Castaldo, Antonio (2019) Development of equivalent plasma-circuits axisymmetric models for existing and future tokamaks. [Ph.D. thesis]
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Abstract (italian or english)
Electromagnetic modelling of tokamak devices assumes a crucial role in scientific research both for the study of operating devices and for the design of future reactors. Having reliable models is fundamental for the design of model-based control systems for the vertical stability of confined plasmas and to provide good performances in terms of plasma shape, current and position control. Finally, it is possible to use these models to optimize geometrical configurations and PF coil systems of future generation devices.
My PhD activities have been focused on the development of plasma equilibria and electromagnetic dynamical models for EAST tokamak, site in Hefei, P.R. China, and the future generation tokamaks DEMO and DTT. CREATE-NL and CREATE-L computation codes have been used to perform the electromagnetic analyses.
An important part of this work has been dedicated to the study of alternative plasma configurations such as Double Null, Snowflake, X-divertor and Super-X. These configurations are currently considered promising by the fusion community in order to tackle the power exhaust problem in view of the construction of the next generation device DEMO. Alternative configurations have been designed on DEMO size tokamak and have been analyzed in terms of costs and benefits illustrating the figure of merits and possible showstopper for the realization of DEMO.
The contents of the thesis are shortly listed below.
In Chapter 1 the nuclear fusion concept will be presented, analyzing the main fusion reactions which involve Hydrogen and his isotopes illustrating extensively Deuterium-Tritium reaction since it represents the most efficient reaction at operative temperatures of a fusion reactor. Moreover, the concept of plasma will be introduced. Different plasma confinement techniques will be presented with particular emphasis on magnetic confinement.
In Chapter 2 magnetohydrodynamic (MHD) theory will be introduced. Starting from MHD equations, plasma equilibrium concept will be illustrated achieving the well-known Grad-Shafranov equation in toroidal axisymmetric geometries. Finally, the finite element code CREATE-NL will be presented, which is widely used in fusion scientific community in order to calculate plasma equilibriums in Tokamak devices.
In Chapter 3 tokamak machines will be introduced, starting from the description of the main components of the reactor (PF coils, Blanket, Vacuum Vessel, etc.) and illustrating the main physical limits which restrict the operation space of the device. A general overview of the main heating techniques (ICRH, ECHR e NBI) and plasma diagnostics employed in a tokamak will be provided. Finally, a brief description of the devices on which the research activity has been focused will be presented.
In Chapter 4 the research activity performed during the last three years on EAST, DTT and DEMO will be presented. EAST modelling activities have been mainly focused on the development of a finite element model of the EAST device and a reliable dynamic simulator able to reproduce EAST experimental shots. Linearized models of the EAST equilibria in different scenario phases have been produces for the design of a model-based closed loop control for the vertical instability and plasma shape control. DEMO activities have been mainly focused on the definition and optimization of alternative plasma configurations for a DEMO size device. For each alternative configuration concept an optimized geometry and PF coil system has been produced. Moreover, a preliminary vertical stability analysis will be provided. Finally, the main activities on the next generation tokamak DTT will be presented making use of the last version (August 2018) of the geometry design with a major radius of 2.10m. For the DTT device, the breakdown and the reference plasma scenarios for Single Null, Double Null and Snowflake configurations will be shown.
In Chapter 5 conclusions and future work will be presented.
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