Numerical investigation of plasma position reflectometry performance with respect to magnetic curvature

In future fusion reactors, O-mode Microwave Reflectometry (MWR) has been proposed as a tool for determining the plasma boundary position—an application known as Plasma Position Reflectometry (PPR). MWR, usually used for density profile measurements, is inherently well-suited for reactor environments, featuring in-vessel components designed to withstand the extreme radiation and thermal loads. The main PPR challenge is the potential degradation of performance in off-midplane regions, where magnetic curvature effects become significant. To investigate this and related issues, a PPR system will be installed on the Divertor Tokamak Test (DTT), currently being built in Frascati (Rome). This work focuses on the application of REFMUL3, a 3D full-wave Finite-Difference Time-Domain (FDTD) code capable of simulating reflectometry diagnostics within the complex geometry of a tokamak, to the High Field Side (HFS) DTT PPR subsystem. Simulations involved the HFS out-of-midplane LOS and modeled the measurements that will be provided by the diagnostic system. They also supported the optimization of the diagnostics design, maximizing measurement accuracy while ensuring the integration within the complex HFS environment. The results assessed how the reflectometer's poloidal positioning and the magnetic curvature correlate with the measurement accuracy in a reactor-relevant machine, and represent a significant advancement in the understanding of poloidally-distributed PPR systems.