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In this work, different plasma parameters, such as electron density, temperature, and negative ion density are measured in both the source and expansion chamber of the Helicon Plasma Source (HeliPS) in a radio frequency (RF) oxygen discharge of 13.56 MHz and are compared with the values obtained numerically using the volume-averaged global model. For this purpose, the global model of RF oxygen discharge suitable for the HeliPS having two chambers (source and expansion) together with the electromagnet in the source chamber and the magnetic cage in the expansion chamber to reduce the radial loss of plasma is developed using the particle and power balance equations. In this model, the radial confinement by the axial field of the electromagnet in the source chamber and the confinement in the expansion chamber by the cusped field of the magnetic cage is incorporated. Studies on the charged particle dynamics by both the model and the experiment show comparable values of the variation of species density and electron temperature with RF power and working pressure as well as with the applied magnetic field of the electromagnet in the source chamber.

An analytical study of the small amplitude electron acoustic double layers in a magnetized plasma consisting of superthermal electrons and ions along with cold fluid electrons is discussed. The dispersion relation allows electron acoustic waves with the frequency within electron and ion gyro-frequency in the modelled plasma. In the process of study of the nonlinear structures, the Sagdeev pseudo-potential method for small amplitude regions is employed. The existence domains for the double layers are investigated in terms of the Mach numbers of the structures and the temperature ratios of the species for different ratios of their concentration. The effects of the compositional parameters on the nature and size of the double layers are also explored and it is observed that the plasma can support both compressive and rarefactive double layers depending on the values of those parameters and the Mach numbers.

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