Making the most of measurements: results from the integrated diagnostic analysis of the ST40 tokamak

The characterization of magnetic-confined-fusion plasmas requires a comprehensive set of diagnostic systems measuring a wide range of parameters. New machines, such as the ST40 high field spherical tokamak owned and operated by Tokamak Energy Ltd, typically start with a small subset and gradually increase the diagnostic suite to include more complex and comprehensive systems. To make the most of these first phases of operation of ST40, in parallel to standard diagnostic analysis methods, forward models of the various diagnostic systems have been developed and integrated in a single workflow together with modelling tools such as FIDASIM and TRANSP. This has enabled the detection of unexpected errors in various diagnostic systems, correction of geometric uncertainties of line-of-sight mapping, and, above all, has allowed to constrain the kinetic profile shapes and their central values despite the absence of profile diagnostics. This contribution explains the analysis philosophy, the details of the methodology, and discusses the most recent achievement of attaining ion temperatures in excess of 10⁸ K (> 8.6 keV) on the ST40 spherical tokamak during the 2021-22 campaign.