Reflectometry in conventional and advanced plasma scenarios on ASDEX Upgrade and perspectives for ITER

The discovery of advanced tokamak scenarios opened new possibilities for the realization of more compact machines with long pulse operation. This requires the simultaneous optimization of the plasma shape, and of the pressure, current and electric field profiles. In this complex process the diagnostics are crucial to understand the plasma physics, to validate the theoretical models and to measure parameters for control purposes. Here we present results obtained in ASDEX Upgrade showing the great potential of reflectometry for conventional and advanced tokamak investigation, derived from the diagnostic capability to perform a wide range of measurements with high spatial and temporal resolution, both at the edge and plasma core. The abrupt formation of sharp density gradients at the zones where internal and external transport barriers are formed, as well as the modifications of the turbulence parameters in those narrow plasma regions are shown. Density profile changes associated with fast events like ELMs and the L-H transition are resolved. Enhanced fluctuations that may be important for the transport across the edge barrier are also detected by reflectometry. The measurement of the radial profile of E x B velocity on ASDEX Upgrade is discussed and results are compared with v E×B profiles obtained in W7-AS stellarator. The first experimental demonstration that edge density profiles from reflectometry can provide accurate and reliable measurements of the temporal evolution of the plasma position is presented. This is essential to prove that reflectometry can be used as an alternative approach to supplement the magnetic measurements, for the control of plasma shape and position in long pulse operation, as it is proposed for HER. Finally new applications of reflectometry under development are discussed.