Another anode holder used in the experiments is shown in figure 3. In this design the anode holder is water cooled and the heat losses by conduction from the anode were determined by measuring the temperature rise of the coolant. To reduce heat transfer from the hot gas to this anode holder outside the region of the arc, a carbon shield was attached to the surface providing an air gap of 1/16 inch between the plate and the surface of the anode holder. In addition, the inner surface of the carbon shield was covered with aluminum foil to reduce radiation. Temperatures of the shield and of the surface of the water cooled anode holder were measured by thermocouples to account for heat received by the coolant but not originating from the anode plug.

The argon flow from commercial bottles was regulated by a pressure regulator and measured with a gas flow rator. The power source was a commercial D.C. rectifier. At 100 Amp the 360 cycle ripple was less than 0.5 V (peak to peak) with a resistive load. The current was regulated by means of a variable resistor and measured with a 50 mV shunt and millivoltmeter. The arc voltage was measured with a voltmeter whose terminals were connected to the anode and cathode holders. Because of the falling characteristic of the rectifier, no ballast resistor was required for stability of operation. A high frequency starter was used to start the arc.