A two-region model for azimuthal striations in an inductively coupled plasma

A two-region discharge model with a perturbation analysis was developed for the azimuthal striations observed in an inductively coupled plasma with an immersed cylindrical coil at pressures of 75-1500 mTorr. This model partitions the discharge area into two distinct regions: a bright region near the coil with intense excitation and ionization processes, and a darker region extending from the boundary of the bright core to the chamber wall. This partition reflects the experimental observation that striations are restricted to the vicinity of the coil and this phenomenon becomes more pronounced with increasing pressure. Through a perturbation analysis, the model indicates that the azimuthal striations manifest only below a critical power threshold, and this threshold decreases with pressure, which aligns with the experimental observations. Additionally, the model-predicted number of striations is in good agreement with the experiment over a wide pressure range.