## 3 Results and Discussion
### Characteristics of DC Arc
The electrical arc at atmospheric pressure appeared as a constricted area of electrical and mechanical forces, which caused plasma fluid to move away from the arc column. In this case, the plasma fluid is replaced by cold gases injected into the arc-reacting zone from the outside. The processes in the electric arc zone include turbulent mixing, chemical reactions, ionization processes, the transfer of electric energy to conducting particles, and the transformation of electric power into thermal energy and radiation. The investigation of the influence of these factors requires the simultaneous characterization of the arc and its characteristics in association with gas and plasma flow parameters. Depending on the values of the electric current strength, gas flow rate, channel diameter, and pressure, the VCC of the plasma torch falls: with an increase in the current strength, the arc burning voltage decreases. Obtaining descending characteristics, an intensive cooling of the anode (in our case, melt) is required, which is realized at a high flow rate or when the arc is compressed by the walls of the arc chamber, which is possible with intensive cooling of the PChR walls. In the presented PChR design, dropping VCC is always obtained. The physics of the descending VCC of the arc formation in the plasma torch can be represented as follows. A so-called free-burning arc is realized when the arc burns in an unlimited space between the two electrodes. The length, diameter, and configuration of such an arc depend on gas properties and the electric current strength. In particular, with increasing current, the diameter of the arc loosely increased because there were no limiting factors in the radial direction. Because the dependence of the arc voltage on its length is linear, the arc's diameter will also be almost constant if it is not affected by any external factors, such as cross-flow or artificial rotation of the arc spot. In the presented plasma torch, the arc burns in a volume between the chamber walls and the flow of the plasma-forming gas. Such an arc is nonstabilized, and its diameter depends on the geometry of the discharge chamber, current strength, gas flow rate through the plasma torch, and gas composition inside the reactor. The anode end diameter is determined by measuring the diameter of the cavity formed on the graphite plate during the plasma processing. Such a study was carried out in a DC electric arc volume reactor. At very low gas flow rates, the influence of flow on the arc diameter can be significant. It was found that the spot's area exceeded the area of the cavity on the anode by approximately 1.5 times. In such a case, the arc appears as \"diffused\", and its stability by the wall is impossible and takes a free form. The arc narrows in the near-cathode area, and the arc properties differ significantly from those of the near-anode region. Therefore, by analyzing the geometry of the arc, it is possible to distinguish the physical processes occurring at the cathode, anode, and space between them. Three characteristic regions (a central zone or arc column, the anode, and the cathode) were visible from the potential distribution along the arc axis. Directly toward the cathode, the region of the cathodic potential drop occurs, which is characterized by the strength of the electric field. The region of the anode (melt) also exhibited a potential drop. The length of this region is several mean free paths of electrons. The potential drop was also insignificant (only a few volts). The near-electrode regions are connected by a conductive channel that is homogeneous in structure, which is called the positive column of an electric arc. Unlike other parts of the arc discharge, which have specific dimensions depending on the nature of the gas, its pressure, and the strength of the discharge current, the length of the positive column is determined by the distance between the electrodes; that is, it can vary over a very wide range.