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Abstract
Aims. We systematically stress a rotationally symmetric 3D magnetic null point by advecting the opposite footpoints of the spine axis in opposite directions. This stress eventually concentrates in the vicinity of the null point, thereby forming a local current sheet through which magnetic reconnection takes place. The aim is to look for a steady state evolution of the current sheet dynamics, which may provide scaling relations for various characteristic parameters of the system.
Methods. The evolution is followed by solving numerically the nonideal MHD equations in a Cartesian domain. The null point is embedded in an initially constant density and temperature plasma.
Results. It is shown that a quasisteady reconnection process can be set up at a 3D null by continuous shear driving. It appears that a true steady state is unlikely to be realised because the current layer tends to grow until it is restricted by the geometry of the computational domain and the imposed driving profile. However, ratios between characteristic quantities clearly settle after some time to stable values, so that the evolution is quasisteady. The experiments show a number of scaling relations, but they do not provide a clear consensus for extending to lower magnetic resistivity or faster driving velocities. More investigations are needed to fully clarify the properties of current sheets at magnetic null points.
Original language  English 

Article number  20 
Number of pages  9 
Journal  Astronomy & Astrophysics 
Volume  529 
DOIs  
Publication status  Published  May 2011 
Keywords
 magnetic reconnection
 magnetohydrodynamics (MHD)
 methods: numerical
 Sun: corona
 magnetic fields
 KINEMATIC RECONNECTION
 SOLAR PHOTOSPHERE
 WAVEPROPAGATION
 ALIGNED CURRENT
 DIMENSIONS
 FIELDS
 CORONA
 FAN
 SPINE
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 1 Finished

Parallel Computing Resources UK MHD: Parallel computing resources
Science & Technology Facilities Council
1/12/09 → 30/11/12
Project: Standard