A collisional-radiative model including radiation trapping and transport phenomena for diagnostics of an inductively coupled argon plasma

Abstract

The collisional-radiative model including radiation trapping and transport phenomena along with electron impact and radiative processes has been extended to the actual argon ICP, i.e. structural and inhomogeneous. The electron temperature ( T e), which is an essential plasma parameter for the collisional-radiative model, was measured from the background continuum without assuming the thermal equilibrium between the higher excited atomic levels and the ionic ground state. Observed T e at the height of 15 mm above the load coil was 8400 K, which was rather lower compared with the literature values determined from the ratio of Ar emission line and continuum in a 40-MHz ICP, while the electron number density was approx. twice larger. The calculated population number densities showed close values to LTE, because the radiation trapping, not only for the resonance lines but also for non-resonance lines, compensated for the overpopulation of low lying levels which might be caused by spontaneous emission. The transport effect of species was negligible in the normal analytical region. In the coaxial zone around 5 mm above the load coil and in the tail flame of the plasma, however, the large inflow of electrons and ions by ambipolar diffusion or convection reduced the number density of argon neutral atoms, where the argon ICP can be denned as a recombining plasma.