Alfvén wave

In plasma physics, an Alfvén wave, named after Hannes Alfvén, is a type of plasma wave in which ions oscillate in response to a restoring force provided by an effective tension on the magnetic field lines.

Discovered theoretically by Alfvén in 1942—work that contributed to his 1970 Nobel Prize in Physics—these waves play a fundamental role in numerous astrophysical and laboratory plasma phenomena. Alfvén waves are observed in the solar corona, solar wind, Earth's magnetosphere, fusion plasmas, and various astrophysical settings. They are particularly significant for their role in the coronal heating problem, energy transport in the solar atmosphere, particle acceleration, and plasma heating.

Unlike some other plasma waves, Alfvén waves are typically non-compressive and dispersionless in the simplest MHD description, though more complex variants such as kinetic and inertial Alfvén waves emerge in certain plasma regimes. The characteristic speed of these waves—the Alfvén velocity—depends on the magnetic field strength and the plasma density, making these waves an important diagnostic tool for magnetized plasma environments.