TM-Mode Gyrotrons

Transverse magnetic (TM) waveguide modes have long been considered as the unsuitable modes for the operation of the electron cyclotron maser (ECM). This study reveals that certain TM modes might be suitable for gyrotrons - ECM based devices. Unlike transverse electric (TE) modes, the linear behavior of the TM modes depends on the sign of the wave number k_z. The negative k_z has much stronger linear efficiency than that of the positive k_z. In addition, the non-linear calculation for a fixed field profile shows that the efficiency of some TM modes could be as high as that of the TE modes. The current findings are encouraging and imply that TM modes might be advantageous to the gyrotron backward-wave oscillators.