The Future of Energy
ASG Superconductors - Italy
All this and much more is the synthesis of energy generation through nuclear fusion, the physical phenomenon that powers the Sun. Observed by generations of scholars and reproduced on a very small scale in the 1930s, this is now becoming a reality due to advancements in physics and technologies. The actual feasibility will be technically and scientifically demonstrated in the next few years thanks to a large research project financed by the European Union, China, India, Japan, Korea, Russia and United States, that will result in the construction of a huge experimental reactor in Cadarache, in southern France. ITER, as the project and reactor is called, will be completed and started up in 2020. It will have to prove itself capable of producing for at least 30 minutes a quantity of energy ten times higher than that needed to power it: 500 MW output against 50 MW of actual consumption. The anticipated success of the experiment will be the driving force behind the continuation of a second project, known as DEMO, which is already underway. In the following 15-20 years, DEMO is expected to lead to the accomplishment of the first real industrial plant for the generation of electricity from nuclear fusion.
As one of the various possible solutions to accomplish a nuclear fusion system, ITER is based on the magnetic confinement of the reaction. The core of the fusion is plasma, a state of matter that in the ITER reactor is achieved when it is heated up at temperatures higher than 150 million °C. The movement of the pairs of plasma atoms as they come together up to their fusion is made possible by a massive thrust from a magnetic field. When the fusion of atomic particles has been achieved into a single nucleus, the latter takes on a mass lower than the sum of the original particles, leading to the emission of huge quantities of energy. After the reaction the magnetic system continues to operate, confining the plasma in a space that enables the use of this heat energy and limits the forces acting on the containment room wall.
Once the bending stage has been completed, the double winding is ready for heat treatment. A 28-day heat treatment cycle involving various stages and temperatures in a special atmosphere-controlled oven, will give the material superconductivity characteristics. From now on, in all subsequent processing stages, the big winding needs to be handled with extra care. The super conductive material becomes extremely fragile after crystallisation and any mechanical strain on it might cause breaks and impair its performance.
Caserza continues, “The heat treatment has been designed to keep winding deformation under control, but it is still necessary to check the actual shape of every winding before going on with the next part of the process. We also have to make very precise adjustments to the mountings that keep the windings’ shape to prepare them for the subsequent assembly stages. We use a second Leica Absolute Tracker AT901 along with a Leica T-Probe contact sensor for this task. A guided inspection procedure allows the operators to make the necessary corrections to the relative positions of the turns, based on the deviations detected with an accuracy of a few hundredths of a millimetre.”
The subsequent assembly stages include the fitting of the windings into a special housing, insulation and sealing of the housing itself with special covers that will be welded with a robotised system. A third Leica Absolute Tracker AT901 laser tracker is used for calibration of the fixture to support the individual pancakes inside the welding station. Once the covers have been welded and after accurate dimensional inspections in a vacuum chamber and electrical inspections, every pancake is carefully wrapped in an insulating coating. Subsequently, it is filled with a resin using a vacuum impregnation process. The last step before delivery is the stacking of the seven components and the final insulation of the assembly. After the second impregnation and the final tests, at last the huge D-shaped winding is ready to leave for its final destination the Higgs boson. So when we acquired the order for the ITER project, we had no doubt about how to address the problems of analysis, checks and corrections of the production cycle. In addition to that, the technology of measurement systems has significantly evolved in the last few years, allowing us to set up procedures that are faster and more accurate than in the past, thus optimising the whole process.”
Alberto Barutti takes his leave with a last comment on the activities performed with Hexagon Metrology: “At the time of the preliminary analysis and design of the equipment, we have carefully assessed various options for the dimensional control of our components. Our past positive experiences directed us towards the solutions offered by Hexagon Metrology. So we also had the opportunity to experience a close cooperation with their technicians. Hexagon Metrology did not just provide us with hardware and software, they also developed programs and procedures dedicated to our specific application, which has unique characteristics and therefore required a deep expertise synergy to achieve the final objective. I’d like to point out that it’s through their availability that we are accomplishing as the first one an equipment that will take the laser tracker technology even in an old-style environment like the one of magnetic measurements. Thanks to these new technologies, the final release of manufactured coils will take advantage of a dramatic reduction in processing time, a significant simplification of the activity, as well as an added value for data quality.