Plasma Spraying—From Single to Multiple Electrodes

It is well known that legacy one-cathode/anode thermal spray guns are sensitive to aging. One reason is the large power density in particular at the arc roots on the cathode tip and the anode wall. Anode wear was studied in showing that it leads to a thinner boundary layer and a reduced motion of the arc root, which increases the local thermal load. This also results in a voltage drop, and thus in power level reduction if the power source is operated in a constant current mode. In this case, it is widely practiced to increase the secondary plasma gas flow, which, however, can only be of some help.