Megawatt power generation of the dual-frequency gyrotron for TCV at 84 and 126 GHz, in long pulses

In the frame of the TCV Tokamak upgrade, two 84/126 GHz/2 s dual frequency gyrotrons designed by SPC and KIT and manufactured by THALES will be added to the existing EC-System. The first unit has been delivered to EPFL-SPC and tested. In the commissioning configuration, a matching optics unit (MOU) is connected to the gyrotron window. The RF is then coupled to the HE11 mode of a 63.5mm corrugated waveguide and dissipated in a load procured by CNR after 4m of waveguide and 2 miter bends. Owing to the flexible triode gun design giving the possibility to adjust the pitch angle parameter, the specifications were met at both frequencies. At 84 GHz (TE17,5 mode), a power of 0.930 MW was measured in the calorimeter, with a pulse duration of 1.1 s. At the high frequency (126 GHz, TE26,7 mode), a power of 1.04 MW was reached for a pulse length of 1.2 s. Accounting for the load reflection and the ohmic losses in the various subcomponents of the transmission line and the tube, it is estimated that the output power at the gyrotron window is in excess of 1 MW at both frequencies, with an electronic efficiency of 32% and 34% at 84 GHz and 126 GHz respectively. The gyrotron behavior is remarkably robust and reproducible, and the pulse length is limited by external systems that will be improved shortly.