Positive column high pressure arcs

High -pressure are diseharges. The positive column of an arc plasma is in quasi equilibrium at pressures exceeding 0.1-0.5 atm. Thermal arcs also operate at very high pressures exceeding 10 atm. The plasma in this case is so dense that most of the discharge power (80-90%) is converted into radiation. 

Positive Column of High-Pressure Arcs Elenbaas-Heller Equation... 

The plasma and metal vapor in the positive column extend out to the shield or container walls encompassing the arc. The metal vapor and metal droplets from the jets will collect on the relatively cool walls. In addition, if the shield is not electrically connected to the arc circuit, it will assume a floating potential that is slightly negative with respect to the plasma and collect ions and electrons at the same rate. If the shield is connected to the cathode, a positive ion sheath is formed over its inner surface adjacent to the plasma. This is in contrast to the flaming sheath that surrounds a high-pressure arc operating in open air. 

The gas in the positive column of glow discharge, in arc discharge at high pressures and in certain other forms of discharge (as well as in the incandescent atmosphere of stars) is in the plasma state. The plasma represents a unique system of interacting particles and possesses specific properties. 

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