Experimental investigations of Cherenkov plasma amplifier

Experimental investigations of Cherenkov plasma amplifier have been carried out. The dependencies of output microwave power on plasma density, interaction length, input microwave power, relativistic electron beam current, and input signal frequency were measured. A pure amplification regime (without accompanying generation) at two frequencies of 9.1 and 13 GHz is achieved. It is shown experimentally that there is a range of plasma densities where the only azimuthally-symmetric plasma waveguide mode with the lowest radial index is excited. The relative bandwidth of the amplifier, according to the experiment, is no less than 40 %. It is experimentally shown that, by changing only one parameter, namely, the plasma density, is possible to achieve maximum output microwave power at any of two frequencies - 9.1 and 13 GHz. At a frequency of 9.1 GHz, the maximum output power amounts to P=40 MW, the efficiency is η=4 %, and the power gain is K_p=800 (29 dB). At a frequency of 13 GHz, these parameters are P=60 MW, η=6 %, and K_p=1000 (30 dB).