I How Conductive is Ionized Air? Investigating the Physics of Plasma Cutters

[rocket100]

So I've been reading about how plasma cutters work, and the way it ignites intrigued me and got me thinking. My question is, how conductive would a stream of ionized air created by a high voltage spark be? If you passed a high current, low voltage through the stream, would it be able to travel along it? Is there an equation that can relate air temperature to resistance?

 

[Charles Link]

You can run relatively high currents at low voltages through ionized gases. This is what your neon lamps are and also fluorescent tubes. In the case of the fluorescent tube, you also have a fluorescent coating to convert the UV (much of the arc emissions are UV) that is emitted from the plasma arc to visible light. In order to get the arc started, it requires high voltages, but once the arc is started, you can get high currents (1 amp or more) at low voltages (typically 20 volts or less). The resistance drops significantly in a plasma as the current increases. In an arc lamp circuit, it often requires a ballast resistor to stabilize the current or the current can increase to very large amounts because the resistance drops as the current increases. Additional item is air in its neutral state has very high electrical resistivity but if it is highly ionized it actually becomes quite conductive.

 

[shjacks45]

So I've been reading about how plasma cutters work, and the way it ignites intrigued me and got me thinking. My question is, how conductive would a stream of ionized air created by a high voltage spark be? If you passed a high current, low voltage through the stream, would it be able to travel along it? Is there an equation that can relate air temperature to resistance?

I think you refer to the one that splits Hydrogen molecules into atoms, so when the Hydrogen recombines the 104 Kcal/mole energy hits the work. It takes 400 Kcal to split Nitrogen molecule and 260 Kcal to split O2, the result would contain a lot of Nitrogen Oxides (think nitric acid).
Lightning originates as a high voltage low current "leader" that travels down the path of least resistance until touching earth, then a 500,000 Amp return bolt from the Earth neutralizes Earth-cloud charge imbalance.

 

[shjacks45]

You can run relatively high currents at low voltages through ionized gases. This is what your neon lamps are and also fluorescent tubes. In the case of the fluorescent tube, you also have a fluorescent coating to convert the UV (much of the arc emissions are UV) that is emitted from the plasma arc to visible light. In order to get the arc started, it requires high voltages, but once the arc is started, you can get high currents (1 amp or more) at low voltages (typically 20 volts or less). The resistance drops significantly in a plasma as the current increases. In an arc lamp circuit, it often requires a ballast resistor to stabilize the current or the current can increase to very large amounts because the resistance drops as the current increases. Additional item is air in its neutral state has very high electrical resistivity but if it is highly ionized it actually becomes quite conductive.

Flourescent bulbs use a filament to emit electrons to ionize argon filling and mercury vapor. The voltage drops and the filament drops out of the heating circuit but filament stays hot by impact of ionized atoms. High voltage to initiate plasma isn't used often, except as microamp triggers.