anode 6 a small flow of inert gas 56 such as argon nitrogen or helium may be introduced into a manifold 3 to protect the cathode 1 from chemical erosion of reactive plasma gases the gas 56 is distributed tangentially into the cathode area 21 through holes 22 formed in a ceramic ring 23 of material working gas 54 may be introduced through a manifold 4 and distributed tangentially into the cathode area 21 through holes 24 formed in a ceramic ring 25 such working gases may include inert gases such as nitrogen argon helium or reactive gases such as hydrogen air oxygen carbon monoxide or hydrocarbons the arrangement of such gases and the means for their introduction is well known to the art gases 56 and 54 introduced through manifolds 3 and 4 respectively enter the constricting portion 5 in a spiralling gas flow in a plane which is normal to the axis of the vortex generating ceramic rings 23 25 as shown in the drawing as a swirl the gas flow spirals through the constricting portion 5 and moves toward the exit portion 6 additional working gases 52 are introduced through the manifold 7 the gas 52 is distributed tangentially into the space 13 through holes 26 formed in a ceramic ring 20 the gas introduced through manifold 7 may be identical to the gas introduced through manifold 4 and it too spirals inwardly as it enters the space 13 between the flanges 14 and 15 the spiralling flow has a linear component of motion perpendicular to the axis of the vortex generating ceramic.