Reconnection

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Reconnection: incoming (top / bottom) and outgoing (left / right) plasma bundles

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. It is believed to be responsible for solar flares , among other things .

principle

Reconnection can occur when there is a strong, variable magnetic field in a plasma , for example in the solar atmosphere . The particles of the plasma then move along spiral paths around the field lines and are thus bound to them.

In a complex magnetic field there can be separate field line bundles that have their base points in different poles. If two such oppositely directed fields are close to each other, a boundary layer forms in which an electrical current flows. As a result, the fields partially cancel each other out. With this field dissolution, but also with the flowing of the current through the plasma, which has an electrical resistance , energy is released.

In addition, new field lines are created perpendicular to the original ones, further plasma penetrates. The plasma around the newly created line bundle is heated up and accelerated away from the location of the reconnection.

Research history and open problems

The basic Sweet reconnection theory discussed so far is based on the work of Peter Alan Sweet from 1956 and Eugene N. Parker . It predicts far too long expiry times for the phenomenon, so that it was modified by Harry E. Petschek in 1963 . According to this fast or Petschek reconnection, there are much smaller border areas, which means that the reconnection is faster.

Although the satellites Yohkoh and, since 2002, RHESSI have provided the best observation material currently available, a final decision cannot yet be made between Sweet or Petschek reconnection; the exact triggers and mechanisms are still not clear.

Occur

Coronal mass ejection as a result of the reconnection of field lines.

The most important occurrence of reconnection is in the solar corona . It is assumed that large magnetic field arcs are compressed in the middle by the plasma dynamics, which creates the required anti-parallel field lines. This leads to reconnection, the upper part of the arches is pinched off and can be detached with the contained plasma as an eruption or coronal mass ejection .

Furthermore, reconnection in the earth's magnetic field contributes to the aurora borealis and, on astronomical scales, to the heating of galactic high-speed clouds . It is a potential problem in the magnetic containment of fusion processes .

The "cluster" - space probes could prove Rekonnexionen in the tail of the Earth's magnetic field. Contrary to expectations, they do not occur in a spatial area of ​​a few 10 km, but of a few 1000 km.

literature

Individual evidence

  1. ^ Cluster satellites find magnetic reconnection . (English, with simulation graphics)