An investigation on digital twin methodologies for the ITER project

The world current energy demand is of 12 TW and due to the world population exponential growing it is expected to increase by 37% by 2040 (according to the IEA 2014 Executive Summary). Today 87% of the global energy consumption is based on fossil fuels, with oil 33% and coal 30% as the primary energy resources, followed by hydropower (7%) and nuclear (4%) energy. Renewable energy has only a small fraction in the energy consumption (2%).The need to change this dependence is critical for the reduction of greenhouse gas emissions and the global warming. Fusion energy is a valuable alternative to today commercial energy sources. Once harnessed it has the potential to be nearly unlimited, safe, free from greenhouse emission and long-lived radioactive by-products. The principle behind fusion energy is the same of the stars: elements are fused together into heavier ones with an associated energy release. While in the sun the nuclear reaction is obtained with the fusion of hydrogen into helium driven by gravity, to achieve the same results on earth a different approach is required. The most efficient one in terms of energy produced versus temperature required is setting the reaction to be between deuterium and tritium, two hydrogen isotopes. The tokamak is one of the solutions designed to make this reaction possible and to harness the energy of fusion. Inside the tokamak, the energy produced is absorbed as heat in the walls of the vessel, then to be converted in electrical energy by means of classical loops (steam generator, turbines) as a conventional power plant. A number of tokamaks are nowadays available as experimental reactors (i.e. the JET machine in the U.K) demonstrating the possibility or reproduce the fusion reaction in a controlled way, however all these machines aren’t able to generate more energy than the one necessary to make the fusion reaction happen. ITER (“The Way” in Latin) is one of the most ambitious energy projects in the world today. In Cadarache, southern France, the ITER members (China, the European Union, India, Japan, Korea, Russia and the United States) are collaborating to build the world’s largest tokamak to prove the feasibility of fusion. ITER will be the first fusion device to produce net energy, with an estimated output of 500 MW of fusion power from 50 MW of input heating power. It will maintain fusion for long periods of time and will test the integrated technologies, materials, and physics regimes necessary for the commercial production of fusion-based electricity. ITER will achieve the fusion reaction of deuterium and tritium using strong magnetic fields (around 12 T) to confine the high temperature plasma (150M C°, ten times the temperature occurring for the hydrogen reaction in the sun) during pulses of 400 s. All the participants to the ITER Project are involved in the procurement of machine components and plant systems. This unique procurement sharing program has an important purpose, allowing all Members to gain direct industrial experience in key fusion technologies. By participating in ITER, the Members are also empowering their scientific, technological and industrial infrastructure with innovative manufacturing processes and cutting-edge technologies in order to achieve the strict requirements set for ITER first of a kind sub-assemblies. Today, in factories on three continents, the components and systems of the ITER plant are taking shape. Design requirements derived from simulations and modelling have been translated in stringent dimensional and geometrical tolerances which, combined with the dimension of the assemblies and the complex production steps, push the industries to a higher quality standard. In order to comply with these requirements, not only the processes need to be redesigned, but the tools to verify the compliance assume a paramount importance in the production. Metrology, the scientific study of measurement, has a key role in the manufacturing process, since it can help in the monitoring of the evolution of the parts and in the evaluation of the best alignment in between the components towards the final product. Together on-market and tailored tools are integrated in the production, feeding the manufacturing with useful information about the status of the items, helping the decision making in the risk management. The management of the information coming from dimensional inspections opened the way to the introduction of Digital Twin methodologies and techniques the industry is developing. The document is divided in five chapters, described below: • The first chapter concerns some theoretical background of GeoSpelling and Surface Skin Models, and their implementation in Industry 4.0, with a mention to the tools used in the development of the procedure; • In the second chapter a brief description of the Toroidal Field Coil system and its functioning is presented, to illustrate the method field of applicability; • In the third chapter a brief description of the Vacuum Vessel and its functioning is presented, to illustrate the method field of applicability; • The fourth chapter is dedicated to the application of the reconstruction operation to the Toroidal Field coil Winding Pack and the Vacuum Vessel Inner Shell; • The fifth chapter is dedicated to the application of the association operation to the Toroidal Field coil and the Vacuum Vessel measurements.