Present status of submillimeter wave gyrotron series in Fukui University

The gyrotrons developed in Fukui University ("Gyrotron FU series") are high frequency, medium power devices, covering a broad frequency band in the millimeter and submillimeter wavelength region. The output frequency can be modulated by the modulation of beam electron energy. While a phase lock control of the energy makes the output frequency highly stable. A high power, high stability submillimeter wave source has just been realized. In this paper, recent advances of Gyrotron FU series are described.