Measuring ion dynamics in the core of European DEMO: a design space exploration for collective Thomson scattering

Abstract Among the feasible options for diagnostics on burning plasma devices, collective Thomson scattering (CTS) is a promising technique for monitoring core ion dynamics. This work aims to identify an optimised CTS configuration for the European DEMOnstration power plant (DEMO) using an accuracy-driven approach. The optimisation procedure combines ray tracing, forward modelling of CTS spectra, and Bayesian inversion to evaluate predicted measurement uncertainties for key plasma parameters. We apply the optimisation methodology to the 2024 low-aspect-ratio DEMO design point. By scanning over the choices of probe frequency, receiver launch angle, and mirror positions, we optimise the CTS system for simultaneous measurements of the ion temperature T i , the bulk ion rotation velocity v φ , and the alpha particle density n α in the centre of the plasma. To inform the optimisation, we estimate the intrinsic toroidal rotation profile, obtaining a core rotation velocity of about 70 km/s. The resulting CTS configuration achieves predicted measurement uncertainties of approximately 4% for T i , 19% for v φ , and 5% for n α at a time resolution of 0.5 s. These results confirm the potential of CTS as a core diagnostic for DEMO and provide a foundation for future work, including sensitivity studies and optimisation for additional parameters such as the fuel-ion ratio.