Development of a 140GHz 3rd cyclotron harmonic gyro-peniotron oscillator

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High power millimetre wave tubes are great important devices in fusion plasma researches for the electron cyclotron resonance heating and plasma diagonostics. The development of tube with shorter wavelength up to submillimetre wave range is especially required in large fusion devices. The high harmonic gyro-peniotron is desirable for such high power and high frequency applications as the above because of its lower magnetic field requirement and higher operation frequency due to the favorable peniotron operation mechanism than these of other cyclotron fastwave tubes.In this project, wa have performed the following tasks concerning with the 3rd cyclotron gyro-peniotron development.1. Design of 140GHz gyro-peniotron We designed the TE<@2021<@D2 mode cavity and the electron gun, thich were used for the test tube operating at the third harmonics of the cyclotron frequency and at the beam conditions of acceleration voltage and curent of 60KV and 10A, respectively. The design specifications of the test tube are as follows: Oscillation frequency is 140GHz, starting current is 4A and the output power and the efficiency are 45.5KW and 9.0%, respectively. The test tube was fabricated at Toshiba corporation.2. Experimental results and discussions The 3rd cyclotron harmonic oscillation at 139.5GHz initiates at the beam current of 5A and the output power increases with increase of the beam current. The mode of oscillation is verified to be TE_<021> mode by measuring the radiation pattern from the output waveguide. Up to date, the maximum output power of 3.3KW was obtained at beam current of 6A. We are expecting to be able to increase considerably its output power by readjusting the arrangement of centre axes of the test tube and the used magnets. No mode compitition has been observed as expected from the simulation results.