Abstract
A two-temperature model (2-T model) was used to predict fundamental properties of pure helium inductively coupled plasmas (He ICPs). Plasma characteristics with the use of the 2-T model were compared to those obtained by the local thermodynamic equilibrum (LTE) model for the He ICP, to those of an Ar ICP, and to the existing experimental data. The distributions of electron and heavy-particle temperatures, electron number density, and electric and magnetic fields were obtained as a function of the internal diameters of the torch, the gas flow rates, the gap between the plasma tube and the MACOR insert, the generator frequency, 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 (~2000 K) at the analytical zone were lower than those of the Ar ICP (4000-6000 K). The high-temperature region in the He ICP was constricted to a smaller region close to the wall of the plasma confinement tube as compared to that in the Ar ICP. Most of the input power in the He ICP was lost through the plasma quartz tube. The magnetic and electric fields inside the induction coil in the helium plasma were approximately one order of magnitude higher than those in the argon plasma.
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