Research on pulsed high power microwave generation in the 1980s

In the study of microwave generation using intense, short pulses of relativistic electrons, a measure of performance is peak power divided by the square of the wavelength (i.e. P/ lambda /sup 2/). This measure has exceeded 1 GW/cm/sup 2/ in several experiments, over a wavelength range from 2 mm to 3 cm. Moreover, these experiments have generally demonstrated high accompanying efficiency in the range 30 to 50%. For lambda >or approximately=1 cm, the highest power and efficiency have been achieved in multiwave Cerenkov generators with large diameter, i.e. D/ lambda >>1. A plasma-filled BWO (backward-wave oscillator) experiment which has shown high efficiency may also be explainable by multiwave effects. At millimeter wavelengths, the most impressive results have been obtained with free electron lasers, that use a tapered wiggler. Both the multiwave effect and the tapered wiggler ensure energy extraction from the electron beam over an extended range as electron energy decreases.<>