The current energy system is nearing its expiration date. The reserves of non-renewable fossil sources are insufficient for the growing demands, decarbonization policies make it obsolete and the successive crises stress it to unprecedented limits. The future goes through a mixture of renewable sources and nuclear fusion, the generation of energy from the union of two nuclei of light atoms to form another nucleus. It is to imitate the Sun to have an inexhaustible, non-polluting and safe source. “A glass of water will supply a family with energy for 80 years,” says Eleonora Viezzer, member of the Department of Atomic, Molecular and Nuclear Physics at the University of Seville (US) and founder of the group Plasma Sciences and Fusion Technologies along with Professor Manuel García Muñoz. Both have participated today in the presentation of a tokamak, a reactor for the fusion of plasma particles installed in the port of the Andalusian capital to connect to the electricity grid after three phases that will be carried out over 10 years. The initial investment exceeds five million euros.
The project that Seville has incorporated into this energy race is called Fusion2Grid and it includes the participation of Princeton University, its Institute for Plasma Physics, General Atomics (California, USA), the Culham Fusion Energy Center (United Kingdom ), the European fusion consortium EUROfusion, the University of Seoul and Skylife, a US spin-out company responsible for the coils. This team has developed the SMART magnetic confinement tokamak (Small Aspect Ratio Tokamak).
This reactor confines the fusion plasma (fuel) at temperatures up to 100 million degrees Celsius and high pressures. Deuterium and tritium are used, heavier hydrogen isotopes that can be extracted from seawater (deuterium) or from the earth’s crust (tritium). By merging, a new particle (Alpha) is created which is helium and releases an energy of 17.6 mega-electron volts [MeV]. As Viezzer, Princess of Girona Award for Research, explains, an amount of deuterium and tritium similar to what fits in a teaspoon of coffee (2.5 grams), for example, can generate a similar amount of energy to that produced by a field football full of burning coal.
The tokamak works by injecting a beam of high-energy neutral particles to access the H-mode, of high confinement, which is characterized by the formation of a very fine barrier where the transport of energy and particles is more reduced. than in the L-mode used in other reactors. This H-mode produces high pressure gradients necessary for fusion and, consequently, to increase the power of the reactor.
But this high confinement process, by registering such high edge pressure gradients, generates magnetohydrodynamic disturbances that produce intermittent high thermal loads on the reactor walls, known as Edge Localized Modes (ELMs). To deal with them and achieve the balance of forces (compensation of the plasma pressure with the fields produced by the coils and the fuel itself), the US device has been designed as a compact spherical tokamak, different from the traditional doughnut-shaped design. , with high-temperature superconducting electromagnets and operating with negative triangularity of the plasma (inverted D-shape). This last feature translates into the ability to obtain the same plasma confinement with half the external power, something essential for system efficiency. “More electricity at a lower cost”, summarizes García Muñoz. The downside is that plasma stability has not yet been studied with this model.
The result is a reactor that, for the first time in the world, will use this negative triangularity, more compact, efficient and robust, capable of reaching higher pressure and fusion temperatures with which to generate up to ten million more energy per gram than in the combustion of fossil fuels.
With this reactor, Seville joins a race for nuclear fusion that has already reached the necessary milestone to make it efficient: generating more energy than it needs for the process, which is known as net profit. It was achieved last December by a US scientific team at the Lawrence Livermore National Laboratorywhere 192 laser beams were focused into a “peppercorn”-sized hydrogen plasma to generate three megajoules of energy using just two.
In this scientific marathon there are many runners. The UK expects to have the first prototype reactor in 2032 and ITER (the three-continent consortium building the largest complex in France) is fighting to keep deadlines within this decade. The Italian energy group Eni, in collaboration with the Massachusetts Institute of Technology (MIT), assures that “it will have its first plant in the United States in 2025,” according to Mónica Spada, head of Research and Technological Innovation of the Italian company. Madrid has a different technology reactor (TJ II Stellarator) from Seville at the CIEMAT National Fusion Laboratory.
The Seville University has also participated in a recent record for power generation by fusion: 59 megajoules for five seconds. The experiment, by the EUROFusion consortium, was carried out at the Joint European Torus (JET) device, located in Oxford and which is the largest magnetic confinement fusion facility currently in operation worldwide. But the result produced an energy that represented 70% of that used to generate it.
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