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Most of the universe is in the plasma state, the fourth state of
matter.
- In a plasma the temperature,
, is so high that the gas
becomes ionised
and the atoms split into positive ions and negative electrons.
- The plasma is treated as a continuous medium, a conducting
gas through which eletric currents can flow and in which there exists a
magnetic field,
. The assumption of a continuous medium
does require the typical lengthscales of the plasma to be
sufficiently large. For example, the lengthscales must be larger than
the typical distance an ion travels before a collision (the
collision length).
- All the phemonena observed on the Sun are created by the
magnetic field and its interaction with the plasma.
In such situations the plasma may be described by the equations of MHD.
Subsections
Prof. Alan Hood
2000-11-06