Non-axisymmetric radiation from surface-wave oscillator driven by weakly relativistic electron beam

In this paper, non-axisymmetric radiation from a W-band surface wave oscillator (SWO) is observed. The SWO is based on a cylindrical corrugated waveguide with a periodic structure on its inner wall. This SWO is driven by electron beams with energy of less than 100 keV and a current on the order of 100 A. The waveguide has transverse magnetic (TM) and transverse electric (TE) modes as its axisymmetric normal modes. Non-axisymmetric modes also appear as a hybrid of TM and TE modes and form surface waves near the periodic structure. The frequencies of the non-axisymmetric modes increase as the azimuthal mode number m increases. By injecting an annular electron beam into the SWO, many non-axisymmetric modes with m up to 30 are excited and intense radiation is generated at frequencies up to 140 GHz. (author)