During the injection of a high-current relativistic electron beam into
a plasma waveguide, the regime of amplification of a slow plasma wave
in a waveguide is realized. For a 30 kW input power at a frequency of
12.7 GHz, a maximum output power of 10 MW is obtained. The effect of
the plasma density on the amplification parameters is studied. The val
ue of the gain factor and the operating range of plasma densities agre
e with the results of calculations based on the linear theory.