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

In summary, plasma cutters use high voltage to ignite a plasma arc, which can then carry high currents at low voltages. The resistance drops significantly in a plasma as the current increases, and air becomes highly conductive when highly ionized. This principle is also used in neon lamps and fluorescent tubes, where a high voltage is used to ionize the gas inside the tube. Additionally, lightning is a natural example of high voltage and low current traveling through ionized air.
  • #1
rocket100
3
0
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?
 
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  • #2
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.
 
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  • #3
rocket100 said:
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.
 
  • #4
Charles Link said:
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.
 

1. How does ionized air affect the conductivity of plasma cutters?

Ionized air, also known as plasma, is a highly conductive state of matter. When air is ionized, it becomes a mixture of positively and negatively charged particles, allowing electricity to flow through it more easily. This increased conductivity is essential for the functioning of plasma cutters, which use high temperatures and ionized air to cut through materials.

2. What factors influence the conductivity of ionized air in plasma cutters?

The conductivity of ionized air in plasma cutters can be influenced by several factors, including the type of gas used, the temperature and pressure of the gas, and the design of the plasma cutter. Different gases have different ionization energies, which can affect the conductivity of the plasma. Additionally, higher temperatures and pressures can increase the number of ions and electrons in the plasma, making it more conductive.

3. How does the conductivity of ionized air affect the cutting speed of plasma cutters?

The conductivity of ionized air plays a crucial role in the cutting speed of plasma cutters. A more conductive plasma allows for a higher current to flow, resulting in a faster and more efficient cutting process. However, if the conductivity is too high, it can cause the plasma to become unstable, leading to a decrease in cutting speed.

4. Are there any safety concerns related to the conductivity of ionized air in plasma cutters?

Yes, there are safety concerns associated with the conductivity of ionized air in plasma cutters. Since plasma is highly conductive, it can pose a risk of electric shock to those operating the plasma cutter. It is essential to follow proper safety protocols and wear protective gear when working with plasma cutters to minimize the risk of injury.

5. How can the conductivity of ionized air be measured in plasma cutters?

The conductivity of ionized air can be measured using a variety of methods, including conductivity meters, oscilloscopes, and voltage probes. These tools can measure the electrical current flowing through the plasma and provide an indication of its conductivity. Additionally, the cutting speed and efficiency of the plasma cutter can also serve as an indirect measure of the conductivity of the ionized air.

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