An Experimental High Power Pulsed Travelling Wave Tube†

Abstract

This paper describes an experimental travelling wave tube with a saturated efficiency of 34%, a power output of 3 megawatts and a gain of 35 dB. An essential feature of this tube was a high impedance slow wave structure, with good thermal dissipation and suitable for use with a high voltage (100 kv) electron beam. The high voltage, which was needed to draw high power from, a practical electron gun, made it necessary to use some other slow wave structure than the conventional wire helix. A stack of pill box cavities coupled together by apertures in their common walls was found to be eminently suitable if made to propagate a forward wave in its fundamental mode. The forward fundamental, winch was very desirable as it gave both high impedance and freedom from parasitic oscillations, was achieved by adopting Chodorow's ‘ clover leaf ’ method of coupling the cavities. Another important feature of the tube was a short attenuator capable of absorbing fair amounts of power without damage. It was found that an attenuator occupying any appreciable length along the beam had an adverse effect on the efficiency of the tube.