Magnetic Rayleigh-Taylor Instability Research Articles

Mixing, heating and ion-neutral decoupling induced by Rayleigh-Taylor instability in prominence-corona transition regions.

This study explores nonlinear development of the magnetized Rayleigh-Taylor instability (RTI) in a prominence-corona transition region. Using a two-fluid model of a partially ionized plasma, we compare RTI simulations for several different magnetic field configurations. We follow prior descriptions of the numerical prominence model (Popescu Braileanu et al. 2021 Astron. Astrophys. 646, A93(doi:10.1051/0004-6361/202039053),Popescu Braileanu et al. 2021 Astron. Astrophys. 650, A181 (doi:10.1051/0004-6361/202140425)and Popescu Braileanu et al. 2023 Astron. Astrophys. 670, A31(doi:10.1051/0004-6361/202142996)) and explore the charged-neutral fluid coupling and plasma heating in a two-dimensional mixing layer for different magnetic field configurations. We also investigate how the shear in magnetic field surrounding a prominence may impact the release of the gravitational potential energy of the prominence material. We show that the flow decoupling is strongest in the plane normal to the direction of the magnetic field, where neutral pressure gradients drive ion-neutral drifts and frictional heating is balanced by adiabatic cooling of the expanding prominence material. We also show that magnetic field within the mixing plane can lead to faster nonlinear release of the gravitational energy driving the RTI, while more efficiently heating the plasma via viscous dissipation of associated plasma flows. We relate the computational results to potential observables by highlighting how integrating over under-resolved two-fluid sub-structure may lead to misinterpretation of observational data. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'.

Turbulent mixing in the vertical magnetic Rayleigh–Taylor instability

The presence of a mean magnetic field aligned with the direction of the acceleration greatly modifies the development of the Rayleigh–Taylor instability (RTI). High resolution direct numerical simulations of the Boussinesq–Navier–Stokes equations under the magnetohydrodynamics approximation reveal that, after an initial damping of the perturbations at the interface between the two miscible fluids, a rapid increase of the mixing layer is observed. Structures are significantly stretched in the vertical direction because magnetic tension prevents small-scale shear instabilities. When the vertical turbulent velocity exceeds the Alfvén velocity, the flow transitions to turbulence, structures break and an enhanced mixing occurs with strong dissipation. Afterwards, the mixing zone slows down and its growth rate is decreased compared to the hydrodynamic case. For larger magnitudes of the mean magnetic field, a strong anisotropy persists, and an increased fraction of potential energy injected into the system is lost into turbulent magnetic energy: as a consequence, the mixing zone growth rate is decreased even more. This phenomenology is embedded in a general buoyancy-drag equation, derived from simplified equations that reflect the large-scale dynamics, in which the drag coefficient is increased by the presence of turbulent magnetic energy.

Particle acceleration by magnetic Rayleigh-Taylor instability: Mechanism for flares in black hole accretion flows

Particle acceleration by magnetic Rayleigh-Taylor instability: Mechanism for flares in black hole accretion flows

Analysis of magnetized Rayleigh–Taylor instability in nanofluids through porous medium

Analysis of magnetized Rayleigh–Taylor instability in nanofluids through porous medium

Three-dimensional solar active region magnetohydrostatic models and their stability using Euler potentials

Active regions (ARs) are magnetic structures typically found in the solar atmosphere. We calculated several magnetohydrostatic (MHS) equilibrium models that include the effect of a finite plasma-β and gravity and that are representative of AR structures in three dimensions. The construction of the models is based on the use of two Euler potentials, α and β, that represent the magnetic field as B = ∇α × ∇β. The ideal MHS nonlinear partial differential equations were solved numerically using finite elements in a fixed 3D rectangular domain. The boundary conditions were initially chosen to correspond to a potential magnetic field (current-free) with known analytical expressions for the corresponding Euler potentials. The distinctive feature of our model is that we incorporated the effect of shear by progressively deforming the initial potential magnetic field. This procedure is quite generic and allowed us to generate a vast variety of MHS models. The thermal structure of the ARs was incorporated through the dependence of gas pressure and temperature on the Euler potentials. Using this method, we achieved the characteristic hot and overdense plasma found in ARs, but we demonstrate that the method can also be applied to study configurations with open magnetic field lines. Furthermore, we investigated basic topologies that include neutral lines. Our focus is on the force balance of the structures, and we do not consider the energy balance in the constructed models. In addition, we addressed the difficult question of the stability of the calculated 3D models. We find that if the plasma is convectively stable, then the system is not prone, in general, to develop magnetic Rayleigh-Taylor instabilities. However, when the plasma-β is increased or the density at the core of the AR is high, then the magnetic configuration becomes unstable due to magnetic buoyancy.

