Study of rotating modes in high frequency whispering gallery mode gyrotrons

An investigation of coupling to the two rotations of TE_m,2,1 modes of a gyrotron oscillator was made. Experiments were performed on a megawatt power level, 3 μs pulsed gyrotron operating at frequencies from 123.5 GHz (TE_13,2,1) to 153.5 GHz (TE_17,2,1). Single rotation operation was observed with the electron beam centered in the cavity. The influence of tube misalignment on rotation mix was studied. The experimental results were in good agreement with predictions of linear coupling theory for an off axis electron beam. Both experiment and theory showed that significant misalignments of the beam are possible before a switch in the rotation direction of the output mode occurs