Alumni Project
Magnetic Reconnection
Center for Magnetic Reconnection Studies
PI and Project Director:
A. Bhattacharjee, Co-PI: B. Chandran (University of Iowa)
PI: R. Rosner (University of Chicago), PI: R. Fitzpatrick
(University of Texas at Austin)
Affiliated Researchers: L.-J. Chen, K. Germaschewski, Z. W. Ma,
C. S. Ng, P. Zhu (University of Iowa); F. Cattaneo, A. Dubey, T. Linde,
and A. Siegel (University of Chicago); F. Waelbroeck, and P. Watson (University
of Texas at Austin)
F. Dobrian, D. Keyes, and B. Smith (TOPS: Terascale Optimal Partial Differential
Equation Simulations Group)
Summary
The Center for Magnetic Reconnection Studies is a multi-institutional
consortium (University of Iowa, University of Chicago and the University
of Texas at Austin) dedicated to physical problems involving magnetic
reconnection in fusion, space and astrophysical plasmas.
Understanding magnetic reconnection is one of the principal challenges
in plasma physics. Reconnection is a process by which magnetic fields
reconfigure themselves, releasing energy that can be converted to particle
energies and bulk flows. Thanks to the availability of sophisticated
diagnostics in fusion and laboratory experiments, in situ probing of
magnetospheric and solar wind plasmas, and X-ray emission measurements
from solar and stellar plasmas, theoretical models of magnetic reconnection
can now be constrained by stringent observational tests. The members
of the Center for Magnetic Reconnection Studies (CMRS)
comprise an interdisciplinary group drawn from applied mathematics,
astrophysics, computer science, fluid dynamics, plasma physics, and
space science communities.
Recent developments in the theory of Hall magnetohydrodynamic (MHD)
reconnection hold the promise for providing solutions to some outstanding
problems in fusion, space and astrophysical plasma physics. While significant
analytical and numerical progress has been made, we have been limited
so far in our ability to settle definitively several outstanding questions
because of the lack of adequate scale separation and resolution in simulations.
The principal computational product of the CMRS---the Magnetic
Reconnection Code (MRC)---is a state-of-the-art, large-scale
Hall MHD code that will carry magnetic reconnection research to the
next level of accuracy and completeness in 2D and 3D, with the multi-scale
separation and spatio-temporal resolution required to be directly applicable
to experiments and observations. The MRC is massively parallel and modular,
has the flexibility to change algorithms when necessary, and uses Adaptive
Mesh Refinement (AMR). The basic strategy for parallel processing within
AMR is to treat every subgrid as an independent task on a processor,
with communication and synchronization between different processors
based on the Message Passing Interface (MPI). In order to make the communication
between processors as efficient as possible, we use a novel method based
on Hilbert-Peano space-filling curves which keep clusters of neighboring
grids on the same processor. We make extensive use of the so-called
CWENO schemes that have been shown in the last decade to combine excellent
shock-capturing properties with robustness and simplicity.
One of the great strengths of the SciDAC program is that it provides
a unique opportunity for physicists to work closely with applied mathematicians
and computer scientists. We are presently collaborating closely with
colleagues in the ISIC TOPS group in the application of fully implicit
numerical methods that enable much larger time steps than have been
traditionally used in reconnection studies. In particular, we have integrated
the MRC with the TOPS group’s PETSc library, and are now exploring thoroughly
the efficacy of fully implicit methods in collaboration with the TOPS
group.
Figure 1. AMR allows us to place refined numerical grids automatically
where the fine spatial structures requires them, as shown in the figure
where thin and intense current sheets are resolved by placing refined
grids at sites of large current density. Our AMR code has the ability
to refine not only in space but also in time, which is more efficient
since one does not need to take unnecessarily small time steps in regions
where the fields are smooth.
Using the MRC, with its flexible range of algorithms, one can now begin
to explore the effects of various types of boundary conditions, expand
the range of aspect ratios in the chosen computational geometry, and
investigate a wide regime of plasma pressure, resistivity, and electron
and ion inertial scales. The resistive MHD version of this code is already
available in the public domain (distributed by the University of Chicago
Flash Center, supported by the DOE ASCI/Alliances Program), and the
Hall MHD version will be available in Spring 2003. Using this code,
CMRS investigators at the University of Texas at Austin and the University
of Iowa have recently uncovered a new regime of fast and impulsive wave-driven
reconnection. We have also established a new scaling relation for forced
reconnection [Physical Review Letters 87, 265003 (2001)],
and tested analytical scaling laws for error-field driven islands in
tokamaks that impose significant design constraints for the ITER device.
Figure 2. A fully 3D simulation of the dynamics of 12 vortex
tubes collapsing towards the center of the box. This simulation, obtained
from the hydrodynamics (HD) version of the MRC, represents a prime candidate
for finite-time singularity of Euler flows and fast vortex reconnection
in the presence of viscosity.
For further information on this subject contact:
Prof. Amitava Bhattacharjee, Project Director
Center for Magnetic Reconnection Studies
Department of Physics & Astronomy
The University of Iowa
Iowa City, IA 52242-1479
amitava-bhattacharjee@uiowa.edu
http://www.physics.uiowa.edu/cmrs/
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