"Plasma Globe"


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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 Tesla's effort to develop a new source of lighting not covered by the Edison patents.

In 1974 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, and sold large versions to science museums world wide.

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/Ionizing radiation 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 cause x-ray fluorescence via "Bremsstralung". USUALLY the x-ray intensity is insignificant. They're far too little to light up a fluorescent screen. (No viewing your own bones! Aww too bad.) They might pass through aluminum foil and cardboard, but they won't pass through steel. But they will make a geiger counter fairly ROAR with clicking, but only if the GM probe has a thin window (for alpha particles and x-rays below 50KeV.). The response of the alpha-window geiger counter on an x-ray light bulb is about the same as that for a hunk of uranium mineral.

X-ray sources: All radio tubes, crt tubes, many types of small appliance bulbs, oblong aquarium lights, lectern bulbs, museum-case bulbs, exit sign lamps, screw-in xmas bulbs, etc., any small cheap incandescent bulbs which lack an argon fill. These will produce weak low-energy ionizing radiation when used as a "plasma globe." I've heard that the x-ray output is a bit higher if the filament is incandescing via 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." Or at the very least, only use bulbs which produce a bright blue/violet gas glow at the filament. If in doubt, use a Geiger Counter to detect any x-rays. 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.

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