Numerical Modeling of Weakly Ionized Plasmas (original) (raw)
Related papers
A three-dimensional numerical method for modelling weakly ionized plasmas
Monthly Notices of the Royal Astronomical Society, 2007
Astrophysical fluids under the influence of magnetic fields are often subjected to single-fluid or two-fluid approximations. In the case of weakly ionized plasmas however, this can be inappropriate due to distinct responses from the multiple constituent species to both collisional and non-collisional forces. As a result, in dense molecular clouds and proto-stellar accretion discs for instance, the conductivity of the plasma may be highly anisotropic leading to phenomena such as Hall and ambipolar diffusion strongly influencing the dynamics.
Multifluid magnetohydrodynamic turbulence in weakly ionised astrophysical plasmas
Initial results from simulations of 4-fluid MHD turbulence in molecular clouds are presented. The species included in the simulations are ions, electrons, negatively charged dust grains and neutrals. The results indicate that, on length scales of a few tenths of a parsec, multifluid effects have a significant impact on the properties of the turbulence. In particular, the power spectra of the velocity and magnetic fields are significantly softened, while the PDF of the densities of the charged and neutral fluids are appreciably different. Indeed, the magnetic field strength displays much less spatial structure on all lengthscales up to 1 pc than in the ideal MHD case. The assumptions of ideal MHD therefore appear to be inadequate for simulating turbulence in molecular clouds at these length scales.
Monthly Notices of the Royal Astronomical Society, 2011
The Kelvin-Helmholtz instability is well known to be capable of converting wellordered flows into more disordered, even turbulent, flows. As such it could represent a path by which the energy in, for example, bowshocks from stellar jets could be converted into turbulent energy thereby driving molecular cloud turbulence. We present the results of a suite of fully multifluid magnetohydrodynamic simulations of this instability using the HYDRA code. We investigate the behaviour of the instability in a Hall dominated and an ambipolar diffusion dominated plasma as might be expected in certain regions of accretion disks and molecular clouds respectively.
Multi-Fluid Modeling of Magnetic Reconnection in Astrophysical and Laboratory Plasmas
Improved models for characterizing collisional and reactive magnetized partially ionized plasma are essential to understand the phenomena taking place in astrophysical and laboratory plasmas. Particularly, scenarios where dissipative processes and thermo-chemical inequilibrium play an important role are beyond the classical single-fluid MHD representation. The multi-fluid models that consider each particle species as a separate fluid offer an alternative approach especially suitable for those situations. In the present work, a multi-fluid model considering two fluids, neutrals and charged species, is applied to simulate the magnetic reconnection taking place in the chromosphere.
Beyond ideal MHD: towards a more realistic modelling of relativistic astrophysical plasmas
Monthly Notices of the Royal Astronomical Society, 2009
Many astrophysical processes involving magnetic fields and quasi-stationary processes are well described when assuming the fluid as a perfect conductor. For these systems, the idealmagnetohydrodynamics (MHD) description captures the dynamics effectively and a number of well-tested techniques exist for its numerical solution. Yet, there are several astrophysical processes involving magnetic fields which are highly dynamical and for which resistive effects can play an important role. The numerical modeling of such non-ideal MHD flows is significantly more challenging as the resistivity is expected to change of several orders of magnitude across the flow and the equations are then either of hyperbolic-parabolic nature or hyperbolic with stiff terms. We here present a novel approach for the solution of these relativistic resistive MHD equations exploiting the properties of implicit-explicit (IMEX) Runge Kutta methods. By examining a number of tests we illustrate the accuracy of our approach under a variety of conditions and highlight its robustness when compared with alternative methods, such as the Strang-splitting. Most importantly, we show that our approach allows one to treat, within a unified framework, both those regions of the flow which are fluid-pressure dominated (such as in the interior of compact objects) and those which are instead magnetic-pressure dominated (such as in their magnetospheres). In view of this, the approach presented here could find a number of applications and serve as a first step towards a more realistic modeling of relativistic astrophysical plasmas.
