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Forcefree magnetic fieldA forcefree magnetic field is a type of field which arises as a special case from the magnetostatic equation in plasmas. This special case arises when the plasma pressure is so small, relative to the magnetic pressure, that the plasma pressure may be ignored, and so only the magnetic pressure is considered. The name "forcefree" comes from being able to neglect the force from the plasma. Additional recommended knowledge
Basic EquationsStart with the simplified magnetostatic equations, in which the effects of gravity may be neglected:
Supposing that the gas pressure is small compared to the magnetic pressure, i.e., ρ < < B^{2} / 2μ then the pressure term can be neglected, and we have: . From Maxwell's equations:
. The first equation implies that: . e.g. the current density is either zero or parallel to the magnetic field, and where alpha is a spatialvarying function which must be determined.. Combing this equation with Maxwell's equations, leads to a pair of equations for alpha and B:
Physical ExamplesIn the corona of the sun, the ratio of the gas pressure to the magnetic pressure is ~0.004, and so there the magnetic field is forcefree. Mathematical Limits
and
See also
References


This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Forcefree_magnetic_field". A list of authors is available in Wikipedia. 