The multiple-beam design philosophy and its application to the traveling-wave klystron (TWK) are described. The TWK was conceived as a superpower device capable of producing broadband power levels many times greater than can be achieved with a single-beam tube. The principles of operation of the device are outlined, as well as the manner in which these have been incorporated in a practical demonstration at

band, in which power levels in excess of 5.0 MW with 16 per cent bandwidth and 23 dB high-level gain were obtained.