Influence of mode conversion and ohmic losses on electromagnetic properties of THz gyrotron cavities

On the basis of a rigorous multimode approach it is shown that mode conversion and ohmic losses can notably influence quality factors of a THz gyrotron cavity. They also lead to the significant distortion of the field distribution inside the output section of the THz gyrotron cavity making it strongly multimode. Influence of these effects on the THz gyrotron operation is also discussed. Specific calculations were performed for the cavity of FU CW III gyrotron, designed in Fukui University to operate in sub-THz and THz ranges.