The Nonlinear Designs on a Frequency-Tunable THz Gyrotron With Three Frequency Regimes at 140, 250, and 263 GHz

Gyrotron, as a most likely practical high-power terahertz (THz) radiation source, has been widely applied to THz dynamic nuclear polarization-enhanced nuclear magnetic resonance (DNP-NMR) spectroscopy. In this article, an iris cavity with high-quality factor is theoretically designed for a frequency-tunable THz gyrotron, which could be tuned at three frequency regimes: 140, 250, and 263 GHz, respectively. Based on the self-developed nonlinear code, the beam wave interactions in the designed cavity are studied in detail when the corresponding high-order axial modes (HOAMs) are TE-6.1.q, TE0.4.q', and TE8.2.q ''. By tuning the applied magnetic field under the condition that the beam voltage U-0 is 20 kV and beam current I-0 is 0.10 A, the output power and frequency tuning ranges could achieve 0.75 kW and 1.15 GHz, 0.63 kW and 3.10 GHz, and 0.59 kW and 2.54 GHz. Meanwhile the calculation results are compared with the 3-D particle software CST, which have confirmed that the frequency and power tuning ranges of TE-6.1.q, TE0.4.q', and TE8.2.q '' could reach 0.46 kW and 1.07 GHz, 0.37 kW and 2.24 GHz, and 0.34 kW and 1.96 GHz. These results could be beneficial for the development of frequency-tunable gyrotron toward some up-and-coming novel THz applications.