Magnetic Pressure Research Articles

Снижение механических напряжений в тонкостенной квазибессиловой магнитной системе, внесенной во внешние скрещенные магнитные поля

The mechanical stresses in the thin-walled quasi-force-free winding of the solenoid, which arise when a strong pulsed magnetic field is produced, can be significantly reduced if the winding is inserted into the area between two magnets creating crossed fields. It is shown that with a rational choice of the amplitude and shape of the external fields pulses the stresses can be reduced to values less than one tenth of the magnetic pressure of the generated field.

The mechanical stresses reduction in a thin-walled quasi-force-free magnetic system inserted into external crossed magnetic fields

The mechanical stresses in the thin-walled quasi-force-free winding of the solenoid, which arise when a strong pulsed magnetic field is produced, can be significantly reduced if the winding is inserted into the space between two magnets creating crossed fields. It is shown that, with a rational choice of the amplitude and shape of the external field pulses, the stresses can be reduced to values less than one tenth of the magnetic pressure of the generated field. Keywords: strong magnetic fields, quasi-force-free field, force-balanced coil.

Effect of dusty plasma parameters on the low frequency Hall current instability

The effect of power-law dust size distribution and dust number density on the low frequency hall current instabilities have been studied in and above the equatorial electrojet altitudes using a linear fluid model consisting of electrons, ions and dust particles. The dispersion relation includes electron and ion drift perpendicular to the equilibrium uniform electric and magnetic field, mass and pressure of the charged species and collision between charged and neutral particles. The effect of dust size variation and dust number density on the instability have been investigated by varying the dust-plasma frequency in the dispersion relation. It has been found that in the region of the electrojet altitudes the variation of dust size for the case of broad dust size distribution and dust number density can substantially increase the growth rate and frequency of the instability. However, above the electrojet region where ions become weakly magnetized, the above two dust parameters have a negligible effect on the instability.The present analysis is applicable to the dusty meteor trail plasma of the ionospheric E-region.

Implementation of advanced Riemann solvers in a neutrino-radiation magnetohydrodynamics code in numerical relativity and its application to a binary neutron star merger

We implement advanced Riemann solvers HLLC and HLLD \cite{Mignone:2005ft,MUB:2009} together with an advanced constrained transport scheme \cite{Gardiner:2007nc} in a numerical-relativity neutrino-radiation magnetohydrodynamics code. We validate our implementation by performing a series of one- and multi-dimensional test problems for relativistic hydrodynamics and magnetohydrodynamics in both Minkowski spacetime and a static black hole spacetime. We find that the numerical solutions with the advanced Riemann solvers are more accurate than those with the HLLE solver \cite{DelZanna:2002rv}, which was originally implemented in our code. As an application to numerical relativity, we simulate an asymmetric binary neutron star merger leading to a short-lived massive neutron star both with and without magnetic fields. We find that the lifetime of the rotating massive neutron star formed after the merger and also the amount of the tidally-driven dynamical ejecta are overestimated when we employ the diffusive HLLE solver. We also find that the magnetorotational instability is less resolved when we employ the HLLE solver because of the solver's large numerical diffusivity. This causes a spurious enhancement both of magnetic winding resulting from large scale poloidal magnetic fields, and also of the energy of the outflow induced by magnetic pressure.

Impact of an MHD Cattaneo-Christov model for a Williamson fluid flow across a wedge with a convective boundary condition: Homotopy Analysis Method

The present study aims to scrutinise the influence of the Cattaneo-Christov (CC) heat flux model on magnetohydrodynamic (MHD) laminar boundary-layer flow through a wedge in a non-Newtonian Williamson fluid along with convective boundary condition embedded in a porous medium. Significantly, the presence of the CC model explores the heat transfer characteristics which forecast the effect of thermal relaxation time on the boundary-layer phenomenon. The governing equations are formulated and modified into non-linear, coupled ODEs by utilising similarity transformations and then tackled by Homotopy Analysis Method (HAM). The obtained results are discussed and presented graphically for various values of emerging parameters on velocity and temperature distributions. The results reveal that the velocity is an enhancing function of the magnetic parameter, permeability parameter and Hartree pressure gradient parameter whereas decreasing with larger values of the Williamson fluid parameter. It is evident that the temperature upsurges due to the Biot number and decays with the relaxation parameter. The numerical values of skin-friction and Nusselt number are tabulated. Comparative reviews between the formerly published literature and the current data are made for specific cases, which are inspected to be in tremendous agreement. Abbreviations: BLF: Boundary layer flow; MHD Magnetohydrodynamic; CC model: Cattaneo-Christov model; NNF: non-Newtonian fluid; ODEs: Ordinary differential equations; PDEs: Partial differential equations

First-Principles Theory of the Relativistic Magnetic Reconnection Rate in Astrophysical Pair Plasmas.

