Hannes Alfvén predicted a wave coupling the motion of an electrically conducting fluid to a background magnetic field. In an Alfvén wave, bent magnetic-field lines provide a restoring effect while the material's inertia resists the displacement.
Linearizing ideal magnetohydrodynamics for a transverse disturbance along a uniform field gives the propagation speed , with background field strength , vacuum permeability and mass density . A stronger field increases the restoring effect; greater material inertia slows propagation. The idea connects plasma dynamics in the laboratory with the behavior of astrophysical magnetic structures.[ref]
Existence of Electromagnetic-Hydrodynamic Waves by Hannes Olof Gösta Alfvén. 1942 paper, combined fluid–magnetic disturbance and propagation-speed relation
Portrait of Hannes Alfvén
. Unknown author. Public domain in Sweden (PD-Sweden, as stated on Commons). Source usage terms, via Wikimedia Commons. Source. Articles by others on the same topic
Hannes Alfvén was a Swedish physicist and electrical engineer, known for his significant contributions to plasma physics and space science. Born on May 30, 1908, and passing away on April 2, 1995, Alfvén is best known for developing the theory of magnetohydrodynamics (MHD), which studies the dynamics of electrically conducting fluids in magnetic fields, including plasmas.