Alfvén wave

Categories: Waves in plasmas | Formula needs explanation

Image:Alfven-wave-double-layer.gif
A cluster of double layers forming in an Alfvén wave, about a sixth of the distance from the left. Click for more details

An Alfvén wave, named after Hannes Alfvén, is a type of magnetohydrodynamic wave.

An Alfvén wave in a plasma is a traveling oscillation of the ions and the magnetic field. The ion mass density provides the inertia and the magnetic field line tension provides the restoring force. The wave propagates in the direction of the magnetic field, although waves exist at oblique incidence and smoothly change into the magnetosonic wave when the propagation is perpendicular to the magnetic field. The motion of the ions and the perturbation of the magnetic field are in the same direction and transverse to the direction of propagation. The wave is dispersionless with a speed of

<math>v_A = B/(\mu_0 n_im_i)^{1/2} = (2.18\times10^{11}\,\mbox{cm/s})\,(m_i/m_p)^{-1/2}\,(n_i/{\rm cm}^{-3})^{-1/2}\,(B/{\rm gauss})</math>


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