Radial Component Of Magnetic Field Research Articles

Effects of Axial and Radial Components of Magnetic Field on the Electromagnetic Resistive Instabilities in Hall Thruster Plasma

Abstract A theoretical model is developed to investigate the effect of the axial component of the magnetic field on the electromagnetic resistive instabilities in the Hall thruster. The axial component of the magnetic field plays a vital role in controlling the plasma flow and generating thrust in Hall thruster. It also affects the magnetic topology and magnetic field lines in the Hall thruster. In the present paper, a dispersion relation for the electromagnetic resistive instabilities under the influence of the axial component of the magnetic field is derived. The obtained dispersion equation is solved numerically to study the propagating and growing waves in the magnetized plasmas. It is observed that the growth rate decreases with an axial component of the magnetic field, but it increases with a radial component of the magnetic field. When the axial component of the magnetic field is considered, the amplitude of the growth rate of the resistive instability dropped with azimuthal wavenumber, collision frequency and electron drift velocity by almost 21 %, 35 %, and 33 %, respectively. When, the value of drift velocity exceeds to 4×10^6 m/s, the influence of the axial component of the magnetic field appeared, and the growth rate reduced drastically.

The effect of adaptive mesh refinement and grid stretching on the magnetized coronal mass ejection model in Icarus

Context. Coronal mass ejections (CMEs) are the main driver of solar wind disturbances near the Earth. When directed toward Earth, the internal magnetic field of the CME can interact with the Earth’s magnetic field and cause geomagnetic storms. In order to better predict and avoid damage coming from such events, the optimized heliospheric model Icarus has been implemented. Advanced numerical techniques, such as gradual radial grid stretching and solution adaptive mesh refinement (AMR) are implemented in the model to achieve better performance and more reliable results. Aims. The impact of a CME at Earth is greatly affected by its internal magnetic field structure. The aim of this work is to enable the modeling of the evolution of the magnetic field configuration of the CME throughout its propagation in Icarus. Thus, we used Icarus to implement a magnetized CME model that is more realistic than the already available simple hydrodynamics cone CME model, allowing us to study the evolution of the magnetized CME during its interactions with the solar wind. The focus of the study is on the global magnetic structure of the CME and its evolution and interaction with the solar wind. Methods. The magnetized CME model implemented in Icarus is the linear force-free spheromak (LFFS) solution that has been imported from EUHFORIA. Simulations with the spheromak model were performed for different effective resolutions of the computational domain. We applied advanced techniques such as grid stretching and AMR. Different AMR levels were applied in order to obtain high resolution locally, where needed. The original uniform medium- and high-resolution simulation results are also shown as a reference. The results of all the simulations are compared in detail and the wall-clock times of the simulations are provided. Results. We analyzed the results from the performed simulations. The co-latitudinal magnetic field component is plotted at 1 AU for both Icarus and EUHFORIA simulations. The time series at Earth (L1) of the radial velocity, density, and different magnetic field components are plotted and compared. The arrival time is better approximated by the EUHFORIA simulation, with the CME shock arriving 1.6 and 1.09 h later than in the AMR level 4 and 5 simulations, respectively. The profile features and variable strengths are best modeled by Icarus simulations with AMR level 4 and 5. The uniform, medium-resolution simulation with Icarus took 6.5 h wall-clock time, whereas with EUHFORIA, the most similar setup takes 18.5 h, when performed on 1 node with 2 Xeon Gold 6240 CPUs at 2.6 GHz (Cascadelake), 18 cores each, on the Genius cluster at KU Leuven. The Icarus simulation with AMR level 4 took only 2.5 h on the same computer infrastructure, while showing better resolved shocks and magnetic field features, when compared to the observational data and the referene uniform simulation results. Conclusions. The results from different Icarus simulations in Icarus are presented using results from the EUHFORIA heliospheric modeling tool as a reference. The arrival time is closer to the observed time in the EUHFORIA simulation, but the profiles of the different variables show more features and details in the Icarus simulations. The simulations with AMR levels 4 and 5 offered the most detailed results. Considering the small difference in the modeled results and the large difference in terms of computational resources, the AMR level 4 simulation is considered to have displayed the most optimal performance. The gradients in the AMR level 4 results are sharper than those in the uniform simulations with both EUHFORIA and Icarus, while the AMR level 4 effective resolution is the most comparable to the standard resolution runs. The AMR level 3 simulation is 15 and 41 times faster than the Icarus and EUHFORIA uniform simulations, respectively; while the AMR level 4 simulation is about three and seven times faster than the uniform simulations, respectively.

