Plasma globes, or Inert Gas Discharge Tubes, were invented by Nikola Tesla at the end of the 19th century. They are essentially Tesla coil terminals enclosed with low-pressure gases inside a glass container. The globes produce moving streams of ionised gas (plasma) that are attracted to the hand of a person touching the globe, which provides a capacitive path to the ground. With some previous electrical experience and the right equipment, simple plasma balls are relatively easy to construct.
- Skill level:
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Things you need
- Flyback transformer
- 2N3055 power transistor
- Power supply
- 250ml round-bottomed glass flask
- Rubber stopper to fit mouth of flask
- 1/8-inch pipe
- Brass valve
- Vacuum pump
Construct a single transistor flyback transformer. This generates the high-voltage AC current required to create plasma. The circuit uses a common flyback transformer that can be found in any equipment with a Cathode Ray Tube (CRT). They can be recognised by their disc-shaped secondary coils and removable primary coils. Connect a 2N3055 power transistor to the transformer so that when the circuit is connected to a power source, the current passes through the transistor to the main set of coil windings. This will induce a field in the transformer's ferrite core that will then induce a current in the feedback winding. This in turn causes the field in the ferrite core to collapse and results in a high-voltage pulse.
Connect the brass valve to the pipe. Drill a 1/8-inch hole in the rubber stopper and slide it onto the pipe behind the brass valve. Insert the assembly into the 250ml round-bottomed flask so that the pipe extends into the centre of the flask.
Evacuate the flask using the pump and then fill it with argon to about 10 torr of pressure. Disconnect the pump and attach the power supply. Turning on the power should result in the globe becoming filled with arcs of purple plasma.
The high voltage breaks down the gas into ions and electrons. The oscillating electromagnetic field excites these particles and causes them to radiate energy in the form of visible light.
Tips and warnings
- Electricity can be fatal. Do not attempt the above without previous electrical experience.
- Do not use electronic devices near the plasma globe, as it may transfer a damaging static charge to the device.
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