Hall Magnetic Field Research Articles

Electron Acceleration via Secondary Reconnection in the Separatrix Region of Magnetopause Reconnection

AbstractMagnetic reconnection is a fundamental process known to play a crucial role in electron acceleration and heating, however, the mechanism of electron energization during reconnection is still not fully understood. This study introduces a novel electron acceleration mechanism in which electrons can be accelerated by secondary reconnection in the separatrix region. The secondary reconnection occurs in a thin current sheet resulted from the shear of the out‐of‐plane Hall magnetic fields of the primary magnetopause reconnection. It results in the intense electron energy fluxes toward the primary X‐line. This mechanism will likely be an important piece in the puzzle of particle acceleration by reconnection.

Cold ion effects in density-asymmetric collisionless magnetic reconnection

The coexistence of low-energy (cold) ions and thermal (warm) ions is commonly observed in space and laboratory plasmas, such as those in magnetopause and fusion fueling processes. In certain events, the cold ion proportion may play a crucial role in plasma processes, especially magnetic reconnection. In this paper, magnetic reconnection with density-asymmetric cold ions is investigated in implicit particle-in-cell (iPIC) simulations. It is found that in such events the reconnection rate decreases as the cold ion distribution depth into the current sheet increases, mainly due to the mass-loading effect. Particularly, a density-peak structure of cold ions is developed in the reconnection region owing to the bounce motion of cold ions entering from the opposite inflow region. In the y–vy phase space where the y-direction is normal to the current sheet, a cold ion ring structure related to the bounce motion is formed and amplified by the Hall electric field. Furthermore, the cold ions become a notable current carrier due to its shorter inertial scale than the warm ions. Consequently, the asymmetry of the cold ion distribution significantly breaks the symmetry in the Hall magnetic field, eventually leading to asymmetric cold ion density peak structure. Such structures can be taken as significant signals of cold ion existence in in situ spacecraft observations.

MMS Observations of Oscillating Energy Conversion and Electron Vorticity in an Electron‐Scale Layer Within a Southward Magnetopause Reconnection Exhaust

AbstractThe MMS satellites traversed a ∼6 di‐wide and ∼500 km/s southward reconnection exhaust at the dayside magnetopause on 6 December 2015 and ∼29 di from the associated X‐line region. A narrow ∼0.26–0.34 di layer of enhanced ±3.5 nW/m3 oscillating energy conversion perpendicular to the magnetic field resides in this exhaust. It contained two regions of diverging in‐plane electric fields in general agreement with two clockwise electron flow vortices and a proposed increase of the electron vorticity ∇ × Ve. The layer developed sunward of a unipolar Hall magnetic field for a duskward BM/BL ∼ 0.9 guide field. Each electron flow vortex supported a local ∆BM ∼ 10 nT strengthening of this Hall field. The presence of this electron‐scale layer in a southward exhaust for a duskward guide field is consistent with a two‐dimensional simulation of a similar structure that evolved from an X‐line into a northward exhaust for a similar strength dawnward guide field.

Analysis of hyperbolic magneto-hydrodynamic [HMHD] wave propagation through neutrino-coupled plasma

By using the Hyperbolic Magneto Hydrodynamic model, we investigated the propagation dynamics of a neutrino-coupled plasma system, with the influence of Hall current, rotation, viscosity and finite electrical resistivity. The general dispersion relation is obtained from the perturbed equations for both the Jean’s and neutrino beam instability. The effect of different parameters has been discussed in both parallel and perpendicular modes of wave propagation. The Jean’s instability condition is modified due to the presence of Hall current, Magnetic field and neutrino in both modes of propagation. The growth rate of the neutrino beam is affected by Hall current, viscosity magnetic field and rotation in both propagating modes. We also show the effect of different parameters on the growth rate of a neutrino-coupled plasma system through a graphical presentation.

Influence of ferromagnetic interlayer exchange coupling on current-induced magnetization switching and Dzyaloshinskii-Moriya interaction in Co/Pt/Co multilayer system.

