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.