Double Layer (plasma)

Double Layer (plasma)

A double layer is a structure in a plasma and consists of two parallel layers with opposite electrical charge. The sheets of charge cause a strong electric field and a correspondingly sharp change in voltage (electrical potential) across the double layer. Ions and electrons which enter the double layer are accelerated, decelerated, or reflected by the electric field. In general, double layers (which may be curved rather than flat) separate regions of plasma with quite different characteristics. Double layers are found in a wide variety of plasmas, from discharge tubes to space plasmas to the Birkeland currents supplying the Earth's aurora, and are especially common in current-carrying plasmas. Compared to the sizes of the plasmas which contain them, double layers are very thin (typically ten Debye lengths), with widths ranging from a few millimeters for laboratory plasmas to thousands of kilometres for astrophysical plasmas.

Other names for a double layer are electrostatic double layer, electric double layer, plasma double layers, electrostatic shock (a type of double layer which is oriented at an oblique angle to the magnetic field in such a way that the perpendicular electric field is much stronger than the parallel electric field), space charge layer. In laser physics, a double layer is sometimes called an ambipolar electric field. Double layers are conceptually related to the concept of a 'sheath' (see Debye sheath).

The adopted electrical symbol for a double layer, when represented in an electrical circuit is ────DL────. If there is a net current present, then the DL is oriented with the base of the L in line with direction of current.

An overview of double layers in space, experiment and simulation is given in the introduction of ref.