First Experiments on Frequency Locked Operation of the 170ghz/1mw Gyrotron

The paper presents the summary of the experiments on the frequency locked operation of the 1MW gyrotron with operating frequency 170GHz. We describe the design and performance of the locking signal source and different gyrotron subsystems used in the experiment. The 20kW "driver" gyrotron, equipped with frequency stabilization by means of PLL-control of modulating anode voltage in short pulses was used as the source of the stabilized locking signal. The input of the radiation into the MW gyrotron was performed by the specially designed transmission line and the quasi-optical mode converter for co- and counter-rotating modes of the cylindrical waveguide. In the experiment the frequency-locked operation of the 1MW gyrotron was demonstrated in different regimes of operation. The maximum output power was increased to 1.2MW while the spectrum width of the radiation of the powerful gyrotron was reduced to 30kHz, limited by the pulse duration. The operating zone of the TE 28,12 mode on the magnetic field was increased twofold by suppression of excitation of parasitic modes. Demonstrated results open up the new prospects for the expansion of the gyrotrons to higher frequencies and output powers for the next generation of fusion plants.