Gyrotron with a mode convertor which reduces EM wave leakage

In a gyrotron having an electron beam generator, an output waveguide, and a dielectric EM output window, a DC magnetic field generating means, an interaction circuit located between said electron beam generator and said output waveguide for receiving and transmitting an electron beam generated from said beam generator in a linear direction toward said output waveguide, said interaction circuit including a resonator capable of supporting and propagating an electromagnetic wave including energy associated therewith in a first transverse electric (TE.sub.nm) mode having an azimuthal mode number n,

• said output waveguide coupled to said interaction circuit for propagating said electromagnetic wave in said first TE.sub.nm wave toward said EM window along a propagation path and for transmitting said electron beam away from said resonator toward a location away from said electron beam generator, said output waveguide having a gap therein, said gap being disposed between said resonator and said dielectric EM output window, said dielectric EM output window being mounted across an interior of said waveguide, THE IMPROVEMENT COMPRISING
• a portion of said output waveguide in the propagation path of said electromagnetic waves between said resonator and said gap being capable of also transmitting a second electromagnetic wave in a TE.sub.nm mode having a radial mode number m, different than the radial mode number of said first mode, and
• at least a part of said portion of said output waveguide in the propagation path of said electromagnetic wave between said resonator and the commencement of said gap being a mode converter for diverting part of the energy from said first mode into said second mode to reduce, in operation, leakage of wave energy from said output waveguide through said gap.