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Abstract

Microwave reflectometry has been proposed as an alternative/backup approach to the usual magnetic systems in long pulse operation on the International Thermonuclear Experimental Reactor (ITER) for plasma position and shape control. This new application of reflectometry must be fully demonstrated in present machines in view of its importance for ITER. First experiments performed in ASDEX Upgrade with frequency modulated continuous wave with reflectometry diagnostic showed that radial variations of the plasma column occurring during preprogrammed horizontal as well as vertical plasma displacements could be followed with sufficient accuracy (1 cm) in phases with approximately constant density. In this article we determine the plasma edge position simultaneously in the inner and outer midplane, of ohmic L-mode density limit and ELMy H-mode discharges in ASDEX Upgrade, both with significant density variations. It is shown that if normalized density layers are selected, at a certain percentage of the average line density, the results from reflectometry are in good agreement with the corresponding data, separatrix position, derived from the magnetics. Further work aiming at the full demonstration of plasma position and shape measurements from reflectometry is discussed.