Diocotron instability

From (The Plasma Universe Wikipedia-like Encyclopedia)

Diocotron instability vortices photographed on a fluorescent screen.

Auroral curls showing Kelvin Helmholtz instabilities, that are sometimes attributed to diocotron instability. Credit: Trond Trondsen / Institute for Space Research, Calgary, Canada.^[1]

The diocotron instability (also called the slipping stream plasma instability), is "one of the most ubiquitous instabilities in low density nonneutral plasmas with shear in the flow velocity [.. that can ..] occur in propagating nonneutral electron beams and layers".^{[2] [3]} It may give rise to electron vortices,^[4], which resembles the Kelvin-Helmholtz fluid dynamical shear instability, and occurs when charge neutrality is not locally maintained.^[5] The term diocotron derives from the Greek διωκειν, meaning "pursue."^[5]

Aurora

Although usually attributed to Kelvin Helmholtz instabilities,^[6] the diocotron instability has been associated with the aurora (where they are known as auroral curls or auroral vortices), the mechanism having been proposed by Hannes Alfvén in 1950.^[5][7]

See image, right.

Galactic arms

The arms of galaxies (eg. NGC 3646) are susceptible to the diocotron instability ^[8] In the simulation of galaxy formation, Peratt found that:

Since Ez is out of the plane of the page, the column electrons spiral downward in counter-clockwise rotation while the column ions spiral upward in clockwise rotation. A polarization induced charge separation also occurs in each arm, which, as it thins out, produces a radial electric field across the arm. Because of this field, the arm is susceptible to the diocotron instability. This instability appears as a wave motion in each arm.^[9]

Pulsars

The Diocotron instability has also been associated with a pulsar's electrosphere.^[10]

References