The spectrum of ideal magnetohydrodynamic (MHD) pressure-driven (ballooning) modes in strongly nonaxisymmetric toroidal systems is difficult to analyze numerically owing to the singular nature of ideal MHD caused by lack of an inherent scale length. In this paper, ideal MHD is regularized by using a k-space cutoff, making the ray tracing for the WKB ballooning formalism a chaotic Hamiltonian bi...

Kinetic theory is used to describe pressure induced magnetic island formation in three-dimensional configurations. The kinetic responses describes currents that arise at rational surfaces that oppose the island producing magnetohydrodynamic (3-D) effects in general 3-D MHD equilibria. The kinetic response is largest at lowest collisionality suggesting that high-β stellarators are more resilient...

Magnetohydrodynamic (MHD) turbulence is pervasive in astrophysical systems. Recent highresolution numerical simulations suggest that the energy spectrum of strong incompressible MHD turbulence is E(k⊥) ∝ k ⊥ . So far, there has been no phenomenological theory that simultaneously explains this spectrum and satisfies the exact analytic relations for MHD turbulence due to Politano & Pouquet. Indee...

Recent developments in the derivation of reduced models for weakly compressible magnetohydrodynamic (MHD) turbulence are discussed. A four-field system of equations has been derived from the compressible magnetohydrodynamic (MHD) equations to describe turbulence in the interstellar medium and the solar wind. These equations apply to a plasma permeated by a spatially varying mean magnetic field ...

Magnetohydrodynamic (MHD) flows are governed by Navier–Stokes equations coupled with Maxwell equations through coupling terms. We prove the unconditional stability of a partitioned method for the evolutionary full MHD equations, at high magnetic Reynolds number, written in the Elsässer variables. The method we analyze is a first-order onestep scheme, which consists of implicit discretization of...

We present results from axisymmetric, time-dependent magnetohydrodynamic (MHD) simulations of the collapsar model for gamma-ray bursts. Our main conclusion is that, within the collapsar model, MHD effects alone are able to launch, accelerate and sustain a strong polar outflow. We also find that the outflow is Poynting flux-dominated, and note that this provides favorable initial conditions for ...

We report the discovery of a family of stationary magnetohydrodynamic (MHD) outÑows from a disk found by time-dependent, axisymmetric MHD simulations. The initial poloidal magnetic Ðeld threading the disk was taken to be a tapered monopole Ðeld, with the Ðeld strength on the disk decreasing outwardly to small values. At the disk surface, matter was given a small initial push with a speed less t...

We present a model for nonlinear decay of the weak wave in three-dimensional incompressible magnetohydrodynamic (MHD) turbulence. We show that the decay rate is different for parallel and perpendicular waves. We provide a general formula for arbitrarily directed waves and discuss particular limiting cases known in the literature. We test our predictions with direct numerical simulations of wave...