Frequency tunable gyrotrons for sub-THz CW radiation sources of DNP-NMR experiment

Summary form only given. Dynamic nuclear polarization (DNP) method can enhance the sensitivity of NMR for extending its application to wide fields including analysis of protein molecule and study on material surface. For this objective, it is needed to develop high power sub-THz radiation sources which operate in long time CW mode. We have already developed a 395 GHz CW gyrotron for 600 MHz proton NMR. The next target is to realize frequency continuous tuning for adjustment to the best condition of DNP-NMR. As a preliminary experiment on frequency continuous tuning of gyrotron, we tried to use backward-wave components with different axial mode numbers. The latest gyrotron of Gyrotron FU CW Series, Gyrotron FU CW IV has already succeeded in frequency tenability in a wide range of 6 GHz around 140 GHz. We will present the design and experimental setup and results in detail.