Power dissipation in the column of a TIG welding arc

The characteristics and structure of power dissipation in Tungsten Inert Gas (TIG) welding arcs is investigated for argon atmospheres at pressures of up to 135 bar. Electrical characteristics are reported and probe measurements of local electric field strength and total radiated power have been made. These have been combined to obtain the radially averaged axial dependence of arc properties (e.g. temperature, mass flow rate, plasma velocity and arc radius). It is found that both anode and cathode fall voltages are substantially independent of pressure P while the column electric field strength increases in accordance with P^0.5. This is associated with an increase in convective and radiative dissipation from the column such that temperature is little affected by pressure and plasma flow velocity falls. The total energy balance of a 100 A, 10 mm argon arc indicates that convective dissipation accounts for about 70% of column power at all pressures investigated. Radiation consists of 18% at 1 bar increasing to 26% at 20 bar with conduction decreasing in significance with pressure.