Experimentally diagnosed transient behavior of pulse modulated inductively coupled thermal plasma

An argon: hydrogen (argon: 89% molar) pulse-modulated radio-frequency inductively coupled thermal plasma was generated at adequate power level (active plasma power up to about 15 kW) and has features such as control of thermal flux in time domain and introduction of nonequilibrium phenomenon. These characteristic features have ample attraction for thermal plasma materials processing. A solid state power source, which supplies the electric power at a nominal frequency of 1 MHz with high matching efficiency of 90%, was used as the pulsing generator to generate the induction plasma. Experimental measurements were carried out to analyze the transient responses of ArI (at 751 nm wavelength) line and current intensities for the imposed pulsing signal. Results were obtained for pressure range from 200 to 760 Torr, with a power on time in the range from 2 to 20 ms while the power off time ranged from 5 to 12 ms. The plate power level was varied from 11 to 17 kW though the results presented in the present article are mainly for the 11 kW(and 200 Torr) case. During the pulse modulated operation where the nonequilibrium exists more or less, the average exciting temperature of Ar atom was estimated to be varied between 5000 and 14 000 K, for pulsation of 5 ms on time with 50% duty factor, corresponding to the on and off of the pulsing signal. At different on times, ArI line intensity changed considerably; with 2 ms on time, steady-state of ICP was not achieved. For higher pressure, the intensities increased obviously and response or relaxation time was longer. (C) 1999 American Institute of Physics. [S0021-8979(99)05603-0].