The conventional method for converting incineration ash to slag employs a plasma type furnace. An analysis of ash melting characteristics was undertaken by changing the inner shield N(2) gas flow rate, assuming a hollow cathode and the ash anode. Results show that heat input intensity characteristics on the ash depend strongly on the gas flow rate through the central hall of the tube cathode arc (TCA). The maximum temperature of the ash surface becomes about 3000-4000 K in a melting state. For a gas flow rate greater than 2 L/min, the shape of the heat input intensity on the ash is annular because of the gas flow. By adjustment of the inner shield gas flow rate, more practical melting of a wider area of the ash can be achieved with the intense annular heat input on the ash. (C) 2009 Elsevier B.V. All rights reserved.