LAUSR

Terahertz gyrotrons in harmonic operation offer the magnetic-field reduction, but they can also still easily generate various competing modes that operate at low harmonics. In this paper, an injection-locking technique for phase control and spectral purity is employed to enhance the operating modes and suppress the competing modes in gyrotrons. The simulation results, using a multi-mode time-independent code, show that gyrotrons driven by backward or forward waves cannot avoid mode competition wherever the input power increases. To avoid the fundamental harmonic competing mode, a second-harmonic gyrotron traveling-wave amplifier (gyro-TWA) with a severed section is used instead of the driven gyrotrons. The gyro-TWA operates at a slightly low external magnetic field and has a uniform interaction structure. The simulation results reveal that the fundamental harmonic TE3,5 competing mode does not occur at Ib< 4.2 A; meanwhile, the second-harmonic TE8,9-mode gyro-TWA can yield a stable output power. The ampli...