ASTRONUM 2011 6th INTERNATIONAL CONFERENCE ON NUMERICAL MODELING OF SPACE PLASMA FLOWS
2011
The study of black holes dynamics in an ambient magnetic field is important for a variety of astrophysical phenomena. In this talk, I will present novel approaches in the numerical simulations of the force-free approximation for tenuous plasma. These techniques are inspired from the treatment of the current and related stiff terms in a relativistic resistive MHD approach. As a direct application, I will show results obtained from a numerical study of the Blandford-Znajek mechanism, in which the electromagnetic field extracts energy from an orbiting black hole binary and leads to emission along jets. Author: Miguel Angel Aloy Title: Powering short GRBs by mergers of moderately magnetized neutron star merger. Abstract: We explore the implications of the process of formation of low-density funnels of magnetized plasma during the process of merger of two neutron stars with initially low magnetization. In particular, we consider the impact on the production of short gammaray bursts that ...
Modeling Weakly-Ionized Plasmas in Magnetic Field: A New Computationally-Efficient Approach
Journal of Computational Physics, 2015
Despite its success at simulating accurately both non-neutral and quasi-neutral weakly-ionized plasmas, the drift-diffusion model has been observed to be a particularly stiff set of equations. Recently, it was demonstrated that the stiffness of the system could be relieved by rewriting the equations such that the potential is obtained from Ohm's law rather than Gauss's law while adding some source terms to the ion transport equation to ensure that Gauss's law is satisfied in non-neutral regions. Although the latter was applicable to multicomponent and multidimensional plasmas, it could not be used for plasmas in which the magnetic field was significant. This paper hence proposes a new computationally-efficient set of electron and ion transport equations that can be used not only for a plasma with multiple types of positive and negative ions, but also for a plasma in magnetic field. Because the proposed set of equations is obtained from the same physical model as the conventional drift-diffusion equations without introducing new assumptions or simplifications, it results in the same exact solution when the grid is refined sufficiently while being more computationally efficient: not only is the proposed approach considerably less stiff and hence requires fewer iterations to reach convergence but it yields a converged solution that exhibits a significantly higher resolution. The combined faster convergence and higher resolution is shown to result in a hundredfold increase in computational efficiency for some typical steady and unsteady plasma problems including non-neutral cathode and anode sheaths as well as quasi-neutral regions.
Modeling and Simulating Flowing Plasmas and Related Phenomena
Space Science Reviews, 2008
Simulation has become a valuable tool that compliments more traditional methods used to understand solar system plasmas and their interactions with planets, moons and comets. The three popular simulation approaches to studying these interactions are presented. Each approach provides valuable insight to these interactions. To date no one approach is capable of simulating the whole interaction region from the collisionless to the collisional regimes. All three approaches are therefore needed. Each approach has several implicit physical assumptions as well as several numerical assumptions depending on the scheme used. The magnetohydrodynamic (MHD), test-particle/Monte-Carlo and hybrid models used in simulating flowing plasmas are described. Special consideration is given to the implicit assumptions underlying each model. Some of the more common numerical methods used to implement each model, the implications of these numerical methods and the resulting limitations of each simulation approach are also discussed.
Electron and Ion Transport Equations in Computational Weakly-Ionized Plasmadynamics
Journal of Computational Physics
A new set of ion and electron transport equations is proposed to simulate steady or unsteady quasi-neutral or non-neutral multicomponent weakly-ionized plasmas through the drift-diffusion approximation. The proposed set of equations is advantaged over the conventional one by being considerably less stiff in quasi-neutral regions because it can be integrated in conjunction with a potential equation based on Ohm's law rather than Gauss's law. The present approach is advantaged over previous attempts at recasting the system by being applicable to plasmas with several types of positive ions and negative ions and by not requiring changes to the boundary conditions. Several test cases of plasmas enclosed by dielectrics and of glow discharges between electrodes show that the proposed equations yield the same solution as the standard equations but require 10 to 100 times fewer iterations to reach convergence whenever a quasi-neutral region forms. Further, several grid convergence studies indicate that the present approach exhibits a higher resolution (and hence requires fewer nodes to reach a given level of accuracy) when ambipolar diffusion is present. Because the proposed equations are not intrinsically linked to specific discretization or integration schemes and exhibit substantial advantages with no apparent disadvantage, they are generally recommended as a substitute to the fluid models in which the electric field is obtained from Gauss's law as long as the plasma remains weakly-ionized and unmagnetized.