Experimental Study of Extended Operating Zone of a 170-GHz/1-MW Gyrotron Locked by a Narrowband External Signal

For a gyrotron with a operating frequency of 170 GHz and a megawatt power level, an expansion of the operating zone by 2.4 times compared to a free-running gyrotron was experimentally demonstrated in the frequency locked regime. The locking signal with the power not exceeding 16 kW was provided by a gyrotron driver (pulse operating mode $100~\mu $ s/10 Hz) stabilized by the phase-lock loop. The expansion of the operating zone of the TE28,12 mode into the region of lower magnetic field (compared to the free-running regime) was accompanied by an increase of output power by 10% and the improvement of efficiency from 32.1% to 35.2% due to advance to a more optimal cyclotron resonance detuning. The significant expansion of the operating zone in the region of greater magnetic field demonstrated the suppression of excitation of parasitic modes. In the frequency-locked regime, the gyrotron radiation spectrum width was reduced to 20 kHz, defined by the locking signal from the stabilized gyrotron driver, compared to the 2–4 MHz in the stand-alone mode.