摘要
This study examines the transverse magnetic (TM) waveguide modes, which have long been considered as the unsuitable ones for the operation of the electron cyclotron maser. The beam-wave coupling strength of the TM modes, as expected, is found to be relatively weak as compared with that of the transverse electric (TE) waveguide modes. Unlike TE modes, surprisingly, the linear behavior of the TM modes depends on the sign of the wave number k z . The negative k z has a much stronger linear efficiency than that of the positive k z . The bunching mechanism analysis further exhibits that the azimuthal bunching and axial bunching do not compete but cooperate with each other for the backward-wave operation (negative k z ). The current findings are encouraging and imply that TM modes might be advantageous to the gyrotron backward-wave oscillators.