170/204 GHz Dual-Frequency Mode Generator for Verification of the Quasi-Optical Output Coupler of a 2 MW Coaxial-Cavity Gyrotron

The 2 MW 170 GHz single-frequency coaxial-cavity short-pulse pre-prototype is upgraded to operate also at 204 GHz. Therefore, the quasi-optical output coupler, which is a gyrotron key component, has been modified. Before the newly manufactured quasi-optical output coupler is installed into the gyrotron, a low-power cold measurement for the verification is performed. Therefore, a mode generator is designed and adjusted to excite the relevant operating gyrotron modes, namely the TE
34,19
mode at 170 GHz and TE
40,23
mode at 204 GHz, with excellent purity and a low counter-rotating amount of < 0.5 % for both modes. The TE
40,23
mode is the mode with the highest eigenvalue ever excited in cold tests. After the successful mode excitation, first the fabricated launcher and then the entire quasi-optical output coupler are verified, showing excellent agreement with the simulation.