core (sometimes called MAC waves). We adopt a beta-plane approximation and show that low-frequency MAC waves are not trapped near the equator when the root-mean-square (rms) radial magnetic field is constant over the surface of the core–mantle boundary. However, equatorial trapped MAC waves emerge when the rms radial magnetic field increases towards the poles. Further confinement of MAC waves occurs when we account for the leading-order effects of spherical geometry. The resulting MAC waves propagate to the east with phase velocities that depend strongly on the thickness of the stratified layer.Waves with periods less than 10 yr are predicted when the layer thickness is less than 30 km. These waves have low quality factors, Q ≈ 1, which means that they propagate only a few thousand kilometers before being dissipated by ohmic losses. Evidence for eastward and westward propagating disturbances in the observations may reflect a superposition of wave propagation and forced motion by an excitation source. Separation of the source from the wave propagation may be possible if the source is due mainly to westward drifting plumes in the equatorial region.

Thermal Stability of Mixed Convection Boundary Layer MHD Flow Over a Horizontal Circular Cylinder Under Convective Boundary Condition

In this paper, the influence of small disturbances three-dimensional on the stability of a mixed convection Magnetohydrodynamic (MHD) boundary-layer flow past a horizontal circular cylinder subjected a radial magnetic field is analyzed. Stream flowing vertically upwards taking into account the thermal convective boundary condition of the cylinder. The stability of flow is studied in presence of effects such as magnetic field and Biot number. The governing differential equations in basic flow are solved numerically by a well-known method named as Keller Box Method. The linear stability is then analyzed using the normal mode decomposition. The resulting eigenvalue problem is then solved numerically by the pseudo-spectral method employing Laguerre’s polynomials. The computed results for the basic flow and the stability have been depicted and discussed in detail through graphs for various parametric conditions. The critical points is illustrated graphically to show interesting features of the solutions. Globally one can observe that effect of magnetic field acts to reduce the instability. The results also show that the critical value of the Richardson number decreases when Bi increases, that is to say that this parameter has a destabilizing effect.

LTCC magnetic sensors at EPFL and TCV: Lessons learnt for ITER

Innovative 3D high-frequency magnetic sensors have been designed and manufactured in-house for installation on the Tokamak à Configuration Variable (TCV), and are currently routinely operational. These sensors combine the Low Temperature Co-fired Ceramic (LTCC) and the thick-film technologies, and are in various aspects similar to the majority of the inductive magnetic sensors currently being procured for ITER (290 out of 505 are LTCC-1D). The TCV LTCC-3D magnetic sensors provide measurements in the frequency range up to 1MHz of the perturbations to the toroidal (quasi-parallel: δBTOR˜δBPAR), vertical (quasi-poloidal: δBVER˜δBPOL), and radial (δBRAD) magnetic field components, the latter being generally different from the component normal to the Last Closed Flux-Surface (δBNOR). The LTCC-3D δBRAD measurements improve significantly on the corresponding data with the saddle loops, which are mounted onto the wall and have a bandwidth of ˜3 kHz (due to the wall penetration time). The LTCC-3D δBTOR measurements (not previously available in TCV) provide evidence that certain MHD modes have a finite δBPAR at the LCFS, as recently calculated for pressure-driven instabilities. The LTCC-3D δBPOL measurements allow to cross-check the data obtained with the Mirnov coils, and led to the identification of large EM noise pick-up for the Mirnov DAQ. The LTCC-3D data for δBPOL agree with those obtained with the Mirnov sensors in the frequency range where the respective data acquisition overlap, routinely up to 125kHz, and up to 250kHz in some discharges, when the EM noise pick-up on the Mirnov DAQ is removed. Finally, we look at what lessons can be learnt from our work for the forthcoming procurement, installation and operation of the LTCC-1D sensors in ITER.

Observation of electromagnetic fluctuation induced particle transport in ETG dominated large laboratory plasma

The large volume plasma device (LVPD), a cylindrically shaped, linear plasma device of dimension (Φ = 2 m, L = 3 m) have successfully demonstrated the excitation of electron temperature gradient (ETG) turbulence (Mattoo et al 2012 Phys. Rev. Lett. 108 1–5). The observed ETG turbulence shows significant power between corresponding to the wave number, where, and ion cyclotron frequency and electron Larmor radius, respectively. The observed frequency and wave number matches well with theoretical estimates corresponding to Whistler-ETG mode. We investigated electromagnetic (EM) fluctuations induced plasma transport in high beta ETG mode suitable plasma in LVPD. The radial EM electron (ion) flux results primarily from the correlation between fluctuations of parallel electron current and radial magnetic field The EM particle flux is observed to be much smaller than the electrostatic particle flux, The EM flux is small but finite contrary to the conventional slab ETG model. The EM flux is non-ambipolar. A theoretical model is obtained for the EM particle flux in straight homogeneous magnetic field geometry. The theoretical estimates are seen to compare well with the experimental observations. Sluggish parallel ion response is identified as the key mechanism for generation of small but finite EM flux.