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this page is about helicity in magnetic fields. For fluid mechanical helicity, see helicity
In electromagnetism, magnetic helicity is the extent to which a magnetic field "wraps around itself". If magnetic field lines follow the strands of a twisted rope, this configuration would have nonzero magnetic helicity; left handed ropes would have negative values and right handed ropes would have positive values.
Formally,
- <math>
H=\int {\mathbf A}\cdot{\mathbf B}\,d^3{\mathbf r}
<math>
where
<math>{\mathbf B}<math> is the magnetic field strength
<math>{\mathbf B}=\nabla\times{\mathbf A}<math> Where <math>\mathbf A<math> is the vector potential of <math>{\mathbf B}<math>
Magnetic helicity is a conserved quantity. It is conserved in electromagnetic fields, even when magnetic reconnection dissipates energy. The concept is useful when considering solar dynamics.
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