Optimizing plasma position reflectometry systems: the DEMO case and future perspectives

Abstract Plasma position reflectometry (PPR) is a leading candidate to complement or replace magnetic diagnostics in DEMO and next-generation fusion devices. The concept of a multi-reflectometer PPR system is currently under development for DEMO, requiring detailed studies of reflectometer performance across different regions of the machine. This work presents the first comprehensive assessment of a multi-reflectometer PPR system using recently developed simulation and data processing automation techniques. A system of reflectometers, located at different poloidal positions around the vessel, is modeled using the 2017 DEMO baseline scenario. The separatrix position error and signal amplitude are evaluated across various plasma and geometry configurations to assess the impact of key system properties, including reflectometer configuration, density curvature, plasma-wall reflections, scrape-off layer decay length, and turbulence-induced errors. Results indicate that while the midplane region meets the 1 cm requirement threshold, further optimization is needed for the divertor and upper poloidal regions. The PPR system’s performance is optimized by adjusting the probing direction and maximizing the average detected signal amplitude across the frequency range. Effective measurement solutions are identified in the upper poloidal and divertor regions. The robustness of the optimized system is assessed by analyzing macroscopic plasma displacements (5–15 cm) and group delay initialization. The results demonstrate that a well-configured PPR system can achieve reliable position measurements across different poloidal regions, confirming its viability for future fusion reactors.