Newsgroups: sci.physics.plasma
From: Robert Couture <rcouture@sciborg.uwaterloo.ca>
Subject: Re: Plasma globe
Message-ID: <34D7164B.54FA4CAA@sciborg.uwaterloo.ca>
Sender: news@watserv3.uwaterloo.ca
Organization: University of Waterloo
References: <34D09806.3590@pophost.eunet.be> <34D2A2F8.2ED5FB07@physics.ubc.ca>
Date: Tue, 3 Feb 1998 13:06:20 GMT


A plasma globe is essentailly a big capacitor. Where the dielectic
plates is between the inner probe and infinity. But you have
dielectrics in between sort of like putting a few capacitors in series.
The first capacitor is your inert gas, the second is the glass globe
itself and third the surrounding air around it.

When you touch the outer glass you are changing the capacitace value
because you are adding another capacitor in series ie. your hand.

The carona (spelling?) discharge is the lighting that you see inside.
Because the electric field is extremely high around the probe inside the
globe it reaches its break down voltage and you see a discharge.

Basically the system works on a resonating DC source between 10 and 100
kHz and a high setup transformer like a telsa coil, fly backtransformer
or ignition coil to a car. Probe voltage is usually around 20kV.

You can basically use any type of gas. The only problem is thermal
expansion as well certain gases are not in the visible range. This is
part of the reason for the gas being at around 1/2 atm. As well
dielectric constant of your gas is determined by your pressure as well.

And as a side note they are neat toys to make of any physics major.