A Fokker–Planck Framework for Studying the Variability of the Magnetic Field Direction in the Alfvénic Streams of the Solar Wind

Turbulent rotations of the magnetic field vector are observed in the Alfvénic streams of the solar wind where the magnetic field strength remains close to a constant. They can lead to reversals of the radial magnetic field component or switchbacks. It is not ruled out from the data that the rotations are divisible into the sum of small random angular deflections. In this work, we develop tools aimed at the analysis of the one-point statistical properties of the directional fluctuations of the magnetic field vector in the solar wind. The angular fluctuations are modeled by a drift-diffusion process which admits the exponential distribution as steady-state solution. Realizations of the stochastic process are obtained by solving the corresponding Langevin equation. It is shown that the cumulative effects of consecutive small-angle deflections can yield frequent reversals of the magnetic field vector even when the concentration parameter of the directional data is large. The majority of the rotations are associated with nearly transverse magnetic field fluctuations in this case.

Fifty years of studying the GCR intensity during inversion of heliospheric magnetic fields I. Observations

The effects of the 22-year variation of solar magnetic fields in the galactic cosmic ray (GCR) intensity were first observed and interpreted as manifestations of inversion of the high-latitude solar magnetic field in properties of heliospheric magnetic fields by the Lebedev Physical Institute team in 1973. Since then, these effects have been studied already for 50 years.
 The situation with the heliospheric magnetic field is clear for periods of medium and low sunspot activity — the heliosphere consists of two unipolar “hemispheres” separated by a wavy global heliospheric current sheet and characterized by a general polarity A (unit quantity with the sign of the radial component of the heliospheric magnetic field in the northern hemisphere). Yet there is no consensus on what the inversion of the heliospheric magnetic field is and which effects in the GCR intensity are connected with this phenomenon.
 In this article, we briefly formulate general concepts of the 22-year variation in characteristics of the Sun, heliosphere, and GCR intensity and discuss the observed effects in the GCR intensity, which we attribute to the heliospheric magnetic field reversal. Models for this phenomenon and the results of GCR intensity calculations with these models will be discussed in the next article.

Пятьдесят лет исследования поведения интенсивности ГКЛ в периоды инверсии гелиосферного магнитного поля. I. Наблюдаемые эффекты

The effects of the 22-year variation of solar magnetic fields in the galactic cosmic ray (GCR) intensity were first observed and interpreted as manifestations of inversion of the high-latitude solar magnetic field in properties of heliospheric magnetic fields by the Lebedev Physical Institute team in 1973. Since then, these effects have been studied already for 50 years.
 The situation with the heliospheric magnetic field is clear for periods of medium and low sunspot activity — the heliosphere consists of two unipolar “hemispheres” separated by a wavy global heliospheric current sheet and characterized by a general polarity A (unit quantity with the sign of the radial component of the heliospheric magnetic field in the northern hemisphere). Yet there is no consensus on what the inversion of the heliospheric magnetic field is and which effects in the GCR intensity are connected with this phenomenon.
 In this article, we briefly formulate general concepts of the 22-year variation in characteristics of the Sun, heliosphere, and GCR intensity and discuss the observed effects in the GCR intensity, which we attribute to the heliospheric magnetic field reversal. Models for this phenomenon and the results of GCR intensity calculations with these models will be discussed in the next article.

