Sep 27, 2007
Electric Currents Big and Small
The novelty plasma ball demonstrates many of the
properties of plasma that can be seen in the Sun, in
nebulae, and in galaxies.
beautiful photo of the spherical electrode in the centre of
a plasma ball shows a blue filamentary streamer as it wavers
during the 8-second exposure. Thousands of volts of
electricity ionize the gas in the globe, ripping electrons
from molecules and atoms. As electrons recombine with the
ions, the gas gives off light. The colors depend on the kind
of gas filling the globe.
The plasma ball
illustrates some of the fundamental characteristics of
plasma. The blue streamer looks flat, but that is an
illusion of the photography. In reality, the filament is as
thin as the light blue edges. It flickers between the two
sides and extends from the electrode in a thin tube to the
outer glass sphere of the ball.
a plasma cable, or plasma rope, the filament is the result
of electrons and ions flowing through the plasma (i.e., an
electric current). The current generates a magnetic field
that surrounds the filament like hoops around a beer barrel.
The magnetic field pinches the current and keeps it
collimated (or wire-like).
When we take off
a nylon sweater in a dark room and we see tiny sparks fly,
we are seeing similar but smaller filamentary discharges. We
see larger filamentary discharges as lightning in storms.
The flares we see erupting from our Sun are even larger
filaments. Because of the greater distances involved and the
different magnetic fields and particle densities, flares
appear to move in slow motion. And finally, filaments the
size of solar systems make up nebulae.
non-neutral plasmas can be created in the laboratory, space
plasmas generally contain equal numbers of negatively
charged electrons and positively charged ions. They are
considered to be electrically neutral. And since plasmas are
also as electrically conductive as a lightning rod, this
suggests that if a charge build-up should occur, then it
would be neutralised quickly. But this view, like that of
the “flat” filament in the plasma ball, is an illusion.
In 1831, Michael
Faraday invented the homopolar motor/generator (also called
a Faraday disk). It consists of a conducting disk in an
axial magnetic field. The disk may be rotated in the
magnetic field to generate an electric current between its
axis and its edge. Or electric current may be passed from
axis to edge to cause the disk to rotate in the magnetic
field. In that way, the conducting atmosphere of the Sun is
caused to rotate faster at the equator than at higher
latitudes, when we should expect the expulsion of the solar
wind to slow it.
described the circuit for this Faraday motor many decades
ago, but he didn’t consider its link with a greater galactic
circuit. The current "disk" of the Sun is the heliospheric
current sheet that flows between the Sun and the outer
reaches of our solar system. And the axial circuit consists
of Birkeland currents flowing along the "open" polar
magnetic field lines.
galactic disk is the disk of a Faraday motor, caused to
rotate by Birkeland currents flowing along the axis and out
along the spiral arms. Stars in the spiral arms receive
their power from those galactic currents. Galaxies, in turn,
are threaded like "Catherine wheels" on intergalactic
Birkeland currents. The cosmic circuitry of Birkeland
currents can be traced by their magnetic fields.
So, far from
being electrically sterile, cosmic plasma is awash with
electric current filaments. And just like Frazier's plasma
ball, we see the same beauty and evidence of currents in
astronomical nebulae, glowing hydrogen HII regions, and
We live in an Electric Universe!
Please visit our
The Electric Sky
and The Electric Universe