W-band tunable, multi-channel, frequency comb Doppler backscattering diagnostic in the ASDEX-Upgrade tokamak

This article presents the design, implementation, and first data of a uniquely flexible, multi-channel, frequency comb Doppler backscattering diagnostic recently made operational in ASDEX-Upgrade tokamak [A. Gruber O. Gruber, Fusion Sci. Technol. 44, 569 (2003)]. It uses double side-band signal fed into ×6 multiplier to produce multiple-frequency output spectrum. Seven these frequencies are simultaneously measured receiver via two-step down-conversion traditional I/Q demodulation. The spectrum is fully tunable sit anywhere W-band. inter-frequency separation also remotely between 0.1 6 GHz without any hardware changes. can be operated both O X-mode polarizations at oblique normal incidence cutoff layer. time evolution backscattered signals, excess 30 dB, from seven distinct sampled presented across an L-to-H-mode confinement regime transition.