No abstract

High frequency, medium power gyrotrons (Gyrotron FU series) have been developed at the Fukui University as radiation sources convering a broad frequency band from millimeter to submillimeter wave region. We have performed cw operation of the Gyrotron FU IV. However, the output power was not stable (approximately several tens %) due to the fluctuation of the cathode potential (40 V). The output power was stabilized within several percent by controlling the anode potential. Such a technique was also used for amplitude modulation of the gyrotron output. Improved stabilization of output power and effective modulation will be achieved by stabilizing the cathode potential

No abstract

No abstract

Special experiments devoted to studying hysteresis in gyrotron oscillators have been performed for the first time. Clear hysteresis-like effects with respect to variation of the cathode voltage have been observed in the mode competition scenario of the Forschungszentrum Karlsruhe coaxial gyrotron [B. Piosczyk et al., IEEE Trans. Plasma Sci. 30, 818 (2002)] and with respect to variation of the magnetic field and voltage in a single-mode operation of the Fukui IV gyrotron [T. Idehara et al., Int. J. Infrared Millim. Waves 19, 793 (1998)]. The observed phenomena are explained theoretically

No abstract

Submillimetre-wave ESR measurements for single crystal have been performed for the first time in the frequency region from 60 to 383 GHz using a pulsed magnetic field up to 16 T. AFMR modes below have been analysed by a model proposed previously, which is essentially the molecular-field theory with the assumption of an S = 1 dimer of two spins. The anisotropies of the system are determined by the analysis, and they are discussed together with the results of our magnetization measurements.

Influence of reflections on operation of gyrotrons with axial output is studied both theoretically and experimentally. By way of example the Fukui large orbit gyrotron with a permanent magnet operating in third harmonic at frequency 89 GHz is considered. In the case of strong reflection (= 0 6), extreme sensitivity of output power on the reflection phase is found. A qualitative agreement between theory and experiment is observed.