Development of CW THz gyrotrons in FIR FU

The new gyrotron series in FIR FU, so-called gyrotron FU CW series is being developed for application to high power THz technologies. Gyrotron FU CW II with an 8 T liquid He free superconducting magnet, the second gyrotron of the series, has been constructed and the operation test was successfully carried out. It will be used for enhancing the sensitivity of 600 MHz proton-NMR by use of dynamic nuclear polarization (DNP). The designed operation mode of the gyrotron is TE2>6 at the second harmonic. The corresponding frequency is 394.6 GHz. The real operation frequency is 394.3 GHz at TE 06 mode, because of fabrication error of the diameter of the cavity. The operation is in complete CW at the output power of around 30 W or higher at the TE 06 cavity mode. There are many other operation modes at the fundamental and the second harmonic. Typical output power of the fundamental and the second harmonic are higher than 100 W and 20 W, respectively. The third gyrotron, Gyrotron FU CW III with 20 T superconducting magnet has already been designed and the construction has been almost completed. The operation test will start soon. Such a present status of high frequency gyrotrons in FIR FU will be introduced.