Abstract
As described in previous papers, a different anode mode, i.e., the glow mode, was observed in a low pressure and small current arc. Mechanism of the glow anode mode and its transition process from the normal mode in case of a hydrogen arc with a water cooled copper anode was discussed from the view points of ionization process in the anode fall region. In an arc with consumable anode such as graphite electrode, however, the above anode mechanism must be modified, since the anode temperature is extremely elevated and considerable heat losses by radiation, evaporation, etc. should be taken into account.
In low pressure helium atmospheres, where no chemical reactions between the electrodes and ambient gas take place, the anode mode of graphite electrode is basically classified into two types as it was in a water cooled copper anode. The glow anode mode, however, is further devided into two stages. The one (G1 mode) is characterized by zero consumption of graphite anode, while the another (G2 mode) is featured by eminent evaporation of carbon from the anode. In G1 glow mode, the current density at the anode is small and then the anode temperature is low. In G2 stage, on the other hand, the anode current density becomes high and eminent evaporation takes place from the anode spot area due to high temperature, hence the anode heat losses due to radiation and evaporation in this mode is higher than that of G1.
