THREE-DIMENSIONAL EFFECTS OF ELECTROMAGNETIC FIELDS IN TOKAMAK PLASMAS
Creators: name: Minucci, Simone
Publisher: name: Università degli Studi di Napoli Federico II
Year: 2015

description: The problem of the energy harvesting to face the more and more increasing energy demand is currently challenging. The higher part of our electrical energy (about 80%) is produced by thermoelectrical power plants, which exploit the so-called Non-renewable energy resources (e.g. oil and gas), whose re-growth rate lasts millions of years and are so to be considered as in a fixed amount.
On the other hand, the Renewable energy resources are not reduced by their exploitation. For instance, solar and wind energy are obviously both permanent renewable resources, because the energy flow is lower than the energy storage, contrary to the oil resource, where the flow exceeds its natural re-growth rate.
Recalling that the renewable energy resources are not able to cover the energy needs (they are often used for the Peak Shaving and not to cover the basis energy demand), it is clear that a new energy resource is necessary to meet the increased energy demand. Moreover, it has to be non-polluting, renewable and continuously available with no interruptions (unlike solar and wind energy, which are affected by the presence of sunlight and wind).
This new energy source can be the Nuclear Fusion Energy, a new kind of energy resource that exploits the energy released by the collision and the fusion of two light atoms (such as hydrogen or its isotopes), according to Einstein equation and the mass-energy balance. Although controlled fusion is extremely technologically challenging, a fusion power plant would offer significant advantages over the existing renewable and non-renewable energy sources, such as the practically infinite fuel supply, the absence or air pollution or greenhouses gas during normal operations and the absence of the risk of a nuclear meltdown.
The collision of two nuclei can occur if and only if their kinetic energy is high enough to overcome the energy barrier opposing the fusion reaction, due to the long-range Coulomb repulsion. Therefore, the hydrogen gas is heated up to very high temperatures (one hundred million degrees and even more), reaching the Plasma state.
Because of this temperature range, the plasma must be confined and must not touch any structure, in order to avoid yielding heat loads as well as mechanical loads. The Tokamak is a fusion machine aimed at the plasma confinement by means of a magnetic field generated by a set of coils surrounding the plasma itself. In principle, the plasma is supposed to be toroidal shaped during normal operations, but this symmetrical condition is ideal, because of many effects which may lead to a non-axisymmetric perturbation of the plasma column.
For these reasons, this PhD thesis is devoted to the analysis of some non-axisymmetric plasma perturbations, their effects during the plasma operations and their modelling. The PhD thesis is divided as follows:
1. The first chapter is a brief overview of the main principles the controlled thermonuclear fusion is based on, focusing on the plasma confinement inside a tokamak, the additional heating and the roadmap towards the fusion energy.
2. The second chapter describes the diamagnetic flux evaluation in ITER tokamak for the estimation of the poloidal beta in the presence of non-axisymmetric effects. In particular, the COMPFLUX procedure used for the analysis is presented, then the effects of the main three-dimensional effects are evaluated and the performance of the compensation system is assessed.
3. The third chapter shows the electromechanical effects due to non-axisymmetric halo currents in ITER tokamak. After discussing the mathematical model, the mechanical effects in terms of forces and torques on the structures surrounding the plasma are evaluated.
4. The fourth chapter is devoted to the flux-density field lines tracing and to the identification of non-axisymmetric plasmas. The mathematical model and the procedures developed for the analysis are presented. Afterwards, the standard and geometrical integrators are compared with reference to test cases for which analytical solutions based on the use of Clebsch potentials are available. Finally, the field line tracing technique is used for the non-axisymmetric plasma boundary reconstruction and a novel technique for the 3-D plasma identification is presented and validated.
5. The fifth chapter reports the main conclusions regarding all the topics dealt with this PhD thesis.