A 28 GHZ GYROTRON WITH A PERMANENT-MAGNET SYSTEM

The design and experimental results of a 28 GHz, TE(0.2) mode gyrotron with a permanent magnet system are presented. The permanent magnet sy stem provided the axial magnetic field of about 5.3 kG, which is requi red to operate the 28 GHz gyrotron at the second cyclotron harmonic. S upplementary coils were wound directly around the gyrotron to adjust t he main and the electron gun magnetic fields to optimize the oscillati on for each electron beam voltage and current. An output power of 11.6 kW was obtained at a beam voltage of 30 kV with a beam current of 1.5 A, corresponding to an efficiency of 25.8%. The experimental results were in good agreement with the calculated results.