Parasitic oscillation in and suppression of a gyro BW mode in a low-Q 8 GHz gyrotron
The parasitic oscillation of the TE(o,21) gyrotron Backward Wave (gyro BW) mode is observed in a low-Q, 8 GHz TE(o,011) gyrotron. At low power (P(BW) less than 5 kW) the oscillation of the gyro BW mode, simultaneously with the gyrotron mode, results in a maximum TE(o,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(o,011) mode indicates that the low-Q cavity behaves as a much higher Q(diff) cavity. Magnetic field gradient and alpha values that are too large favour the TE(o,012) longitudinal mode, which oscillates in place of the TE(o,011) mode and limits its maximum output power. This competitive process is responsible for the high-Q like behaviour of the optimum efficiency curve.
Bibliographic Reference: Report: LRP 447/91 EN (1991)
Availability: Available from Confédération Suisse, Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Fédérale de Lausanne, 21 avenue des Bains, 1007 Lausanne (CH)
Record Number: 199210255 / Last updated on: 1994-12-02
Original language: en
Available languages: en