Electronically and Calorimetrically Measured Energy Balances of a Thermal Induction Plasma

The plasma efficiency is one of the most important factors for industrial applications of thermal induction plasmas. An analysis of all the terms contributing to the energy balance of the rf-generator and the induction plasma is presented. In order to measure the plasma power faster than with usual calorimetric methods, a new approach to the instantaneous measurement of electric power was developed, which allowed power measurements at several Megahertz in the oscillator circuit of a self-excited induction generator. Systematic measurements under 26 different operating conditions were carried out on a 12 kW, 5 MHz argon induction plasma and were checked by parallel calorimetric energy balances. The agreement of both methods is within an accuracy of 5%. The total plasma efficiency is over 50% of the plate power. It varies only slightly with the operating parameters (plate voltage and gas flow rates). The measurements indicate clearly where modifications of the system would improve the overall efficiency.