**2. Arc cutting torch**

The high energy density cutting torch used in this numerical study consisted of a cathode centered above an orifice in a converging-straight copper nozzle. The cathode was made of copper (7 mm in diameter) with a hafnium tip (1.5 mm in diameter) inserted at the cathode center. A flow of oxygen gas cooled the cathode and the nozzle and was also employed as the plasma gas. The gas passed through a swirl ring to provide arc stability. The nozzle consisted in a converging-straight bore (with a converging length of 1 mm, and a bore 1 mm in diameter, 4.5 mm length) in a copper holder surrounding the cathode (with a separation of 0.5 mm between the holder and the cathode surface). To avoid plasma contamination by metal vapors from the anode (usually the work piece to be cut), a rotating steel disk with 200 mm in diameter and 15 mm thickness was used as the anode (Freton et al., 2002). In this study, the disk upper surface was located at 6 mm from the nozzle exit. The arc was transferred to the edge of the disk, and the rotating frequency of the disk was equal to 24 Hz. At this velocity, a wellstabilized arc column was obtained, and the lateral surface of the anode disc was completely not melted. Thus, practically no metal vapors from the anode were present in the arc. A scheme of the torch indicating several geometric dimensions is presented in Fig. 1.

By performing a small orifice (1 mm in diameter) on the lateral of the cathode surface the pressure in the plenum chamber (*pch*) was measured by connecting a pressure meter at the upper head of the cathode. The gas mass flow (*dm/dt*) injected in the torch was also registered. In this experiment, the arc current, the plenum pressure and the gas mass flow, were fixed to values of 30 A for the arc current, *pch* = 0.7 MPa and *dm/dt* = 0.71 g s-1, respectively.

**Figure 1.** Schematic of the Cutting torch.
