Design of a Variable Frequency Comb Reflectometer System for the ASDEX Upgrade Tokamak

Comb reflectometers offer the advantage of measuring at several radial positions in the plasma simultaneously. This allows the investigation of fast timescales during L-H transitions, I-phases, I-mode bursts, transients during heat wave propagation, etc. A drawback of many present-day systems is that they use a fixed frequency difference between the probing frequencies. Hence, although the central probing frequency can be varied, usually the probing frequency difference is fixed. The new design presented in this work uses an advanced microwave generation and detection scheme, which allows for arbitrary probing frequencies and probing frequency separations.