Development of THz gyrotrons in FIR FU for application to high power THz technologies

Recently, a gyrotron in FIR FU with a 21 T pulse magnet achieved the breakthrough of 1 THz. In the gyrotron, a demountable gyrotron tube is installed on the center axis of 21 T pulse magnet. In the operation test, a high voltage pulse is applied to electron gun installed in the region of the additional coils for controlling the injection point of electron beam in the cavity region. When B in the cavity region is changed, many cavity modes are excited at the fundamentals and second harmonics of electron cyclotron frequency. The second harmonic radiation is separated from the fundamental by using a high pass filter. Observed frequencies range from 395 GHz to 1,016 GHz. The maximum frequency 1,016 GHz is achieved by the second harmonic operation of TE_4.12 cavity mode. Corresponding field intensity B is 19.1 T. Now we are trying to increase the frequency by increasing B. For the convenience of the application, CW gyrotrons (Gyrotron FU CW Series) are being developed. Gyrotron FU CW I has been developed and succeeded in the CW operation at 300 GHz under high power of 2.2 kW. The next gyrotrons, Gyrotron FU CW II and III have also been developed. The parameters are as follows: around 400 GHz, 100 W for Gyrotron FU CW II and 1 THz, 100 W for Gyrotron FU CW III under CW operation. These gyrotrons will be used for development of high power THz technologies, for example, Plasma diagnostics, DNP-NMR for protein research, etc.