We compare the properties of ordinary strong magnetohydrodynamic (MHD) turbulence in a strongly magnetized medium with the recently discovered viscosity-damped regime. We focus on energy spectra, anisotropy, and intermittency. Our most surprising conclusion is that in ordinary strong MHD turbulence the velocity and magnetic fields show different high-order structure function scalings. Moreover ...

There is abundant observational evidence that the energization of plasma particles in space is correlated with an enhanced activity of large-scale MHD waves. Since these waves cannot interact with particles, we need to find ways for these MHD waves to transport energy in the dissipation range formed by small-scale or high-frequency waves, which are able to interact with particles. In this paper...

[1] In order to better describe the space plasmas where pressure anisotropy has prominent effects, we extend the BATS-R-US magnetohydrodynamics (MHD) model to include anisotropic pressure. We implement the anisotropic MHD equations under the double adiabatic approximation with an additional pressure relaxation term into BATS-R-US and perform global magnetospheric simulations. The results from i...

به کارگیری روش رؤ در حل معادلات هیدرودینامیک مغناطیسی اگرچه باعث کاهش لزجت حل عددی و افزایش دقت آن می شود، اما با افزایش نسبت مجذور جریان تخلیه الکتریکی به دبی جرمی ورودی( ) در رانشگرهای پلاسمایی مغناطیسی که با وقوع انبساط های قوی در نوک الکترودها همراه است، به حل غیرفیزیکی منجر می گردد. برای رفع این مشکل، استفاده از یک الگوریتم ریمانی ترکیبی مدنظر قرار گرفته است. در این الگوریتم با جایگزینی رو...

New theory developments and experimental observations of two classes of energetic particle driven instabilities are reported. First is a new class of global MHD solutions resulting from coupling of the Alfvénic and acoustic fundamental MHD oscillations due to geodesic curvature. These modes, predicted theoretically and numerically and called Beta-induced Alfvén-Acoustic Eigenmodes (BAAEs), have...

Performing a stable, long duration simulation of driven MHD turbulence with a high thermal Mach number and a strong initial magnetic field is a challenge to high-order Godunov ideal MHD schemes because of the difficulty in guaranteeing positivity of the density and pressure. We have implemented a robust combination of reconstruction schemes, Riemann solvers, limiters, and Constrained Transport ...

The magnetohydrodynamic ~MHD! stability of negative central magnetic shear toroidal equilibria with q.2 everywhere and ebpol@1 is investigated. Here, q is the safety factor of the equilibrium magnetic field in a torus with inverse aspect ratio e , and bpol is the ratio of the plasma pressure to the pressure in the poloidal magnetic field. At small ebpol!1, the elimination of the q52 resonant su...

Recent advances in understanding of the basic properties of compressible Magnetohydrodynamic (MHD) turbulence call for revisions of some of the generally accepted concepts. First, MHD turbulence is not so messy as it is usually believed. In fact, the notion of strong non-linear coupling of compressible and incompressible motions is not tenable. Alfven, slow and fast modes of MHD turbulence foll...

Two-dimensional (2-D) homogeneous magnetohydrodynamic (MHD) turbulence has many of the same qualitative features as three-dimensional (3-D) homogeneous MHD turbulence. These features include several ideal invariants, along with the phenomenon of broken ergodicity. Broken ergodicity appears when certain modes act like random variables with mean values that are large compared to their standard de...

The study of incompressible magnetohydrodynamic (MHD) turbulence gives useful insights on many astrophysical problems. We describe a pseudo-spectral MHD code suitable for the study of incompressible turbulence. We review our recent works on direct three-dimensional numerical simulations for MHD turbulence in a periodic box. In those works, we use a pseudo-spectral code to solve the incompressib...