A plasma diagnosis has been carried out by spectroscopic methods. The behavior of temperature and concentration of charged particles was measured along the stream as a function of polarity for a stream with a shock wave and a stream with periodic structure. An explanation of the observed phenomena is given. The physical processes occuring in a supersonic plasma stream are quite distinctive , Spectroscopic investigations are necessary since they provide more detailed information on the physical state of the plasma. It is also of interest to study wave processes taking place in the stream from the point of view of the additional plasma heating thus obtained.