Implementation of real-time reflectometry for electronic density profile reconstruction on the WEST tokamak

Abstract In nuclear fusion research, diagnostics measure various plasma parameters serving for tokamak control or physics studies. Reflectometry is a non-perturbative diagnostic for plasma density estimation based on the radar principle: it emits microwaves (tens of gigahertz) that are reflected inside the plasma, depending on the probing frequency and on plasma density. The probing frequency is increasing linearly along time, allowing to probe further inside the plasma along the radial direction. The phase shift or time delay of the reflected signal compared to the emitted wave is computed along the probing frequency ramp, and used to reconstruct the radial profile of the electron density. Density profiles are currently reconstructed through post-discharge processing. Real-time measurement of the density profile could open up numerous opportunities for the detection of plasma phenomena and the control of plasma performance. Thanks to the development of an innovative fast acquisition card for the Thomson scattering diagnostic, a real-time reflectometry measurement is being implemented on the WEST tokamak in Cadarache. A new data processing have been developed to be faster and simpler, and hence more suitable for real-time measurements. It includes a new data extraction and a new algorithm of density profile reconstruction in X-mode. Single profile reconstruction in less than a millisecond has been achieved. The algorithm have been implemented in the reflectometer PC, and the first real-time measurements have been performed during fall 2024 experimental campaign. The reflectometer have been linked to the plasma control system (PCS), and the density profile measurements are written in real-time on the PCS since January 2025. Density control experiments were not performed yet, and are planned for early 2025 campaign.