Nonequilibrated situations of pulse modulated Ar–H₂ and Ar–N₂ thermal plasmas at atmospheric pressure

Atmospheric pressure inductively coupled thermal plasmas with pulsing mode are generated for 104 slpm standard liters per minute total flow rate of Ar-H₂ and Ar-N₂ mixtures (Ar 94% molar concentration) inside a torch of 55 mm inner diameter. The inverter-type power source of 22 kW maximum output supplied coil current of 1 MHz fundamental frequency at 17.3 kW level, and the coil current is modulated by an external pulsed signal to produce the desired pulse modulated plasmas. Spectroscopic measurements are carried out for the temporal radiation intensity and coil current intensity. In addition, a time-dependent, two-dimensional model, which works with coil current input, is solved by using the same coil current profile measured in the experiment. Experimental and theoretical results for 67% duty factor with 10 ms on-time are compared. The theoretical predictions are found comparable with the experimental findings although the theoretical time-dependent response is seen slower, especially over the time just after on-pulsation. An estimation of electron temperature helps to describe this discrepancy fairly adequately. Experimentally the shimmer current level is found to vary with gas composition as well as with on- and off-time of pulsing signal. Both the experimental and theoretical findings suggest that plasma responds slowly at any axial positions below midcoil compared to that at midcoil level. © 2003 American Institute of Physics.