We develop a first-principles model for the relativistic magnetic reconnection rate in strongly magnetized pair plasmas. By considering the energy budget and required current density near the x-line, we analytically show that in the magnetically dominated relativistic regime, the x-line thermal pressure is significantly lower than the upstream magnetic pressure due to the extreme energy needed to sustain the current density, consistent with kinetic simulations. This causes the upstream magnetic field lines to collapse in, producing the open outflow geometry which enables fast reconnection. The result is important for understanding a wide range of extreme astrophysical environments, where fast reconnection has been evoked to explain observations such as transient flares and nonthermal particle signatures.

The circumgalactic medium of Milky Way-like galaxies in the TNG50 simulation – I: halo gas properties and the role of SMBH feedback

ABSTRACT We analyse the physical properties of gas in the circumgalactic medium (CGM) of 132 Milky Way (MW)-like galaxies at z = 0 from the cosmological magneto-hydrodynamical simulation TNG50, part of the IllustrisTNG project. The properties and abundance of CGM gas across the sample are diverse, and the fractional budgets of different phases (cold, warm, and hot), as well as neutral H i mass and metal mass, vary considerably. Over our stellar mass range of $10^{10.5} < M_\star /{\rm M}_\odot < 10^{10.9}$, radial profiles of gas physical properties from $0.15 < R/R_{\rm 200c} < 1.0$ reveal great CGM structural complexity, with significant variations both at fixed distance around individual galaxies, and across different galaxies. CGM gas is multiphase: the distributions of density, temperature, and entropy are all multimodal, while metallicity and thermal pressure distributions are unimodal; all are broad. We present predictions for magnetic fields in MW-like haloes: a median field strength of $|B|\sim 1\,\mu{\rm G}$ in the inner halo decreases rapidly at larger distance, while magnetic pressure dominates over thermal pressure only within ${\sim}0.2 \times R_{\rm 200c}$. Virial temperature gas at ${\sim}10^6\,{\rm K}$ coexists with a subdominant cool, $\lt 10^5\,{\rm K}$, component in approximate pressure equilibrium. Finally, the physical properties of the CGM are tightly connected to the galactic star formation rate, in turn dependent on feedback from supermassive black holes (SMBHs). In TNG50, we find that energy from SMBH-driven kinetic winds generates high-velocity outflows (≳500–2000 km s−1), heats gas to supervirial temperatures (>106.5–7 K), and regulates the net balance of inflows versus outflows in otherwise quasi-static gaseous haloes.

A Study of One-dimensional Weak Shock Propagation Under the Action of Axial and Azimuthal Magnetic Field: An Analytical Approach

The present paper presents an analytical study of the one-dimensional weak shock wave problem in a perfect gas under the action of a generalized magnetic field subjected to weak shock jump conditions (R-H conditions). The magnetic field is considered axial and azimuthal in cylindrically symmetric configuration. By considering a straightforward analytical approach, an explicit solution exhibiting time-space dependency for gas-dynamical flow parameters and total energy (generated during the propagation of the weak shock from the center of the explosion) has been obtained under the significant influence of generalized magnetic fields (axial and azimuthal) and the results are analyzed graphically. From the outcome, it is worth noticing that for an increasing value of Mach number under the generalized magnetic field, the decay process of physical parameters (density, pressure, and magnetic pressure) is a bit slower, whereas the velocity profile and total energy increase rapidly with respect to time. Moreover, for increasing values of Shock-Cowling number the total energy grows rapidly with respect to time.

