Perpendicular Pressure Research Articles

Juno Observations of Jupiter's Magnetodisk Plasma: Implications for Equilibrium and Dynamics.

The Jovian magnetodisk plays an essential role in the dynamics of the Jupiter system by coupling its various components. Here, we investigate the Juno (JADE, JEDI, and MAG) observations of the magnetodisk within 20-80 Jupiter radii ( ) in the 0-6hr local time sector. JADE and JEDI data are combined to generate equatorial plane distributions of density, pressure, temperature, and anisotropy of electrons, protons, and heavy ions. Results show: (a) Heavy ions dominate both the number density and pressure. (b) The number density and pressure of all species decrease with radial distance. (c) The temperature increases for electrons and heavy ions and decreases for protons as radial distance increases. (d) On average, the parallel pressure exceeds the perpendicular pressure for all species. Based on these distributions, we explore the equilibrium and dynamics of the magnetodisk and show that: (a) Radial force balance is primarily achieved between the inward magnetic stress and the outward plasma anisotropy force. (b) An examination of the kappa parameters indicates that electrons, protons, and heavy ions primarily undergo adiabatic motion, magnetic moment diffusion, and stochastic motion, respectively. (c) A radial diffusion coefficient is derived from the radial profile of mass, providing an estimate of the timescale for radial transport from 20 to 80 of 7hr (d) The total mass ( kg) and thermal energy ( eV) of the magnetodisk between 20 and 80 are obtained.

Going Beyond the MHD Approximation: Physics-based Numerical Solution of the CGL Equations

We present a new numerical model for solving the Chew–Goldberger–Low system of equations describing a bi-Maxwellian plasma in a magnetic field. Heliospheric and geospace environments are often observed to be in an anisotropic state with distinctly different parallel and perpendicular pressure components. The Chew–Goldberger–Low (CGL) system represents the simplest leading order correction to the common isotropic MHD model that still allows the incorporation of the latter’s most desirable features. However, the CGL system presents several numerical challenges: the system is not in conservation form, the source terms are stiff, and unlike MHD, it is prone to a loss of hyperbolicity if the parallel and perpendicular pressures become too different. The usual cure is to bring the parallel and perpendicular pressures closer to one another, but that has usually been done in an ad hoc manner. We present a physics-informed method of pressure relaxation based on the idea of pitch-angle scattering that keeps the numerical system hyperbolic and naturally leads to zero anisotropy in the limit of very large plasma beta. Numerical codes based on the CGL equations can, therefore, be made to function robustly for any magnetic field strength, including the limit where the magnetic field approaches zero. The capabilities of our new algorithm are demonstrated using several stringent test problems that provide a comparison of the CGL equations in the weakly and strongly collisional limits. This includes a test problem that mimics the interaction of a shock with a magnetospheric environment in 2D.

Thermodynamic properties of quasi-one-dimensional fluids.

We calculate thermodynamic and structural quantities of a fluid of hard spheres of diameter σ in a quasi-one-dimensional pore with accessible pore width W smaller than σ by applying a perturbative method worked out earlier for a confined fluid in a slit pore [Franosch et al. Phys. Rev. Lett. 109, 240601 (2012)]. In a first step, we prove that the thermodynamic and a certain class of structural quantities of the hard-sphere fluid in the pore can be obtained from a purely one-dimensional fluid of rods of length σ with a central hard core of size σW=σ2-W2 and a soft part at both ends of length (σ - σW)/2. These rods interact via effective k-body potentials veff(k) (k ≥ 2). The two- and the three-body potential will be calculated explicitly. In a second step, the free energy of this effective one-dimensional fluid is calculated up to leading order in (W/σ)2. Explicit results for, e.g., the perpendicular pressure, surface tension, and the density profile as a function of density, temperature, and pore width are presented and partly compared with results from Monte-Carlo simulations and standard virial expansions. Despite the perturbative character of our approach, it encompasses the singularity of the thermodynamic quantities at the jamming transition point.

Weak solutions for extended magnetohydrodynamics using linear combination of entropies

It is commonplace to solve the extended magnetohydrodynamics (MHD) system of equations in non-conservative form, in particular using equations for pressures. This approach leads to unpredictable behavior at discontinuities such as shock fronts. Here we propose using a linear combination of entropy densities to distribute the non-adiabatic heating among the various pressure components in a deterministic manner. In particular, we describe algorithms that can distribute the non-adiabatic heating between electrons and ions when the electron and ion temperatures are solved separately, and between parallel and perpendicular pressures for anisotropic pressure MHD. The same approach can also be used for extended hydrodynamic equations. The algorithm is based on conservation laws, which provides proper convergence to weak solutions as demonstrated by numerical tests.

