Axial modes in terahertz high-harmonic large-orbit gyrotrons

Terahertz (THz) gyrotrons can operate with a lower applied magnetic field in harmonic operation, but the weakened harmonic interactions in harmonic gyrotrons can introduce serious challenges when mode competition occurs. The use of an axis-encircling electron beam can greatly alleviate mode competition in a harmonic gyrotron. In this paper, we study axial modes for third-harmonic [Formula: see text]-mode large-orbit gyrotrons. Simulation results reveal that the minimum current for oscillation to begin in each axial mode in the gyrotron regime is associated with a specific range of applied magnetic field. To avoid mode competition, tapered applied magnetic fields and waveguide radii are employed to enhance the high-order axial modes and suppress the low-order axial modes. Furthermore, spurious transverse modes in a THz gyrotron are discussed below. A stable third-harmonic [Formula: see text]-mode large-orbit gyrotron at the third-order axial mode is predicted to yield peak output power of 6.5 kW at 768.1 GHz with an efficiency of 10% for a 75-kV, 0.85-A electron beam with an axial velocity spread of 3%.

CW subterahertz gyrotron operating at high cyclotron harmonics

At the IAP RAS, a subteraherz continuous-wave large orbit gyrotron (LOG) operating directly at the second, third, and fourth cyclotron harmonics at frequencies of 0.26, 0.39, and 0.52 THz, is developed and created. The paper presents the results of experimental testing of LOG at the second and third harmonics carried out to date in the long-pulses regime (duration 0.1–60 s) with the transition to continuous- wave generation regime.