Identifying the Structure and Propagation of Dawnside Pc5 ULF Waves Using Space‐Ground Conjunctions

AbstractPc5 ultralow frequency waves are important for transferring energy between the magnetosphere and ionosphere. While many observations have been performed on Pc5 waves properties, it has been difficult to determine the source region, signal propagation path, and the two‐dimensional structure of Pc5 waves beyond coverage by a small number of satellites. Pc5 waves often show a dawn‐dusk asymmetry, but the cause of the asymmetry is under debate. To address these issues, we used conjunction events between the THEMIS satellites and all‐sky imagers and analyzed two Pc5 wave events that were stronger on the dawnside. For both events, the Pc5 waves propagated from dawnside magnetopause toward the nightside magnetosphere. The Pc5 waves were also associated with dawnside magnetopause surface waves, which were probably induced by the Kelvin‐Helmholtz instability. The ionospheric equivalent currents identified multiple vortices on the dawnside associated with quasi‐periodic auroral arcs and much weaker perturbations on the duskside. Global auroral imaging also presented a similar dawn‐dusk asymmetry with multiple arcs on the dawnside, while only one or two major arcs existed on the duskside. Pc5 waves in the magnetosphere had an anti‐phase relation between the total magnetic field and thermal pressure, with a slower propagation velocity compared with magnetohydrodynamic waves. The Poynting flux was anti‐sunward with an oscillating field‐aligned component. These properties suggest that Pc5 waves were slow or drift mirror mode waves coupled with standing Alfven waves. The ground‐based and multi‐satellite observations provide crucial information for determining the Pc5 waves properties, possible source region, and signal propagation path.

Delta shocks and vacuum states in the Riemann solutions of Chaplygin Euler equations as pressure and magnetic field drop to zero

The aim of this study is to solve the Riemann problem of isentropic magnetogasdynamics equations for a more realistic version of the extended Chaplygin gas model. The analysis demonstrates that under some special circumstances, delta shock and vacuum appear in the solution, describing the phenomena of concentration and cavitation, respectively. By examining the limiting behavior, it is obtained that solutions coincide with corresponding Riemann solutions of the transport equations when both the magnetic field and pressure drop to zero.

The JCMT BISTRO Survey: A Spiral Magnetic Field in a Hub-filament Structure, Monoceros R2

We present and analyze observations of polarized dust emission at 850 μm toward the central 1 × 1 pc hub-filament structure of Monoceros R2 (Mon R2). The data are obtained with SCUBA-2/POL-2 on the James Clerk Maxwell Telescope (JCMT) as part of the B-fields in Star-forming Region Observations survey. The orientations of the magnetic field follow the spiral structure of Mon R2, which are well described by an axisymmetric magnetic field model. We estimate the turbulent component of the magnetic field using the angle difference between our observations and the best-fit model of the underlying large-scale mean magnetic field. This estimate is used to calculate the magnetic field strength using the Davis–Chandrasekhar–Fermi method, for which we also obtain the distribution of volume density and velocity dispersion using a column density map derived from Herschel data and the C18O (J = 3 − 2) data taken with HARP on the JCMT, respectively. We make maps of magnetic field strengths and mass-to-flux ratios, finding that magnetic field strengths vary from 0.02 to 3.64 mG with a mean value of 1.0 ± 0.06 mG, and the mean critical mass-to-flux ratio is 0.47 ± 0.02. Additionally, the mean Alfvén Mach number is 0.35 ± 0.01. This suggests that, in Mon R2, the magnetic fields provide resistance against large-scale gravitational collapse, and the magnetic pressure exceeds the turbulent pressure. We also investigate the properties of each filament in Mon R2. Most of the filaments are aligned along the magnetic field direction and are magnetically subcritical.

Quasi-periodic and chaotic structure of Alfvén waves in a plasma containing double spectral distributed electrons

The nonlinear characteristics of Alfvén waves in a plasma medium composed of double spectral electron distribution and positive and negative ions are investigated. A Korteweg–de Vries (KdV-type) equation is derived using the reductive perturbation technique. The periodic and soliton structures are investigated. The effects of the two spectral indices r and q on the produced periodic structures are studied. It is found that the amplitude of the rarefactive periodic wave increases by increasing the values of r and q. Some external perturbation intruders on the system are considered, and the quasi periodic and chaotic structures of Alfvén waves are discussed. It is found that by decreasing the values of β− (knowing that β known as the ratio of kinetic to magnetic pressures), the periodic structure is converted gradually into chaotic structure passing through the quasi-periodic one. The results of this study are helpful in describing the behavior of the Alfvénic structure of periodic waves and other related events in the ionosphere region.

