Cherenkov Instability due to Unmagnetized Electron Beam in Periodically Corrugated Waveguide

Abstract

Cherenkov instability driven by an unmagnetized electron beam in a periodically corrugated waveguide is studied by developing a new version of self-consistent linear theory. The conventional space charge and cyclotron modes of magnetized beam degenerate in this case. The normal electromagnetic modes are pure transverse magnetic (TM) and transverse electric (TE) modes in axisymmetric cases and are hybrid modes having both TM and TE components in nonaxisymmetric cases. Using the developed linear theory, the axisymmetric and nonaxisymmetric Cherenkov instabilities due to the unmagnetized beam in the periodic system are examined numerically. The unmagnetized beam can excite the axisymmetric TM and nonaxisymmetric hybrid modes. A comparison of the numerically obtained results is made with those of the recent C-band Pasotron experiment.