Effects of plasma diameter and operating frequency on dynamic behaviour of induction thermal plasma

A numerical approach is presented for the analysis of the dynamic behaviour of the induction thermal plasma under step-like change of the sustaining magnetic field. The time-dependent energy conservation equation which includes thermal conduction, radiation and convection loss terms was solved numerically in conjunction with the continuity equation and Maxwell's electromagnetic field equations. A one-dimensional model with radial direction is adopted here for the first approximation to analyse the transient aspects of the radial distributions of the temperature, the penetrating electromagnetic fields and the input and losses. Calculations were carried out for an Ar-induction thermal plasma with a diameter from 2 to 7 cm. operated at a frequency of 3 MHz and a pressure of 760 Torr. Special attention was given to the time constant which is a measure of the time necessary for the plasma to converge to a new steady state. The response time of the induction thermal plasma was found to be a few milliseconds and had a strong dependence upon the diameter of the plasma across which the mass and energy diffusions take place under the off-balancing condition between the input and the loss. The transient aspect of a high-power induction plasma operated with a low frequency of 300 kHz is also discussed.