THE STRUCTURE OF 3-DIMENSIONAL MAGNETIC NEUTRAL POINTS

The local configurations of three-dimensional magnetic neutral points are investigated by a linear analysis about the null. It is found that the number of free parameters determining the arrangement of field li nes is four. The configurations are first classified as either potenti al or non-potential. Then the non-potential cases are subdivided into three cases depending on whether the component of current parallel to the spine is less than, equal to or greater than a threshold current; therefore there are three types of linear non-potential null configura tions (a radial null, a critical spiral and a spiral). The effect of t he four free parameters on the system is examined and it is found that only one parameter categorizes the potential configurations, whilst t wo parameters are required if current is parallel to the spine. Howeve r, all four parameters are needed if there is current both parallel an d perpendicular to the spine axis. The magnitude of the current parall el to the spine determines whether the null has spiral, critical spira l or radial field lines whilst the current perpendicular to the spine affects the inclination of the fan plane to the spine. A simple method is given to determine the basic structure of a null given M the matri x which describes the local linear structure about a null point. (C) 1 996 American Institute of Physics.