On the arbitrary amplitude ion-acoustic structures in an anisotropic non-Maxwellian electron–positron–ion magnetoplasma

This paper comprehensively investigates the oblique propagation of ion-acoustic solitary waves (IASWs) with arbitrary amplitude in a magnetoplasma consisting of inertialess non-Maxwellian (nonthermal) electrons, inertialess Maxwellian positrons, and inertial adiabatically heated ions. It is postulated that the positive ions demonstrate adiabatic behavior that is distinguished by anisotropic thermal pressure. The study utilizes Sagdeev's pseudopotential theory to analyze the fluid equations of the plasma model and reduce them to the energy equation. Different plasma configuration factors, such as nonthermal parameters, positron concentration, and parallel and perpendicular ion pressure, are being studied to see how they affect the properties of solitary waves with large amplitudes. The findings demonstrate the simultaneous coexistence of compressive and rarefactive IASWs, significantly influenced by positrons and nonthermal electron parameters. The study provides valuable insights into wave phenomena in magnetized plasmas and presents possible applications in both Space and laboratory plasma environments.

The effect of the track plan on the damage to rails by contact fatigue crambling

An analysis of foreign and domestic experience in improving traffic safety while extending the service life of rails and improving their interaction with the wheels of rolling stock shows that the working conditions of rails are much more difficult in curved sections of the track, especially in the outer thread, due to the intense impact of the ridges of the wheels of rolling stock on the lateral working One of the reasons for the formation of contact fatigue stains on the lateral working surface of the rail head is the presence of tangential stresses that occur in the absence of perpendicular pressure of the wheel on the rail head. In addition, the movement of the wheels on the rails is accompanied by slippage, which appears due to the taper of the wheels and the occurrence of the wheel crest on the rail head. A typical case of the wheel crest running over the rail head is the movement of the crew along curved sections of the track. In this case, the guide axle runs over one of the wheels on the rail head. As a result, there is a transverse slip of the wheel on the rolling surface and friction forces between the wheel and the rail are appropriately oriented to the axes. These processes, enhanced by an increase in dynamic action, cause more intense damage to the rail heads by defects 11 in the curves, while defects mostly appear on the outer rail thread.

On the shock wave structures in anisotropy magnetoplasmas

In this work, the propagation of nonlinear electrostatic shock wave structures in an anisotropy pressure magnetoplasma composed of warm inertial ions and inertia-less Maxwellian electrons is reported. For this purpose, the technique of reductive perturbation is applied for reducing fluid equations of the current model to the Korteweg–de Vries Burgers (KdVB) equation with a second-order dissipative term and the KdVB–Kuramoto (KBK) equation with both second- and fourth-order dissipative terms. The impact of various plasma parameters, including the parallel ion pressure, perpendicular ion pressure, and dissipation parameter, on the significant characteristics of the shock wave profile is examined and discussed. In addition, a comparison between the profiles of KdVB shocks and KdVB–Kuramoto shocks is reported. We expect that KBK shock wave amplitudes become larger than the KdVB ones by taking the fourth-order dissipative into consideration. Thus, the results of the KBK equation may treat the difference between the theoretical and laboratory results or satellite observations.

Oblique Arbitrary Amplitude Dust Ion Acoustic Solitary Waves in Anisotropic Non-Maxwellian Plasmas with Kappa-Distributed Electrons

In this paper, we investigate the behavior of dust ion acoustic solitary waves (DIASWs) with arbitrary amplitudes in a magnetized anisotropic dusty plasma that includes inertial hot ion fluid, electrons following a Kappa distribution, and negatively charged dust particles in the background. An ambient magnetic field aligns with the x-direction, while the wave propagation occurs obliquely to the ambient magnetic field. In the linear regime, two distinct modes, namely fast and slow modes, are observed. We employ the Sagdeev pseudo-potential method to analyze the fundamental properties of arbitrary amplitude DIASWs. Additionally, we examine how various physical parameters influence the existence and characteristics of symmetric planar dust ion acoustic solitary structures (DIASs). The characteristics of the solitary structures are greatly influenced by the dust concentration, the electrons superthermality (spectral) index, the obliquity parameter, the magnetic field, the parallel ion pressure and the perpendicular ion pressure. The results show that the amplitude and width of both compressive and rarefactive DIASWs are sensitive to the degree of electron superthermality and dust concentration. Additionally, it is shown that the propagation features of DIASWs are highly affected by the parallel component of ion pressure as compared to perpendicular component of ion pressure.

