A multi-model system-identification comparison with the global particle dynamics in TCV

This work compares physics-based dynamic exhaust models with frequency D response measurements of the global particle dynamics in the Tokamak à Configuration Variable (TCV). The aim is to understand and model the experimental in-vessel dynamic response of plasma and neutrals to deuterium gas puff modulations with three models of varying fidelity: a 0D three chamber model (TCM); DIV1D, which models the edge plasma in 1D; and SOLEDGE3X for 2D-axisymmetric modelling. We find that the dynamic behavior of the global particle balance as observed in TCV can be reproduced by SOLEDGE3X and with specific parameter settings also by TCM and DIV1D, for frequency response measurements between 3 and 40 Hz. For TCM and DIV1D the coupling to a core reservoir and a realistic time for neutrals to ionize are important to align with measurements. We argue from this comparison that for dynamics driven by particle kinetics it is almost impossible to investigate one domain irrespective of others; and that one should formally consider the coupled nature of the particle dynamics over domains. In TCV this means that one cannot ignore that over 60% of the neutral ionization takes place inside the core confined region, for the scenarios considered in this study. The presented dynamic model validation should be detailed much further and extended to other devices to better understand exhaust dynamics, providing essential building blocks required to design exhaust control systems in future fusion reactors.