2023-09-19 19:13:04
Stellarator vs. tokamak. It is not the title of a science fiction movie. It is the name given to the two types of containers of stars on Earth (fusion reactors) that are under development. AND Stellarator just gained positions.
Its name refers to the stars (“stella”) and the use of the same physical principle that supports them to generate energy (“generator”).
Containing a star in a tank long enough to take advantage of the burst of energy it generates and spending less than what was spent producing it is, in essence, the goal and objective of the highest level research institutes in the world.
Scientists, that community committed to achieving advances that eventually not even they themselves will see come true, are convinced that one day nuclear fusion will be the energetic, abundant and sustainable manna that will give peace to a humanity stressed to its limits. Tokamak formally it is a donut, stellarator it seems like a love de Moebius.
Without it being a duel or a competition, the donut (tokamak) and tape (stellarator) are two different horses in the bid to contain nuclear fusion in an efficient way. Tokamak seems to be going ahead, but stellarator has just gained positions, supported by a recent proposal developed from Spain, in the National Fusion Laboratory, belonging to the Center for Energy, Environmental and Technological Research (CIEMAT).
What does it mean to contain a star
In a fusion reactora gas of light atomic nuclei and electrons called plasma It is confined in extreme conditions of pressure and temperature. In such a way that the light nuclei, which constitute the fuel of the reactor, fuse forming other heavier nuclei and releasing a gigantic amount of energy in the process.
Stars, including the Sun, are fusion reactors that confine fuel thanks to the gravitational attraction produced by their enormous mass. Logically, gravitational confinement is not an option for a reactor on Earth, so other avenues must be followed. The most promising is to confine the fuel using intense magnetic fields at temperatures of order of ten times that of the center of the Sunat 150 million degrees Celsius.
The international fusion program is now entering an exciting new phase.
The broken records
In 2022, two records were broken that made headlines in the international press: the one achieved in the European facility Joint European Torus (based on magnetic confinement) and that of the National Ignition Facility estadounidense, (based on inertial confinement).
These are results that show that controlled fusion on Earth is already a dream come true. But we haven’t reached the goal yet. The next challenge is to have devices that produce more energy than that invested in their operation.
ITER, a milestone for humanity
The first experiment with this explicit objective is already under construction in the south of France thanks to a collaboration involving 35 countries, including the 27 of the EU. The success of ITER (this is the name of the experiment) will be a milestone in the scientific and technological development of humanity.
ITER is a tokamakthe most developed concept of magnetic confinement over the last decades.
He tokamak confines the plasma very well and its design is relatively simple (we can imagine the magnetic field of the tokamak like a donut). Although it will be the basis of the first reactor prototypes, stellarator represents a more robust option for commercial fusion reactors.
He stellaratorthanks to a much more complex and sophisticated magnetic field structure, allows operation in continuous mode and free of some instabilities that affect the tokamaks.
Illustration of a tokamak type magnetic field. The red color indicates greater intensity of the magnetic field and blue, lower intensity. (CIEMAT), CC BY
The idea of stellarator was introduced by Lyman Spitzer in 1951, but only at the end of the last century did they begin to be designed stellarators with a quality of confinement that could compete with that of the tokamak.
The sweet moment of stellarators
You can talk about the present as a sweet moment for those stellarators. On the one hand, the device Wendelstein 7-Xin operation since 2015 in Germany, has represented a qualitative leap in this line of research and has established this concept as a serious candidate to be the basis of a commercial fusion reactor.
On the other hand, the theoretical advances of recent years, accompanied by the extraordinary development of supercomputers and the computing power they offer, allow us to address the computational design of stellarators with a quality of confinement not only comparable to that of tokamak but enough for a reactor.
To date no one has been built stellarator whose magnetic field is capable of simultaneously confining the fuel and the highly energetic ions generated in the fusion reactions (essential to heat the fuel and ensure that the reaction is maintained). But this may be closer to changing thanks to the results published in the journal Nuclear Fusion by scientists from the National Fusion Laboratory, belonging to the Center for Energy, Environmental and Technological Research (CIEMAT).
The Mobius strip
In it articlethe authors use a strategy known as “optimization of stellarators”, consisting of the intelligent exploration and evaluation of a very high number of magnetic configurations using supercomputers. In this way they have obtained a configuration in which all the elements involved in fusion reactions are confined to the quality level required by a reactor.
Stellar-type magnetic field obtained by the National Fusion Laboratory. The red color indicates greater intensity of the magnetic field and blue, lower intensity. (CIEMAT), CC BY
Key to this discovery have been the lessons learned and the experience acquired over the years in both Wendelstein 7-X and TJ-IIhe stellarator which has been in operation at the National Fusion Laboratory, in Madrid, since 1997.
In these two experiments, among many other things, the experimental verification of the theories used in the design of new configurations is carried out.
We need materials that do not yet exist
The new magnetic configuration obtained at the National Fusion Laboratory is the first step towards the design and construction of the next generation of stellarators and a reactor based on this concept. This construction will involve challenges not only for physicists, but also for technological and engineering, the resolution of which is essential to complete the route to the commercial fusion reactor.
For example, from a technological point of view, the development of reactors requires finding materials that are resistant to large fluxes of highly energetic neutrons. This is one of the objectives of the IFMIF-DONES project, an initiative of the National Fusion Laboratory – CIEMAT that is currently being developed by the Consortium. IFMIF-WOMEN Spain in Granada.
Something substantial is changing. The path to the fusion reactor, although full of challenges, is becoming clearer.
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