Nuclear fusion, the physical reaction that powers the stars, is a possible safe and potentially unlimited source of energy and the construction of industrial plants to produce electricity from an artificial sun is one of the greatest scientific challenges of our time. In Saint-Paul-lès-Durance in the south of France, 35 nations are collaborating to build ITER, the largest tokamak in the world, a magnetic fusion reactor designed to demonstrate the feasibility of fusion as a large-scale energy source with no carbon emissions. The Iter reactor is funded by the European Union, the United States, Russia, China, India, Japan and South Korea, and is now one of the most ambitious energy projects in the world aiming to harness the energy of the sun to help solve many of the problems related to the sustainability of life on Earth.
The Machine
In stars, hydrogen fuses into helium, releasing enormous amounts of energy. The construction of The Machine (as the Iter scientists call their project) is taking place in the countryside of Provence, but San Paul les Durance is not the only privileged location of this gigantic energy project.
Italian research in the field of fusion plays a decisive role in this global initiative. In a hangar of 18,000 square meters in the territorial area of the National Research Council of Padua, two prototypes are being built for the external heating of the Iter plasma: the “Mitica” and “Spider” experiments, the first one with a neutral particle injector, one source of negative ions the second.
The Neutral Beam Test Facility (NBTF) is located in the premises of the RFX Consortium, an Italian research laboratory that has been studying plasma physics and controlled nuclear fusion since 1996. The components made in the Padua test facility will be reproduced in France: the outcome experiments conducted in Italy will offer scientists the opportunity to investigate challenging physical and technological problems and validate concepts before the system is installed on Iter.
The scientific objective of the NBTF project is to develop a system to obtain a beam of high energy (1MeV) and power (16.5 megawatts) negative ions that will be used to heat the plasma in the ITER reactor. These are performances never achieved until now, hence the need to create a laboratory where to design, build and test such a complex device.
The main heating system of ITER will consist of two neutral beam injectors (NBI), each with an energy of 1 MeV and a beam of negative Deuterium ions of 40 A, to provide the plasma with a power of approximately 16.5 MW per an hour. The required requirements have never been obtained experimentally, so it was decided to produce two prototypes to test the system in the Neutral Beam Test Facility installed in Padua: SPIDER, the most powerful negative ion source in the world and MITICA the prototype in scale 1:1 of the ITER injector, capable of operating at full power and voltage.
The Neutral Beam Test Facility will offer scientists the opportunity to investigate challenging physical and technological issues and validate concepts before the neutral beam system is installed on ITER.
Mitica is the acronym for Megavolt Iter Injector and Concept Advancement, a life-size prototype of a heating neutral particle injector. It is an impressive device capable of heating Iter’s plasma through the input of millions of watts of power through the injection of neutral particles.
Plasma heating occurs when a particle beam penetrates its interior and, by collision with those it encounters, transfers the energy to the plasma itself, increasing its temperature.
The fuel used to generate the plasma in fusion reactors is a deuterium-tritium gas, both isotopes of hydrogen, the most widespread element in the universe. In order for it to reach the plasma state and the fusion reaction to take place, the temperatures inside the reactor must reach 150 million degrees Celsius, ten times those of the sun’s core. Iter’s tokamak will rely on three external heating sources similar to Mitica that will work in concert to provide the input power needed to bring the plasma to melting temperature.
About two hundred people work in the Paduan factory of the stars, including researchers, physicists, engineers and technical personnel, divided between Mitica and Spider (Source for the Production of Ions of Deuterium Extracted from a Radio frequency plasma), the largest source of negative ions in the world entered into operation for the first time in 2018. This device consists of a particle extraction and acceleration system consisting of a series of three electrode grids, each with 1280 perfectly calibrated holes, through which the negative particles generated in the plasma they are extracted and subsequently accelerated.
It is fascinating to be able to observe the passion and energy of the teams at work in France and Italy. In these centers of excellence the teams of researchers work tirelessly to build enormous machines to generate, extract and accelerate portions of matter of subatomic dimension: invisible, imperceptible, inconsistent. Yet measuring, calculating and interpreting this invisibility of matter is decisive for the progress of the experiments and for responding to the energy urgency that animates the colossal Iter project.
