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Reflectometry

Microwave reflectometry is an active plasma diagnostics technique used to reconstruct the plasma density profile by measuring the round-trip group delay of a probe beam of variable frequency reflected on the cutoffs (i.e. locations where plasma behaves like a mirror). Since the frequencies are in the submillimeter range, the phase change on probe beam on the tokamak spatial scale (~meters) largely exceeds 2π. To overcome the arising phase ambiguity, issue an intuitive arrangement, so called Amplitude Modulation (AM), has been developed. With a method similar to that used in radio communication.