The Structure of MHD Turbulence
Joanne Mason, University of Exeter
Incompressible magnetohydrodynamics (MHD) provides the simplest theoretical
framework for studying the most basic properties of magnetised plasma
turbulence. Establishing a solid theoretical foundation for MHD turbulence is of
great importance for understanding a variety of problems in astrophysics, space
physics, laboratory plasma physics and classical dynamo theory.
As a result of the enormous increase in computational power that has been
realised over recent years, significant progress with the fundamental theory of
MHD turbulence has been made. In 2006, Boldyrev (Phys. Rev. Lett. 96, 115002)
introduced a new phenomenological model of the energy cascade in
incompressible field-guided MHD. Subsequently, with the aim of testing the new
theoretical predictions, a series of high-resolution numerical simulations have
been performed on some of the world’s largest computing architectures (see, for
example, Perez, J.C, Mason, J., Boldyrev, S. & Cattaneo, F., Phys. Rev. X, 2012, 2,
041005, and references therein). Of particular interest is the three-dimensional
ribbon-like structure of the small-scale fluctuations (Figure 1), and the intriguing
scale-dependent alignment of the velocity and magnetic field in the plane
perpendicular to the background field (Figure 2). Current work, funded by EPSRC
(EP/M004546/1), aims to study the transport properties of scale-dependently
aligned MHD turbulence.
The simulations have been made possible with allocations of advanced computing
resources provided by XSEDE, INCITE and PRACE.
Figure 1: Magnetic field fluctuations from a direct numerical simulation of driven,
incompressible, field-guided MHD turbulence. The fluctuations take the form of
ribbons stretched in the direction of the background magnetic field, which points out of
the left-hand face.
Figure 2: Three grey-scale plots of the cosine of the alignment angle between the
velocity and magnetic field fluctuations in a plane perpendicular to the background
magnetic field. Black (white) regions denote highly aligned (anti-aligned) fluctuations.
The velocity and magnetic field have been filtered at decreasing scales (left - right).