Mode transitions in low pressure rare gas cylindrical ICP discharge studied by optical emission spectroscopy

We report optical emission spectroscopy (OES) measurements in cylindrical inductively coupled plasma (ICP) discharges, focusing on E-to-H mode transition in rare gases (Ar, Kr, Xe). The discharge configuration is designed primarily as a radical source for treatment in a high vacuum system, but little is known about its characteristics. Two discharge modes are observed in Ar and Kr on increasing the power injected into the discharge (E-mode at low injected power and H-mode at high injected power). In this paper, we use OES measurements and calculations to infer rare gas discharge characteristics and mode transitions for this geometry in rare gases. It is shown that emission line intensity ratios from the OES signal of a level that is strongly coupled to a metastable state with one whose principal production mechanism is by direct excitation can be used to infer information about the electronic parameters of the discharge.