REFLECTOMETRY TECHNIQUES FOR DENSITY PROFILE MEASUREMENTS ON FUSION PLASMAS

Reflectometry applied to the measurement of density profiles on fusion plasmas has been subject to many recent developments. After a brief r eminder of the principles of reflectometry, the theoretical accuracy o f reflectometry measurements is discussed. The main difficulties limit ing the performance, namely the plasma fluctuations and the quality of the transmission lines, are analysed. The different techniques used f or reflectometry are then presented grouped into three different categ ories, depending on the frequency spectrum of the probing wave: single frequency, few discrete frequencies, or broad spectrum. The present s tatus and achievements of actual implementations of these techniques a re demonstrated, with an analysis of their respective limitations and merits, as well as foreseen developments. Finally, a discussion of the various reflectometry techniques is made, in particular their ability to cope with plasma fluctuations and complex transmission lines, in v iew of the application to next step machines and very severe environme nts.