Measuring of Mean Plasma Electrical Conductivity in Anode Area of Plasma Torches with an External Anode
Abstract
Direct current (DC) arc plasma torches with external anode are used in many industrial applications. The plasma electrical conductivity in hot anode areas of those plasma torches can be computed indirectly from plasma temperatures measured spectroscopically.
However, it cannot be measured directly by any probes because of high plasma temperature (above 10,000 K) and high mass plasma density (up to 6 g/m3). We developed a non-intrusive direct procedure of measuring an average electrical conductivity of a plasma volume in hot anode areas of those plasma torches.
For our measurements, we used a high-speed camera (frame rate 300,000 fps), a highvoltage probe (sample rate 80 MS/s, bandwidth 50 or 75 MHz), and a hybrid water-argon plasma torch. The measurements were made for various values of ambient pressure, arc electric current, and argon flow rate.
The measured plasma conductivity is in agreement with a model, camera observations and indirectly also with spectroscopy measurements. The procedure provides missing experimental data on the average plasma electrical conductivity and estimates average plasma temperature in the anode areas.
The procedure can be theoretically used in every plasma torch where the anode arc attachment movement can be observed during a restrike process.