2-TEMPERATURE MODEL FOR THE SIMULATION OF ATMOSPHERIC-PRESSURE HELIUMICPS

A two-temperature model (2-T model) was used to predict fundamental pr operties of pure helium inductively coupled plasmas (He ICPs). Plasma characteristics with the use of the 2-T model were compared to those o btained by the local thermodynamic equilibrum (LTE) model for the He I CP, to those of an Ar ICP, and to the existing experimental data, The distributions of electron and heavy-particle temperatures, electron nu mber density, and electric and magnetic fields were obtained as a func tion of the internal diameters of the torch, the gas flow rates, the g ap between the plasma tube and the MACOR insert, the generator frequen cy, and the active power. Overall, the He ICP was predicted to have a much higher electron temperature (>12,000 K) in the load coil region, but its axial heavy-particle and electron temperatures (similar to 200 0 K) at the analytical zone were lower than those of the Ar ICP (4000- 6000 K). The high-temperature region in the Re ICP was constricted to a smaller region close to the wall of the plasma confinement tube as c ompared to that in the Ar ICP. Most of the input power in the He ICP w as lost through the plasma quartz tube. The magnetic and electric fiel ds inside the induction coil in the helium plasma were approximately o ne order of magnitude higher than those in the argon plasma.