Reflectometry techniques are employed to study density fluctuations in fusion plasmas either using one channel or two channels with slightly different frequencies, to probe simultaneously closely spaced plasma layers (for radial correlation studies)., The present paper describes a novel system with increasing measuring capability utilizing only one single frequency that can be hopped during the discharge. This Broadband Fast Hopping mm-Wave Reflectometer (BFHR) has been developed for both ASDEX upgrade tokamak and TJ-II stellarator. The BFHR incorporates frequency synthesizers at microwave frequencies multiplied into the millimeter-wave range and uses heterodyne detection for sensitive phase and amplitude measurements. The system can switch between frequencies in a very short time (sub milliseconds) enabling to probe several plasma layers during the discharge to study the radial distribution of plasma fluctuations and to perform correlation measurements. |
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