Operation results of a high harmonic gyrotron with axis-encircling electron beam and permanent magnet

Summary form only given, as follows. Summary form only given. A gyrotron with an axis-encircling electron beam is useful for high frequency operation, because the higher beam efficiency is kept even at high harmonic of electron cyclotron resonance. We have designed and constructed such a gyrotron with a permanent magnet. The gyrotron has already succeeded in the operations at the third harmonic and the fourth harmonic resonance. The frequencies are 84.88 GHz and 112.8 GHz, respectively. Operation cavity modes are TE/sub 311/ and TE /sub 411/. The magnet system consists of the main permanent magnet and additional coils for controlling the field intensities at cavity and electron gun regions. The magnetic field at the cavity region can be varied from 0.97 T to 1.18 T. At the optimum condition of the magnetic field intensity, the output powers at the third harmonic operation is 1.2 kW. The operation is pulsed, the pulse length is 1 ins and the repetition frequency is 1 Hz. Starting current, beam efficiency and emission pattern also have been measured. In this paper, the operation results of the gyrotron and comparison with the computer simulation results are described.