A photonic model of the High-Resolution Thomson Scattering diagnostic of WEST tokamak

A High-Resolution Thomson scattering diagnostic (HRTS) is being finalized on the WEST tokamak to measure electron density and temperature in the core to scrape off layer regions. It comprises two independent optical collecting systems (edge and core) with 6 mm and 25 mm spatial resolution, respectively, two sets of polychromators and two Nd:YAG lasers. The paper reviews the different modules of a synthetic diagnostic model, covering the implementation of incoherent Thomson scattering spectra, the volume of sight description, light collection, and transfer through optical components and polychromators down to output voltage simulation. A least square minimization method has been implemented to infer electron temperature and density from polychromator data. The photon budget of the two collecting systems is above 1800 photo-electrons at n e = 10 19 m -3 , which shall ensure good data quality from polychromators, based on experience from other instruments worldwide. Uncertainty propagation from alignment errors and noise added to signals were evaluated and showed acceptable sensitivity (of order 1), with expected uncertainties on the inference of temperature and density below 5%. The data processing method has been validated with this synthetic diagnostic and is now employed to analyze the first experimental data from WEST.