Amber wave

Amber waves are longitudinal waves in plasmas . A distinction is made between electron-amber waves and ion-amber waves , depending on which part of the plasma carries out the wave movement.

Electron amber waves

Electron-amber waves (also EBW ) are electrostatic waves of electrons that occur in magnetized plasmas . Electrostatic means here that the wave represents a disturbance in the density distribution of the electrons and spreads like a longitudinal pressure wave. In contrast to an electromagnetic wave, the EBW cannot propagate in a vacuum, since the propagation is maintained by the cyclotron movements of the electrons.

The propagation takes place perpendicular to the background magnetic field of the plasma. This is called a hot plasma because the approach of the cold plasma does not include these waves.

The wavelengths of the EBW are in the range of the Larmor radius of the electrons, i.e. in the order of magnitude of the radius that describes the gyration movement of an electron around a magnetic field line.

In large fusion experiments, EBW are used to heat the plasma.

Ionic amber waves

With ion-amber waves (also IBW ) the density of the plasma ions is traversed by longitudinal waves. These waves behave analogously to the electron-amber waves and also propagate perpendicular to the background magnetic field of the plasma. However, because of the smaller charge to mass ratio of the ions, they have a lower frequency. The driving moment is the cyclotron movement of the ions.

Here, too, the order of magnitude of the wavelength is in the range of the Larmor radius of the ion.

History

In 1958, Ira B. Bernstein dealt with the propagation of waves in a magnetized hot plasma by applying a certain mathematical procedure to this problem for the first time. This process produced the waves that are now known as amber waves.

literature

• Ira B. Bernstein: Waves in a Plasma in a Magnetic Field . Phys. Rev. 109 (1958) 10-21