If you're anything like me, in
the 1980s you wanted to have a plasma globe, because those things looked so damn cool. And now on
the rare occasions when you still see one, you wonder vaguely how those suckers work. Well, get ready for
the answer as provided by
Plasma globe (T-H-L):
A
plasma globe or
plasma lamp (also called plasma ball, dome, sphere, tube or orb, depending on shape) is (usually) a clear glass sphere filled with a mixture
of various noble gases with a high-voltage electrode in
the center
of the sphere.
Plasma filaments extend from
the inner electrode to
the outer glass insulator, giving
the appearance
of multiple constant beams
of colored light (see corona discharge and electric glow discharge). Plasma globes were most popular as novelty items in
the 1980s.[1]
The plasma lamp was invented by Nikola Tesla[2] after his experimentation with high-frequency currents in an evacuated glass tube for
the purpose
of studying high voltage phenomena, but
the modern versions were known to be first designed by Bill Parker.[1] Tesla called this invention an inert gas discharge tube.
There are a lot
of links in this highly useful lede (got to love that "(usually)" in
the very first sentence), but I've only linked here
the one related to what I wanted to know. What it links to is this part
of Plasma (physics) (T-H-L):
Filamentation
Striations or string-like structures,[27] also known as Birkeland currents, are seen in many plasmas, like the plasma ball, the aurora,[28] lightning,[29] electric arcs, solar flares,[30] and supernova remnants.[31] They are sometimes associated with larger current densities, and the interaction with the magnetic field can form a magnetic rope structure.[32] High power microwave breakdown at atmospheric pressure also leads to the formation of filamentary structures.[33] (See also Plasma pinch)
Filamentation also refers to the self-focusing of a high power laser pulse. At high powers, the nonlinear part of the index of refraction becomes important and causes a higher index of refraction in the center of the laser beam, where the laser is brighter than at the edges, causing a feedback that focuses the laser even more. The tighter focused laser has a higher peak brightness (irradiance) that forms a plasma. The plasma has an index of refraction lower than one, and causes a defocusing of the laser beam. The interplay of the focusing index of refraction, and the defocusing plasma makes the formation of a long filament of plasma that can be micrometers to kilometers in length.[34] One interesting aspect of the filamentation generated plasma is the relatively low ion density due to defocusing effects of the ionized electrons.[35] (See also Filament propagation)
The general-purpose encyclopedia for
the non-expert reader!
The "Description" section
of the plasma ball article is a complete mess
of technical detail. And,
of course, it also doesn't explain what plasma is.
The article's first citation is to an article on that well-regarded reference source, Softpedia, called
How Do Plasma Lamps Work? Which has provided a helpful source for plagiarism.
Softpedia wrote:
Plasma lamps are mostly used as curiosities and to obtain unique light effects.... They also have educational purpose, that is, they can be used to explain several physical aspects of electrical currents.
'Plasma globe' on Wikipedia wrote:
Plasma lamps are mainly used as curiosities or toys for their unique lighting effects and the "tricks" that can be performed on them by users moving their hands around them. They might also form part of a school's laboratory equipment for demonstration purposes.
No credit to
the source text.