Vertical stray field measurements using an electron beam in the MEPhIST-0 tokamak

In the MEPhIST-0 tokamak, toroidal magnetic coil system is implemented as a single continuous toroidal solenoid. This design ensures synchronized operation of each segment of the solenoid and requires only one power supply line to operate. However, this configuration has the downside of introducing stray vertical and radial magnetic field components, which result from the inclination of the solenoid segments. Such stray fields can be measured using an electron beam, as previously demonstrated in experiments on T-15, TEXTOR, KSTAR, and SST-1. This paper describes the parameters of the experiment and presents the main results obtained from the MEPhIST-0 tokamak. Two experimental techniques for measuring the vertical magnetic field are discussed: one with a change in the current direction in the toroidal solenoid and one without. The ratio of the stray vertical field to the toroidal field was found to be approximately 0.5%. The conducted experiments highlight the necessity of compensating for the stray vertical field using additional poloidal coils.

Statistical Temporal Variations in the Auroral Electrojet Estimated With Ground Magnetometers in Fennoscandia

AbstractWe present the implementation of an improved technique to coherently model the high‐latitude ionospheric equivalent current. Using a fixed selection of 20 ground magnetometers in Fennoscandia, we present a method based on Spherical Elementary Current Systems (SECS) to model the currents coherently during 2000–2020. Due to the north‐south extent of the magnetometers, we focus on the model output along the 105° magnetic meridian. Our improvements involve fixed data locations and SECS analysis grid and using a priori knowledge of the large‐scale currents improving the robustness of the inverse problem solution. We account for contributions from ground induced currents assuming so‐called mirror currents. This study produces a new data set of divergence‐free (DF) currents and magnetic field perturbations along the 105° magnetic meridian with 1‐min resolution. By comparing averages of the data set with an empirical model of the ionosphere we demonstrate the validity of the data set. We show how our data set, in particular its temporal nature, is distinct from empirical models and other studies. Not only can the temporal evolution of the DF currents and magnetic field perturbations be investigated, but the time derivative of said quantities can be analyzed. For application in ground induced currents, we present the statistical properties of where (in magnetic latitude and local time) and at what rate (∂Br/∂t) the radial magnetic field component fluctuates, a temporal derivative that has received very little attention. We show that ∂Br/∂t is dependent on latitude, local time, and solar cycle. We present other applications such as Ultra Low Frequency Waves monitoring.

Clarifying Physical Properties of Magnetic Fields in Sunspots

We demonstrate that the radial magnetic-field component at the outer boundary of the sunspot penumbra is about 550 Mx cm$^{-2}$ independent of the sunspot area and the maximum magnetic field in the umbra. The mean magnetic-field intensity in sunspots grows slightly as the sunspot area increases up to 500 -- 1000 millionth of visual hemisphere (m.v.h.) and may reach about 900 -- 2000 Mx cm$^{-2}$. The total magnetic flux weakly depends on the maximum field strength in a sunspot and is determined by the spottedness, i.e. the sunspot number and the total sunspot area; however, the relation between the total flux and the sunspot area is substantially nonlinear. We suggest an explicit parametrization for this relation. The contribution of the magnetic flux associated with sunspots to the total magnetic flux is small, not achieving more than 20% even at the maximum of the solar activity.

