The appearance, motion, and disappearance of threedimensional magnetic null points 

Nicholas Murphy Submitted: 20150930 15:16
While theoretical models and simulations of magnetic reconnection often assume symmetry such that the magnetic null point when present is colocated with a flow stagnation point, the introduction of asymmetry typically leads to nonideal flows across the null point. To understand this behavior, we present exact expressions for the motion of threedimensional linear null points. The most general expression shows that linear null points move in the direction along which the vector field and its time derivative are antiparallel. Null point motion in resistive magnetohydrodynamics results from advection by the bulk plasma flow and resistive diffusion of the magnetic field, which allows nonideal flows across topological boundaries. Null point motion is described intrinsically by parameters evaluated locally; however, global dynamics help set the local conditions at the null point. During a bifurcation of a degenerate null point into a nullnull pair or the reverse, the instantaneous velocity of separation or convergence of the nullnull pair will typically be infinite along the null space of the Jacobian matrix of the magnetic field, but with finite components in the directions orthogonal to the null space. Not all bifurcating nullnull pairs are connected by a separator. Furthermore, except under special circumstances, there will not exist a straight line separator connecting a bifurcating nullnull pair. The motion of separators cannot be described using solely local parameters, because the identification of a particular field line as a separator may change as a result of nonideal behavior elsewhere along the field line.
Authors: Nicholas A. Murphy, Clare E. Parnell, and Andrew L. Haynes
Projects: None

Publication Status: Submitted to Physics of Plasmas
Last Modified: 20151007 12:56




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