Development of Terahertz FU CW Gyrotron Series for DNP

The new gyrotron series in FIR FU, so-called Gyrotron FU CW Series, isbeing 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 magnethas been constructed and the operation test was successfully carried out. It will be usedfor enhancing the sensitivity of 600 MHz proton-NMR by use of Dynamic NuclearPolarization (DNP). The designed operation mode of the gyrotron is TE2,6 at the secondharmonic. The corresponding designed frequency is 394.6 GHz. The real operationfrequency is 394.3 GHz at TE06 mode, because of fabrication error of the diameter ofthe cavity. The operation is in complete CW at the output power of around 30 W orhigher at the TE06 cavity mode. There are many other operation modes at thefundamental and the second harmonics. Typical output power of the fundamental andthe 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 constructedand the operation test has been almost completed. The highest frequency is around 980GHz at the second harmonic operation. This gyrotron demonstrates a possibility ofapplication to higher frequency DNP/NMR up to 1 GHz