Two-temperature modeling of a magnetically rotating arc

A three-dimensional, two-temperature MHD model of a DC plasma torch has been developed to study the behavior of a magnetically rotating arc in argon at atmospheric pressure. The torch consists of a 10~mm long rod-type cathode with a diameter of 3~mm surrounded by a 25~mm long hollow anode with a diameter of 10~mm. The arc is supplied by a current of 200~A. Without external axial magnetic field a heavy particle temperature $T_{h}$ of about 14000~K and 8000~K is obtained near the cathode tip and downstream in the plume, respectively. Significant temperature differences between the electron temperature $T_{e}$ and $T_{h}$ up to a factor of 1.4 are found in the arc fringes. When applying an external axial magnetic field of 0.04~T, the high temperature plasma inside the torch is retracted axially and expanded radially. It is involved in rotation due to the Lorentz force and a backflow appears in front of the cathode close to the axis. The inflow and backflow gases impinge onto the anode. $T_{e}$ and $T_{h}$ are about 18000 and 13500~K, respectively, at maximum. The $T_{e}$ profile gets broader than that of $T_{h}$. Both profiles are prolonged towards the anode. A similar behavior is observed for the arc power density and the electron density distribution.