Plasma instability

Instabilities in plasmas are often referred to as 'modes'. Strictly speaking, these terms correspond to different concepts:

• Instability: the existence of an instability is determined by calculating the growth rate of an infinitesimal perturbation. If this growth rate is positive, the perturbation is unstable.
• Mode: a (normal) mode is a (global) solution of a (linear) evolution equation. Typically, this solution is a (standing or propagating) wave. The linearity of the equation allows any solution to be decomposed into a sum of mutually orthogonal normal modes. If the equation is non-linear, the term 'mode' has to be used with caution.

Plasma instabilities can be classified into a number of types according to their drive (or free energy source):

• Rayleigh-Taylor instabilities due to density gradients or boundaries, associated with non-electromagnetic forces (e.g., gravity)
• Gradient driven instabilities, associated with thermodynamic forces due to gradients in an otherwise Maxwellian plasma
• Kinetic instabilities, associated with deviations from Maxwellianity, i.e., the anisotropy of the velocity distribution function
• Streaming instabilities, associated with energetic particles or electric currents interacting with the plasma, producing waves

Below is a list of some instabilities relevant to fusion plasmas (to be completed).

• Alfvén eigenmodes
• Ballooning instability
• Drift wave instability
• Edge Localized Modes
• Electron Temperature Gradient instability
• Flute instability
• Geodesic Acoustic Mode (GAM)
• Interchange instability
• Ion Temperature Gradient instability
• Kink instability
• Sausage instability
• Tearing mode instability, see also Magnetic island
• Whistler mode

See also

• Wikipedia:Plasma stability