Ion energy distribution function (IEDF), current voltage characteristics are investigated in Xe-Ar and Ar plasmas discharges in a hall effect ion source. The investigations were carried out on a constant Xe flow rate and for different Ar flow rates. The comparison between Xe and Xe- Ar discharges were done for evaluation of Ar ionisation probabilities in plasma discharge governed by Xe ions. Two different behaviors were underscored depending on the filling fraction of Ar. Firstly we have studied a plasma dominated by Xe ion population and it was found that the electron temperature (Te) increases when a small part of argon was injected. Secondly the Xe-Ar plasma dominated by Ar plasma discharges parameters have been also investigated. These measurements coupled to Optical Emission Spectroscopy (OES) and to the ion characterisation by Retarded Field Analyser give a new insight of the discharge properties such as ionization processes, efficiency, and ion current density variation.