A 20 kW pulsed travelling-wave tube

A sealed-off S-band travelling-wave tube has been made with an efficiency greater than 20% and a saturation output power of 40 kW. The interaction circuit was a ring-and-bar structure operating with a 25kV beam. The tube was required to be stable under short-circuit operation and to have a high mean power-handling capacity. The attenuator problem was tackled by splitting the structure into two parts, with external loads on each side of the split. Experimental work has been carried out on the maximum efficiency of this type of tube by using a single section only, thus eliminating the adverse effects of the attenuator. A conversion efficiency of 33% was obtained by this means.