This paper investigates the relationship among interlayer exchange coupling (IEC), Dzyaloshinskii-Moriya interaction (DMI), and multilevel magnetization switching within a Co/Pt/Co heterostructure, where varying Pt thicknesses enable control over the coupling strength. Employing Brillouin Light Scattering to quantify the effective DMI, we explore its potential role in magnetization dynamics and multilevel magnetization switching. Experimental findings show four distinct resistance states under an external magnetic field and spin Hall effect related spin current. We explain this phenomenon based on the asymmetry between Pt/Co and Co/Pt interfaces and the interlayer coupling, which, in turn, influences the DMI and subsequently impacts the magnetization dynamics. Numerical simulations, including macrospin, 1D domain wall, and simple spin wave models, further support the experimental observations of multilevel switching and help uncover the underlying mechanisms. Our proposed explanation, supported by magnetic domain observation using polar-magnetooptical Kerr microscopy, offers insights into both the spatial distribution of magnetization and its dynamics for different IECs, thereby shedding light on its interplay with DMI, which may lead to potential applications in storage devices.

Study on a hybrid-produced magnetic-field Hall thruster

The increasing interest in all-electric, low-Earth orbit satellite constellations has stimulated the rapid development of electric propulsion technology, particularly low-power Hall thrusters. In this study, the difficulties in magnetic field design were analyzed in low-power Hall thrusters, and a new and efficient hybrid production technique is proposed. Hybrid production combines the advantages of coil and permanent magnet production; the main magnetic field is generated by permanent magnets, and the regulating magnetic field is generated by coils in parallel. Accordingly, a prototype of a 600-W hybrid-produced magnetic field Hall thruster, HPHT-600, was designed and tested. The HPHT-600 has a small size (channel outer diameter 54 mm), light weight (1.2 kg), low area–volume ratio (0.148), and low magnetic power. In addition, it exhibits a power envelope of 300–1000 W and a total efficiency of 53.5 % at the discharge voltage of 300 V, anode volume flow rate of 35 sccm, and total specific impulse of 1900 s at 500 V and 20 sccm.

Improving the specific impulse of Hall thrusters using a wide channel design

This paper proposes increasing the width of the discharge channel to improve the specific impulse of Hall thrusters. In our study, we significantly increased the achievable channel width by optimizing the magnetic circuit topology, and the design freedom of the Hall thruster was improved. A prototype of a wide-channel high-specific-impulse Hall thruster was designed and experimentally verified. The effects of channel width on the discharge process and the characteristics of an aft-loaded magnetic field Hall thruster were investigated. The high-intensity luminous region did not diffuse radially with an increase in the channel width, and the plasma was always concentrated near the channel centerline. A wider channel is more conducive for improving the propellant utilization efficiency, thereby effectively improving the specific impulse of the Hall thruster. By optimizing the discharge channel width, the upper limit of the discharge voltage was increased, and the maximum specific impulse was increased from 3170 to 3794 s, a relative improvement of 20%. The effect of the specific impulse improvement at the same discharge voltage was analyzed and discussed. The results of this study are significant for the design of high-specific-impulse Hall thrusters.

The Topological Hall Effect in CoGd Films Controlled by Hydrogen Migration under Gate Voltage

AbstractThe topological Hall effect (THE) presents hump signals in the Hall resistance versus magnetic field hysteresis loop, showing promise for future spintronics due to its robust chiral magnetic textures. Here, it is shown that solid‐state protonic gating can control possible topological magnetic structures in CoGd thin films. Injecting H+ leads to sizable hump signals in the film. Magneto‐optical Kerr microscopy shows that induced hump signals in transporting measurements do not scale with magnetization, supporting topological magnetism. Successive hydrogen ion extraction completely erases the effect. Thus, topological magnetism manipulations are reversible, nonvolatile, and effective. Ab inito calculations and effective chiral spin models demonstrate that hydrogen injection remarkably enhances the Dzyaloshinskii–Moriya interaction over fourfold, stabilizing chiral structures contributing to the large THE. These findings reveal the vital role of hydrogen ions in topological magnetism and suggest that amorphous ferrimagnetic CoGd thin films are outstanding platforms for realizing controllable topological spintronics at room temperature.

