Development of terahertz FUCW gyrotron series for DNP

The new gyrotron series in FIR FU, so-called Gyrotron FU CW Series, is being developed for application to high power THz technologies. The second gyrotron, of the series, Gyrotron FU CW II with an 8 T liquid He-free superconducting magnet 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 designed frequency is 394.6 GHz. The real operation frequency is 394.3 GHz at TE06 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 TE06 cavity mode. There are many other operation modes at the fundamental and the second harmonics. 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 constructed and the operation test has been almost completed. The highest frequency is around 980 GHz at the second harmonic operation. This gyrotron demonstrates a possibility of application to higher frequency DNP/NMR up to 1 GHz