  Within the framework of quasilinear theory it has been found that when radio
bursts of III type are generated by the inhomogeneous system of electron beam -
solar wind plasma, only time of development of the primary stage of
instability, i.e., agnetohydrodynamic, is more than the total time of
relaxation of an electron beam derived within the homogeneous model. During the
development of hydrodynamic instability the electron beam is spread from the
Sun to the distance of 4 astonomical unities. The hydrodynamic stage is
followed by the development of kinetic instability leading, ultimately, to the
formation of horizontal plateau in the beam region at the tail of Maxwell
distribution. Parameters of the plateau, such as its length and height, have
been calculated as characteristic parameters of an electron beam generated by
the active solar bursts. In the development of kinetic beam instability more
than a half of kinetic energy of the beam is transmitted to plasma
oscillations.
