Title :
Parasitic oscillation in and suppression of a gyrotron backward wave mode in a low-Q 8 GHz gyrotron
Author :
Muggli, P. ; Tran, M.Q. ; Tran, T.M.
Author_Institution :
Centre de Recherches en Phys. des Plasmas, Ecole Polytechnique Federale de Lausanne, Switzerland
fDate :
8/1/1992 12:00:00 AM
Abstract :
The parasitic oscillation of the TE°21 gyrotron backward-wave (gyro BW) mode is observed in a low-Q, 8 GHz TE°011, gyrotron. At low power (PBW<5 kW), the oscillation of the gyro BW mode, simultaneously with the gyrotron mode, results in a maximum TE°011, mode efficiency of less than 0.25. The parasitic oscillation is suppressed by operating the gyrotron with a negative magnetic field gradient along the electron beam, which allows the maximum efficiency to reach 0.40 and the output power to be multiplied by a factor varying from 1.4 to 1.7. The optimum efficiency curve of the TE°011 mode indicates that the low-Q cavity behaves as a much higher Qdiff cavity. Excessive values of magnetic field gradient and α favor the TE°012 , longitudinal mode, which oscillates in place of the TE°011 mode and limits its maximum output power. This competitive process is responsible for the high-Q-like behavior of the optimum efficiency curve
Keywords :
backward wave tubes; gyrotrons; microwave oscillators; 5 kW; 8 GHz; TE°011, gyrotron; TE°012, longitudinal mode; TE°21 mode; competitive process; electron beam; gyrotron backward wave mode; low-Q cavity; low-Q gyrotron; mode suppression; negative magnetic field gradient; optimum efficiency curve; parasitic oscillation; Cyclotrons; Dielectric losses; Electron beams; Gyrotrons; Helium; Magnetic field measurement; Magnetic fields; Power generation; Resonance; Tellurium;
Journal_Title :
Plasma Science, IEEE Transactions on
