Megawatt Power Generation of the Dual- Frequency Gyrotron for TCV at 84 and 126 GHz, in Long Pulses.

Abstract--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 MSI will be added to the existing EC-System. The first unit has been delivered to EPFL-SPC and tested. In the commissionning 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 waveguides 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 0.930MW was measured in the calorimeter, with a pulse duration of 1.1s. At the high frequency (126 GHz, TE26,7 mode), a power of 1.04 MW was reached for a pulse length of 0.5 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 1MW at both frequencies, with an electronic efficiency of 32% and 34% at 84 GHz and 126 GHz respectively. The gyrotron behaviour is remarkably robust and reproducible, suggesting that the ongoing implementation in the gyrotron control and protection system of an already tested novel collector sweeping modulation scheme will permit the straightforward extension of the pulse length to 2s.