COMPUTER-SIMULATION OF ATMOSPHERIC-PRESSURE HELIUM INDUCTIVELY-COUPLED PLASMA DISCHARGES

Computer simulation was used to predict fundamental properties of pure helium inductively coupled plasmas (He ICPs) in a torch most often used in experimental studies of He ICPs. Plasma characteristics for the He ICP were compared to those of an Ar ICP formed in the same torch and to the existing experimental data. The distributions of temperature, gas velocity, power dissipation, and electric and magnetic fields were obtained as a function of active power, the number of turns (length) for the induction coil, the gap between the plasma tube and the MACOR insert, injector gas flow rate, injector tube orifice, and plasma gas flow rate. Overall, the He ICP was predicted to have a higher plasma temperature, but its axial temperature at 10-30 mm above the induction coil was lower than that of the Ar ICP. Heat dissipation was concentrated in a smaller area in the He ICP as compared to the Ar ICP. The magnetic and electric fields inside the induction coil in He plasma were approximately one order of magnitude higher than those in Ar plasma, These theoretical predictions, based on an LTE model of the plasma, also were used to interpret existing analytical results, and to devise new directions for research in He ICP spectrometry.