B. Birkeland Currents in Cosmic Plasma
As far as we know, most cosmic low-density plasmas also depict a filamentary structure. For example, filamentary
structures are found in the following cosmic plasmas, all of which are observed to be associated with electric currents.
1) In the aurora, filaments parallel to the magnetic field are very often observed. These can sometimes have dimensions down to about 100 m.
2) Inverted V events and the in-situ measurements of strong electric fields in the magnetosphere (105-106 A, 108 m) demonstrate the existence of filamentary structures.
3) In the ionosphere of Venus, "flux ropes," whose filamentary diameters are typically 20 km, are observed.
4) In the sun, prominences (1011 spicules, coronal streamers, polar plumes, etc., show filamentary structure whose dimensions are of the order 107-108 m.
5) Cometary tails often have a pronounced filamentary structure [28].
6) In the interstellar medium and in interstellar clouds there is an abundance of filamentary structures, e.g., the Veil nebula, the Lagoon nebula, the Orion nebula (Fig.1), the Crab nebula, etc.
7) The center of the Galaxy, where twisting plasma filaments, apparently held together by a magnetic field
possessing both azimuthal and poloidal components, extend for nearly 500 light years (5 x 1018 m) [29].
8) Within the radio bright lobes of double radio galaxies, where filamental lengths may exceed 20 kpc (6 x 1020 m) [30]. [......]
It is the purpose of this paper to extend the study of cosmic plasma to the case of galactic-dimensioned (50 kpc in width) Birkeland filaments by means of three-dimensional, fully electromagnetic, and relativistic particle-incell simulations. Fig. 1 is a contrast-enhanced photograph of the Orion nebula but serves the purpose of representing the morphology to be expected by an observer situated within a much larger filamentary metagalactic structure. The simulation model consists of modeling a magneticfield- aligned neutral plasma filament (column) in the presence of a field-aligned electric field. (Strictly speaking, because of the parallel electric field, the portion of the filament simulated is a double layer [35].) To study the evolution of interacting filaments, a second filament (nearly identical to the first) is placed adjacent as depicted in Fig. 3. (As many as six filaments have been investigated by simulation while up to 12 filaments have been studied experimentally. However, because of the r-1 force between filaments, it would appear that a majority of cosmic plasma phenomena are the result of two, or at most three, interactions among the closest filaments.)