Research on Environmental Magnetic Field of Two-Pole Permanent Magnet Motor Considering Cogging

The peripheral magnetic field of the motor may cause magnetic field interference to the surrounding sensors, which would reduce the accuracy of sensors and affect the safety and concealment of vessel. This article explored the environmental magnetic field distribution law of a permanent magnet (PM) motor with two-pole parallel magnetization. A no-cogging magnetic field model was obtained by solving Maxwell equations, and the relationship between the air gap flux density and the environment flux density was built considering the motor cogging effect. In addition, a mathematical model of connections between the back electromotive force (EMF) and the environmental flux density was built, and the correctness of the model was verified by COMSOL. It is concluded that the circumferential and radial components of the environmental magnetic field are distributed sinusoidally, and the magnetic flux density modulus remains constant on the equidistant circumferential line, but attenuates squarely with the distance from the motor. It provides ideas for magnetic field analysis in the peripheral environment of other types of motors, sensors, and other anti-motor electromagnetic interference, magnetic field compensation for geomagnetic measurement, and motor fault diagnosis.

Rate of Change of Large-Scale Solar-Wind Structure

Quantifying the rate at which the large-scale solar-wind structure evolves is important for both understanding the physical processes occurring in the corona and for space-weather forecast improvement. Models of the global corona and heliosphere typically assume that the ambient solar-wind structure is steady and corotates with the Sun, which is generally expected to be more valid at solar minimum than solar maximum, but this has not been well tested. Similarly, assimilation of solar-wind observations into models requires quantitative knowledge of how the reliability of the observations changes with age. In this study we examine 25 years of near-Earth in situ solar-wind observations and 45 years of observation-constrained solar-wind simulations to determine how much the 1-AU solar-wind speed, V, and radial magnetic-field component, B_{R}, vary between consecutive Carrington rotations (CRs). For the in situ spacecraft observations, we find the rate of change of V and B_{R} is similar during solar maximum and minimum, particularly when transient interplanetary coronal mass ejections are removed from the data. This is somewhat counter to expectations. Conversely, the rate of change in V and B_{R} obtained from global heliospheric simulations is strongly correlated with the solar cycle, with the corona and heliosphere being more variable at solar maximum, as expected. Limiting the analysis of the simulations to the solar equatorial region, however, strongly reduces the difference between solar maximum and minimum, bringing the result into close agreement with the in situ observations. This latitudinal sensitivity is explained in terms of the global solar-wind structure over the solar cycle. For the purposes of assimilating in-ecliptic solar-wind observations, we suggest the uncertainty in V should increase by around 3 km s−1 per day since the observation was made and 0.1 nT per day for B_{R}. For observations made at higher latitude, the effect of observation age will be solar-cycle dependent.

Pulse Reverse Plating of Copper Micro-Structures in Magnetic Gradient Fields

Micro-structured copper layers are obtained from pulse-reverse electrodeposition on a planar gold electrode that is magnetically patterned by magnetized iron wires underneath. 3D numerical simulations of the electrodeposition based on an adapted reaction kinetics are able to nicely reproduce the micro-structure of the deposit layer, despite the height values still remain underestimated. It is shown that the structuring is enabled by the magnetic gradient force, which generates a local flow that supports deposition and hinders dissolution in the regions of high magnetic gradients. The Lorentz force originating from radial magnetic field components near the rim of the electrode causes a circumferential cell flow. The resulting secondary flow, however, is superseded by the local flow driven by the magnetic gradient force in the vicinity of the wires. Finally, the role of solutal buoyancy effects is discussed to better understand the limitations of structured growth in different modes of deposition and cell geometries.

Ferrofluid annulus in crossed magnetic fields.

We study the dynamics and pattern formation of a ferrofluid annulus enveloped by two nonmagnetic fluids in a Hele-Shaw cell, subjected to an in-plane crossed magnetic field configuration involving the combination of radial and azimuthal magnetic fields. A perturbative, second-order mode-coupling analysis is employed to investigate how the ferrofluid annulus responds to variations in the relative strength of the radial and azimuthal magnetic field components, as well as in the thickness of magnetic fluid ring. By tuning the magnetic field components and the annulus' thickness, we have found the development of several stationary annular shapes, presenting polygon-shaped structures typically having skewed, peaked fingers. Such fingered structures may vary their skewness, sharpness, and number and arise on the inner, outer, or even both boundaries of the annulus. In addition to controlling the morphologies of the ferrofluid annuli, the external field can be used to put the annulus into a rotational motion, with an angular velocity having prescribed magnitude, and direction. Our second-order theory is utilized to obtain a correction to the linear stability analysis prediction of such angular velocity, usually resulting in a decreased weakly nonlinear value as compared with the magnitude predicted by purely linear theory. These theoretical results suggest the use of magnetic-field-controlled ferrofluid annuli in Hele-Shaw cells as a potential laboratory for microscale applications related to the manipulation of shape-programmable magnetic fluid objects and tunable fluidic-mixing devices in confined environments.