Crystal Chemistry and Physics of UCd11.

In the phase diagram U-Cd, only one compound has been identified so far─UCd11 (space group Pm3̅m). Since the discovery of this material, the physical properties of UCd11 have attracted a considerable amount of attention. In particular, its complex magnetic phase diagram─as a result of tuning with magnetic field or pressure─is not well-understood. From a chemical perspective, a range of lattice parameter values have been reported, suggesting a possibility of a considerable homogeneity range, i.e., UCd11-x. In this work, we perform a simultaneous study of crystallographic features coupled with measurements of physical properties. This work sheds light on the delicate relationship between the intrinsic crystal chemistry and magnetic properties of UCd11.

A finite volume method for ferrohydrodynamic problems coupled with microscopic magnetization dynamics

A finite volume method is developed for the ferrohydrodynamics (FHD) dealing with the mechanics of fluid motion influenced by strong forces of magnetic polarization. The Shliomis model consisting of the continuity equation, the momentum equation, the angular momentum equation, the magnetization equations, and the Poisson's equation of magnetostatics is adopted to describe the FHD problems, where the hydrodynamics are strongly coupled with the magnetization dynamics. Unlike most of the previous FHD simulations, where the Debye-like magnetization equation was frequently used, we employ the microscopically derived magnetization equation to describe the evolution of ferrofluid magnetization in order to be valid in a wide range of flow rates, magnetic field strengths and oscillating frequencies. In the proposed method, each governing equation is discretized by employing the finite-volume scheme, and the variables in FHD, including the magnetic field, velocity, pressure, and magnetization are uncoupled by using an iteratively uncoupled strategy. The magnetization field is obtained by iteratively solving a Langevin equation using Newton method and the microscopical magnetization equation employing finite volume method in an inner iterative loop. Comparisons of the results obtained by the proposed method with the corresponding analytic or asymptotic solutions for the Couette–Poiseuille flows of ferrofluids in the absence or subjected to magnetic fields validate its feasibility in solving the pure hydrodynamics, pure magnetization dynamics, and the general FHD problems with hydrodynamic-magnetic coupling effects.

Accretion process, magnetic fields, and apsidal motion in the pre-main sequence binary DQ Tau

ABSTRACT Classical T Tauri stars (CTTSs) are young stellar objects that accrete materials from their accretion disc influenced by their strong magnetic field. The magnetic pressure truncates the disc at a few stellar radii and forces the material to leave the disc plane and fall onto the stellar surface by following the magnetic field lines. However, this global scheme may be disturbed by the presence of a companion interacting gravitationally with the accreting component. This work is aiming to study the accretion and the magnetic field of the tight eccentric binary DQ Tau, composed of two equal-mass (∼ 0.6 M⊙) CTTSs interacting at different orbital phases. We investigated the variability of the system using a high-resolution spectroscopic and spectropolarimetric monitoring performed with ESPaDOnS at the CFHT. We provide the first ever magnetic field analysis of this system, the Zeeman–Doppler imaging revealed a stronger magnetic field for the secondary than the primary (1.2 and 0.5 kG, respectively), but the small-scale fields analysed through Zeeman intensification yielded similar strengths (about 2.5 kG). The magnetic field topology and strengths are compatible with the accretion processes on CTTSs. Both components of this system are accreting, with a change of the main accretor during the orbital motion. In addition, the system displays a strong enhancement of the mass accretion rate at periastron and apastron. We also discovered, for the first time in this system, the apsidal motion of the orbital ellipse.

Bayesian inference of axisymmetric plasma equilibrium

We present a Bayesian method for inferring axisymmetric plasma equilibria from the magnetic field and plasma pressure measurements. The method calculates all possible solutions for plasma current and pressure distributions consistent with the measurements and magnetohydrodynamic (MHD) force balance. Toroidal plasma current and magnetic field coils are modelled as a set of axisymmetric current-carrying solid beams. The other parameters such as plasma pressure and poloidal current flux are given as a function of poloidal magnetic flux, which is determined given a 2D current distribution. Plasma pressure and poloidal current flux profiles are modelled as Gaussian processes whose smoothness is optimally chosen based on the principle of Occam’s razor. To find equilibrium solutions, we introduce an MHD force balance constraint at every plasma current beam as a part of the prior knowledge. Given all these physical quantities, predictions calculated by the predictive (forward) models for diagnostics are compared to the observations. The high dimensional complex posterior probability distribution is explored by a new algorithm based on the Gibbs sampling scheme.

