An Exact Backward Wave Theory for a Thin Tape Helix Traveling-Wave Tube*

The exact small-signal hot-tube dispersion relation for a thin tape helix traveling-wave tube (TWT) was recently derived [1]. When applied to the forward wave, it gives an exact determination of Pierce’s  “AC space charge” parameter Q. In addition, it predicts a significant detune, by as much as 2%, of the cold tube circuit.  Here we extend the work to the backward wave mode so as to reexamine Johnson’s classical theory for the threshold of backward wave oscillation in a TWT. [2]

[1] P. Wong, D. Chernin, and Y. Y. Lau, “Modification of Pierce’s Classical Theory of Traveling-Wave Tubes,” IEEE Electron Device Lett. (in press, 2018)

[2] H. R. Johnson, Proc. IRE. 43, 684 (1955)