Measuring the Magnetic Field Vector of Earth

The magnetic field of Earth, Be, is an intriguing topic in the introductory physics curriculum that engages students’ curiosity and inspires numerous speculations about the nature of this phenomenon. There are several methods for measuring Earth’s magnetic field. Probably, the most widespread and visual method of measuring the field in student lab experiments utilizes a tangent galvanometer. Recently, PASCO scientific suggested to use a magnetic field sensor for this goal, in a procedure where a magnetic field sensor combined with a rotary motion sensor is rotated in a 2-D plane containing the magnetic field vector of Earth. In this case, the magnetic field detected by the magnetic field sensor is a component of the magnetic field vector oriented relative to the direction of the magnetic field sensor probe (radial component of magnetic field). This means that the detected magnetic field considered as a function of the angle of rotation of the sensor will be a sinusoidal function. The amplitude of this function is the magnitude of Earth’s magnetic field. In conducting this experiment, initially the sensor is set to zero by placing it in a Zero Gauss Chamber (mu-metal). The equipment setup of the experiment is depicted in the figure shown in Ref. 9. The described experiment requires the use of a dip needle that is a compass pivoted to move in the plane containing the magnetic field vector of Earth. The dip needle shows the dip angle θ (inclination) that Earth’s magnetic field makes with the horizontal. Besides the previously mentioned devices, this experiment requires the use of an aluminum table clamp, adjustable angle clamp, and angle indicator to ensure proper alignment of the rotary motion sensor in a 2D plane containing the magnetic field vector.

Development, Implementation and Testing of Algorithm to Detect Ionopause-Like Structure Using Parallel Processing in the Martian Atmosphere

Abstract: This study assesses the Martian ionopause using MAVEN datasets between periapsis and 150-600 km. Ionopause is an abrupt reduction of the electron density with increasing altitude. It is also required to verify the simultaneous increase of the electron temperature and variability below 400 km. To address this issue, we have adopted a computational approach in determining the ionopause-like density structure of the ionospheric profile. From computing thermal & magnetic pressures, radial magnetic field components, ionopause-like density gradient are detected and stored. The ionopause (theoretically) is formed where the total ionospheric pressure equals solar wind dynamic pressure. The present algorithm consists of a comprehensive set of conditions to be performed on the dataset sequentially. These include datasets from various instruments simultaneously observed. The primary objective of the present study is to describe the implementation and testing of this algorithm for big datasets of the Martian ionosphere and extract ionopause-like density gradient using automation. Keywords: Ionopause, Mars, Remote sensing, MAVEN dataset, Parallel-processing

Magnetic and Velocity Fluctuations in the Near-Sun Region from 0.1−0.3 au Observed by Parker Solar Probe

