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Parameters of accelerated plume of electric thrusters are of great importance for proper consideration of it's interaction with a spacecraft. Most of analytical models and computer codes describing this interaction are based on experimental data in regard to initial distribution of the plasma plume parameters. So that accuracy of this data determines accuracy of further computation and analysis. But available plume data measured in different facilities and by different measurement equipment differ significantly, and there is no clear criteria for applicability of the equipment and test conditions for proper measurements. In the presented paper requirements for Hall thruster plasma plume diagnostic and possible diagnostic set are analyzed. The measurement of ion current density, plasma potential and electron temperature by means of different types of electric probes are considered. The results of verification of different probes and comparison of experimental data obtained at the distance of 300, 500 and 1000mm from thruster exit plane are represented. Significant influence of the probe design and size on measured value of ion flow density has been identified. Applicability of O2mm small flat probes for electron temperature and plasma potential measurements is experimentally demonstrated and proven. The results of plasma plume parameters mapping using flat oriented probes are presented. Electron temperature, plasma potential, ion energy and flow density values data base for D-55 thruster plume has been collected for number of regimes with different discharge voltage (200-400 V) and variable test conditions. The influence of test condition and operation mode of thruster on plasma plume parameters is studied and significant influence of the test conditions on measured plasma parameters identified. Experimental data showing dramatic influence of residual pressure in the vacuum chamber on measured electron temperatures and plasma potential are presented.