High-gain high-efficiency TWT (traveling wave tube) amplifiers

John A. Nation; J. D. Ivers; G. Kerslick; Donald A. Shiffler; Levi Schaechter

doi:10.1117/12.43478

1 April 1991 High-gain high-efficiency TWT (traveling wave tube) amplifiers

John A. Nation, J. D. Ivers, G. Kerslick, Donald A. Shiffler, Levi Schaechter

Proceedings Volume 1407, Intense Microwave and Particle Beams II; (1991) https://doi.org/10.1117/12.43478
Event: Optics, Electro-Optics, and Laser Applications in Science and Engineering, 1991, Los Angeles, CA, United States

Abstract

Results are presented from recent research carried out on the development of high efficiency, high power traveling wave tube amplifiers. A rippled wall traveling wave tube is used as a slow wave structure for wave interactions with an 850 kV, 1 kA electron beam. A 100 kW signal from a magnetron is injected at the front end of the device and amplified by 15-30 dB giving an output power of 100 MW from a single stage amplifier. At higher gains the system tends to oscillate due to feedback from impedance mismatches at the structure ends. To overcome this we have used a severed amplifier consisting of two identical amplifiers in series and separated by an absorbing graphite section between the two amplifiers. With this device we have obtained 400 MW output power with an energy conversion efficiency of 48%. We shall present a comparison between the amplifier characteristics for the single and two stage amplifiers. Peak output powers are obtained in the severed amplifier at a beam current of 900 A; however, sidebands have developed and the output is no longer single frequency. It should be noted that the relative distribution of power in the sidebands compared to the center frequency varies with the beam current and that the sideband power can approach 50% of the total radiated intensity at high beam currents. The sidebands are asymmetrically located on either side of the carrier frequency with the upper sideband displaced from the carrier by about three times the frequency shift for the lower sideband. The authors discuss mechanisms leading to the sideband behavior described. It seems likely that most of the phenomena observed can be accounted for by finite structure length effects, which lead to resonances in the transmission coefficient for the structure. Other effects of importance include a substantial spread in the electron energy spectrum as the wave develops.

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John A. Nation, J. D. Ivers, G. Kerslick, Donald A. Shiffler, and Levi Schaechter "High-gain high-efficiency TWT (traveling wave tube) amplifiers", Proc. SPIE 1407, Intense Microwave and Particle Beams II, (1 April 1991); https://doi.org/10.1117/12.43478

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KEYWORDS

Amplifiers

Microwave radiation

Medium wave

Electron beams

Particle beams

Particles

Oscillators

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