Abstract The fluctuations observed in the slow solar wind at 1 au by the WIND spacecraft are shown by recent studies to consist of mainly magnetic-field directional turning and magnetic-velocity alignment structure (MVAS). How these structures are created has been a question because the nature of the fluctuations in the near-Sun region remains unknown. Here, we present an analysis of the measurements in the slow solar wind from 0.1−0.3 au by Parker Solar Probe during its first six orbits. We present the distributions in the C vb ′ – σ r plane of both the occurrence and average amplitudes of the fluctuations, including the magnetic field, the velocity, and the Elsässer variables, where C vb ′ is the correlation coefficient between the magnetic and velocity fluctuations multiplied by the opposite sign of the radial component of the mean magnetic field and σ r is the normalized residual energy. We find that the dominant composition is the outward-propagating Alfvénic fluctuations. We find Alfvénic fluctuations with C vb ′ > 0.95 , in which the amplitudes of z + reach 60 km s−1 and those of z − are close to the observational uncertainty. We also find a region with high C vb ′ and moderate minus σ r in which the fluctuations are considered MVAS being magnetic dominated with the amplitude of magnetic fluctuations reaching 60 km s−1. We provide empirical relations between the velocity fluctuation amplitude and C vb ′ . The comparison between these results and those observed at 1 au may provide some clues as to the nature and evolution of the fluctuations.

Investigation on arc characteristics in cup‐shaped contacts with different structure for transverse magnetic field vacuum circuit breaker

AbstractThe cup‐shaped transverse magnetic field (TMF) contacts contain radial components and tangential components in the TMF generated when the current is interrupted. The tangential force generated by the radial magnetic field component drives the vacuum arc to rotate, and the tangential magnetic field component generates a radial force that causes the vacuum arc to move radially outward. In this paper, in order to study the influence of the arc force direction on the arc characteristics, the influence of the contact structure parameters such as the inclination of the inner wall on the arc force direction is simulated, and the breaking tests of different levels of current are carried out on the contact with different structure parameters. It is found that the direction of the Lorentz force has a significant effect on the breaking characteristics of the current, and the tangential and radial force components have varying degrees of influence on the motion characteristics of the arc during the start process and the metal droplet splashing.

Characterization of High‐m ULF Wave Signatures in GPS TEC Data

AbstractGPS total electron content (TEC) measurements were used to investigate high‐m ultralow frequency (ULF) waves during the recovery phase of a geomagnetic storm. ULF wave signals in TEC data show high coherence and significant common power in the wavelet coherence and cross wavelet transform analyses with magnetic field radial component data from GOES‐15. They did not cause significant ionospheric scintillation or ground magnetic signatures due to ionospheric screening effects. An automatic identification procedure is developed to identify ULF wave signature in TEC data from 10 GPS receivers on January 25, 2016. The waves were mainly distributed on the dayside and post dusk sector from ∼64° to ∼71° magnetic latitude. This is the first time that the large‐scale 2D spatial structure and temporal evolution of high‐m ULF waves are revealed, which demonstrates TEC measurements as an effective high‐m ULF wave remote sensing tool.

Correlation analyses between solar activity parameters and cosmic ray muons between 2002 and 2012 at high cutoff rigidity

• The impacts of seven solar, interplanetary, and geophysical parameters on CR data have been investigated. • CR data for the period 2002–2012 from KACST muon detector located at high cutoff rigidity have been used. • CR data from Oulu neutron monitor for the same period have been used for comparisons. • Multivariable models were developed to predict CR variability at KACST and Ouu. Solar activity modulates cosmic ray (CR) flux with different magnitudes on different time scales. Several investigations from locations with different, mainly low, cutoff rigidity utilizing different solar activity parameters have been carried out to characterize their influence on the observed CR flux. In this study, the effect of seven solar, interplanetary, and geophysical parameters on the secondary CR muons has been investigated and established using correlation analyses. Daily mean values of the CR data for the period between 2002 and 2012 were obtained from the King Abdulaziz City for Science and Technology (KACST) muon detector, Riyadh, central Saudi Arabia (Rc = 14.4 GV). Considered parameters are sunspot number, radial component of the interplanetary magnetic field, Kp index, solar radio emission flux at 10.7 cm, Dst index, solar wind speed, and solar wind density. Same analyses have been carried out using data from the Oulu neutron monitor (Rc = 0.8 GV) for comparison purposes. Obtained results showed that the intensities of the secondary CRs from both stations are significantly correlated with the Dst index and plasma density, and anti-correlated with the rest of the variables. These results are in agreement with those obtained by several investigators. Magnitude and strength of the correlations between the considered variables and CRs were higher and stronger for the CR neutrons than the CR muons. These findings may be due to the greater influence of seasonal variations on the CR muons than on the CR neutrons. Additionally, the muon detector is sensitive (due to its high cutoff rigidity) to higher-energy CR particles, which are less affected by solar disturbances. Time-lag cross-correlation analyses between the monthly mean CR values from both stations and the monthly mean values of the considered variables were conducted. Comparable results with the previous investigations were found. Multivariable models using the seven parameters were developed to predict the CR variations for both sites. For the data from the KACST detector, the model was able to predict the measured data with a correlation coefficient of 0.48 and a standard deviation of 0.60%. On the other hand, the developed model for the Oulu neutron monitor has a correlations coefficient of 0.77 and a standard deviation of 3.7%.

