A Brief History
Plasma Globes were invented by Nikola Tesla some time before 1892.
Glass-enclosed Tesla coil terminals containing low-pressure gases were
part of his effort to develop a new source of lighting not covered by the
Edison patents. The same device became an art object when William
Parker,
an intern at the Exploratorium museum in SF, redesigned the older "Argon
Candle" science exhibit to produce a long plasma streamer. Parker named
the device
"AM Lightning". His later devices were spherical and contained
various gas mixtures producing a wide variety of nonlinear plasma
phenomena. Parker exhibited these in Cambridge MA at the
MIT Compton Gallery in 1985.
Bill B's short Plasma Sphere instructions for experienced
electronics hobbyists:
First built a tiny Tesla Coil based on a
flyback trans former. Flyback units can be had
from old TV sets or dead computer monitors. Build your Tesla
Coil using one of the following schematics:
Your coil needs to be able to generate a spark of about 1.5cm
length. Next, obtain a "decorator" 40 watt 4-inch clear spherical light
bulb. Large hardward stores like Ernst or Fred Meyer carry these.
Connect the high voltage lead from your mini tesla coil to the base of the
light bulb. (It doesn't matter which light bulb contact you use.) Turn off
the lights and turn on your coil, and you'll see purple "plasma fingers"
spewing out of the filament supports in the light bulb. (In some cases
you can
improve this by taping some aluminum foil to one side of the bulb.
Connect the foil to ground. Even better, you can improve the visual
contrast. Just use black spray-paint to coat the foil.)
If you want to get ambitious you can eliminate the light bulb.
Instead build your own glass globe. Use a glass jar, or better yet a
boiling flask from a mailorder chemistry
supplier or a lab
glass outfit. Stopper with a 3-hole stopper. Provide two hoses, one
to inject gas, the other as an outlet. Push the inlet hose deep into the
flask so the injected gas can push the air ahead of it. Tape a layer of
paper towel around the end of the gas tube inside the bulb. (Or perhaps
stuff some fiberglas in the tube end.) This acts as a gas diffuser to
prevent turbulent mixing. Insert a wire into one hole as the H.V.
terminal, with the tip of the wire centered in the flask. Turn on the
tesla coil, turn out the lights, then use pure Argon to slowly flush the
nitrogen out of the glass globe (welding argon is pure enough. Note that
argon is slightly heavier than air.) As the N2 and O2 is replaced by the
Argon, the small corona discharge on the wire in the globe will grow
larger and larger. When the discharge is large and white, turn off the
argon and clamp the hoses. Seal the stopper holes with epoxy if desired
(don't use silicone caulk, the acetic acid fumes destroy the plasma
effect.)
X-rays from light bulbs
A note about x-rays. When placed atop
a Tesla coil, some small bulbs fail to produce purple streamers of
plasma. Instead the space inside the bulb remains dark. But the glass
flickers blue, or white, or sometimes green. This shows that the bulb
contains a fairly hard vacuum. And at high voltage (above 10KV,) such a
bulb will produce soft x-rays as electrons slam into the glass and make it
fluoresce. USUALLY the x-ray intensity is insignificant. They're far too
little to light up a fluorescent screen. (No viewing your own bones! Aw
too bad.) They might pass through aluminum foil and cardboard, but they
won't pass through steel. But they will make a geiger counter click, but
only if the GM probe has a thin window (for alpha particles.). The
response of the alpha-window geiger counter is about the same as that for
a hunk of uranium mineral.
Most types of small appliance bulbs, aquarium
lights, exit sign lamps, etc., will produce weak low-energy x-rays when
used as a "plasma globe." I've heard that the x-ray output is a bit higher
if the filament
is lit by a floating battery. And it's much higher if a piece of
grounded metal foil is glued to the
end of the bulb. So, to avoid even the slightest x-ray hazard, use only
the large 4-inch spherical bulbs for your "plasma globe." Stay away from
those small green-fluorescing aquarium bulbs! Here's some radiation info, compare
x-ray hazards to the risk of canoe trips and eating peanut butter .
Construction Articles in Magazines
- Aug 1997 ELECTRONICS NOW (magazine), Build the Poor Man's Plasma
Globe, by R. Iannini and Marc Spiwak. Use a decorative spherical light
bulb and a 12v power supply based on FETs and a flyback xformer.
- 1990 RADIO
ELECTRONICS ELECTRONIC EXPERIMENTERS HANDBOOK (magazine), ELECTRONIC
TORNADO, by Robert Iannini. Schematic and construction instructions for a
variable power supply for a plasma sphere, with audio input, variable
pulse and intensity (note: plasma spheres don't really need a vacuum pump,
use a jar full of pure helium or pure argon at 1-ATM)
- 1990 RADIO ELECTRONICS ELECTRONIC EXPERIMENTERS HANDBOOK (magazine),
(magazine), BUILD THE LIGHTNING BULB, By Vinny Vollono. Plans for a simple
plasma sphere based on an automotive ignition coil, a triac, and a 6"
light bulb
Back issues of RADIO ELECTRONICS magazine, HANDS-ON ELECTRONICS magazine,
and EXPERIMENTER'S HANDBOOK magazine are available from your local
public library via the Interlibrary Loan service. Contact the reference
desk.
Also see Plasma Sphere
without vacuum pump for more info.
OLD LINKS GONE BAD? Try http://archive.org, "The Wayback Machine"
It offers billions of old websites and even some of the graphics. But
it's not searchable. You have to know the URL of the old site.
Quick link to old sites: simply
add this prefix to any expired URL: http://web.archive.org/web/*/
