A UHF traveling-wave amplifier tube employing an electrostatically focused hollow beam

The increasing importance of beam-type microwave devices has stimulated interest in focusing methods other than the usual uniform magnetic field. One such method applicable to hollow cylindrical beams, proposed by L. A. Harris, utilizes a radial electric field acting on a spinning beam to counterbalance the space-charge divergence forces. A traveling-wave amplifier operating in the 300 to 600 mc region, employing this focusing method, was designed and constructed. Experimental results obtained with this tube are presented. Beam transmissions as high as 90 per cent and net gain over 15 db were obtained. Practical considerations and tube design factors are discussed. The primary advantage of this kind of focusing is in the elimination of the solenoid, and consequent reduction in power supply requirements and weight, accessibility of rf connections to the tube, and elimination of capsule and aligning adjustments. This focusing method appears to have great potential usefulness in hollow-beam applications, and particularly in devices where the spiral motion of the beam can be made to interact with a spirally traveling wave.