Experimental demonstration of an emission-gated traveling-wave tube amplifier

This paper reports the results of the development of a traveling-wave tube (TWT) amplifier designed and operated using a high-frequency emission-gated field emitter array (FEA) cold cathode. The TWT was conservatively designed to operate with only 1% cathode current modulation but results show that 30% modulation of the current was achieved in the C-Band frequency range. The emission-gated TWT prototype was operated up to a current of 5 mA and RF output power of 280 mW using a 300-μm diameter FEA cathode having 10 000 emitter tips with testing performed in single-pulse mode using 100-μs pulses. Excellent beam control was demonstrated under all experimental conditions tested. Simulation shows that, with the same TWT circuit and demonstrated cathode modulation level, a 1-mm diameter cathode would generate ∼60 W of output power in the same frequency band and ∼80 W if the circuit were optimized for the measured level of modulation. Measurements also show that performance of the device does not degrade with frequency up to at least 7.0 GHz, which is the maximum operating frequency of the TWT. Cold measurements of the FEA electron gun alone indicate operation of the cathode up through 20 GHz might be possible. These results represent the first operation of an emission-gated cathode in a TWT and the highest power operation ever recorded in a microwave vacuum device using an emission-gated electron source.