Isernia, Nicola (2022) The electromagnetic interaction of Magneto-Hydro-Dynamic plasmas with conducting structures. [Tesi di dottorato]

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Abstract

The tight coupling between the macroscopic evolution of Tokamak plasmas and the induced currents in the surrounding Vacuum Vessel (VV) and Plasma Facing Components (PFCs) has been known for decades. In the present Thesis we critically review some aspects of the electromagnetic interaction. In conditions of significant plasma-wall contact the gas mixture is generally only partially ionized. We try to model this situation in a consistent thermodynamic framework, allowing for ionization and recombination phenomena, in Chapter 1. This represents the occasion to review the whole MHD theory in the wider framework of Non-Equilibrium Thermodynamics, also discussing the implications of the Curie principle on the closure relations generally adopted. A self-consistent coupling of 3D non-linear MHD models with fully volumetric 3D structures models is still missing in the literature. We explore some possibilities in Chapter 2, hinting also the first preliminary results in the JOREK-CARIDDI coupling. Several possible formulations are discussed, together with the possible implications of halo currents in the modelling. In Chapter 3 we discuss the mass-less hypothesis and the fundamental aspects of MHD evolutionary equilibrium models. Here we also review the key aspects of the numerical model CarMa0NL. In the last Chapter we apply the evolutionary equilibrium tools previously discussed to practical problems. We first successfully cross-check analytical and numerical computation of forces during off-normal events called disruptions, providing some hints on the magnetic tensions, besides on the magnetic pressures. Further, we propose a procedure for the estimation of plasma losses during disruptions via evolutionary equilibrium models, which we apply to a simple test case. We find also in this case the fundamental role of the electromagnetic time constant, which regulates the plasma dissipated heat during the current quench phase. Further we validate CarMa0NL by direct comparison with JET and TCV experiments, benchmarking simulated and real magnetic diagnostics measurements. For JET, we find that the halo width is a crucial element for a realistic simulation. In the TCV studies we show that the disruption trajectory is dependent on the pre-disruption plasma shape.

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