## 3 Results and Discussion
### Characteristics of DC Arc  
As previously mentioned, a linear plasma torch (Figure 3) with a hafnium cathode was designed and constructed for experimental waste decontamination. Insulated from the plasma-chemical reactor, the casing shell also served as an intermediate electrode for igniting an arc. The electric arc in the plasma-chemical reactor was ignited by lowering the plasma torch so that the gap between the anode and the plasma torch was 3-5 mm. A high-voltage discharge ignites the so-called initial arc between the cathode and intermediate electrode. The low-power plasma jet that reaches the anode ignites the main electric arc. When the electric arc was ignited, the plasma torch was raised; then, the expected power of the plasma torch was obtained. Figure 4 shows the dependence of the voltage of the electric arc on its length (between the cathode and a graphite anode). In our case, the voltage drop per unit length of the arc column has a constant value. Therefore, the arc voltage's dependence on the arc length is linear (Figure 4). The stability of the steady arc is determined by the relationship between the current and voltage. The electric arc in the plasma-chemical reactor is considered to be free, although the walls slightly limit its development in the reactor's space. However, the shielding gas does not limit the arc; the gas flow only stabilizes it. Air, as plasma-forming gas in the PT, is supplied from the cathode side for its protection, while air consumption does not influence the arc characteristics. In the presence of internal energy sources, heat flux to the reactor walls can be determined according to [16]. Under the influence of electromagnetic forces, a plasma-forming gas stream flows from the cathode toward the anode [17]. Because the anode is a surface of solid processing material, the gas jets of the evaporated material outflow from it, and the vapor jet is thicker than the cathode gas stream but much shorter. These two jets collided to form a plasma plume. In such a case, the arc operation is unstable. When the surface of the melted material serves as the anode (Figure 2), a plasma plume is not formed because the anode steam jet does not have a strict direction. The electric arc operates in a more stable mode than that in the case of a solid anode. With such a PT, it is possible to generate highly concentrated heat fluxes using air as a plasma-forming gas for hazardous waste utilization. By contacting the raw material with plasma in the PChR, a high local heat flux destroys it; all organic matter and its harmful compounds are destroyed and removed from the reactor in the form of gas. Waste, an inert material with a high melting point, such as various aluminosilicates, carbides, nitrides, and  
Figure 4: Dependence of arc voltage on its length. Arc current (A): 1—160, 2 and 3—150, 4—200, 5 and 6—180. Line A—plasma torch operates with waste, B—without waste. Air inlet flow rate: plasma torch—1 g/s, protecting gas—2.63 g/s. inorganic metal oxides with melting points of up to 2500 K, become a melt. The melting process involves the interaction of a highly concentrated local heat flux generated by a plasma torch with inert materials. Consequently, they melted and accumulated on the graphite anode. Owing to its high melt temperature, it is an electrically conductive material; when the melt overlays the anode, the electric arc continues to burn between the anode and melt layer, maintaining its high temperature owing to its ohmic resistance. In the PChR, the VCC of a free arc in an air atmosphere with an anode as melted waste was measured at different arc lengths (Figure 4). It was observed that, up to \(x=150\) mm, the arc voltage was almost independent of the arc current. This implies that, by increasing the arc length, the arc voltage changes depending on the plasma torch position concerning the anode (the arc length was manually altered by changing the electrode position). The electric arc voltage also depends on the processes occurring in the reaction chamber.