Microphysically modified magnetosonic modes in collisionless, high-β plasmas

With the support of hybrid-kinetic simulations and analytic theory, we describe the nonlinear behaviour of long-wavelength non-propagating (NP) modes and fast magnetosonic waves in high-$\beta$collisionless plasmas, with particular attention to their excitation of and reaction to kinetic micro-instabilities. The perpendicularly pressure balanced polarization of NP modes produces an excess of perpendicular pressure over parallel pressure in regions where the plasma$\beta$is increased. For mode amplitudes$|\delta B/B_0| \gtrsim 0.3$, this excess excites the mirror instability. Particle scattering off these micro-scale mirrors frustrates the nonlinear saturation of transit-time damping, ensuring that large-amplitude NP modes continue their decay to small amplitudes. At asymptotically large wavelengths, we predict that the mirror-induced scattering will be large enough to interrupt transit-time damping entirely, isotropizing the pressure perturbations and morphing the collisionless NP mode into the magnetohydrodynamic (MHD) entropy mode. In fast waves, a fluctuating pressure anisotropy drives both mirror and firehose instabilities when the wave amplitude satisfies$|\delta B/B_0| \gtrsim 2\beta ^{-1}$. The induced particle scattering leads to delayed shock formation and MHD-like wave dynamics. Taken alongside prior work on self-interrupting Alfvén waves and self-sustaining ion-acoustic waves, our results establish a foundation for new theories of electromagnetic turbulence in low-collisionality, high-$\beta$plasmas such as the intracluster medium, radiatively inefficient accretion flows and the near-Earth solar wind.

Oblique propagation of arbitrary amplitude ion acoustic solitary waves in anisotropic electron positron ion plasma

The oblique propagation of arbitrary ion acoustic solitary waves (IASWs) in magnetized electron-positron-ion plasmas is investigated by employing Sagdeev pseudopotential approach. Ions are assumed to be adiabatic having anisotropic thermal pressure. Electrons and positrons are considered to be isothermal, following Maxwellian distribution. In terms of electrostatic potential, Sagdeev potential function is obtained and analyzed numerically in the context of relevant plasma configuration parameters. The existence region of solitary pulses is defined accurately. It is investigated how several plasma configuration parameters, such as the positron concentration, parallel, and perpendicular ion pressure affect soliton characteristics.

Effect of roughness and pore pressure on shear behavior of rock joint under true triaxial loading conditions

This paper presents the direct shear test to investigate the effect of the joint roughness and pore pressure on the shear behavior of rock joints. Recently, we have developed an experimental method for the direct shear test using true triaxial apparatus that can control three mutually perpendicular loads and pore pressure independently. The morphological properties of the joints were quantified using a non-contact 3D laser scanner to investigate the change in surface roughness due to shear and the effect of pore pressure. In addition, the time variation of shear load, normal displacement, and flow rate on the joint during shear sliding were measured, and the relationship with the change of the discontinuous surface after the experiment was discussed.

Anisotropic pressure effects on nanoconfined water within narrow graphene slit pores.

There is an increasing interest toward disclosing and explaining confinement effects on liquids, such as water or aqueous solutions, in slit pore setups. Particularly puzzling are the changes of physical and chemical properties in the nanoconfinement regime where no bulk-like water phase exists between the two interfacial water layers such that the density profile across the slit pore becomes highly stratified, ultimately leading to bilayer and monolayer water. These changes must be quantified with respect to some meaningful reference state of water, the most natural one being bulk water at the same pressure and temperature conditions. However, bulk water is a homogeneous liquid with isotropic properties, whereas water confined in slit pores is inhomogeneous, implying anisotropic properties as described by the perpendicular and parallel components of the respective tensors. In the case of pressure, the inhomogeneous nature of the setup results in a well-defined difference between the perpendicular and parallel pressure tensor components that is uniquely determined by the interfacial tension being a thermodynamic property. For bilayer water constrained in graphene slit pores that are only about 1 nm wide, we demonstrate that there exists a thermodynamic point where the pressure tensor of the inhomogeneous fluid, nanoconfined water, is effectively isotopic and the pressure is thus scalar as in the homogeneous fluid, bulk water. This specific point of vanishing effective interfacial tension is proposed to serve as a well-defined reference state to compare the properties of nanoconfined liquids to those of the corresponding bulk liquid at the same (isotropic) pressure and temperature conditions. In future work, this idea could be applied to assess confinement effects on chemical reactivity in aqueous solutions as well as to other nanoconfined liquids in other pores such as layered minerals.