Magnetic field amplification and structure formation by the Rayleigh-Taylor instability

We report our results from a set of high-resolution, two-fluid, non-linear simulations of the magnetized Rayleigh Taylor instability (RTI) at the interface between a solar prominence and the corona. These data follow results reported earlier on linear and early non-linear RTI dynamics in this environment. This paper is focused on the generation and amplification of magnetic structures by RTI. The simulations use a two-fluid model that includes collisions between neutrals and charges, including ionization and recombination, energy and momentum transfer, and frictional heating. The 2.5D magnetized RTI simulations demonstrate that in a fully developed state of RTI, a large fraction of the gravitational energy of a prominence thread can be converted into quasi-turbulent energy of the magnetic field. The RTI magnetic energy generation is further accompanied by magnetic and plasma density structure formation, including dynamic formation, break-up, and merging of current sheets and plasmoid sub-structures. The flow decoupling between neutrals and charges, as well as ionization and recombination reactions, are shown to have significant impact on the structure formation in a magnetized RTI.

Growth rate of the turbulent magnetic Rayleigh-Taylor instability.

The Rayleigh-Taylor instability is strongly modified in the presence of a vertical mean magnetic field. Perturbations are first stretched in the vertical direction with no mixing due to the inhibition of small-scale shear instabilities. Then smooth elongated fingers eventually break after transition to turbulence, and a strong anisotropy persists. For increasing Alfvèn velocities, the growth rate of the mixing zone in the fully turbulent regime is decreased due to the conversion of potential energy into turbulent magnetic energy. A new theoretical prediction for the growth rate based on turbulent quantities is proposed and assessed with high-resolution direct numerical simulations of the Boussinesq-Navier-Stokes equationsunder the magnetohydrodynamics approximation.

Study of the effect of magnetic field characteristics on Rayleigh-Taylor instability with density gradient layers

Inertial confinement fusion (ICF) is a possible path of fusion technology for fusion ignition, but during the implosion of a magnetized plasma target by compression, the magnetic Rayleigh-Taylor (R-T) instability similar to that at the interface of the denser and less dense phases can arise when the plasma is subjected to gravitational and magnetic forces, which in turn affect the confinement characteristic and the process of fusion burn. In this study, the R-T instability of two phases in the presence/ absence of a magnetic field in a two-dimensional rectangular duct is simulated based on the MHD model adopted in ANSYS FLUENT. The simulation results show that the R-T instability is substantially weakened for the case with an Atwood number of 0.29 where a constant (DC) magnetic field is imposed in the opposite direction to the gravitational acceleration, meanwhile, a strong countercurrent flow, which occurs near the side walls, enhances the heat and mass transport process, which is related to the M-shape velocity profile formed in the flow channel. Besides, when a DC magnetic field perpendicular to the direction of the gravitational acceleration is introduced, the R-T instability vanishes from the initial moment to the end. When a sinusoidal wave form of varying (AC) magnetic field is introduced, the R-T instability is substantially facilitated. The evolutions of the interface and pressure field distribution are significantly correlated with the change in intensity and direction of the AC magnetic field. After about one cycle of the magnetic field's variation, the density gradient layers in the vertical direction are entirely converted to a density stratification in the horizontal direction with the denser phase occupying the region near the sidewalls of the duct, and ever since then, the R-T instability disappears completely. These findings can provide supports for the design of nuclear fusion devices and magnetic fields.

Magnetised winds in transition discs

Context. Protoplanetary discs are cold, dense, and weakly ionised environments that witness planetary formation. Among these discs, transition discs (TDs) are characterised by a wide cavity (up to tens of au) in the dust and gas distribution. Despite this lack of material, a considerable fraction of TDs are still strongly accreting onto their central star, possibly indicating that a mechanism is driving fast accretion in TD cavities. Aims. The presence of radially extended ‘dead zones’ in protoplanetary discs has recently revived interest in magnetised disc winds (MDWs), where accretion is driven by a large magnetic field extracting angular momentum from the disc. We propose that TDs could be subject to similar disc winds, and that these could naturally explain the fast-accreting and long-lived cavities inferred in TDs. Methods. We present the results of the first 2.5D global numerical simulations of TDs harbouring MDWs using the PLUTO code. We imposed a cavity in the gas distribution with various density contrasts, and considered a power-law distribution for the large-scale magnetic field strength. We assume the disc is weakly ionised and is therefore subject to ambipolar diffusion, as expected in this range of densities and temperatures. Results. We find that our simulated TDs always reach a steady state with an inner cavity and an outer ‘standard’ disc. These models also maintain an approximately constant accretion rate through the entire structure, reaching 10−7 M⊚ yr−1 for typical surface density values. The MDW launched from the cavity is more magnetised and has a significantly larger lever arm (up to 10) than the MDW launched from the outer disc. The material in the cavity is accreted at sonic velocities, and the cavity itself is rotating at 70% of the Keplerian velocity due to the efficient magnetic braking imposed by the MDW. Overall, our cavity matches the dynamical properties of an inner jet emitting disc (JED) and of magnetically arrested discs (MADs) in black-hole physics. Finally, we observe that the cavity is subject to recurring accretion bursts that may be driven by a magnetic Rayleigh-Taylor instability of the cavity edge. Conclusions. Some strongly accreting TDs could be the result of magnetised wind sculpting protoplanetary discs. Kinematic diagnostics of the disc or the wind (orbital velocity, wind speeds, accretion velocities) could disentangle classic photo-evaporation from MDW models.

