Morphology and Radiation Characteristics of Blue Core in Argon Helicon Plasma Discharge

Argon helicon plasma is typically associated with a blue core, namely a radially localized central area of strong ion light emission. An experimental study was carried out to study the morphology and radiation characteristics of blue core in argon helicon plasma discharge. Experiments were carried out with two technics including Local Optical Emission Spectroscopy (LOES) and time-integrated images with digital camera. In particular, the helicon mode, characterized by the intense blue core plasma, can be achieved by adjusting the input parameters such as RF power, magnetic field, and operating pressure. Analysis of a prominent characteristic line (ArII 481.0 nm) of blue core indicates that the intensity of ion line increases linearly with the RF power, magnetic field, or operating pressure in certain intervals (when 1000 W< P< 2000 W or 250 Gauss < B0 < 500 Gauss or 0.1 Pa< p< 1.0 Pa). Apart from this, blue core width increases with the power while decreases with an increase in magnetic field or operating pressure. In order to further understand the formation of the blue core, parameter regarding electron temperature is adopted to reveal that the increase of the intensity of ion line depends strongly on the increase of electron temperature.