Research on Theory and Simulation of Magnetic Liquid Micro Differential Pressure Sensor

With magnetic liquid micro differential pressure sensor as the research object, using the finite element analysis software COMSOL, magnetic liquid micro differential pressure sensor are analyzed and calculated by first hall element in the location of the magnetic field change curve, and then analyzed the magnetic liquid micro differential pressure sensor restoring force curve, analyzes the three different change trend of the spacing between the initial magnetic field force, And the change equation of magnetic force is fitted. Finally, the pressure resistance of the magnetic liquid micro-differential pressure sensor is calculated to ensure the integrity of the magnetic liquid sealing ring in the range of measurement, so that it has good sealing performance. The results show that when the distance between two cylindrical permanent magnets L=10mm, the magnetic flux density B at the central axis changes approximately linearly with the distance. The recovery force curve of permanent magnet has good linearity in the spacing range of 24mm ~ 40mm. The sensor has a four-stage magnetic liquid sealing ring, the overall pressure resistance value is four times the unilateral pressure resistance capacity, the theoretical pressure resistance value of magnetic liquid is 5000Pa.

Effects of applied magnetic field and pressure on the diamagnetic susceptibility and binding energy of donor impurity in GaAs quantum dot considering the non-parabolicity model’s influence

ABSTRACT In this article, we investigate the influence of the hydrostatic pressure, magnetic field, and conduction band non-parabolicity on both the diamagnetic susceptibility and the binding energy of shallow donor impurity in a quantum disk made out of GaAs. The Hamiltonian of the investigated problem has been solved within the framework of the effective-mass approximation. The energy minimisation has been performed using a variational approach. Our results reveal that both the diamagnetic susceptibility and binding energy have been reduced with increasing the disk size. Moreover, the diamagnetic susceptibility increases as the impurity moves from the extremity to the centre of the disk. However, both the diamagnetic susceptibility and binding energy have been improved under applied magnetic field, hydrostatic pressure, and by considering the conduction band non-parabolicity model as well. We hope that the reported results will be a modest contribution to further theoretical research in the field of nanostructures.

Dynamics of magnetic microbubble transport in blood vessels

Magnetic microbubbles (MMBs) can be controlled and directed to the target site by a suitable external magnetic field, and thus have potential in therapeutic drug-delivery application. However, few studies focus on their dynamics in blood vessels under the action of magnetic and ultrasonic fields, giving little insight into the mechanism generated in diagnostic and therapeutic applications. In this study, equations of MMBs were established for simulating translation, radial pulsation and the coupled effect of both. Meanwhile, the acoustic streaming and shear stress on the vessel wall were also presented, which are associated with drug release. The results suggest that the magnetic pressure increases the bubble pulsation amplitude, and the translation coupled with pulsation is manipulated by the magnetic force, causing retention in the target area. As the bubbles approach the vessel wall, the acoustic streaming and shear stress increase with magnetic field enhancement. The responses of bubbles to a uniform and a gradient magnetic field were explored in this work. The mathematical models derived in this work could provide theoretical support for experimental phenomena in the literature and also agree with the reported models.

A characterization of plasma properties of a heterogeneous magnetized low pressure discharge column

An approach is presented for characterizing heterogeneous magnetized plasma discharge tubes through the scattering of electromagnetic plane waves. Here, we formulate the analytical problem of electromagnetic scattering from a gyrotropic plasma column. The scattering accounts for the heterogeneous composition of the cylindrical discharge plasma and facilitates determining its propensity for gyrotropic scattering, particularly when electron collisional damping may be prevalent. The analytical results are validated using computational simulations. Scattered fields from the magnetized plasma are measured experimentally, and, by comparing the analytical and experimental results, the unknown parameters of the discharge, i.e., characteristic plasma and electron collisional damping frequencies, are determined. The technique is relatively straight-forward to use and removes the need for commercial computational electromagnetic simulations when experimental data on scattering characteristics of such cylindrical discharge plasmas are available.