Reflectometry inconventional and advanced plasma scenarios on ASDEX Upgrade andperspectives for ITER

Abstract

The discovery of advanced tokamak scenarios opened new possibilities forthe realization of more compact machines with long pulse operation. Thisrequires the simultaneous optimization of the plasma shape, and of thepressure, current and electric field profiles. In this complex processthe diagnostics are crucial to understand the plasma physics, tovalidate the theoretical models and to measure parameters for controlpurposes.Here we present results obtained in ASDEX Upgrade showing the greatpotential of reflectometry for conventional and advanced tokamakinvestigation, derived from the diagnostic capability to perform a widerange of measurements with high spatial and temporal resolution, both atthe edge and plasma core. The abrupt formation of sharp densitygradients at the zones where internal and external transport barriersare formed, as well as the modifications of the turbulence parameters inthose narrow plasma regions are shown. Density profile changesassociated with fast events like ELMs and the L-H transition areresolved. Enhanced fluctuations that may be important for the transportacross the edge barrier are also detected by reflectometry. Themeasurement of the radial profile of E×B velocity on ASDEXUpgrade is discussed and results are compared with vE×Bprofiles obtained in W7-AS stellarator.The first experimental demonstration that edge density profiles fromreflectometry can provide accurate and reliable measurements of thetemporal evolution of the plasma position is presented. This isessential to prove that reflectometry can be used as an alternativeapproach to supplement the magnetic measurements, for the control ofplasma shape and position in long pulse operation, as it is proposed forITER. Finally new applications of reflectometry under development arediscussed.