Review of data processing techniques for density profile evaluation from broadband FM-CW reflectometry on ASDEX Upgrade

Broadband FM-CW reflectometry is foreseen to be used on ITER to measure the electron density profile, both in the main and divertor plasmas. These measurements should provide crucial information for machine control and operation, in complement to magnetic diagnostics, and require the automatic evaluation of the density profile in all relevant plasma scenarios. This is a complex task due to the effects of plasma turbulence on the probing microwaves. A major and continued effort both on hardware development and data processing has been made in the ASDEX Upgrade broadband reflectometry diagnostic since 1991, which has led to noticeable improvements of density profile measurements. Here we review the evolution of the data processing techniques for profile evaluation. We first describe the standard methods that have been applied in ASDEX Upgrade (as well as in other machines) and discuss their advantages and limitations. Secondly, the novel techniques implemented in ASDEX Upgrade are presented and the resulting improvements on profile evaluation are discussed. It is shown that these are due to the ability to use both the a priori knowledge about profile measurements and the advanced features of the ASDEX Upgrade reflectometry diagnostic.