High-harmonic THz gyrotrons and gyro-multipliers

Terahertz gyrotrons are not widespread yet since a very strong magnetic field is required for operation at the fundamental and second cyclotron harmonics. The magnetic field can be significantly decreased by using higher operating harmonics if the complicated problem of the spurious modes discrimination is solved. A significant mitigation of the problem is possible in the so-called large orbit gyrotron (LOG). In this way, an unique third-harmonic 1 THz/80 kV/0.7 A LOG was realized recently. A stable single-mode operation was observed for the third harmonic modes TE_3,6 and TE_3,7 at the frequencies of 0.87 and 1.00 THz, respectively, with the output efficiency of about 1%. In 2012, this experiment was repeated. An improvement of the electron-optic system resulted in an increase of the output efficiency up to 1.5%. A further improvement of this LOG can be achieved by solving the main problem of this gyrotron, which is using a long-length operating cavity with a very high diffraction Q factor that leads to dissipating a large fraction of the radiated rf power in Ohmic losses.