Long-wavelength closures for collisional and neutral interaction terms in gyro-fluid models

A collisional gyro-fluid model is presented. The goal of the model is edge and scrape-off layer turbulence. The emphasize in the model derivation heavily lies on ”implementability” with today’s numerical methods. This translates to an avoidance of infinite sums, strongly coupled equations in time and intricate elliptic operator functions. The resulting model contains the four moments density, parallel momentum, perpendicular pressure and parallel energy and is closed by a polarisation equation and parallel Ampere law. The central ingredient is a collisional long-wavelength closure that relies on a drift-fluid gyro-fluid correspondence principle. In this way the extensive literature on fluid collisions can be incorporated into the model including sources, plasma-neutral interactions and scattering collisions. Even though this disregards the characteristic finite Larmor radius terms in the collisional terms the resulting model is at least as accurate as the corresponding drift-fluid model in these terms. Furthermore, the model does enjoy the benefits of an underlying variational principle in an energy-momentum theorem and an inherent symmetry in moment equations with regards to multiple ion species. Consistent particle drifts as well as finite Larmor radius corrections and high amplitude effects in the advection and polarization terms are further characteristics of the model. Extensions and improvements like short-wavelength expressions, a trans-collisional closure scheme for the low-collisionality regime or zeroth order potential must be added at a later stage.

Action principles and conservation laws for Chew–Goldberger–Low anisotropic plasmas

The ideal Chew–Goldberger–Low (CGL) plasma equations, including the double adiabatic conservation laws for the parallel ($p_\parallel$) and perpendicular pressure ($p_\perp$), are investigated using a Lagrangian variational principle. An Euler–Poincaré variational principle is developed and the non-canonical Poisson bracket is obtained, in which the non-canonical variables consist of the mass flux${\boldsymbol {M}}$, the density$\rho$, the entropy variable$\sigma =\rho S$and the magnetic induction${\boldsymbol {B}}$. Conservation laws of the CGL plasma equations are derived via Noether's theorem. The Galilean group leads to conservation of energy, momentum, centre of mass and angular momentum. Cross-helicity conservation arises from a fluid relabelling symmetry, and is local or non-local depending on whether the gradient of$S$is perpendicular to${\boldsymbol {B}}$or otherwise. The point Lie symmetries of the CGL system are shown to comprise the Galilean transformations and scalings.

Dissipative solitons in magnetized anisotropic plasma

The propagation of ion-acoustic (IA) dissipative solitons (DSs) is investigated in magnetized plasma with the presence of pressure anisotropy and Maxwellian distributed electrons. A nonlinear damped Korteweg-de Vries (d-KdV) type equation is derived for the potential by employing the reductive perturbation method (RPM) and its dissipative soliton solution is analyzed. The effect of plasma parameters like parallel anisotropic ion pressure p 1, perpendicular anisotropic ion pressure p 2, obliqueness l 3, ion-neutral collisional parameter γ and magnetic field strength Ω on the characteristics of DSs are investigated. The present investigation could be useful in space and astrophysical plasma systems.

Ion temperature effects on plasma flow in the magnetic mirror configuration

Effects of finite ion temperature on the plasma flow in the converging–diverging magnetic field, the magnetic mirror, or equivalently, magnetic nozzle configuration are studied using a quasineutral paraxial two-fluid MHD model with isothermal electrons and warm magnetized ions. The ion acceleration was studied with an emphasis on the role of the singularity at the sonic point transition. It is shown that the regularity of the sonic point defines a global solution describing plasma acceleration from subsonic to supersonic velocity. Stationary accelerating solutions were obtained and compared with the time dependent dynamics, confirming that the solutions of the time-dependent equations converge to the stationary solutions and, therefore, are stable. The effects of the ion pressure anisotropy were analyzed using the Chew–Golberger–Low model and its generalization. It is shown that the mirror force (manifested by the perpendicular ion pressure) enhances plasma acceleration. The role of ionization and charge exchange on plasma flow acceleration have been investigated.

