Experimental study of the high power broadband microwave emission from beam-plasma interaction

We have carried out experiments on interaction of an intense relativistic electron beam (IREB) with a plasma which is an interesting subject from a point of view of nonlinear phenomena. From the interaction broadband microwaves radiated and its power reached about 2 MW. For the radiation, the ratio of the beam and the plasma densities (nb/np) is an important parameter. We found that there was an optimum on nb/np at which the power density in the observing window (18 – 40 GHz) was maximum. When the value of nb/np was among 0.001∼0.01, the radiated microwave was intensified. An existence of the optimum condition can be explained by an energy input from beam to plasma by two stream instability.