Status of the EUROfusion Enabling Research Project “Advances in real-time reflectometry plasma tracking for next generation machines.”

One of reflectometry’s expected major roles for DEMO will be plasma positioning, shaping and tracking, complementing or effectively substituting magnetic diagnostics. The first steps to achieve this goal have already been taken experimentally, theoretically and with simulations but a great amount of groundwork remains to be done. An Enabling Research (EnR) Project was built involving a team of experts and developers of reflectometry systems in Europe aiming to tackle many of the still remaining open questions and come out with a coherent and unified approach allowing to implement a reflectometry system able to provide control inputs not only in steady-state operation (flattop) but also during the initial stage of the discharge (ramp-up phase) and, in the sequence of the ErR project, at the end of the discharge (ramp-down phase). The objectives and associated outcomes are divided in two main branches with its own specificities and requiring different approaches: (i) The ability to track and monitor the position and shape of the plasma in the initial stage of the discharge, in the start-up phase and also at the ramp-down phase; (ii) To improve the capabilities of operation in the stationary phase (flattop) in order to provide an accurate and precise substitute to the positioning magnetic diagnostics in real time. An important issue that must be addressed is the synchronization between all reflectometers. An experimental validation on the tokamak WEST will prove the concepts of synchronizing several reflectometers sharing the same clock and synchronizing triggering events. The project also contemplates advances on hardware with a prototype of a compact coherent fast frequency sweeping radio frequency (RF) back-end being developed using commercial Monolithic Microwave Integrated Circuits (MMIC) with Direct Digital Synthesis (DDS), which allows for full control of the signal’s frequency and phase, both with very high precision and resolution.