Magnetic reconnection
The magnetic reconnection ( reconnection ) is a physical phenomenon in which the structure of a magnetic field changes abruptly and large amounts of energy are released. Presumably, it is responsible for, among other solar flares.
Principle
For reconnection can occur when a strong, changing magnetic field is present in a plasma, such as in the solar atmosphere. The particles of the plasma then move along helical paths around the field lines and are therefore bound by them. In a complex magnetic field, there may be separate field line bundles, which have their base points in different poles. Are now two oppositely directed fields close to each other, so a boundary layer in which an electric current flows out forms. Thus, the fields to delete from partially each other, and beyond arise perpendicular to the original field lines new. More plasma penetrates to. Energy, in the free-field resolution, as well as by the flow of current through the plasma, which has an electrical resistance. Thus, the plasma is heated to the line bundle newly formed and accelerated away from the site of reconnection.
History of research and open problems
The previously executed, basic theory goes back to works by Peter Alan Sweet from 1956 and Eugene N. Parker. However, this so-called Sweet- reconnection predicts much too low flow times for the phenomenon, so it was modified in 1963 by Harry E. Petschek. After this fast reconnection or Petschek reconnection there is much small border areas, which the reconnection occurs faster. The current best observational material for Rekonnexionsfrage provided the satellite Yohkoh and RHESSI since 2002. However, can not yet be decided between sweet or Petschek reconnection, and the exact cause and mechanisms of reconnection have still not been clarified.
Occurrence
The main occurrence of reconnection, as already mentioned, in the corona. It is believed that this large magnetic sheets are compressed by the plasma dynamics in the middle, creating the necessary anti-parallel field lines emerge. Thus it comes to reconnection, the upper part of the arches is pinched off and may peel off with the contained plasma as eruption or coronal mass ejection.
Furthermore bears reconnection at the Earth's magnetic field to auroral and on astronomical scales for heating of galactic high velocity clouds. It is a potential problem with magnetic containment fusion processes.
The Cluster spacecraft were able to demonstrate Rekonnexionen in the tail of the geomagnetic field. Contrary to expectations, they do not occur in a region of space of a few 10 km, but some 1000 km on.