Resolving the solar prominence/filament paradox using the magnetic Rayleigh–Taylor instability

Resolving the solar prominence/filament paradox using the magnetic Rayleigh–Taylor instability

Characterization of the stability and dynamics of a laser-produced plasma expanding across a strong magnetic field

Magnetized laser-produced plasmas are central to many studies in laboratory astrophysics, in inertial confinement fusion, and in industrial applications. Here, we present the results of large-scale three-dimensional magnetohydrodynamic simulations of the dynamics of a laser-produced plasma expanding into a transverse magnetic field with a strength of tens of teslas. The simulations show the plasma being confined by the strong magnetic field into a slender slab structured by the magnetized Rayleigh–Taylor instability that develops at the plasma–vacuum interface. We find that when the initial velocity of the plume is perturbed, the slab can develop kink-like motions that disrupt its propagation.

Magnetic Rayleigh–Taylor instability at a contact discontinuity with an oblique magnetic field

Aims.We investigate the nature of the magnetic Rayleigh–Taylor instability at a density interface that is permeated by an oblique homogeneous magnetic field in an incompressible limit.Methods.Using the system of linearised ideal incompressible magnetohydrodynamics equations, we derive the dispersion relation for perturbations of the contact discontinuity by imposing the necessary continuity conditions at the interface. The imaginary part of the frequency describes the growth rate of waves due to instability. The growth rate of waves is studied by numerically solving the dispersion relation.Results.The critical wavenumber at which waves become unstable, which is present for a parallel magnetic field, disappears because the magnetic field is inclined. Instead, waves are shown to be unstable for all wavenumbers. Theoretical results are applied to diagnose the structure of the magnetic field in prominence threads. When we apply our theoretical results to observed waves in prominence plumes, we obtain a wide range of field inclination angles, from 0.5° up to 30°. These results highlight the diagnostic possibilities that our study offers.

On a variational formulation of the weakly nonlinear magnetic Rayleigh–Taylor instability

The magnetic-Rayleigh–Taylor (MRT) instability is a ubiquitous phenomenon that occurs in magnetically-driven Z-pinch implosions. It is important to understand this instability since it can decrease the performance of such implosions. In this work, I present a theoretical model for the weakly nonlinear MRT instability. I obtain such a model by asymptotically expanding an action principle, whose Lagrangian leads to the fully nonlinear MRT equations. After introducing a suitable choice of coordinates, I show that the theory can be cast as a Hamiltonian system, whose Hamiltonian is calculated up to the sixth order in a perturbation parameter. The resulting theory captures the harmonic generation of MRT modes. It is shown that the amplitude at which the linear magnetic-Rayleigh–Taylor instability exponential growth saturates depends on the stabilization effect of the magnetic-field tension. Overall, the theory provides an intuitive interpretation of the weakly nonlinear MRT instability and provides a systematic approach for studying this instability in more complex settings.

Magnetic Rayleigh–Taylor Instability in an Experiment Simulating a Solar Loop

Abstract A hoop force driven magnetic Rayleigh–Taylor instability (MRTI) is observed in a laboratory experiment that simulates a solar coronal loop. Increase of the axial wavelength λ is observed when the axial magnetic field increases. This scaling is consistent with the theoretical MRTI growth rate , which implies that if is parallel to (i.e., undular mode), the fastest-growing mode has .

Laser-Produced Magnetic-Rayleigh-Taylor Unstable Plasma Slabs in a 20T Magnetic Field.

Magnetized laser-produced plasmas are central to many novel laboratory astrophysics and inertial confinement fusion studies, as well as in industrial applications. Here we provide the first complete description of the three-dimensional dynamics of a laser-driven plasma plume expanding in a 20T transverse magnetic field. The plasma is collimated by the magnetic field into a slender, rapidly elongating slab, whose plasma-vacuum interface is unstable to the growth of the "classical," fluidlike magnetized Rayleigh-Taylor instability.

