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Influence of magnetic filter position on negative ion density in oxygen RF discharge

In this study, the influence of the position of a magnetic filter on electron temperature and hence on the negative ion density in helicon oxygen discharge is investigated. This study is performed with the view to improve negative ion density in radio frequency (RF) plasma. RF plasma is produced in the source region of Helicon Plasma Source (HeliPS) and the variation of electron temperature, density, and negative ion density in case of oxygen discharge is studied to determine the optimum position of the magnetic filter relative to the position of the antenna where RF power is applied. It is observed that the RF field can penetrate beyond the magnetic filter and cause additional ionization in the expansion chamber and thereby produce high energy electrons and decrease the negative ion density. Therefore, the position of the magnetic filter should be sufficiently away from the location of the antenna as it influences the formation of negative ions.