Frequency measurements of the gyrotrons used for collective Thomson scattering diagnostics at TEXTOR and ASDEX Upgrade

High resolution frequency measurements of the $110GHz$ gyrotron at TEXTOR and the $105GHz$ mode of the two-frequency gyrotron (Odissey-1) at ASDEX Upgrade (AUG) have been made in support of fast ion collective Thomson scattering diagnostics. Measurements were done by harmonic heterodyne methods using both fast Fourier transform spectroscopy with digital oscilloscopes and fast scanning spectrum analyzers. Accurate frequencies were obtained with a frequency counter. At TEXTOR, at $180kW$ forward power the starting frequency was $109.970±0.005GHz$ and chirped down as much as $27MHz$ depending on the duty factor. At AUG, at $500kW$ forward power the frequency started at $104.786GHz$ and chirped down $104MHz$⁠, with 90% of the chirp occurring in the first $100ms$⁠. Plasma perturbation of the TEXTOR gyrotron was observed when both ion cyclotron resonance heating antennas and neutral beam injection were operating, producing modulation at 29 and $58MHz$ in the gyrotron output. Each gyrotron was observed to have an instrumental measurement limited linewidth of $120kHz$ full width at half maximum.