The High Current Carbon Arc and Its Mechanism

Abstract

The high current carbon arc with maximum crater brightness of 2000 candles per mm2, axial intensity of 1.2×106 candles, power inputs up to 200 kw, light efficiencies exceeding 90 lumens per watt, radiation efficiency of 73 percent, crater temperatures up to 8000°K, and arc stream temperatures of the order of 12,000°K is the most powerful and one of the most interesting radiation sources known. The rising voltage characteristic, the anodic vapor stream which causes its excellent radiation properties, and the contracted arc stream distinguish the high current carbon arc from the well-known normal low current carbon arc. The properties of the contracted arc stream are discussed and a general theory of arc streams is presented. Starting from the anodic mechanism for the low current carbon arc, the anodic mechanism of the high current arc is developed. The rising voltage characteristic, the anodic vapor stream, and the high crater brightness are explained as a consequence of an abnormal voltage drop in front of the anode which increases with increased current density and is caused by a very rapid evaporation of the anodic material. The important role which the magnetic field of the arc current plays in the stabilization of all high current arcs is pointed out. The author believes that this unique high temperature arc has bearing on other arc and spark discharges, and also will play an important role in future developments of high temperature physics and chemistry.