Hall physics during magnetic reconnection with collision effect

The Hall effect, decoupling between the ion and electron motions, is the core mechanism triggering fast reconnection. In plasmas with collision effects such as laboratory facilities, collision can suppress the Hall effect and influence the triggering of fast reconnection. Here, by conducting a series of kinetic simulations with varying collision parameters, we show that collisions can suppress the electron outflow, impairing the quadrupole Hall magnetic field. Besides, collision weakens the inflow of magnetic flux by reducing the charge separation and increasing the thermal pressure at the reconnection site, leading to a reduction of the Hall electric field. As the collisionality becomes larger, the Hall electric field diminishes more easily than the Hall magnetic field. We propose that the quadrupolar Hall magnetic field can be a significant indicator in reflecting Hall reconnection.

Observation of Interchange Reconnection on Mars

Without a global dipole magnetic field, Mars has magnetic anomalies, i.e., crustal fields, in the southern hemisphere and interesting flexible magnetic fields in the magnetotail. The magnetic field topology is complex and flexible in the Martian magnetotail, especially over regions of strong crustal fields. However, the answer to how the magnetic field topology within crustal field regions transitions is elusive. Here we report the first case of interchange reconnection between open and closed crustal fields in the near-Mars magnetotail, using Mars Atmosphere and Volatile Evolution (MAVEN) observations. While MAVEN crossed from a region of closed crustal field to one of open crustal field, several characteristics of reconnection, such as the Hall magnetic field and plasma outflow, were observed. And plasmas are exchanged in the reconnection region. Our observations demonstrate that interchange reconnection can occur between open and closed crustal fields in the Martian near-magnetotail. Interchange reconnection occurring on the nightside changes the magnetic field topology within the crustal field regions and contributes to the escape of heavy ions.

MHD peristaltic flow of hybrid nanomaterial between compliant walls with slippage and radiation

In this paper, we have discussed the MHD peristaltic flow of Al2O3 − Cu/H2O hybrid nanomaterial in a channel whose walls are taken to be compliant in nature. We also examined the effects of joule heating, thermal slip boundary conditions, thermal radiation, hall current, porous medium, heat source/sink, and viscous dissipation. The flow rotates at a constant angular velocity. The main aim of this work is to study the effects of various physical parameters on the peristaltic flow of a hybrid nanofluid in a rotating channel with complaint walls and heat transfer. The model is presented by using the conservation laws of mass, momentum, and energy along with boundary conditions. Selected variables have been used to simplify the nonlinear equation and the hypotheses of large wavelengths and small Reynolds numbers. The simplified form of the system of equations is solved using Adam’s Bashforth method, which is a multistep predictor–corrector method. To explore the potential applications of hybrid nanofluids in biomedical engineering, nanotechnology, and industrial processes, the effects of emerging parameters on both axial and secondary velocities and the temperature profile are analyzed with the help of graphs. The flow and temperature profiles are influenced by the hall effect, magnetic field, thermal slip, thermal radiation, viscous dissipation, porous medium, and heat source/sink parameters. We find that both velocities increase with hall effect and first-order slippage but decrease with magnetic field parameter. The temperature of the nanoparticles increases with dissipation effects but decreases with thermal radiation.

Magnetic Reconnection in the Martian Magnetotail: Occurrence Rate and Impact on Ion Loss

AbstractThe current sheet is crucial in releasing magnetic free energy in cosmic plasmas via fast magnetic reconnection or wave excitation. This research investigates the characteristics of the Martian tail current sheet by analyzing data acquired from the Mars Atmosphere and Volatile EvolutioN spacecraft over 7 years. For the first time, we find that approximately 15% of the current sheet events display reconnection signatures, including Hall magnetic fields and fast proton flows. These reconnecting current sheets are detected more frequently on Mars than on Earth. The Martian tail current sheet is first demonstrated to be on the proton scale, which can explain the high reconnection occurrence rate. The research also reveals that the current sheets are thinner in regions closer to Mars and in the –E hemisphere. On average, reconnecting current sheets carry high fluxes of protons rather than oxygen ions.

