Analysis of pi-point instability in an asymmetric helical slow-wave structure in helix traveling wave tubes

The energy exchange takes place between the linear electron beam and the electromagnetic wave propagating in the helix (E.I. Lien, IEDM Tech. Digest, pp. 412-415, 1979; T. Onodera, IEEE Trans. ED, vol. 35, no 10, 1988; B. Levush, Int. Vacuum Electron. Conf., pp. 71-72, 2002; B. N. Basu, Electromagnetic Theory and Applications in Beam-Wave Electronics, World Publ. Co. Inc. 1996; J. R. Pierce, Traveling Wave Tubes, D Van Nostrand, New York, 1950; L. N. Loshakov et al., Radio Eng. Electron Phys., vol. 13, 1968). For the efficient operation of the device, the beam velocity should be nearly synchronous with the axial phase velocity of the wave over the frequency range. Thus, the dispersion characteristics of helix SWS become of great importance. In this study, rigorous field analysis (B.N. Basu, et al., J. Appl. Phys., vol. 58, no. 9, 1985) of a general asymmetric helical SWS was done.