Linear TWT development

Summary form only given, as follows. The digital communication industry requires RF amplifiers that provide constant gain at steadily increasing rated output power levels. One method to obtain linear operation in a traveling wave tube (TWT) is to operate the device well below its saturated power and to use a multi-stage depressed collector for energy recovery. This method, while effective, still has the disadvantage of operating at lower device efficiency than possible near saturation. One approach regularly used for extending the linear output power range of the device is to use an external linearizer circuit to condition the drive to the tube. While effective, the linearizer presents additional cost to the system while providing diminished effectiveness close to saturation. It is of continuing interest, therefore, to investigate and develop high power TWT designs with ultra-linear phase and amplitude transfer characteristics. The design of a linear TWT was approached on several fronts. First, simple Pierce theory was used to obtain a baseline design and to investigate many of the tradeoffs between design parameters and the device transfer characteristics. Next, Christine 1D, a 1-dimensional, large-signal, helix TWT code developed by the Naval Research Laboratory was used to optimize and verify the design. Finally, Christine 3D, a 2 1/2-dimensional, large-signal, TWT code will be used to model RF beam expansion and to calculate the spent beam distribution for collector optimization. The optimized design is scheduled to be built and tested in the Spring, 2002. Available test data will be presented, as will the design tradeoffs and analysis.