On non-Newtonian fluid flow generated via complex metachronal waves of cilia with magnetic, hall, and porous effects

Cilia beating influences bio-fluid flow, and conduits with ciliated surfaces serve numerous purposes. Cilia are hair-like adjuncts that produce liquid drive and cell locomotion. This novel research integrates magnetohydrodynamics, Hall effects, and porous medium with the cilia-driven flow. The developed problem is further simplified by utilizing famous assumptions, i.e., low Reynolds number and large wavelength. The bvp5c function in MATLAB (2023a) is adopted to achieve a convergent solution. The graphical illustrations of streamlines, pressure drop, and axial velocity under the influence of pertinent parameters are thoroughly examined. The findings suggest that when a high magnetic field (Hall current) and porous media are combined with the Carreau–Yasuda fluid, the pumping equipment operates better than the viscous liquid. In addition, fluid movement in biological organs is improved by metachronal ciliary motion. Furthermore, it is predicted that this study will make a significant contribution to biomedical engineering in terms of the upgrading and advancement of various types of drug-delivery technologies.

Characteristics of Magnetic Reconnection With a Finite X‐Line Length

AbstractThe characteristics of magnetic reconnection with a finite x‐line length are studied using three‐dimensional (3D) particle‐in‐cell (PIC) simulations. We simulate two cases: anti‐parallel reconnection and guide field reconnection. In both cases, reconnection is triggered by an initial perturbation that is localized in the current direction, and then, an active reconnection region extending around 20 ion inertia length along the current direction is developed. In both cases, the electron inertia term plays an important role in balancing the reconnection electric field near the two edges of the x‐line along the current direction. On the ion drifting side, ions are heated while electron heating is not significant; while on the electron drifting side, electrons are heated while ion heating is weak. In the anti‐parallel case, the out‐of‐plane Hall magnetic field on the ion and electron drifting side of the reconnection region shows reversed polarization, while in the guide field case, the in‐plane Hall electric field shows reversed polarization. These features can be used as identifications for reconnection with a finite x‐line length during observations in the magnetotail, they also provide an estimation of the satellite location in the dawn‐dusk direction of the reconnection region.

MAVEN Observations of the Interloop Magnetic Reconnections at Mars

Magnetic reconnection between neighboring magnetic field loops, the so-called interloop reconnection, is a common process to drive flares in the solar atmosphere. However, there is no direct evidence that a similar but less explosive process can take place on planets. The strong crustal fields on Mars generate plenty of magnetic loops in the near-Mars regions, providing a unique environment to research the interloop reconnection on a planet. Here, we report magnetic reconnection events between crustal field loops in the Martian ionosphere observed by Mars Atmosphere and Volatile EvolutioN (MAVEN) for the first time. During the current layer crossing, MAVEN recorded the characteristic signals of collisionless magnetic reconnection, including the Hall magnetic field, Alfvénic outflow, and electron energization. This finding implies that the interloop reconnection in the Martian ionosphere could contribute to the localized energy deposition and particle energization, which provides the seed source for aurora in the Martian atmosphere.

Observations of Dynamical Flux Ropes and Active Multiple X‐Line Reconnection at Earth's Magnetopause

AbstractThis paper presents the magnetospheric multiscale (MMS) observations of three flux ropes (FRs) sequentially in a reconnection exhaust at Earth's magnetopause. Three active X‐lines, which are responsible for the formation of these FRs, were also detected by MMS, providing strong evidence that the FRs were generated by multiple X‐line reconnection. We find that the core field inside the FRs considerably affects the Hall current in the adjacent X‐lines. The intense core field of the FRs deflected the electron outflow jet, forming the electron‐scale Hall magnetic field on the magnetosheath side. Additionally, an active secondary reconnection was observed at the center of one FR. This secondary reconnection split the FR into two smaller FRs and produced sharp density gradients and intense fluctuations of electric field and current within the FR. These observations advance the understanding of the formation and evolution of FRs during multiple X‐line reconnection at magnetopause.

