Multiphysics approach for the evaluation of electromagnetic behaviour of tokamak 3d structures during plasma disruptions and application to eu demo, DTT and st40 projects
Author(s)
Lombroni, Riccardo
Date Issued
April 29, 2022
Type
Doctoral Thesis
Abstract
Ever since its conception in the 1950s, the tokamak has arguably been considered the most promising approach to harness the energy of fusion in a controlled way. In tokamaks, the thermal and electro-magnetic loads emerging during so-called normal and off-normal operations represent important input for the structural assessment of the components. In particular, among all these events, the so-called plasma disruptions are one of the major concerns. A plasma disruption is a complex phenomenon involving plasma instabilities which results in a abruptly termination of the plasma and the complete transfer of the plasma thermal and magnetic energy to the surrounding structures on very short timescales. The uncontrolled release of this energy has the potential to inflict severe damages to components, especially in the future reactor-scale tokamaks, such as ITER and DEMO, where the energy stored during a burning plasma pulse will significantly exceed that in present devices. Modern tokamaks, even the largest operating devices such as JET and JT-60U, have generally been able to manage the consequences of disruptions with only limited impact on operational schedules. This is also the case of ST40 and the DTT project, in which a certain disruptions rate is expected and tolerated without compromise their overall scientific mission. Anyway, disruptions have the capability to cause considerable damages also in these devices. Therefore, even if disruptions implications differ between ITER, DEMO and present tokamaks in terms of intensity of the loads, prevention and mitigation requirements, systems and strategies, the evaluation of the related effects always represent one of the main driver of the design of their components, to ensure they reach the projected lifetime and fulfil their function even in the worst scenario. In this context, reliable modelling tools able to predict these loads in details are strongly desired.
This Thesis deals with the EM aspects of plasma disruptions. The evaluation of the EM loads in tokamak reactors is not straightforward and must cope with different problems, such as the implementation of all sources of magnetic field (in particular the plasma during its evolution) and the identification of conductive structures that contribute to the behaviour of the induced currents inside the region of interest. In this Thesis, a novel multiphysics and multicode approach aimed at 3D detailed evaluation of the electro-magnetic loads experienced by the tokamak structures both in normal and off-normal conditions is proposed. Based on the use of MAXFEA code in combination with ANSYS, this new engineering tool was developed and successfully applied in the context of DEMO, DTT and ST40. In particular, the EM response of the main components of these devices, such as the Vacuum Vessel (VV) and the In-Vessel Components (IVCs), were investigated during plasma disruptions. The methodology proposed in this Thesis demonstrated to be a reliable tool to support the design of such components both in conceptual (DEMO) and in detailed phase of the design (DTT, ST40), proving at the same time to have a wide range of applications: from present experimental devices to DEMO, from conventional to non-conventional aspect ratio tokamaks, from standard to advanced plasma configurations.
Additional information
Dottorato di ricerca in Engineering for energy and environment
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