A CW, 94 GHz Second Harmonic Gyrotron with a Continuous Operation Solenoid Cooled by Water

Design and experimental results of a continuous wave (CW), 94 GHz second harmonic gyrotron with a 1.8 T continuous operation solenoid are presented. In order to reduce power consumption of the solenoid, a carbon steel shell was designed to concentrate the magnetic flux into the gyrotron cavity region. The inner hole is 66 mm in diameter. That is big enough to insert a CW, medium power gyrotron. When driven by a current of 476 A, maximum magnetic field of 1.8 T in the cavity region was detected and the power consumption was 25 kW. The solenoid was cooled effectively with a water flow of 1.5 L/s. Based on the 1.8 T solenoid, a compact triode magnetron injection gun (MIG) was used to generate gyrating electron beam for the second harmonic gyrotron. The gyrotron operated at the TE 0,2 mode with a conventional cylindrical cavity. And a high-efficiency quasi-optical mode converter with a dimpled-wall launcher was designed, the mode conversion efficiency was 97%, and the Gaussian content of the output beam was 98%. During the CW test, continuous operation of 5 min was realized. Its operational frequency stabilized at 93.9 GHz. The output power was 12 kW with an electron beam of 45 kV, 1.6 A. The output efficiency was 24% with a single-stage depressed collector.