MESSENGER Observations of Reconnection in Mercury's Magnetotail Under Strong IMF Forcing

AbstractThe MESSENGER spacecraft typically crossed Mercury's magnetotail current sheet relatively close to the planet, that is, less than 2.5 RM (planet radius; 2,440 km). Magnetometer measurements are used to detect active reconnection events by identifying the quadrupole Hall magnetic field signatures that form about X‐lines. Statistical analyses of the 51 active reconnection events detected in this manner indicate that they occur most frequently on the duskside and typically at a mean altitude greater than 1.5 RM. In contrast, the dawnside events occur at altitudes of ∼1 RM. In addition, a higher recurrence rate of flux ropes formed in the Hall region was observed on the dawnside. Applying the Kan‐Lee solar wind‐magnetosphere coupling function confirmed that these near‐tail reconnection events at Mercury are observed under strong forcing by the interplanetary magnetic field. We further propose that the reconnection‐driven nightside magnetosphere‐planet interaction is characterized by a pronounced dawn‐dusk asymmetry and may significantly influence the near‐Mercury space environment.

Division of Magnetic Flux Rope via Magnetic Reconnection Observed in the Magnetotail

AbstractUsing high‐resolution data from Magnetospheric Multiscale (MMS) mission, we report an intense current layer at the center of a flux rope (FR) in the magnetotail. The intense current layer is caused by the compression of the ion bulk flows at the center of a FR rather than two interlaced flux tubes reported at the magnetopause previously. The intense current layer has been identified as an electron diffusion region of the magnetic reconnection, and the hall magnetic field generated by magnetic reconnection makes the FR show crater‐shaped. The reconnecting current layer is supported by the poloidal magnetic field of the FR, and it is dividing the FR into two secondary FRs. The observations suggest that magnetic FR can be compressed easily to excite instability inside it as it is propagating in the magnetotail current sheet, thus changing its magnetic topology.

Hall Fields and Current Systems of Magnetic Reconnection under Asymmetric Conditions

The Hall effect is a key component of collisionless reconnection. A previous study showed that a quadrupolar Hall pattern under symmetric conditions degenerates into a bipolar pattern under highly asymmetric conditions. We study the properties of Hall magnetic fields and current systems during three reconnection events observed by the Magnetospheric Multiscale mission at the dayside magnetopause. Although the asymptotic density ratio between the magnetosheath and magnetospheric plasmas is very high for all three events, clear quadrupolar Hall field patterns are observed in all three events. The quadrupolar Hall magnetic fields in the three events display their respective properties on the intensity asymmetry and the distributing location. Among these events, a quadrupolar Hall field pattern is observed for the first time in in situ observations: the magnetosheath Hall pattern occupies the whole midplane region, while the magnetosphere Hall pattern still exists under highly asymmetric conditions. Observations show that the plasma mixture modulates the density asymmetry in the Hall region, which can be very different from the asymptotic density asymmetry in the magnetosheath and magnetospheric inflow plasma. The analyses indicate that the different density asymmetry inside the Hall region, but not the asymptotic density asymmetry, is an exact indicator that explains the different observed Hall patterns. Based on the observed facts, we suggest that the three reconnection events studied here are in different phases of their development after they are triggered under highly asymmetric conditions. Our results provide new insights into how the Hall effect works with the evolution of asymmetry during reconnection.

The three-fluid generalized Ohm's law: A theoretical study

The two-fluid generalized Ohm's law (GOL) is based on the assumption that plasma is composed of only protons and electrons. The three-fluid GOL is obtained theoretically for the three-fluid plasma consisting of heavy ions, light ions, and electrons, which prevails in planetary ionospheres and magnetospheres. Three inertial lengths corresponding to the three-scale diffusion region in the three-fluid magnetic reconnection are derived. The ion inertial lengths and reconnection rate as well as the Hall magnetic and electric fields are modified due to the two-step decoupling process of ions. Our results provide a framework to extend the reconnection theory for even more ion species.