Diagnostics in cutting arc plasmas

LEANDRO PREVOSTO; HÉCTOR KELLY

Santiago

Congreso; XV LAWPP + ICPP; 2010

Cutting arcs are created by a narrow nozzle (1 mm) inside a torch, where a gas is tangentially injected at a high pressure. The intense gas-vortex convective cooling at the arc fringes enhances the power dissipation in the arc column ( 10^12 W m^-3) resulting in extremely sharp plasma quantities gradients, very high heat fluxes (up to 10^10 W m^-2 in the jet core), high plasma enthalpies ( 10^8 J kg`-1) and high plasma velocities (M > 1, being M the Mach number). As a consequence, the experimental data of such arcs are hard to obtain. In practice, most of the available experimental data are related to spectroscopic measurements in the external plasma region, giving information of only part of the variables involved, mostly temperatures and species concentrations [1]. On the other hand, several remote and invasive diagnostics of cutting arcs have been developed and applied in our Laboratory, such as rotating Langmuir probes, nozzle charge collection, time-of-flight plasma velocimetry and optical refractive techniques. These diagnostics were developed and used with the purpose of basic experimental research and theoretical model validation. In this work, an over-view of such developed plasma diagnostics techniques is given. The following results correspond to an oxygen high-energy density cutting torch. To avoid plasma contamination by metal vapors from the anode, a rotating steel disk (rotating frequency of the disk equal to 23 s^-1) was used as the anode. During the experiment the arc current and the anode ?nozzle exit gap were kept constant at 30 A and 8 mm; respectively.