Magneto-hydrodynamic simulations of young supernova remnants and their energy-conversion phase

ABSTRACT Supernova remnants (SNRs) can be rich sources of information on the parent SN (supernova) explosion. Thus, investigating the transition from the phase of SN to that of SNR can be crucial to link these two phases of evolution. Here, we aim to study the early development of SNR in more detail, paying the major attention to the transition from the early expansion stage to the Sedov stage and the role played by magnetic field in this transition. To this end, spherical magnetohydrodynamic simulations of SNRs have been performed to study the evolution of magnetic field in young SNRs and explore a sequence of the SNR evolutionary stages in the pre-radiative epoch. Remnants of three supernova types are considered, namely, SNIa, SNIc, and SNIIP, that covers a wide space of parameters relevant for SNRs. Changes in global characteristics and development of spatial distributions are analysed. It is shown that the radial component of magnetic field rapidly drops downstream of the forward shock. Therefore, the radially aligned polarization patterns observed in few young SNRs cannot be reproduced in the 1D MHD simulations. The period SNR takes for the transition from the earliest ejecta-driven phase to the Sedov phase is long enough, with its distinctive physical features, headed by the energy conversion from mostly kinetic one to a fixed ratio between the thermal and kinetic components. This transition worth to be distinguished as a phase in SNR evolutionary scheme. The updated sequence of stages in SNR evolution could be the free expansion (of gas) – energy conversion – Sedov–Taylor – post-adiabatic – radiative.

New unexpected flow patterns in the problem of the stellar wind interaction with the interstellar medium: stationary ideal-MHD solutions

ABSTRACT The astropause (heliopause for the Sun) is the tangential discontinuity separating the stellar wind from the interstellar plasma. The global shape of the heliopause is a matter of debates. Two types of the shape are under discussion: comet-like and tube-like. In the second type, the two-jets oriented towards the stellar rotation axis are formed by the action of azimuthal component of the stellar magnetic field. We explore a simplified global astrosphere in which (1) the surrounding and moving with respect to the star circumstellar medium is fully ionized, (2) the interstellar magnetic field is neglected, (3) the radial component of the stellar magnetic field is neglected as compared with the azimuthal component, and (4) the stellar wind outflow is spherically symmetric and supersonic. We present the results of numerical 3D MHD modelling and explore how the global structure depends on the gas-dynamic Mach number of the interstellar flow, M∞, and the Alfvenic Mach number in the stellar wind. It is shown that the astropause has a tube-like shape for small values of M∞. The wings of the tube are distorted towards the tail as larger as larger the Mach number is. The new (to our knowledge) result is the reverse interstellar flow in the vicinity of the astropause in the tail. The larger the interstellar Mach number is the narrower the reverse flow is. At some values of the Mach number, the stellar wind overcomes the reverse interstellar flow and moves out in downwind. In this regime, the astropause changes its topology from tube-like to sheet-like.