Prediction of quantum anomalous Hall effect in CrI3/ScCl2 bilayer heterostructure

Based on first-principles calculations, a two-dimensional (2D) van der Waals (vdW) bilayer heterostructure consisting of two topologically trivial ferromagnetic (FM) monolayers CrI3 and ScCl2 is proposed to realize the quantum anomalous Hall effect (QAHE) with a sizable topologically nontrivial band gap of 4.5 meV. Its topological nature is attributed to an interlayer band inversion between the monolayers and critically depends on the symmetry of the stacking configuration. We further demonstrate that the topologically nontrivial band gap can be increased nearly linearly by the application of a perpendicular external pressure and reaches 8.1 meV at 2.7 GPa, and the application of an external out-of-plane electric field can also modulate the band gap and convert the system back to topologically trivial via eliminating the band inversion. An effective model is developed to describe the topological phase evolution in this bilayer heterostructure. This work provides a new candidate system based on 2D vdW materials for realization of potential high-temperature QAHE with considerable controllability.

Triggering tearing in a forming current sheet with the mirror instability

We study the time-dependent formation and evolution of a current sheet (CS) in a magnetised, collisionless, high-beta plasma using hybrid-kinetic particle-in-cell simulations. An initially tearing-stable Harris sheet is frozen into a persistently driven incompressible flow so that its characteristic thickness gradually decreases in time. As the CS thins, the strength of the reconnecting field increases, and adiabatic invariance in the inflowing fluid elements produces a field-biased pressure anisotropy with excess perpendicular pressure. At large plasma beta, this anisotropy excites the mirror instability, which deforms the reconnecting field on ion-Larmor scales and dramatically reduces the effective thickness of the CS. Tearing modes whose wavelengths are comparable to that of the mirrors then become unstable, triggering reconnection on smaller scales and at earlier times than would have occurred if the thinning CS were to have retained its Harris profile. A novel method for identifying and tracking X-points is introduced, yielding X-point separations that are initially intermediate between the perpendicular and parallel mirror wavelengths in the upstream plasma. These mirror-stimulated tearing modes ultimately grow and merge to produce island widths comparable to the CS thickness, an outcome we verify across a range of CS formation timescales and initial CS widths. Our results may find their most immediate application in the tearing disruption of magnetic folds generated by turbulent dynamo in weakly collisional, high-beta, astrophysical plasmas.

Nonlinear excitation of geodesic acoustic mode by drift waves in anisotropic tokamak plasmas with toroidal rotation

Nonlinear excitation of geodesic acoustic mode (GAM) by ions drift waves is investigated in anisotropic toroidally rotating tokamak plasmas by using an ideal magnetohydrodynamic model and standard double adiabatic equations. It is found that the radial wave number kx of the effectively excited GAM and the GAM frequency increase with the ratio of the perpendicular pressure to the parallel pressure χ as well as the toroidal rotation Mach number. The equilibrium anisotropy and the ratio of the radial scale length of the equilibrium density to the tokamak major radius are shown to play a significant role in the growth rate and frequency shift of GAM. The growth rate increases with the normalized GAM frequency first and then decreases to zero as the GAM frequency increases. When the GAM frequency increases again, the growth rate continues to increase but with a relatively smaller magnitude.

Statistical investigation of electric field fluctuations around the lower-hybrid frequency range at dipolarization fronts in the near-earth magnetotail

Dipolarization fronts (DFs) are thin magnetic boundary structures, embedded in short-duration, fast earthward-moving plasma flows, so-called bursty bulk flows. Previous case studies have shown that the density gradient at DFs can excite the lower-hybrid drift instability (LHDI) and resulting kinetic-scale waves. These waves feature strong electric field fluctuations perpendicular to the ambient magnetic field and associated effective particle acceleration/heating. In this study, we statistically examine electric field fluctuations in the lower-hybrid (LH) frequency range of 61 DF events, using data from the Magnetospheric Multiscale (MMS) Mission between 2017 and 2018 when the MMS apogee was in the magnetotail. We observed that all DF events exhibit enhanced power in the electric field fluctuations in the LH frequency range. Among the observed events, the power can vary by several orders of magnitude. The waves are detected for both high and low values of the perpendicular electron density or pressure gradient. In addition, the peak wave power within the DF is often observed at the time of steepest density gradient within the DF. The results also reveal that the wave power correlates with the magnetic flux transport rate of the DFs. These findings suggest that enhanced density and pressure gradients, which can be formed by large-scale flux transport at DFs, lead to LHDI-related kinetic-scale wave signatures at the DFs, and this may modify the original gradient layer profile of the DF in the course of its propagation from the source to the observation point.