A broadband megawatt traveling wave tube utilizing a ring-loaded Meander line interaction circuit

An experimental traveling-wave tube utilizing a broad-band open interaction structure called the ring-loaded Meander Line is described. The interaction structure consisting of a series of rings supported on two ziz-zag wires has high interaction impedance combined with capability of 40% bandwidth and is free from interfering backward wave modes. Attenuation and mechanical support is obtained with the use of carbon impregnated ceramic rods. rigid coax input and output lines are well matched to the circuit over an octave. Feedback due to fast waveguide modes is prevented by special attenuators. Cold test data is presented on the circuit and the matches. Experimental small signal gain and power data are presented. The first tube achieved 250 Kw peak at 15% efficiency, db variation over 20% bandwidth. Power output was limited by arcing in output region rather than by saturation. A second tube is being built which should yield 1 megawatt over 30% bandwidth at 30% efficiency. Methods of making the circuit out of tubing through which coolant can be pumped have been developed. Liquid cooling will provide average power capability comparable to klystrons and loaded waveguide tubes.