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Name: John M. S.
Status: educator
Age: 50s
Location: N/A 
Country: N/A
Date: 11/15/2004


Question:
The plasma cutting process works by passing a gas between a cathode and anode which is conducting a very high electrical current. As this gas pass through the electrical current it becomes ionized. The temperature of the gas now increases to approximately 50,000 degrees F. What causes the gas to become so hot?


Replies:
A normal electric current is a flow of electrons. Moving electrons have energy and will heat whatever atoms or molecules they strike. As you have noticed, normal air does not conduct electricity very well. If a voltage is imposed across two metal electrodes, no current flows because the electrons cannot jump the gap from the negative to the positive electrode, nor do the electrons travel on any air molecules. If ionized gas (free electrons and positively charged atoms) is present between the electrodes then the situation is different. The electrons move toward the positive electrode and the ions toward the negative electrode.

A voltage difference of only a few volts will accelerate an electron to pretty high energies, and the electron will transfer energy to anything it strikes, including atoms in the gas. So the gas gets hot because moving electrons, which get energy from the electric field, strike atoms and heat them up. (Neutral atoms in the gas will then ionize because the impact of the electrons, which then can participate in more ionization, so the plasma keeps on going. )

A plasma can be started by either using high temperature, or a really large voltage, or by touching the electrodes together.

Bob Erck



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