An electrostatically focused high power traveling-wave tube

Previous work on periodic electrostatic focusing of the electron beam in traveling-wave tubes was confined primarily to bifilar helices. Most structures of the helical type, however, are severely limited in their power-handling capabilities. This paper discusses the application of periodic electrostatic focusing to high-power slow-wave structures to allow the development of extremely light-weight, high power amplifiers. It has been shown recently that a solid beam of high perveance can be focused by the use of a prescribed potential distribution between alternating focusing electrodes. Two slow-wave structures, a crossed-bar type and a folded-line type, were developed which incorporate the required focusing-electrode arrangement without impairing the rf properties of the basic slow-wave circuit. "Hot-test" results are presented for a crossed-bar structure designed for operation at X-band with a peak power output of five kilowatts. To date, a relatively short structure without attenuator, tested in a continuously pumped bell jar system, has given a peak power of six kilowatts with an efficiency of 17 percent. The tests proved the feasibility of incorporating electrostatic focusing into high power, periodic, slow-wave structures.