Operation of a high-hartonic gyrotron

The operation of a millimeter-wave harmonic gyrotron is described in which the interaction is between axis-encircling electrons and cylindrical cavity TEnll modes. Gyrotron cavities operating on this principle are well matched to low current, moderate energy, rfaccelerated electron beams. Efficiencies up to 15% have been measured for moderate harmonic interactions, multi-kW power levels have been attained at the eleventh harmonic of the cyclotron frequency, and 65 GHz waves have been produced. The concept allows the magnetic field of the gyrotron to be reduced by an order of magnitude, thereby making a submillimeter-wave gyrotron feasible. However, mode competition problems must be considered for high-harmonic, sub-millimeter wave operation, We have been successful in suppressing mode competition by destroying unwanted modes.