Reconnection at a null point pair in cylindrical geometry

Dynamic reconnection at a null point pair


Animations of transient magnetic field disturbances, modelling dynamic reconnection in the presence of a null point pair connected by a generic fan-fan separator, in incompressible cylindrical geometry (see image below).

There are two regimes of behaviour, depending on the relative magnitudes of the background plasma flow and magnetic field. If the background magnetic field is strongest, then a `wave-like' regime results. A given initial disturbance develops ingoing and outgoing components, which travel along the background field lines. The ingoing pulse steepens as it localises, resulting in a current buildup which is attracted to either.....

.... one of the fan planes....

..... one of the spines......

..... or along the separator joining the two nulls......

The links above lead to animations of these processes, where the disturbance magnetic field and resulting current are displayed.

In the other regime, when the background plasma flow is stronger than the magnetic field, the entire disturbance localises, either toward the spine, fan, or separator (the `flux pile up' regime). However, in this strongly driven regime, the strong flow along the separator tends to localise the pulse toward one of the nulls, and hence a current sheet on the separator, but distinct from the location of the nulls, is harder to achieve. What is required is for the length scales across the separator field to be much shorter than the length of the separator, at realistic (low) values of the resistivity.


Return to David's homepage