Generation of powerful subnanosecond microwave pulses by intense electron bunches moving in a periodic backward wave structure in the superradiative regime

Experimental results of the observation of coherent stimulated radiation fr om subnanosecond electron bunches moving through a periodic waveguide and i nteracting with a backward propagating wave are presented. The subnanosecon d microwave pulses in Ka and W bands were generated with repetition frequen cies of up to 25 Hz. The mechanism of microwave pulse generation was associ ated with self-bunching, and the mutual influence of different parts of the electron pulse due to slippage of the wave with respect to the electrons; this can be interpreted as superradiance. The illumination of a panel of ne on bulbs resulted in a finely structured pattern corresponding to the excit ation of the TM01 mode. Observation of rf breakdown of ambient air, as well as direct measurements by hot-carrier germanium detectors, leads to an est imate of the absolute peak power as high as 60 MW for the 390-ps pulses at 38 GHz. These results are compared with numerical simulations. The initial observation of 75-GHz, 10-15-MW radiation pulses with a duration of less th an 150 ps is also reported. [S1063-651X(99)00709-6].