Effect of Charge accumulation on Magnetic Rayleigh-Taylor Instability

The intuitive physical description of magnetic Rayleigh-Taylor instability in some textbooks is generally considered to be: a small perturbation causes current discontinuity, which produce charge accumulation, the electric field produced by the accumulated charge amplify the initial perturbation. However, in calculating the linear growth rate of magnetic Rayleigh-Taylor instability (MRTI), the displacement current term in the Maxwell’s equations is ignored, which means the contribution of charge accumulation to the growth of MRTI is totally ignored. In this article, we calculated the linear growth rate of MRTI with the displacement current term in Maxwell’s equations retained. We show that the contribution of charge accumulation to the growth of MRTI is negligible only when the nominal Alfvén speed is much smaller than the light speed. For space plasma whose nominal Alfvén speed is generally much smaller than the light speed, the linear growth rate previous calculated is right but the intuitive physical description of MRTI is wrong. For laboratory plasma whose nominal Alfvén speed maybe comparable to light speed, the intuitive physical description of MRTI is also inaccurate and the linear growth rate of MRTI is undervalued.

Particle Acceleration by Induced Electric Fields in Course of Electric Current Oscillations in Coronal Magnetic Loops

A mechanism for acceleration of electrons driven by the oscillations of the electric current in solar magnetic loops is considered. The magnetic loop is presented as an equivalent RLC-circuit with the electric current generated by convective motions in the photosphere. Eigen oscillations of the current in a loop induce the electric field directed along to the loop axis. It is shown that pulsating type III bursts and the sudden reductions that occur in the course of type IV continuum in solar flares provide evidence for acceleration and storage of energetic electrons in the coronal magnetic loops. Energization rate of electrons accelerated by sub-Dreicer electric field are determined. The energy spectra of fast electrons under both intermediate and strong regimes of pitch-angle diffusion are discussed. Two examples of the electron acceleration in the pulsating type III solar bursts are considered. We also discuss the efficiency of suggested mechanism as compared with the electron acceleration during 5-min photospheric oscillations and with the acceleration driven by the magnetic Rayleigh-Taylor instability.

The magnetic Rayleigh–Taylor instability around astrophysical black holes

We investigate the development of the magnetic Rayleigh-Taylor instability at the inner edge of an astrophysical disk around a spinning central black hole. We solve the equations of general relativity that govern small amplitude oscillations of a discontinuous interface in a Keplerian disk threaded by an ordered magnetic field, and we derive a stability criterion that depends on the central black hole spin and the accumulated magnetic field. We also compare our results with the results of GR MHD simulations of black hole accretion flows that reach a magnetically arrested state (MAD). We found that the instability growth timescales that correspond to the simulation parameters are comparable to the corresponding timescales for free-fall accretion from the ISCO onto the black hole. We thus propose that the Rayleigh-Taylor instability disrupts the accumulation of magnetic flux onto the black hole horizon as the disk reaches a MAD state.

Prominence activation by increase in electric current

We consider activation of a solar prominence by sharp increase in electric current in the frame of the Kuperus-Raadu model. The dynamics of the prominence is described in terms of the Ampère force, gravity, and the drag force. We suggest that the drag force is determined by the ion viscosity of ambient plasma. The upward Ampère force acting on the filament increases with the electric current in the filament, which results in the increase in the height of the filament. As a result of the dynamical process, a new equilibrium state corresponding to the new value of the electric current is reached. The maximum height and velocity of the prominence are estimated using the nonlinear equation for prominence dynamics. A sharp increase in the electric current can be due to the magnetic Rayleigh-Taylor instability in the chromospheric footpoints of the filament. Two examples of solar active filaments are analyzed in the context of the proposed model. Failed or two-stage eruption of the prominences is also discussed.

Angular momentum transport in thin magnetically arrested discs

In accretion disks with large-scale ordered magnetic fields, the magnetorotational instability (MRI) is marginally suppressed, so other processes may drive angular momentum transport leading to accretion. Accretion could then be driven by large-scale magnetic fields via magnetic braking, but large-scale magnetic flux can build-up onto the black hole and within the disk leading to a magnetically-arrested disk (MAD). Such a MAD state is unstable to the magnetic Rayleigh-Taylor (RT) instability, which itself leads to vigorous turbulence and the emergence of low-density highly-magnetized bubbles. This instability was studied in a thin (ratio of half-height H to radius R, $H/R \approx 0.1$) MAD simulation, where it has a more dramatic effect on the dynamics of the disk than for thicker disks. We find that the low-density bubbles created by the magnetic RT instability decrease the stress (leading to angular momentum transport) in the disk rather than increasing magnetic torques. Indeed, we find that the dominant component of the stress is due to turbulent magnetic fields, despite the suppression of the axisymmetric MRI and the dominant presence of large-scale magnetic fields. This suggests that the magnetic RT instability plays a significant role in driving angular momentum transport in MADs.