Research
The study of magnetohydrodynamics (MHD) of waves,
instabilities, and supersonic flows of magnetized plasmas has been
conducted for many years in the separate disciplines of laboratory
fusion research and plasma-astrophysics. Yet, these widely
separate physical situations are described by the same equations!
This offers numerous common viewpoints for research of plasmas in
the coronae of sun and stars, magnetospheres about planets and
about pulsars, accretion disks about compact objects, the winds
and jets ejected from them, etc. Since the early nineties, this
starting point has been the basis of a multitude of collaborative
efforts between FOM Rijnhuizen and the Utrecht Astronomy
Department on Coronal plasma dynamics, Parallel Magneto-Fluid
Dynamics, Rapid Changes in Complex Flows (with additional input
from numerical mathematics, fluid dynamics, and physical
informatics), and Magnetoseismology of accretion disks. At
present, the studies of magnetized plasmas are continued with both
linear (with an important analytical component) and nonlinear
(numerical) techniques.
MHD spectroscopy and transonic MHD flows.
The linear
efforts concentrate on spectral analysis of MHD waves and
instabilities: MHD spectroscopy has become a new powerful tool for
plasma diagnostics (analogous to helioseismology) for different
astrophysical systems (sunspots, coronal flux tubes, accretion
disks, and jets). It has also led to a general set of
state-of-the-art spectral codes for the analysis of MHD waves and
instabilities for realistic laboratory experiments and
astrophysical objects. The fundamental aspects of stationary MHD
flows with transonic transitions through the critical MHD speeds
proved to present many obstacles in understanding the subtleties
of plasma dynamics. Having resolved those, permitted
reinvestigating the MHD waves and instabilities of axisymmetric
rotating plasmas with new numerical techniques. This activity is
presently producing a veritable abundance of new instabilities of
interest for the production of turbulence and angular momentum
transport in accretion disks about compact objects.
Nonlinear dynamics.
The numerical effort concentrates
on three-dimensional MHD modeling of laboratory plasma flows,
stellar winds, astrophysical jets, and accretion flows, with
coupling between the linear stability properties of the moving
magnetized systems and the evolution towards discontinuous,
shock-dominated, nonlinear dynamics. It exploits the Versatile
Advection Code (VAC), developed by Gabor Tóth as part of the
Massively Parallel Computing project mentioned above, which is a
fully implicit, shock-capturing, and massively parallel MHD solver
that bridges the huge time-scale disparities encountered in
realistic astrophysical simulations. Designed to permit inclusion
of almost all present discretization methods, it became an
extremely versatile research instrument which is used by a rapidly
increasing number of scientists, here and abroad. The code was
steadily developed further by Rony Keppens (head of the Rijnhuizen
Numerical Plasma Dynamics group), and applied to basic plasma
dynamics like the Kelvin-Helmholtz instability and jets, solar and
stellar winds (producing the anisotropy observed by the Ulysses
spacecraft), and recently extended with adaptive mesh refinement
and a relativistic module: another step towards simulating
realistic astrophysical plasma flows.
Teaching
The course on Magnetohydrodynamics of Astrophysical
Plasmas has been transformed into a regular annual course, which
is part of the masters curriculum. With the completion of the
textbook Principles of Magnetohydrodynamics, with
Applications to Laboratory and Astrophysical Plasmas (Cambridge
University Press, Cambridge, 2004), by Hans Goedbloed and Stefaan
Poedts, and the extension of the course with a numerical
laboratory by Rony Keppens, the common field of
magnetohydrodynamics of laboratory and astrophysical plasmas is
now getting the momentum that we have dreamed of for a long time.
Our new textbook just appeared:
Principles of Magnetohydrodynamics
This textbook provides a modern and accessible introduction to magnetohydrodynamics (MHD). It describes the two main applications of plasma physics, laboratory research on thermo-nuclear fusion energy and plasma astrophysics of the solar system, stars and accretion disks, from the single viewpoint of MHD. This approach provides effective methods and insights for the interpretation of plasma phenomena on virtually all scales, from the laboratory to the universe. It equips the reader with the necessary tools to understand the complexities of plasma dynamics in extended magnetic structures. The classical MHD model is developed in detail without omitting steps in the derivations and problems are included at the end of each chapter. This text is ideal for senior-level undergraduate and graduate courses in plasma physics and astrophysics.
See also the Workshops site at the bottom (right).
Contact staff
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