A Re-Examination of Johnson's Theory of Backward Wave Oscillation in a Traveling Wave Tube

Most recently, Wong et al. derived an exact hot tube dispersion relation for a tape helix TWT l, based on the exact cold tube dispersion relation obtained by Chernin et al. 2 for the same tape helix model. It was found that Pierce's classical 3-wave TWT dispersion relation needs to be modified,...

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Bibliographic Details
Main Authors: Jassem, A., Wong, P., Lau, Y.Y.
Format: Conference Proceeding
Language:English
Subjects:
Conferences
Contracts
Dispersion
Oscillators
Plasmas
Space charge
Traveling wave tubes
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Summary:Most recently, Wong et al. derived an exact hot tube dispersion relation for a tape helix TWT l, based on the exact cold tube dispersion relation obtained by Chernin et al. 2 for the same tape helix model. It was found that Pierce's classical 3-wave TWT dispersion relation needs to be modified, in particular the circuit mode is modified by a new term, which they call q. This q for the modification of circuit mode at high beam currents is entirely analogous to Pierce's space charge parameter, Q, for the modification of the beam mode. For forward wave amplification, q may lead to a detune in the circuit mode phase velocity by as much as two percent in a realistic example 1 . Since Johnson's theory of backward wave oscillation (BWO) in a TWT 3 was based solely on Pierce's 3-wave dispersion relation, we analyze the effect of q on Johnson's threshold condition for BWO. The value of q, together with of the values of the Pierce parameters C and Q, will be determined for the backward wave mode using the exact hot-tube dispersion relation 1 .
ISSN:2576-7208
DOI:10.1109/ICOPS35962.2018.9575831