Broadband microwave generation by beam-plasma turbulence

A potentially powerful new mechanism for microwave radiation appears in relativistic beam-plasma experiments when beam density approaches plasma density, n_b/n_p >0.1. Recent theory and experiment are reviewed. Emission was observed up to seven times the background plasma frequency, at power levels 100 times the radiation seen in the plasma line alone. Some controversy surrounds both theory and experiment, which may reflect differing responses of the beam to the plasma turbulence which it has itself produced. The effect may be important in astrophysics as well